University of Münster
Department of Behavioural biology
Do small mammals affect plant
diversity?
Field studies in Namaqualand, South Africa,
a biodiversity-hotspot
Diploma thesis
Presented by
Christina Keller
- April 2005 -
University of Münster
Department of Behavioural biology
Do small mammals affect plant
diversity?
Field studies in Namaqualand, South Africa,
a biodiversity-hotspot
Diploma thesis
Presented by
Christina Keller
- April 2005 -
Contents
I
1.1. Abstract...........................................................................................................1
1.2. Zusammenfassung.........................................................................................2
2. Introduction .......................................................................................................3
3. Subjects, Material and Methods.......................................................................9
3.1. Study area....................................................................................................9
3.2. Animals ......................................................................................................11
3.3. Correlation between small mammals and plants........................................14
3.3.1. Trapping............................................................................................14
3.3.2. Vegetation survey .............................................................................14
3.3.3. Soil samples .....................................................................................16
3.3.4. Altitude..............................................................................................17
3.3.5. Rainfall..............................................................................................17
3.3.6. Statistics ...........................................................................................17
3.4. Food Preference tests................................................................................18
3.5. Plant biodiversity around bush Karoo rat nests ..........................................19
3.6. Fence line...................................................................................................20
4. Results .............................................................................................................22
4.1. Correlation between small mammals and plants........................................22
4.1.1. Comparison between winter and summer.........................................22
4.1.2. Winter trapping season .....................................................................24
4.1.3. Summer trapping season..................................................................26
4.1.4. Correlation between plant cover and small mammals.......................29
4.1.5. Soil survey ........................................................................................29
4.1.6. Cluster-analyses ...............................................................................32
4.1.7. General linear model.........................................................................32
4.2. Food Preference tests................................................................................34
Contents
II
4.2.1. Pilot study .........................................................................................34
4.2.1.1. Striped mouse (R. pumilio) ....................................................34
4.2.1.2. bush-Karoo rat (O. unisulcatus).............................................34
4.2.2. Second set of tests ...........................................................................35
4.2.2.1. Striped mouse (R. pumilio) ....................................................35
4.2.2.2. bush-Karoo rat (O. unisulcatus).............................................36
4.3. Plant biodiversity around bush Karoo rat nests ..........................................37
4.4. Fence line...................................................................................................38
5. Discussion .......................................................................................................39
5.1 Correlation between small mammals and plants.........................................39
5.2. Food-preference-tests................................................................................42
5.2.1. Pilot study .........................................................................................43
5.2.2. Second set of tests ...........................................................................43
5.3. Plant diversity around bush-Karoo rat nests...............................................44
5.4. Other factors that might influence plant biodiversity...................................45
5.5. Fence line...................................................................................................47
6. Conclusions.....................................................................................................50
7. References .......................................................................................................51
8. Appendix ..........................................................................................................57
9. Acknowledgements.........................................................................................66
Abstract
1
1.1. Abstract
The conservation of species is one of the most important duties of our century.
Basic ecological knowledge is essential in order to perform it. Conservation is
particularly effective in hotspots of biodiversity, because many species can be
protected here at the same time in a relative small area. One of these biodiversity
hotspots is the Succulent Karoo in southern Africa, which holds an extraordinary
high number of plant species. Small mammals are abundant in the Succulent
Karoo and might be of crucial importance as herbivores in this ecosystem. For the
first time the influence of small mammals on plant diversity was investigated in my
study. It is known from earlier studies that herbivores can increase floral diversity
by reducing dominant plant species and thus providing space for subdominant
species, which would be outcompeted otherwise. In a correlative study I tested if
this mechanism might exist in the Succulent Karoo. The plant diversity in 10
ecological different study sites in Goegap Nature Reserve was correlated with the
number of small mammals living there. Additionally two rodent species
(Rhabdomys pumilio and Otomys unisulcatus) were taken as example-species
and tested in food-preference-tests for a preference for subdominant or dominant
plant species. Additionally the influence of O. unisulcatus on the plant community
surrounding their nests was also investigated. I found several positive correlations
between plant diversity and the number of individuals and especially the species
number of small mammals. The direct surroundings of occupied O. unisulcatus
nests showed a significantly higher plant diversity than control areas, although
food-preference tests revealed that O. unisulcatus prefers subdominant foodplants. In the contrary R. pumilio preferred dominant food-plants. All in all this
results indicate a distinct influence of small mammals on plant diversity. The
results of my study are of great importance for conservation programs in the
Succulent Karoo in which small mammals should be included in the future.
Zusammenfassung
2
1.2. Zusammenfassung
Artenschutz ist eine der wichtigsten Aufgaben unserer Zeit. Für seine
Durchführung ist ökologisches Basiswissen zwingend erforderlich. Besonders
effektiv ist Artenschutz an Schwerpunkten der Artenvielfalt (Biodiversität), denn
hier lassen sich viele Arten gleichzeitig und auf kleinem Raum schützen. Einer
dieser Biodiversitätshotspots ist die Sukkulentenkaroo im südlichen Afrika, die sich
im Besonderen durch ihre extrem artenreiche Flora auszeichnet. Kleinsäuger sind
hier als Pflanzenfresser von großer Bedeutung. Erstmals wurde in dieser Studie
der Einfluss von Kleinsäugern auf die Artenvielfalt der Pflanzen in der
Sukkulentenkaroo untersucht. Es ist aus andern Studien bekannt, dass
Pflanzenfresser einen positiven Einfluss auf die Diversität ihrer Futterpflanzen
haben können, indem sie dominante Pflanzenarten reduzieren und auf diese
Weise Platz für subdominante Arten schaffen, die andernfalls verdrängt würden.
Ob dies in der Sukkulentenkaroo der Fall ist wurde mit einer korrelativen Studie
untersucht.
Die
Pflanzendiversität
an
10
ökologisch
verschiedenen
Untersuchungsgebieten im Goegap Nature Reserve wurde mit den dort lebenden
Kleinsäugern in Zusammenhang gebracht. Zusätzlich wurde mit Futter-PräferenzTests exemplarisch an zwei Nagerarten (Rhabdomys pumilio, Otomys unisulcatus)
getestet ob sie dominante Futterpflanzen bevorzugt fressen. Bei einer dieser Arten
wurde außerdem ihr Einfluss auf die Pflanzendiversität in unmittelbarer Umgebung
ihres Nestes untersucht. Es wurden mehrfach positive Korrelationen zwischen der
Anzahl der Kleinsäugerindividuen und besonders der Anzahl ihrer Arten und der
Pflanzendiversität gefunden. Dieser Zusammenhang war im Winter deutlicher als
im Sommer. Im Vergleich zu unbewohnten Gebieten wurden in unmittelbarer
Umgebung von bewohnten Otomys unisulcatus-Nestern signifikant mehr Pflanzen
gefunden, obwohl Futter-Präferenz-Tests zeigten, dass diese Art subdominante
Pflanzenarten bevorzugt. Rhabdomys pumilio hingegen bevorzugte dominante
Futterpflanzen.
Diese
Ergebnisse
zeigen
einen
deutlichen
Einfluss
von
Kleinsäugern auf die Diversität der Pflanzen ihrer Umgebung. Der ökologische
Hintergrund ist von großer Bedeutung für Artenschutzprogramme in diesem
gefährdeten Gebiet, in die Kleinsäuger in Zukunft einbezogen werden sollten.
Introduction
3
2. Introduction
The phenomenon of biodiversity is one of the most fascinating in biology. In this
study biodiversity is understood as the number of different species in a certain
area without regards to endemism or abundance. When Darwin first described the
process of evolution, biologists began to understand the scientific basis of
diversity. In the process of adaptive radiation and adaptation to ecological niches,
evolution created numerous different species of plants and animals. But these
species are not distributed evenly over the planet.
In 2000 Myers et al identified 25 hotspots of biodiversity. These areas were
chosen for their species richness, endemism, taxonomic uniqueness, unusual
ecological or evolutionary phenomena and global rarity. Myers et al. saw the
identification of diversity hotspots as a tool for the improvement of conservation
management. All the hotspots are facing extreme threats from human interference.
As conservation budgets are insufficient given the number of species threatened
with extinction it is highly important to be able to support the greatest number of
species at the least cost. This is much easier after identifications of biodiversityhotspots, since all hotspots together cover only 11.8 percent of the planet’s land
surface, but include no less then 44 percent of the worlds plants and 35 percent of
terrestrial vertebrates. Myers included only terrestrial ecosystems. Examples of
these hotspots are Madagascar, Brazil’s Atlantic forest and the Tropical Andes.
Identifying biodiversity is the first step understanding is the second. Several
authors established hypotheses trying to explain gradients of biodiversity.
Biodiversity is for example often connected with the number of available niches
and the strength of genetic drift (Ihlenfeldt 1994, Connell 1964). According to
Jürgens et al. (1999) a high population turnover can decrease the competition for
an ecological niche in plants. Normally competition for resources limits the sharing
of the same ecological niche by several species, but if species have a short
lifespan, this exposure to competition is of relative short duration. In addition there
is always space for new recruits to become establish. This can lead to increased
biodiversity.
Another potential mechanism to create or maintain diversity is the predation
hypothesis first formulated by Paine (1966). By keeping the abundance of their
prey in check and thus prevent competitive exclusion, predators can maintain a
Introduction
4
higher diversity of prey species than would occur in their absence (Paine 1966,
1971). Already Darwin realised in 1859 that the diversity in a meadow decreases if
cutting is stopped. Paine (1966) investigated connections between predators and
their prey on a reef. He found that the removal of predators (i.e. the sea star
Pisaster ochraceus) led to decreased diversity of their prey, mussels (e.g. Mytilus
californianus) in this case. Lubchenco (1978) noticed the same phenomenon in
tidal pools. Here, the presence of snails led to higher diversity of algae species, as
predicted by the predation hypothesis. But the number of algae species decreased
again when the snail population exceeded a limit, causing the extinction of the
preferred food plants. The diversity of the prey, here the algae, reached a
maximum under the influence of a medium population density of predators, here
the snails. An interesting aspect of Lubchencos study is the extension of Paine’s
predation hypothesis by including plants as prey species. In contrast to the study
by Lubchenco (1978) Harper (1969) found that herbivores decrease plant
diversity. This variable result may be due to the fact that herbivores can only
increase the diversity of plants if they preferentially feed on the competitive
dominant plant species, preventing them from displacing subdominant plant
species. They decrease plant diversity if they prefer the subdominant plant
species. In conclusion herbivores can potentially do both, increase or decrease
plant diversity (Lubchenco 1978).
This study focuses on the rich plant diversity in Namaqualand, part of the
Succulent Karoo, a biodiversity hotspot. The Succulent Karoo is situated on the
West Coast of South Africa and Namibia. Namaqualand is the part of the
Succulent Karoo, which lies in South Africa. This area is a semi-desert to desert
environment. The temperatures can reach over 40° in summer and can be below
0° in winter. During daytime the temperature fluctuations are also very high. The
average annual rainfall is between 50 and 400 mm depending on the area
(Cowling et al. 1999), with rain falling mainly in winter (June to August).
Compared to other desert ecosystems Namaqualand has many unique
biological features (Cowling et al. 1999). The rainfall is rare, but highly predictable
(Desmet & Cowling 1999). Droughts are very rare and have a disastrous effect on
the plants that are not adapted to it. There is nearly every year enough rain for
plants to germinate, grow and to produce seeds that can establish successfully
afterwards. Thus plants are not forced to invest in robustness or longevity, abilities
Introduction
5
that are crucial in other deserts with droughts lasting for years. The high
population turnover in plants in the Succulent Karoo, especially after droughts, is
one reason for the high plant diversity here (Jürgens 1999).
Usually, a semi-desert is not expected to be among the 25 most diverse
places in the world. Connell (1964) suggested that diversity is associated with the
stability within a system, because in a stable environment less energy is required
for homeostasis. He pointed out that diversity increases if species have higher
productivity due to more available energy. The Succulent Karoo however is not a
very stable environment, at least not compared to equatorial rain forests. There
are high temperature fluctuations during the day and rainfall is usually restricted to
the winter months.
Determining the reasons for the extraordinary high number of plant species
in the Succulent Karoo can be of great importance for its conservation. If herbivore
predators have a positive influence on plant diversity, it would be essential to
include these animals in conservation programs for plants. The conservation of
plants, and nature in general, is extremely important in this area because the
plants are a tourist attraction and tourism is an important economic factor in
Namaqualand. Furthermore, maintenance of plant biodiversity is also important for
the local farmers, as livestock feeds on a large variety of plant species, mainly
succulents and annuals. Grass is nearly absent in the Succulent Karoo, and a
decrease of biodiversity (e.g. because of overgrazing) is characterized by an
increase in abundance of unpalatable shrub species (i.e. Galenia africana, Todd &
Hoffman 1999).
Another reason why desert ecosystems are increasingly important for
conservation is global warming. Because there is a strong likelihood of a rapid
increase in temperature all over the world, the genetic stock held by desert
ecosystems might be of enormous importance for mankind in the future (Cowling
et al. 1999). The current rate of extinction is a loss we can ill afford. Additionally,
the Succulent Karoo is an inadequately protected biome (Hilton-Taylor & Le Roux
1989).
Botanically the Succulent Karoo is part of the Greater Cape Flora (Jürgens
et al. 1991). The Succulent Karoo is home to about 1954 endemic plant species,
making it the world’s richest succulent flora (Lombard 1999). Characterised by an
open dwarf shrubland (Milton et al. 1997), the vegetation is dominated by leaf-
Introduction
6
succulents and numerous species of highly abundant ephemeral geophytes
flowering in spring (Cowling et al. 1999). Namaqualand harbours probably 10% of
the succulent species in the world (Van Jaarsveld 1987). One of the most
abundant families is the Mesembryanthemaceae (also called Aizoaceae), which
are overwhelmingly concentrated in the Succulent Karoo (Hartmann 1991). In
contrast to other winter rainfall-deserts, leaf succulents with a shallow rooting
system dominate the vegetation. This rooting system makes the plants very
vulnerable for droughts (Cowling et al. 1999). To grow in the cool wintertemperatures some plants have low temperature-optima for photosynthesis
(Rossa & von Willert 1998).
Namaqualand can be divided in smaller regions based on geology,
topography, amount and season of rainfall. Goegap Nature Reserve, where this
study was conducted, falls within the Hardeveld or Namaqualand Rocky Hills
(Hilton-Taylor 1996) extending from Steinkopf in the north to Bitterfontein in the
south. The vegetation cover here is relatively dense compared to other regions of
Namaqualand. The landscape in the Hardeveld can be divided into hills (local
name: koppies), plateaus and plains. Different soil features characterize each of
these regions. On koppies there is usually shallow soil, as sand is continually
removed by water. Wind and water deposit finer soil particles on plains and along
drainage lines. The soil of plains is deeper and supports different plant
communities.
There are various species of small mammals occurring in Namaqualand.
Some of them are endemic. In fact 85% of South Africa’s endemic mammal
species are small (Gelderblom 1995). Especially in the Hardeveld, the region of
Namaqualand where this study was conducted, the population densities of small
mammals can be extraordinary high (Schradin & Pillay 2005; Jackson 1999), while
large mammals are relatively rare in species and numbers. Most of the small
mammals are muroid rodents, like the striped mouse (Rhabdomys pumilio), the
bush-Karoo-rat (Otomys unisulcatus) and several species of gerbils. But elephant
shrews and mole rats are also represented with some species.
There are no obvious reasons for the extraordinary number of plant species
in the Succulent Karoo, but several hypotheses might apply. The plants in this
area are food for many herbivores. Thus, the plants can be regarded as prey and
the herbivores as their predators or consumers. The present study investigates if
Introduction
7
the predation-hypothesis can be applied to the Succulent Karoo, and if the
presence of small mammals as the dominant plant predators can at least partly
explain the high number of plant species.
It is suggested that small mammals of the Succulent Karoo have an
influence on the plant diversity in their surroundings. According to Andrews and
O`Brien (2000) small mammal distribution is representative for the distribution of
mammals in general. Thus, bigger herbivores such as zebras and antelopes were
not included in this study.
Furthermore, small mammals have the advantage of a small range of action
in comparison to larger mammals, like ungulates. This is highly useful for a study
like this where small-scale differences in species assemblage and population
densities were investigated.
In detail, I tested the following hypotheses:
1. The presence of small mammals as plant predators correlates with plant
diversity.
2. Small mammals as plant predators affect competition between plant species by
preferably feeding on dominant or subdominant plant species. According to
Lubchenco (1978) herbivores increase plant diversity if they prefer dominant
plant species. In this case they provide space for subdominant species that
would otherwise be outcompeted.
3. The effect of small mammals on plant diversity is supposed to be greatest in
the direct surrounding of their nests, especially in case of central place foragers
like O. unisulcatus (bush-Karoo rats). This would predict differential diversity
around occupied nests of bush-Karoo rats compared to abandoned areas.
While small mammals might have an influence on plant diversity, the
evolution and maintenance of plant biodiversity is very likely also dependent on
many other factors. While the focus of this study was on the role of small
mammals in this process, data regarding several other ecological factors were
collected, as well. In the first place some edaphic (soil concerning) parameters
were investigated that are hypothesised to have a great influence on species
diversity. The focus was on soil nutrients. The concentration of the ions from
sodium, potassium, calcium, manganese, magnesium and iron were measured. In
Introduction
8
addition the pH-value in the soil solution was measured. The nutrient status and
pH are important edaphic factors for characterisation of Succulent Karoo soil
(Lechemere-Oertel & Cowling 2001). Curiously, Succulent Karoo seedlings
accumulate more biomass if they grow in nutrient-poor soil in comparison to
nutrient-rich soil (Lechemere-Oertel & Cowling, 2001). Another recorded factor
was altitude. In the Andean forests, for example, there is a general tendency for
plant diversity to decrease with increasing altitude (Gentry 1988). These data on
edaphic parameters were used for descriptive statistical analyses (Cluster
analysis) to create hypotheses and predictions for future research into the
understanding of plant biodiversity in the Succulent Karoo.
In addition a possible impact of large ungulate herbivores on plant- and
small mammal diversity was investigated. The history of grazing by domestic
animals in Namaqualand dated back more than 2000 years (Smith 1999). The
keeping of livestock especially goats and sheep is common in the Succulent
Karoo, which might have a great influence on this biome. According to the
predation-hypothesis it can be expected that, like small mammals, livestock might
have an influence on plant diversity. Maybe very high stocking rates have a
negative effect on small mammal diversity because overgrazed rangelands show a
lack of cover for predator avoidance (Joubert & Ryan 1999). In this context Milton
et al. (1994) found that there is a progressive degradation of rangelands resulting
in irreversible changes in diversity and abundance of Karoo vegetation. Although
several studies found no differences in plant diversity between a reserve and a
lightly grazed, neighbouring farm (Todd & Hoffman 1999 inter alia), I investigated
this topic again by comparing plant biodiversity between a farm, which had a
history of overgrazing by livestock, and a nature reserve. I tested the following
prediction:
4. There is an effect of grazing on the number of plant/small mammal species.
Subjects, materials and methods
9
3. Subjects, Materials and Methods
3.1. Study area
The study was conducted in June-December of 2004 in Goegap Nature Reserve.
This reserve is near the town Springbok in the northwest of South Africa (Northern
Cape). Goegap Nature Reserve is situated in the middle of Namaqualand, which
is part of the Succulent Karoo. It is situated in the Namaqualand Rocky Broken
Veld (Acocks 1988) also called Hardeveld (Hilton-Taylor 1996). The area is
semiarid. Rain falls mainly in winter and the annual average is 160mm (Rösch
2001). The vegetation type is Succulent Karoo (Milton et al. 1997), dominated by
leaf succulent shrubs and many ephemeral species, mainly flowering in spring.
This biome is a bioregion of exceptional succulent plant diversity and endemism
(Hilton-Taylor 1996).
Within Goegap Nature Reserve ten areas differing with regards to structural
and floristic features were chosen for the main project (s. 3.3.). To avoid a bias in
the dataset it was important to choose more or less homogenous places, which
were ecologically different from each other. The areas were designed to be
representative for the plant assemblage of five different management units that
were identified in Goegap Nature Reserve by Rösch (2001). The distribution of the
ten areas is showed on the map (Fig. 1) while their characteristics are listed in
Table 1.
Subjects, materials and methods
10
Figure 1: Goegap Nature Reserve with the ten investigated areas, the neighbouring farm
and two public roads. The main road of the reserve is also shown. The map shows the
distribution of the ten areas in the reserve. The two transects where the Fence line (s.
3.6.) was conducted are marked with an F. Reference: Software MapSource, South Africa
Table 1: Overview about the ten investigated areas; Rainfall: 0-50mm/year = sparse, 100150mm/year = moderate, >150mm/year = plenty; all edaphic factors, altitude, soil texture and plant
cover: results from this study (s. 4.1.3.) organic soil components in % referring the dry weight; soil: +
= yes, - = no
soil
altitude
Areas (m o. NN) rocky
1
954.2 +
2
935.96 +
3
934.9 +
4
895.35 +
5
855.3 +
6
873.63 +
7
901.85 +
8
977.3 +
9
1062 +
10 1109.85 -
sandy
+
+
+
plant cover (%)
Edaphic factors
organic soil
c (Na) c (K) c (Mg) c (Ca)
mg/l mg/l
mg/l
rainfall
Winter Summer components (%) mg/l
moderate
10
10
2.20 5.15 13.01
5.89 48.14
moderate
1
5
0.93 1.16 5.78
4.70 13.72
sparse
0
1
0.97 2.68 10.81
3.10 11.24
sparse
40
25
0.44 1.03 1.89
1.94 7.23
sparse
40
45
2.27 65.68 23.40 23.85 95.51
sparse
0
1
0.98 10.78 10.26
2.87 8.95
moderate
35
40
1.47 7.54 4.53
5.50 86.12
moderate
50
60
1.69 4.10 6.09
2.37 14.54
plenty
40
50
2.28 1.94 2.15
3.48 17.54
plenty
80
50
2.95 3.70 1.26
6.79 33.67
Subjects, materials and methods
11
3.2. Animals
Ten different small mammal species were trapped during the study. The only
exclusively diurnal species was the striped mouse (Rhabdomys pumilio). The
striped mouse is a muroid rodent (Brooks 1982; Dewsbury & Dawson 1979) with
an adult mass range of 40-85g (Schradin 2003) in both sexes. It occurs in many
parts of southern Africa, including grasslands, marsh, forest, desert and the
Succulent Karoo (Kingdon 1974). In the Succulent Karoo R. pumilio lives in social
groups of one breeding male, 1-4 breeding females and their nonreproductive,
adult offspring (Schradin & Pillay 2003). Group-members sleep together in one
nest (Schradin & Pillay 2004), built in bushes. Sometimes they occupy old nests of
bush Karoo rats (Schradin in press). In spite of their group-living organisation
striped mice forage alone during the day (Schradin in press). Their diet is
omnivorous and contains herbage, fruits, insects and seeds (Curtis & Perrin 1979;
Kerley 1992).
The bush-Karoo rat (Otomys unisulcatus) is a rodent endemic to the subarid regions of southern Africa (Skinner & Smithers 1990). It is confined to the
Karoo region of the South West Arid Zone (Davis 1974; Skinner & Smithers 1990)
and is often associated with the courses of ephemeral streams and rivers
(Shortridge 1934; Diekmann 1979). O. unisulcatus is a medium sized rodent with
an adult mass range of 70-135g (Pillay 2001). It has a shaggy pelage, which is ash
grey dorsally and buff white ventrally. (Pillay 2001) Its nest is a large stick lodge up
to 1.0m in diameter and up to 1.5m high (Schradin in press). It is usually situated
at the base of shrubs such as Zygophyllum retrofractum or under large rocks
(Dieckmann 1979, pers. observ.). They are constructed of sticks, twigs and
flowering ephemerals, sometimes enclosing the shrub completely (Dieckmann
1979; Plessis & Curley 1991). Passages are made within the dense shrub. A small
nest of finer material is constructed at the centre of the large structure in a shallow
burrow or depression. They always contain some green material if the nest is
occupied (Dieckmann 1979, pers. observ.). The literature disagrees concerning
the activity period of the bush Karoo rat. It is described as diurnal (Plessis & Kerley
1991, Plessis et al. 1990) or as crepuscular (inter alia Skinner & Smithers 1990).
O. unisulcatus is exclusively herbivorous (Kerley 1992; (Brown & Willan 1991).
Shrubs dominate their diet (Plessis et al. 1990). The feeding on highly hydrated
plant material is critical to the rat’s survival (Brown & Willan 1991). Mostly the
Subjects, materials and methods
12
litters consist of 2 semi-precocial young that are weaned as early as eight days of
age (Pillay 2001). Interestingly the bush Karoo rat is not physiologically well
adapted to the arid environment it lives in (Du Plessis et al. 1989; Pillay et al.
1994). O. unisulcatus uses behavioural adaptations to cope with xeric conditions
such as building stick lodges and feeding on succulent plants to get access to
water.
One of the numerous nocturnal species was the Namaqua-Rock mouse
(Aethomys namaquensis). A. namaquensis is restricted to the central Karoo in the
Northern Cape Province. This rat like rodent has an average body mass of 50g. Its
fur is reddish brown to yellowish light brown with a white underpart. The tail is
longer than the body and happens to have dandruffs. A. namaquensis lives in
small colonies in rocky areas, where they hide in nests under rock crevices or in
burrows under shrubs. Their diet consists of seeds from grass and other plants. A.
namaquensis gives birth to 3-5 pups in summer month (Stuart &Stuart 2001).
The smallest of the trapped species was the pygmy mouse (Mus
minutoides). This mouse is widely spread over different habitats in southern Africa
and weighs just about 6g. Its fur is grey to reddish brown with a white underpart.
Not much is known about the social behaviour of this species. In this study more
than one animal was trapped in tha same place mostly. more than one animal in
one place. The birth weight of the up to seven pups is under 1g. They are often
born in self-dug burrows, but deserted burrows from other species or other
hideouts are also used (Stuart &Stuart 2001).
Three species of Gerbils were trapped, two pygmy gerbils (Gerbillurus
vallinus, Gerbillurus paba) and the short tailed-gerbil (Desmodillus auricularis).
The last is much heavier than the pygmy gerbils weighing about 50g compared to
25-35g. D. auricularis also has got a tail which is shorter than the body, which is
most uncommon for gerbils. The fur colour of the three species is nearly equal
varying from reddish brown to grey. All species have a white belly. In contrast to
the other species D. auricularis has got white patches at the base of its ears. The
diet of gerbils consists of seeds and sometimes insects. All these gerbils occur in
dry, sandy areas with G. paeba being most common. These nocturnal animals dig
their own burrows. G. vallinus lives in colonies whereas G. paeba build small
groups and D. auricularis is solitary or monogamous (Stuart &Stuart 2001).
Subjects, materials and methods
13
In addition to all these rodents three elephant shrew species were trapped
(order Macroscelidae). Macroscelidae belong to the clade Afrotheria, which also
includes aardvarks, elephants, hyraxes, golden moles, tencres and serenians
(Murphy et al. 2001). The round-eared elephant shrew (Macroscelides
proboscidreus) has a long pelage that is light grey-brown on the dorsum, yellowbrown on the flanks and white on the ventrum (Corbet & Hanks, 1968). M.
proboscideus has long slender legs and a long, narrow, semi-flexible snout
(Nowak 1991). The average adult body mass is 45g. M. proboscideus is endemic
to Africa and native to Namibia, southern Botswana and the Cape Province of
South Africa (Corbet & Hanks 1968; Nowak 1991). According to Nowak (1991) the
round-eared elephant shrew is mainly diurnal and just sometimes crepuscular or
nocturnal. In this study no elephant shrew was ever trapped during the day. So it
is likely, that the animals switched their schedule to avoid the threat of diurnal
predators like birds of prey (i.e. jackal buzzards, Buteo rufofuscus), which are
common in the study area. Their diet is dominated by insects along with roots,
berries (Nowak 1991), herbage and seeds (Kerley 1992). It lives on sandy and
thornbrush plains and seeks shelter in burrows under bushes (Nowak 1991) or
rock crevices (Dieckmann 1979). The animals breed in August and September. M.
proboscideus is mainly solitary according to Nowak (1991), but it is also
suggested to be monogamous (Rathbun pers. commun.) Once a year 1-2
precocial young are born, that are nearly immediately able to move. They are
weaned at 16-25 days and reach sexual maturity after about 43 days (Rathbun &
Fons).
The two Rock-elephant shrew species, the Smith-Rock-Elephant shrew
(Elephantulus rupestris) and the Cape-Rock-Elephant-shrew (Elephantulus
edwardii) are more common in rocky areas as the name implies. There are heavier
than M. proboscideus, weighing 65g and 50g, respectively. These two species are
difficult to distinguish from each other in the field. In contrast to E. edwardii, E.
rupestris has a clear white eye ring, a larger brown pelage at the neck, and a very
hairy tail. They have various fur colours (Stuart &Stuart 2001). In other aspects
they are similar to M. proboscideus.
Subjects, materials and methods
14
3.3. Correlation between small mammals and plants
3.3.1. Trapping
To determine the diversity of small mammals, trapping was performed at
the ten different sites. Thirty locally hand-made Shearman-traps (26 x 9 x 9cm)
were placed 10m apart, in a line. The trapping transects were 290m long. Each
Trap contained bait and a piece of cotton wool, to avoid trap-death caused by
frost. The bait was a mixture of bran flakes, currants, sea salt, salad oil and
peanutbutter. Prebaiting was done for two days in the afternoon before trapping.
One day before trapping, no prebaiting was performed. Small mammals were
trapped in each area for four days. On the first two trapping days trapping
occurred in the afternoon, three hours before and three hours after sunset
followed by a day without trapping. On the last two trapping days trapping was
performed in the morning three hours before until three hours after sunrise. This
time schedule was chosen in order to trap the diurnal as well as the nocturnal
animals. Traps were checked every 90min to avoid the occurrence of trap deaths
and to open traps for other small mammals present at the transects. Trapped
animals were marked individually with hair dye (method from Weiß et al. 1996),
weighed and sexed. Trapping was done twice, July/August (winter) and the
second one during October/November (summer). No trapping was performed in
the rain or after a temperature drop of more than 5°C from one night to the other.
3.3.2. Vegetation survey
Vegetation analyses were performed after first trapping in August and
before second trapping in October. The surveys were distributed evenly along the
trapping-transect.
At each transect, plant species in and around five squares (each 2x2m)
were determined. All plant species present, the number of individuals per species
and the ground cover was noted. The mean ground cover in five vegetation
surveys was used for statistics (s. 3.2.7.)The seedlings found in spring were not
classified, as they were not present during the preceding trapping session. Plants
were divided in annual and perennials species. The number of individuals was
categorized as follows (after the Braun-Blanquet Method as described Wilmanns
1998).
Subjects, materials and methods
r=
1 - 2 Individuals
+=
3 - 10 Individuals
1=
11 - 100 Individuals
15
2m = > 100 Individuals
If one species covered more than 5% of the ground the following classification
was used.
2a = 5 - 12,5 %
2b = 12,5 - 25 %
3=
25 - 50 %
4=
50 - 75 %
5=
> 75 %
Figure 2: Field assistant performing a vegetation analysis in a 2x2m square in area 8
Subjects, materials and methods
16
3.3.3. Soil samples
Three samples of soil (100g) were collected in each area from a depth of
3cm. Samples were taken on open positions, not under shrubs or rocks. Collection
took place after a period without rainfall in the beginning of November. The
parameters pH-value and elemental composition (Na +, K +, Mg2+, Fe+, Mn2+) were
measured. The soil was air dried and sifted through a mesh with a mesh-size of
2mm.
To measure pH-value 10g of soil from each area was mixed with 25 ml
dH2O and measured with a pH-Meter (pH 91, WTW).
For the determination of the elemental composition with an AAspectrometer
(Unicom 939), an extract from 2.5g soil was produced. Two extracts and three
blind tests were analysed for each area. The soil was mixed with 50ml NH4Cl
(1mol/l) and left untouched for 4h. Afterwards the extracts were shaked for 2h on
an automatic shaker (Schüttelmaschine LS20, Gerhardt) and left untouched over
night. The extract was filtered. To measure Ca and Mg 10ml of extract was mixed
with 1ml buffer (7.6g KCl + 2.5ml 37%HCl in 200ml dH2O.). For the measurement
of Fe and Mn, three standards were prepared with 1ppm, 2ppm and 5ppm of Fe
and Mn. For the measurement of the other elements, four standards were
prepared with the following composition:
1. 1ppm Na, 2ppm K, 2ppm Ca, 0.1ppm Mg
2. 2ppm Ca, 5ppmCa, 5ppm K, 0.2ppm
3. 5ppm Na. 10ppm K, 10ppm Ca, 0.5ppm Mg
4. 10ppm Na, 20ppm K, 20ppm Ca, 1ppm Mg
Standards were used to calibrate the AAspectrometer. Samples were
diluted if necessary to fit in the range of the standards. Extracts were measured
with a Unicom 939 AAspectrometer.
To measure the percentage of organic components in the soil, two samples
(≈ 4g) were dried in a cabinet desiccator (Heraeus thermicon P) over night,
weighed (Mettler Type AE 163, accuracy of 0,001g ), cooled down to 20° in an
Exicator and stored in a muffle furnace (Heraeus Function line Typ 12) for 15h. In
the first 2h the oven heated the samples up to 400° temperature remained here for
3h. Than the oven heated the samples up to 600° in another 2h and kept them on
this temperature for 6h. Afterwards the samples needed 2h to cool down to 20°
Subjects, materials and methods
17
and were weighed again. The weightloss in reference to the weight after drying
was calculated.
3.3.4. Altitude
The altitude of each transect in the ten areas was measured with a GPS
(eTrex Venture, GARMIN International, USA) at the start- and end-point. The
mean value was used for statistics (s. 3.3.7.).
3.3.5. Rainfall
The mean value of rainfall from the years 1998 to 2002 was taken
(information provided by Goegap Nature Reserve) with nine gauging stations
distributed in the whole Nature Reserve. The rainfall in the trapping areas was
assumed according to the nearest gauging station. No measurements had been
taken in the years 2003 and 2004.
3.3.6. Statistics
Correlations between the number of plant species and the number of small
mammal species and total number of small mammals were calculated as the
Spearman-Rank-correlation
coefficient
(rs).
Results
were
corrected
with
Bonferroni.
The influence of the number of small mammal species, the total number of
trapped animals, the soil characteristics, and the altitude on plant diversity were
calculated with a general linear model with the program Statistika. First all data
were tested for their normal distribution with a KS normality test. The data did not
differ significantly from the normal distribution. Plant diversity was taken as
dependent factor and all other factors were considered independent. No
interactions between the factors were taken into account. In a step-wise procedure
the independent factors with the highest p-value were left out one by one until all
remaining factors were significant.
To compare the different areas a Cluster-analysis was calculated. The
following factors were included in the Cluster-analysis for winter and summer:
small mammal number, small mammal species number, ground cover and number
of plant species. In addition the altitude and some soil characteristics were
included, as there were, the percentage of organic components and the
Subjects, materials and methods
18
concentration of the ions Na+, K+, Mg2+, Ca2+. The statistic program SPSS was
used. Differences were considered significant if their probability of occurring by
chance was less than 0.05 (two tailed).
3.4. Food-preference tests
This experiment was performed with two species, bush-Karoo-rats (O.
unisulcatus) and striped mice (R. pumilio). Ten rats and eleven mice were tested.
Striped mice were chosen as a representative, medium sized, diurnal species
(Schradin, Pillay 2004) and bush-Karoo-rats were chosen as a representative,
larger, crepuscular species (Brown & Willan 1991).
Animals were trapped for food-preference-tests as described above.
Trapping was performed in Goegap Nature Reserve and, in case of bush-Karoorats, on the neighbouring farm. Trapped animals were sexed, weighed and
marked with hair dye and/or eartags to identify them in case of recapture. Each
animal was used only once. The animals were put into a cage with sand as
substrate and pieces of six plant species. The plant pieces were all 3cm long but
of different weight, because equating weight would have led to immense
differences in surface and length (some plant species were succulent). It was
assumed that similar length ensures similar conditions for each plant species
better than similar weight. An equal number of dominant and subdominant plant
species were provided. The determination of dominance of plant species in areas
were the species lived was based on the previous studies (s. 3.3.). Plants were
freshly collected and stored in a refrigerator in airtight plastic bags containing wet
tissue paper. Plant species were arranged in a row on the short side of the cage.
Dominant species altered with subdominant species. Order was changed
systematically every experiment. The animals were left alone in a quiet room.
Beginning at 1h, the cage was checked every 30min. The experiment was
terminated when visible damage was done to one or more plant pieces, or a
maximum of 4h had elapsed. Tissue paper was positioned on top of the cage to
provide cover. Immediately after the experiment animals were released at the
place of capture. Plant species were weighed (Mettler Type AE 163, accuracy of
0,001g) before and after testing to determine the weight loss. To consider the
weight loss due to evaporation eight controls experiments were conducted. Here
the same procedure was used, but without an animal in the cage. The median of
Subjects, materials and methods
19
the eight control experiments was subtracted from the measured weight loss in all
experiments. In the event of negative results due to this subtraction the weight
loss was assumed to be 0. Tests were performed during the active period of the
species. In the first set of tests Euphorbie spec., Mesembryanthemum
guerichianum and Leipoldtia pauciflora were used as dominant plant species for
O. unisulcatus, Osteospermum sinuatum, Cheiridopsis denticulata and Aptosimum
spinescens were used as subdominant plant species. For R. pumilio Zygophyllum
retrofractum, Lycium cinereum and Leipoldtia pauciflora were used as dominant
plant species and Galenia africana, Lessertia dfiffusa and Rhus spec. as
subdominant species.
Because the first set of tests (pilot study) revealed that a mixture of
perennial and annual plant species can cause a bias in the dataset, a second set
of tests was performed, including only perennial plant species. In the second set
of tests two plant species were left out for each small mammal species. O.
unisulcatus was tested with Euphorbie spec, and Leipoldtia pauciflora as dominant
plant species and Osteospermum sinuatum and Aptosimum spinescens as
subdominant plant species. R. pumilio was tested with Zygophyllum retrofractum
and Leipoldtia pauciflora as dominant plant species and Galenia africana and
Rhus spec. as subdominant species.
The weight loss of the dominant/subdominant plant species in percentage
referred to the weight at the beginning of the experiment was added. Dominant
species were compared to subdominant species with the Wilcoxon matched pairs
rank sign test. For in depth analyses, the Friedman test for multiple paired
comparisons was used, followed by a Wilcoxon-Wilcox test as post test.
3.5. Plant biodiversity around occupied and unoccupied bush Karoo rat
nests
The vegetation around occupied nests of bush-Karoo-rats (Otomys unisulcatus)
was compared to that around unoccupied nests. Always one occupied and one
unoccupied nest in areas as similar to each other as possible were investigated.
The two nests of each pair were situated as close to each other as it was possible
to ensure that the inhabitants of the occupied nest did not influence the area
around the unoccupied one. Changes in the landscapes (i.e. riverbeds, rocks)
were taken into account. One pair was situated on an adjoining farm (cf. 3.6.); all
Subjects, materials and methods
20
other pairs (11) were in Goegap Nature Reserve. The diversity of plant species
around the nests was compared with the Wilcoxon matched pairs rank sign test.
The sample size was twelve pairs. Occupied nests were identified by fresh
droppings and fresh plant material, as indicators. Vegetation survey was
performed in a 10m radius around the nests. The same methods for data
recording were used that were described above (cf. 3.3.3.).
3.6. Fence line
The number of small mammal species on both sides of a fence between a farm
and the Goegap Nature Reserve was determined (Fig. 1). The farm has not been
used for stocking for two years, but great differences relative to the nature reserve
were still obvious in the assemblage of plant species. Trapping was performed in
a 290m transects as described above. The two trapping transects were situated
parallel to the fence. To exclude an influence of the fence itself and to avoid
trapping small mammals from the nature reserve on the farm or vice versa, that
were attracted by the traps themselves, traps were placed 20m away from the
fence.
Figure 3: Fence between Goegap Nature Reserve (left side) and a neighbouring farm (right
side)
Subjects, materials and methods
21
Eleven vegetation analyses on each side were performed to compare the
plant diversity. The vegetation analysis was done as described above. Squares
were distributed almost evenly along the transects. The numbers of plant species
in the eleven pairs of squares were compared with the Wilcoxon matched-pairs
signed-rank test. The number of small mammal species and the number of
trapped small mammal individuals were compared descriptively as sample sizes
were too small for statistics.
Results
22
4. Results
4.1. Correlation between small mammals and plants
4.1.1. Comparison between winter and summer
Significantly more plant species were found in summer (p=0.007; T=1). The
comparison between the plant cover of summer and winter revealed no significant
difference (p=0.514; T=17).
70 small mammal individuals were trapped in winter compared to 119
animals in summer (p=0.007; T=0). In the first trapping season (August/November)
ten species of small mammals were trapped. In the second trapping season
(October/November) nine species of small mammals were trapped. The species
were the same as in winter without the brush-tailed Hairy-footed Gerbil (G.
valinus). There was no significant difference concerning the number of species
(p=0.334; T=4). The detailed trapping data from winter and summer can be found
in Tables 4 and 5 (Appendix).
Results
23
Table 2: Summary about the trapped small mammal species in the ten investigated area, their
number (sM-species) and the number of trapped individuals of all species combined (sMnumber). First value stands for winter, second for summer.
Area
sM-species
sM-number
G. peaba
1 2
3 2
2 2
5 6
8 12
4
10
3 4
3
2 2
4
2 7
2
1 5
1
5 6 7 8 9
1
1 4 4
1
2 4 6
2
9 17 12
8
12 28 26
2
9 11 7
4 8 10
10
4
4
15
16
G. valinus
1
1
D. auricularis
2
12
2
R.pumilio
1
6
2
1
M. minutoides
A. namaquensis
1
6
2
O. unisulcatus
2
3
7
8
2
8
M. proboscideus
E. edwardii
E. rupestris
1
5
3
4
3
2
2
4
2
1
4
2
2
3
2
Results
24
4.1.2. Winter trapping season
The number of plant species in the ten investigated areas showed a significant
positive correlation with the total number of trapped animals (p=0.032; rs= 0.732;
Fig. 4) and with the number of small mammal species occurring there (p=0.004;
rs=0.895; Fig.5).
Winter
25
plant species total
20
15
10
5
0
0
2
4
6
8
10
12
14
16
18
sM-number
Figure 4: Correlation between the number of plant species and the total number auf trapped
small mammals (sM-number) in ten different areas. Spearman-Rank-Correlation-test:
p=0.032; rs= 0.732
Winter
25
plant species total
20
15
10
5
0
0
1
2
3
4
5
sM-species
Figure 5: Correlation between the number of plant species and the number auf occurring
small mammal species (sM-species) in ten different areas. Spearman-Rank-Correlation-test:
p=0.004; rs=0.895
Results
25
93.1% of the plant species in winter were perennial. The number of
perennial plant species showed a nearly significant correlation with the total
number of small mammals (p=0.056; rs=0.713; Fig. 6) and a significant correlation
with the number of small mammal species (p=0.002; rs=0.882; Fig. 7). A
correlation between small mammals and annual plant species was not calculated,
because they were nearly absent in winter. In half of the areas there were no
annuals at all and in the other areas there were only one or two species.
Winter
25
perennial plant species
20
15
10
5
0
0
2
4
6
8
10
12
14
16
18
sM-number
Figure 6: Correlation between the number of perennial plant species and the total number of
small mammals (sM-number) in ten different areas. Spearman-Rank-Correlation-test: p=0.056;
rs=0.713
Results
26
Winter
25
perennial plant species
20
15
10
5
0
0
1
2
3
4
5
sM-species
Figure 7: Correlation between the number of perennial plant species and the number of
occurring small mammal species (sM-species) in ten different areas. Spearman-RankCorrelation-test: p=0.002; rs=0.882
The red point represents two areas with the same values.
4.1.3. Summer trapping season
The total number of plant species did neither correlate with the number of
small mammal species (p=0.12; rs=0.559; Fig. 8) nor with the total number of
trapped small mammals (p=0.598; rs=0.334; Fig 9).
Summer
40
plant species total
35
30
25
20
15
10
5
0
5
10
15
20
25
30
sM-number
Figure 8: Correlation between the number of plant species and the total number of trapped
small mammals (sM-number) in ten different areas. Spearman-Rank-Correlation-test: p=0.12;
rs=0.559
Results
27
Summer
40
plant species total
35
30
25
20
15
10
5
0
1
2
3
4
5
6
7
sM-species
Figure 9: Correlation between the number of plant species and the number of occurring small
mammal species (sM-species) in ten different areas. Spearman-Rank-Correlation-test: p=0.598;
rs=0.334
The red point represents two areas with the same values.
There was no significant correlation between perennial plant diversity and the total
number of trapped small mammals (p=0,12; rs =0,612; Fig. 10). However the
number of perennial plants species and the number of small mammal species
showed a significant positive correlation (p=0.03; rs=0.763; Fig. 11). Compared to
the winter there were considerable more annual species in this season (Wilcoxon
matched pairs rank sign test; p=0,005 t=0). There was no significant correlation
between annual plant species and small mammals, neither with the number of
small mammal species (p=0.859; rs= 0.032) nor with the total number of small
mammals (p=0.815; rs= -0.110).
Results
28
Summer
25
perennial plant species
20
15
10
5
0
0
5
10
15
20
25
30
sM-number
Figure 10: Correlation between the number of perennial plant species and the number of
trapped small mammal (sM-number) in ten different areas. Spearman-Rank-Correlation-test:
p=0.12; rs=0,612
Summer
25
perennial plant species
20
15
10
5
0
0
1
2
3
4
5
6
7
sM-species
Figure 11: Correlation between the number of perennial plant species and the number auf
occurring small mammal species (sM-species) in ten different areas. Spearman-RankCorrelation-test: p=0.03; rs=0.763
Results
29
4.1.4. Correlation between plant cover and small mammals
The Spearman-Rank-Correlation-test revealed that plant cover correlated with the
number of trapped small mammals in the ten areas, as well as with the number of
trapped small mammal species. The correlations were significant for winter (plant
cover–sM-number: p=0.014, rs=0.741; plant cover–sM-species: p= 0.004, rs=0.811)
and summer (plant cover–sM-number: p=0.002, rs=0.844; plant cover – sMspecies: p= 0.038, rs=0.660).
4.1.5. Soil survey
Data of the soil survey are included into the cluster-analyses (4.1.6) and here
described descriptively. The pH-values of the ten areas had a range from 5.7 to
8.5 (Fig. 12). The lowest pH-values were found in the highest areas (9, 10).
Soil survey
10
8
pH
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10
11
Areas
Figure 12: pH-value of the ten areas, measured with dH2O as solvent.
Results
30
The percentage of organic component in the soil samples had a range from 0.92 to
2.97 % (Fig. 13).
Soil survey
3,5
Organic components in %
3,0
2,5
2,0
1,5
1,0
0,5
0,0
0
1
2
3
4
5
6
7
8
9
10
11
Areas
Figure 13: Organic components of soil samples from the ten areas in % from the oven-dry
mass. The median from 2 samples is given.
Results
31
The concentration of Fe2+ was too low to be measured. Mn2+ concentrations were
also very low and had a range from 0.076 mg/l to 0.382 mg/l. The concentrations
of the other ions are given in Figure 14.
Soil survey
Concentration of Ions in mg/l
100
Natrium
Calcium
Magnesium
Kalium
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
10
11
Areas
Figure 14: Concentration of the ions from Na, Ca, Mg, K in the soil of the ten areas.
Mean value of two soil solutions is given.
Results
32
4.1.6. Cluster-analysis
The following factors were included in the Cluster-analysis for winter and summer:
small mammal number, small mammal species number, ground cover and number
of plant species. In addition the altitude and some soil characteristics were
included, as there were, the percentage of organic components and the
concentration of the ions Na+, K+, Mg2+, Ca2+. Three Clusters were identified with a
hierarchic Cluster-analysis. Areas 8, 9 and 10 belonged to the first cluster, area 5
stood alone in the second one and areas 1, 2, 3, 4, 6 and 7 were in the third
cluster. The areas in the first cluster were characterised by high values concerning
small mammals and plants, whereas the second cluster (area 5) had very high
concentrations of soil nutrients. The areas in the third clusters had moderate values
in most of the factors (Tab. 3).
4.1.7. General linear model
The general linear model for winter revealed a significant result (p<0.05, F=5.87).
Floral diversity was explained by the number of small mammals (p=0.0006,
F=29.86) and by the concentration of Manganese in the soil (p=0.0034, F=16.94).
The model for summer was also significant (p<0.0001, F=48.27), and the only
remaining significant factor explaining plant diversity was the number of small
mammals species (p=0.000008, F=81.31).
Results
Cluster - analysis
Table 3: Mean value and standard deviation of all factors included in the hierarchic cluster-analyses. Cluster 1 includes the
areas 8, 9 and 10. Cluster 2 includes area 5 alone and Cluster 3 consists of the areas 1, 2, 3, 4, 6 and 7.
Winter
number of
2
plant
number of
sM-
sM-
plant
Altitude
(m)
organic
c (Na) c (K) c (Mg) c (Ca)
particles (%) mg/l
mg/l
mg/l
mg/l
n=3 Mean
18.33
14.67
4.00
56.67
25.33
23.33
4.67
53.33
1049.72
2.31
3.25
3,17
4.21 21.91
SD
4.51
2.52
0
20.82
5.77
6.43
1.15
5.77
67.12
0.63
1,15
2.57
2.30 10.29
n=1 Mean
9.00
2.00
1.00
40.00
11.00
8.00
1.00
45.00
855.30
2.27
65,68 23.40 23.85 95.51
.
.
.
.
.
.
.
.
.
.
.
.
n=6 Mean
8.67
4.00
1.50
14.33
21.00
6.83
1.67
13.58
915.98
1,16
4,72
7.71
4.00 29.23
SD
5.54
3.52
1.38
18.40
10.32
5.00
0.82
15.77
30.45
0.60
3,88
4.29
1.59 31.79
SD
3
sM-
Edaphic factors
plant species number species cover (%) plant species number species cover (%)
Cluster
1
sM-
Summer
.
.
33
Results
34
4.2. Food-Preference-tests
4.2.1. Pilot study
4.2.1.1. Striped mouse (R. pumilio)
The Friedman-test revealed an overall significant difference in how much was
eaten from the four different plant species (p=0.0001). The following WilcoxonWilcox-test showed that Lycium cinereum (dominant) and Lessertia diffusa
(subdominant) are different from Leipoldtia pauciflora (dominant) and Rhus spec.
(subdominant) concerning the consume by R. pumilio. The other plant species
were not different from each other.
4.2.1.2. Bush-Karoo rat (O.unisulcatus)
The Friedman-test revealed an overall significant difference in how much was
eaten from the four different plant species (p=0.004). However the following
Wilcoxon-Wilcox-test showed no differences between certain plant species.
Figure 15: bush-Karoo rat (Otomys unisulcatus) with ear tag in a cage in which the foodpreference test were performed
Results
35
4.2.2. Second set of tests
4.2.2.1. Striped mouse (R. pumilio)
R. pumilio showed a significant food preference for the dominant plant species Z.
retrofractum and L. pauciflora in comparison to subdominant plant species G.
africana and Rhus spec. (data for dominant species and subdominant species
combined; Wilcoxon matched pairs rank sign test; T=6; p = 0.007). The median
percentage of eaten dominant plants was 18.10 and 11.04 for subdominant plants,
respectively (Fig. 16).
Food-preference-test R. pumilio
50
eaten plant pieces in %
40
30
20
10
0
dominant plants
subdominant plants
Figure 16: Comparison of the quantity R. pumilio ate from two dominant /subdominant plant
species provided in a food-preference-test. Data were corrected for evaporation by control
experiments. t=6; p = 0.007
The Friedman-test revealed an overall significant difference in how much was
eaten from the four different plant species. The following Wilcoxon-Wilcox-test
showed that Z. retrofractum is different from all other plant species concerning the
consume by R. pumilio. The dominant shrub Z. retrofractum was the preferred
food-plant. The other plant species were not different from each other.
Results
36
4.2.2.2. Bush Karoo rat (O. unisulcatus)
O. unisulcatus showed a significant food preference. In contrast to the striped mice
they preferred the subdominant plants Osteospermum sinuatum and Aptosium
spinescens to the dominant plant species L. pauciflora and Euphorbia spec. (data
for dominant species and subdominant species combined; Wilcoxon matched
pairs rank sign test; T=1; p = 0.002). The median percentage of eaten
subdominant plants was 95.33 and 3.41 for dominant plants (Fig. 17).
Food-preference-tests O.unisulcatus
140
eaten plant pieces in %
120
100
80
60
40
20
0
dominant plants
subdominant plants
Figure 17: Comparison of the quantity of dominant and subdominant plants eaten by O.
unisulcatus provided in a choice test. Data were corrected for evaporation by control
experiments. T=1; p = 0.002
The Friedman-test revealed an overall significant difference in how much was
eaten from the four different plant species. The following Wilcoxon-Wilcox-test
showed that O. sinuatum is different from all other plant species concerning the
consume by O. unisulcatus. The other plant species were not different from each
other. O. sinuatum was the preferred food-plant.
Results
37
4.3. Plant biodiversity around bush Karoo rat nests
The effect of bush-Karoo rats on their direct environment was investigated by
counting the plant species in a circuit of 10m around occupied and unoccupied
bush-Karoo rat nests.
The comparison between the surrounding of occupied and unoccupied
bush-Karoo-rat nests (Fig. 18) showed a significant difference concerning the
number of plant species found in a circuit of 10m. Significantly more plant species
were found around occupied nests (Wilcoxon matched pairs rank sign test;
T=16.5; p = 0.05).
.
BKR-nests
30
number of plant species
25
20
15
10
5
0
unoccupied
occupied
Figure 18: Comparison between the number of plant species in a circuit of 10m around
occupied and unoccupied nests of O. unisulcatus. Median and original data are given. A
line connects the data of one pair of nests in the same area. T=16.5; p = 0.05
Results
38
4.4. Fence line
A significant difference concerning the plant diversity in Goegap Nature
Reserve and the farm was found (Wilcoxon matched pairs rank sign test T=2.5;
p = 0.01; Fig. 19). In nine of eleven pairs there were more plant species on the
farm. Median number of plant species on the farm was 7 compared to 6 in the
Nature Reserve.
Fence line
18
number of plant species
16
Nature reserve
Farm
14
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10
11
12
vegetation surveys
Figure 19: Comparison between the number of plant species on both sides of a fence between
Goegap Nature Reserve and a farm. I made 11 pairs of vegetation surveys on the same level.
T=2.5; p = 0.01
There were too few small mammals trapped for statistical comparisons. On the
Farm one G. paeba and three A. namaquensis were trapped. In the nature reserve
four R. pumilio and one G. paeba were trapped. Trapping data can be found in
Table 6 (Appendix).
Discussion
39
5. Discussion
Conservation (i.e. the maintenance and protection of natural habitats) is one of the
main challenges and duties of our time, as it also functions to protect our own
endangered habitat. An important part of conservation is the protection of species.
All species in an ecosystem are connected to each other in a more or less direct
way (Begon et al. 1998). The extinction of one species often has severe
consequences for other species in its ecosystem (Begon et al. 1998). Humans are
also involved given the fact that earth itself is the biggest known ecosystem.
Biodiversity is also of immense value with regards to adaption. No matter if from
human interference or more natural caused, our environment will change during
the following decades. With a more variable genpool it will be much easier for life
to adapt to these changes. Given the current rate of extinction and the explosion of
human population density, conservation is of increasing importance. In places
where many species live in a small area, conservation is most effective (Myers et
al. 2000). One of these places is the Succulent Karoo with its extraordinary floral
diversity (Myers et al. 2000). To provide effective conservation methods for plant
diversity, it is essential to find out which factors influence or maintain biodiversity.
Herbivore animals feeding on plants might be one of these factors. In the
Succulent Karoo small mammals are of special importance, because they have
high population densities here and larger herbivores are relatively rare. The
influence of small mammals on plant diversity was investigated in this study for the
first time.
5.1. Correlation between small mammals and plants
Previous studies on the influence of predators on biodiversity revealed
contradictory results with predators either increasing (Paine 1966, Lubchenco
1978) or decreasing (Harper 1969; Lubchenco 1978) the diversity of their foodplants. This difference might be due to whether the preferred prey species belongs
to the dominant or subdominant species in each case. It is crucial to know about
this because predators are only assumed to increase the diversity of their prey if
they prefer dominant prey species, making space for subdominant species, which
would otherwise be outcompeted (Lubchenco 1978). This predation-hypothesis
was first described by Paine (1966) and has so far been tested only in habitats
Discussion
40
with average biodiversity. To my knowledge my study is the first to test the
predation hypothesis on a biodiversity hotspot: the Succulent Karoo (Myers et al.
2000).
I found that plant diversity correlated significantly with the number of
trapped small mammals and the number of their species in winter (July/August).
This was true for the total number of plant species and for the perennial plant
species separately. In summer (November/December) only the association
between perennial plant species and the number of small mammal species
showed a significant, positive correlation. A correlation between perennial plant
species and the number of trapped small mammals however could not be
demonstrated. These results support the predation-hypothesis and indicate that
small mammals could increase biodiversity in the Succulent Karoo. However I
cannot be sure in this stadium, whether the relation I found was due to an
influence of small mammals on plants or the other way around. Maybe small
mammals have a positive influence on plant diversity, but not from reducing
dominant plant species. Indirect ways of influence are possible. Small mammals
digging burrows might for example increase plant diversity, because their burrows
store water during rainfall and keep it available for plants. However, only three of
the 10 trapped small mammal species burrowed (the three gerbil species).
Furthermore it is possible that other factors, such as altitude and edaphic factors
(see 3.3.4, 3.3.5 and 3.3.6) influenced plants and small mammals in a similar way,
although this is highly unlikely, because of the results the general linear model
revealed.
In winter plant biodiversity correlated more strongly with the number of
small mammal species than with the total number of small mammals, and in
summer the only significant correlation I found was also with to the number of
small mammal species and not with the total number of trapped individuals. The
stronger influence of small mammal species on plant diversity is probably due to
the range of their diet. One small mammal species alone affects possibly only a
few plant species that it prefers as food-plants. Many small mammal species
together, however, are likely to have a more variable diet and therefore a stronger
influence.
Additionally different species feed on different parts of their food plants (e.g.
seeds, leaves, roots). Therefore a plant species eaten by only one small mammal
Discussion
41
species might not be influences severely because the damage is done to only one
part of the plant. Many small mammal species together however might have a
much stronger influence, even if they have a low population density.
One reason for the stronger correlation between small mammals and plants
in winter might be the smaller cruising radius small mammals typically have in
winter (Schubert 2005). The larger the cruising radius of herbivores is, the smaller
should be the effect on plants in their surrounding, because the influence of a
single individual is spread over a larger area. It is also possible that small
mammals choose their habitat based on the diversity of their food plants, which is
why the correlation between small mammals and plant diversity would be stronger
in winter, when food is a more limited factor than in the early summer.
The Succulent Karoo is a seasonal environment with abundant plant growth
by ephemerals in spring, which is also the breeding season of most small
mammals (Schradin & Pillay 2005; Jackson 1999). In my study as well I found
both a higher abundance of small mammals and annual plant species at the
beginning of summer. The correlation between small mammals and annual plant
species could not be calculated for the winter-trapping-season season because
annuals were nearly absent during this season (Cowling 1999). Even in summer
when there were numerous annuals there was no significant correlation. Obviously
small mammals and annuals have no remarkable influence on each other.
Possibly the short time-span in which the two can interact plays a part here. Most
of the annual plant species in Namaqualand are ephemeral and have a lifespan of
only a few months. Small mammals on the one hand do not have enough time to
reduce certain dominant or subdominant plant species significantly because
annuals occur in great numbers for a relatively short period in spring and vanish
quickly when it gets dry in summer. On the other hand, due to their short lifespan,
annuals are not important for the over-winter survival of small mammals. Annuals
are essential for their breeding season, but small mammals cannot rely on annuals
over the whole year. This reduces the influence of annual plant species on the
species composition of small mammals.
In the future it would be good include other small mammal species that
were not sampled in my study. With different types of traps for example it would be
possible to trap small mammal species that do not enter the Shearman traps I
used. Whistling rats (Parotomys brantsii, Parotomys littledalei) and subterranean
Discussion
42
species like mole rats (Bathyergus janetta, Cryptomys hottentotus) belong to this
group. Dassie rats (Petromus typicus) are probably not attracted by the bait I used.
Another aspect that has not been taken into account in my studies is that insects
certainly also are important herbivores (Zeller 2002) and to my knowledge there
are no studies on their influence on biodiversity in Namaqualand or anywhere else.
Another constraint of this study could be the unevenly distribution of the ten
areas within the nature reserve. For methodological reasons the distances
between the areas are very different (Fig. 1). The areas were chosen in order to
be ecologically different, but nevertheless it cannot be excluded that the data from
some areas are more similar to each other than others, because of the varying
distance between them.
The correlations I found support the hypothesis that small mammals affect
floral diversity. However it cannot be said at the moment if there is a causal
connection between small mammals and plants. A clear statement would require
further investigations using an experimental approach. There are several fenced
monitoring plots in Goegap Nature Reserve. The fence protects the plants growing
inside the plots from bigger herbivores but not from small mammals. To prove the
influence of small mammals on plant diversity it would be useful to fence these
plots in a way that also excludes small mammals. A comparison between these
fenced plots and adjacent unprotected areas over several years and during
different seasons would make it possible to test the influence of small mammals
on plant biodiversity experimentally.
5.2. Food-preference-test
If small mammals influence plant biodiversity in the way predicted by the
predation-hypothesis it would be expected that at least some of them prefer
dominant plant species. Dominant plant species are not seriously threatened even
if they are the preferred food-plants. Being eaten just prevents them from
displacing subdominant plant-species. A preference for subdominant food-plants
however could lead to their extinction.
Discussion
43
5.2.1. Pilot study
The pilot study revealed that R. pumilio preferred the two plant species
Lessertia. diffusa and Lycium. cinereum. Lessertia. diffusa is an annual plant
species and therefore just available for the mice in spring and early summer. This
is also true for L. cinereum. Although this is a perennial shrub it foliates only in
spring. R. pumilio seems to prefer this fresh food in general. The same seems to
apply to O. unisulcatus. Nine out of the ten animals I tested preferred
Mesembryanthemum guerichianum, which was the only annual plant species in
the test. This can be easily explained by the higher nutrient value of annuals in
comparison with perennials (Oftedal 2002). To exclude the preference for fresh
plant material, only perennial shrubs, which are available throughout the year,
were used in the second set of tests.
5.2.2. Second set of tests
The influence of herbivores on their food-plant’s diversity depends
decisively on the preference of herbivores for dominant or subdominant plants
(Lubchenco 1978). In fact both of the tested species, O. unisulcatus and R.
pumilio, showed a significant preference. Interestingly the two preferences did not
point in the same direction. Whereas R. pumilio preferred the dominant food-plants
in the tests, O. unisulcatus favoured the subdominant plant species. This result
implies a positive influence from R. pumilio on plant diversity and a negative one
from O. unisulcatus as explained above (see 5.1.).
The choice of the tested plant species was done randomly. So it can be that
some species were chosen that are not included in the animals’ diet or are even
unpalatable. To be unpalatable is an effective strategy for plants to protect
themselves from being eaten. This way subdominant or formerly subdominant
plants can resist their palatable competitors that would probably outcompete them
otherwise. This can be seen most clearly on rangeland, where plants that are
unpalatable for livestock can spread unchecked. One of these plants is the shrub
Z. retrofractum, which is unpalatable for livestock, but the preferred food-plant of
R. pumilio. Z. retrofractum leaves contain toxic substances in their sap but not all
leaves are toxic to the same extend (pers. commun. du Toit, state botanist,
Northern Cape Province). R. pumilio might be able to feed specifically only on the
non-toxic very small leaves and seeds (size of a pinhead), which bigger ungulates
Discussion
44
like goats and sheep are unable to do. Livestock cannot choose the few palatable
leaves out of the large number of leaves growing on one branch. Z. retrofractum is
a dominant plant species and its population density can only be regulated by small
mammals. This can be of great interest for the farmers in Namaqualand, who
prefer to have palatable plants on their land, but support Z. retrofractum without
meaning to by high stocking rates, i.e. reducing its palatable competitors. Small
mammals are often seen as pests and their profitable side is overlooked.
There is certainly a need for food-preference-tests with other herbivore
species and it would be beneficial to repeat them with more plant species on R.
pumilio and O. unisulcatus. This would lead to a more general understanding of
the influence herbivores have on their food-plants in the Succulent Karoo.
5.3. Plant biodiversity around bush-Karoo rat nests
To measure a possible effect of small mammals on biodiversity directly, the plant
diversity around occupied/unoccupied nests of O. unisulcatus, was determined. O.
unisulcatus is a central place forager and therefore especially qualified for this
study. They feed in the direct surroundings of their nests so that an influence of a
rat’s presence can be determined by investigating the area around an occupied
nest. The population density of O. unisulcatus was not as high as usual, because
a drought during the previous year made them locally extinct on the study site,
which they only started to colonise again (from a neighbouring farm) in 2004, when
this study took place. Therefore there were occupied and abandoned areas, which
could be compared to each other. These circumstances were for example not true
for R. pumilio, which have a different foraging strategy and roam their homerange
searching for food. A study on R. pumilio was also made impossible by the fact
that it builds its nest in bushes in such a way that one cannot see them from
outside. Although several nesting sites were known from other studies, a study
was not possible because in the concerning area the population density was so
high that it was impossible to find unoccupied areas for comparison.
While the results of the food-preference-tests indicated that O. unisulcatus
might have a negative influence on plant diversity, the vegetation surveys around
the nests suggested the opposite. As the study was designed to have occupancy
as the only difference between the compared nests, the higher diversity around
Discussion
45
occupied nests could be due either to rats increasing plant biodiversity or rats
choosing nesting sites with higher plant biodiversity. I cannot say which possibility
is correct with this correlative study. Additionally, there might be other factors,
unrecognised by me, influencing the presence of rats and plant diversity in the
same way. Should the rats choose their nesting site according to floral diversity,
the duration of occupancy in the moment of investigation might affect the result.
Since the food-preference-tests implied a negative influence of O. unisulcatus, it is
possible that a recently occupied nest has a high plant diversity in its
surroundings, because the animals have chosen the nesting site according to
plant diversity. The surroundings of a nest that has been exposed to the potentially
negative influence of O. unisulcatus for a long time could have reduced plant
diversity. It is known, however, that many nests are used for several years (Brown
& Willan 1991; Schradin unpublished data). Therefore, it is not likely that O.
unisulcatus do lasting damage to their environment by, for example, causing the
extinction of subdominant plant species because they would not be able to live in
the same region for years in that case.
The high plant diversity around occupied nests of O. unisulcatus can also
be reconciled with the results of the food-preference tests in another way. It is
possible that other small mammals, which in contrast to O. unisulcatus prefer
dominant food-plants, but also prefer to stay next to O. unisulcatus, compensate
for the negative influence of O. unisulcatus. R. pumilio for example use
unoccupied nests of O. unisulcatus (Schradin in press). In this case I measured
not the direct effect of O. unisulcatus on the surroundings of their nests, but the
influence of other small mammals that are associates with O. unisulcatus.
5.4. Other factors that might influence plant biodiversity
The pH-values of the soil samples from the ten areas showed little variation.
Only the areas 9 and 10 had remarkably low pH-values. These two areas were at
a much higher altitude compared to the others and are also most distant from
them, which is a probable explanation for this deviation. Areas 9 and 10 also have
high percentages of organic particles in the soil that are known to decrease pHvalue because of their humic substances (Gisi 1997).
The highest percentage of organic components in the soil was found in
areas 1, 5, 9 and 10. Area 10 consists mainly of big rocks, so the soil samples
Discussion
46
were taken from the sandy patches in between. Probably organic soil particles are
concentrated in these places. The same could be true for the areas 1 and 9, which
are both situated on the foot of a hill, where wind and rain might deposit organic
particles. Area 5 did not only have a high percentage of organic soil components,
but also high concentrations of different metal ions. The area is situated next to an
old cooper mine. Strong winds, which are quite common in Namaqualand, often
blew grey dust from the mining dump to area 5. Most probably this is the reason
for the high concentrations of metal ions. The high concentration of organic
particles however remains surprising. In spite of high nutrient concentrations and
the organic particles in the soil, there was no extraordinarily high plant diversity or
plant cover in area 5. The sparse vegetation in areas 3, 4 and 6 can explain the
low percentage of organic components there.
The Cluster-analysis that included additional measured factors showed
clearly that small mammals and plants are more abundant in areas 8, 9 and 10 (cf.
Tab. 2). These areas are also at the highest average altitude and have the highest
average percentage of organic particles in the soil. The plant diversity might
directly affect the organic soil particles and the small mammal number and species
number, or the other way around. The altitude, however, is independent from plant
diversity. It is surprising on the first view that biodiversity seems to increase with
increasing altitude, because in the Andean forests the opposite effect can be
found (Gentry 1988). On the second view one can see that areas 8, 9, and 10 also
have moderate or plenty rainfall (cf. Tab. 1). Higher areas seem to have a
tendency to get more rainfall, which would explain the high plant diversity. Clouds
coming from the Atlantic rain out on the higher slopes whereas they often just pass
by in lower regions. For this reason the Kamiesberg area, the bioregion with the
highest altitude in Namaqualand, has got the highest average annual rainfall of all
bioregions here (Cowling 1999).
The general linear model showed that plant diversity could be explained by
small mammal diversity in winter and in summer. Concerning this result I can now
exclude the alternative explanation that other factors influenced plants and small
mammals in the same way and caused the correlation I found. Combining this
result with the others I can say now that small mammals indeed affect plant
diversity in Namaqualand. It was, however, surprising that plant diversity in winter
can also be explained by the concentration of manganese in the soil. Manganese
Discussion
47
is an essential nutrient for plants, but this is also true for other nutrients. It is even
more surprising that this connection between manganese and plant diversity was
only found in winter. So the importance of manganese seems to vary within the
year.
5.5. Fence line
The comparison between the floras of a Nature Reserve with those of a
neighbouring farm showed a significantly higher diversity on the farm. The plants
of the farm have been exposed to the influence of goats, sheep and cattle for
many years. If the stocking had a positive influence on the diversity of plants, this
could be due to livestock preferring dominant plant species and thereby keeping
them away from outcompeting subdominant food-plants. Because herbivores
decrease the diversity of their food-plants if they prefer subdominant plant species
(Lubchenco 1978) and the farm had a higher plant diversity in comparison to the
ungrazed nature reserve, it is unlikely that there is a preference for subdominant
plants.
The edibility of the plants was however unaccounted for in this study.
Possibly many of the subdominant plant species are unpalatable and therefore not
eaten by ungulates. This possibility requires further investigation. A high
reproduction of unpalatable plants (e.g. Galenia africana) was found in several
studies (Todd & Hoffman 1999).
Furthermore, one can think of other ways for livestock to increase
biodiversity. Their dung for example might be an advantage for plants growing on
farmland. The investigated farm has not been grazed for nearly 2 years and thus
might be in a phase of regeneration in which many pioneer-plants increase the
population density.
The season in which the study was conducted might also be of importance.
The vegetation surveys were done in spring and many annual plant species were
included in the investigation. Grazing has a particularly negative influence on
different shrubs, which were reduced by livestock. Unpalatable plants, like Z.
retrofractum and G. africana are left behind with sandy patches between them. On
these sandy patches a great number of annuals can be found in spring. Because
the investigated farm was not grazed in 2004, annual plant species could easily
Discussion
48
establish themselves. Probably the study would have had another result if it had
been conducted in winter.
Besides stock farming, other factors might be responsible for the species
richness on the farm. The farmers planted some trees for example and the areas
on the two sides of the fence differed in heterogeneity. The study area on the farm
was much more heterogeneous. Although there was a plain area and a sandy and
rocky area on both sides, there also was a waterhole on the farm. Water is of
enormous importance for plants, especially in arid regions. So it is likely that this
water hole had a positive effect on the plants of the farm. For methodological
reasons it was not possible to conduct this study in a more homogeneous area. It
would be important to repeat this study in a more appropriate area. This would
also be interesting with regards to small mammals. Joubert and Ryan (1999)
mentioned that the species composition on high stocking rate rangeland is a
subset of the species occurring in areas with lower stocking rates. In my study
there was neither a remarkable difference in small mammal species number nor in
number of trapped individuals. Only species composition differed. G. paeba was
trapped on the farm and on the nature reserve. This species is one of the most
abundant ones in the Hardeveld (this study) and seems to be very tolerant
regarding its habitat. As G. paeba is nocturnal (Stuart & Stuart 2001) and lives in
burrows, one can imagine that it is not so dependent on plant cover because there
is no need to hide from birds of prey, which are mainly diurnal and no shrubs are
required as nesting sites. G. paeba was also trapped on highly overgrazed
rangeland in other studies (Joubert & Ryan 1999). It does not seem to be a good
indicator species. A. namaquensis was also trapped on the farm. This species is
highly dependent on rocky areas (Stuart & Stuart 2001), but was trapped here
near the reeds at the mentioned water hole. Next to this place is a heap of stone
wreckage that might have been used by the mice as substitute for rock crevices.
R. pumilio was only trapped in the Nature Reserve, which had considerably more
shrubs providing cover and nesting sites.
When trapping for food choice tests on the farm and investigating bushKaroo rat nests, I also trapped several O. unisulcatus, a few R. pumilio and one
Mus minutoides on the farm right next to my transect. Additionally it is known from
earlier studies that O. unisulcatus and Macroscelides proboscideus live in the
nature reserve next to the fence (Schradin unpublished data). It is surprising that
Discussion
49
these species were not trapped during the actual fence-line-study (four trapping
days/nights). Possibly the trapping sites were not optimally chosen. Should this
study be reproduced in another place, it is advisable to increase the number of
trapping days. Although a clear statement about the effect of grazing on plant
diversity cannot be given in the end, the study still has value if one considers it to
be a pilot study for following investigations, which can hopefully be conducted
under better circumstances.
Conclusions
50
6. Conclusions
The results of my studies, though being mainly correlative, indicate an influence of
small mammals on plant diversity in the Succulent Karoo. This knowledge could
make it easier in the future to protect this biodiversity-hotspot. Conservation is
hardly possible without knowing the ecological background. From this study it is
now clear that it is not enough to protect the threatened plant species directly. It is
also necessary to consider small mammals in conservation programs, even if they
are not threatened themselves. Additionally, further investigations are urgently
needed, especially experimental ones that exclude small mammals from certain
areas and allow a direct comparison between areas influenced and protected from
small herbivorous mammals.
References
51
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Appendix
58
8. Appendix
Table 4: Trapping data from the winter-trapping season
species
number date
1 6.7.2004
M. minutoides
2 8.7.2004
M. minutoides
0 6.7.2004
A. namquensis
1 5.7.2004
A. namquensis
1 8.7.2004
A. namquensis
1 8.7.2004
E. rupestris
1 5.7.2004
G. paeba
2 5.7.2004
G. paeba
3 6.7.2004
G. paeba
4 9.7.2004
G. paeba
1 5.7.2004
M. proboscideus
2 5.7.2004
M. proboscideus
6 10.7.2004
G. paeba
7 11.7.2004
G. paeba
1 10.7.2004
R. pumilio
1 10.7.2004
R. pumilio
1 11.7.2004
R. pumilio
1 14.7.2004
R. pumilio
1 10.7.2004
G. valinus
1 15.7.2004
G. paeba
2 19.7.2004
G. paeba
1 20.7.2004
G. paeba
2 20.7.2004
G. paeba
2 21.7.2004
G. paeba
3 20.7.2004
G. paeba
4 20.7.2004
G. paeba
5 20.7.2004
G. paeba
12 21.7.2004
G. paeba
17 23.7.2004
G. paeba
18 23.7.2004
G. paeba
20 28.7.2004
G. paeba
1 21.7.2001
R. pumilio
1 21.7.2004
R. pumilio
1 28.7.2004
R. pumilio
1 28.7.2004
R. pumilio
2
23.7.2004
R. pumilio
1 20.7.2004
O. unisulcatus
6 20.7.2004
G. paeba
7 20.7.2004
G. paeba
8 20.7.2004
G. paeba
9 21.7.2004
G. paeba
10 21.7.2004
G. paeba
11 21.7.2004
G. paeba
13 21.7.2004
G. paeba
14 21.7.2004
G. paeba
15 21.7.2004
G. paeba
time area station weight (g) sex
20:05
1
30 08:06
1
28 19:55
1
15 19:55
1
29 m
06:31
1
29 m
07:53
1
7m
21:20
2
14 21:30
2
29 20:22
2
10 06:45
2
4
27 20:20
2
28 f
20:25
2
30 f
21:28
4
27
23 19:42
4
29
24 19:45
4
11
32 21:12
4
11 21:12
4
9
37 07:00
4
7
30 21:13
4
15
26 m
21:10
5
19
29 06:25
5
5
26 21:00
7
4
25 21:05
7
10
27 19:20
7
4
27 21:10
7
12
26 m
21:17
7
24
27 m
21:17
7
27
30 m
20:50
7
5
24 f
06:20
7
19
27 06:30
7
30
27 m
06:30
7
1
25 16:43
8
3
52 m
18:10
8
3
m
09:35
8
2
50 m
11:10
8
2
m
11:00
8
1
37 m
18:12
8
2
106 m
21:45
8
13
27 21:50
8
19
25 f
22:02
8
24
25 f
19:40
8
26
30 m
19:47
8
9
30 20:00
8
2
26 21:15
8
30
25 f
21:25
8
19
28 21:30
8
13
25 -
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
number date
time area station weight (g) sex
16 21.7.2004 21:36
8
5
28 G. paeba
16 23.7.2004 06:50
8
24
25 G. paeba
19 23.7.2004 06:59
8
21
26 G. paeba
1 20.7.2004 21:55
8
24
23 f
M. proboscideus
2 21.7.2004 20:03
8
1
49 f
M. proboscideus
3 28.7.2004 06:50
8
11
40 f
M. proboscideus
9
29
55 m
1 4.8.2004 10:45
G. paeba
1 31.7.2004 19:43
9
8
27 m
G. paeba
1 4.8.2004 06:12
9
4
24 m
G. paeba
2 31.7.2004 21:05
9
29
20 f
G. paeba
3 3.8.2004 06:09
9
5
28 m
G. paeba
3 4.8.2004 06:20
9
6
27 m
G. paeba
9
4
25 4 3.8.2004 07:46
G. paeba
5 4.8.2004 06:12
9
3
26 G. paeba
9
8
25 m
6 4.8.2004 06:26
G. paeba
7 4.8.2004 06:37
9
25
22 G. paeba
3 31.7.2004 18:02
9
26
55 E. edwardii
4 31.7.2004 18:10
9
30
54 f
E. edwardii
4 4.8.2004 07:55
9
28
53
E. edwardii
9
5
41 m
1 29.7.2004 19:30
M. proboscideus
1 31.7.2004 19:38
9
5
40 m
M. proboscideus
1 3.8.2004 06:14
9
9
45 m
M. proboscideus
1 4.8.2004 06:31
9
13
46 m
M. proboscideus
1 4.8.2004 07:50
9
2
43 M. proboscideus
2 29.7.2017 19:37
9
12
54 f
M. proboscideus
2 31.7.2004 19:34
9
2
45 f
M. proboscideus
2 3.8.2004 07:54
9
13
57 f
M. proboscideus
1 29.7.2004 19:56 10
3
10 m
M. minutoides
2 31.7.2004 20:06 10
3
10 M. minutoides
0 4.8.2004 07:04 10
28
12 M. minutoides
1 29.7.2004 18:31 10
28 f
A. namaquensis
1 31.7.2004 18:35 10
28
47 f
A. namaquensis
1 31.7.2004 20:42 10
28
46 f
A. namaquensis
2 29.7.2004 18:40 10
29
39 f
A. namaquensis
2 29.7.2004 20:27 10
26
44 f
A. namaquensis
2 31.7.2004 18:36 10
29
38 f
A. namaquensis
2 3.8.2004 06:43 10
27
40 A. namaquensis
2 4.8.2004 07:04 10
29
43 f
A. namaquensis
2 4.8.2004 08:22 10
27
46 f
A. namaquensis
3 29.7.2004 18:40 10
29
39 m
A. namaquensis
3 29.7.2004 20:40 10
29
50 m
A. namaquensis
3 31.7.2004 18:36 10
30
47 m
A. namaquensis
3 31.7.2004 20:46 10
29
46 m
A. namaquensis
3 31.7.2004 21:22 10
23
44 m
A. namaquensis
3 3.8.2004 08:37 10
28
46 m
A. namaquensis
4 29.7.2004 20:10 10
17
52 m
A. namaquensis
4 3.8.2004 08:06 10
1
58 m
A. namaquensis
5 29.7.2004 20:27 10
28
57 m
A. namaquensis
5 31.7.2004 20:20 10
11
51 m
A. namaquensis
6 29.7.2004 21:35 10
28
46 A. namaquensis
59
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
E. edwardii
E. edwardii
E. edwardii
E. edwardii
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
60
number date
6 31.7.2001
7 31.7.2004
7 3.8.2004
7 4.8.2004
X
29.7.2004
1 3.8.2004
1 4.8.2004
2 29.7.2004
2 31.7.2004
1 29.7.2004
1 3.8.2004
1 4.8.2004
2 31.7.2004
2 3.8.2004
0 4.8.2004
time area station weight (g) sex
20:34 10
25
39 20:25 10
17
46 f
08:16 10
10
46 f
08:59 10
21
45 f
20:20 10
22 06:30 10
1
50 m
06:50 10
3
52 m
21:20 10
3
52 16:38 10
1
60 18:18 10
25
74 f
08:25 10
20
64 f
07:04 10
30
65 f
18:33 10
23
59 08:30 10
21
58 f
08:10 10
20
63 m
Table 5: Trapping data from the summer-trapping season
species
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
R. pumilio
R. pumilio
R. pumilio
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
number date
time area station weight (g) sex
1
10
30 0 8.11.2004 22:24
0 10.11.2004 04:40
1
13
33 20 7.11.2004 22:18
1
9
28 f
30 8.11.2004 22:19
1
9
57 0 7.11.2004 20:58
1
9
25 f
20 7.11.2004 17:48
1
9
61 m
20 10.11.2004 06:00
1
30
64 m
20 11.11.2004 07:36
1
12
65 30 7.11.2004 17:55
1
12
73 f
30 7.11.2004 20:55
1
730 8.11.2004 18:02
1
5
73 f
30 8.11.2004 19:07
1
730 8.11.2004 21:05
1
10 30 10.11.2004 07:30
1
5
78 30 11.11.2004 06:05
1
4
80 100 8.11.2004 18:03
1
10
28 f
100 8.11.2004 21:00
1
9
29 f
100 10.11.2004 06:01
1
9
30 100 11.11.2004 06:10
1
9
34 200 10.11.2004 04:37
1
10
31 f
200 11.11.2004 06:08
1
7
25,5 0 10.11.2004 07:50
2
30
44 m
0 11.11.2004 07:50
2
29
48 m
561 11.11.2004 09:00
2
30
48 m
0 11.11.2004 05:00
2
4
16,5 f
2 7.11.2004 22:41
2
19
30 m
2 11.11.2004 05:11
2
17
34 4 7.11.2004 22:44
2
21
33 m
4 8.11.2004 22:50
2
21
30 4 11.11.2004 05:05
2
7
34 10 11.11.2004 05:14
2
25
29 m
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
R. pumilio
O. unisulcatus
O. unisulcatus
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
M. proboscideus
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
M. proboscideus
61
number date
time area station weight (g) sex
20 7.11.2004 22:36
2
11
16 m
2
30
25 f
30 7.11.2004 22:47
100 8.11.2004 22:42
2
7
29 200 8.11.2004 22:46
2
11
15 m
300 10.11.2004 04:54
2
11
18 m
300 11.11.2004 05:09
2
11
18 300 11.11.2004 06:00
2
11 2
30
29 X
10.11.2004 05:00
X
11.11.2004 05:17
2
26
28 3 18.10.2004 06:17
3
27
32 3
4
36 f
1 19.10.2004 04:39
4
5
113 m
1 15.10.2004 19:25
2 18.10.2004 06:32
4
5
91 f
4
19
8f
0 15.10.2004 21:00
1 15.10.2004 21:10
4
26
13 m
X
18.10.2004 04:55
4
72 18.10.2004 04:58
4
9
23 2 19.10.2004 05:05
4
23
27 m
4
27
32 3 18.10.2004 06:17
7 19.10.2004 04:58
4
10
26 f
4
30
32 f
1 19.10.2004 05:10
5
15
14 0 2.11.2004 10:31
0 3.11.2004 10:28
5
11
14 f
20 2.11.2004 10:34
5
17
33 f
30 2.11.2004 09:10
5
5
16 m
30 6.11.2004 04:50
5
5
15 100 2.11.2004 10:39
5
23
28 f
100 5.11.2004 04:55
5
17
31 200 5.11.2004 04:48
5
3
15 m
300 5.11.2004 04:58
5
30
22 m
800 6.11.2004 03:17
5
17
31 m
10 6.11.2004 05:00
5
28
30 f
2 21.10.2004 22:14
7
25
33 2 22.10.2004 22:10
7
28
31 m
2 25.10.2004 06:10
7
3
30 m
6 24.10.2004 04:28
7
9
33 f
10 25.10.2004 04:31
7
7
30 f
11 25.10.2004 04:40
7
21
28 m
0 25.10.2004 06:20
7
17
37 m
1 21.10.2004 19:04
7
1
30 f
1 24.10.2004 04:20
7
4
32 f
1 25.10.2004 06:05
7
1
37 f
2 21.10.2004 20:55
7
19
51 f
2 24.10.2004 04:35
7
19
53 f
7
28
52 f
3 21.10.2004 21:00
3 24.10.2004 04:40
7
30
53 f
4 21.10.2004 21:00
7
29
41 m
6 21.10.2004 22:08
7
9
38 m
7 22.10.2004 20:45
7
4
38 m
7 24.10.2004 07:19
7
4
42 m
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
O. unisulcatus
O. unisulcatus
O. unisulcatus
O. unisulcatus
O. unisulcatus
O. unisulcatus
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
M. proboscideus
M. proboscideus
M. minutoides
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
R. pumilio
62
number date
time area station weight (g) sex
0 22.10.1004 17:54
8
11
55 m
0 24.10.2004 09:17
8
2
52 m
0 25.10.2004 07:55
8
12
50 m
1 21.10.2004 17:56
8
30
46 m
2 21.10.2004 19:20
8
29
44 f
2 22.10.2004 17:50
8
30
41 f
2 22.10.2004 19:15
8
30
41 2 24.10.2004 07:36
8
28
35 f
2 25.10.2004 07:50
8
29
41 3 24.10.2004 07:52
8
2
55 m
4 24.10.2004 09:17
8
4
60 f
8
1
59 5 25.10.2004 06:55
6 25.10.2004 06:55
8
2
60 f
8
11
59 m
7 25.10.2004 09:20
8 25.10.2004 09:25
8
29
41 f
9 25.10.2004 09:25
8
29
18 f
10 25.10.2004 09:13
8
5
15 m
11 24.10.2004 09:16
8
27
14 8
15
100 m
0 25.10.2004 06:37
1 22.10.2004 18:01
8
2
114 m
2 22.10.2004 21:12
8
2
121 m
3 24.10.2004 06:16
8
29
131 f
4 24.10.2004 07:45
8
10
102 5 25.10.2004 06:40
8
13
105 f
8
30
31 0 21.10.2004 22:30
0 24.10.2004 04:58
8
19
34 f
3 21.10.2004 22:38
8
4
29 f
4 22.10.2004 21:10
8
15
28 5 22.10.2004 22:28
8
27
25 f
5 21.10.2004 21:20
8
29
33 f
8
26
27 m
7 24.10.2004 04:54
7 25.10.2004 04:55
8
27
28 m
8 24.10.2004 05:02
8
17
30 m
8 25.10.2004 04:59
8
26
32 m
9 24.10.2004 05:08
8
2
28 f
12 25.10.2004 05:08
8
5
25 f
5 21.10.2004 21:20
8
29
33 f
8 25.10.2004 06:49
8
9
45 m
0 30.10.2004 05:03
9
28
18 X
26.10.2004 17:37
9
1
49 0 29.10.2004 07:47
9
29 juv.
1 26.10.2004 19:10
9
22
38 f
1 27.10.2004 17:40
9
26
37 f
1 29.10.2004 07:39
9
17 1 30.10.2004 09:00
9
17
34 10 27.10.2004 17:28
9
2
57 f
11 27.10.2004 17:30
9
5
24 m
12 27.10.2004 18:58
9
10
62 m
12 30.10.2004 07:18
9
10
62 13 27.10.2004 18:58
9
11
65 m
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
R. pumilio
R. pumilio
R. pumilio
R. pumilio
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
G. paeba
E. edwardii
E. rupestris
E. rupestris
E. rupestris
E. rupestris
E. rupestris
M. macroscelides
M. macroscelides
M. macroscelides
M. macroscelides
M. macroscelides
M. macroscelides
M. macroscelides
M. macroscelides
63
number date
time area station weight (g) sex
13 29.10.2004 07:44
9
23 13 29.10.2004 09:00
9
23 13 30.10.2004 07:25
9
23
59 13 30.10.2004 08:55
9
11
58 1 26.10.2004 20:42
9
17
13 1 27.10.2004 21:06
9
19
13 f
1 30.10.2004 04:48
9
15
15 9
23
13 2 26.10.2004 20:46
2 27.10.2004 21:16
9
28
15 m
2 29.10.2004 04:56
9
25
18 2 30.10.2004 05:00
9
27
17 f
9
25
13 m
3 26.10.2004 20:50
3 27.10.2004 21:14
9
26
16 3 29.10.2004 04:54
9
21
15 4 26.10.2004 22:02
9
3
11 m
4 27.10.2004 20:55
9
4
13 m
4 27.10.2004 22:00
9
3
11 4 29.10.2004 04:35
9
4
15 4 30.10.2004 06:04
9
3
16 5 26.10.2004 22:00
9
1
29 f
5 29.10.2004 04:29
9
1
30 5 30.10.2004 06:07
9
5
29 5 30.10.2004 04:32
9
5
30 f
6 26.10.2004 20:35
9
3
36 f
9
4
32 f
8 26.10.2004 22:06
8 27.10.2004 20:46
9
3
34 f
8 27.10.2004 22:02
9
78 29.10.2004 04:37
9
5
35 8 29.10.2004 05:59
9
5
36 8 29.10.2004 07:30
9
4
34 8 30.10.2004 04:39
9
7
37 9 26.10.2004 22:12
9
10
29 f
9 27.10.2004 21:00
9
15
30 f
9 29.10.2004 04:44
9
15
34 9 30.10.2004 04:45
9
12
34 f
20 30.10.2004 04:54
9
21
17 m
7 26.10.2004 19:20
9
28
77 f
4 27.10.2004 17:26
9
1
38 f
3 30.10.2004 04:28
9
1
67 m
3 30.10.2004 06:17
9
30
65 m
10 27.10.2004 20:45
9
1
79 f
0 29.10.2004 06:06
9
30
80 f
1 26.10.2004 19:05
9
7
45 f
1 29.10.2004 04:40
9
9
49 f
1 30.10.2004 04:31
9
4
47 f
1 30.10.2004 06:10
9
11
46 f
10 27.10.2004 21:10
9
21
18 m
10 29.10.2004 04:50
9
19
21 10 30.10.2004 04:52
9
19
22 f
11 29.10.2004 04:59
9
29
35 m
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
species
M. macroscelides
M. macroscelides
M. minutoides
M. minutoides
M. minutoides
M. minutoides
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
A. namaquensis
E. rupestris
E. rupestris
E. edwardii
E. edwardii
E. edwardii
E. edwardii
64
number date
time area station weight (g) sex
12 29.10.2004 07:34
9
10
42 m
12 30.10.2004 04:41
9
11
37 m
25
91 27.10.2004 22:27 10
2 27.10.2004 22:29 10
27
9m
3 29.10.2004 05:36 10
27
13 m
70 30.10.2004 05:19 10
4
14 m
11 26.10.2004 22:28 10
1 29.10.2004 05:14 10
2
52 1
54 2 26.10.2004 20:59 10
2 27.10.2004 21:28 10
1
59 2 27.10.2004 22:17 10
12 29.10.2004 06:16 10
2
60 2 30.10.2004 05:14 10
1
56 f
6 26.10.2004 21:12 10
28
54 f
11
53 f
7 26.10.2004 19:34 10
7 27.10.2004 21:37 10
11
56 f
7 29.10.2004 05:25 10
17
57 7 26.10.2004 21:08 10
11 f
7 30.10.2004 05:35 10
21
57 30
24 f
10 27.10.2004 21:44 10
11 29.10.2004 05:19 10
11
33 f
7
28 m
20 30.10.2004 05:24 10
26
29 f
30 30.10.2004 05:40 10
3 26.10.2004 22:35 10
18
67 m
1 27.10.2004 17:55 10
21
63 f
2 26.10.2004 19:25 10
1
71 f
7 27.10.2004 19:15 10
2
74 f
7 29.10.2004 06:20 10
4
80 f
7 30.10.2004 05:31 10
16
78 f
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Appendix
65
Table 6: Trapping data from the fence-line study
species
number date
1 10.8.2004
G. paeba
1 11.8.2004
G. paeba
1 10.8.2004
A. namaquensis
1 11.8.2004
A. namaquensis
1 14.8.2004
A. namaquensis
2 10.8.2004
A. namaquensis
2 13.8.2004
A. namaquensis
2 13.8.2004
A. namaquensis
2 13.8.2004
A. namaquensis
2 14.8.2004
A. namaquensis
3 10.8.2004
A. namaquensis
3 13.8.2004
A. namaquensis
3 14.8.2004
A. namaquensis
11.8.2004
A. namaquensis X
2 10.8.2004
G. paeba
2 14.8.2004
G. paeba
429 13.8.2004
R. pumilio
433 13.8.2004
R. pumilio
91 13.8.2004
R. pumilio
91 14.8.2004
R. pumilio
141 13.8.2004
R. pumilio
time area
station weight (g) sex
19:56 Farm
26
24 m
19:54 Farm
26
25 m
21:22 Farm
18
50 f
21:15 Farm
19
49
08:00 Farm
19 21:22 Farm
19
37 06:50 Farm
19
37 f
09:30 Farm
19
36 f
11:20 Farm
19 06:20 Farm
19
40 f
21:35 Farm
21
46 f
06:55 Farm
21
50 f
06:31 Farm
20
50 f
19:18 Farm
21
52 21:05 Goegap
19
27 f
06:47 Goegap
13
30 f
09:20 Goegap
15
62 m
09:25 Goegap
23
50 m
11:00 Goegap
13
57 m
09:40 Goegap
13
57 m
11:05 Goegap
17
60 m
- = no data available
m = male
f = female
X =animal escaped before it
could be marked
Recapture
Acknowledgements
66
9. Acknowledgements
A lot of people made their contribution during this diploma thesis.
First, I want to thank Prof. Norbert Sachser, who gave me the possibility to make
this external diploma thesis and had the trust to send me half around the world in
order to do it. Most of all I have to thank my supervisor Dr. Carsten Schradin. He
showed a really exceptional engagement for my diploma thesis and me and even
lent me his beloved Landrover to collect my data. The data collection would not
have been possible without the help of my field assistants. My special thanks go to
Philipp Widmann and Annette Wiedon for bearing my bad mood during many
trapping nights and the effective help with dragging traps and mountain climbing.
For further field assistance I thank Eva Krause, Madeleine Scriba, Melanie
Schubert, Carola Schneider and Brigitte Britz. The whole team from the research
station in Goegap Nature Reserve owes my great thanks for a lot of social support
and motivation during difficult times.
I got a lot of useful tips and lessons in
distinguishing E. rupestris from E. edwardii from Galen Rathbun and therefore also
send my thanks to California.
For the warm reception back in Münster and a lot of advises I thank the
whole team of the Department of Behavioural Biology. Most support came from
Oliver Ambreé, who spent a great deal of time helping me to solve all my little
problems. For the correction of my English I thank Prof. Dr. Michael Hennessy. For
their patience and competent help for an ignorant zoologist, who tried to analyse
soil samples, I thank Dr. Nicole Armbrüster and Hildegard Schwitte. For providing
a scale and managing to bring it to South Africa I thank Prof. Dr. von Willert.
I also have to thank Jens Mecklenborg for providing his laptop and
bolstering me, along with many other friends and family members. Especially I
want to mention my flatmate Jörg Holle, who had to deal with an interim tenant for
six month and was still so generous to provide me an extra desk. I also thank
Ruben Böhmer for constantly telling me that everything can be managed.
I would like to thank the Northern Cape Department of Agriculture, Land Reform,
and Environment for their permission to conduct my studies in Goegap Nature
Reserve, and the staff of Goegap for their assistance.
For financial support I thank the University of the Witwatersrand,
Johannesburg and especially Prof. N. Pillay the Frauenförderung of the University
of Münster and my parents, who supported me during my whole course of studies.
Erklärung
Hiermit versichere ich, die vorliegende Arbeit selbstständig verfasst und keine
anderen als die angegebenen Quellen und Hilfsmittel verwandt zu haben.
Münster, den 30.04.2005
.
Christina Keller