Total number of invertebrates caught in fynbos and marsh using
pitfall traps and active searching
Chrissie Slabbert 25269321
Abstract
Invertebrates were caught, by using pitfall traps and doing active searching, in the fynbos and
marsh areas in Jonkershoek. Pitfall traps was an easy and simple way for catching invertebrates. A
disadvantage is that it would cause a disturbance in nature and make it difficult for insects to move
around. The vegetation structure such as the percentage cover, growth forms and average height
were recorded. The aim of the study was to see if there was a relationship between the plant-insect
diversity and richness in Jonkershoek as well as the effect the vegetation structure had on the
invertebrate diversity and richness. One of the hypotheses was that the pitfall traps will have higher
invertebrate abundance and order richness than active searching. Five pitfall traps were placed in
the ground one meter apart and a 20 meters line was measured to record the vegetation types and
height in both fynbos and marsh. 2 members out of a group of 5 did direct active searching using a
net to catch the insects. More vegetation types were found in fynbos than in marsh, but marsh had
greater percentage vegetation coverage than fynbos. Chao 1 values indicated that both active
searching and the marsh region had the higher invertebrate order richness. Invertebrate diversity
was higher in fynbos when the Simpson’s index gave a value of 0,3. The hypothesis was rejected.
There were not enough data about weather conditions, slope and altitude to establish the
difference it would make in the invertebrate abundance and diversity.
Introduction
The Cape Floristic Region (CFR), a biodiversity hotspot containing more than 9000 plant species
and with high endemism in insects, is one of the six floristic kingdoms in Africa. The plant species
richness in the CFR is more than two times as rich as other major floristic areas around the world.
The little bit of work already done on relationship between plant and insect diversity, it does appear
as if there could be a positive correlation. It was also possible that this correlation could be due to
similar responses to extrinsic factors and environmental variables (Jurene E. Kemp et al., 2017).
The CFR is known for its high endemism in species and high plant diversity as well as low insect
diversity. According to Giliomee, not much research was done, and not enough attempts were
made to demonstrate the species richness and endemism of invertebrae in the CFR and to find out
whether the invertebrate diversity corresponds to the plant diversity. This was due to the huge
number of species and the requirements of the trapping methods as well as data that were less
available and information about the distribution of the species richness.
Our aim with this study was to find out which factors had an influence on invertebrate order
richness and diversity in the CFR and we wanted to find out what the effect of the 2 different
vegetation types, fynbos and marsh, had on the abundance, order richness and diversity of the
invertebrate in these 2 areas.
With order and/or species richness is meant how many orders or species are found in an area
even though there may be only 1 individual in one order and many individuals in another order.
Order and species diversity combines species richness with how evenly the individuals in the
species is distributed across the different orders. If the individuals are more evenly spread over the
different species the diversity of the species would be higher. So, if most of the individuals appear
in only 1 or 2 species they will be unevenly distributed and the diversity would be low (socratic.org)
The questions were thus, was there a relationship between vegetation type and diversity and
invertebrate order richness and diversity. We also wanted to find out if the different sampling
techniques, that was used, had different results.
Data about the vegetation structure such as the average height, the % cover and the growth forms
were recorded in the two different sites, Fynbos and Marsh, in the Jonkershoek area. This data
was compared to the insects that were captured to find out if the plant richness influenced species
richness and diversity.
There were many ways in catching invertebrates which included pitfall traps and direct active
searching. These methods were mainly used as it was easier to collect ground-dwelling insects or
invertebrates. An advantage of using the pitfall trap method is that it was easy to use and quite
simple (Berghe, 1992). Pitfall traps can also differ in sizes depending on the invertebrates that you
want to catch. It also is quicker to place the traps in the ground as a smaller hole is needed to be
dug. It also takes up less space when you put it in a carrying bag. The disadvantages included
flooding that led to less invertebrates being caught which made it less affective, the duration of the
sample and the fact that it was required to be checked regularly to ensure that the preservative
would not rot. Another disadvantage was that the killing agent either dried out or it was depleted
due to heavy rain. It also caused a physical disturbance in the nature which led to invertebrates
using more energy to move around (Berghe, 1992).
The first hypothesis of this study is that the pitfall traps will have higher invertebrate abundance
and order richness than the active searching. The second hypothesis is that there is a direct
correlation between the specific vegetation type and the invertebrate abundance, order richness
and diversity.
Methods
Each group of five went to Assegaaibosch in Jonkershoek to catch invertebrates by using two
different sampling methods which includes pitfall trapping and direct active searching. Both these
methods were used in two vegetation types, the fynbos region, and the marsh region. To get into
Jonkershoek, a permit was needed (CN44-59-12619).
Key:
Figure 1: Map of Cape town and Jonkershoek
The groups approached the fynbos region first. The five pitfall traps were placed five meters from
the road to avoid any inaccurate sampling as there would be less invertebrates closer to the road.
Five holes were dug into the ground, one meter apart, for the pitfall traps. Each pitfall trap was a
plastic cup, filled with a 2:1 mixture of 70% ethanol and ethanediol which killed the invertebrates as
they were collected. The traps were even with the ground to avoid any difficulty for the
invertebrates to enter the trap. The area where the pitfall traps were, were marked to avoid any
confusion on where they were placed and to avoid stepping on them.
While three people of the group dealt with the pitfall traps, the other two dealt with the direct active
searching. For the direct active searching a timer was set for 10 minutes to catch the invertebrates
by using a net to sweep the vegetation and lift the rocks. They were also caught by hand. Another
plastic cup, filled with 70% ethanol, were used to put the invertebrates in for the direct active
sampling. A measuring tape was then used to measure a 20 meters line transect to estimate the
vegetation structure. A long stick with measurements helped with the recording of data of 1 meter
between each vegetation. The vegetation type was either recorded as bare ground, grass, shrub,
tree or other. The vegetation type’s maximum height in meters was measured by using the stick,
putting it down next to the vegetation and recording the data. The same thing was done in the
marsh region. The GPS coordinates were taken in both the fynbos (33,58,09.3 S; 18,55,22.6 E) and
marsh (33,58,05,3 S; 18,55,32,7 E), seen in figure 1, areas to know exactly where the spot of the
traps was, as well as the altitude (240 m for fynbos, 234 m for marsh), angle and weather
conditions. The fynbos area was recorded to have some slopes whereas the marsh area was flat.
The weather conditions included a very light breeze and a sunny appearance for both the areas.
After collecting the traps from the field, a week later, the traps were taken to the laboratory to sort
and identify the invertebrates. A filter bucket was used to make it easier to identify and to count the
number of invertebrates under the same order. The invertebrates were taken out by a tweezer and
were put on paper to see if it can be identified by the eye. The invertebrates that were too small to
be able to identify just by looking at it were placed in a petri-dish and put under a stereomicroscope
to make it easier. The invertebrates were identified according to their order level. A book of insects
was used to identify the different insect orders that was caught in the field (Mike Picker). Two
people in the group counted the invertebrates of the marsh region (active searching included) and
the rest counted the fynbos region (active searching included). Chao 1 was used to estimate the
order richness and Simpson’s index was used to estimate the invertebrate diversity. The total
number of vegetation was also calculated in each vegetation site as well as the percentage
vegetation cover.
Results
30 out of 37 possible invertebrate orders were collected by the pitfall traps for both fynbos and
marsh. The mean abundance of the insect orders was 44,8 and 81,1 in the fynbos and marsh
respectively.
Total vegetation
vegetation count (fynbos vs marsh)
80
60
40
20
0
shrub
grass
tree
bare
Vegtation type
Fynbos
Marsh
Figure 2: The vegetation type in each vegetation site with the total number of vegetations that occur.
Fynbos
Marsh
10
23,33
76,67
90
% vegetation cover
%Bare
Figure 3a
% vegetation cover
%Bare
Figure 3b
Figure 3a and b: The percentage cover and % bare in each vegetation site as well as the average height of
vegetation.
Table 1: average height in fynbos and marsh
Vegetation
mean height (cm)
Fynbos
Marsh
35,59
47,47
Less vegetation types were found in marsh than in fynbos (Figure 2). More grass was found in
marsh, more bare ground was found in fynbos whereas the total number of shrubs occurred
equally in both marsh and fynbos (Figure 2). The percentage vegetation cover in Marsh (90 %)
was much higher than in fynbos (76,67 %) (Figure 3a and b). The average height of the vegetation
in fynbos were 35,59 and 47,47 in marsh (table 1).
Table 2: Chao 1 (order richness estimator) method for the calculation of order richness for active searchingand pitfall sampling method respectively. Sobs: number of observations, a = number of species represented
by one individual, b = number of species represented by two individuals, Smax= the maximum number of
orders that are expected to be found.
Orders
Amphipoda (sand lice)
Annelida (earthworm)
Araneae (spiders)
Archaeognatha (bristletail)
Blattodea (cockroaches)
Chilopoda (centipedes)
Coleoptera (beetles)
Collembola (springtails)
Dermaptera (earwigs)
Diplopoda (Millipedes)
Diptera (true flies)
Ephemeroptera (mayflies)
Hemiptera (true bugs)
Neuroptera (antlions)
Heteroptera (stinkbugs)
Hymenoptera (ants, bees and
wasps)
Isopoda (crustacea - woodlice)
Isoptera (termites)
Lepidoptera (butterflies)
Mantodea (mantis)
Orthoptera (grasshoppers)
Plecoptera (stone flies)
Scorpiones
Thysanura (fishmoths)
slugs
Acari (ticks and mites)
Other
Opiliones
Siphonaptera (fleas)
Diplura
Thysanoptera
Sobs
A
b
a^2/2b
Smax
Active searching total Pitfall total
0
0
14
0
3
5
18
2
0
8
19
1
19
1
2
103
30
9
3
1
20
0
6
1
5
1
0
2
0
0
1
31
6
3
6
37
4
2
45
1
1
4
226
2470
1
52
74
8
17
1
1
298
26
11
2
0
12
3
0
2
17
327
2
7
13
2
2
31
5
6
2,1
33,1
Table 3: Simpson’s index used for calculations of invertebrate diversity in relationship between the two
vegetation sites (Fynbos and Marsh). If D = 1 then there is no diversity. If D = 0 then the diversity is high.
Simpson’s index
Orders
Amphipoda (sand lice)
Annelida (earthworm)
Araneae (spiders)
Archaeognatha
(bristletail)
Blattodea
(cockroaches)
Chilopoda (centipedes)
Coleoptera (beetles)
Collembola
(springtails)
Dermaptera (earwigs)
Diplopoda (Millipedes)
Diptera (true flies)
Ephemeroptera
(mayflies)
Hemiptera (true bugs)
Neuroptera (antlions)
Heteroptera
(stinkbugs)
Hymenoptera (ants,
bees and wasps)
Isopoda (crustacea woodlice)
Isoptera (termites)
Lepidoptera
(butterflies)
Mantodea (mantis)
Orthoptera
(grasshoppers)
Plecoptera (stone flies)
Scorpiones
Thysanura (fishmoths)
slugs
Acari (ticks and mites)
Other
Opiliones
Siphonaptera (fleas)
Diplura
Thysanoptera
Sum total
Fynbos
5E-06
5E-07
4E-04
Marsh
Total
Proportion,
abundance
P
1
0,0004
1
0,0004
31
0,0123
0,0007
5E-07
0
0
0
3
2
79
0,0022
0,0014
0,0568
5E-06
2E-06
3E-03
1
7
165
0,0004
0,0028
0,0656
2E-07
8E-06
4E-03
605
0
6
59
0,4353
0
0,0043
0,0424
2E-01
0
2E-05
2E-03
1867
1
54
34
0,7423
0,0004
0,0215
0,0135
6E-01
2E-07
5E-04
2E-04
3
29
2
0,0022
0,0209
0,0014
5E-06
4E-04
2E-06
6
7
0
0,0024
0,0028
0
6E-06
8E-06
0
3
0,0022
5E-06
0
0
0
305
0,2194
5E-02
96
0,0382
1E-03
1
13
0,0007
0,0094
5E-07
9E-05
55
7
0,0219
0,0028
5E-04
8E-06
4
0
0,0029
0
8E-06
0
1
1
0,0004
0,0004
2E-07
2E-07
21
3
4
3
2
191
1
5
12
0
1
1390
0,0151
0,0022
0,0029
0,0022
0,0014
0,1374
0,0007
0,0036
0,0086
0
0,0007
2E-04
5E-06
8E-06
5E-06
2E-06
2E-02
5E-07
1E-05
7E-05
0
5E-07
D = 0,3
11
0
2
0
20
137
1
4
1
2
2
2515
0,0044
0
0,0008
0
0,0080
0,0545
0,0004
0,0016
0,0004
0,0008
0,0008
2E-05
0
6E-07
0
6E-05
3E-03
2E-07
3E-06
2E-07
6E-07
6E-07
D = 0,6
Total
abundance
3
1
28
Proportion,P
0,0022
0,0007
0,0201
1
P^2
P^23
2E-07
2E-07
2E-04
Table 4: Chao 1 method used to calculate order richness estimate for invertebrates in fynbos and marsh
respectively. Sobs: number of observations, a = number of species represented by one individual, b = number
of species represented by two individuals, Smax= the maximum number of orders that are expected to be
found.
Invertebrate Orders
Amphipoda (sand lice)
Annelida (earthworm)
Araneae (spiders)
Archaeognatha (bristletail)
Blattodea (cockroaches)
Chilopoda (centipedes)
Coleoptera (beetles)
Collembola (springtails)
Dermaptera (earwigs)
Diplopoda (Millipedes)
Diptera (true flies)
Ephemeroptera (mayflies)
Hemiptera (true bugs)
Neuroptera (antlions)
Heteroptera (stinkbugs)
Hymenoptera (ants, bees and wasps)
Isopoda (crustacea - woodlice)
Isoptera (termites)
Lepidoptera (butterflies)
Mantodea (mantis)
Orthoptera (grasshoppers)
Plecoptera (stone flies)
Scorpiones
Thysanura (fishmoths)
slugs
Acari (ticks and mites)
Other
Opiliones
Siphonaptera (fleas)
Diplura
Thysanoptera
Sorbs
A
b
a^2/2b
Smax
Fynbos Total
invert
Marsh total invert
3
1
28
1
3
2
79
605
0
6
59
3
29
2
3
305
1
13
4
0
21
3
4
3
2
191
1
5
12
0
1
31
5
3
4,2
35,2
1
1
31
0
1
7
165
1867
1
54
34
6
7
0
0
96
55
7
1
1
11
0
2
0
20
137
1
4
1
2
2
31
8
2
16
47
Discussion
More different vegetation types were found in the fynbos area than in the marsh area (Figure 2).
Meaning that the plant diversity was higher in fynbos than in marsh. Even though fynbos had more
vegetation types and a larger plant diversity, marsh had a greater percentage vegetation cover of
90% whereas fynbos had a 76,67% cover. (Figure 3a and 3b). It could seem as if there should be
a link between plant diversity and invertebrate diversity as the d-values from Simpson’s index
showed (Table 3). Simpson’s index indicated a D-value of 0,3 for fynbos and a D-value of 0,6 for
marsh. A D-value of 0 means that the diversity is high and a D-value of 1 means that there is no
diversity. The fynbos D-value of 0,3 reflected a higher invertebrate diversity in fynbos than what the
0,6 D-value of marsh reflected (Table 3). The individual invertebrates were thus more evenly
distributed across the different orders in the fynbos area. In the mars area we found more
individuals of the same order as can be seen in table 3 with the amount of Collembola (springtails)
being more than 1 800. The individual invertebrate in the marsh seemed to be less evenly
distributed, but it is possible that the very large number of the springtails can cause the data to be
skewed.
The Smax value for fynbos and marsh was 35,2 and 47 respectively (table 4). Chao 1 works with
abundance data and represents the order richness. The higher the Smax value, the greater the total
number of invertebrate orders that were collected for the site. The lower Smax value for fynbos
means thus that the order richness is less in fynbos than in the marsh area. The Smax value for
active searching and pitfall traps were 37 and 33,1 respectively (table 2). There was a higher
invertebrate order richness in the active searching technique than in the pitfall traps as the Smax
value were higher for the active searching technique (table 2).
With the higher Smax of the active searching technique hypothesis 1 was rejected.
There were more vegetation types in fynbos but the % coverage was lower and fynbos had less
grass than the marsh. The vegetation height in the fynbos was also lower than the marsh. The
diversity of the invertebrate is higher in fynbos, but the order richness is lower. The higher diversity
means the individuals are more evenly distributed across the orders.
The marsh area had less vegetation types, but a higher % coverage with more grass and a higher
mean height. The invertebrate diversity was lower in the marsh but the order richness was higher.
So, although there were more orders the individuals were less evenly distributed. It seems as if
there is not a positive relationship between the number of different vegetation type and order
richness. There could be a positive relationship between the % coverage of vegetation and order
richness but an inverse relationship between % coverage and diversity.
Thus hypothesis 2 was partly accepted and partly rejected because there was a direct correlation
between vegetation coverage and order richness and abundance, a direct correlation between
vegetation type and invertebrate diversity but an inverse correlation between the % vegetation
coverage and order richness.
One of the factors that had led to the low diversity of insects in marsh, was that the vegetation
height was more, and it was more difficult for the invertebrates to move from one plant to the other.
Invertebrates were forced to use more energy and effort to get to a specific plant, so they were less
evenly distributed leading to a lower diversity (Giliomee, 2003).
Conclusion
The vegetation type in the fynbos area was more diverse than in the marsh area. More invertebrate
diversity was also found in the fynbos area which led to a conclusion that more diverse vegetation
type would result in a more diverse invertebrate order. It was also found that the % vegetation
coverage had an influence on the invertebrate order richness with a higher coverage resulting in a
higher order richness. A lower average vegetation height resulting in higher invertebrate order
diversity in the fynbos area and higher average vegetation height lead to a lower invertebrate
diversity in marsh even though the percentage cover of the fynbos area was less than that of
marsh lands. Although the GPS coordinates, weather conditions, slope and altitude were recorded,
these conditions were very much the same for both vegetation sites as the research was done on
the same day. Thus, it was difficult to talk about the influence of these variables.
It is necessary to get more data to be able to get a better correlation between vegetation diversity
and order richness and invertebrate diversity and order richness.
Extending the research over a larger area and more days with different weather conditions could
also provide us with more data to get more significant information and results. It would then be
easier to investigate the influence of the environmental variables on the diversity of the
invertebrates.
References
Berghe, E. v. (1992). On pitfall trapping invertebrates. Entomology news, 149-156.
Christine Haaland, R. E.-F. (2011). Sown wildflower strips for insect conservation: a review. Insect
conservation and Diversity, 60-80.
Daniel Matenaar, C. S. (2015). Simple tools for the evaluation of protected areas for the conservation of
grasshoppers. Biological conservation, 192-199.
Giliomee, J. H. (2003). Insect diversity in the Cape Floristic Region. African Journal of Ecology, 237-244.
Jurene E. Kemp, A. G. (2017). Significant Local-Scale Plant-Insect Species Richness Relationship Independent
of Abiotic Effects in the Temperate Cape Floristic Region Biodiversity Hotspot. PLoS ONE (2017)
12(1).
Jurene E. Kemp, A. G. (2017). Significant Local-Scale Plant-Insect Species Richness Relationship Independent
of Abiotic Effects in the Temperate Cape Floristic Region Biodiversity Hotspot. Plos one.
Mike Picker, C. G. (2002). Field guide to insects in South Africa. penguin random house.
https://socratic.org/questions/what-is-the-difference-between-species-diversity-and-species-richness
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