An Investigation into the Abundance, Diversity and
Microhabitat use of Anuran Species within the
Pacaya-Samiria National Reserve, Peru.
Abigail Rebecca Wills
BSc Wildlife Conservation
University of Kent
DICE
2011
Contents
Title
Abstract
1. Introduction
1.1 Global Distribution of Amphibians
1.2 Global Amphibian Declines
1.2 Threats to Amphibians
1.2.1 Disease
1.2.2 Climate Change
1.2.3 Chemical Pollution
1.2.4 Habitat Destruction and Fragmentation
1.3 Anurans
1.3.1 Neotropical Anurans
1.3.1 Anurans of Peru
1.3.2 Conservation Efforts
1.4 Research Objectives
2. Study Site
2.1 Ecology
2.2 Habitat types
2.2.1 Low levee
2.2.2 High levee
2.2.3 Terrace
3. Methodology
3.1 Terrestrial Surveys
3.1.1 Daytime
3.1.2 Nocturnal
3.2 Aquatic Surveys
3.2.2 Aquatic Sites
3.3 Anuran Identification
3.4 Statistical Analysis
4. Results
4.1 Relative Abundance of Species across Terrestrial Habitat types
4.2 Species Diversity across Habitat types
4.3 Temperature and Humidity across Habitat types
4.4 Anuran Microhabitat Use across Terrestrial Habitat types
4.5 Relative Abundance of Species across Aquatic Habitat types
4.6 Patterns in Microhabitat Use by Aquatic Anurans
5. Discussion
5.1 Community Structure
5.2 Variation in Abundance and Diversity across Habitat Types
5.3 Influence of Temperature and Humidity on Anuran Abundance and Diversity
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5.4 Influence of Habitat and Time of Activity on Anuran Microhabitat Use
5.5 Habitat Use by Aquatic Anurans in a Homogenous Environment
5.6 Conclusions
Literature Cited
Abstract
A larger proportion of Amphibian species are at risk of extinction than those of any other
taxon. While an emergent infectious disease has caused rapid declines in some populations,
habitat destruction remains the most common threat to amphibians to date. In any case,
research into the ecology of anuran species is necessary to aid in conservation efforts
2|Page
toward saving this group. The aims of this study, conducted within the Pacaya-Samiria
National Reserve, Peru were: to investigate the community organization of anuran species
present at the site; to compare the abundance, diversity and microhabitat use of species
between habitat types; to investigate the role of temperature and humidity in influencing
the abundance and diversity between habitats and to establish if the microhabitats used by
aquatic species differs between sites. The results obtained indicated that, while
physiognomic differences between habitat types didn’t directly affect the abundance,
diversity and microhabitat use of species, it may have done so indirectly through altering
temperature and moisture gradients.
1. Introduction
Since the beginning of the 20th century, following industrialization, human population
growth has been exponential (Gallant, A. L et al, 2007). This has resulted in new
anthropogenic pressures which, both directly and indirectly, are having profound effects on
the natural environment (Wake, D. B and Vredenburg, V. T. 2008). Many plant and animal
species are at risk of extinction as a result of increased anthropogenic activities (Lande, R.
3|Page
1998). Putting this into context; of the 41,415 species listed on the International Union for
Conservation of Nature (IUCN) Red List in 2007, 16,306 are now threatened with extinction
(Wake, D. B and Vredenburg, V. T. 2008). It is no surprise; therefore, that many scientists
argue we are entering a sixth great mass extinction (Wake, D. B and Vredenburg, V. T. 2008).
Among the groups most affected by the current extinction crisis are amphibians (Wake, D. B
and Vredenburg, V. T. 2008) and there is now a general understanding that a larger
proportion of amphibian species are at risk of extinction than those of any other taxon
(Wake, D. B and Vredenburg, V. T. 2008).
1.1 Global distribution of amphibians
Like many other taxonomic groups, amphibians aren’t distributed uniformly around the
globe (Gallant, A. L et al, 2007). Humid ecoregions support comparatively rich amphibian
fauna (Gallant, A. L et al, 2007) and, while salamanders present one of the few species
assemblages that are more diverse in temperate zones (Wake, D. B and Vredenburg, V. T.
2008), frogs and caecilians do follow the general tendency for taxonomic groups to show
high species richness in the tropics (Kritcher, J. 1997).
1.2 Global Amphibian Declines
It first became apparent that amphibians were undergoing severe global decline in 1989
(Wake, D. B and Vredenburg, V. T. 2008). Reports of declines, however, stem from 25 years
prior to this and it has now been estimated that over one third of all amphibian species have
undergone severe decline or become extinct (Wake, D. B and Vredenburg, V. T. 2008).
In the initial stages of this decline, much attention was directed towards anuran
populations; the most numerous and widely distributed of living amphibians (Wake, D. B
and Vredenburg, V. T. 2008). The data obtained seemed to indicate sharp declines in
population numbers within areas where they were once abundant and where human
disturbance was minimal (Vitt, L. J and Caldwell, J. P. 1993). It has since been identified that
an emergent infectious disease, Chytridiomycosis, has caused dramatic declines in
populations of frogs and salamanders (Vitt, L. J and Caldwell, J. P. 1993). Perhaps one of the
most startling of cases occurred within the Monteverde Cloud Forest Preserve, Costa Rica
(Wake, D. B and Vredenburg, V. T. 2008). Here, a five year study indicated that 40% of the
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amphibian fauna there had been lost; including twenty species of frog (Wake, D. B and
Vredenburg, V. T. 2008).
1.3 Threats to Amphibians
A large number of factors have been implicated with global amphibian declines including
habitat destruction, epidemics of infectious disease and climate change (Wake, D. B and
Vredenburg, V. T. 2008). While it is likely that a combination of factors are contributing
towards declines (Beebee, J. C and Griffiths, R. A. 2005), Chytridiomycosis, having been
implicated in serious declines and extinctions of over 200 species of amphibians, is
considered to pose the greatest threat to biodiversity of any known disease (Wake, D. B and
Vredenburg, V. T. 2008).
1.3.1 Disease
First identified in 1998 and described in 1999, Chytridiomicosis was detected almost
simultaneously in Costa Rica and Australia (Wake, D. B and Vredenburg, V. T. 2008). Chytrid
is a fungal disease which occurs as a result of contamination by the fungus
Batrachochytrium dendrobatidis (Bd) (Vitt, L. J and Caldwell, J. P. 1993).
Amphibians act as hosts for Bd and, following infection, this fungus attacks the keratinized
skin cells of adult amphibians (Vitt, L. J and Caldwell, J. P. 1993). When the cells become
infected, they are no longer able to function effectively in respiration and maintaining an
effective water balance (Vitt, L. J and Caldwell, J. P. 1993). Subsequently, this can lead to
mass mortalities in amphibian populations (Vitt, L. J and Caldwell, J. P. 1993).
Because Bd is spread via aquatic zoospores; it is easily transmitted throughout amphibian
populations and is now known in every continent except Antarctica (Vitt, L. J and Caldwell, J.
P. 1993). Although scientists have recently documented how climate change, precipitation
and increased temperature may be attributed to its spread in the tropical mountains of
Costa Rica (Vitt, L. J and Caldwell, J. P. 1993), the reasons behind the sudden spread of this
fungal disease among amphibian communities is unclear (Vitt, L. J and Caldwell, J. P. 1993).
5|Page
1.3.2 Climate Change
It is no secret that human activities may have resulted in anthropogenic induced climate
change and this has been implicated with amphibian declines since disappearances were
first documented at Monteverde (Wake, D. B and Vredenburg, V. T. 2008). Because
amphibians rely on a complex balance between temperature and moisture in order to
regulate their respiratory activities and to monitor the uptake of water through their
permeable skin cells, they are especially sensitive to small changes in microclimate
(Faulkner, A. 2004). Temperature is also one of several cues that control when breeding
occurs in frog populations; such that changing atmospheric temperatures have had
detectable effects on the breeding phenology of some species (Faulkner, A. 2004).
1.3.3 Chemical Pollution
Second to habitat loss and degradation, the next most common threat to amphibians, as
deduced by the IUCN Global Amphibian Assessment 2008 (See Appendix 1), is pollution
(http://www.iucnredlist.org/initiatives/amphibians/analysis/geographic-patterns, Accessed
20.03.2011). Chemical pollution encompasses an array of environmental contaminants from
agrochemicals used in fertilizers to atmospheric pollution. Pesticides and herbicides may
have both carcinogenic and mutagenic effects on amphibians as a result of direct poisoning
and hormone mimicking (Vitt, L. J and Caldwell, J. P. 1993). These can affect anurans of all
life stages (Vitt, L. J and Caldwell, J. P. 1993) and, when in widespread use, have deleterious
consequences similar to those associated with habitat destruction (Beebee, J. C and
Griffiths, R. A. 2005).
1.3.5 Habitat Destruction and Fragmentation
Closely linked with human population growth, the intensity of habitat destruction and
fragmentation is a direct result of industrialization and the development of intensive arable
farming techniques (Beebee, J. C and Griffiths, R. A. 2005). Indeed, with nearly 50% of the
world’s tropical forests having been lost since the 1970’s (Gallant, A. L et al, 2007); these
processes are the leading cause of species declines and extinctions worldwide (Lande, R.
1998). They are by far the greatest threat to amphibians at present; of which almost 5,000
species
depend
on
forests
throughout
their
life
cycle
(http://www.iucnredlist.org/initiatives/amphibians/analysis/geographic-patterns, Accessed
20.03.2011).
6|Page
Although not restricted to the tropics, much of the recent loss of natural forests has
occurred in tropical eco regions (Gallant, A. L et al, 2007). Accordingly, Gallant, A. L et al
found that many of the regions of the earth supporting the richest assemblages of
amphibians are currently undergoing the highest rates of landscape modification (Gallant, A.
L et al, 2007). They found there to be a disturbing correspondence between patterns of high
amphibian species richness and patterns of high rates of change; especially in tropical
rainforests (Gallant, A. L et al, 2007).
As well as habitat fragmentation for agricultural purposes, the development of road
networks has proven to have a significant effect on amphibian populations (Beebee, J. C and
Griffiths, R. A. 2005). Here, edge effects may prevent migrations to breeding sites and
summer foraging areas during which some species are known to migrate over 1km (Dodd, K.
C. 2009). Not only do edge effects such as this restrict dispersal (Lande, R. 1998); they can
result in microclimate alterations and vegetation changes for considerable distances inside
suitable habitat patches (Lande, R. 1998). The consequences of habitat alteration on the
viability of isolated frog populations, however, are often underestimated (Beebee, J. C and
Griffiths, R. A. 2005).
1.3
Anurans
Of the 6,638 described amphibian species, anurans form the most diverse and widely
distributed group (Vitt, L. J and Caldwell, J. P. 1993); consisting of around 5,858 known
species (Peloso, P. L. V. 2010), distributed among 25 families and around 333 genera
(Faulkner, A. 2004). While being able to persist in most terrestrial and aquatic habitats,
anurans are most diverse in moist tropical regions (Kritcher, J. 1997) and around half of all
known species reside in the New World Tropics (Vitt, L. J and Caldwell, J. P. 1993); nearly
1,600 of which live in South America (Rodríquez, L. O & Duellman, W. E. 1994).
1.4.1 Neotropical Anurans
While frogs often have relatively small geographic ranges; this is accentuated for tropical
montane species and those that have adopted terrestrial modes of reproduction (Wake, D.
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B and Vredenburg, V. T. 2008). In the tropics, high humidity and temperature have allowed
for many terrestrial reproductive modes to occur and, in the Amazon region especially, over
half of all species have terrestrial eggs (Rodríquez, L. O & Duellman, W. E. 1994). For this
reason, many tropical sites harbour species with especially small distributions (Vitt, L. J and
Caldwell, J. P. 1993) making them extremely susceptible to extinction (Wake, D. B and
Vredenburg, V. T. 2008). And, in general, greater numbers as well as proportions of species
are at risk in tropical countries (Wake, D. B and Vredenburg, V. T. 2008).
1.4.1 Anurans of Peru
With around 461 known amphibian species, Peru is among one of the most important
countries worldwide with regards to the rich amphibian fauna residing there
(http://www.iucnredlist.org/initiatives/amphibians/analysis/geographic-patterns, Accessed
20.03.2011). Frogs are especially diverse in this region. Indeed, in some areas surveyed in
the upper Amazon basin of Peru and Ecuador, up to 80 species of frog have been recorded
at single sites (Kritcher, J. 1997). This is more than three times the number of species known
from all of Europe (Rodríquez, L. O & Duellman, W. E. 1994). Nonetheless, within South
America, Peru, in particular, is relatively poorly sampled and it has been predicted that this
country will experience a substantial increase in its species total within the upcoming years
(http://www.iucnredlist.org/initiatives/amphibians/analysis/geographic-patterns, Accessed
20.03.2011). With over 200 endemics and over 20% of known species within the country
currently
threatened
(http://www.iucnredlist.org/initiatives/amphibians/analysis/geographic-patterns, Accessed
20.03.2011), however, the reality of this conjecture is hazy at best. In any case, the
responsibility placed on this country to ensure the survival of its diverse amphibian fauna is
indisputable.
1.5 Conservation Efforts
As a result of concerns arising from global declines, an Amphibian Survival Alliance has been
constructed within the Amphibian Specialist Group of the IUCN (Vitt, L. J and Caldwell, J. P.
1993). The aims of this alliance are to form a coordinated response to the GAD crisis. It aims
to archive this through the creation of regional centres for disease research and captive
8|Page
management, continuing survey and monitoring efforts to inform effective habitat
management programmes and through instigating salvage operations in cases that are
thought to be most critical (Vitt, L. J and Caldwell, J. P. 1993).
Effective conservation strategies at a specific level are difficult to plan without specific
information on species numbers, ranges, distributions and ecological needs (Peloso, P. L. V.
2010). It is crucial to consistently update this information in light of current declines (May, R.
V et al. 2008). And with relevant ecological data lacking in such a large proportion of the
countries which harbour the largest proportion of threatened amphibian fauna worldwide,
the need for substantive research into the ecology and habitat requirements of these
species is a matter of urgency (May, R. V et al. 2008).
1.5
Research Objectives
Within this study, the relative abundance, diversity and microhabitat use of anuran species
within the Pacaya-Samiria National Reserve was investigated. Accordingly, the aims of the
study were:
1. To create a list of anuran species present at the study site and investigate the
community structure there.
9|Page
2. To establish whether the abundance and diversity of anuran species differs
significantly between terrestrial habitat types.
3. To investigate the role of temperature and humidity in influencing anuran
abundance and diversity between terrestrial habitat types.
4. To establish whether anuran microhabitat use differs significantly between
terrestrial habitat types.
5. To establish whether the abundance of aquatic species differs between habitat
types.
2. Study Site
The study site was located within the Department of Loreto in North East Peru (Padoch, C.
1999). The Amazonian forests of Loreto reside in the western Amazon basin in which the
largest protected area in Peru is located: the Pacaya-Samiria National Reserve. Within the
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boundaries of this 2,080,000ha reserve is where the study was conducted (Faulkner, A.
2004).
Figure 1: Map of the Pacaya-Samiria National Reserve, Peru. Displaying the location of the
PV3 Ungurahui guard station.
The base for this study was located at the PV3 Ungurahui guard station (figure 1) near the
upriver section of the Samiria River (Bodmer, R et al. 2010). Here, the Lobo de Rio research
vessel was moored for the duration of the study.
2.1Ecology
Within Peru, the two largest tributaries of the Amazon, the Ucayali and the Maranon, form
the boundaries to the Pacaya-Samiria National Reserve; these come together to form the
11 | P a g e
Amazon River Proper which marks the reserves extreme North East corner (Bodmer, R et al.
2010).
With their headwaters originating principally from the Maranon and Ucayali respectively,
the Pacaya and the Samiria Rivers serve as two major drainage basins within the reserve
(Bodmer, R et al. 2010). The Samiria River basin is the largest geological feature of the
reserve (Bodmer, R et al. 2010).
While there is no wet or dry season within the reserve, the ecology of the Pacaya-Samiria
area is characterised by fluctuations in water levels between high water and low water
seasons (Bodmer, R et al. 2010). These levels range from large scale flooding during the
summer months (October to May) to the low water period throughout the winter months
(June to September) (Bodmer, R et al. 2010).
On a broader scale, however, the Pacaya-Samiria area is classified as moist tropical forest
(Padoch, C. 1999). It is dominated by white water flooded forest which takes up
approximately 92% of the reserve (Bodmer, R et al. 2010). In Amazonia, these are known as
Varzea forests (Faulkner, A. 2004). Despite being highly productive, the biological diversity
within these heavily flooded areas is limited by the harsh ecological conditions (Bodmer, R
et al. 2010).
2.2 Habitat types
2.2.1 Low levee
Low levee represents one of the many low lying forest habitats present within the Peruvian
Amazon (Padoch, C. 1999). Out of the three habitat types, this seasonally inundated forest is
subject to the most flooding during the high water season (Faulkner, A. 2004).
Subsequently, when compared with the high levee and terrace habitats, the low levee
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would be expected to contain less plant species (Bodmer, R et al. 2010). Lowland habitats
such as this tend to have an increased density of individual tree species (Padoch, C. 1999).
2.2.2 High levee
High levees, while still subject to some seasonal flooding, experience much less pressure
from annual floods than low levee habitats (Hiraoka, M. 1995). Thus, while the plant and
animal species occurring here must still withstand some of the habitat pressures associated
with low lying forests, this pressure is to a much lesser degree. Nonetheless, as a result of
annual fluctuations in water levels, both low levee and high levee habitats tend to have a
lower and patchier canopy and less vigorous understory when compared with upland sites
(Padoch, C. 1999).
2.2.3 Terrace
Terrace forests are not inundated by flooded rivers during the high water season
(http://rainforests.mongabay.com/0103.htm. Accessed 30.01.2011). As a result, these
habitats
are
noticeably
taller
and
more
diverse
than
flooded
forests
(http://rainforests.mongabay.com/0103.htm. Accessed 30.01.2011). They are often found
on dry, well drained soils and, despite being comparatively nutrient poor, terrace habitats
are usually more species rich when compared with seasonally inundated environments
(Padoch, C. 1999). They are often characterized by species such as rubber trees, Brazil nut
trees and many tropical hard wood trees (http://rainforests.mongabay.com/0103.htm.
Accessed 30.01.2011)
3. Methodology
The study was carried out from 15th June – 10th July 2010. In this time, a total of 28 surveys
were conducted.
Linear transects were chosen as a suitable survey method. This form of distance sampling
causes minimal disturbance to vegetation (Dodd, K. C. 2009) and, if cut across a good length
13 | P a g e
of habitat; can help to average out patchiness in an environment (Dodd, K. C. 2009). There
was no time limit placed on transects and, instead, these were travelled at a set pace. The
overall time of each transect was dependent on the number of frogs found.
A Visual Encounter Survey (VES) method was adopted when searching for frogs. This is the
most widely employed method in Rapid Assessments of Amphibian Diversity (Dodd, K. C.
2009) and presented an appropriate method given the duration of this study. It can be
implemented in a variety of habitat types, requires little equipment, and is effective for
building species lists rapidly (Dodd, K. C. 2009).
The VES method itself involved searching the focal habitat systematically for a known period
of time (Dodd, K. C. 2009). The search time was deduced using a timer to measure the
duration of each survey. This was paused when processing frogs so the time displayed at the
end of surveys represented only the time spent actively searching for frogs.
A VES method assumes that all individuals were equally detectable and that each individual
is only recorded once during each survey (Dodd, K. C. 2009). As a result, because frogs of
different life stages are not equally conspicuous, and because foraging modes and
microhabitat use may vary with ontogeny, only post metamorphic frogs were included
within the study (Dodd, K. C. 2009).
For each survey conducted, a separate data sheet was used. The date, as well as transect (or
site) name and location was recorded. The time, ambient temperature (oC) and relative
humidity were recorded at the start and finish of each survey and, upon completion, the
time actively searching was deduced and recorded. Information on environmental variables,
such as weather conditions, were noted down for each transect to act as covariates in
analysis (Dodd, K. C. 2009)
Where possible, individuals were captured by hand using latex gloves. Individuals that
escaped were discounted from the survey completely; this was the standardized approach
adopted in order to reduce bias. When an individual was captured, the species could usually
be identified in the field. Detailed pictures were taken of each individual, however; these,
along with basic size measurements were taken to aid in reaffirming species identifications
made in the field at a later date. Once all the appropriate measurements had been taken,
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individuals were released at the same position from which they were captured and active
searching continued. This data collection method was applied to all terrestrial and aquatic
transects.
3.1 Terrestrial Surveys
A total of four terrestrial transects were travelled on foot. These were sampled twice during
the day and twice at night resulting in a total of sixteen terrestrial surveys being conducted
throughout the study period. Transects were placed with predetermined knowledge of
habitat types within the area. Subsequently, these were distributed among three habitat
types: low levee, high levee and terrace. One transect was placed within the low levee
habitat, one within the terrace habitat, and two in the high levee habitat.
One of the transects placed within the high levee habitat was located near to the forest
edge along a clearing. This had been previously cut back for access to the forest and was
used frequently on a daily basis. For study purposes, this transect was sampled in order to
facilitate a comparison between disturbed and undisturbed areas of forest and to assess the
affects that disturbance might have on the anuran community there. For this reason, this
habitat will be referred to as “disturbed” throughout the duration of this report.
Each transect sampled was 1km in length and any frogs spotted over 4 metres either side of
the transect central line were discounted from the study; frogs weren’t actively searched for
beyond this distance. Similarly, frogs above 3 metres from ground level were not included
within the survey.
The distance of each transect was initially measured with tape and markers were placed at
100 metre intervals. When a frog was spotted, the distance along the transect was
determined by measuring the distance from the closest 100 metre marker. The distance
from the transect central line was measured from the position at which the individual was
first sighted; as was the microhabitat the individual was initially spotted in. The ambient
temperature and humidity were also recorded each time a frog was spotted. Frogs were
then collected for identification and data collection.
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3.1.1 Daytime
Daytime terrestrial transects were typically conducted between 10am and 2pm. During
these transects, the forest floor was searched for frogs. In order to provoke movement and
aid in the detection of frogs, sticks were used to probe the leaf litter (Table 1). Specific
attention was also paid towards buttresses and fallen logs (Table 1) as these microhabitats
were most likely to contain frogs. This technique has been found to yield more individuals
and species per unit effort than random approaches (Dodd, K. C. 2009). Any surface cover
objects that were overturned were then replaced in order to minimize disturbance; this is
concordant with intermediate level searches for amphibians associated with low intensity
VES methods (Dodd, K. C. 2009).
3.1.2 Nocturnal
Nocturnal transects are a regularly used method in surveying forest frogs in tropical habitats
(Dodd, K. C. 2009) and, for the purpose of this study, were conducted between 8:00pm and
11:30pm. Unlike transects carried out during the day, head torches were used to search for
frogs at night. Particular attention was paid to vegetation above the forest floor during
these transects.
3.2 Aquatic Surveys
Aquatic transects were conducted in the evenings between 8:00pm and 11:30pm. A total of
four transects were sampled twice at night. These were carried out by canoe along the
banks of the Samiria River and the distance of each 1 kilometre transect was measured
using a GPS. Head torches were used to search for frogs and, in doing so; attention was paid
to the appropriate river bank and any vegetation present along the edge of the river. When
spotted, the location of the individual along the transect was recorded with a GPS waypoint
and the microhabitat it was spotted in was noted. Frogs were collected in polythene bags
and brought to the canoe for identification and data collection. Aquatic transects weren’t
conducted during the day as species only became active at dusk (Dodd, K. C. 2009).
3.2.1 Aquatic Sites
An additional two aquatic sites were sampled during the study period. These consisted of a
macrophyte raft which had been suspended by fallen sticks along the Samiria River and an
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inlet located along the right edge of the Ungurahui channel. Each site was sampled twice at
night. These additional sites were sampled with a view to build on the inventory of species
found at the study site. Due to differences in sample size, however, these are not directly
comparable with other data collected.
Table 1: Microhabitat Ethogram
Terrestrial
Microhabitat
Leaf litter
Fallen log
Description
Buttress
Tree roots that protrude from the ground; including the leaf litter and any
other decaying matter between them.
Temporary bodies of water on the forest floor; either as a result of rainfall
or remain from flooding during the high water season.
Any portion of the body of a shrub, small tree or plant which is no taller
than 3 metres and that is not a leaf.
A leaf which is still attached to a living tree or plant above the forest floor.
The section of a tree from the ground up to approximately 3 metres.
Any branch of a tree within 3 metres of the forest floor.
Description
Temporary
pond
Plant
(stem/branch)
Leaf
Tree trunk
Tree branch
Aquatic
Microhabitat
Emergent
vegetation
Floating
vegetation
Suspended
vegetation
Alluvial soil
Palizada
Decomposing leaves on the forest floor.
The trunk of a tree which has fallen and is decomposing on the forest floor.
Any form of vegetation which is rooted to the ground but remains
submerged, in part, by water.
Aquatic vegetation which is not rooted to the ground but floats on the
water surface.
Vegetation which was once floating but has become suspended on
emergent vegetation or palizada as a result of water levels dropping.
Soil constituting the majority of the River bank as it becomes exposed as a
result of low water levels
A collection of logs or fallen branches that have collected along the river
bank.
3.4 Statistical Analysis
Statistical analysis was carried out using PASW Statistics 18. Some additional calculations
were undertaken using Microsoft Excel.
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3.4.1 Shannon Weiner Diversity Index
The following index was used to estimate the species diversity within each of the habitats
sampled.
H = -  pi ln pi
The term pi is the proportional abundance of species i in the sample which is multiplied by
the natural logarithm of itself.
3.4.2 Chi-Square test
In the test, the difference between the observed and the expected frequency is squared and
divided by the expected frequency
X2 = (O – E)2/E
3.4.3 Two-way Analysis of Variance
This analysis was carried out in order to estimate the effects of two independent variables
on a dependent variable.
4. Results
Throughout the study, a total of 475 individuals were recorded consisting of 25 species, 11
genus, and 5 families. The most diverse family within the study site was Hylidae.
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Nonetheless, the family Leptodactylidae harboured the greatest number of individuals out
of any of the families present at the site. This is largely as a result of one species, however:
Leptodactylus leptodactyloides which was by far the most abundant species present;
accounting for nearly half (45.26%) of all anuran observations.
Table 2: Inventory of species found throughout the study period.
Family
LEPTODACTYLIDAE
Genus
Leptodactylus
HYLIDAE
Dendropsophus
Hypsiboas
AROMOBATIDAE
STRABOMANTIDAE
BUFONIDAE(Toad)
Osteocephalus
Sphaenorhynchus
Scinax
Trachycephalus
Scarthyla
Allobates
Pristimantis
Rhinella
Species
Leptodactylus leptodactyloides
Leptodactylus petersi
Leptodactylus pentadactylus
Leptodactylus discodactylus
Leptodactylus gr andreae
Leptodactylus hylaedactylus
Dendropsophus triangulum
Dendropsophus rossalleni
Dendropsophus parviceps
Dendropsophus haraldschultzi
Dendropsophus allenorum
Hypsiboas boans
Hypsiboas punctatus
Hypsiboas lanciformis
Hypsiboas geographicus
Hypsiboas fasciatus
Osteocephalus taurinus
Sphaenorhynchus dorisae
Scinax pedromedinae
Trachycephalus resinifictrix
Scarthyla goinorum
Allobates femoralis
Pristimantis altamazonicus
Rhinella marina
Frequency
215
34
5
25
8
6
56
7
5
2
1
9
21
7
1
2
11
8
19
2
7
2
4
17
Rhinella margaritifera
TOTAL
1
475
4.1 Relative Abundance of Species across Terrestrial Habitat types
19 | P a g e
Number of Individuals
25
20
Disturbed
Terrace
15
High Levee
Low Levee
10
5
0
Species
Figure 2: The number of individuals from each species recorded within each terrestrial
habitat during the day. N=44.
The majority of species found within the forest during the day were of the genus
Leptodactylus. Out of the species recorded during terrestrial transects, Leptodactylus
discodactylus was the most abundant species overall. Although some individuals were found
at night (figure 3), more were recorded during the day where it was most frequently found
in the low levee habitat (figure 2). Both fewer species and fewer individual frogs were
recorded within the disturbed habitat during the day when compared with the other three
habitats surveyed. While, out of the three non-disturbed habitats surveyed, Low levee had
the fewest species present, those species that did occur within this habitat were recorded
here more than anywhere else.
20 | P a g e
Number of Individuals
20
18
16
14
12
10
8
6
4
2
0
Disturbed
Terrace
High Levee
Low Levee
Species
Figure 3: The number of individuals from each species recorded within each terrestrial
habitat during the day. N=62.
While some species were found both during the day and at night (figure 2,3), the results
indicate that time has a profound influence on the number and type of species found. The
two most abundant species encountered at night were also the only two species to be
recorded in all four of the habitats sampled. While only two individuals were recorded
within the disturbed habitat during the day, a number of species were found in this habitat
at night. One species was only found within this habitat.
21 | P a g e
4.2 Species Diversity across Habitats types.
2
1.8
1.6
Diversity
1.4
1.4202
1.2
1
1.0127
0.8
0.6
0.4
0.2
0.2812
0
0
Low levee
High levee
Terrace
Disturbed
Macrohabitat
Figure 4: The estimated mean and standard deviation for species diversity within each
terrestrial habitat during the day.
Although frogs were present, because only two individuals were observed within the
disturbed habitat during the day, a diversity index could not be calculated for this habitat.
With only two species being detected during the day (figure 2), the low levee habitat also
exhibited a relatively low diversity.
22 | P a g e
2
1.8
Diversity Indices
1.6
1.4
1.5249
1.425
1.4015
1.2
1
0.9831
0.8
0.6
0.4
0.2
0
Low levee
High levee
Terrace
Disturbed
Habitat
Figure 5: The estimated mean and standard deviation for species diversity within each
terrestrial habitat at night.
The estimated species diversity within the four habitats at night is very different from the
diversity during the day. While the terrace habitat had the highest species diversity during
the day (figure 4), it had a low species diversity when compared with the other three
habitats at night (figure 5). Similarly, the low levee habitat, which, apart from the disturbed
area of forest, had the lowest species diversity during the day, now has the highest
estimated species of the four habitats.
23 | P a g e
Table 3: Two-way ANOVA comparing the mean species diversity of four terrestrial habitat
types during the day and at night.
Sum of squares
d.f
Mean square
F
P
Habitat
0.749
3
0.25
2.593
0.125
Time of Day
1.717
1
1.717
17.822
0.003
Habitat*Time
2.155
3
0.718
7.459
0.011
Error
0.771
8
0.096
Corrected Total
5.392
15
While a two-way analysis of variance showed that there is not a significant difference in
species diversity between the four habitat types, a highly significant difference was found
between the species diversity and the time of day. The interaction between time of day and
habitat type also had a significant impact on the species diversity present (table 3).
24 | P a g e
1.8
1.6
Mean Diversity
1.4
1.2
1
Low levee
0.8
High levee
Terrace
0.6
Disturbed
0.4
0.2
0
Day
Night
Time of day
Figure 6: The effect of habitat and time of day on mean species diversity within four
terrestrial habitat types.
While species diversity was lower during the day than at night in the majority habitats
sampled, the diversity within the terrace habitat decreased at night (figure 6).
25 | P a g e
4.3 Temperature and Humidity across Habitat types
34
Mean Temperature (°C)
32
32.2385
30
28
28.2571
28.3421
High levee
Terrace
27.9
26
24
22
20
Low levee
Disturbed
Habitat
Figure 7: The estimated mean ambient temperature (°C) within each terrestrial habitat
during the day.
26 | P a g e
34
Mean Temperature (°C)
32
30
28
27.1556
26
24
25.3882
25.3182
Low levee
High levee
25.98
22
20
Terrace
Disturbed
Habitat
Figure 8: The estimated mean ambient temperature (°C) within each terrestrial habitat at
night.
All four habitats exhibited a reduction in ambient temperature at night. Similar to the
pattern that occurred with relative humidity, however, the temperature of some habitats
dropped more than others (figure 7,8).
27 | P a g e
Table 4: Two-way ANOVA comparing the mean temperature (following logarithmic
transformation) of four terrestrial habitat types during the day and at night.
Sum of Squares
d.f
Mean Square
F
P
Habitat
0.011
3
0.004
12.331
<0.001
Time
0.036
1
0.036
120.137
<0.001
Habitat*Time
0.025
3
0.008
27.662
<0.001
Error
0.029
96
0
Corrected Total
0.143
103
A two-way analysis of variance showed that there is a highly significant difference in the
mean temperature between the four habitat types. A significant difference was also found
in the ambient temperature during at night when compared with during the day. The effect
that the interactions between habitat type and time of day have on ambient temperature
was also found to be highly significant (table 4).
28 | P a g e
33
Mean Temperature (°C)
32
31
30
Low levee
29
High levee
28
Terrace
Disturbed
27
26
25
Day
Night
Time of Day
Figure 9: The effect of habitat type and time of day on mean ambient temperature (°C)
within four terrestrial habitat types.
While terrace and disturbed habitats get cooler at night, the high and low levee habitats do
so to a more substantial degree. The low levee habitat, in particular, experiences the
greatest decrease in mean temperature (figure 9).
29 | P a g e
100
90
85.05
Mean Humidity
80
80.6286
70
60
74.3
66.8462
50
40
30
20
Low levee
High levee
Terrace
Disturbed
Habitat
Figure 10: The estimated mean humidity within each terrestrial habitat during the day.
100
90
Mean Humidity
80
92.1579
87.4412
83.6
86.38
70
60
50
40
30
20
Low levee
High levee
Terrace
Disturbed
Habitat
Figure 11: The estimated mean humidity within each terrestrial habitat at night.
While all four of the habitats sampled experienced an increase in humidity at night, the
extent of this increase differed between habitats. Both the High levee and the low levee
habitats exhibited the greatest change (figures 10 and 11).
30 | P a g e
Table 5: Two-way ANOVA comparing the mean humidity (following logarithmic
transformation) of four terrestrial habitat types during the day and at night.
Sum of Squares
d.f
Mean Square
F
P
Habitat
0.026
3
0.009
15.45
<0.001
Time
0.044
1
0.044
78.734
<0.001
Habitat*Time
0.044
3
0.015
26.256
<0.001
Error
0.048
85
0.001
Corrected Total
0.218
92
A two-way analysis of variance showed that there is a highly significant difference in the
mean humidity between the four habitat types. A significant difference was also found in
the humidity during the day and at night. Finally, a highly significant difference was found in
the effect that the interaction between habitat type and time of day have on mean humidity
(table 5).
31 | P a g e
95
Mean Humidity
90
85
Low levee
80
High levee
Terrace
75
Disturbed
70
65
Day
Night
Time of Day
Figure 12: The effect of habitat type and time of day on mean humidity within four
terrestrial habitat types.
While the humidity of the low levee and high levee habitats increased at similar degrees at
night when compared with during the day, the humidity of both the terrace and disturbed
habitats changed very little (figure 12). Subsequently, while these habitats had the highest
humidity during the day, their relative humidity was lower than the other two habitats at
night.
32 | P a g e
4.4 Anuran Microhabitat Use across Terrestrial Habitats
Number of Individuals
35
X2=67.578
d.f=8
P<0.001
30
25
20
Day
15
Night
10
5
0
Microhabitat
Figure 13: The number of individuals found within each terrestrial microhabitat during the
day and at night; N=45 and N=54 respectively.
A Chi-squared test showed that there was a highly significant difference in the number of
individuals found within each microhabitat during the day and at night (figure 13). All of the
microhabitats in which frogs were found during the day also harboured frogs at night. More
microhabitats were utilized by frogs at night.
33 | P a g e
90
X2=15.849
d.f=12
P=0.198
80
Percentage
70
60
Disturbed
Low levee
High Levee
Terrace
50
40
30
20
10
0
Leaf litter
Buttress
Temporary
pond
Fallen Log
Snail shell
Plant
(stem/branch)
Microhabitat
Figure 14: The percentage of individuals within each habitat occupying each microhabitat
during the day. N=45.
Leaf litter and tree root were the only microhabitats to be used by frogs in all three habitats
during the day. Leaf litter was found to harbour the largest number of frogs in all of the
habitats except in the disturbed area of forest where only two individuals were recorded
(figure 2); one in leaf litter and one in a tree buttress.
A Chi-squared test showed that there was no significant difference in the number of
individuals found in each microhabitat between the four habitats sampled than would
otherwise be expected by chance (figure 14).
34 | P a g e
60
X2=54.586
d.f=24
P<0.001
Percentage
50
40
Disturbed
30
Low levee
High Levee
20
Terrace
10
0
Microhabitat
Figure 15: The percentage of individuals within each habitat occupying each microhabitat at
night. N=54.
Unlike observations made during the day, A Chi-squared test revealed that there was a
highly significant difference in the number of individuals found in each microhabitat
between the four habitats sampled at night (figure 15).
35 | P a g e
4.5 Patterns in Microhabitat use by Terrestrial Anuran Species
18
X2=4.640
d.f=4
P=0.326
Number of Individuals
16
14
12
10
8
6
4
2
0
Leaf litter
Buttress
Fallen log
Microhabitat
Leptodactylus discodactylus
Leptodactylus gr andreae
Leptodactylus hylaedactylus
Figure 16: The number of individuals in each named microhabitat from the three most
abundant species found throughout all four terrestrial habitats during the day. N=32.
A Chi-squared test indicated that there wasn’t a significant difference in the frequency of
individuals from each species found within each microhabitat (figure 16). Leaf litter served
as the most frequently used microhabitat by all three species and the results indicate that
there is no difference in the microhabitat use of these three species.
36 | P a g e
9
X2=7.639
d.f=4
P=0.106
Number of Individuals
8
7
6
5
4
3
2
1
0
Leaf
Plant (stem/branch)
Tree trunk
Microhabitat
Scinax pedromedinae
Scarthyla goinorum
Osteocephalus taurinus
Figure 17: The number of individuals in each named microhabitat from the three most
abundant species found throughout all four terrestrial habitats during the night. N=25.
A Chi-squared test indicated that there wasn’t a significant difference in the frequency of
individuals from each species found within each microhabitat (figure 17). Subsequently, the
results indicate that the species presented here do not differ in their microhabitat use.
37 | P a g e
4.6 Relative Abundance of Species within Aquatic Habitats
Number of Individuals
250
200
AT4
AT3
150
AT2
AT1
100
50
0
Species
Figure 18: The number of individuals from each species recorded within each aquatic
transect. N=289.
While a number of species were encountered within aquatic transects, it is clear from the
results that one species, Leptodactylus leptodactyloides, was present in substantially higher
abundance (figure 18). This species, and two others, were recorded within all four aquatic
transects. Leptodactylus leptodanctyloides and Rhinella marina were most abundant within
aquatic transect 1.
38 | P a g e
Number of Individuals
35
30
25
20
15
Channel inlet
10
Macrophyte raft
5
0
Species
Figure 19: The number of individuals from each species found within the macrophyte raft
and channel inlet. N=79.
Five species that were recorded within the two additional aquatic study sites weren’t
present in along the river (figure 19).
39 | P a g e
4.7 Patterns in Microhabitat use by Aquatic Anurans
Number of Individuals
250
X2=322.096
d.f=12
P<0.001
200
150
100
50
0
Emergent Vegetation
Floating vegetation
Alluvial soil
Palizada
Microhabitat
Dendropsophus triangulum
Hypsiboas punctatus
Leptodactylus petersi
Leptodactylus leptodactyloides
Rhinella marina
Figure 20: The number of individuals in each named microhabitat from the five most
abundant species found throughout all aquatic habitats sampled. N=323.
Alluvial soil was, by far, the microhabitat containing the largest number of individuals during
aquatic transects (figure 20). This microhabitat was largely dominated by one species,
however, which accounted for over 75% of the frogs encountered there.
40 | P a g e
5. Discussion
5.1 Community structure
Members of the family Hylidae form a major contribution to the Amazon frog fauna
(Rodríquez, L. O & Duellman, W. E. 1994) and these formed by far the most diverse species
assemblage present at the study site (table 2). This is unsurprising as hylids represent one of
the most diverse anuran families worldwide (http://amphibiaweb.org/lists/Hylidae.shtml.
Accessed 20.03.2011). Consisting of over 800 known species, this family, although
widespread,
is
especially
well
represented
(http://amphibiaweb.org/lists/Hylidae.shtml.
in
Accessed
the
New
20.03.2011)
World
as
this
tropics
study
demonstrates. With a few exceptions, members of this group are nocturnal (Rodríquez, L. O
& Duellman, W. E. 1994) which accounts for few individuals being encountered during the
day (figure 2). Nonetheless, many reproductive modes are found within this family
(http://amphibiaweb.org/lists/Hylidae.shtml. Accessed 20.03.2011). The constant high
temperature and humidity which has allowed for such adaptive radiation to occur (Kritcher,
J. 1997), has most likely facilitated in the persistence of these species throughout all
habitats sampled within this study (figure #).
Another
large
and
diverse
group
are
the
leptodactylids
(http://amphibiaweb.org/lists/Hylidae.shtml. Accessed 20.03.2011). Unlike hylid frogs,
however,
this
family
occurs
solely
in
the
New
World
Tropics
(http://amphibiaweb.org/lists/Hylidae.shtml. Accessed 20.03.2011). Although second to the
hylids in terms of species richness within this study (table 2), the family leptodactylidae
remain highly diverse in the Amazon Basin (Rodríquez, L. O & Duellman, W. E. 1994).
Despite consisting of four genera, only species of the genus Leptodactylus, the most diverse
of the four genus (Vitt, L. J and Caldwell, J. P. 1993), were found at the study site (table 2).
The high abundance of individuals from this group within the study was largely represented
by one species, Leptodactylus leptodactyloides, which was encountered in substantial
numbers along the alluvial soil river bank (figure 20).
41 | P a g e
5.2 Factors Influencing Species Abundance and Diversity across Habitat
types
5.2.1 Disturbance
Because of their small geographic ranges, tropical anurans are at a heightened susceptibility
to environmental disturbance (Kritcher, J. 1997). This was highlighted throughout the study
whereby, in the disturbed habitat, human presence and the clearing of understory
vegetation had a comparatively large influence on the abundance and diversity of diurnal
anuran species (figure 2,4).
Common belief that environmental disturbance has detrimental impacts on all amphibian
communities is not always the case (Gallant, A. L et al. 2007). Responses of species to
environmental change can vary (Gallant, A. L et al. 2007). Among the species encountered
within this study, Leptodactylus hylaedactylus is commonly associated with human activities
(Hodl, W. 1990). Indeed, while most agricultural practices are considered to negatively
affect amphibians, until recent decades, traditional Old World agriculture has supported
many species (Gallant, A. L et al, 2007).
5.2.2 Hydroperiod
Of the three non-disturbed habitats sampled, low levee exhibited lowest species diversity
during the day (figure 4). It is likely that this is a direct result of it being the least elevated
out of the three habitats sampled and, subsequently, is subject to more flooding during the
high water season (Faulkner, A. 2004). Following the onset of the low water period, at the
beginning of June, the low levee would remain waterlogged for a longer period of time
(Padoch, C. 1999). This is likely to impede the rate at which terrestrial litter frogs are able to
re-colonize this low lying habitat when compared with high levee and terrace areas.
The only two species that were recorded within the low levee habitat during the day (figure
2), Leptodactylus discodactylus and Leptodactylus leptodactyloides, are both members of
the melanonotus group within the genus Leptodactylus (Heyer, R.W. 1969). This is one of
five groups that have been used to categorize species of this diverse genus with regards to
similar life history traits (Heyer, R.W. 1969). Subsequently, the adults within this group
harbour characteristic toe fringes (Heyer, R.W. 1969). This is a morphological adaptation
which serves to increase the surface area of the foot (Heyer, R.W. 1969) and is important for
42 | P a g e
species associated with water (Heyer, R.W. 1969). When on land, however, the fringes
adhere to the sides of the toes so as not to impede terrestrial locomotion (Heyer, R.W.
1969). Indeed, this morphological feature may have permitted these species to re-colonize
the low levee’s forest floor habitat more readily than other species without this adaptive
trait. Similarly, it may explain why these species were more abundant here than in any other
habitat.
While seasonally fluctuating water levels may have resulted in a diversity of species within
the low levee habitat; this is not the case for the terrace habitat. The flora and fauna within
this habitat aren’t subject to the pressures imposed by seasonal flooding (Bodmer, R et al.
2010). Accordingly, terrace was found to harbour the highest species diversity during the
day (figure 4). These patterns indicate that, similar to flora, the faunal abundance and
diversity within the floodplain on the Samiria River is largely affected by extent of annual
flooding there. Subsequently, although rarely considered, this indicates how the relative
lengths of seasons can be influential in limiting the species which can occur in a particular
habitat type (Vitt, L. J and Caldwell, J. P. 1993).
5.2.3 Time of Day
The majority of frogs were encountered at night (figure 2,3) which is unsurprising as most
species were active just after dusk (37). Indeed the majority of frogs encountered at night
were of the family hylidae; members of which are all nocturnal and arboreal with only a few
exceptions (Rodríquez, L. O & Duellman, W. E. 1994). Only one hylid frog was found during
the day (figure 2). This finding could have been enhanced, however, as a result of the
sampling methodology which, during the day, was more destructive. Although an effort was
made to reduce disturbance through replacing moved objects, processes such as probing
the forest floor and overturning logs may have degraded the suitability of forest floor
microhabitats resulting in less frogs being found during the day (Dodd, K. C. 2009).
While the three habitats: Low levee, high levee, and disturbed, showed a significant increase
in species abundance and diversity at night when compared to the day, the terrace habitat
experienced a notable decrease in diversity (figure 4,5). This is surprising as upland sites
such as this are known for their diverse tree populations and dense understory when
compared with lowland forests (Padoch, C. 1999). As a result, the greater spatial and
43 | P a g e
structural heterogeneity present in habitats like this are usually associated with higher
anuran species richness (Vitt, L. J and Caldwell, J. P. 1993).
Nonetheless, the richness and abundance of species within a habitat is dependent on a
number of ecological variables; none of which are mutually exclusive (Vitt, L. J and Caldwell,
J. P. 1993). Therefore, while vegetation may be affecting the species present to some
extent, other selection processes are likely to be occurring. As a major component of most
terrestrial habitats, however, vegetation can have less obvious and indirect effects on
suitability. Vegetation structure can strongly influence habitat suitability through effects on
microclimate (Dodd, K. C. 2009).
5.3 Influence of Temperature and Humidity on Anuran Abundance and
Diversity
Due to the constant high humidity, anuran reproductive behaviour has undergone
impressive adaptive radiation in the tropics (Kritcher, J. 1997). High levels of moisture in the
air facilitate moist skin; a prerequisite to amphibian survival (Vitt, L. J and Caldwell, J. P.
1993). It is no surprise, therefore, that patterns in the abundance and diversity of anuran
species present between terrestrial habitats at different times of the day can be attributed
to thermal and moisture gradients (figure 6).
Anuran species can experience substantial weight loss when subjected to high temperatures
(Jameson, D. L. 1965). This can occur in a relatively short period of time and may explain
why few species were found within the low levee habitat during the day (figure 2). Not only
did this habitat exhibit the highest ambient temperatures during the daytime, it also had the
lowest humidity out of the four habitats (figure 9,12).
The low levee habitat, demonstrated the greatest increase in anuran species diversity at
night when compared with the day (figure 6). Similarly, temperature and humidity gradients
in this habitat experienced the greatest shift from a high temperature with low humidity
during the day, to a high humidity with low temperature at night (figure 9,12). This indicates
that the relative temperature and humidity of different habitat types has a direct influence
on the species diversity present there.
44 | P a g e
The disturbed habitat exhibited an optimum combination of high humidity and low
temperature during the day (figure 9,12). In theory, this should make it the most suitable
habitat for anuran species. It is likely, however, that, along with seasonal inundation, the
negative effects caused by disturbance may have outweighed the benefits within this
habitat resulting in few species present here (figure 2).
The terrace habitat was the only area of forest which was found to be more diverse during
the day than at night (figure 6). Although it had a similar temperature during the day to the
high levee habitat and still experience a decrease in temperature at night along with a
marginal increase in humidity (figure 9,12). This habitat had a considerably higher
atmospheric humidity during the day when compared to the other non-disturbed habitats
(figure 9). Further, the fact that the area is more elevated than the other habitats means
that the terrace doesn’t become seasonally inundated. Jameson, L. D (1965) undertook a lab
experiment which found that the rate of weight loss of hylid frogs at a given temperature
was greater at lower humidity’s. From this, it could be inferred that a combination of
elevated ground level and heightened relative humidity during the day allowed for a greater
diversity of anuran species to be active within the terrace habitat during the day (figure 2).
It is likely that the different vegetation present within each habitat type had an influence on
the thermal gradients there by providing shade, impacting humidity and moisture retention,
adding litter to the ground stratum and altering wind flows (Dodd, K. C. 2009). All of these
factors affect the rate of water loss experienced by frog species (Dodd, K. C. 2009).
5.3 Influence of Habitat and Time of Activity on Anuran Microhabitat Use.
A larger number of microhabitats were found to be utilised by frogs during the night (figure
13). This could be because many of the species encountered at night were of the family
Hylidae (figure 3). The majority of frogs recorded during the day were tropical litter frogs
and so were limited to forest floor microhabitats (figure 13). Although one individual of the
species Scarthyla goinorum was observed on a plant stem above the forest floor during the
day (figure 13), this species is a member of the Hylidae family. Different behavioural and
morphological traits, such as expanded discs at the ends of fingers and toes, mean that the
majority of hylid species are specialized for climbing (Rodríquez, L. O & Duellman, W. E.
1994). The arboreal nature of this family is what inherited them the common name “tree
45 | P a g e
frogs” and means that they have the ability to utilise a wider range of the layered forest
microhabitats available to them (Faulkner, A. 2004). This includes leaf litter and other
decaying matter, low level and understory vegetation along with medium sized trees, and
the dense upper canopy (Faulkner, A. 2004). Most species of hylid frog are known to
descend to low lying vegetation near the forest floor for breeding (Rodríquez, L. O &
Duellman, W. E. 1994) which could explain the overlap in microhabitats used by frogs during
the day and night (figure 13).
Leaf litter was the most frequently used microhabitat by frogs in all four macrohabitats; this,
and tree buttresses were the only microhabitats which were utilised in all three habitats
(figure 14). This is unsurprising as leaf litter provides good camouflage for many forest floor
dwelling anuran species to the point where some have morphologically adapted to closely
resemble this substrate (e.g: Rhinella margaritifera). Leaf litter also provides an abundance
of insect prey for many frogs (Vonesh, J. R. 2006). It is surprising, however, that so few frogs
were found occupying fallen logs during the day (figure 14) as other studies have found the
presence of these to be a significant positive predictor of herpetofaunal presence (Vonesh,
J. R. 2006). This could be as a direct result of availability in which, while leaf litter and
buttresses accounted for a substantial proportion of the available microhabitats on the
forest floor, fallen logs were more sporadically distributed throughout the four habitats
sampled. Leaf litter and buttresses, therefore, would have had the capacity to support more
individuals per given area than other microhabitats.
It is also likely that this is a result of observer bias which can be substantial in visual search
methods (Dodd, K. C. 2009) whereby, during daytime transects, sticks were used to probe
the leaf litter in search for frogs. Not only would this have increased the detectability of
frogs within the leaf litter through provoking movement, but this method meant that search
effort was increased within the leaf litter. When searching for frogs during the day,
particular attention was also paid to tree roots and fallen logs. Although yielding more
individuals and species per unit effort than random approaches, microhabitats were
searched in a bias manner. This limits the ability to generalise about habitat associations
(Dodd, K. C. 2009). It was found that there wasn’t a significant difference in the
microhabitats used by frogs between the four habitats during the day indicating that a
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degree of consistency was maintained in habitat selection provided these conditions existed
within the study area.
The overlap in microhabitat use observed by the three most abundant frogs encountered
within the forest during the day (figure 16) could be directly related to the heterogeneity in
microhabitats available to them (Menin, M et al. 2005). In this case, leaf litter is likely to be
an abundant resource which can harbour a number of individuals from different species
without inducing competition. Such coexistence of similar species within ecological
communities, however, has long been a problem in the field of ecology and the degree of
overlap in resource use among co-occurring species is variable (Menin, M et al. 2005). While
the species discussed here are members of the same genus and so are likely to have
inherited similar behavioural traits regarding microhabitat selection, this is not always the
case which poses problems in ecology (Dure, M. I. 2004). Variation in resource use by two
or more sympatric amphibian species, however, may not necessarily reflect competition
(Dure, M. I. 2004). Dure and Kehr (2004) found that two species of leptodactylids in NorthEastern Argentina may have been exhibiting niche complementarity through displaying a
low overlap in microhabitat use but a high overlap in diet. Similarly, the species mentioned
here may be exhibiting such complementarity through a low overlap in diet but a high
overlap in microhabitat use. Thus, differentiation in diet may counteract an overlap in
microhabitat use by these species indicating that diet may be a more important niche
dimension (Dure, M. I. 2004).
The results discovered here are consistent with conclusions made by Toft’s (1985) who
found that, in homogenous locations such as the Amazon Basin, litter frogs do not partition
microhabitat. Instead, food size and type as well as seasonal and deil time may be
partitioned. And, being in the floodplain of the Samiria River, it is likely that seasonal time
will be partitioned considerably by species of the genus Leptodactylus which are primarily
terrestrial and are likely to migrate with changing water levels (Toft, C. A. 1985).
Similarly, the three most abundant species found during evening terrestrial surveys didn’t
display significant differences in microhabitat use (figure 17). This is not an uncommon
finding in studies of herpetological communities; however, many have found microhabitat
use to vary little among study areas for species occurring in more than one (Block, W. M &
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Morrison, M. L. 1998). It is possible, however, that microhabitat use could be varying among
frogs at spatial scales that are smaller than the broad categories allocated for this study.
This is likely as many species are found to forage within a few metres of each other (Lima, A.
P and Magnusson, W. E. 1998), Another factor, as with species found during the day, could
be due to taxonomic relatedness as the three species Scinax pedromedinae, Scarthyla
goinorum, and Osteocephalus taurinus, although representing different genus, are all
members of the family Hylidae (table 2) and so would have evolved from a common
ancestor (Menin, M et al. 2005). Processes beyond interspecific competition such as
predation, environmental variability and environmental heterogeneity may be occurring,
meaning that a wide niche overlap doesn’t necessarily mean competition is occurring;
especially if resources aren’t in short supply (Menin, M et al. 2005).
5.4 Relative Abundance and Microhabitat Use by Aquatic Anuran Species
Although a transient microhabitat, being submerged by water during the high-water period
from December to June and exposed during the low-water period (Padoch, C. 1999), alluvial
soil was categorised as an aquatic microhabitat for the purpose of this study. This is
because, although predominantly utilised by terrestrial species (figure 20), this microhabitat
was only available to anurans outside of the forest edge along the river bank and therefore
was only observed during aquatic transects. This microhabitat was not available to species
that remained in the forest.
Although alluvial soil had the largest abundance of individuals when compared with other
aquatic microhabitats, it was largely dominated by Leptodactylus leptodactyloides which
accounted for over 75% of all frog observations there (figure 20). As frogs of the genus
Leptodactylus are primarily terrestrial with only a few exceptions (Rodríquez, L. O &
Duellman, W. E. 1994), it is surprising that such a large proportion of this species was
encountered during aquatic transects. Goin (1960), however, indicated that there are
numerous amphibian life histories which remain intermediate between a completely
aquatic and completely terrestrial lifestyle and, indeed, frogs of the genus Leptodactylus
present a group of amphibians which have made an evolutionary transition from a riparian
life history to a more terrestrial ecology (Heyer, R.W. 1969). This is likely to contribute to
how species of this genus have been so successful in inhabiting regions with markedly
seasonal rainfall (Heyer, R.W. 1969). As aforementioned, adults of the species Leptodactylus
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leptodactyloides, in particular, possess toe fringes which are a common morphological
feature associated with aquatic species (Heyer, R.W. 1969). Just as this may have allowed
some individuals to recolonize the low levee habitat more readily, similarly, this feature may
have enabled Leptodactylus leptodactyloides to dominate the alluvial soil as a transient
microhabitat.
During the study, many Leptodactylus leptodactyloides and Leptodactylus petersi were
observed not only along the alluvial soil river bank but in close proximity to small shallow
depressions, or burrows, which were frequently observed along the bank. Breder (1946)
observed Leptodactylus pentadactylus foam nests in potholes either in contact or little
removed from bodies of water. It has been suggested that this species congregates at
bodies of water solely for breeding purposes and that breeding may occur in these burrows
(Heyer, R.W. 1969). Although L. pentadactylus is a member of the Pentadactylus group
within the genus Leptodactylus, it is therefore, divergent from L. Leptodactyloides and L.
Petersi in some respects. Most of the genetic changes which have occurred throughout the
genus Leptodactylus, leading to a more terrestrial life history, are behavioural (Heyer, R.W.
1969); such as the creation of foam secretions and burrows which are characteristics
associated with fewer, larger eggs (Heyer, R.W. 1969). It is possible; therefore that L.
leptodactylus and L. petersi may share this life history trait, along with the production of
foam nests during breeding, to protect larvae against pond predators and desiccation
(Heyer, R.W. 1969).
5.5 Habitat Use by Aquatic Anurans in a Homogenous Environment
While methodological differences regarding survey technique and sample size inhibit the
validity of comparisons that can be made between aquatic transects and the two aquatic
study sites: macrophyte raft and channel inlet; it is likely that these may serve as refugia for
some aquatic species during the low water period. This may become more valuable in years
during which abnormal variations in hydro period, which are known to occur fairly
frequently within the study area (Padoch, C. 1999), results in water levels that are
abnormally low. This was the case for the period in which this study was carried out and it is
likely that this resulted in a reduction in suitable habitat available to aquatic frog species.
Indeed, it was noticeable that there was a substantial increase in the amount of river bank
exposed towards the end of the study period.
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In total, five species were discovered at the two study sites that weren’t observed in any of
the surveys carried out along the main river (figure 18,19). In particular, hypsiboas
punctatus was recorded in relatively high abundance within the macrophyte raft along the
river (figure 19). This species seemed to have similar ecological preferences with regards to
Dendropsophus triangulum; both of which utilized floating vegetation as a primary habitat.
Although in disagreement with the theory of limited similarity between coexisting species,
Menin et al (2005) also found a general overlap in microhabitat use between two species of
hylid frog and concluded that this could be because they are descendents of a common
ancestor and therefore experience a degree of taxonomic relatedness.
Similarly, it has been suggested that spatial overlap may only be present between species of
similar size and that, while small species are often found on low submerged vegetation,
large species occur on high vegetation around the water bodies (Dodd, K. C. 2009). Although
sample sizes weren’t large enough to reach these conclusions regarding the community
organization within the channel inlet, it is likely that this provided a more lentic
environment (Dodd, K. C. 2009) which may be more suitable for species such as Hypsiboas
boans which breeds in the dry season by constructing nests in the sand at stream edges
(Vitt, L. J and Caldwell, J. P. 1993). Many species of frog that reside in the tropics exhibit an
extended breeding season (Kritcher, J. 1997). It might be that the living and decaying plants,
present in and around both the macrophyte raft and the channel inlet, which affect the
productivity of the surrounding habitat, may also affect its structural and chemical suitability
(Dodd, K. C. 2009). Water temperature, influenced by vegetation impact amphibians at
multiple scales and can influence food availability and development rates (Dodd, K. C. 2009).
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6. Conclusions
6.1 Summary
The relative abundance and diversity of anuran species was found to differ significantly
between terrestrial habitat types. Relative hydroperiod of each habitat had an influence on
the diversity of species able to persist in that habitat. While abundance and diversity could
not be directly attributed to physiognomic differences between habitat types, it is likely that
vegetation structure had an influence on the relative temperature and humidity within each
habitat. Subsequently, the ambient temperature and humidity of each habitat type was
found to have a profound influence on the abundance and diversity of species present.
Nonetheless, where disturbance occurred, the costs of disturbance was found outweigh any
benefits of optimum temperature and humidity. While it was possible to associate species
with microhabitat attributes to some degree, it is likely that, in the floodplain of the Samiria
River, seasonal time is a more important resource dimension for many species.
6.2 Recommendations for Future Study
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