Download PP251 The role of floating vegetation mats in the Pacaya

PP251 The role of floating vegetation mats in the Pacaya-Samiria Reserve, Peru in
providing breeding habitat for amphibians
Katy Upton and Hannah Clark
Amphibians were the first vertebrate group to colonise terrestrial environments, yet the
features that permitted them to do so has left them vulnerable to a range of threats. The
thin, permeable skin that enables frogs to breathe under water renders them susceptible to
moisture loss on land. This restricts temperate frog species to habitats adjacent to water,
but the humidity of the Amazonian rainforest enables a wider range of niches to be
exploited by tropical frogs. Some have moved laterally and may be found far from the river,
whilst others have moved vertically and have taken to the trees. Such niche expansion may
in part explain the increase in amphibian diversity seen with increasing latitude from the
Polar Regions to the Equator, with 481 species of predominantly anuran (frog) amphibians
identified from the Peruvian Amazon alone.
Despite the range of habitats available to adult frogs in the tropics, they produce eggs that
are unprotected from desiccation and the emerging tadpoles require an aquatic
environment for development. Several anurans are known to lay their eggs in the water
pooled in bromeliads or in moist or flooded soil, thus protecting the eggs and tadpoles from
aquatic predators such as fish and shrimp. Others, such as the Surinam toad (Pipa pipa),
have developed unique physiological adaptations to enable the young frogs to develop
within folds of skin on the back of their parent. The majority of Amazonian frog species,
however, return to the main water bodies to breed.
In the oxbow lakes and along the rivers and channels in the Amazon basin are floating
meadows, rafts of herbaceous plants that provide suitable anuran breeding habitats. During
the day, these floating meadows offer little in the way of protection from either the direct
sunlight or from a variety of predators and so rarely harbour frogs, yet at night may host
relatively high densities. Furthermore, the males of the various frog species segregate
themselves at different positions within the vegetation to call for mates, with some species
preferring low vegetation only a few centimetres from the water while others select the
higher emergent vegetation.
In recent decades scientists have observed a significant number of population declines and
extinctions of amphibians, which suggests a general Global Amphibian Decline (GAD) is
taking place. At present almost one-third of the worlds 5,743 described amphibian species
are threatened with extinction; at least 122 species are believed to have already gone
extinct since 1980, and a further 130 species have not been found in recent years and are
presumed extinct. Declines have spread geographically and the numbers of species affected
are still increasing. Many factors appear to be contributing to this decline, including habitat
loss, pollution, extreme climatic events and diseases such as chytridiomycosis, caused by a
devastating infectious fungal pathogen.
This study will survey the anurans present at both terrestrial and aquatic sites along the
Samiria River in the Pacaya Samiria National Reserve, Peru. The data collected will provide a
more accurate picture of species abundance and distribution in the Peruvian Amazon, and
this baseline data can be used in conjunction with previous surveys to help long-term
monitoring. In addition, a greater knowledge of the ecology of the various frog species
found on the reserve would both aid conservation and potentially further our understanding
of the increased diversity of anurans in the tropics. Evaluating the abundance and age
distributions of the frogs found in terrestrial habitats and on the floating meadows will be
used to indicate the importance of the aquatic vegetation as a breeding site. Finally,
comparisons of the number and species of frogs found in different terrestrial and aquatic
microhabitats will enable ecological trends across different habitat types to be investigated.
Methods
Visual encounter surveys (VES) will be used to census the amphibians present at the reserve,
with both day and night transects conducted to understand the ecology of the species
found. Diurnal transects will be carried out between approximately 7am-2pm and night
transects between approximately 8pm-1am.
For the terrestrial surveys, groups of 3-4 researchers and field assistants will traverse
established 500m transects with the help of a local guide to direct the team through the
forest and assist in amphibian detection. Each transect will take between 1-3 hours to
complete, depending on the number of amphibians encountered. During the VES all
possible microhabitats will be searched, which for the terrestrial transects include leaf litter,
tree trunks, decayed logs, fallen palm leaves and bromeliads. Due to the cryptic nature of
anurans the disturbance of this vegetation is the most systematic method of detection. This
will be achieved by methodically probing through the area directly in front of the observers,
including up to approximately 2m on either side of the trail. The majority of frog species are
more active at night, where the cooler temperatures reduce water loss from their
permeable skin. A visual search by torchlight rather than probing through the leaf litter will
be used to detect anurans on night transects.
The transects bisect different habitats within the flooded forest such as open understorey,
liana forest and levee, and so for each anuran the habitat type and the microhabitat from
which it was collected (e.g. leaf litter, tree trunk, palm leaf etc.) will be documented, as well
as the time of collection. Finally, the length travelled along the transect, determined using a
GPS (Global Positioning System), the height and the distance from the transect at which the
frog was first observed will also be logged.
To survey the frogs present on the floating meadows, a small motorised boat will be used to
reach randomly selected floating vegetation mats. The engine will be cut and the boat
wedged into the raft of vegetation, then up to six researchers will use a head torch to collect
every frog present within safe reach of the side of the boat over the course of 15 minutes.
For each frog detected, the time, distance from the boat, height from the water,
macrohabitat (river, channel or lake) and the microhabitat (e.g. emergent vegetation, water
lettuce, water hyacinth, submerged tree trunk or open water) will be recorded.
Upon detection, each frog will be captured and carefully handled using clean latex gloves.
The snout to vent length (SVL) of each specimen will be measured using Vernier callipers,
and the weight taken using a top-pan balance. Characteristics such as body shape,
colouration, presence and patterning of dorsolateral, cranial, belly, ventricular, leg and feet
markings, webbing between the digits, number and length of toes and phalanges, iris and
pupil colour and the presence of tympana will also be recorded and/or photographed. Along
with the morphometric measurements these features will be used to identify the frog to
species level. If possible, the sex and developmental stage (juvenile, adult) of each
individual will also be noted. Every frog captured will be photographed to help with any
identification difficulties/changes.
Statistical analyses will compare the frog diversity between macro and micro habitat types,
using density, abundance and diversity analyses. Density will be determined using DISTANCE
analysis, a software programme that estimates densities based on transect observation data.
Morphometric data and body weights will be compared for common species found in
different habitats, to look for ecological trends. Diversity indices will be used to combine
species richness and abundance measures in a single analysis. In addition, data from
previous years will be available and allow for a longitudinal comparison between years to
look at changes in diversity and abundance.
Suggested reading
Blair, C. and Doan. T. M. (2009). Patterns of community structure and microhabitat usage in
Peruvian Pristimantis (Anura: Strabomantidae). Copeia, Vol. 2, pp. 303-312
Doan, T. M. (2003). Which methods are most effective for surveying rain forest
herpetofauna? Journal of Herpetology, Vol. 37, Issue 1, pp.72-81
Hödl, W. (1977). Call differences and calling site segregation in anuran species from central
Amazonian floating meadows. Oecologia, Vol. 28, Issue 4, pp 351-363
Nowacki, A. M., Weir, N. A., Rodriguez, D., Sogunro, O. A. and Doan, T. M. (2011). Lake
proximity as a determinant of anuran abundance at Lago Sachavacayoc, Amazonian Peru.
South American Journal of Herpetology, Vol. 6, Issue 3, pp. 234-238
Schiesari, L., Zuanon, J., Azevedo-Ramos, C., Garcia, M., Gordo, M., Messias, M. and
Monteiro Vieira, E. (2003). Macrophyte rafts as dispersal vectors for fishes and amphibians
in the lower Solimões River, Central Amazon. Journal of Tropical Ecology, Vol. 19, No. 3, pp.
333-336
Whitfield, S. M. and Pierce, M. S. F. (2005). Tree buttress microhabitat use by a neotropical
leaf-litter herpetofauna. Journal of Herpetology, Vol. 39, Issue 2, pp. 192-198
Upton, K. April 2013. The Importance of Floating Meadows for Amphibians in a Flooded Forest.
Froglog 106, Vol. 21, No. 2, pp. 62-64
Upton, K. Steadman, J. Popplewell, D. Rogers, I. Wills, A. 2011. Amazonian Frog Diversity and
Microhabitat use. Herpetological Bulletin: 118, 10