Dynamic and diverse amphibian assemblages: Can we differentiate natural processes from human induced changes?

Abstract

Amphibians are sensitive to anthropogenic habitat alterations but also respond to natural drivers of assemblage composition at many levels. Additionally, they are usually hard to detect in field inventories. We used a multiscale approach, from microhabitat to the landscape levels, to try to understand the effects of natural changes, and try to distinguish them from the effects of landscape level anthropogenic changes, on dynamic and diverse anuran assemblages, taking imperfect detection into account. We conducted thorough field inventories in 16 streams at Serra do Cipó, in the southern portion of Espinhaço Mountain Range, southeastern Brazil, during two time periods separated by 16 years. We compared species richness and diversity between periods, sampling both tadpoles and adult frogs. We quantified tadpole microhabitat availability, alterations in immediate riparian vegetation, and changes in classes of land cover within buffers around streams (adult habitats) to test for their effects on species composition. We also tested for effects of human occupancy around streams on nestedness and turnover components of species diversity. Microhabitats and riparian vegetation explained some of the changes in species composition (or detection) between time periods. Nestedness seemed to be influenced by the stability of the landscape. Detectabilities were too low to support robust occupancy estimates for most species. Natural changes in local habitats occupied by anurans in montane meadows are likely to influence species distribution. Some species with robust estimates experienced change in their occupancy over the studied 16-year interval, although no anthropogenic causes could be directly associated with such changes. The low detectability of most species, even with thorough sampling effort, makes it very hard to detect amphibian declines and possibly tell them apart from natural population fluctuations. New techniques are needed that improve species detectability in such diverse tropical habitats.

Factors influencing fine-scale occupancy and detectability of an insular Atlantic Forest frog

“…One possible explanation is that it is harder to perceive the presence of the individuals when they are on the leaf litter. Some reasons why certain frog species tend to have low detectability may include small body size, a potential level of camouflage when on the litter because of their colouration, secretive habits, or rarity in nature, which may result in them becoming less perceptible during visual encounter surveys (de Sá et al 2015;Lima et al 2019). In the case of H. fredi, which is not rare in stream environments of the island, the dorsal colouration may concur to explain the decrease in detectability as one moves towards the stream margins and away from the stream.…”

“…Some reasons why certain frog species tend to have low detectability may include small body size, a potential level of camouflage when on the litter because of their colouration, secretive habits, or rarity in nature, which may result in them becoming less perceptible during visual encounter surveys (de Sá et al . 2015; Lima et al . 2019).…”

Random placement models explain species richness and dissimilarity of frog assemblages within Atlantic Forest fragments

“…First, it is likely that not all species were detected during field samplings, despite the considerable sampling effort employed. Some anuran species have low detectability due to their small body size, rarity, pattern of calling or their ability to camouflage among the leaf litter or underground, making them difficult to detect through visual encounter surveys (de Sá et al, 2019; Lima et al., 2019). However, we highlight that our analysis taking into account imperfect detection returned very similar results, indicating that our sampling effort was reasonably complete in most sites (see Figure S1 in Appendix 1).…”

High species turnover shapes anuran community composition in ponds along an urban-rural gradient

“…This is considered the most efficient method to detect anurans (Doan 2003, Flint and Harris 2005, Grover 2006. We also used acoustic identification because some anuran species have low detectability due to their small body size, rarity, or their ability to camouflage among the leaf litter or underground (Sá et al 2018, Lima et al 2019. However, while this alternative method allowed for the detection of species with predominantly subterranean habits (which otherwise would have been overlooked), only the abundances of two comparatively rare species (Elachistocleis helianneae and Elachistocleis bicolor) were estimated by acoustic identification.…”