The Costs of Evaluating Species Densities and Composition of Snakes to Assess Development Impacts in Amazonia

Abstract

Studies leading to decision-making for environmental licensing often fail to provide accurate estimates of diversity. Measures of snake diversity are regularly obtained to assess development impacts in the rainforests of the Amazon Basin, but this taxonomic group may be subject to poor detection probabilities. Recently, the Brazilian government tried to standardize sampling designs by the implementation of a system (RAPELD) to quantify biological diversity using spatially-standardized sampling units. Consistency in sampling design allows the detection probabilities to be compared among taxa, and sampling effort and associated cost to be evaluated. The cost effectiveness of detecting snakes has received no attention in Amazonia. Here we tested the effects of reducing sampling effort on estimates of species densities and assemblage composition. We identified snakes in seven plot systems, each standardised with 14 plots. The 250 m long centre line of each plot followed an altitudinal contour. Surveys were repeated four times in each plot and detection probabilities were estimated for the 41 species encountered. Reducing the number of observations, or the size of the sampling modules, caused significant loss of information on species densities and local patterns of variation in assemblage composition. We estimated the cost to find a snake as $ 120 U.S., but general linear models indicated the possibility of identifying differences in assemblage composition for half the overall survey costs. Decisions to reduce sampling effort depend on the importance of lost information to target-issues, and may not be the preferred option if there is the potential for identifying individual snake species requiring specific conservation actions. However, in most studies of human disturbance on species assemblages, it is likely to be more cost-effective to focus on other groups of organisms with higher detection probabilities.

The combined influence of riverine barriers and flooding gradients on biogeographical patterns for amphibians and squamates in south‐eastern Amazonia

“…The Tapajós had a weak barrier effect for lizard assemblages and historically is not considered to be a barrier for this group (Ávila‐Pires, ; da Silva & Sites, ). The river had no effect on snake assemblages, which was expected as most of these species are widely distributed in Amazonia because of their high dispersal capacity (da Silva & Sites, ), but it may also be a result of the greater difficulty in detecting them, resulting in fewer records and unknown broader distributional patterns (Fraga et al ., ).…”

Amphibians and reptiles from Floresta Nacional de Pau-Rosa, Amazonas, Brazil: an important protected area at the heart of Amazonia

“…Several species distributed across the Amazonian basin were not found in our inventory and are likely to be encountered once additional sampling is performed. This is particularly true for several species of snakes and lizards, which are naturally more difficult to sample in short term assessments (RibeiroJúnior et al 2008;Fraga et al 2014).…”

“…On the other hand, the reptile list is certainly far from complete and additional effort is needed for a better estimate of the species composition therein. Short-term studies are particularly ineffective for sampling the snake community at a given place (Fraga et al 2014). Therefore, for a better estimate of terrestrial squamates at FNPR, a medium to long-term assessment is necessary to inventory the species present there.…”

Checklist of chelonians from the upper Madeira River and the lower Madeira-Purus interfluvium (Brazilian Amazon), including a range expansion for Podocnemis sextuberculata Cornalia, 1849

“…Sampling was carried out in standardized RAPELD modules (see Fraga et al [2014] for a description of the terrestrial sampling infrastructure in the area) or during faunal rescue operations in areas to be flooded by the Santo Antônio dam reservoir and therefore subjected to deforestation. We had access to rescue animals brought to the wild animal screening center of the Santo Antonio hydroelectric power plant.…”