Sampling design may obscure species–area relationships in landscape-scale field studies

We investigated 1) the role of area per se in explaining anuran species richness on reservoir forest islands, after controlling for several confounding factors. We also assessed 2) how sampling design affects the inferential power of island species–area relationships (ISARs) aiming to 3) provide guidelines to yield reliable estimates of area-induced species losses in patchy systems. We surveyed anurans with autonomous recording units at 151 plots located on 74 islands and four continuous forest sites at the Balbina Hydroelectric Reservoir landscape, central Brazilian Amazonia. We applied semi-log ISAR models to assess the effect of sampling design on the fit and slope of species–area curves. To do so, we subsampled our surveyed islands following both a 1) stratified and 2) non-stratified random selection of 5, 10, 15, 20 and 25 islands covering 1) the full range in island size (0.45–1699 ha) and 2) only islands smaller than 100 ha, respectively. We also compiled 25 datasets from the literature to assess the generality of our findings. Island size explained ca half of the variation in species richness. The fit and slope of species–area curves were affected mainly by the range in island size considered, and to a very small extent by the number of islands surveyed. In our literature review, all datasets covering a range of patch sizes larger than 300 ha yielded a positive ISAR, whereas the number of patches alone did not affect the detection of ISARs. We conclude that 1) area per se plays a major role in explaining anuran species richness on forest islands within an Amazonian anthropogenic archipelago; 2) the inferential power of island species–area relationships is severely degraded by sub-optimal sampling designs; 3) at least 10 habitat patches spanning three orders of magnitude in size should be surveyed to yield reliable species–area estimates in patchy systems

A framework for quantifying soundscape diversity using Hill numbers

Soundscape studies are increasingly used to capture landscape-scale ecological patterns. Yet, several aspects of soundscape diversity remain unexplored. Although some processes influencing acoustic niche usage may operate in the 24-hr temporal domain, most acoustic indices only capture the diversity of sounds co-occurring in sound files at a specific time of day. Moreover, many indices do not consider the relationship between the spectral and temporal traits of sounds simultaneously. To provide novel insights into landscape-scale patterns of acoustic niche usage at broader temporal scales, we present a workflow to quantify soundscape diversity through the lens of trait-based ecology. Our workflow quantifies the diversity of sound in the 24-hr acoustic trait space. We introduce the Operational Sound Unit (OSU), a unit of diversity measurement that groups sounds by their shared acoustic properties. Using OSUs and building on the framework of Hill numbers, we propose three metrics that capture different aspects of acoustic trait space usage: (i) soundscape richness, (ii) soundscape diversity and (iii) soundscape evenness. We demonstrate the use of these metrics by (a) simulating soundscapes to assess whether the indices possess a set of desirable behaviours and (b) quantifying soundscape richness and evenness along a gradient in species richness. We demonstrate that (a) the indices outlined herein have desirable behaviours and (b) the soundscape richness and evenness are positively correlated with the richness of sound-producing species. This suggests that more acoustic niche space is occupied when the species richness is higher. Additionally, species-poor acoustic communities have a higher proportion of rare sounds and use the acoustic space less evenly. Our workflow generates novel insights into acoustic niche usage at a landscape scale and provides a useful tool for biodiversity monitoring. Moreover, Hill numbers can also be used to measure the taxonomic, functional and phylogenetic diversity. Using a common framework for diversity measurement gives metrics a common behaviour, interpretation and standardised unit, thus ensuring comparisons between soundscape diversity and other metrics represent real-world ecological patterns rather than mathematical artefacts stemming from different formulae

Composition and ecology of a snake assemblage in an upland forest from Central Amazonia

Abstract: Most species of Amazonian snakes have wide geographic distributions. However, local environmental factors influence the formation of assemblages in different localities. In this study, we investigated the composition of the assemblage and the effect of environmental variables on the distribution of the species inhabiting an upland forest in the Experimental Farm area of the Federal University of Amazonas in Manaus, Brazil. Data collection was carried out in 24 standardized plots. Each plot was sampled four times between July 2015 and April 2017 by active search method. We recorded 83 individuals from 29 species belonging to six families. The richness in the study area corresponded to 78% of the snake species and 100% of the families previously recorded for Manaus. As observed in other localities, the most abundant species was the Amazonian lancehead (Bothrops atrox). Multiple linear regression models did not detect any effect of environmental variables on species richness and abundance of individuals. However, quadratic polynomial regression models revealed that intermediate canopy opening percentages positively influence the richness and abundance of snakes. It is possible that the result is related to a tradeoff between the thermoregulation behavior of these animals and to their susceptibility to predation