Abstract
Worldwide, amphibian populations have been declining rapidly. This decline can be attributed to many factors including climate change, pesticide exposure, and emerging infectious diseases, among other important factors, but few studies have examined the influence of species interactions. In this study, we examined how habitat factors and co-occurring avian and mammalian species, as well as humans, exert direct and indirect effects on Neotropical amphibian population dynamics. We further examined how these habitat and species interactions could affect our ability to reliably detect amphibian presence to robustly estimate population trends. We conducted amphibian visual encounter surveys at 26 randomly selected sites in the La Selva Biological Station, in northeastern Costa Rica, as well as 26 sites across five additional forest fragments in the region. Furthermore, we used camera traps to collect data on avian and mammalian communities and human visitation at those amphibian survey plots. From these data, we were able to estimate species occupancy probabilities for leaf litter frogs across sites and their relationships to habitat and interspecific species interaction covariates. We also conducted an experiment with plastic model frogs to estimate detection probabilities when a population is known to occur at a site with certainty. Our results suggested that strawberry poison dart frog (Oophagapumilio) occupancy was positively related to secondary forest and their detection was negatively related to increasing air temperatures at the times of the surveys. Leaf litter frog occupancy was negatively related to core La Selva sites and human detections at sites, yet their detection was positively related to human trail presence, which might be related to reduced leaf litter cover due to heavy trampling. Our experimental surveys suggested that Neotropical leaf litter frog communities are difficult to detect when present and future studies should explicitly account for this detection bias to effectively monitor population trends.
Highlights
Amphibian populations worldwide have declined rapidly over the last few decades (Carey 2000)
We considered all other frogs that were cryptic among leaf litter (e.g., Bufonidae, Craugastoridae, etc.) to belong to the group “leaf litter frogs”
We did not calculate species-specific densities so our inferences differ from previous research because they are general to strawberry poison dart frog and all ‘leaf litter frogs’ occurrence as opposed to abundance, which would be more indicative of species-specific declines
Summary
Amphibian populations worldwide have declined rapidly over the last few decades (Carey 2000). Many other potential avian and mammalian predators of frogs commonly occur in and around La Selva (e.g., great curassow [Crax rubra Linnaeus, 1758] and white-nosed coati [Nasua narica Linnaeus, 1766] – Paluh et al 2015; Pardo et al 2016; Pardo et al 2017), which could have an effect on amphibian communities due to predation or trampling and rooting of leaf litter habitat at various scales. Humans and their use of trails may further influence frog communities due to additional trampling of leaf litter affecting the microclimate and cover from predators
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