Making leaps in amphibian ecotoxicology: translating individual‐level effects of contaminants to population viability

Abstract

Abstract. Concern that environmental contaminants contribute to global amphibian population declines has prompted extensive experimental investigation, but individual-level experimental results have seldom been translated to population-level processes. We used our research on the effects of mercury (Hg) on American toads (Bufo americanus) as a model for bridging the gap between individual-level contaminant effects and amphibian population viability. We synthesized the results of previous field and laboratory studies examining effects of Hg throughout the life cycle of B. americanus and constructed a comprehensive demographic population model to evaluate the consequences of Hg exposure on population dynamics. Our model explicitly considered density-dependent larval survival, which is known to be an important driver of amphibian population dynamics, and incorporated two important factors that have seldom been considered in previous amphibian modeling studies: environmental stochasticity and sublethal effects. We demonstrated that decreases in embryonic survival and sublethal effects (e.g., reduced body size) that delay maturation have minor effects on population dynamics, whereas contaminant effects that reduce late-larval or post-metamorphic survival have important population-level consequences. We found that excessive Hg exposure through maternal transfer or larval diet, alone, had minor effects on B. americanus populations. Simultaneous maternal and dietary exposure resulted in reduced population size and a dramatic increase in extinction probability, but explicit prediction of population-level effects was dependent on the strength of larval density dependence. Our results suggest that environmental contaminants can influence amphibian population viability, but that highly integrative approaches are needed to translate individual-level effects to populations.

Integrating copper toxicity and climate change to understand extinction risk to two species of pond‐breeding anurans

“…, Willson et al. ). Complex combinations of stressors (climate‐induced UV‐B radiation and pathogens) have been implicated in amphibian declines from empirical evidence as well (Kiesecker et al.…”

“…Willson et al. () correctly point out that if toxicity occurs at metamorphic climax (after larval density‐dependent effects have taken place) large effects on the population occur.…”

“…, Willson et al. , Willson and Hopkins ). Much of the empirical modeling has focused on the effects of metals (Salice et al.…”

Effects of metal and predator stressors in larval southern toads (Anaxyrus terrestris)

“…We show here that parental and larval exposure to metal contamination increases larval period length and reduces size at metamorphosis, both of which have the potential to decrease survival to adulthood and reduce lifetime reproductive output. Our results suggest that multistressor studies that examine interactive effects provide more environmental realism than single stressor studies-given the importance of the early months post-metamorphosis to juvenile survival in amphibian population models (sensu Taylor and Scott 1997;Salice et al 2011;Willson et al 2012), similar studies that examine the potential carryover effects of larval stressors to the terrestrial stage will be an important research direction in order to better predict the effects of environmental contaminants.…”

Effects of timber harvesting on terrestrial survival of pond-breeding amphibians

“…Additionally, Peterman et al (2011) and Semlitsch et al (2008) both reported higher levels of emigration away from harvested forests by resident amphibians. Our study was designed to prevent emigration using enclosures to examine in isolation the degree to which survival is affected by forest harvesting, especially given that terrestrial survival can have the greatest consequences for population persistence in amphibians (Biek et al, 2002;Willson et al, 2012). Increased mortality reduces the regenerative capacity of a population by eliminating current (via adult mortality) and future (via juvenile mortality) reproductive output.…”