Simulated developmental and reproductive impacts on amphibian populations and implications for assessing long-term effects

Abstract

Fish endpoints measured in early life stage toxicity tests are often used as representative of larval amphibian sensitivity in Ecological Risk Assessment (ERA). This application potentially overlooks the impact of developmental delays on amphibian metamorphosis, and thereby reduced survival, in amphibian populations constrained by habitat availability. Likewise, the effects of reduced productivity or altered sexual development as a result of chemical exposure are not presented in terms of lower population fecundity in these surrogate tests. Translating endpoints measured in toxicity tests to those that are more representative of amphibian ecology and population dynamics provides a means of identifying how developmental effects result in long-term impacts. Here we compare effects of developmental delay on metamorphosis success in six anuran species and simulate population-level impacts of subsequent reductions in larval survival as well as potential reductions in fecundity as a result of developmental impacts. We use deterministic matrix models to compare realistic combinations of amphibian demographic rates and relative impacts of reduced growth on larval survival and subsequently on population growth. Developmental delays are less detrimental in species with longer and less synchronous larval periods. All six species were most sensitive to changes in first-year survival, and damping ratios were generally a good indicator of resilience to perturbations in both larval survival and fecundity. Further identification of species and population-level vulnerabilities can improve the evaluation of sublethal effects in relevant context for ERA.

Keywords: Aquatic toxicology; Comparative matrix model; Ecological risk assessment.

Figure 1

Amphibian life cycle stages and parameters used in matrix models.

Figure 2

Estimated baseline cumulative distribution curves of metamorphosis times in seven different species.

Figure 3

Percent metamorphosis cumulative distribution functions for a) southern toad (Anaxyrus terrestris) and b) California red-legged frog (Rana draytonii) with delayed metamorphosis up to fifteen days.

Figure 3

Percent metamorphosis cumulative distribution functions for a) southern toad (Anaxyrus terrestris) and b) California red-legged frog (Rana draytonii) with delayed metamorphosis up to fifteen days.

Figure 4

Proportional reductions in population growth rate (PGR) as a result of reductions in larval survival due to delayed growth and metamorphosis (a) and for reduced fecundity (b) for six amphibian species. Y-axes are the same scale.

Figure 4

Proportional reductions in population growth rate (PGR) as a result of reductions in larval survival due to delayed growth and metamorphosis (a) and for reduced fecundity (b) for six amphibian species. Y-axes are the same scale.