Determinants of size at metamorphosis in an endangered amphibian and their projected effects on population stability

Abstract

Roughly 80% of animal species have complex life cycles spanning a major habitat shift, and delayed life history effects play an important role in their population dynamics. Through their effect on size at metamorphosis, factors in the pre‐ metamorphic environment often have profound effects upon survival and fecundity in the post‐metamorphic environment. Here, we adopted a combined experimental and field observational approach to investigate the factors that determine size at metamorphosis in pond‐breeding amphibians, and to predict some of their downstream effects on population stability. We set up ecologically realistic mesocosm communities for the endangered California tiger salamander Ambystoma californiense to test the effects of larval density, prey density and hydroperiod on mean size at metamorphosis. We found significant effects for all three factors, with mean size at metamorphosis negatively correlated with larval density and positively correlated with prey density and hydroperiod. We also used six years of field survey data to identify the most informative model explaining mean size at metamorphosis and thus validate our mesocosm results. The optimal three‐term model identified terms that were roughly analogous to each of the mesocosm treatments and with similar effect sizes, providing strong field confirmation of our experimental results. The field data also provide correlations between each factor and the number of metamorphs recruited to the population, allowing us to predict the effect of each factor on population stability. Finally, we show that these populations of the endangered A. californiense are strongly resource limited, which has important implications for their management and recovery as an endangered taxon.

Ecological equivalency as a tool for endangered species management

“…A previous experiment that used identical mesocosm stocking densities for most of these taxa (excluding beetle larvae and backswimmers) recovered CTS size distributions that closely mimicked those observed in nature, suggesting that they replicate the dynamics of natural vernal pool communities (Searcy et al. ). Pure CTS were collected from three ponds at the Jepson Prairie Preserve (Solano County), superinvasives from three ponds at Fort Ord National Monument (Monterey County), and full hybrids from three ponds at Garlinger Ranch (Monterey County).…”

Altered thyroid hormone levels affect body condition at metamorphosis in larvae of Xenopus laevis

“…Amphibians have highly permeable skin, which makes them particularly vulnerable to chemical contaminants (Hayes et al, ; Strong, Martin, Jones, Shore, & Halsall, ). Furthermore, particularly larval amphibians are limited in their capacity for habitat selection (Sanzo & Hecnar, ; Yu, Wages, Cai, Maul, & Cobb, ), and are particularly sensitive to EDs due to their critical hormone‐regulated development (Hayes, Falso, Gallipeau, & Stice, ; Searcy, Snaas, & Shaffer, ).…”

The challenge of modeling niches and distributions for data‐poor species: a comprehensive approach to model complexity

“…These models have seen wide application throughout environmental biology, including use in conservation, agriculture, zoonotic diseases, and many other areas (Elith and Leathwick ). When copious data are available, ENMs even can be used for studying the variables driving population abundance, demography, and recruitment (Williams et al , Martínez‐Meyer et al , Searcy et al , Muscarella and Uriarte ). Linked with such demographic information as well as genetic data, ENMs also hold promise for studying the effects of past and ongoing climate change (Pearson and Dawson , Waltari et al ).…”