Abstract. Theory and empirical studies suggest that cannibalism in age-structured populations can regulate recruitment depending on the intensity of intraspecific competition between cannibals and victims and the nature of the cannibalism window, i.e., which size classes interact as cannibals and victims. Here we report on a series of experiments that quantify that window for age-structured populations of salamander larvae and paedomorphic adults. We determined body size limits on cannibalism in microcosms and then the consumptive and nonconsumptive (injuries, foraging and activity, diet, growth) effects on victims in mesocosms with seminatural levels of habitat complexity and alternative prey. We found that cannibalism by the largest size classes (paedomorphs and !age 3þ yr larvae) occurs mainly on young-of-the-year (YOY) victims. Surviving YOY and other small larvae had increased injuries, reduced activity levels, and reduced growth rates in the presence of cannibals. Data on YOY survival in an experiment in which we manipulated the density of paedomorphs combined with historical data on the number of cannibals in natural populations indicate that dominant cohorts of paedomorphs can cause observed recruitment failures. Dietary data indicate that ontogenetic shifts in diet should preclude strong intraspecific competition between YOY and cannibals in this species. Thus our results are consistent with previous empirical and theoretical work that suggests that recruitment regulation by cannibalism is most likely when YOY are vulnerable to cannibalism but have low dietary overlap with cannibals. Understanding the role of cannibalism in regulating recruitment in salamander populations is timely, given the widespread occurrences of amphibian decline. Previous studies have focused on extrinsic (including anthropogenic) factors that affect amphibian population dynamics, whereas the data presented here combined with long-term field observations suggest the potential for intrinsically driven population cycles.
Historically, ecological risk assessments have rarely included amphibian species, focusing preferentially on other aquatic (fish, invertebrates, algae) and terrestrial wildlife (birds and mammal) species. Often this lack of consideration is due to a paucity of toxicity data, significant variation in study design, uncertainty with regard to exposure, or a combination of all three. Productive risk assessments for amphibians are particularly challenging, given variations in complex life history strategies. Further consideration is needed for the development of useful laboratory animal models and appropriate experimental test procedures that can be effectively applied to the examination of biological response patterns. Using these standardized techniques, risk estimates can be more accurately defined to ensure adequate protection of amphibians from a variety of stress agents. Patterns in toxicity may help to ascertain whether test results from 1 amphibian group (e.g., Urodela) could be sufficiently protective of another (e.g., Anura) and/or whether some nonamphibian aquatic taxonomic groups (e.g., fish or aquatic invertebrates) may be representative of aquatic amphibian life stages. This scope is intended to be a guide in the development of methods that would yield data appropriate for ecological risk decisions applicable to amphibians. Integr Environ Assess Manag 2017;13:601-613. © 2016 SETAC.
Since the ELS study has long been the standard test design for chronic effects to 3 fish (OECD, 2013; U.S. EPA, 2016), its inclusion here provides important historical 3 grounding for our analysis and provides an alternative fish study design for comparison 3 with the AMA. In addition to different numbers of test concentrations, there are other 3 important ways in which the FSTRA and ELS differ that could affect the pattern and 3 magnitude of sensitivity. While the FSTRA is always conducted on P. promelas, the ELS 3 can also be conducted with O. mykiss (Table 1; Supplemental Table 1), bluegill sunfish 3 (Lepomis macrochirus), Atlantic silverside (Menidia menidia), inland silverside (M.3 beryllina), or tidewater silverside (M. peninsulae). Also, the FSTRA is conducted on 3 early sexually mature fish while the ELS begins with embryos and is terminated prior to 3 sexual maturity: therefore, these tests represent fish sensitivity at different life stages. 3The relationship of growth data between the two fish studies (FSTRA and ELS) is 3 not as strong as between FSTRA and AMA studies, with slopes closer to 1 and similar or 3 higher coefficients of determination values between the two EDSP studies. This may 3 indicate that the strength of the relationship among toxicity data has as much to do with 3 study design as with the study organism, which is supported by the more similar 3 concentration regimes in the FSTRA and AMA (Fig. 1). However, it is also possible that 3 some of the discrepancy between FSTRA and ELS studies could be due to the different 3 life stages tested in the two fish studies, or other sources of variability which should be 3 certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.further explored in the future. The analysis suggests though that study design may 3 influence the magnitude of endpoints, which may support the strength of using the two EDSP studies for making more robust fish-frog comparisons.
1 0 1 1 1 2 2 ABSTRACT 1 3 Ecological risk of chemicals to aquatic-phase amphibians has historically been evaluated 1 4 by comparing estimated environmental concentrations in surface water to surrogate 1 5 toxicity data from standard fish species. Despite their obvious similarities, there are 1 6biological disparities among fish and amphibians that could affect their exposure and 1 7 response to chemicals. Given the alarming decline in amphibians in which anthropogenic 1 8 pollutants play at least some role, evaluating the potential risk of chemicals to amphibians 1 9 is becoming increasingly important. Here, we evaluate relative sensitivity of fish and 2 0 larval aquatic-phase amphibians to 45 different pesticides using existing data for three 2 1 standardized toxicity tests: (1) amphibian metamorphosis assay (AMA) with the African 2 2 clawed frog (Xenopus laevis); (2) fish short-term reproductive assay (FSTRA) with 2 3 freshwater fathead minnow (Pimephales promelas); (3) fish early life stage test with P. 2 4 promelas or rainbow trout (Oncorhynchus mykiss). The advantage of this dataset over 2 5previous work is that these studies show high consistency in exposure method and 2 6 exposure concentration validation, study duration, test species, endpoints measured, and 2 7 number of concentrations tested. We found very strong positive relationships between 2 8 fish and tadpole lowest adverse effect concentrations (LOAEC) for survival (r 2 =0.85, 2 9 slope=0.97), body weight (r 2 =0.77, slope=0.98), and length (r 2 =0.77, slope=0.92) with 3 0 only one out of 45 chemicals exhibiting 100-folder greater sensitivity in frogs relative to 3 1 fish. While these results suggest comparable toxicity for pesticides between these two 3 2 groups of vertebrates, testing with a greater diversity of amphibians will help determine 3 3 the generalizability of these results across all amphibians. 3 4 3 5 3
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