Revisiting “what do tadpoles really eat?” A 10‐year perspective

Abstract

Tadpoles are diverse and abundant consumers, and knowledge of their feeding ecology and trophic status is essential in understanding their functional roles within aquatic habitats. Here we revisit Altig, Whiles, and Taylor (2007)'s paper, which highlighted the knowledge gaps in tadpole feeding ecology and the application of modern techniques, such as stable isotope and fatty acid analyses to better quantify dominant food resources, food assimilation, and the trophic status of tadpoles. We reviewed the ecological studies that have been published since 2007 that used stable isotopes and fatty acid analyses, also metagenomics and ecological stoichiometry analyses. We describe the ecological roles of tadpoles in freshwater ecosystems and identify knowledge gaps regarding tadpole feeding ecology across biogeographic regions. Worldwide declines in amphibian abundance and diversity create an urgent need to document their feeding ecology and trophic status. As consumers, tadpoles play important functional roles in nutrient cycling, energy flow, and bioturbation. They also exhibit context‐dependent trophic plasticity in response to abiotic and biotic gradients, which complicates understanding of their trophic roles. Most studies of tadpole trophic ecology have been conducted primarily on species from the families Ranidae, Bufonidae, and Hylidae from Neotropic and Nearctic regions, while species in tropical regions such as Africa and Asia lack ecological information for tadpoles. There continues to be a need for studies of tadpole diets and/or trophic ecology in Africa and Southeast Asia regions where species endemism is threated by the growth of anthropogenic activities. The majority of studies have focused on trophic ecology of tadpoles from the perspective of single species or at relatively small spatial and temporal scales. Studies that address questions from an ecosystem perspective were scarce, but are critical for conservation and management. Future research should aim to address the role of tadpoles as consumers across broader spatiotemporal scales.

Food source determines stable isotope discrimination factors ΔN and ΔC in tadpoles

“…Analyses of stable isotope ratios are widely applied in studies on a large variety of aspects in trophic ecology. Either as a standing alone analysis, or in combination with direct studies such as direct observations of feeding or gut analyses, isotope ratios indicate trophic position within a food web (δ 15 N) or identify major energy sources (δ 13 C) (DeNiro and Epstein, 1981;Peterson and Fry, 1987;Post, 2002;Montana et al, 2019). One essential factor in these studies is the discrimination factor (also called the fractionation factor), that reflects the fractionation or differences in isotope ratios of a certain element between an animal's diet and its tissue.…”

“…The analysis of stable isotopes is a rather recent yet well-established and easy-to-perform method that can be used to assess a variety of relevant parameters in food web ecology. It has proven to be a more effective tool than conventional methods (e.g., gut analyses) for interpreting diet relationships as the isotopic signature of a species' niche reflects temporally and spatially integrated data, whereas stomach content data alone reflect rather a temporary snap-shot of food choice (Winemiller, 1990;Post, 2002;Winemiller and Layman, 2005;Montana et al, 2019).…”

“…Stable isotope ratios are seen as "recorders" that can be used to reconstruct ecological processes in a wide variety of organisms (West et al, 2006;Montana et al, 2019). Most applications refer to specific energy flow pathways leading to one (or a few) species of interest, i.e., they are used to calculate trophic positions (Vander Zanden et al, 1997;Post, 2002;Layman et al, 2007a), relative contribution of prey items to consumers (Vander Zanden and Vadeboncoeur, 2002), niche shifts (Post, 2003;Barnum et al, 2013;Schalk et al, 2017), and intraspecific diet variability (Bolnick et al, 2003;Bearhop et al, 2004;Matthews and Mazumder, 2004).…”

Herbivory by spadefoot toad tadpoles and reduced water level affect submerged plants in temporary ponds

“…Aquatic turtles also graze aquatic vegetation as part of their omnivorous diet (Lodge et al 1998, Pérez-Santigosa et al 2011). In the case of anuran amphibians, although postmetamorphic stages rarely consume plants, tadpoles are commonly herbivorous (Altig et al 2007, Montaña et al 2019. Taking into account the proportion of aquatic macrophytes consumed by vertebrates, Lodge et al (1998) considered that this group could have a higher impact on vascular plants than any other taxonomic group, even though the impact of amphibians was not considered in their study.…”

“…Tadpoles are often primary consumers or even omnivorous, with diet mostly consisting of algae, phytoplankton, and periphyton. Nevertheless, they can shift their diet in response to the availability of resources or as a result from competition and predation risk (Altig et al 2007, Arribas et al 2018, Montaña et al 2019. Tadpole diets of some Iberian species have been described in detail (Díaz-Paniagua 1985).…”