Ontogenetic and individual diet variation in amphibian larvae across an environmental gradient

Abstract

Summary 1. Variation among individuals within size or age classes can have profound effects on community dynamics and food‐web structure. We investigated the potential influence of habitat disturbance on intrapopulation niche variation. 2. Amphibians occupy a range of lentic habitats from short‐hydroperiod intermittent ponds to long‐hydroperiod permanent ponds. We quantified ontogenetic diet variation and individual specialisation in wood frog tadpoles (Lithobates sylvaticus) and blue‐spotted salamander larvae (Ambystoma laterale) to investigate the influence of hydroperiod on population niche width across a natural hydroperiod gradient using stable isotope and gut content analyses. In one of the few tests using larval forms, we tested the niche variation hypothesis, which predicts that populations with larger niche widths also have increased individual variation. 3. Our results support the niche variation hypothesis, indicating that more generalised populations exhibit higher within‐individual diet variation. We report gradual changes in the relative importance of diet items, decreased dietary overlap and increased trophic position in L. sylvaticus throughout development. A. laterale became more enriched in δ13C and increased in δ15N throughout its larval period. We did not find a relationship between hydroperiod and niche parameters, indicating that niches are conserved across heterogeneous habitats. In contrast to most documented cases, we estimated low levels of individual specialisation in amphibian larvae. 4. Amphibians are an important link between aquatic and terrestrial ecosystems, whereby diet shifts can influence food‐web structure by altering energy flow pathways and the trophic position of higher consumers, ultimately changing food‐chain length.

Trophic specialization at the individual level in a terrestrial generalist salamander

“…In any case, the overall realized trophic niche of a species or population is obtained by summing the dietary habits of different individuals and, therefore, the behaviour of each individual will contribute to the observed mean value (Bolnick et al 2003;Schriever and Williams 2013). Thus, a generalist population may consist entirely of generalist individuals, who all exploit a similar array of resources, or consist of many differently specialized individuals, who feed on a narrower but diverse set of trophic categories.…”

Stable isotopes reveal an invasive plant contributes more than native sources to anuran larvae diets

“…In Missouri (MO) and South Carolina (SC), breeding typically occurs between January and March in fish-free, ephemeral woodland pools or wetlands (Redmer & Trauth 2005). Wood frogs complete metamorphosis between 65 and 130 days; prior to metamorphosis larvae feed primarily on detritus, plant/algal material, and some zooplankton (Redmer & Trauth 2005;Schiesari et al 2009;Schriever & Williams 2013). Southern leopard frogs are most abundant in the southeastern portion of the United States with large densities in the Appalachian Highlands (Garrett & Barker 1987;Butterfield et al 2005).…”

Time to feed: How diet, competition, and experience may influence feeding behaviour and cannibalism in wood frog tadpoles Lithobates sylvaticus

“…The effects of these traits become increasingly pronounced over time causing size disparity among individuals within the population (Lomnicki, 1988;Peacor and Pfister, 2006;Uchmanski, 1985). Schriever and Williams (2013) identified ontogenetic shifts in the trophic positioning and specialization of individual wood frog tadpoles through their larval development. The observed niche specialization may result from increasing differentiation in foraging success among individual tadpoles, which corresponds with what would be expected based on the results of Peacor and Pfister (2006).…”