Seasonal Patterns of Intraguild Predation and Size Variation among Larval Salamanders in Ephemeral Ponds
Predation among potential competitors, or intraguild predation (IGP), is dependent on size disparities between competing predators and prey and strongly influences the ecology of larval amphibians in ephemeral ponds. Although intraguild prey are hypothesized to exhibit faster growth rates than intraguild predators and, therefore, outgrow predation risk through time, intraguild predation also is associated with significant increases in predator growth rates that are hypothesized to increase the potential for future predation. Given these conflicting hypotheses, how predation among amphibian larvae early in development should influence size disparities and ontogenetic shifts in predation risk is unclear. To clarify the effects of intraguild predation on predator and prey growth, we quantified size variation among larval salamanders (Ambystomatidae) in forested ephemeral ponds while concurrently monitoring seasonal patterns of intraguild predation through gut content analyses. Intraguild predation had no discernible effect on either interspecific size disparities between intraguild predators and prey, or intraspecific size variation within predator populations, and factors of larval density, tadpole density, and pond area were more important than larval size variation in predicting IGP. Our results do not support previous assertions regarding the consequences of intraguild predation for predator–prey size disparities, because top predators not actively engaging in IGP appeared to maintain growth rates equivalent to successful conspecific IG predators, and the frequency of intraguild predation did not significantly change during larval ontogeny. The lack of consistent increases or decreases in predator–prey size disparities suggests that intraguild prey may not experience predictable ontogenetic shifts in intraguild predation risk.Abstract
Competing hypotheses for temporal trends in community size variation and frequency of intraguild predation (IGP; stippled lines). A) Prey outgrow the gape limitations of IG predators, resulting in decreasing size disparities between predator and prey (D) and decreases in IGP; B) increased growth through IGP increases size disparities (D) between predator and prey and subsequent rates of future predation. For predators feeding on basal prey, IG prey growth ultimately reduces the likelihood of future predation; C) increased growth of IG predators only serves to keep pace with growth of IG prey, resulting in unchanging size disparities and frequencies of IGP.
Locations of focal ponds within the Shawnee National Forest, southern Illinois. Black stars denote the relative locations of pond networks, with the number of focal ponds within a network indicated above the star.
Frequency of intraguild predation among salamander assemblages based on levels of interspecific size variation among Ambystoma opacum and Ambystoma maculatum or Ambystoma tigrinum and A. maculatum observed in 14 ephemeral ponds in southern Illinois from 2006–08. All instances of predation reflected intraguild predation on A. maculatum and not cannibalism.
A) Larval size; B) intra- and interspecific larval size variation (coefficient of variation in monthly head width ± 1 SE); and C) larval densities (individuals/m2) among larval Ambystoma opacum, Ambystoma tigrinum, and Ambystoma maculatum as derived from monthly estimates collected from 14 ephemeral ponds from 2006–08 in southern Illinois. For larval size measurements, each data point represents the mean head width of at least 30 larvae, and larval densities reflect those larvae collected in sediment cores.
Contributor Notes
