Introduced invertebrates are important prey for a generalist predator

Abstract

Concern over biological invasions has drawn increased attention to the impacts of introduced predators or competitors, but not to the importance of introduced prey. North American forests are rich in introduced invertebrates, including species that represent relatively novel taxonomic or trophic guilds and show biased distributions among forest types. We analysed the diets of red‐backed salamanders, Plethodon cinereus, from three upland and three lowland forests to determine whether introduced prey are important contributors to geographical or temporal variation in salamander food resources. We found several introduced species were volumetrically important salamander prey, and were responsible for resource differences between forest types and much of the seasonal fluctuation in food resources in both forest types. In lowland forests, rain had a stronger effect on salamander predation on non‐native earthworms than native taxa, creating more dynamic resource fluctuations in resource levels than was observed in upland forests where earthworms were absent. With one exception, predation on non‐native species was positively associated with predation on native species, suggesting non‐native prey have added to salamander resources rather than replaced salamander predation on native taxa. We hypothesize that the novel resource gradients created by non‐native prey introductions are contributing to patterns of geographical and temporal phenotypic variation among salamander populations.

Realistic Fasting Does Not Affect Stable Isotope Levels of a Metabolically Efficient Salamander

“…Hatase et al (2006) found that stable isotope differences among Green Sea Turtles (Chelonia mydas) were consistent with individual differences in feeding habits. At the population level, plethodontid salamanders consume a wide range of prey that fluctuate at fine spatial scales among habitats, seasons, and with climatic events such as rain (Maerz et al 2005). Maerz et al (2006) showed that P. cinereus exhibit fine scale trophic polymorphisms related to differences in head morphology and diet within and among local habitats.…”

Earthworms, as ecosystem engineers, influence multiple aspects of a salamander’s ecology

“…Earthworms may also indirectly affect salamanders: some species of earthworms ingest recently fallen leaf litter and many species break down partially decayed organic matter (Edwards and Bohlen 1996), thereby potentially competing with the aboveground microinvertebrate community (reviewed in Brown 1995;Migge-Kleian et al 2006), the main food source for terrestrial salamanders (reviewed in Petranka 1998). There is also a direct trophic link between salamanders and earthworms, with salamanders consuming size-appropriate earthworms as a portion of their diet in some areas (Maerz et al 2005). Therefore, as in any typical three species 'community module' (sensu Holt 1997), earthworms and salamanders (with microinvertebrates) can interact directly and indirectly.…”

Diet of Western Slimy Salamander, Plethodon albagula (Caudata: Plethodontidae), from Two Mountain Ranges in Arkansas

“…Biomass (volume of prey item) was estimated by measuring maximum width (widest lateral points) and length {widest anterior to posterior points) for some prey items using a dissection microscope. Volume (mm^) was estimated as a cylinder using length as the axis and width as the diameter (Maerz et al 2005). Whenever possible, volume was estimated for up to five individuals from each family, and a mean volume was used to calculate biomass.…”