Academic journal article The American Midland Naturalist

Interactions among Forest-Floor Guild Members in Structurally Simple Microhabitats

Academic journal article The American Midland Naturalist

Interactions among Forest-Floor Guild Members in Structurally Simple Microhabitats

Article excerpt

ABSTRACT. -

Intraguild predation in structurally complex habitats is thought to weaken trophic cascades and increase food web stability. However, many predators commonly found in leaf litter become restricted to simple microhabitat beneath rocks and logs during periods between rains. It is within this structurally simple microhabitat that some predators defend rich prey resources and are likely to interact strongly as the surrounding forest becomes too dry to forage broadly in space. We conducted a 4-y press experiment where we removed focal predators from unfenced field plots. To evaluate the effects of predators on one another we removed either salamanders or centipedes from beneath artificially placed cover objects and compared abundances of these and other intraguild predators to those in non-removal controls. We predicted that salamanders and centipedes would have strong negative effects on each other and on carabid beetles and spiders. We removed a total of 1288 salamanders and 1056 centipedes over 98 sampling dates. In salamander removal plots spider abundance increased by 34%, and carabid beetles decreased by 15% relative to the control. In centipede removal plots salamanders increased by 18% and carabid beetles increased by 29%, but spider abundance decreased by 15%. Interaction strengths were strongest in the drier summer months when territorial predators were confined in spatially fixed microhabitats. It is during these periods that predators may strongly regulate the abundances of guild members. In territorial species that defend areas beneath natural cover, the effect of intraguild predators may be an important mechanism that regulates distribution and abundance of forest floor predators.

INTRODUCTION

Early studies of community dynamics used simple models to predict distribution and abundance patterns of species in various systems. Hairston and Hairston (1993) noted that simple models operated under a number of assumptions. For example, it was assumed that links in food chains were equal in value, and early models may have ignored the multitude of interactions (e.g., intraguild prédation (IGP) and competition) within trophic levels that are likely to affect the remainder of the web. More recently ecologiste have begun to focus on the kinds of biotic interactions that influence the ecology of organisms in communities. Ecologiste now understand that IGP and omnivory are widespread (Polis and Holt, 1992; Polis, 1998; Wise and Chen, 1999; Moya-Larano and Wise, 2007) and that it may be insufficient to look at linear chains if we are to understand the variables that affect community structure, stability, and ecosystem function (Polis, 1991, 1994; Bascompte, 2009). A more effective approach to understanding the consequences of perturbations on communities is to apply network theory which emphasizes connections within a web rather than focusing on pair-wise interactions between species (Bascompte, 2009). Research investigating behavior among generalist predators in food webs is important because die strength of non-trophic interactions can influence organisms at other positions within die web. For example, IGP is diought to weaken trophic cascades in terrestrial habitats (Holt and Polis, 1997) and increase web stability (McCann et al., 1998) because prédation within trophic compartments should reduce pressure on more basal trophic levels. One way to further our understanding of the consequences of competition and/or IGP at the community level is to study die numerical response of potentially interacting guild members to changing densities of single predator groups in complex terrestrial webs (Moya-Lareño and Wise, 2007).

Our research was conducted in a temperate deciduous forest-floor system. Such systems are diought to have characteristics (e.g., high species diversity, structural habitat complexity, IGP, and omnivory) diat should attenuate the effects of predators at more basal trophic levels (Finke and Denno, 2004). …

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