Diffuse competition and continuous niche shifts in size-structured populations of predatory salamanders

Resetarits Jr., W. J. and Fauth, J. E. (2005) Diffuse competition and continuous niche shifts in size-structured populations of predatory salamanders. Community Ecology, 6 (1). pp. 101-107. ISSN 1585-8553

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Abstract

Size-specific interactions between predators can affect both species population dynamics and the structure and biodiversity of communities they inhabit. Interactions between size-structured populations of predators, especially those with complex life-cycles, often change with resource-use changes driven by ontogenetic niche shifts. However, if resource use is determined largely by prey size, generalist predators may compete across a wider range of body sizes and life stages resulting in diffuse intra- and interspecific competition. We examined size- and stage-specific interactions between juvenile sirens (Siren intermedia) and adult newts (Notophthalmus viridescens dorsalis) in the context of previous experiments demonstrating competitive equality of larvae and strong effects of adult S. intermedia on adult N. viridescens. Competition between juvenile siren and adult newts was mutually negative and roughly symmetrical. Two S. intermedia reduced growth of three N. viridescens by 21%, while three N. viridescens reduced growth of two S. intermedia by 29%. Together with previous work, this implicates diffuse competition as a critical feature in the ecology of these species across the range of body sizes and suggests that intensity of competition varies more with size than species identity. Competition that varies incrementally with body size expands the realm of possibilities for continuous niche changes and diffuse competition across large size gradients. For generalist predators such as S. intermedia and N. viridescens, body size, except at the extremes, is not an adequate niche difference either intra- or interspecifically.

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