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Interactions Between Intraspecific Competition and Predation in an Amphibian Predator‐Prey System
Author(s) -
Morin Peter Jay
Publication year - 1986
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1937694
Subject(s) - intraspecific competition , tadpole (physics) , predation , biology , guild , interspecific competition , predator , ecology , notophthalmus viridescens , crucifer , competition (biology) , larva , metamorphosis , hyla , habitat , botany , physics , particle physics , regeneration (biology) , microbiology and biotechnology
The predatory salamander Notophthalmus viridescens indirectly facilitates the growth and survival of herbivorous tadpoles of Hyla crucifer, when the latter are embedded in guilds of superior competitors. I used experimental manipulations of N. viridescens and H crucifer densities in artificial ponds to explore the dependence of facilitation on guild composition, by testing whether N. viridescens facilitated H. crucifer when it was the only species in the tadpole guild. I also measured the independent relative contributions of intraspecific competition and predation to tadpole survival and growth, to test whether competition among prey influenced the impact of predation on prey survival. Tadpole survival was independent of intraspecific density and negatively affected by predator density. In communities without predators, increased tadpole densities decreased growth rates, prolonged larval development, and reduced froglet mass at metamorphosis. Predation tended to increase metamorph mass slightly within a given level of initial tadpole density. However, the impact of predators on tadpole survival was independent of density—dependent tadpole growth. Predators failed to reduce competition substantially among larval H. crucifer, because tadpoles altered their microhabitat used to avoid predators. Consequently, tadpole densities and competitive interactions were only slightly moderated by predators. Predator avoidance exacted no cost in terms of reduced mass at metamorphosis or prolonged larval periods. Although predators may greatly reduce the intensity of interspecific competition among prey by reducing densities of particularly susceptible competitively superior species, the intensity of intraspecific competition among remaining predator—resistant species may remain unaffected. The failure of N. viridescens to facilitate H. crucifer in the absence of other species of competing anurans indicated that previously documented facilitation was indirect and dependent on guild structure.