The Ecological Consequences of Shared Natural Enemies

The Ecological Consequences of Shared Natural Enemies When multiple vi ctim spe cies (e.g. prey, host) are attacked by one or more shared enemy species (e.g. predator, pathogen), the potential exists for apparent competition between victim populations. We review ideas on apparent com­ petition (also called "competition for enemy-free space") and sketch illustrative examples. One puzzling aspect of this indirect interaction is the repeated rediscovery of the essential ideas. Apparent competition arises between focal and al ternativ e pr ey population s because, in the long term, enemy abundance depends on total prey availability; by increasing enemy numbers, alternative prey intensify predation on focal prey. A frequent empirical finding, consistent with theory, is exclusion of victim species from local communities by resident enemies. Theory suggests victim-species coexistence depends on particular conditions. To understand fully the consequences of shared enemies requires a body of contingent theory, specifying the time-scale of the interactions (short­ and long-term consequences of sharing enemies generally differ), the structure of the food-web encompassing the interactions, its spatial context, etc. The "core criterion" for a focal victim species to invade a community supporting a resident, polyphagous enemy is r> aP (the invader's intrinsic rate of increase 0066-4162/94/1120-0495$05.00 HOLT & LAWTON should exceed attack http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Annual Review of Ecology, Evolution, and Systematics Annual Reviews

The Ecological Consequences of Shared Natural Enemies

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Publisher
Annual Reviews
Copyright
Copyright 1994 Annual Reviews. All rights reserved
Subject
Review Articles
ISSN
0066-4162
DOI
10.1146/annurev.es.25.110194.002431
Publisher site
See Article on Publisher Site

Abstract

When multiple vi ctim spe cies (e.g. prey, host) are attacked by one or more shared enemy species (e.g. predator, pathogen), the potential exists for apparent competition between victim populations. We review ideas on apparent com­ petition (also called "competition for enemy-free space") and sketch illustrative examples. One puzzling aspect of this indirect interaction is the repeated rediscovery of the essential ideas. Apparent competition arises between focal and al ternativ e pr ey population s because, in the long term, enemy abundance depends on total prey availability; by increasing enemy numbers, alternative prey intensify predation on focal prey. A frequent empirical finding, consistent with theory, is exclusion of victim species from local communities by resident enemies. Theory suggests victim-species coexistence depends on particular conditions. To understand fully the consequences of shared enemies requires a body of contingent theory, specifying the time-scale of the interactions (short­ and long-term consequences of sharing enemies generally differ), the structure of the food-web encompassing the interactions, its spatial context, etc. The "core criterion" for a focal victim species to invade a community supporting a resident, polyphagous enemy is r> aP (the invader's intrinsic rate of increase 0066-4162/94/1120-0495$05.00 HOLT & LAWTON should exceed attack

Journal

Annual Review of Ecology, Evolution, and SystematicsAnnual Reviews

Published: Nov 1, 1994

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