Apparent competition occurs when two species have a common predator. In Figure 1b an abundant population of species 1 sustains a high-density population of predator 2, who, in turn, may limit the population of another prey species 3. From practical point of view, it is worth noting here that this situation sometimes happens as an
(b) Apparent competition
(c) Trophic cascade 4
(d) Indirect mutualism involving exploitative competition
(e) Indirect mutualism involving interference competition
(f) Interaction modification
Figure 1 Diagrams of the most commonly studied indirect affects. Direct effects are shown using solid lines, while indirect effects (only the effects relevant to the accompanying discussion are illustrated) using dotted lines. Interaction modification is illustrated using a dashed line. Numbers in the compartments are used solely for labeling to distinguish between different compartments, and do not relate to any kind of hierarchy. Likewise, the box sizes do not bear any relevance to the sizes or significance of the compartments drawn, and the relative size of the arrows relates neither to the effect's strength no to the preferential directionality. See further explanations in the text. (a) Interspecific competition; (b) apparent competition; (c) trophic cascade; (d) indirect mutualism involving exploitative competition; (e) indirect mutualism involving interference competition; (f) interaction modification. Modified from Wootton JT (1994) The nature and consequences of indirect effects in ecological communities. Annual Review of Ecology and Systematics 25: 443-466.
unwanted result in biocontrol, when a biocontrol agent (species 2), specifically introduced to control a target (species 1), may increase the risk of a nontarget's (species 3) extinction.
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