Positive Interspecific Interactions

Abstract

Cooperative relationships between species have been recognized for centuries but, until recently, their acceptance as important forces in community ecology has lagged behind that of antagonistic interactions. Interspecific positive interactions are defined as relationships between different species that result in better growth, reproduction and/or survival for at least one species involved in the interaction without negatively affecting the other species. They may be trophic or nontrophic and act directly or indirectly (through a third species). Positive interactions are not static but vary in their strength and symmetry depending on the context under which they occur. They can act to promote species coexistence especially under harsh physical or biological stress and thus are important to species diversity, species invasions and the conservation and management of highly impacted systems.

Key concepts:

  • Recent attention to the cooperative relationships among species shows that they are important forces in shaping community structure.

  • Positive interspecific interactions are defined as cooperative relationships between different species that result in better growth, reproduction and/or survival for at least one species involved in the interaction without negatively affecting the other species.

  • Positive interactions can be trophic and nontrophic, can act directly or indirectly (mediated by a third species) and can be symmetric (species have equal effects) or asymmetric (species have unequal effects).

  • Positive species interactions are not static but vary in their outcome depending on the context under which they occur.

  • Theory and experiments show that positive interactions are more likely to occur under stressful physical or biological contexts.

  • Studies demonstrate that succession in any community is driven by a complex array of species interactions but that positive interactions are important forces especially early when physical and biological conditions may be harsh.

  • Positive interactions should promote species coexistence and thus increase species diversity.

  • Species invasions are facilitated by other species although positive feedbacks between multiple non‚Äźnative species have rarely been shown.

  • Restoration of degraded communities can involve reintroducing dominant species that promote the colonization and maintenance of rare species by providing basic habitat and/or favourable physical modifications to the environment.

Keywords: mutualism; commensalism; context dependence; succession; species diversity

Figure 1.

Two hypothetical mutualistic interactions between plants and pollinators that vary in their costs and benefits and thus their net positive effects on one another. (a) The plant B and pollinator A have equivalent costs (left arrow) and benefits (right arrow) and thus show a net symmetrical interaction. (b) The two species have unequal costs and benefits and thus show a net asymmetrical interaction.

Figure 2.

Four interaction webs that display positive indirect effects. Keystone effect occurs when a predator (P) eats a victim (V) resulting in an indirect positive effect (dashed arrow) for the victim's competitor (C). Trophic facilitation occurs when a facilitator (F) positively affects a victim (V) resulting in an indirect positive effect (dashed arrow) for the victim's predator (P). Indirect facilitation occurs when predators (P) mediate the competitive interaction between their victims (V) thus having an indirect positive effect (dashed arrow) on one another. Competitive network is a circular set of interactions between competitors (C) in which positive indirect effects (dashed arrow) emerge.

Figure 3.

The intermediate disturbance hypothesis modified to include positive interactions. The traditional model describes the unimodel relationship between species diversity and increasing predation, physical disturbance and physical stress considering competitive interactions only (solid line curve), whereas the modified version includes positive interactions as well (dashed line curve). Reproduced with permission from Hacker and Gaines .

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Hacker, Sally D(Dec 2009) Positive Interspecific Interactions. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021901]