Chapter 14 Summary
CONCEPT 14.1 Positive interactions occur when neither species is harmed and the benefits of the interaction are greater than the costs for at least one species.
- Mutualism and commensalism are ubiquitous interactions that are important in both terrestrial and aquatic communities.
- Mutualism and commensalism can evolve from other kinds of interactions in many ways.
- Mutualism may or may not be species-specific, obligate, and coevolved. Commensalism is always facultative for the species that does not benefit and is not coevolved.
- Positive interactions cease to be beneficial under some circumstances because the costs and benefits of an interaction may vary from one place and time to another.
- Positive interactions may be more common in stressful environments.
CONCEPT 14.2 Each partner in a mutualism acts to serve its own ecological and evolutionary interests.
- Mutualisms can be categorized by whether one partner provides the other with food (a trophic mutualism), a place to live (a habitat mutualism), or an ecological service (a service mutualism).
- The partners in a mutualism are in it for themselves—it is not an altruistic interaction.
- Some mutualists have mechanisms to prevent overexploitation by cheaters.
CONCEPT 14.3 Positive interactions affect the distributions and abundances of organisms as well as the composition of ecological communities.
- Positive interactions can provide benefits that increase the growth, survival, or reproduction of one or both of the interacting species.
- As a result of such demographic effects, positive interactions can determine the distributions and abundances of populations of the interacting species.
- Positive interactions can also affect interactions among organisms and hence the composition of ecological communities and the properties of the ecosystems of which those communities are a part.
