Understanding Species Interactions

Species interactions, categorized by their impact on fitness (+, -, or 0), form the foundation of ecosystems, influencing community structure, biodiversity, and evolutionary trajectories.

Core Principles

Interspecific interactions are relationships between different species within a community.
Competition (-/-) occurs when species compete for limited resources, negatively impacting both.
Consumer-Resource interactions (+/-) involve one species benefiting by feeding on another, which is harmed.
Mutualism (+/+) is a cooperative relationship where both species benefit.
Commensalism (+/0) occurs when one species benefits, and the other is unaffected.

Action Steps

Identify the type of interaction (competition, consumption, mutualism, commensalism) based on the effects on each species' fitness.
Apply shorthand notation (+, -, 0) to denote the outcome of each interaction for the participating organisms.
Analyze how these interactions influence community structure, biodiversity, and evolutionary paths.

Key Terms

Interspecific Competition: Occurs when species compete for a resource in short supply, negatively impacting both.
Competitive Exclusion Principle: States that two species competing for the same limiting resources cannot coexist permanently in the same place.
Ecological Niche: The specific set of biotic and abiotic resources that an organism uses in its environment; its ecological role or 'profession'.
Resource Partitioning: The differentiation of ecological niches, enabling similar species to coexist by utilizing different resources or habitats.
Predation: An interaction where one species (predator) kills and consumes another species (prey).
Herbivory: An interaction where an animal consumes parts of a plant or algae, typically without killing the plant outright.
Parasitism: A relationship where one organism (parasite) derives nourishment from another (host), which is harmed.
Mutualism: An interaction where both species benefit.
Commensalism: An interaction that benefits one species while the other is neither helped nor harmed.

Real World Examples

Two species of Anolis lizards living in close proximity on Hispaniola.: They partition their habitat (canopy, trunks, ground) to minimize competition and coexist.
Galápagos finches on Santa María island.: Beak sizes diverged due to competition, allowing G. fuliginosa (shallower beaks) and G. fortis (deeper beaks) to coexist by specializing on different seed sizes.
A lion hunting and eating a zebra.: This is an example of predation, where the predator benefits and the prey is harmed.
A caterpillar eating the leaves of a plant.: This is an example of herbivory, where the herbivore benefits and the plant is harmed.
Mycorrhizal fungi and plant roots.: A mutualistic relationship where fungi help plants absorb nutrients, and plants provide fungi with sugars.
Cattle egrets and grazing cattle.: Commensalism, where egrets benefit from insects flushed out by cattle, and cattle are unaffected.