Interdependence Links Species

1. Interdependence is the way organisms in a community depend on other species for resources or services needed for survival and reproduction.
2. Food relationships create dependence because consumers need their food organisms, while predators depend on enough prey being available.
3. Shelter relationships create dependence when one species uses another as a place to live, nest or hide from predators.
4. Pollination depends on animals transferring pollen between flowers, which allows many flowering plants to reproduce.
5. Seed dispersal depends on animals carrying seeds away from the parent plant, which can reduce competition between the parent and seedlings.

One Change Can Affect Many Species

1. A fall in one population affects every species that feeds on it, shelters in it, pollinates it or disperses its seeds.
2. Food-web effects spread: fewer flowering plants can mean less nectar for insects, fewer insects can mean less food for insect-eating birds, and bird populations may then fall.
3. An increase can also spread: more prey may support more predators, which can later increase the rate at which the prey is eaten.
4. The effect depends on alternatives: a consumer with several food sources may be less affected than a specialist that relies on one species.

Interdependence Affects Community Stability

1. A stable community has population sizes that remain within a limited range because interactions and environmental conditions are balanced over time.
2. Stability does not mean no change: births, deaths, predation and seasonal changes continue, but populations do not rise or fall without limit.
3. Removing one species can disturb this balance and cause increases or decreases in several other populations.