Ch 17: Biological Communities

17.1 – How Organisms Interact in Communities

  1. Evolution in Communities

A. Species within a community have adjusted to one another over time so that they may

interact; coevolution is what we call these back-and-forth evolutionary adjustments

between interacting members of a community

Ex) flowering plants evolved ways to promote the dispersal of their pollen, and the

pollinators (insects and animals that spread the pollen) evolved to be able to more

easily obtain the pollen (i.e the long pointed beak of a humming bird)

B. Predators and prey coevolve: prey evolve ways to escape being eaten and predators

evolve ways to overcome the defenses of their prey

1. predation – the act of one organism killing another for food

2. parasitism – one organism feeds on an usually lives on or in another larger

organism

3. secondary compounds – defensive chemicals found in plants that keep them from

becoming prey to herbivores

  1. Symbiotic Relationships

A. Symbiosis – when two or more species live together in a close, long-term association

which can be beneficial to both organisms or benefit only one and harm or not affect

the other

1. parasitism is a symbiotic relationship that benefits the parasite but is harmful to the

host

2. mutualism is a symbiotic relationship in which both species benefit

3. commensalism is a symbiotic relationship in which one species benefits and the

other is not affected