populations expand into new areas. A number of processes can initiate this
process, including disturbance and abiotic environmental change. Localized
extinction results in the elimination of populations from all or part of their
former range and can be caused by biotic interactions or abiotic environmental
change.
Plants have developed a number of different mechanisms for dispersing their
offspring:
■ The use of specialized structures to aid the transport of an individual by
wind ■ The employment of particular structures to transport the
individual by moving water ■ The production of fruit-encased seeds that
other organisms consume and disperse ■ Adhesion mechanisms
■ The physical ejection of seeds
Sites within ecosystems can become devoid of organisms through
disturbances caused by predation, climate variations, earthquakes, volcanoes, or
fires.
Ecological Succession
Succession is the gradual and orderly process of ecosystem development brought
about by changes in community composition and the production of a climax
community. It describes the changes in an ecosystem through time and
disturbance.
■ Facilitation is when one species modifies an environment to the extent
that it meets the needs of another species.
■ Inhibition is when one species modifies the environment to an extent that
it is not suitable for another species.
■ Tolerance is when species are not affected by the presence of other
species.Earlier successional species, frequently called pioneer species, are
generalists. Pioneer plants have short reproductive times (annuals), and pioneer
animals have low biomass and fast reproductive rates. Later successional species
include larger perennial plants and animals with greater biomass, longer
generational times, and higher parental care.