A community may also be defined according to the classification of and the geographic
distribution of species, as in an oak-hickory forest. On the other hand, a community might
be defined according to function and behavior, as in a forest that is moderate in temperature
(temperate) and sheds leaves annually (deciduous).
Community Interactions
Community interactions can be either intraspecific, that is between members of the same
species, or interspecific, between members of different species. There are a number of dif-
ferent types of interactions, such as competition, predation, and symbiosis, which can be
described as beneficial, detrimental or neutral. For example, competition could be looked
at as having negative effects on the competing individuals or species, whereas mutualism, a
type of symbiosis, could be determined as positive for individuals involved.
As we examine different types of interactions in the next few sections, we will see more
specifically why interactions are considered positive, negative, or neutral. We usually look
at costs and benefits in terms of fitness, or survival and reproduction. These types of
interactions may alter populations, communities, and even ecosystems, and the evolution of
interacting species.
Competition
Competitioncan be defined as an interaction between organisms of the same or different
species, in which the “fitness” of one is lowered by the presence of another. Individuals
compete for a limited supply of at least one resource, such as food, water, or territory.
Fitness refers to the ability of a species to survive and reproduce.
Competition can be described in terms of the mechanisms by which it occurs, either directly
orindirectly. Forexample,competitionmayoccurdirectlybetweenindividualsviaaggression
or some other means, whereby individuals interfere with survival, foraging or reproduction,
orbyphysicallypreventingthemfromoccupyinganareaofthehabitat. Indirectcompetition
is when a common limiting resource which acts as an intermediate. For example, use of a
specific resource or resources decreases the amount available to others, thereby affecting the
others’ fitness, or competition for space results in negatively affecting the fitness of one of
the competing individuals.
Another type of indirect competition also occurs when two species are both preyed upon
by the same predator. If the population size of one species increases, this would cause
the predator population to increase, and would result in the other species’ population size
decreasing.
Intraspecific competitionoccurs when members of the same species compete for the same
resources, like food, nutrients, space, or light. Two organisms competing for the same re-