source can adapt to such conditions. Thus, if two trees growing close together are competing
for light, water, and nutrients, one may out-compete the other by growing taller to get more
available light or be developing a larger root system to get more water and nutrients. Such
a situation results in survival for the organism that has better adapted to that environment.
Interspecific competition occurs when individuals of different species share a limiting
resource in the same area, resulting in one of the species having lowered reproductive success,
growth, or survival. For example, cheetahs and lions feed on similar prey. If prey is limited,
then one species may catch more prey than the other and force the other species to either
leave the area or to directly affect its survival. Lions sometimes steal prey killed by cheetahs.
This could negatively affect the survival of the cheetahs.
According to the competitive exclusion principle, species less suited to compete for
resources will either adapt, be excluded from the area, or die out. This is similar to what
happens within a species. Evolutionary theory says that competition for resources within
and between species plays an important role in natural selection (Table(23.4)).
In order for two species within the same area to adapt, they may develop different special-
izations in order to coexist. This is known ascharacter displacementand an example of
this is the different feeding adaptations, such as bill structure, that developed in Darwin’s
Finches (Figure23.11).
Figure23.11: Anexampleofcharacterdisplacement, showingdifferentbillstructures, reflect-
ing different feeding strategies, in Darwin’s or Galapagos Finches. From Darwin’s Journal,
1845, during the voyage of the H.M.S. Beagle. ( 17 )