Visualizing Environmental Science

114 CHAPTER 5 How Ecosystems Work

and many other locations. Where they became estab-

lished, brown anoles drove green anoles out from all but

wetlands and tree crowns, so the green anoles’ realized

niche—the areas where it could survive—became smaller

(Figure 5.15c and d). Natural communities consist of

numerous species, and the interactions among species

produce the realized niche of each.

When two species are similar—as are green and

brown anoles—their ecological niches may appear to

overlap. However, many ecologists think no two species

indefinitely occupy the same niche in the same com-

munity. Resource partitioning is one way some species

avoid or at least reduce niche overlap. Resource par-

titioning is the reduction in competition for environ-

mental resources such as food among coexisting species

as a result of the niche of each species differing from

the niches of others in one or more ways. Evidence of

An example helps illustrate the difference between

fundamental and realized niches. The green anole, a

lizard native to Florida and other southeastern states,

perches on trees, shrubs, walls, or fences during the day

and waits for insect and spider prey (Figure 5.15a). In

the past, these little lizards were widespread in Florida.

Several years ago, a related species, the brown anole, was

introduced from Cuba into southern Florida and quickly be-

came common (Figure 5.15b). Suddenly the green anoles

became rare, apparently driven out of their habitat by com-

petition from the slightly larger brown anoles. Careful in-

vestigation revealed that green anoles were still present but

were now confined largely to the wetland vegetation and to

the leafy crowns of trees, where they were less obvious.

The habitat portion of the green anole’s fundamental

niche includes all of the places where it originally lived in

Florida: trunks and crowns of trees, exterior house walls,

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Green anole Brown anole

Overlap

Green anole Brown anole

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c. The fundamental niches of the two lizards initially overlapped.

b. The brown anole was introduced in Florida.

d. The brown anole out-competed the green anole, restricting

its realized niche.

a. The green anole is native to Florida.