Ecosystem, community, and population ecology 91predators; the moth species adapted over generations and became darker and
less visible. In contrast,acclimation(or acclimatization) is an adjustment of a
single individual to gradually changing conditions. Also an animal may become
habituatedor accustomed to a continuous or frequent human activity so that the
animal is no longer disturbed by the activity.
Several other types of species are especially important in urban regions.Rare
specieshave small populations, and are inherently in jeopardy near urbaniza-
tion. Conservation biologists recognize different types of native rare species,
some decreasing and some stable in population size.Non-native species(sometimes
calledexotic,introduced, alien, or non-indigenous species) originated elsewhere.
Residential areas are major centers of non-native species for the urban-region
ring.Invasive speciesare non-natives that successfully colonize and reproduce in
anatural community.Naturalized speciesare effectively former invasives which
have become well integrated into, rather than unnaturally dominant in, native
food webs and ecosystems (Sorrie 2005, Muehlenbach 1979).Interior specieslive in
alarge patch only or mainly distant from its boundary. In contrast,edge species
are only or mainly near the boundary of a patch of any size.Specialist specieshave
anarrow genetic tolerance and are typically limited to a specific type of habitat.
Generalist species,onthe other hand, have a wide genetic tolerance and thrive in
avariety of habitats and edge conditions.Keystonespecieshave an influence on
thenatural community far in excess of their biomass or abundance, and may be
of major importance for land-use planning (Figures4.1and4.2). Finally,species of
conservation importanceis a general concept mostly referring to rare species or key-
stone species recognized to be of particular ecological or societal value in an area.
An organism increases growth rate as resources increase, typically growing
until a limiting resource is no longer sufficient to permit further growth (Smith
1996,Ricklefs and Miller2000,Townsendet al.2000).Competitionforlimiting
resources benefits one species and inhibits the other. Environmental conditions,
such as pH and temperature, influence an organism’s use of resources, but are
not depleted by the process.Diffuse competitionwhere a species competes with
many species for many resources, each resource being a small portion of the
total used, is widespread.Species coexistencein nature is also the norm, and largely
results from: environmental heterogeneity, such as hiding places and varied-size
food patches; the use of many rather than one resource; having different food
preferences; and switching diets as food availability fluctuates.
Unlike competition between species at one trophic level, predators and prey
represent two levels in the food chain (Morin1999).Predators(including top
predators) are animals that consume other organisms, whilepreyare organisms
consumed by a predator. When prey density changes, the predator changes its
rate of food consumption.Predator--prey cyclesillustrate anegative feedback system,