Environmental Engineering Reference
In-Depth Information
able, any development within the land matrix between habitat patches that
hinders or impedes species migration could also be devastating to the pop-
ulation.The implication here is that well-intentioned habitat conservation
aimed at protecting local habitat patches on a landscape may still paint a
species into a proverbial corner of the
landscape if a species' movement dy-
namics among habitat patches is not
carefully considered.
Habitat fragmentation and conse-
quent metapopulation process stand
also to alter the fundamental structure
of ecological communities. Within
intact habitats, species that tend to
thrive in high abundances are com-
petitive dominants—those species
that are best able to exploit local re-
sources or preempt other species for
gaining access to resources (Kareiva and Wennergren 1995). However, habi-
tat fragmentation can change the playing field by strongly favoring mobil-
ity at the expense of competitive ability (Nee and May 1992). If we were
to pit species with high competitive ability but low mobility (the compet-
itive species) against species with low competitive ability but high mobil-
ity (the dispersing species) in a hypothetical game-of-life scenario, significant
habitat fragmentation should shift the species dominance from the compet-
itive type to the dispersing type.This is because the competitive species can-
not colonize vacant patches faster than the rate at which it becomes locally
extinct (Nee and May 1992).This is wholly counterintuitive because one
would normally guess that highly successful, abundant species are the ones
least at risk to human disturbance (Kareiva and Wennergren 1995).
An important feature of the popula-
tion dynamics in fragmented habi-
tats is that landscape-scale persist-
ence and maximum size of the
newly created metapopulation
depends not only on the number
and size of habitat patches but
importantly on the ability of individ-
uals to migrate among the local
habitat patches.
Habitat Fragmentation and Extinction Debt
The effects of habitat fragmentation on the species composition of com-
munities may not be immediate when species can be ranked in a competi-
tive hierarchy from strong competitor but weak disperser to weak competitor
but strong disperser. Under these conditions, lags can exist between the time
a habitat is fragmented and the time when a species disappears altogether
from all habitat fragments. In tropical forests, this lag can be between ten
