A mesoscale approach to extinction risk in fragmented habitats
Authored by R Casagrandi, M Gatto
Date Published: 1999
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Abstract
Assessing the fate of species endangered by habitat framentation(1-3)
using spatially explicit and individual-based models(4-7) can be
cumbersome and requires detailed ecological information that is often
unavailable. Conversely, Levins-like(8) macroscale models(9,10) neglect
data on the distribution of local numbers, which are frequently
collected by field ecologists(11-13). Here we present an alternative, mesoscale approach for metapopulations that are subject to demographic
stochasticity, environmental catastrophes and habitat loss. Starting
from a model that accounts for discrete individuals in each patch and
assumes a birth-death stochastic process with global dispersal(14,15), we use a negative-binomial approximation(16) to derive equations for the
probability of patch occupancy and the mean and variance of abundance in
each occupied patch(17). A simple bifurcation analysis(18) can be run to
assess extinction risk. Comparison with both the original model and a
spatially explicit model with local dispersal proves that our
approximation is very satisfactory. We determine the sensitivity of
metapopulation persistence to patch size, catastrophe frequency and
habitat loss, and show that good dispersers are affected more by habitat
destruction than by environmental disasters.
Tags
models
Dynamics
Dispersal
population