Species as indicators of large-scale environmental change: A computer simulation model of population decline

An explicitly spatial computer simulation model of local and regional population dynamics is used to characterize the spatio-temporal patterns of population decline for mobile animal species that exhibit varied degrees of habitat selection and for different landscapes comprised of two habitat types. The model included terms for local, within-habitat processes involving birth and death, and between-patch processes of immigration and emigration. Ten replicate simulations of 108 different factor-level combinations were used to examine relationships between increasing rates of mortality and local patterns of abundance. Results showed that a region-wide decrease in survivorship increased the absolute and relative differences in species abundances among habitats and over landscapes. Declining populations were detected earlier in poorer than in better habitats, in landscapes with proportionately lower amounts of poorer habitats, and for species that actively select habitats than for those that did not. A better understanding of within- and between-habitat patterns of population decline may help decrease uncertainty in regional risk assessments and facilitate the further development of some species as indicators in large-scale environmental monitoring.