POPULATION EXTINCTIONS IN CORRELATED ENVIRONMENTS

For a spatial population assemblage, extinction risk should be greatly affected by features of local population dynamics and interpatch migr ation patterns. In a variable environment, the magnitude of environmen tal correlation between local population patches map have great impact on local dynamics and thereby global extinction risk. We examined the effect of correlated environmental variation on global extinction ris k in a coupled lattice model consisting of local populations governed by density dependent population growth and density independent interpa tch migration. We let each local population experience a stochastic en vironment expressed as a variation in maximum birth rate and let this environmental variation be correlated among local populations. We simu lated global population growth under different magnitudes of environme ntal variability, correlation of environmental variability, emigration rate and migration survival, in order to evaluate the magnitude of th eir effect on local population dynamics and global extinction risk. Th e risk of global extinction increases with increasing magnitude of env ironmental correlation and environmental variability. The major determ inant of global extinction risk is the balance between local populatio n variability and the synchrony in local population fluctuations. A lo w rate of successful interpatch migration connects the local populatio ns to each other, exposing them to less extinction risk than when they are isolated. High levels of interpatch migration are often negative for population persistence. The reason for this is that increased migr ation survival causes an increased risk of population crashes, due to overcompensatory population growth. This effect is amplified by a high emigration rate. Thus, local dynamics are affected by temporal and sp atial variability in birth rates as well as interpatch migration level s. An assemblage of local populations in a variable environment will s uffer least risk of global extinction when environmental correlation i s low and interpatch migration is moderate.