GEOGRAPHICAL SYNCHRONY IN MICROTINE POPULATION-CYCLES - A THEORETICAL EVALUATION OF THE ROLE OF NOMADIC AVIAN PREDATORS

Predation by nomadic predators, capable of rapidly tracking the local prey densities, may have a synchronizing effect, but the model requires no additional mechanism than predation (eg behavioural response of prey to predation) to produce synchronous prey cycles. In addition to the synchronizing effect, heavy predation pressure by nomadic predators is expected to shorten the period and dampen the amplitude of the prey cycles. Non-migrating predators having impact on their prey year round have a stronger synchronizing effect than migrating predators absent during the winter. Geographic regions with few non-migration predators are predicted to be less likely to have synchronized microtine populations than regions with many such predators, and highly synchronized microtine populations have cycles with smaller amplitudes and shorter periods than microtine populations in geographic regions where local populations are not synchronized. -from Authors