TEMPORAL AND SPATIAL ASPECTS OF PREDATOR-PREY DYNAMICS

Abstract

Ungulates are both major consumers of vegetation and are themselves consumed by carnivores, so food web dynamics, both top down (predation) and bottom-up (food and weather effects), are prominent in theoretical and applied research involving ungulates. The long generation time of ungulates induces long lags in population responses. Over broad geographic regions, ungulates commonly achieve high density only when predation is relatively low (< 2 species of predator), suggesting that predation provides a pervasive limitation of large herbivores. Ungulate stability is fundamentally a trophic-dynamics issue, usually a mix of top-down and bottom-up influences. The Isle Royale case history, spanning 4 decades, reveals a wolf-moose system fluctuating at 2-decade intervals with significant predation, food, and weather effects on ungulates. After a century, an equilibrium between moose and forest vegetation has not yet been reached, and a historical context seems necessary to understand trophic relationships. Components of predation compared at large spatial scales reveal different predator-prey patterns than the single system at Isle Royale, and analyses involving substitution of space for time also run counter to studies of single systems. Choice of spatial and temporal scales for field studies and meta-analyses appear to have a strong bearing on the results and their interpretation. Thus temporal and spatial scales enter influentially in the actual dynamics of carnivore-ungulate interaction as well problematically in our analyses of them.