Ratio-Dependent Predation

Ecology 76:995-1004 (1995)

Ratio-Dependent Predation: An Abstraction That Works

H. Resit Akçakaya
Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, USA

Roger Arditi
Institute of Zoology and Animal Ecology, University of Lausanne, CH-1015 Lausanne, Switzerland, and Institut national agronomique Paris-Grignon, France

Lev R. Ginzburg
Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, USA

Abstract  Recent papers opposing ratio dependence focus on four main criticisms: (i) the empirical evidence we present is insufficient or biased, (ii) ratio-dependent models exhibit pathological behavior, (iii) ratio dependence lacks a logical or mechanistic base, and (iv) more general models incorporate both prey and ratio dependence and there is no need for either of the two simplifications. We review these arguments in the light of empirical evidence from field and experimental studies. We argue that (i) empirical evidence shows that most natural systems are closer to ratio dependence than to prey dependence, (ii) "pathological" dynamics in a mathematical sense is not only realistic, but the lack of such dynamics in prey-dependent models actually makes them pathological in a biological sense, (iii) the mechanistic base of ratio dependence is (direct and indirect) interference and resource-sharing, and (iv) although more general models (with extra parameters) can never fit natural patterns worse than either prey- or ratio-dependent models, there are theoretical, practical, and pedagogical reasons for attempting to find simpler models that can capture the essential dynamics of natural systems.