170 pages, b/w illustrations
Understanding the functioning of ecosystems requires the understanding of the interactions between consumer species and their resources. How do these interactions affect the variations of population abundances? How do population abundances determine the impact of predators on their prey? The view defended in this book is that the "null model" that most ecologists tend to use (derived from the Lotka-Volterra equations) is inappropriate because it assumes that the amount of prey consumed by each predator is insensitive to the number of conspecifics.
In this book, the authors argue that the amount of prey available per predator (rather than the absolute abundance of prey) is the basic determinant of the dynamics of predation. This so-called ratio dependence is shown to be a much more reasonable "null model". Lessons can be drawn from a similar debate that took place in microbiology in the 1950's. Currently, populations of bacteria are known to follow the analogue of ratio dependence when growing in real-life conditions. Three kinds of arguments are developed.
First, it is shown that available direct measurements of prey consumption are "in the middle" but most are close to ratio dependence and all are clearly away from the usual Lotka-Volterra relationship; an example is the system of wolves and moose on Isle Royale.
Second, indirect evidence is based on the responses of food chains to nutrient enrichment: all empirical observations at the community level agree very well with the ratio-dependent view.
Third, mechanistic approaches explain how ratio dependence emerges at the global scale, even when assuming Lotka-Volterra interactions at the local scale; this is illustrated by microcosm experiments, by individual-based models and by mathematical models.
Changing the fundamental paradigm of the predator-prey interaction has far-reaching consequences, ranging from the logical consistency of theoretical ecology to practical questions of eco-manipulation, biological control, conservation ecology.
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Roger Arditi is a "professor of exceptional class" in Paris, France. He works for INRA, the French National Institute for Agronomic Research, in the research unit of Ecology and Evolution at University Pierre et Marie Curie in Paris. He has published both in theoretical and applied areas of population and community ecology, authoring more than 100 scientific publications. His theoretical and experimental work on trophic interactions is focused on a reappraisal of the foundations of the dynamics of predation.
Lev Ginzburg has been a professor of ecology and evolution at Stony Brook University since 1977. He has published widely on theoretical and applied ecology, population genetics, and risk analysis, and has authored or edited eight books and more than 100 scientific papers. His research in population inertia and interactions in food chains has sparked a controversial revision of the fundamental equations used in ecological theories.