Food limitation and complex dynamics in herbivorous insects.
Abbott, Karen*,1, Dwyer, Greg1, 1 University of Chicago, Chicago, IL, USA
ABSTRACT- Population outbreaks are common in herbivorous insects, but in most cases, we cannot identify the factor driving these dynamics. Popular hypotheses are that herbivore outbreaks are caused by temporary escape from natural enemies or by inducible responses in the host plant. While these processes are undoubtedly important in many systems, intraspecific competition for food amongst herbivores occurs simultaneously. Traditional consumer-resource theory (predator-prey and host-parasitoid models) is based on biological assumptions which are unsuitable for plant-herbivore systems. As a result, the expected dynamics of food-limited herbivores remain largely unknown. To understand the effects of food limitation on herbivore populations and to determine whether food limitation alone can drive realistic population dynamics in herbivores, I consider a series of simple and general difference equation models which relate the abundance of a host-plant to the abundance of its herbivore. The models show that complex dynamics, such as outbreaks, can be accurately predicted by changes in plant abundance alone. This novel result demonstrates that neither inducible defenses nor higher trophic levels, such as predators, parasitoids, or pathogens, need be present for herbivore outbreaks to occur.
Key words: plant-herbivore model, difference equation model, insect outbreak, population dynamics
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