Including the life cycle in food webs

• Introduction: To grow and reproduce is fundamental for living organisms. In essence all organisms go through a life cycle with ontogenetically driven changes in their physiological rates and trophic interactions (Figure 9.1; Box 9.1). This ontogenetic development occurs even in unicellular organisms but is more striking in other groups. For example: dragonflies undergo metamorphoses that span several habitats, Atlantic marlin increase up to 500 times their length, and the cod-worm has different host requirements for each life-history stage. All of these ontogenetic changes correspond to large shifts in the ecological role of an individual. In spite of the drastic changes many individuals undergo over their life history, classical ecological theory typically assumes that all individuals within a population are identical. As a consequence, a large part of our ecological understanding relies on this assumption. This is surprising considering that ecological theory strongly links to evolution, which is critically dependent on variation among individuals. Acknowledging ecological variation of individuals within the species is relatively recent to food-web ecology. While individual variation can arise from genetic or stochastic processes, this chapter focuses on individual variation that relates to ontogenetic development. Biological interactions that are susceptible to ontogenetic variation include: resource use, vulnerability to predators and parasites, mutualistic interactions, cannibalism, and commensalism. Therefore the consideration of ontogeny has major implications for the way we consider food-web topology (Box 9.2). In a broader sense, the function of an organism, such as the nutrient fluxes it contributes to and the ecosystem services it takes part in, may also change over ontogeny. By ignoring the individual life history, ecologists focus on interactions between populations rather than between individuals, an abstraction that may be biologically inaccurate. In fact, differences between individuals within species can exceed, and have larger effects on food-web dynamics, than differences between individuals of different species. This suggests that the consideration of differences between life stages within populations is essential for our understanding of food-web structure and ecosystem functioning.

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NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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