Abstract
One of the main characteristics of ecological systems is their hierarchical organisation – communities are collections of species interacting with each other, species are groups of populations distributed spatially and connected through dispersal, and populations are made up of individuals. Despite the widespread opinion that individual variation is the raw material of ecological and evolutionary dynamics, ecological approaches at the level of communities or ecosystems have tended to ignore the large variation among individuals seen in their morphology, behaviour, or life histories (Bolnick et al., 2003). One of the reasons for this is that there are serious methodological constraints in our ability to identify and track individuals of most animal species within complex communities. Indeed, most communities are made up of relatively small species, which are extremely challenging to mark and equip with sensors. For example, a large part of the world’s mammals weigh less than 100g (see figure 1, Gardezi and da Silva, 1999) and the median body size of birds is around 30-40g (Blackburn and Gaston, 1994). Yet, small animal species contributed a lot to our understanding of ecological and evolutionary processes within natural populations, including population demography, dispersal ecology and evolutionary ecology (e.g. Clobert et al., 2001). They also play an important part in many terrestrial and aquatic ecosystems on Earth, where they include a large number of herbivores, small predators, as well as parasitoids, pollinators and plant mutualists.