Speed of exploration and risk-taking behavior are linked to corticosterone titres in zebra finches

The existence of consistent individual differences in behavioral strategies ("personalities" or coping styles) has been reported in several animal species. Recent work in great tits has shown that such traits are heritable and exhibit significant genetic variation. Free-living birds respond to environmental stresses by up-regulating corticosterone production. Behavior during mild stress can occur in accordance to two types of coping styles, i.e. active and passive. Using artificially selected lines of zebra finches that vary in the amount of corticosterone produced in response to a manual restraint stressor we ran three "personality" experiments. We show that birds in the different corticosterone lines differ in their exploratory and risk-taking behaviors. There was an increase in exploratory behavior as corticosterone titre increased but only in the low corticosterone line. Birds in high corticosterone line showed greater risk-taking behavior than birds in the other lines. Thus, in general, higher levels of circulating corticosterone following a mild stress result in greater exploratory behavior and greater risk taking. This study shows that lines of animals selected for endocrine hormonal responses differ in their "coping" styles or "personalities". © 2007 Elsevier Inc. All rights reserved.Link_to_subscribed_fulltex

Size constraints in a real food web: predator, parasite and prey body-size relationships.

In the absence of well-resolved food webs that include both information on predators and parasites, body-size has been proposed as the biological mechanism underlying the assumption of a trophic hierarchy in the cascade model and its variants. We show that parasites consume prey larger than themselves, and therefore the logical conclusion is that the trophic hierarchy cannot be justified on the basis of body-size when food webs include parasites. Two other assumptions central to the cascade model and its variants, the link-species scaling law and the probability of predation, are not supported by the empirical data presented here. We show that linkage density is scale-dependent rather than independent, but that the relationship between linkage density and web size is far from clear. Specifically, the webs that exclude parasites examined here, overestimate the values of linkage density and connectance by more than one order of magnitude. There is little evidence for a relationship between predator generalisation (the number of prey exploited by a predator), prey vulnerability (the number of predators exploiting a prey) and trophic position within each web, when trophic position corresponds to an ordering by size. Therefore the probability of predation neither remains constant as assumed under the original cascade model, nor increases with trophic position (increasing body-size) as assumed under some of its variants. The present study however, does show some support for the notion that the cascade model's assumption of constant predation probability should be replaced by heterogeneous predation probabilities. We also examined the relationship between the morphological niche of consumers, a metric where resources falling within a defined size are always taken, and a parameter that may be closely linked to the connectance of whole food webs, but rarely examined in empirical webs. Although we could find no evidence for trends in morphological niche with trophic position, further investigation of the consequences of individual or species-level feeding constraints on the connectance of webs may repay further investigation. We contend that the organisms often most neglected in food web studies e.g. parasites and pathogens, must be included in food webs if we are able to make more realistic descriptions of the trophic structure of natural communities, and to develop mechanistic explanations for the structure of natural food web