Modelling state‐dependent interference in common cranes

Abstract

Summary 1.Interference is a key component of food competition, but is difficult to measure in natural animal populations. Using data from a long-term study, we show that interference between common cranes Grus grus L., feeding on patches of cereal seeds, reduces intake rates at high competitor densities, and that the strength of interference is unrelated to food abundance.2. An alternative to measuring interference directly is to predict its strength using behaviour-based models. We test an interference model, originally developed for shorebirds feeding on invertebrate prey, for cranes. We compare the predictions of a rate-maximizing model, in which animals steal food if this increases intake rate, and a state-dependent model, in which they only rate-maximize if their intake rate is below a target value, otherwise they minimize injury risk by not stealing food. State-dependent aggression occurs in cranes. 3. The state-dependent model predicts more accurately the relative aggression rates of cranes of different dominance. However, both models predict accurately the observed strength of interference, that the strength of interference is unrelated to food abundance, at least within the observed range of crane and seed densities, and that cranes of a higher dominance have a higher intake rate than those of lower dominance. 4. This paper shows how state-dependent behaviour can be incorporated into an interference model, and that the model can produce accurate predictions for a system quite different to that for which it was developed.

The behavioral mechanism of competition for food between tilapia ( Oreochromis hybrid) and crayfish ( Cherax quadricarinatus )

“…Apparently, interspecific competition in the bottom patch did not affect individual fish diferentially, by changing their relative competitive ability and aggression, thus the interspecific effect on fish could be revealed at the group level. The lack of crayfish influence on fish aggression does not conform the prediction of individual-based models that aggressiveness should increase with competitors density (Stillman et al, 1997(Stillman et al, , 2002Sirot, 2000). It also does not correspond with studies on competition between fish species that did show interspecific effects on dominance relations within groups, including differential effects on behavioral strategies (Blanchet et al, 2007;Harwood et al, 2002) as well as on brain gene transcription patterns of dominant and subordinate individuals (Roberge et al, 2008).…”

Social effects on foraging behavior and success depend on local environmental conditions

“…Similarly, Stillman et al. () found that in common cranes ( Grus grus ) high‐ranking individuals only engaged in aggressive behavior in environments where their intake fell below a certain threshold. Fewer studies have investigated the environment‐dependent effects of social bonds and kinship on foraging behavior.…”

Distribution Patterns Predict Individual Specialization in the Diet of Dolphin Gulls

“…However, individuals in many species also show differences in diet preference independent of age or sex (e.g. [4], [5]). Two recent reviews [1], [6] suggested that individual specialization is a widespread but under-appreciated phenomenon.…”