Begging Scrambles with Unequal Chicks: Interactions between Need and Competitive Ability
Parker, G. A., Royle, N. J., and Hartley, I. R. (2002) Begging scrambles with unequal chicks: interactions between need and competitive ability. Ecol. Let. 5: 206-215.
Parker et al. 2002a.pdf
MEMO
スクランブル競争においても、これまでの信号理論と同様の予測が成り立つ。すなわち、コストがあるために信号は正直になり、親は信号の強さに応じて食物を分配する。
違いは、beggingのエスカレーションが起こるかどうかという点。competitive asymmetryがない、としている点（ただし、Johnstone 2004ではこれがあると思う）。
違いは、beggingのエスカレーションが起こるかどうかという点。competitive asymmetryがない、としている点（ただし、Johnstone 2004ではこれがあると思う）。
Cited by
- Kolliker & Richner 2004
- 1) Under scramble competition, siblings compete for parental resources and parents passively distribute the resources following the outcome of competition (Parker et al. 2002, Parker et al. 2002b). 2) Theoretical models have shown that scrambling can be, ..., one possible mechanism underlying the resolution of the parent-offspring conflict and the evolution of conspicuous begging displays (Parker et al. 2002).
- Royle et al. 2004
- 1). 2) Under both active and passive feeding mechanisms begging is 'honest' in that any escalation in solicitation by offspring is balanced by costs to the offspring (Parker et al. 2002). 3). 4) control of food allocation is likely to be a dynamic process (Royle et al. 2002), and despite the difficulties outlined above there are notable differences in predictions between the different modelling approaches. In particular, scramble models predict that competitive asymmetries between offspring will primarily determine the outcome, whilst signalling models predict the outcome will be primarily determined by relative need (Parker et al. 2002). 5). One of the fundamental differences between scramble models and honest signalling models for parent-offspring communication is that, whereas in scramble models begging strategies are determined by escalated competition among brood members (MacNair & Parker 1979, Parker et al. 2002), this does not happen under honest signalling. 6). 7) Honest signalling models (i.e. active food allocation and parental control) do not predict that competitive asymmetries between chicks dominate food gains, as found in their study, as food is predicted to be allocated primarily according to need, discounting differences in competitive ability (Parker et al. 2002). In contrast, in scramble models competitive asymmetries modify the overall begging stimulus that each chick presents, so that begging does not necessarily relate directly to need (Parker et al. 2002).
- Smiseth et al. 2003a
- 1) The finding that begging reflects need has been interpreted as support for honest-signaling models, which assume that food allocation is under parental control (Godfray 1991, Godfray 1995a). However, scramble competition models, assuming that food allocation is under offspring control, make the same prediction (Parker et al. 2002, Rodriguez-Girones et al. 2001a). Thus, although the two types of models differ fundamentally in the assumptions they make about who controls food allocation, they are indistinguishable in light of current evidence (Parker et al. 2002, Royle et al. 2002). 2) Theoretical considerations suggest that only scramble competition models can be extended to situations in which food is limited and nestlings differ in competitive ability (Parker et al. 2002, Royle et al. 2002).
- Royle et al. 2002
- 1) recent models of sibling scramble competition (Rodriguez-Girones et al. 2001a, Parker et al. 2002), which show that the primary predictions generated by honest-signalling models and scramble models are not mutually exclusive. 2). 3). 4). 5). 6). 7).
Abstract
When offspring compete for the attentions of provisioning parents, empirical and theoretical work has generally concluded that chicks honestly signal their "need " for resources and that parents control allocation. Here, we develop models to show that when allocation of food resources is determined by competitive begging scrambles between sibs, the offspring's ESS begging levels, shares of food and personal fitness gained will be determined by an interaction between their competitive abilities and their true needs. Many of the predictions of this scramble competition model are qualitatively very similar to models of honest signalling of need, where parents, not offspring, control the allocation of food. Consequently it will be difficult to distinguish between the two mechanisms of food allocation based on empirical observations of the responsed of chicks to feeding by parents.
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