Data from: A game-theoretical model of kleptoparasitic behaviour in an urban gull (Laridae) population.

Kleptoparasitism (food stealing) is a significant behaviour for animals that forage in social groups as it permits some individuals to obtain resources whilst avoiding the costs of searching for their own food. Evolutionary game theory has been used to model kleptoparasitism, with a series of differential equation based compartmental models providing significant theoretical insights into behaviour in kleptoparasitic populations. In this paper we apply this compartmental modelling approach to kleptoparasitic behaviour in a real foraging population of urban gulls (Laridae). Field data was collected on kleptoparasitism and a model developed that incorporated the same kleptoparasitic and defensive strategies available to the study population. Two analyses were conducted: 1. An assessment of whether the density of each behaviour in the population was at an equilibrium. 2. An investigation of whether individual foragers were using Evolutionarily Stable Strategies (ESS) in the correct environmental conditions. The results showed the density of different behaviours in the population could be at an equilibrium at plausible values for handling time and fight duration. Individual foragers used aggressive kleptoparasitic strategies effectively in the correct environmental conditions but some individuals in those same conditions failed to defend food items. This was attributed to the population being composed of three species that differed in competitive ability. These competitive differences influenced the strategies that individuals were able to use. Rather than gulls making poor behavioural decisions these results suggest a more complex three-species model is required to describe the behaviour of this population.

盗寄生（Kleptoparasitism，即食物偷窃行为）对于结群觅食的动物而言是一类至关重要的行为，因其可使部分个体在规避自行搜寻食物所需成本的同时获取生存资源。进化博弈论（Evolutionary Game Theory）已被应用于盗寄生行为的建模研究，一系列基于微分方程的分室模型（compartmental models）为盗寄生种群的行为机制提供了重要的理论洞察。本研究将该分室建模方法应用于真实的城市鸥类（Laridae）觅食种群的盗寄生行为研究中。研究人员收集了该种群的盗寄生行为野外数据，并构建了贴合该研究种群可用盗寄生与防御策略的数学模型。本研究开展了两项分析：其一，评估种群中各类行为的密度是否处于均衡状态；其二，探究个体觅食者在适宜环境条件下是否采用了进化稳定策略（Evolutionarily Stable Strategies，ESS）。研究结果表明，在处理时长与打斗时长的合理参数取值下，种群内不同行为的密度可达到均衡状态。个体觅食者在适宜环境条件下能够有效运用攻击性盗寄生策略，但在相同环境中仍有部分个体无法成功防御食物资源。该现象被归因于研究种群由三个竞争能力存在差异的物种构成，此类竞争能力差异影响了个体所能采用的行为策略。研究结果显示，并非鸥类做出了欠佳的行为决策，而是需要构建更为复杂的三物种种群模型，方能准确描述该种群的行为特征。