Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
Department of Biology, University of Auckland, Auckland, New Zealand.
J Anim Ecol. 2020 Jul;89(7):1581-1592. doi: 10.1111/1365-2656.13214. Epub 2020 May 18.
Allee effects occur when individual or population survival decreases due to populations being small or sparse. A key mechanism underlying Allee effects is difficulty in finding mates at low densities. Species may be particularly vulnerable to mate-finding Allee effects if females rely on an abundance of males to reproduce successfully. In sexually cannibalistic species, females may consume males before or after copulation, potentially reducing the supply of males to the point where a mate-finding Allee effect occurs. In this study, we investigate the extent to which sexual cannibalism can modulate mate-finding Allee effects, and the conditions under which sexual cannibalism is likely to be particularly detrimental to population viability. We created an individual-based model that tracked specific females throughout the breeding season and used extinction risk and per capita growth rate to measure the strength of the Allee effects. We varied both founder population size and mate encounter rate independently of each other to expose the mechanism driving the Allee effects. We also analysed how cannibalism-derived female fecundity benefits affected extinction risk. We found that sexual cannibalism could lead to high extinction risk, particularly when cannibalism occurred before copulation, founder population size was small and mate encounter rates were low. However, post-copulatory cannibalism reduced extinction risk, if cannibalism increased female fecundity enough. We found that there were strong threshold effects, in which small changes in encounter rate could strongly alter population extinction risk. We find that sexual cannibalism is likely to negatively impact population survival as population size and mate encounter rate decrease. This may be exacerbated if male quality declines and female hunger increases in declining populations. As many top invertebrate predators, such as spiders and mantises, are sexually cannibalistic, this may have ecosystem-wide impacts. We also suggest that other reproductive behaviours, such as rejecting all but high-quality mates or requiring multiple mates to ensure fertility, are also likely to cause mate-finding Allee effects when habitat quality degrades.
当个体或种群由于数量较少或稀疏而导致生存能力下降时，就会出现阿利效应。阿利效应的一个关键机制是在低密度下寻找配偶的困难。如果雌性依赖大量雄性来成功繁殖，那么物种可能特别容易受到寻找配偶的阿利效应的影响。在有性食同类的物种中，雌性可能在交配前或交配后吃掉雄性，从而潜在地减少雄性的供应，以至于出现寻找配偶的阿利效应。在这项研究中，我们研究了性食同类行为在多大程度上可以调节寻找配偶的阿利效应，以及性食同类行为在哪些情况下可能特别不利于种群生存。我们创建了一个基于个体的模型，该模型可以在整个繁殖季节跟踪特定的雌性，并使用灭绝风险和人均增长率来衡量阿利效应的强度。我们独立地改变了创始种群大小和配偶相遇率，以揭示驱动阿利效应的机制。我们还分析了食同类行为导致的雌性繁殖力收益如何影响灭绝风险。我们发现，性食同类行为可能导致高灭绝风险，尤其是在交配前发生食同类行为、创始种群较小且配偶相遇率较低的情况下。然而，如果食同类行为足以增加雌性的繁殖力，那么交配后的食同类行为会降低灭绝风险。我们发现存在强烈的阈值效应，即相遇率的微小变化可能会强烈改变种群的灭绝风险。我们发现，随着种群大小和配偶相遇率的下降，性食同类行为可能会对种群的生存产生负面影响。如果在下降的种群中雄性质量下降和雌性饥饿增加，情况可能会更糟。由于许多顶级无脊椎捕食者，如蜘蛛和螳螂，都是有性食同类的，这可能会对整个生态系统产生影响。我们还建议，当栖息地质量下降时，其他生殖行为，如拒绝所有低质量的配偶或需要多个配偶来确保生育能力，也可能导致寻找配偶的阿利效应。
