Data from: Compensatory life history responses of a mesopredator may undermine carnivore management efforts

Lethal carnivore management, aimed at reducing carnivore impacts, is a global phenomenon threatening the persistence of many carnivores. Black-backed jackals Canis mesomelas, the dominant cause of livestock predation in southern Africa, are widely hunted to reduce livestock predation. Despite centuries of lethal management, jackals persist. Smaller canids, like jackals, are highly adaptable and display variable responses to mortality sources, which may affect management outcomes. The effects of killing carnivores will depend on their behaviour, social organization, reproduction and dispersal patterns. We predicted that hunted jackals will alter demographic and reproductive patterns to compensate for increased mortality. Here, we collected demographic and reproductive information from harvested jackals and compared it between continually hunted (farms) and unmanaged populations (reserves). The removal of jackals from farms results in a decrease in median age from 5–6 years (reserves) to 2–3 years (farms). Hunting also changed the age structure of jackal populations from a stable population to an expanding population. This may be ascribed to the compensatory immigration of individuals from neighbouring unmanaged areas, suggesting the formation of a source–sink system. Unmanaged areas may act as source populations exporting young, dispersing individuals to hunted areas which may act as sinks. This is likely driven by disruptions in the normal, mutually exclusive territorial system resulting in low densities of conspecifics on farms. The low density of conspecifics allows younger individuals that would be socially precluded from reproducing to reproduce. Jackals on farms compensated for increased mortality by increasing the pregnancy rate of young individuals and increasing the litter size at younger ages, thereby increasing reproductive output. Synthesis and applications. The lethal management of predators is the prevailing strategy to reduce livestock predation. However, the highly adaptable nature of jackals and the combination of compensatory mechanisms such as increased reproduction and potential for immigration allow these predators to persist in the face of severe anthropogenic mortality, possibly through the formation of a source–sink system. These compensatory processes will continue to counter population management actions as long as recruitment from unmanaged areas persists.

旨在降低食肉动物危害的致死性食肉动物管理（lethal carnivore management）是一种全球性现象，却威胁着众多食肉动物的种群存续。黑背胡狼（Black-backed jackal, Canis mesomelas）是南非地区家畜捕食的主要元凶，为减少家畜被捕食的情况，这类胡狼遭到了大范围猎杀。尽管已有数百年的致死性管理措施，黑背胡狼仍得以存续。体型较小的犬科动物（如胡狼）适应性极强，对致死因素的响应存在显著差异，这可能会影响管理措施的实施效果。捕杀食肉动物所产生的效应，取决于其行为、社会组织、繁殖与扩散模式。我们推测，受猎杀的黑背胡狼会改变种群人口统计学与繁殖模式，以弥补死亡率上升带来的损失。本研究从被猎杀的黑背胡狼样本中收集种群人口统计学与繁殖相关数据，并将其与持续受猎杀的农场种群以及未受管理的保护区种群进行对比。农场区域的黑背胡狼清除行动使得种群中位年龄从保护区的5~6岁降至农场的2~3岁。猎杀行为还使黑背胡狼的种群年龄结构从稳定型转变为增长型。这一现象可归因于周边未受管理区域的个体向猎杀区域进行补偿性迁入，表明该系统形成了源-汇种群系统（source–sink system）。未受管理的保护区可作为源种群，将年轻的扩散个体输出至作为汇种群的猎杀区域。该现象可能源于农场区域内正常的排他性领地系统遭到破坏，导致同种个体密度较低。较低的同种个体密度使得原本会被社会机制阻止繁殖的年轻个体得以参与繁殖。农场区域的黑背胡狼通过提高年轻个体的妊娠率以及增加年轻个体的窝仔数，来弥补死亡率上升带来的损失，进而提升繁殖产出。综合与应用：当下，捕食者致死性管理仍是减少家畜被捕食的主流策略。然而，黑背胡狼极强的适应性，加上繁殖能力提升、潜在迁入等补偿机制的共同作用，使得这类捕食者即便面临严重的人为致死因素仍能存续，这一过程可能通过源-汇种群系统得以实现。只要未受管理区域仍有个体迁入补充，这类补偿机制就会持续抵消种群管理措施的效果。