Department of Ecology, Institute of Entomology, Biology Centre CAS, Branišovská 31, 37005, České Budějovice, Czech Republic.
Odum School of Ecology, University of Georgia, 140 E. Green St., Athens, GA, 30602-2202, USA.
J Anim Ecol. 2018 Jan;87(1):24-35. doi: 10.1111/1365-2656.12662. Epub 2017 Apr 3.
Sexually reproducing organisms require males and females to find each other. Increased difficulty of females finding mates as male density declines is the most frequently reported mechanism of Allee effects in animals. Evolving more effective mate search may alleviate Allee effects, but may depend on density regimes a population experiences. In particular, high-density populations may evolve mechanisms that induce Allee effects which become detrimental when populations are reduced and maintained at a low density. We develop an individual-based, eco-genetic model to study how mating systems and fitness trade-offs interact with changes in population density to drive evolution of the rate at which males or females search for mates. Finite mate search rate triggers Allee effects in our model and we explore how these Allee effects respond to such evolution. We allow a population to adapt to several population density regimes and examine whether high-density populations are likely to reverse adaptations attained at low densities. We find density-dependent selection in most of scenarios, leading to search rates that result in lower Allee thresholds in populations kept at lower densities. This mainly occurs when fecundity costs are imposed on mate search, and provides an explanation for why Allee effects are often observed in anthropogenically rare species. Optimizing selection, where the attained trait value minimizes the Allee threshold independent of population density, depended on the trade-off between search and survival, combined with monogamy when females were searching. Other scenarios led to runaway selection on the mate search rate, including evolutionary suicide. Trade-offs involved in mate search may thus be crucial to determining how density influences the evolution of Allee effects. Previous studies did not examine evolution of a trait related to the strength of Allee effects under density variation. We emphasize the crucial role that mating systems, fitness trade-offs and the evolving sex have in determining the density threshold for population persistence, in particular since evolution need not always take the Allee threshold to its minimum value.
有性繁殖的生物需要雄性和雌性相互寻找才能繁殖。随着雄性密度的下降，雌性寻找配偶的难度增加，这是动物中最常报道的阿利效应机制。进化出更有效的配偶搜索可能会减轻阿利效应，但这可能取决于种群所经历的密度范围。特别是，高密度种群可能会进化出诱导阿利效应的机制，当种群减少并维持在低密度时，这些机制就会变得有害。我们开发了一种基于个体的生态遗传模型，以研究交配系统和适应性权衡如何与种群密度的变化相互作用，从而驱动雄性或雌性寻找配偶的搜索速度的进化。有限的配偶搜索率在我们的模型中引发了阿利效应，我们探索了这些阿利效应如何对这种进化做出反应。我们允许一个种群适应几个种群密度范围，并检查高密度种群是否有可能逆转在低密度下获得的适应。我们在大多数情况下发现了与密度有关的选择，导致在保持在较低密度的种群中，搜索率导致阿利阈值降低。这主要发生在对配偶搜索施加繁殖力成本的情况下，并且为为什么阿利效应经常在人为稀少的物种中观察到提供了解释。在优化选择中，当达到的性状值独立于种群密度最小化阿利阈值时，取决于搜索和生存之间的权衡，以及当雌性搜索时的一夫一妻制。其他情景导致了对配偶搜索率的失控选择，包括进化自杀。因此，在确定密度如何影响阿利效应的进化时，配偶搜索中的权衡可能是至关重要的。以前的研究没有研究在密度变化下与阿利效应强度有关的性状的进化。我们强调了交配系统、适应性权衡和进化的性别在确定种群持续存在的密度阈值方面的关键作用，特别是因为进化不一定总是将阿利阈值降低到最小值。
