Disentangling the roles of mobility and propagule pressure in species responses to landscape structure

物种灭绝的主要原因是自然栖息地的丧失，特别是在加拿大南部等原生生物多样性很高的地区。连通性保护被认为是减缓这些地区物种丧失的一种手段。在高度连通的景观中，自然栖息地的安排使生物可以在剩余的栖息地之间安全地移动。连通性保护保留了连接生境斑块的自然生境要素(例如树篱)。这种对连通性保护的强调在很大程度上是因为研究表明，具有较高分散能力的物种更有可能在人类修改的景观中坚持下去。然而，连通性保护和扩散能力之间的联系并不简单，因为扩散能力是以两种方式概念化的：(I)移动性--个体迁移到遥远地点的能力--和(Ii)殖民能力--一个物种殖民到遥远地点的能力。定植能力既取决于迁移率，也取决于分散的个体数量，这称为繁殖压力。繁殖压力反过来又取决于种群大小和繁殖力。超过90%的关于扩散能力在物种对景观结构(森林数量、道路密度等)反应中的作用的研究用结合机动性和繁殖压力的方法测量扩散能力。这是有问题的，因为如果扩散能力更强烈地受到繁殖压力的驱动，而不是由迁移率驱动，那么我们应该专注于通过增加栖息地的数量和质量来增加繁殖压力，而不是优先考虑连通性保护。这将增加种群规模和繁殖力，从而增加分散的个体数量(繁殖压力)。我建议确定迁移性本身在物种对景观结构的反应中的作用。我们将进行空间模拟，以预测当迁移率或繁殖压力应该驱动物种反应的情况。我们将进行荟萃分析以确定当前的知识状况，我们将利用我们自己和其他人关于广泛分类群的现有数据，对模型预测进行实证测试，并在需要的地方收集额外的数据。总体而言，我预测迁移性在物种对景观结构的反应中扮演着次要的角色，尽管我准备对结果感到惊讶。但如果我是正确的，那么保护工作的目标应该是最大限度地扩大栖息地的总面积和质量，而不考虑其在促进迁徙方面的假定作用。换句话说，政府和非政府组织应该抓住并鼓励每一个机会来保护、恢复和改善自然栖息地，因为即使是小的或孤立的地块也会增加人口规模，从而增加繁殖压力。

Species extinctions are driven mainly by loss of natural habitats, especially in regions with high native biodiversity such as southern Canada. Connectivity conservation has been suggested as a means of slowing species losses in such regions. In a landscape with high connectivity the natural habitat is arranged such that organisms can safely move between remnant habitat patches. Connectivity conservation preserves elements of natural habitat (e.g. hedgerows) that link habitat patches. This emphasis on connectivity conservation arises largely from research suggesting that species with higher dispersal abilities are more likely to persist in human-modified landscapes. However, the link between connectivity conservation and dispersal ability is not straightforward, because dispersal ability is conceptualized in two ways: (i) mobility - the ability of individuals to move to distant sites -, and (ii) colonizing ability - the ability of a species to colonize distant sites. Colonizing ability depends on both mobility and the number of dispersing individuals, called propagule pressure. Propagule pressure, in turn, depends on population size and fecundity. Over 90% of studies of the role of dispersal ability in species responses to landscape structure (forest amount, road density etc.) measure dispersal ability in ways that combine mobility and propagule pressure. This is problematic because, if dispersal ability is more strongly driven by propagule pressure than by mobility then, rather than prioritizing connectivity conservation, we should focus efforts on increasing propagule pressure by increasing habitat amount and quality. This will increase population sizes and fecundity and therefore increase the number of dispersing individuals (propagule pressure). I propose to determine the role of mobility itself in species responses to landscape structure. We will conduct spatial simulations to predict situations when mobility or propagule pressure should drive species responses. We will conduct meta-analyses to determine the current state of knowledge, and we will conduct empirical tests of the model predictions, using our own and others' existing data on a wide range of taxa, and collecting additional data where needed. Overall, I predict that mobility plays a minor role in species responses to landscape structure, though I am prepared to be surprised by the results. But if I am correct, then conservation efforts should aim to maximize the total area and quality of habitat, irrespective of its presumed role in facilitating movement. In other words, governments and NGO's should take and encourage every opportunity to preserve, restore, and improve natural habitat, because even small or isolated parcels can increase population size and therefore increase propagule pressure.