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

物种灭绝主要是由于自然栖息地的丧失，特别是在加拿大南部等本地生物多样性高的地区。连通性保护被认为是减缓这些地区物种损失的一种手段。在高连通性的景观中，自然栖息地的安排使生物可以安全地在剩余的栖息地斑块之间移动。连通性保护保护连接栖息地斑块的自然栖息地元素（如树篱）。这种对连通性保护的强调很大程度上源于研究表明，具有较高扩散能力的物种更有可能在人类改造的景观中持续存在。然而，连通性保护和扩散能力之间的联系并不是直截了当的，因为扩散能力被概念化为两种方式：(1)移动性——个体迁移到遥远地点的能力；(2)殖民化能力——一个物种在遥远地点定居的能力。殖民化能力取决于机动性和分散个体的数量，称为繁殖体压力。而繁殖压力则取决于种群大小和繁殖力。在物种对景观结构（森林数量、道路密度等）的响应中，超过90%的扩散能力研究是通过结合迁移和繁殖体压力来衡量扩散能力的。这是有问题的，因为如果传播能力更强烈地受到繁殖体压力的驱动，而不是流动性，那么我们应该把重点放在通过增加栖息地数量和质量来增加繁殖体压力上，而不是优先考虑保护连通性。这将增加种群规模和繁殖力，从而增加分散个体的数量（繁殖压力）。我建议确定流动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，以预测迁移或传播压力应驱动物种反应的情况。我们将进行荟萃分析，以确定目前的知识状态，我们将对模型预测进行实证检验，使用我们自己和他人在广泛的分类群上的现有数据，并在需要时收集额外的数据。总的来说，我预测在物种对景观结构的反应中，流动性起着次要的作用，尽管我准备好了对结果感到惊讶。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，而不管它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.