Department of Ecology, Evolution, Behavior, University of Minnesota Twin Cities, Saint Paul, Minnesota, USA.
Ecology. 2024 Jan;105(1):e4171. doi: 10.1002/ecy.4171. Epub 2023 Nov 20.
Species engage in mutually beneficial interspecific interactions (mutualisms) that shape their population dynamics in ecological communities. Species engaged in mutualisms vary greatly in their degree of dependence on their partner from complete dependence (e.g., yucca and yucca moth mutualism) to low dependence (e.g., generalist bee with multiple plant species). While current empirical studies show that, in mutualisms, partner dependence can alter the speed of a species' range expansion, there is no theory that provides conditions when expansion is sped up or slowed down. To address this, we built a spatially explicit model incorporating the population dynamics of two dispersing species interacting mutualistically. We explored how mutualisms impacted range expansion across a gradient of dependence (from complete independence to obligacy) between the two species. We then studied the conditions in which the magnitude of the mutualistic benefits could hinder versus enhance the speed of range expansion. We showed that either complete dependence, no dependence, or intermediate degree of dependence on a mutualist partner can lead to the greatest speeds of a focal species' range expansion based on the magnitude of benefits exchanged between partner species in the mutualism. We then showed how different degrees of dependence between species could alter the spatial distribution of the range expanding populations. Finally, we identified the conditions under which mutualistic interactions can turn exploitative across space, leading to the formation of a species' range limits. Our work highlights how couching mutualisms and mutualist dependence in a spatial context can provide insights about species range expansions, limits, and ultimately their distributions.
物种之间存在互利的种间相互作用（互惠共生），这会影响它们在生态群落中的种群动态。参与互惠共生的物种在对其伙伴的依赖程度上存在很大差异，从完全依赖（例如丝兰和丝兰蛾互惠共生）到低度依赖（例如具有多种植物物种的普通蜜蜂）。虽然目前的实证研究表明，在互惠共生中，伙伴的依赖程度会改变物种的扩散速度，但没有理论提供了关于扩张速度加快或减缓的条件。为了解决这个问题，我们建立了一个空间显式模型，其中包含两种相互作用的扩散物种的种群动态。我们探讨了互惠共生如何在两个物种之间的依赖程度（从完全独立到专性）梯度上影响范围扩张。然后，我们研究了互惠共生中互惠利益的大小在什么情况下会阻碍或增强范围扩张的速度。我们发现，根据互惠物种之间交换的利益的大小，完全依赖、没有依赖或与互惠伙伴的中等程度依赖都可以导致焦点物种的范围扩张速度最快。然后我们展示了物种之间不同程度的依赖如何改变扩张种群的空间分布。最后，我们确定了互惠相互作用在空间上如何从互利转变为剥削，从而形成物种的范围限制。我们的工作强调了如何在空间背景下将互惠共生和互惠伙伴的依赖纳入物种范围扩张、限制以及最终分布的研究中。
