Data from: Fitness declines toward range limits and local adaptation to climate affect dispersal evolution during climate-induced range shifts

Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low-latitude/low-elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: a) climate-induced fitness declines toward range limits, and b) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual-based model. We compare range-wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines toward range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. Dispersal decreased toward stable RLs when range-wide fitness was uniform, but increased when fitness declined toward RLs, due to highly dispersive genotypes maintaining sink populations at RLs, increased kin selection in smaller populations, and an emergent fitness asymmetry that favoured dispersal in low-quality habitat. However, this initial dispersal advantage at low-fitness RLs did not facilitate climate tracking, as it was outweighed by an increased probability of extinction. Locally-adapted genotypes benefited from staying close to their climate optima; this selected against dispersal under stable climates but for increased dispersal throughout shifting ranges, compared to cases without local adaptation. Dispersal increased at expanding RLs in most scenarios, but only increased at the range centre and contracting RLs given local adaptation to climate.

扩散能力（dispersal ability）在很大程度上决定了物种能否在气候变化过程中追踪其气候生态位（climatic niche），这一过程对于处于收缩型分布范围边界（range limits，低纬度/低海拔区域）的种群尤为关键，此类种群若无法追踪气候则面临灭绝风险。我们探究收缩型分布范围边界处的扩散演化是否可通过两类过程得以促进——这两类过程可使边缘种群在气候恶化导致灭绝前，就能感知并适应其影响：a) 气候驱动的适合度（fitness）随分布范围边界递减；b) 对动态气候梯度的局部适应（local adaptation）。我们借助空间显式基于个体的模型（spatially explicit, individual-based model），模拟了沿温度梯度连续分布的物种种群。我们对比了以下多种情境下全分布范围的扩散演化：气候稳定与定向气候变化两种气候背景；适合度均匀分布与适合度随分布范围边界递减两种适合度模式；仅单一气候基因型与多个适配温度的局部基因型两种遗传结构。当全分布范围适合度均匀时，扩散水平随稳定的分布范围边界递减；但当适合度随分布范围边界递减时，扩散水平反而上升——这是因为高扩散基因型可维持分布范围边界处的汇种群（sink populations），小型种群内的亲缘选择（kin selection）作用增强，且出现了一种新兴的适合度不对称性，使得低质量生境中的扩散更受青睐。然而，这种在低适合度分布范围边界处的初始扩散优势，并未促进气候追踪：因为其收益被灭绝概率的上升所抵消。局部适应的基因型更倾向于停留在其气候最适值（climate optima）附近；相较于无局部适应的情境，这种选择会在稳定气候下抑制扩散，但在动态分布范围中会选择更高的扩散水平。在多数情境下，扩张型分布范围边界处的扩散水平会上升；但仅当存在气候局部适应时，分布范围中心与收缩型分布范围边界处的扩散水平才会提升。