Schtickzelle Nicolas, Mennechez Gwénaëlle, Baguette Michel
Biodiversity Research Centre, Catholic University Louvain, 4 Place Croix du Sud, B-1348 Louvain-la-Neuve, Belgium.
Ecology. 2006 Apr;87(4):1057-65. doi: 10.1890/0012-9658(2006)87[1057:ddwhfi]2.0.co;2.
Habitat fragmentation is expected to impose strong selective pressures on dispersal rates. However, evolutionary responses of dispersal are not self-evident, since various selection pressures act in opposite directions. Here we disentangled the components of dispersal behavior in a metapopulation context using the Virtual Migration model, and we linked their variation to habitat fragmentation in the specialist butterfly Proclossiana eunomia. Our study provided a nearly unique opportunity to study how habitat fragmentation modifies dispersal at the landscape scale, as opposed to microlandscapes or simulation studies. Indeed, we studied the same species in four landscapes with various habitat fragmentation levels, in which large amounts of field data were collected and analyzed using similar methodologies. We showed the existence of quantitative variations in dispersal behavior correlated with increased fragmentation. Dispersal propensity from habitat patches (for a given patch size), and mortality during dispersal (for a given patch connectivity) were lower in more fragmented landscapes. We suggest that these were the consequences of two different evolutionary responses of dispersal behavior at the individual level: (1) when fragmentation increased, the reluctance of individuals to cross habitat patch boundaries also increased; (2) when individuals dispersed, they flew straighter in the matrix, which is the best strategy to improve dispersal success. Such evolutionary responses could generate complex nonlinear patterns of dispersal changes at the metapopulation level according to habitat fragmentation. Due to the small size and increased isolation of habitat patches in fragmented landscapes, overall emigration rate and mortality during dispersal remained high. As a consequence, successful dispersal at the metapopulation scale remained limited. Therefore, to what extent the selection of individuals with a lower dispersal propensity and a higher survival during dispersal is able to limit detrimental effects of habitat fragmentation on dispersal success is unknown, and any conclusion that metapopulations would compensate for them is flawed.
栖息地破碎化预计会对扩散率施加强大的选择压力。然而，扩散的进化反应并非显而易见，因为各种选择压力的作用方向相反。在这里，我们使用虚拟迁移模型在集合种群背景下解析了扩散行为的组成部分，并将其变化与专食性蝴蝶优红蛱蝶（Proclossiana eunomia）的栖息地破碎化联系起来。与微景观或模拟研究不同，我们的研究提供了一个几乎独一无二的机会来研究栖息地破碎化如何在景观尺度上改变扩散。实际上，我们在四个具有不同栖息地破碎化水平的景观中研究了同一物种，在这些景观中收集了大量实地数据，并使用相似的方法进行分析。我们发现扩散行为存在与破碎化加剧相关的数量变化。在破碎化程度更高的景观中，从栖息地斑块扩散的倾向（对于给定的斑块大小）以及扩散过程中的死亡率（对于给定的斑块连通性）更低。我们认为，这些是扩散行为在个体层面上两种不同进化反应的结果：（1）当破碎化加剧时，个体穿越栖息地斑块边界的不情愿程度也增加；（2）当个体扩散时，它们在基质中飞行得更直，这是提高扩散成功率的最佳策略。根据栖息地破碎化情况，这种进化反应可能在集合种群水平上产生复杂的扩散变化非线性模式。由于破碎化景观中栖息地斑块面积小且隔离度增加，总体迁出率和扩散过程中的死亡率仍然很高。因此，集合种群尺度上的成功扩散仍然有限。所以，具有较低扩散倾向和较高扩散存活率的个体选择能够在多大程度上限制栖息地破碎化对扩散成功的不利影响尚不清楚，任何认为集合种群能够弥补这些影响的结论都是有缺陷的。
