Abstract Habitat fragmentation entails major effects on many ecological processes. Theory offers two contradicting hypotheses for the expected effects of fragmentation on seed dispersal strategy. On the one hand, fragmentation may select for increased dispersal by purging poor dispersers that are incapable of moving between patches (spatial sorting). On the other hand, fragmentation may select for reduced dispersal due to the increased cost of leaving a colonized patch; especially whenever the surrounding matrix is hostile. Furthermore, fragmentation can have additional indirect effects on dispersal through its' effects on abiotic and biotic environmental characteristics, but these pathways are rarely accounted for. Empirical evidence testing these hypotheses in plants comes mainly from distinctly fragmented landscapes at either very large scales or very small scales, whereas studies at intermediate scales, such as those that characterize many agricultural landscapes are lacking. Here, we quantified direct and indirect effects of fragmentation-related characteristics, such as patch size and isolation level, on multiple dispersal-related traits of a heterocarpic annual plant in a fragmented agricultural landscape. Using a structural equation modelling approach, we examined whether fragmentation had positive or negative effects on seed dispersal potential and seed dispersal-related traits. Overall, we found more support for the spatial sorting hypothesis. However, the patterns were not simple, nor consistent across all traits and paths. The positive association between fragmentation and dispersal was mainly via a negative effect of connectivity on seed dispersal potential, but the effect of patch area on dispersal traits was less clear. We identified multiple direct and indirect effects of fragmentation-related patch characteristics on dispersal-related traits. Furthermore, the relative importance of direct and indirect effects was qualitatively different between overall effects. Our findings show that different characteristics of fragmented habitats may differentially affect different dispersal-related traits, and that these effects may take place via multiple paths, often leading to a complex relationship between fragmentation and dispersal.

中文翻译：

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碎片化对碎片化农业景观中种子传播性状的直接和间接影响

摘要 栖息地破碎化会对许多生态过程产生重大影响。对于碎片化对种子传播策略的预期影响，理论提供了两个相互矛盾的假设。一方面，碎片化可能会通过清除无法在斑块之间移动的不良分散体（空间分类）来选择增加分散。另一方面，由于留下定植斑块的成本增加，碎片化可能会选择减少扩散；尤其是当周围的矩阵充满敌意时。此外，碎片化可以通过其对非生物和生物环境特征的影响对扩散产生额外的间接影响，但这些途径很少被考虑在内。在植物中检验这些假设的经验证据主要来自非常大尺度或非常小尺度的明显碎片化景观，而缺乏中等尺度的研究，例如那些表征许多农业景观的研究。在这里，我们量化了碎片相关特征（例如斑块大小和隔离水平）对碎片化农业景观中异果树一年生植物的多个扩散相关性状的直接和间接影响。使用结构方程建模方法，我们检查了碎片化是否对种子传播潜力和种子传播相关性状有正面或负面影响。总体而言，我们发现对空间排序假设的更多支持。然而，这些模式并不简单，在所有特征和路径上也不一致。破碎和传播之间的正相关主要是通过连通性对种子传播潜力的负面影响，但斑块面积对传播性状的影响不太清楚。我们确定了碎片相关的斑块特征对分散相关性状的多种直接和间接影响。此外，直接和间接影响的相对重要性在整体影响之间存在质的差异。我们的研究结果表明，破碎栖息地的不同特征可能对不同的扩散相关特征产生不同的影响，并且这些影响可能通过多种途径发生，通常导致破碎和扩散之间的复杂关系。但斑块面积对传播性状的影响不太清楚。我们确定了碎片相关的斑块特征对分散相关性状的多种直接和间接影响。此外，直接和间接影响的相对重要性在整体影响之间存在质的差异。我们的研究结果表明，破碎栖息地的不同特征可能对不同的扩散相关特征产生不同的影响，并且这些影响可能通过多种途径发生，通常导致破碎和扩散之间的复杂关系。但斑块面积对传播性状的影响不太清楚。我们确定了碎片相关的斑块特征对分散相关性状的多种直接和间接影响。此外，直接和间接影响的相对重要性在整体影响之间存在质的差异。我们的研究结果表明，破碎栖息地的不同特征可能对不同的扩散相关特征产生不同的影响，并且这些影响可能通过多种途径发生，通常导致破碎和扩散之间的复杂关系。直接和间接影响的相对重要性在总体影响之间存在质的差异。我们的研究结果表明，破碎栖息地的不同特征可能对不同的扩散相关特征产生不同的影响，并且这些影响可能通过多种途径发生，通常导致破碎和扩散之间的复杂关系。直接和间接影响的相对重要性在总体影响之间存在质的差异。我们的研究结果表明，破碎栖息地的不同特征可能对不同的扩散相关特征产生不同的影响，并且这些影响可能通过多种途径发生，通常导致破碎和扩散之间的复杂关系。