Rachel Germain

In fragmented landscapes, distinct habitats are separated by abrupt edges, resulting in a high proportion of dispersers that land short of their habitat type – known as failed dispersal. Although failed dispersers are presumed dead in population models because they do not contribute to the next generation, their demographic fate may not be so simple. Here, I explore two alternative fates of individuals that enter unsuitable habitat: dormancy and sink populations. In a fragmented Californian grassland, these transient fates may enhance dispersal or facilitate invasion, outcomes that contribute to long term community dynamics. To examine diversity and abundance as both communities enter unsuitable habitat, I surveyed both the seedbank and adult life stages across the invaded matrix habitat and the embedded serpentine patch communities within one generation. Here I show that the fates of failed dispersers vary by community type: as patch specialists cross boundaries they retained a high abundance through dormancy, whereas a dominant matrix invasive, Avena fatua, rarely survived and suffered low seed production in serpentine patches. By revealing the distinct demographic fates of each community type, these results motivate future investigations into dormant life-stage dispersal as a possible method of patch connectivity in spatially structured systems.

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