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Data and code from: Dispersing across habitat boundaries: uncovering the demographic fates of populations in unsuitable habitat

Szojka, Megan1; Germain, Rachel2

Published Feb 23, 2024 on Dryad. https://doi.org/10.5061/dryad.jsxksn0hj

Data files

Feb 23, 2024 version files 18.63 MB
Feb 23, 2024 version files 18.63 MB

Abstract

Patchy landscapes are characterized by abrupt transitions among habitats, forcing species to cross habitat boundaries in order to spread. Although individuals that disperse into unsuitable habitat are often presumed dead in population models, their demographic fates may not be so simple. If survival within unsuitable habitat is possible (however transiently), then through time, individuals may be able to reach distant, suitable habitat, buffering species from extinction. In a fragmented Californian grassland, we explored the fates of individuals that crossed habitat boundaries, and if those fates differed among habitat specialists dispersing between two habitat types: serpentine habitat patches and the invaded non-serpentine matrix. We surveyed the diversity of seedbank and adult life stages along transects that crossed boundaries between patches and the matrix. First, we considered how patch specialists might transiently survive in the matrix via seed dormancy. We found that dormancy maintained populations of patch specialists deep into the matrix, as abundances of individuals in the seedbank and in the germinated adult communities increasingly differed with distance into the matrix; these patterns were not observed for matrix specialists in serpentine patches. Seeds of patch specialists that lacked morphologies for assisted dispersal accumulated downslope of patches, suggesting that even the most dispersal-limited species could eventually reach suitable patches even if they first land in the matrix. Second, we investigated dispersal of an invasive matrix specialist (Avena fatua) into patches to assess if sink populations existed across the habitat boundary. We found that A. fatua was largely absent deep in patches, where reproductive outputs plummeted and there was no evidence of a dormant seedbank (in contrast to a sizeable seedbank of patch specialists in the matrix). Our results not only reveal the demographic fates of individuals that land in unsuitable habitat, but also that their ecological consequences differ depending on the direction by which the boundary is crossed (patch ➝ matrix ≠ matrix ➝ patch). Dormancy is often understood as a mechanism for persisting in face of temporal variability, but it may serve as a means of traversing unsuitable habitat in patchy systems, warranting its consideration in estimates of habitat connectivity.