Using site-based spatial planning to enhance population viability for an endangered butterfly
Dispersal behavior drives conservation planning for many at-risk species in fragmented landscapes. For many species, designing restoration strategies requires spatial planning at both the landscape level and site level. We seek to address questions posed by USFWS and other constituents about the importance of spatial planning in establishing reproductive resources for an endangered Oregon butterfly, Fender’s blue (Plebejus icaricia icariodes). Spatially implicit models predict that the butterfly requires 6 Ha of high quality reproductive habitat for persistence. We use a spatially-explicit individual based model parameterized with demography and edge-mediated dispersal behavior from prior field studies to test whether this critical patch size can be fragmented into smaller patches within a site and retain population persistence, and if so, the degree to which smaller patches can be spread across a site before losing connectivity.
Our model predicts smaller, closely-spaced patches leads to higher probability of persistence than a single patch and “over-spreading” the patches results in population extinction. These are highly influenced by edge-mediated behavior displayed by this species. A key outcome of this work for local planning agencies is that 6 Ha of reproductive habitat planted across 40 Ha can be arranged across a large diversity of designs, but that population viability is sensitive to details of spatial planning if strategies spread reproductive habitat over larger areas. This framework provides an approach for conservation planning of other at-risk species in which active restoration strategies can be designed in concert with behavioral ecology of those species.