Designing a network for butterfly habitat restoration: where individuals, populations and landscapes interact.
Abstract
Restoring biologically appropriate habitat networks is fundamental to the persistence and connectivity of at-risk species surviving in highly fragmented environments. For many at-risk species, this landscape planning problem requires combining detailed biological information about the species with the landscape, economic and social realities of the restoration effort. Here, we assess the ability of potential restored landscapes to create persistent and connected populations of the federally endangered Fender's blue butterfly (Icaricia icarioides fenderi) in Oregon's Willamette Valley. Like many other at-risk species, a very small amount (0.5%) of historic habitat remains and much of this habitat is highly degraded. To do this, we combine extensive demography and behaviour data from prior studies of Fender's blue with landscape maps of potential restoration sites by building and running a spatially explicit landscape model. We chose a simulation approach because previous attempts using more traditional population modelling did not provide sufficiently informative answers for this restoration problem. From our simulations, we: (a) provide a solution to the general landscape restoration problem of determining whether patches that are available according to social, economic and ecological realities are sufficient to restore persistence and connectivity; (b) supported our predictions from our previous models about persistence of our large patches and expanded our inference to include connectivity and persistence of small patches; and (c) found several emergent properties of our system, including identifying stepping-stone patches, observing asymmetric connectivity and uncovering reciprocal effects of connectivity and population dynamics. Synthesis and applications. Assuming no large disturbances, and relying on our 14 years of data collection and models, restoring all currently degraded and potentially available habitat patches to high quality native prairie would be sufficient for long-term persistence of Fender's blue butterfly in the West Eugene area, Oregon. This conclusion resolves many of the shortcomings of our previous population and metapopulation models that were not able to combine the necessary landscape complexity with species behaviour to address this restoration problem.