There is no place on Earth that has not been affected by human activity. One of the most prevalent and essential human impacts is land conversion to agriculture. Most (> 90%) of the land in North Dakota is privately owned and in production. Yet, despite a century of drainage and upland conversion, the Prairie Pothole Region of the northern plains remains a preeminent domain for wetland ecosystems and associated biodiversity. Little land is protected or managed for conservation, although Farm Bill programs include some protections in a piecemeal fashion across the region. Our question is simple, but difficult to answer: does this intensively and extensively worked landscape offer sufficient biodiversity conservation value and resilience, particularly for environmentally sensitive species with limited mobility? To seek some insight, we combined analysis of (1) landscape change derived from available land classifications (NLCD and NASS) and our own higher resolution analysis of NAIP imagery, spanning a period in which there was known loss of Conservation Reserve Program (CRP) participation and considerable climate variability, including drought, (2) spatial processes estimated for the wood frog (Lithobates sylvaticus) from a 17-yr capture-recapture study and genetic population structure based on microsatellites, and (3) simulation models of dispersal dynamics.
Results/Conclusions
CRP in North Dakota declined by nearly 50% from 2007-2012. This is consistent with reduced wetland and grassland cover and increased crop cover in our study area over the same span, a trend which continued through the present. Wetland numbers fluctuated in relation to winter snow and warm season precipitation. Connectivity across the landscape likely depends on the number and arrangement of wetlands, as well as availability of non-crop intervening habitat. Recapture rates of photo-identified individuals were generally low (~8% for adults and < 1% for metamorphs), but yielded estimates of interannual movements for adults (n = 301) of 31% and of individuals captured as metamorphs (n = 23) of 65%. Distances were generally short (avg=187m) and to nearest-neighbor ponds, supporting the idea that stepping-stone dispersal is the most common mode, although maximum distances occasionally exceeded 1 km. There was little evidence for genetic structure at less than 5 km, which is consistent with short-scale dispersal data, but genetic distances increased rapidly beyond 20 km. Together with the emerging picture of dynamic landscape structure, amphibians appear to be capable of maintaining dispersal as long as connectivity is retained. Recruitment and connectivity are highly sensitive to precipitation and land use, however.