Habitat fragmentation is one of the principle threats to biodiversity, and in developing landscapes, urbanization is a leading agent of fragmentation and primary cause of species endangerment. Such is the case in coastal southern California, one of the largest megalopolitan regions in North America where the dramatic growth of human populations and resulting sprawl has severely fragmented native habitat in this biodiversity hotspot. Connectivity, the degree of movement of organisms or processes among habitat patches (Taylor et al. 1993), is essential to maintaining the ecological integrity across fragmented areas by allowing for movement and dispersal of wildlife. Such animal movements may be critical to facilitate the exchange of genetic material among otherwise isolated populations, and maintaining functional levels of connectivity may be essential to allow natural range shifts in response to short and long-term environmental transitions, such as fires and global climate change. The preservation of functional levels of connectivity undoubtedly lends strength to efforts to protect wildlife, their habitats, and the ecosystem services they provide.
Mammalian carnivores can be effective focal species to evaluate the degree of landscape-level connectivity, or fragmentation, in a region. Large carnivores are particularly vulnerable to extinction in fragmented habitat because of wide ranges and resource requirements, low densities, slow population growth rates, and direct persecution by humans (Noss et al. 1996, Woodroffe and Ginsberg 1998, Crooks 2000, 2002). Consequently, top predators may not be able to persist in landscapes that are not connected by functional movement corridors. Further, their disappearance may generate cascades that ripple down the food web. In fragmented habitat in San Diego, Crooks and Soulé (1999) demonstrated that the extirpation of dominant predators such as coyotes (Canis latrans) can result in the ecological release of smaller predators and increased extinction rates of their avian prey. Thus, top predators may function as keystone species - animals whose disappearance causes the increase in some species and the decline and extinction of others (Mills et al. 1993).
Carnivores therefore are ecologically pivotal organisms whose status can be indicative of the functional connectivity of ecosystems. Using mammalian carnivores in conservation planning adds a critical layer of conservation strategy that may provide a robust method for protecting other species with less demanding needs. Bobcats (Lynx rufus) are an excellent focal species to evaluate connectivity. They are less sensitive to fragmentation than larger felids and are thus valuable indicators of connectivity at local (finer) spatial scales and intermediate levels of fragmentation and urbanization. They have relatively large home ranges and can disperse long distances. Bobcats can persist in habitat fragments, but only those that have adequate connections to larger natural areas. Coyotes can also serve as good indicators of connectivity and are a good choice of focal species, because certain populations are vulnerable to localized extinction in habitat fragments that are too small, disturbed, or isolated. Thus, habitat connectivity appears to be the key to the persistence of these species and their associated biodiversity.
Due to the threat that habitat fragmentation poses to natural environments, connectivity conservation is increasingly becoming incorporated into land-management plans worldwide. Here we are studying the movements and dispersal behavior of carnivores, with a primary focus on bobcats, to evaluate functional connectivity in southern California and provide information to managers to help sustain carnivore populations across fragmented reserves.
We are continuing examinations of over ten years of carnivore monitoring data from five contiguous counties in southern California, with a focus on how urbanization across this region has influenced the distribution and movement ecology of bobcats. In FY10, we will add to this regional dataset from a related project that will double the total number of data records.
Recent findings of our research on bobcats have identified vehicle strikes as a major source of mortality and that notoedric mange, which may be linked to rodenticide exposure, is an emerging threat. Thus we are continuing examinations of bobcat health and mortality. Specifically we will continue recording and collecting bobcats killed on roads, examining the characteristics of the locations, and conducting necropsies of carcasses. We will also continue other disease surveys, with a focus on FIV in collaboration with Colorado State University.
We continue examining internal connectivity within lands managed by the Irvine Ranch Conservancy and other land management groups. We are using previously collected data on bobcats to determine locations where bobcats might be particularly susceptible to mortality from vehicle strikes and where there are natural corridors. After identifying these important locations, we will conduct detailed field surveys of the roadways and potential corridors to identify characteristics influencing bobcat movement patterns and mortality.
Finally, we are examining our 10 years of camera trap surveys in Orange County to identify longer-term trends in bobcat population health and distribution patterns with respect to urbanization. We will conduct a meta-analysis of GPS-telemetry data collected on bobcats since 2002 to study how fragmentation at varying scales impacts their activity patterns, space utilization, and genetic relatedness. These analyses should help identify factors contributing to the decline of bobcats in fragmented areas. In one analysis, we will compare the movement rates of bobcats to determine if the same environmental characteristics, such as temperature and moonlight, that seem to influence bobcat activity levels in relatively pristine areas also operate in areas where bobcats live in smaller habitat patches that are closer to urbanized areas. In another analysis, we will examine whether genetic patterns seen at coarse scales, where bobcats in a more fragmented and isolated area exhibited higher levels of inbreeding than those in a more in-tact area, are found at local scales. Specifically, we will examine whether bobcats living closer together have higher levels of relatedness than those that are farther apart, and whether dispersal appear to be inhibited by fragmentation and the hazards of crossing through an urban environment.
USGS Contact For This Project
Bevins, SN, S Carver, EE Boydston, LM Lyren, M Alldredge, KA Logan, SPD Riley, RN Fisher, TW Vickers, W Boyce, M Salman, MR Lappin, KR Crooks, S VandeWoude. 2012. Three pathogens in sympatric populations of pumas, bobcats, and domestic cats: implications for infections disease transmission. PLoS ONE 7(2): e31403. doi:10.1371/journal.pone.0031403
Lee, JS, EW Ruell, EE Boydston, LM Lyren, RS Alonso, JL Troyer, KR Crooks, S VandeWoude. 2012. Gene flow and pathogen transmission among bobcats (Lynx rufus) in a fragmented urban landscape. Molecular Ecology, 21, 1617-1631 doi: 10.1111/j.1365-294X.2012.05493.x
Jennings, M., R. Lewison, K. Crooks, E. Boydston, L. Lyren, W. Vickers, and W. Boyce. 2012. Corridor Conservation in Southern California under Climate Change: Understanding Wildlife Response to Burned Landscapes. Society for Conservation Biology, North American Congress for Conservation Biology, Oakland, CA, July 15-18.
Ruell, E. W., Riley, S. P. D., Douglas, M. R., Antolin, M. F., Pollinger, J. P., Tracey, J. A., Lyren, L. M., Boydston, E. E., Fisher, R. N., & Crooks, K. R. (2012). Urban habitat fragmentation and genetic population structure of bobcats in coastal southern California. American Midland Naturalist, 168, 265-280.