Desperately Seeking Stable 50-Year-Old Landscapes with Patches and Long, Wide Corridors

Human activities such as urbanization and roads have disrupted movement and gene flow for plants, reptiles, mammals, sedentary birds, and arthropods [1,2]. Indeed, human-caused habitat fragmentation is a leading threat to biodiversity [3]. As plant and animal populations become smaller and more isolated they become more susceptible to stochastic events and reduced genetic diversity via drift and inbreeding [4]. The primary conservation interventions to counteract habitat fragmentation are conservation corridors and increased reserve size; conservation corridors are also the most frequently cited recommendation to conserve the ability of species and ecosystems to adapt to climate change [5]. Because corridors are such a promising conservation intervention, they are being designed and implemented in many parts of the world. For example, one of us (PB) has helped develop high-resolution plans, each of which is being implemented by government agencies and nongovernmental organizations, to conserve corridors in Bhutan [6], coastal southern California (http://www. scwildlands.org), Arizona (http://www. corridordesign.org/arizona), southeastern California, and northern California. Each corridor (n = 72) is a swath of natural land 500 m to 80 km long identified for conservation so that it can support gene flow and demographic interactions between a pair of natural landscape blocks after ‘‘build-out’’—i.e., after lands adjacent to the corridor and the natural landscape blocks have been converted to urban, agricultural, or industrial uses that are incompatible with wildlife movement. Despite the large body of research confirming that corridors promote wildlife movement [7,8], there is no strong evidence that these 72 corridors will promote gene flow and demographic movement among plants and animals connected by the corridors as intended. Nonetheless, it’s clear that swaths of land much smaller than conservation corridors and embedded in a matrix that is not intensely modified by human activities do support presence and movement of plants and animals [7,9]. These results suggest that corridors may be a useful conservation intervention. However, evidence that such movements occur often enough to promote genetic connectivity and patch occupancy across longer distances in human-dominated landscapes is generally lacking (but see [10]). Evidence is lacking primarily because most corridor studies have been conducted in landscapes that are vastly smaller and different than the landscapes conservation corridors are designed for and have measured species response variables weakly related to corridor utility. That’s why we’re issuing a call for help to identify appropriate sites to test the effectiveness of conservation corridors on a global scale.