Representing connectivity: quantifying effective habitat availability based on area and connectivity for conservation status assessment and recovery

Abstract

We apply a comprehensive suite of graph theoretic metrics to illustrate how landscape connectivity can be effectively incorporated into conservation status assessments and in setting conservation objectives. These metrics allow conservation practitioners to evaluate and quantify connectivity in terms of representation, resiliency, and redundancy and the approach can be applied in spite of incomplete knowledge of species-specific biology and dispersal processes. We demonstrate utility of the graph metrics by evaluating changes in distribution and connectivity that would result from implementing two conservation plans for three endangered plant species (Erigeron parishii, Acanthoscyphus parishii var. goodmaniana, and Eriogonum ovalifolium var. vineum) relative to connectivity under current conditions. Although distributions of the species differ from one another in terms of extent and specific location of occupied patches within the study landscape, the spatial scale of potential connectivity in existing networks were strikingly similar for Erigeron and Eriogonum, but differed for Acanthoscyphus. Specifically, patches of the first two species were more regularly distributed whereas subsets of patches of Acanthoscyphus were clustered into more isolated components. Reserves based on US Fish and Wildlife Service critical habitat designation would not greatly contribute to maintain connectivity; they include 83–91% of the extant occurrences and >92% of the aerial extent of each species. Effective connectivity remains within 10% of that in the whole network for all species. A Forest Service habitat management strategy excluded up to 40% of the occupied habitat of each species resulting in both range reductions and loss of occurrences from the central portions of each species’ distribution. Overall effective network connectivity was reduced to 62–74% of the full networks. The distance at which each CHMS network first became fully connected was reduced relative to the full network in Erigeron and Acanthoscyphus due to exclusion of peripheral patches, but was slightly increased for Eriogonum. Distances at which networks were sensitive to loss of connectivity due to presence non-redundant connections were affected mostly for Acanthoscyphos. Of most concern was that the range of distances at which lack of redundancy yielded high risk was much greater than in the full network. Through this in-depth example evaluating connectivity using a comprehensive suite of developed graph theoretic metrics, we establish an approach as well as provide sample interpretations of subtle variations in connectivity that conservation managers can incorporate into planning.

Multiscale analysis of canopy arthropod diversity in a volcanically fragmented landscape

“…Integral index of connectivity describes landscape connectivity by weighing patch area and number of links between all pairs of patches in a landscape for a given dispersal distance (Pascual‐Hortal and Saura , Neel et al. ). It increases monotonically with area and proximity across the entire fragmentation gradient and thus is easy to interpret.…”

“…Because it is a binary metric (the landscape is either connected or not connected at a given distance), it emphasizes threshold distances at which network connectivity changes dramatically (Pascual‐Hortal and Saura , Saura and Rubio , Neel et al. ). We chose IIC because metrics that include area within a threshold distance are more accurate at estimating movement (Moilanen and Nieminen , Bender et al.…”

Species‐level persistence probabilities for recovery and conservation status assessment

“…First, a graph theoretic analysis is conducted to quantify the 3 Rs in terms of connectivity and habitat availability in the focal species’ landscape (Neel et al. ). This information is then used to develop habitat‐based recovery criteria, such as a specific network of habitat patches or populations that would meet the elements of the 3 Rs (Neel et al.…”

“…The effects of these conservation strategies on structural landscape connectivity for these species have been described (Neel et al. ).…”

“…We used existing habitat as a baseline to evaluate 2 conservation and 2 threat scenarios. Existing habitat included all patches that supported each species as of 2011, and patches were discrete polygons of occupied habitat mapped through field surveys by the U.S. Department of Agriculture Forest Service, The Nature Conservancy, and the California Natural Heritage Program (as in Neel et al 2014). The conservation scenarios were areas designated as critical habitat by the FWS (2002), and habitat protected under the Carbonate Habitat Management Strategy (CHMS) proposed by the Forest Service (provided by S. Eliason, San Bernardino National Forest).…”