Managing Fragmented Landscapes: A Macroscopic Approach

Habitat fragmentation is generally thought to be a leading cause of loss of biodiversity. In fragmented landscapes, maintenance of habitat connectivity is an important consideration in conservation planning. In this paper, we develop methods for quantifying habitat connectivity at multiple scales and assigning conseervation priority to habitat patches based on their contribution to connectivity. By representing the habitat mosaic as a mathematical "graph" we show that percolation theory can be used to quantify connectivity at multiple scales from empirical landscape data. Our results indicate that connectivity of landscapes is highly scale dependent, exhibiting a marked transition at a characteristic distance and varying significantly for organisms with different dispersal behavior. More importantly, we show that the sensitivity and importance of landscape pattern is also scale dependent peaking at scales associated with the percolation transition. The sensitivity analysis allows us in addition to identify critical "key-stone" patches that when removed from the landscape cause large changes in connectivity. These methods are applied to the distribution of forest habitats throughout the Southwestern U.S. and management implications for the threatened Mexican Spotted Owl (Strix occidentalis lucida) are discussed.