DETERMINING MINIMUM HABITAT AREAS AND HABITAT CORRIDORS FOR COUGARS

I simulated population dynamics of cougars to predict the minimum areas and levels of immigration needed to avoid population extinction caused by demographic and environmental stochasticity for a period of 100 years. Under most plausible parameter values, the model predicted very low extinction risk in areas as small as 2200 km2, and (in the absence of immigration) increasing risk as area decreased below 2200 kM2. If as few as one to four animals per decade could immigrate into a small population, the probability of population persistence increased markedly. Thus a corridor for immigration will benefit a small population in an area where further loss of habitat will occur. The model was applied to the cougar population in the Santa Ana Mountain Range of southern California (2070 kM2, with about 20 adults). Field data support the model's conclusion that this population is demographically unstable There will be a high risk of extinction if the habitat is reduced to currently protected and connected areas (1114 km2). A movement corridor allowing immigration from the adjacent population and intra-range corridors would greatly enhance the prognosis. However, the last corridor for immigration has been degraded by recent human activity. Within the mountain range, cougars recently became extinct in a 75-km2 habitat fragment recently isolated by development, and cougars will become extinct in another 150-km2 of habitat if a Proposed housing project occludes a critical corridor Radio tracking bas confirmed use of this and other important corridors. Neither the model nor the field data alone would bave much influence in the face of development pressure, together they bave stimulated interest in restoring and protecting critical corridors in this range. Nonetheless, the long-term prognosis for this population is bleak, because 22 local governments review potential impact on a case-by-case basis.