A Dynamic Analysis of Northern Spotted Owl Viability in a Fragmented Forest Landscape*
Roland H. Lamberson
Department of Mathematics
Humboldt State University
Arcata, CA 95521
Robert McKelvey
Department of Mathematic
University of Montana
Missoula,MT 59812
Barry R. Noon, Curtis Voss
U.S.D.A. Forest Service
Redwood Sciences Laboratory
1700 Bayview Drive, Arcata CA 95521
Abstract:
The Northern Spotted Owl is closely associated with mature and old-growth coniferous forests in the Pasific Northwest. There has been a rapid loss and fragmentation of this habitat over the last half century, which may jeopardize the long-term survival of the species through reduction of dispersal success. In this paper we report results of a population model for the Northern Spotted Owl that incorporates both juvenile dispersal and search for mates. We analyze both deterministic and stochastic version of the model in search efficiency, population density, and amount of suitable habitat. In addition, we analyze the model under the nonequilibrium conditions that currently exist due to timber harvest in the owls' preferred habitat. Our results predict a sharp threshold below which populations cannot persist, and suggest that inferences from population models that incorporate equilibrium assumptions may be highly misleading.
Paper submitted January 18, 1991; revised manuscipt accepted November 15, 1991
* The model described in this paper is the inividual territory model from the conservation plan for
Northern Spotted Owls(Thomas et al.1990)