| A controversy exists in the Pacific Northwest of the United States between conservation of northern spotted owl populations and logging of old-growth coniferous forests. This species has a strong association with old-growth forests that are also economically valuable as timber. Research questions relevant to conservation of this species include how temporal trends in northern spotted owl populations are influenced and how the spatial configuration of old-growth forests affect these populations. To address these questions, I studied a population of marked northern spotted owls on 95 territories in northwestern California from 1985 through 1994. I examined the magnitude of temporal and spatial variation in life-history traits (survival, reproductive output, and recruitment), the effects of climate and landscape characteristics on temporal and spatial variation in these traits, respectively, and how this variation affected aspects of population dynamics. I used a components of variation analysis to partition sampling from process variation and a model selection approach, with which life-history traits were estimated using mark-recapture and random-effects models. Climate explained most of the temporal variation in life-history traits. Annual survival varied the least over time whereas recruitment rate varied the most, suggesting a "bet-hedging" life-history strategy. A forecast of annual rates of population change ({dollar}lambda{dollar}), estimated from life-history traits, suggested that northern spotted owl populations may experience declines solely due to climate influences, even with unchanging habitat conditions. In terms of spatial variation, annual survival on territories was positively associated with both amounts of interior old-growth forest and length of edge between those forests and other vegetation types. Reproductive output was negatively associated with interior forest but positively associated with edge. A gradient existed in territory-specific estimates of fitness derived from these life-history estimates. This gradient suggested that some degree of habitat fragmentation promoted high fitness in northern spotted owls. Habitat quality, as defined by fitness, appeared to buffer variation in annual survival but did not buffer reproductive output. I postulated that the magnitude of {dollar}lambda{dollar} was determined by habitat quality whereas variation around {dollar}lambda{dollar} was influenced by recruitment and reproductive output. As habitat quality declines, variation in {dollar}lambda{dollar} should become more pronounced. |
