David N. Koons

Effects of habitat fragmentation on avian nesting success: a review of the evidence at multiple spatial scales

We reviewed published literature to examine the effect of habitat fragmentation on avian nesting success at three spatial scales (i.e., edge, patch, and landscape scales). We identified 86 relevant manuscripts that provided 117 individual tests of hypotheses regarding the effects of habitat fragmentation on nesting success. Most papers and reviews on this topic have been narrow in scope and have not examined multiple spatial scales. However, our results suggest that the scale at which fragmentation is measured (i.e., edge, patch and landscape) and the duration of the studydo influence the probabilitythat a studywill detect a fragmentation effect. Studies that measured fragmentation at landscape scales and studies conducted over several years were more likely to detect effects of fragmentation on nesting success. A recent review of research on nest predators and habitat fragmentation found a verysimilar scale-dependent pattern; predator effects were more prevalent when fragmentation occurs at landscape scales than patch or edge scales. Based on these findings, we recommend future research on the topic should be conducted at the landscape scale, over several years, and incorporate accompanying work on nest-predator ecology. Correspondingly, conservation actions that limit fragmentation at landscape scales should have positive impacts on nesting success rates and bird populations. # 2003 Elsevier Ltd. All rights reserved.

Population Momentum: Implications for Wildlife Management

Abstract Maintenance of sustainable wildlife populations is one of the primary purposes of wildlife management. Thus, it is important to monitor and manage population growth over time. Sensitivity analysis of the long-term (i.e., asymptotic) population growth rate to changes in the vital rates is commonly used in management to identify the vital rates that contribute most to population growth. Yet, dynamics associated with the long-term population growth rate only pertain to the special case when there is a stable age (or stage) distribution of individuals in the population. Frequently, this assumption is necessary because age structure is rarely estimated. However, management actions can greatly affect the age distribution of a population. For initially growing and declining populations, we instituted hypothetical management targeted at halting the growth or decline of the population, and measured the effects of a changing age structure on the population dynamics. When we changed vital rates, the age structure became unstable and population momentum caused populations to grow differently than that predicted by the long-term population growth rate. Interestingly, changes in fertility actually reversed the direction of short-term population growth, leading to long-term population sizes that were actually smaller or larger than that when fertility was changed. Population momentum can significantly affect population dynamics and will be an important factor in the use of population models for management.