Summary 1.Resource selection estimated by logistic regression is used increasingly in studies to identify critical resources for animal populations and to predict species occurrence. 2. Most frequently, individual animals are monitored and pooled to estimate populationlevel effects without regard to group or individual-level variation. Pooling assumes that both observations and their errors are independent, and resource selection is constant given individual variation in resource availability. 3. Although researchers have identified ways to minimize autocorrelation, variation between individuals caused by differences in selection or available resources, including functional responses in resource selection, have not been well addressed. 4. Here we review random-effects models and their application to resource selection modelling to overcome these common limitations. We present a simple case study of an analysis of resource selection by grizzly bears in the foothills of the Canadian Rocky Mountains with and without random effects. 5. Both categorical and continuous variables in the grizzly bear model differed in interpretation, both in statistical significance and coefficient sign, depending on how a random effect was included. We used a simulation approach to clarify the application of random effects under three common situations for telemetry studies: (a) discrepancies in sample sizes among individuals; (b) differences among individuals in selection where availability is constant; and (c) differences in availability with and without a functional response in resource selection. 6. We found that random intercepts accounted for unbalanced sample designs, and models with random intercepts and coefficients improved model fit given the variation in selection among individuals and functional responses in selection. Our empirical example and simulations demonstrate how including random effects in resource selection models can aid interpretation and address difficult assumptions limiting their generality. This approach will allow researchers to appropriately estimate marginal (population) and conditional (individual) responses, and account for complex grouping, unbalanced sample designs and autocorrelation.
Riparian corridors and fencerows are hypothesized to increase the persistence of forest animals in fragmented landscapes by facilitating movement among suitable habitat patches. This function may be critically important for forest birds, which have declined dramatically in fragmented habitats. Unfortunately, direct evidence of corridor use has been difficult to collect at landscape scales and this limits support for corridors in conservation planning. Using telemetry and handheld GPS units, we examined the movement of forest birds by translocating territorial individuals of barred antshrikes (Thamnophilus doliatus; a forest specialist) and rufous-naped wrens (Campylorhynchus rufinucha; a forest generalist) 0.7-1.9 km from their territories in the highly fragmented tropical dry forest of Costa Rica. In each translocation, the directly intervening habitat comprised 1 of 3 treatments: forested riparian corridor, linear living fencerow, or open pasture. Antshrikes returned faster and with greater success in riparian corridors relative to pasture treatments. This species also traveled more directly in riparian corridor treatments, detoured to use forested routes in the other 2 treatments, and did not use fencerows even when they led directly to their home territories. By contrast, wrens were more likely to use fencerows when returning, and return time and success were equivalent among the 3 treatments. Both species crossed fewer gaps in tree cover during riparian corridor treatments than in fencerow or pasture treatments. We conclude that antshrikes, which may be representative of other forest specialists, use forested corridors for movement in this landscape and that fencerows are avoided as movement conduits.animal movement ͉ Campylorhynchus rufinucha ͉ habitat connectivity ͉ hedgerows ͉ Thamnophilus doliatus
Summary1. The ability of animals to move through a landscape is a fundamental determinant of population persistence in fragmented habitats. This movement can be affected by both the composition and configuration of the remaining habitat. To date, few studies have examined the habitat selection of animals moving in novel landscapes or addressed whether animals exhibit a functional response in selection as available habitat changes. 2. To assess habitat selection during movement, we translocated 60 individuals of two species of birds with differing forest dependency in three configuration treatments in a highly fragmented, tropical dry forest landscape: along a forested riparian corridor, along a fencerow (row of live trees) or across pasture. We closely followed the return routes of translocated birds to determine their choice of habitat and proximity to the forest edge. We then tested whether habitat composition or configuration (treatment) best explained individual variation in habitat selection. 3. Both species preferred habitat closer to the forest edge, but this preference was weaker in the forest specialist, the barred antshrike Thamnophilus doliatus. This species selected routes in forest habitat, which included riparian corridors, over fencerow and stepping stone habitat, which were all preferred over pasture habitat. 4. By contrast, the forest generalist, the rufous-naped wren Campylorhynchus rufinucha preferred forest equally to fencerow and stepping stone habitat over pasture habitat. For it, fencerows were selected more strongly than stepping stones. 5. Analysis of the individual variation in selection for forest habitat revealed that both species exhibited a functional response to habitat configuration, selecting forest more strongly in riparian corridor treatments where it was also more abundant. The forest specialist also reduced its preference for edge habitat in riparian corridor treatments. 6. Synthesis and applications. The unprecedented precision of our route information demonstrates the extent to which our forest specialist preferred to travel in forest relative to fencerow and stepping stone habitat. Functional responses to habitat configuration indicated that both species make more use of other habitats when forested corridors are not present. Stepping stones in particular may be important features to the conservation of forest birds in highly fragmented habitats.
Whitebark pine (Pinus albicaulis Engelm.), a keystone species in subalpine ecosystems of western North America, is under threat across its range from white pine blister rust, mountain pine beetle, fire exclusion, and climate change. Loss of whitebark pine is predicted to have cascading effects on many ecosystem services. We remeasured 115 whitebark pine plots in the Canadian Rocky Mountains to determine whether infection and mortality rates from blister rust were changing over time and (or) latitude. Average rust infection of trees among plots increased from 42% in 2003–2004 to 52% in 2009, while mortality increased from 18% to 28%. In eight plots that have been measured three times, infection increased from 43% of live trees in 1996 to 70% in 2003 and 78% in 2009. Mortality increased from 26% to 65% in the same time period. Overall, infection and mortality have increased 3%/year over the 13 years of the study. Incidence of infection and mortality was highest among plots in the southern part of the study area, particularly on the western side of the Continental Divide. The slowing rates of infection and mortality that we found suggest that some level of natural selection may already be occurring in areas with high levels of both.
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