Gene Flow in Complex Landscapes: Testing Multiple Hypotheses with Causal Modeling.

Predicting population-level effects of landscape change depends on identifying factors that influence population connectivity in complex landscapes. However, most putative movement corridors and barriers have not been based on empirical data. In this study, we identify factors that influence connectivity by comparing patterns of genetic similarity among 146 black bears (Ursus americanus), sampled across a 3,000-km2 study area in northern Idaho, with 110 landscape-resistance hypotheses. Genetic similarities were based on the pairwise percentage dissimilarity among all individuals based on nine microsatellite loci (average expected heterozygosityp0.79). Landscape-resistance hypotheses describe a range of potential relationships between movement cost and land cover, slope, elevation, roads, Euclidean distance, and a putative movement barrier. These hypotheses were divided into seven organizational models in which the influences of barriers, distance, and landscape features were statistically separated using partial Mantel tests. Only one of the competing organizational models was fully supported: patterns of genetic structure are primarily related to landscape gradients of land cover and elevation. The alternative landscape models, isolation by barriers and isolation by distance, are not supported. In this black bear population, gene flow is facilitated by contiguous forest cover at middle elevations

Wolverine Gene Flow Across a Narrow Climatic Niche

Wolverines (Guio guio) are one of the rarest carnivores in the contiguous United States. Effective population sizes in Montana, Idaho, and Wyoming, where most of the wolverines in the contiguous United States exist, were calculated to be 35 (credible limits, 28 52) suggesting low abundance. Landscape features that influence wolverine population substructure and gene flow are largely unknown. Recent work has identified strong associations between areas with persistent spring snow and wolverine presence and range. We tested whether a dispersal model in which wolverines prefer to disperse through areas characterized by persistent spring snow cover produced least-cost paths among all individuals that correlated with genetic distance among individuals. Models simulating large preferences for dispersing within areas characterized by persistent spring snow explained the data better than a model based on Euclidean distance. Partial Mantel tests separating Euclidean distance from spring snow-cover-based effects indicated that Euclidean distance was not significant in describing patterns of genetic distance. Because these models indicated that successful dispersal paths followed areas characterized by spring snow cover, we used these understandings to derive empirically based least-cost corridor maps in the U.S. Rocky Mountains. These corridor maps largely explain previously published population subdivision patterns based on mitochondrial DNA and indicate that natural colonization of the southern Rocky Mountains by wolverines will be difficult but not impossible

Invasion of an exotic forb impacts reproductive success and site fidelity of a migratory songbird

Abstract Although exotic plant invasions threaten natural systems worldwide, we know little about the speciWc ecological impacts of invaders, including the magnitude of eVects and underlying mechanisms. Exotic plants are likely to impact higher trophic levels when they overrun native plant communities, aVecting habitat quality for breeding songbirds by altering food availability and/or nest predation levels. We studied chipping sparrows (Spizella passerina) breeding in savannas that were either dominated by native vegetation or invaded by spotted knapweed (Centaurea maculosa), an exotic forb that substantially reduces diversity and abundance of native herbaceous plant species. Chipping sparrows primarily nest in trees but forage on the ground, consuming seeds and arthropods. We found that predation rates did not diVer between nests at knapweed and native sites. However, initiation of Wrst nests was delayed at knapweed versus native sites, an eVect frequently associated with low food availability. Our seasonal fecundity model indicated that breeding delays could translate to diminished fecundity, including dramatic declines in the incidence of double brooding. Site Wdelity of breeding adults was also substantially reduced in knapweed compared to native habitats, as measured by return rates and shifts in territory locations between years. Declines in reproductive success and site Wdelity were greater for yearling versus older birds, and knapweed invasion appeared to exacerbate diVerences between age classes. In addition, grasshoppers, which represent an important prey resource, were substantially reduced in knapweed versus native habitats. Our results strongly suggest that knapweed invasion can impact chipping sparrow populations by reducing food availability. Food chain eVects may be an important mechanism by which strong plant invaders impact songbirds and other consumers

Improving Population Monitoring of Wolverines by Integrating Noninvasive Genetic Monitoring and Remote Camera Trapping

Wolverines (Gulo gulo) are a rare species of conservation concern that inhabit high-elevation montane climates in North America. Because of their remote habitat and rarity, wolverines are difficult to monitor and there is limited information on the population status of wolverines. Scientists are concerned that wolverines may be adversely affected by climate change as they rely on persistent spring snowpack, which increases the need for effective wolverine monitoring. Wolverines in the Bitterroot National Forest (BNF) were monitored for six years (2014-2020) with noninvasive genetic sampling via hair snag and individual identification via remote camera trap, which allowed for the identification of 27 genetically unique wolverines. Identified wolverines were genotyped at 20 microsatellite loci which were analyzed with the software Cervus for genetic relatedness. Potential first-order relationships (parent-offspring or siblings) were identified via exclusion of genetically mismatched candidates, which were used to construct potential family groups and relationships. Individuals detected at more than two locations were fitted with minimum convex polygons estimating their home range extent using the R package adehabitatHR. Potential relationships revealed two distinct subgroups (of 8 and 14 individuals) connected by no potential relationships that correspond to generally different spatial areas. The combination of familial relationships and spatial patterns illustrates the connections between individual wolverines and related groups on the landscape. This research provides important information describing the population status of wolverines in western Montana, which will inform decisions about the conservation of wolverines and provide an improved baseline status for future monitoring. Additionally, integration of genetic and spatial data for wolverines presents a novel approach to monitoring other rare and remote species that may yield a wealth of powerful information about their populations