Proximate Cues and Ultimate Consequences for Natal Dispersal and Settlement in an Altered Forest Landscape: Influence of Experience, Behavior, and Habitat

Abstract

Natal dispersal is at the nexus of ecology, ethology, population genetics, and evolution. While abundant research exists on emigration and associated proximate and ultimate causes, less is known about exploration, settlement, and factors that influence settlement decisions. Further, the role of individual behavioral phenotypes in the domains of wildlife ecology and conservation, which include natal dispersal, is a recent and expanding area of inquiry. Understanding the relationships among individual phenotype, environmental conditions, and natal dispersal is increasingly important as landscapes become altered by disturbance, fragmentation, and climate change. I investigated natal dispersal in endangered Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis), an isolated, peripheral subspecies of North American red squirrel persisting at the southern edge of the species' range. We tested hypotheses about the importance of proximate and ultimate drivers of emigration, dispersal distance, and settlement, and estimated perceived landscape connectivity within a mosaic of forest damage in the Pinaleño Mountains, Arizona. Compared to other red squirrel populations in North America, natal dispersal in Mt. Graham red squirrels is sex-biased and non-philopatric with mean dispersal distance over 8 times that observed in non-peripheral populations. Resources, indicated by mother's body mass in spring (a reflection of her intrinsic quality and territory quality) and individual body condition, contribute to individual behavioral tendencies for movement and exploration. Individuals with behavioral tendencies for movement and exploration dispersed the farthest, and for both males and females the longest observed dispersal distances and proportion of individuals dispersing occurred in a year of lowest food availability. Our research highlights the important role individual behavioral syndromes may play in observed heterogeneity in life history strategies with populations. Following emigration from the natal area, we provide evidence that individual dispersers rely upon forest structural cues similar to their natal area to select locations for settlement; the first test of natal habitat preference induction in a single vegetation community type. We used circuit theory to evaluate landscape connectivity and identify areas important for long-distance dispersal movements. Because single connectivity models may not adequately represent functional connectivity for an entire population, we summarized landscape connectivity across varying levels of landscape resistance to identify areas that promote movement and long-distance dispersal for individuals with different perceptions of landscape resistance. We show that composite connectivity models are a useful method to identify forest areas important for the promotion of long-distance movements as well as areas that constrain movement.