Abstract
Natal dispersal outcomes are an interplay between environmental conditions and individual phenotypes. Peripheral, isolated populations may experience altered environmental conditions and natal dispersal patterns that differ from populations in contiguous landscapes. We document nonphilopatric, sex‐biased natal dispersal in an endangered small mammal, the Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis), restricted to a single mountain. Other North American red squirrel populations are shown to have sex‐unbiased, philopatric natal dispersal. We ask what environmental and intrinsic factors may be driving this atypical natal dispersal pattern. We test for the influence of proximate factors and ultimate drivers of natal dispersal: habitat fragmentation, local population density, individual behavior traits, inbreeding avoidance, competition for mates, and competition for resources, allowing us to better understand altered natal dispersal patterns at the periphery of a species’ range. A juvenile squirrel's body condition and its mother's mass in spring (a reflection of her intrinsic quality and territory quality) contribute to individual behavioral tendencies for movement and exploration. Resources, behavior, and body condition have the strongest influence on natal dispersal distance, but affect males and females differently. Male natal dispersal distance is positively influenced by its mother's spring body mass and individual tendency for movement; female natal dispersal distance is negatively influenced by its mother's spring body mass and positively influenced by individual tendency for movement. An apparent feedback between environmental variables and subsequent juvenile behavioral state contributes to an altered natal dispersal pattern in a peripheral population, highlighting the importance of studying ecological processes at the both range center and periphery of species’ distributions.
Highlights
Natal dispersal is a key process promoting gene flow, population viability, and species persistence in the face of rapid environmental change (Dieckmann, O’Hara, & Weisser, 1999; Gaines & McClenaghan, 1980)
Dispersal outcomes are the product of interplay between extrinsic and intrinsic proximate factors (Clobert, Le Galliard, Cote, Meylan, & Massot, 2009), including site-specific variation in density and conspecific sex ratios (Gaines & McClenaghan, 1980; Matthysen, 2005), availability and predictability of resources (Bowler & Benton, 2005; Le Galliard, Rémy, Ims, & Lambin, 2012), landscape patchiness (Matthysen, Adriaensen, & Dhondt, 1995), and phenotypic differences such as body size and condition (Debeffe et al, 2012), and systematic interindividual behavior differences, or personalities (Bowler & Benton, 2005; Cote, Clobert, Brodin, Fogarty, & Sih, 2010; Debeffe et al, 2013; Dingemanse, Both, Van Noordwijk, Rutten, & Drent, 2003; Duckworth, 2008), that may vary among populations
We examine the relationship between natal patch size and distance to the nearest patch and the probability of dispersing and dispersal distance
Summary
Natal dispersal is a key process promoting gene flow, population viability, and species persistence in the face of rapid environmental change (Dieckmann, O’Hara, & Weisser, 1999; Gaines & McClenaghan, 1980). We examine the influence of intrinsic and extrinsic factors on natal dispersal distance and the probability of nonphilopatric dispersal to include local population parameters (local male and female density), litter sex ratios, mother spring body mass, juvenile body condition, natal habitat patch size, and individual behavior traits.
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