Abstract
Adults sometimes disperse, while philopatric offspring inherit the natal site, a pattern known as bequeathal. Despite a decades‐old empirical literature, little theoretical work has explored when natural selection may favor bequeathal. We present a simple mathematical model of the evolution of bequeathal in a stable environment, under both global and local dispersal. We find that natural selection favors bequeathal when adults are competitively advantaged over juveniles, baseline mortality is high, the environment is unsaturated, and when juveniles experience high dispersal mortality. However, frequently bequeathal may not evolve, because the fitness cost for the adult is too large relative to inclusive fitness benefits. Additionally, there are many situations for which bequeathal is an ESS, yet cannot invade the population. As bequeathal in real populations appears to be facultative, yet‐to‐be‐modeled factors like timing of birth in the breeding season may strongly influence the patterns seen in natural populations.
Highlights
In this paper, we develop the first evolutionary models of bequeathal
Bequeathal is a type of breeding dispersal, which occurs when a par‐ ent disperses to a new site, leaving a philopatric offspring to inherit the natal site and its resources
We know bequeathal occurs in na‐ ture from field studies of four mammal species: Columbian ground squirrels, Urocitellus columbianus (Harris & Murie, 1984); kangaroo rats, Dipodomys spectabilis (Jones, 1986); red squirrels, Tamiasciurus hudsonicus (Berteaux & Boutin, 2000; Price & Boutin, 1993); and woodrats, Neotoma macrotis (Cunningham, 2005; Linsdale & Tevis, 1951)
Summary
We develop the first evolutionary models of bequeathal. Bequeathal is a type of breeding dispersal, which occurs when a par‐ ent disperses to a new site, leaving a philopatric offspring to inherit the natal site and its resources. Our model considers parent– offspring conflict, competition for territories, local and global dispersal, and survival rates of adults and juveniles with overlapping generations. It is not easy to specify the distribution of immigrants for any population frequency of Bequeath, p, because local dispersal generates spatial correlations in genotypes—the population residency rate R will not tell us the relevant residency probability at every locale It is possible, to completely define the model for in‐ vading B and invading S, that is, for p ≈ 0 and p ≈ 1. Constraining p ∊ {0, 1}, the distribution of immigrants is defined by a simple binomial process, as each neighboring site con‐ tributes an immigrant half of the time (it can go in either direction), discounted by the probabilities of residency R and dispersal survival dA and dJ. The Mathematica notebook in the Supplemental contains all of these expressions and computes fitness differences from them
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