Simple life-history traits explain key effective population size ratios across diverse taxa

Abstract

Effective population size (N e ) controls both the rate of random genetic drift and the effectiveness of selection and migration, but it is difficult to estimate in nature. In particular, for species with overlapping generations, it is easier to estimate the effective number of breeders in one reproductive cycle (N b ) than N e per generation. We empirically evaluated the relationship between life history and ratios of N e , N b and adult census size (N) using a recently developed model (AGENE) and published vital rates for 63 iteroparous animals and plants. N b /N e varied a surprising sixfold across species and, contrary to expectations, N b was larger than N e in over half the species. Up to two-thirds of the variance in N b /N e and up to half the variance in N e /N was explained by just two life-history traits (age at maturity and adult lifespan) that have long interested both ecologists and evolutionary biologists. These results provide novel insights into, and demonstrate a close general linkage between, demographic and evolutionary processes across diverse taxa. For the first time, our results also make it possible to interpret rapidly accumulating estimates of N b in the context of the rich body of evolutionary theory based on N e per generation.

Life-history traits and effective population size in species with overlapping generations revisited: the importance of adult mortality

“…Here we assume that the time steps are years, but periods such as days, weeks or months can also be used and might be appropriate for some species (see Waples et al, 2013 for examples of each). Following Felsenstein (1971) and Hill (1972), the underlying model used here assumes that population size is constant, age structure is stable and probabilities of survival and reproduction are independent across time.…”

Effective number of breeders, effective population size and their relationship with census size in an iteroparous species,Salvelinus fontinalis

“…However, this estimation has recently been shown to be problematic if applied to iteroparous species, with estimates ofN b sometimes exceeding N e [9]. Fortunately, the actual ratio ofN e tô N b can be predicted if several simple life-history traits are known: age at maturation, adult lifespan (AL) or number of reproductive cycles and variance among breeders in reproductive success [9,10] (and see [6]). Using the empirical quantitative relationships described by Waples et al [10], it is now possible to obtain unbiased estimates of N b or N e for iteroparous species from single cohort estimates of N b based on LD.…”

“…GenerationalN e has traditionally been approximated as the productN b  G (G: generation length) [7,8]. However, this estimation has recently been shown to be problematic if applied to iteroparous species, with estimates ofN b sometimes exceeding N e [9]. Fortunately, the actual ratio ofN e tô N b can be predicted if several simple life-history traits are known: age at maturation, adult lifespan (AL) or number of reproductive cycles and variance among breeders in reproductive success [9,10] (and see [6]).…”

Population size, habitat fragmentation, and the nature of adaptive variation in a stream fish

“…Notably, previous work found no consistent difference in the characteristics of habitat fragments that small and large populations occupied, but rather more divergent habitat characteristics and greater spatial habitat variability among small populations [7]. Importantly, both the adult census population size (N) and the effective number of breeders (N b ) were considered in our analyses, the latter being an analogue of effective population size (N e ) but for a single breeding event [18]. Although some research has assumed a correspondence between N and N b [5], N b /N ratios can vary widely among populations of closely related species (e.g.…”