When are genetic methods useful for estimating contemporary abundance and detecting population trends?

Abstract

The utility of microsatellite markers for inferring population size and trend has not been rigorously examined, even though these markers are commonly used to monitor the demography of natural populations. We assessed the ability of a linkage disequilibrium estimator of effective population size (N e ) and a simple capture-recapture estimator of abundance (N) to quantify the size and trend of stable or declining populations (true N = 100-10,000), using simulated Wright-Fisher populations. Neither method accurately or precisely estimated abundance at sample sizes of S = 30 individuals, regardless of true N. However, if larger samples of S = 60 or 120 individuals were collected, these methods provided useful insights into abundance and trends for populations of N = 100-500. At small population sizes (N = 100 or 250), precision of the N e estimates was improved slightly more by a doubling of loci sampled than by a doubling of individuals sampled. In general, monitoring N e proved a more robust means of identifying stable and declining populations than monitoring N over most of the parameter space we explored, and performance of the N e estimator is further enhanced if the N e ⁄ N ratio is low. However, at the largest population size (N = 10,000), N estimation outperformed N e . Both methods generally required ‡ 5 generations to pass between sampling events to correctly identify population trend.

Estimation of effective population size in continuously distributed populations: there goes the neighborhood

“…Precision also can be limiting for practical application; fortunately, considerable empirical information regarding precision of the LD method based on realistic samples of individuals, loci and alleles is available (England et al, 2010;Tallmon et al, 2010;Waples and Do, 2010;Antao et al, 2011;Waples and England, 2011). Results of these evaluations can be summarized as follows: (1) As is the case for all methods that estimate contemporary effective size, precision is inversely related to true N e ; (2) When N e is small (oB100), the drift signal is strong and precision can be high with amounts of data readily available from most field studies; (3) If N e is large (4500-1000), precise estimates generally cannot be achieved without large sample sizes and large numbers of genetic markers; (4) The distributions ofN e andN b can be highly skewed toward large values, so the harmonic mean is the best measure of central tendency.…”

The relationship between abundance and genetic effective population size in elasmobranchs: an example from the globally threatened zebra shark Stegostoma fasciatum within its protected range

“…Palstra and Ruzzante (2008) proposed sampling at least 10 % of the N e to achieve finite point estimates of N e with the temporal method. Simulation studies by Tallmon et al (2010) demonstrated that for small populations (N c * 100-250) samples sizes of 60 (equates to *24-60 % of N c ) with 15 loci resulted in precise N e estimates. For larger populations (N c * 500), samples sizes needed to be increased to *120 (equates to *24 % of N c ).…”

Temporal genetic and demographic monitoring of pond-breeding amphibians in three contrasting population systems

“…Conventional capture-recapture methods are often time and resource intensive, whereas genetic markers can provide insights into population processes with less intense sampling (Schwartz et al 2007;Tallmon et al 2010;Devillard et al 2011). By genetically monitoring populations over time it may be possible to gauge extinction risk and identify management needs (sensu Schwartz et al 2007).…”