Changes in genetic diversity and differentiation in Red‐cockaded woodpeckers (Dryobates borealis) over the past century

Abstract

Red‐cockaded woodpeckers (RCW; Dryobates borealis ) declined after human activities reduced their fire‐maintained pine ecosystem to <3% of its historical range in the southeastern United States and degraded remaining habitat. An estimated 1.6 million RCW cooperative breeding groups declined to about 3,500 groups with no more than 10,000 birds by 1978. Management has increased RCW population abundances since they were at their lowest in the 1990s. However, no range‐wide study has been undertaken since then to investigate the impacts of this massive bottleneck or infer the effects of conservation management and recent demographic recoveries. We used mitochondrial DNA sequences (mtDNA) and nine nuclear microsatellite loci to determine if range‐wide demographic declines resulted in changes to genetic structure and diversity in RCW by comparing samples collected before 1970 (mtDNA data only), between 1992 and 1995 (mtDNA and microsatellites), and between 2010 and 2014 (mtDNA and microsatellites). We show that genetic diversity has been lost as detected by a reduction in the number of mitochondrial haplotypes. This reduction was apparent in comparisons of pre‐1970 mtDNA data with data from the 1992–1995 and 2010–2014 time points, with no change between the latter two time points in mtDNA and microsatellite analyses. The mtDNA data also revealed increases in range‐wide genetic differentiation, with a genetically panmictic population present throughout the southeastern United States in the pre‐1970s data and subsequent development of genetic structure that has remained unchanged since the 1990s. Genetic structure was also uncovered with the microsatellite data, which like the mtDNA data showed little change between the 1992–1995 and 2010–2014 data sets. Temporal haplotype networks revealed a consistent, star‐like phylogeny, suggesting that despite the overall loss of haplotypes, no phylogenetically distinct mtDNA lineages were lost when the population declined. Our results may suggest that management during the last two decades has prevented additional losses of genetic diversity.

Neighboring group density is more important than forest stand age to a threatened social woodpecker population

“…RCW populations continued to decline through the 1980s, but increased to more than 5500 group territories and >14 000 birds by the early 2000s (USFWS 2003). Populations across the species' range have remained stable or continued to increase, with range-wide population size recently estimated at more than 7800 group territories (Miller et al 2019). As a social species, increases in group density that contribute to population recovery result in increasing group size trends over the long-term due to improved demographic connectivity Mikusinski 1998, Schiegg et al 2006).…”

Contrasting genetic responses to habitat fragmentation for two Lycaenid butterfly species

“…Other studies found a decreasing genetic diversity and increasing genetic differentiation, e.g. in plants (Finger et al, 2012), mammals (Miller & Waits, 2003), birds (Miller et al, 2019), and insects (Gauthier et al, 2020;Harper et al, 2006;Nakahama & Isagi, 2018). Most of the above-mentioned studies investigated relatively long time periods of 25 years or longer (e.g.…”