Among- and within-patch components of genetic diversity respond at different rates to habitat fragmentation: an empirical demonstration

Abstract

Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulations and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetic data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in populations of an alpine meadow-dwelling butterfly, which have become fragmented by increasing forest cover over five decades. We show that genetic differentiation among subpopulations (G ST ) is most highly correlated with contemporary forest cover, while genetic diversity within subpopulations (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulations can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.

Contemporary and historic factors influence differently genetic differentiation and diversity in a tropical palm

“…Others studies also show correlation between genetic differentiation and contemporary landscape features, and between genetic diversity and historical factors (i.e. Keyghobadi et al, 2005a). Matrix resistance was the most important factor explaining variation in AR and genetic differentiation (AR and F ST , G ST ' and Jost' D).…”

“…The different pattern in the effect of landscape features may be because of a higher temporal lag in genetic diversity and inbreeding in comparison with AR (Keyghobadi et al, 2005a). AR tends to respond faster than genetic diversity, because of the loss of rare alleles due to marked reduction in habitat (Young et al, 1996;Keyghobadi et al, 2005a).…”

“…This approach, however, does not provide direct insights into the factors affecting genetic variability (Storfer et al, 2010). One effective way to address the impact of habitat loss and fragmentation on genetic variability and differentiation at the landscape scale is comparing multiple landscapes while taking into account the influence of landscape structure (Keyghobadi et al, 2005a;Storfer et al, 2010). This approach is particularly important in human-modified landscapes with high levels of biodiversity, such as the Atlantic forest in Brazil (Ribeiro et al, 2009).…”

“…Although studies emphasize the effects of habitat loss and fragmentation on genetic variability, most of them compare patterns across sites or only focus on a given landscape (Keyghobadi et al, 2005a;Balkenhol et al, 2013). This approach, however, does not provide direct insights into the factors affecting genetic variability (Storfer et al, 2010).…”

Encroaching forests decouple alpine butterfly population dynamics

“…1), has demonstrated that movement (7)(8)(9) and gene flow (10,11) are severely limited by encroaching forests. These butterflies are restricted to open alpine meadows in the Rocky Mountains where their larval host plant, lance-leaved stonecrop, Sedum lanceolatum, and adult nectar resources are present (12).…”