Birds in space and time: genetic changes accompanying anthropogenic habitat fragmentation in the endangered black-capped vireo (Vireo atricapilla)

Abstract

Anthropogenic alterations in the natural environment can be a potent evolutionary force. For species that have specific habitat requirements, habitat loss can result in substantial genetic effects, potentially impeding future adaptability and evolution. The endangered black-capped vireo (Vireo atricapilla) suffered a substantial contraction of breeding habitat and population size during much of the 20th century. In a previous study, we reported significant differentiation between remnant populations, but failed to recover a strong genetic signal of bottlenecks. In this study, we used a combination of historical and contemporary sampling from Oklahoma and Texas to (i) determine whether population structure and genetic diversity have changed over time and (ii) evaluate alternate demographic hypotheses using approximate Bayesian computation (ABC). We found lower genetic diversity and increased differentiation in contemporary samples compared to historical samples, indicating nontrivial impacts of fragmentation. ABC analysis suggests a bottleneck having occurred in the early part of the 20th century, resulting in a magnitude decline in effective population size. Genetic monitoring with temporally spaced samples, such as used in this study, can be highly informative for assessing the genetic impacts of anthropogenic fragmentation on threatened or endangered species, as well as revealing the dynamics of small populations over time.

Keywords: anthropogenic fragmentation; bottlenecks; evolutionary dynamics; fragmentation; genetic differentiation; genetic diversity.

Figure 1

A map showing the distribution of breeding habitats of the black-capped vireo in central Texas and south-central Oklahoma. The shaded regions denote the historical breeding range of the species, but the current breeding range is considerably limited (not depicted). Filled ovals represent sites where we have both historical and contemporary samples.

Figure 2

(A) Posterior probabilities of 11 evaluated scenarios, showing that scenario 8, requiring a decline in population size from 5000 to a lesser value (200–1000), was the best supported over a 110 000 closest data sets. (B) Posterior probability for the estimated parameter N8, which as estimated as 450 (95% CI, 320–821). (C) Posterior probability of an event t generations ago when bottleneck occurred (x-axis, generations 10–90). t was estimated to as 67 (95% CI, 36–81) generations before present.