Abstract
AbstractUnderstanding the effects of landscape modification on gene flow of fauna is central to informing conservation strategies that promote functional landscape connectivity and population persistence. We explored the effects of large‐scale habitat loss and fragmentation on spatial and temporal patterns of gene flow in a threatened Australian woodland bird: the Grey‐crowned Babbler Pomatostomus temporalis. Using microsatellite data, we (1) investigated historical (i.e., pre‐fragmentation) and contemporary (i.e., post‐fragmentation) levels of gene flow among subpopulations and/or regions, (2) identified first‐generation migrants and likely dispersal events, (3) tested for signatures of genetic bottlenecks, (4) estimated contemporary and historical effective population sizes, and (5) explored the relative influences of drift and migration in shaping contemporary population structure. Results indicated that the functional connectivity of landscapes used by the Grey‐crowned Babbler is severely compromised in the study area. The proportion of individuals that were recent immigrants among all subpopulations were low. Habitat fragmentation has led to a clear division between subpopulations in the east and west, and the patterns of gene flow exchange between these two regions have changed over time. The effective population size estimates for these two regions are now well below that required for long‐term population viability (Ne < 100). Demographic history models indicate that genetic drift was a greater influence on subpopulations than gene flow, and most subpopulations show signatures of bottlenecks. Translocations to promote gene flow and boost genetic diversity in the short term and targeted habitat restoration to improve landscape functional connectivity in the long term represent promising conservation management strategies that will likely have benefits for many other woodland bird species.
Highlights
Habitat loss and fragmentation have a substantial influence on the structure and viability of animal populations (Hanski et al 1995, Villard et al 1999, Ortego et al 2015)
Differences in gene flow patterns over time that were observed here suggest that these regions are or are becoming, isolated, and are consistent with a loss of functional connectivity resulting from large-scale habitat loss and fragmentation since the mid-1800s in this area (Fig. 1, Table 3)
Given a lack of functional landscape connectivity is a likely driver in this threatening process, there is potential to reverse this decline in gene flow
Summary
Habitat loss and fragmentation have a substantial influence on the structure and viability of animal populations (Hanski et al 1995, Villard et al 1999, Ortego et al 2015). Landscape-scale anthropogenic habitat modification can fragment populations into small, isolated subunits that are at an increased risk of local patch extinction (Hanski 1998, Saccheri et al 1998, Fuhlendorf et al 2002, Banks et al 2005). Small populations lose genetic diversity through random genetic drift, leaving them vulnerable to the negative effects of inbreeding and reducing their capacity to adapt to environmental change (Saccheri et al 1998, O’Grady et al 2006, Pavlacky et al 2012). Reduced fitness as a result of inbreeding can have negative implications for a species’ reproductive rate, population size, and likelihood of long-term population persistence (Keller 1998). Population sizes when Ne > 100 should limit loss of fitness over five generations to ≤10%, it is widely accepted that much larger population sizes (e.g., Ne > 1000) are required to maintain a population’s ability to adapt to environmental change (Jamieson and Allendorf 2012, Frankham et al 2014)
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