Mechanistic insights into landscape genetic structure of two tropical amphibians using field‐derived resistance surfaces

Abstract

Conversion of forests to agriculture often fragments distributions of forest species and can disrupt gene flow. We examined effects of prevalent land uses on genetic connectivity of two amphibian species in northeastern Costa Rica. We incorporated data from field surveys and experiments to develop resistance surfaces that represent local mechanisms hypothesized to modify dispersal success of amphibians, such as habitat-specific predation and desiccation risk. Because time lags can exist between forest conversion and genetic responses, we evaluated landscape effects using land-cover data from different time periods. Populations of both species were structured at similar spatial scales but exhibited differing responses to landscape features. Litter frog population differentiation was significantly related to landscape resistances estimated from abundance and experiment data. Model support was highest for experiment-derived surfaces that represented responses to microclimate variation. Litter frog genetic variation was best explained by contemporary landscape configuration, indicating rapid population response to land-use change. Poison frog genetic structure was strongly associated with geographic isolation, which explained up to 45% of genetic variation, and long-standing barriers, such as rivers and mountains. However, there was also partial support for abundance- and microclimate response-derived resistances. Differences in species responses to landscape features may be explained by overriding effects of population size on patterns of differentiation for poison frogs, but not litter frogs. In addition, pastures are likely semi-permeable to poison frog gene flow because the species is known to use pastures when remnant vegetation is present, but litter frogs do not. Ongoing reforestation efforts will probably increase connectivity in the region by increasing tree cover and reducing area of pastures.

Landscape genetics in a changing world: disentangling historical and contemporary influences and inferring change

“…When found, estimated time lags range from less than a decade (Nowakowski et al . ) to tens of thousands of years (Fant et al . ; Ramirez‐Barahona & Eguiarte ).…”

Surface water network structure, landscape resistance to movement and flooding vital for maintaining ecological connectivity across Australia’s largest river basin

“…Circuit theory has been used extensively in amphibian genetic studies to model how landscape resistance to movement affects gene flow (e.g., Moore et al 2011;Richardson 2012;Peterman et al 2014;Nowakowski et al 2015a). Comparisons of experimentally derived resistance surfaces suggest connectivity estimates based on circuit theory modelling can diverge significantly from Euclidean and least-cost equivalents, particularly in complex landscapes containing many potential paths for movement (Nowakowski et al 2015b).…”

State of the World's Amphibians

“…For example, conversion of forest into open habitat reduced dispersal rates of juvenile amphibians in a temperate forest: Juvenile amphibians moved slower over shorter distances and were recaptured less often in old-field habitats than in the forest (61). In addition to limiting dispersal, higher landscape resistance of open habitats may hinder migration of breeding individuals and the ability to colonize new habitats (62). Comparative landscape genetics is a promising approach to assess the effects of fragmentation and land-use conversion on amphibian populations (63).…”