Eastern Indigo Snake – Ben Stegenga

One of the key concepts in conservation biology is landscape connectivity. In other words, how easy is it for animals to move between discrete habitat patches and what are the features that either impede or facilitate movement? Connectivity is often thought about in terms of linking protected areas in an increasingly human-dominated landscape, but the same processes also play out in natural landscapes. For example, a certain habitat type may expose an animal to greater predation risk, decreasing the connectivity between the habitat patches that it separates. Ultimately, connectivity can impact a wide variety of processes that occur over both short and long time periods. Frequent movements of an animal within it’s home range may have different ecological consequences than rare dispersal movements made by only a few individuals within a population.

A recent paper published by Orianne Society scientist Javan Bauder and CEO Chris Jenkins (along with other co-authors) in the journal Molecular Ecology examines how landscape features impact genetic connectivity in a Florida population of Eastern Indigo Snakes. The paper, titled Multiscale assessment of functional connectivity: Landscape genetics of eastern indigo snakes in an anthropogenically fragmented landscape in central Florida, used 102 indigo snake genetics samples from the southern Lake Wales Ridge to answer several questions about landscape connectivity from a genetic perspective. This region of Florida is broadly important for indigo snake conservation but has lost between 78–85% of its native vegetation cover to a rapidly changing landscape. Thus, it is important to understand how this landscape change has impacted genetic connectivity and identify whether there are pressing issues that need to be addressed.

To examine genetic connectivity, the authors used an approach that creates a resistance surface for the study area based on the genetic samples and a host of variables that describe the landscape. When examined at multiple spatial scales, this technique can provide insights on the types of ecological processes that are having the biggest impact on connectivity. The results of this study indicate that urban areas have a high resistance to indigo snake movement but that some natural habitat types, including open water and some wetlands, also have high resistance values. Similarly, there was a strong negative correlation between undeveloped upland habitat and resistance, indicating that this type of habitat allows indigo snakes the easiest path across the landscape. The paper’s results also strongly indicated that considering multiple spatial scales is important for this type of study to be successful. Furthermore, including variables other than just landcover (i.e., metrics describing vegetation cover) also improved the modeling results. For indigo snakes in this region of Florida (and likely elsewhere in the range), landscape resistance to gene flow was best estimated at broad spatial scales, potentially because gene flow is a process that occurs over multiple generations and must incorporate dispersal movements in addition to individual-level home range movements.

The best landscape resistance surface for indigo snakes in central Florida – Javan Bauder

So, what does all this tell us about indigo snake conservation? First, as multiple studies have indicated, indigo snakes need large areas of undeveloped upland habitats to be able to effectively move across the landscape. Second, roads did not act as strong barriers to indigo snake movements in this study area, suggesting that at least some individuals are able to consistently cross roads (perhaps by traveling through culverts or under bridges). Importantly, even though roads may not be negatively impacting genetic connectivity, they could still impact demographic connectivity by limiting the number of individuals that can successfully move between patches. Finally, the authors suggest caution when transferring these results to other parts of the indigo snake’s range, especially in southern Georgia where movement characteristics are different from those in Florida.

The full publication is available here.

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