Posted on February 3rd, 2015

Back to School – Snakes on the Plains

Researchers from Spain and Portugal conducted a study that looked at the role of environmental factors in impacting viper habitat and distribution along the Ebro River in northern Spain. The study hoped to create a better understanding of how spatial displacement of species affected genetic development. The species under examination were all geographically isolated from one another which leads to the potential for reproductive isolation and thus an increase in certain deleterious biological traits. The three species studied were Iberian vipers: the Pelias (Vipera berus, V. seoanai), native to northern Europe; the V. aspis (including V. latasei), primarily located in the Italian peninsula, southern France and the northeastern Iberian peninsula; and V. ammodytes, most common in the Balkan region. Northern Ebro is the only place where all three species intermingle.

species_presencePresence record of the three species studied here in the high Ebro River region of Spain.
forecastingConsensus forecasting area of half of the study population and areas of probable sympatry.

The study area is comprised of plateaus excavated by the flow of the Ebro River and its tributaries, Rudrón and Panero. The climate is humid and typical of that associated with the Mediterranean region. Altitudes range from 600 to 1200 meters, making it a mountainous habitat. Records of vipers and their movement and displacement were kept over a three year period, and all specimens were captured by hand. The spatial behavior and activity patterns were a challenge for data collection, as the vipers live in a small range and are only active for a very short period of time. In addition, they commonly stay in heavily vegetated areas, making them hard to locate.

The researchers used Maximum Entropy to collect their data. This process relies on machine-learning methods of presence-only occurrence data. Maximum Entropy was selected because research that characterizes unknown events must rely on the most accurate and uniform distribution analysis. Using the MaxEnt model, the authors found that V. aspis distribution is related to altitude, slope, precipitation and land cover; V. latstei is reliant upon slope, precipitation and maximum temperature; and V. seoanei distribution is related to altitude, slope, precipitation and minimum temperature.

The researchers found that ecological niche-based models developed in a specific spatial context were beneficial to a greater understanding of species displacement and critical habitat for reproduction. While all related, each viper species under consideration needed specific environmental and climatic conditions to thrive. This study was beneficial to learning more about sympatric species (i.e. two or more species that exist in the same geographic area) and the hybrid zones that allow for multiple species to coexist and repopulate. The use of GIS technology was particularly useful in mapping contact zones and how they are impacted by climate change, urban sprawl and predator/prey relationships. The authors plan to continue their study to better evaluate conservation needs for future species success.

Justin Harmon
Staff Writer

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