Wednesday, March 2, 2011

Two Snakes Surviving Agriculture

Agricultural landscapes result from converting natural ecosystems into agroecosystems and contribute to a loss of biodiversity. Species that are habitat specialists may be isolated in patches of  habitat and have reduced gene flow, subsequent loss genetic diversity, and genetic differentiation may occur within the isolated populations. Two recent papers suggest that corridors that connect the populations may keep the populations in contact, allowing genes to move from one group to another.

The Grass Snake (Natrix natrix persa). 
Taken in Ephesus, Greece. Photo Credit: 
Fafner
Barbara Meister and colleagues (2010) examined the genetic structure of the amphibian-eating Grass Snakes (Natrix natrix) in remnants of pristine wetland habitat embedded in an intensively used agricultural landscape in north-western Switzerland. Using seven microsatellite markers they found no genetically distinct grass snake populations in the study area that covered about 90 km2. They hypothesized that their results implies an exchange of individuals between small remnants of original habitat. In fact, they found radio tracked female snakes in agricultural situations while they were moving to egg-laying sites. Thus, gene flow may prevent  genetic differentiation of subpopulations distributed over a relatively large area. Their study area contained canals that could act as corridors for movement despite their concentrations of agricultural chemicals. Their results suggest the Grass Snake can survive in an intensively used agricultural landscape, provided suitable patches of habitat are interconnected.

In a second study Page E. Klug and colleagues looked at genetic differences in Yellow-bellied Racer (Coluber constrictor flaviventris) populations in the highly fragmented tall grass prairies of Kansas. An estimated 4% of the original widespread prairie habitat remains. The study looked at racer populations spread out over 13,500-km of landscape in northeastern Kansas. The racer population had high allelic diversity, high heterozygosity, and was maintaining a migration-drift equilibrium. Racers exhibited restricted dispersal within 3 km, and significant isolation-by- distance occurred on broad regional scales of about 100 km. However, like the Grass Snakes there was sufficient gene flow between locations, and the authors were unable to define discrete subpopulations. In northeastern Kansas, Yellow-bellied Racer appear to be abundant and continuously distributed, suggesting the fragmented landscape is not impeding gene flow.

While these studies suggest the Grass Snake and the Yellow-bellied Racer can continue to survive in fragmented landscapes, other species may not be so lucky.

Literature
Meister, B., U. Hoffer, S. Ursenbacher, B. Baur. 2010. Spatial genetic analysis of the grass snake, Natrix natrix (Squamata: Colubridae), in an intensively used agricultural landscape. Biological Journal of the Linnean Society, 101: 51–58. doi:10.1111/j.1095-8312.2010.01474.x

Klug, P. E.. S. M. Wisely and K. A. With. 2011. Population genetic structure and landscape connectivity of the Eastern Yellowbelly Racer (Coluber constrictor flaviventris) in the contiguous tallgrass prairie of northeastern Kansas, USA. Landscape Ecology 26(2):281-294. DOI: 10.1007/s10980-010-9554-2

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