Response to habitat fragmentation

Hi guys,

Im currently looking to test the role of habitat fragmentation in influencing sub-population size and structure of the adder on some of my sites this soming spring. However, when predicting a species response, I have found that I have come to a bit of a cross roads.

According to population genetic theory, small, fragmented populations are at high risk of extinction due to genetic drift and inbreeding potential. I would expect the carrying capacity of patch habitats to become reduced with increased fragmentation, and therefore inndividuals to disperse and colonise sub-optimal habitats. However, is this a justified prediction given that the species is well known for its high degrees of site fidelity?

HELP!!

Thanks for your input Steve. My study sites feature predominantly on a local AONB, where by the majority of the established sub-populations are within SSSI's. so I am lucky in that there is immediate protection from development. So from what I have observed over the past years, is that it is habitat disturbance,manifested from recreational activity and inappropriate habitat management, that are considered the foremost threats here. I am currently working with the local landowners and managing authorities to provide increased security to some of the more vulnerable habitats (e.g. hibernacula and lying out areas. Certainly there is an issue of potential isolation of sub-populations here, but Im still conducting baseline surveys here to map the distribution of spring assemblages for the area.

What is interesting in particular is a small sub-population that became isolated on a single linear remanant fragment following heath burns being implemented on the site in 2004. I have not observed any female activity on this site for over three years, and so I may have a "bachelor" group of males on my hands here. I suspect that many individuals have dispersed and recolonised new areas as the heath has gradually regenerated over the past five years.

Best

Anecdotal observation, I think adder attempt to carry on 'business as usual' in these situations. I have first hand observations of them attempting to cross entirely barren soil scrapes using what limited habitat remained as cover. My gut feeling is that this leads to higher mortality rates and the population crashes. I don't see any evidence of them 'moving' to suitable habitat elsewhere, simply some individuals become more and more sedentary in what existing habitat remains, the others being lost to predation as they attempt to carry on as normal. I have also observed this with spring dispersal and the males setting up surface dens, they continued to utilise the habitat they had tradionally used that remained, even in cases where it was a tiny fragment of what existed before management. Other 'apparently' suitable habitat nearby being ignored.

Be interesting if your studies support my pessimistic view Kevin.