Hormones signal habitat loss

Posted on July 25, 2012

The effects of habitat loss on resident animal species are usually investigated by conducting population surveys to monitor changes in occurrence.  However, population sampling can be very time-consuming, especially when species are rare or retiring.  An alternative monitoring strategy is to focus at the individual rather than the population level, by concentrating on physiological processes that underlie ecological responses.  Two such physiological indicators, namely body condition (an animal’s weight at a given length) and the status of stress hormones have been used by researchers  to explore the effects of landscape fragmentation on common toads (Bufo bufo) in the Rhone-Alps region of south-east France.  Toads were chosen as a study species because amphibians are known to be highly sensitive to habitat loss.  Data were collected on toad occurrence,  the area of forest surrounding a pond, and the number of forest fragments.  Toads from 17 of the 212 ponds were sampled for body condition and the concentration of urinary corticosteroid hormones.  Toad occurrence was well predicted by total forest cover but not by the number of forest fragments.  In comparison, body condition and corticosteroid levels were significantly predicted by both forest cover and forest fragmentation, and these landscape effects were strongest at the lowest spatial scale (within a radius of 500m of the pond).  Habitat loss may increase competition for food and thereby reduce body condition, while habitat fragmentation can increase the costs of migration to high quality sites.  This study suggests that physiological parameters may be more sensitive early warning indicators of future species decline than population occurrence.  

Reference: Janin, A., Lena, J.-P. & Joly, P.  2011.  Beyond occurrence: body condition and stress hormone as integrative indicators of habitat availability and fragmentation in the common toad.   Biological Conservation 144, 1008–1016.