Common-ToadAssessing the resistance a landscape imposes on movement between habitat fragments is critical for estimating landscape connectivity. While several methods have been used to estimate landscape resistance, many of these methods are time consuming and biased in one way or another. Janin and coworkers recently proposed that physiological parameters, as a proxy for energy cost and risk perception, may provide an unbiased and relatively simple means to estimate the level of resistance an animal experiences while moving through a landscape. Using common toads (Bufo bufo) as study system, the authors compared levels of the stress hormone corticosterone before and after exposure to substrates they may encounter in a natural landscape.

Confirming their predictions, hormone levels in adult frogs was lower in suitable habitat (forest litter), compared to unsuitable matrix habitat (ploughed soil). These results provide support that physiological parameters can be used as a proxy of the resistance an individual may experience while moving through certain habitat types. Interestingly, stress levels in juvenile toads seemed unaffected by substrate, which the authors attributed to either experimental design, differences in sensory perception, or differences in cognitive processes between adults and juveniles (I propose a fourth hypothesis, that there may be a hormonal basis in juvenile frogs’ dispersal drive).

Resources

Janin, A, J-P Lena, S Deblois, and P Joly. 2012. Use of stress-hormone levels and habitat selection to assess functional connectivity of a landscape for an amphibian. Conservation Biology 26:923-931. (E-mail: pierre.joly@niv‐lyon1.fr)

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