The effect of environmental variables on amphibian breeding phenology

Grant, Rachel Anne (2012). The effect of environmental variables on amphibian breeding phenology. PhD thesis The Open University.



Amphibian breeding phenology has generally been associated with temperature and rainfall, but these variables are not able to explain all of the variation in the timing of amphibian migrations, mating and spawning. This thesis examines some additional, previously under-acknowledged geophysical variables that may affect amphibian breeding phenology: lunar phase and the K-index of geomagnetic activity. A serendipitous observation of a large earthquake during the amphibian breeding season enabled a rare record of animal behaviour prior to an earthquake and led to an investigation into the effect of seismicity on amphibians. Data were collected on breeding migrations at three sites in the UK and Italy for frogs (Rana temporaria) and toads (Bufo bufo). Additional data were collated from published literature. Data on the arrivals of two newt species (Triturus cristatus and Lissotriton helveticus) were also analysed. Lunar phase was found to be important in Rana temporaria and Bufo bufo, with more individuals migrating, in amplexus and spawning around the full moon. Newts' response to the full moon was less clear. A meta-analysis of published data revealed that the effect of the lunar cycle on amphibians may be more prevalent than previously supposed and is species-specific, depending on the unique ecology of each species. The effects of the K- index on amphibian reproduction are unclear because of the low number of days when geomagnetism was high. Five days before a large earthquake in L'Aquila, Italy the majority of toads left the breeding site, only re- appearing when the earthquake was over. Numbers of toads were significantly correlated with days since the earthquake but not with weather variables. Finally I attempted to use the variables of interest (two measures of moon phase, plus the K-index of magnetic activity), along with weather variables to construct statistical models of amphibian breeding phenology and to predict arrivals and spawning / amplexus in single years based on the models. This met with variable success; there was a high variability between years in the ability of the models to predict breeding phenology, which could be due to site-specific factors, unmeasured environmental variables, or an endogenous component to breeding phenology.

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