Unpredictable responses of garden snail (Helix aspersa) populations to climate change

We studied the impact of climate change on the population dynamics of the garden snail (Helix aspersa) in the Ecotron controlled environment facility. The experimental series ran for three plant generations, allowing the snails to reproduce. We investigated the isolated and combined effects of elevated CO2 (current + 200 mu mol mol(-1)) and warming (current + 2 degreesC) in three consecutive runs (CO2, Temperature and Combined). In the CO2 Run, the number of juvenile snails recorded at the end of the experiment did not differ between ambient and elevated CO2, whereas in the Temperature Run, fewer juveniles were found at elevated temperatures. An opposite response was observed in the Combined Run, where significantly more juveniles were found in elevated temperature and CO2 compared to elevated CO2 on its own. Within each run, juvenile emergence was not affected by treatments but juvenile presence was first observed about 70 days earlier in the Combined Run than in the Temperature Run. The differences in snail performance in the different runs were not correlated with differences in community structure or leaf quality measured as C:N ratios and neither with the abundance of the most preferred host plant species, Cardamine hirsuta. ne abundance of this species, however, was significantly altered in all runs. The results illustrate clearly the degree of difficulty in making predictable generalisations about the consequences of climate change for certain species. [KEYWORDS: behaviour; Ecotron; elevated CO2; temperature; herbivory; mollusc Elevated atmospheric co2; terrestrial ecosystems; herbivore interactions; calcareous grassland; insect performance; model ecosystem; plant-responses; carbon-dioxide; temperature; phytochemistry