Water temperature stability modulates insect thermal responses at spring fens

Thermal responses of spring insects are poorly understood, yet critically important because temperature regimes of spring habitats can be modified by climate warming. Here, we examined the species-specific responses of aquatic insects to variation in water temperature at 43 undamaged spring fens. Temperature was recorded for 1 year using dataloggers and used to model the abundance of taxa representing spring habitat specialists and generalists, as well as traits indicative of species sensitivity to climate change. Sites differed significantly in thermal conditions, forming a gradient that was largely independent of other principal environmental gradients in the spring fens. Significant responses to temperature parameters were found for 25 of the 56 taxa analysed, showing two types of species associations, with stable or variable thermal conditions. The species significantly responding to temperature variables by an increase or decrease in their abundance were primarily spring specialists, often associated with thermally stable sites with higher winter temperatures. The number of climate-sensitive traits within the insect assemblage was also higher at these sites. Thus, any reduction of water temperature stability may negatively affect many spring specialists and species vulnerable to climate changes. Our results highlight the importance of thermal conditions, particularly temperature stability, for spring insects.