Effects of elevation and microclimatic temperatures on butterfly-flower interaction networks in a Mediterranean mountain range

Researching the properties of mutualistic networks over environmental gradients is a promising but underexplored means to test how global change can affect ecosystem assembly and functioning. We examined how elevation and microclimate influenced butterfly-flower interaction networks at the hottest time of year in a Mediterranean mountain range.

Throughout July 2023, we recorded weekly butterfly-flower interaction networks from 36 transects in nine sites, across an 800 m elevation gradient in the Sierra de Guadarrama (Central Spain). We quantified the connectance, nestedness, modularity and robustness to species loss of networks, and related these descriptors using Generalized Additive Mixed Models to elevation, microclimate temperature (modelled using Microclima), date and time of day.

The networks were dominated at all sites by one or two abundant butterfly and flower species, but these varied with elevation. Butterfly networks were more robust to plant species loss at higher elevations, where communities showed increased linkage density. Butterfly-plant networks became less nested at higher microclimatic temperatures in July. Network properties also varied through the day, with connectance decreasing markedly from morning to afternoon.

In the Mediterranean mountains studied, summer butterfly-flower interaction networks were more resilient to disturbance at high elevations and in cooler microclimates. Nectar availability could become an important limiting factor for insects in a warming climate, and understanding the mechanisms influencing the properties of flower visitor networks is therefore likely to become increasingly important for adapting the conservation of insects to climate change.