Changes in Mediterranean high mountain Trichoptera communities after a 20-year period

Rivers in Mediterranean high mountains are especially vulnerable to climate change because these areas are characterized by extreme climatic conditions of snowy winters and relatively frequent summer droughts. Climate induced alterations in temperature and the magnitude of high and low river flows are expected to have significant effects on aquatic fauna. Here, we analysed changes in the caddisfly communities of the Sierra Nevada during a 20-year period on an altitudinal gradient range of 952-3050 m. Furthermore, we related these changes to an observed increase in air temperature and decrease in river flow over the last 40 years. Overall, caddisfly species richness increased but patterns varied depending on altitude in a non-linear shape. Richness increased in altitude with maximum values at sites of intermediate-high altitude (1800-2000 m). The effects of the observed climate change may be explained by the colonization of headwaters and middle reaches from mid-lowland species or by those from streams and rivers in nearby mountain chains at lower altitude. The observed richness increase and its association with environmental conditions suggest that mountains with a considerable altitudinal gradient may function as refuges for species and populations during periods of climatic change, which strength the importance of the conservation of mountainous habitat.