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Universitat de Barcelona (2022)

Facing global change drivers : how do Mediterranean butterflies respond ?

Ubach Permanyer, Andreu

Titre : Facing global change drivers : how do Mediterranean butterflies respond ?

Auteur : Ubach Permanyer, Andreu

Université de soutenance : Universitat de Barcelona

Grade : Doctoral Tesis 2022

The current context of global change is causing many threats to biodiversity worldwide, and the profound and rapid transformations of the environment have led to a severe insect decline. Because of their sensitivity to landscape and climate agents, butterflies have become an ideal bioindicator group to reveal how global change drivers impact at the local and regional scales. Moreover, butterfly monitoring schemes (BMS) that use a common and standard methodology have spread through most of Europe in recent decades, allowing to record with unprecedented detail year-to-year population changes and species trends. However, many open questions remain about how natural and anthropogenic processes affect butterfly populations and how their responses differ between climatic regions. Here I made use of the Catalan BMS data to explore how natural processes such as weather and vegetation encroachment affect butterfly populations, and how butterfly communities have changed during the last decades as a result of global change. I explored how these responses are mediated through life-history traits, and how do they vary across different climatic regions. I also studied the factors shaping species richness and abundance of plants and herbivorous insects (butterflies and grasshoppers) in the Pyrenees (which harbour most of butterfly diversity in the continent), with a particular interest on the impact of cattle grazing on subalpine grasslands. To do so, I designed an experiment combining grazed control plots with enclosure plots where grazing was excluded. The climatic study identified a general positive effect of spring rainfall on butterfly populations occurring in the Mediterranean region, and of winter rainfall (i.e. snowy winters) in the Alpine region. I also found a strong negative effect of mild winters on butterfly populations. In the second study I developed an index to measure a species preference for closed vs open habitats. I found that the vast majority of the species are strongly associated with open habitats, and describe a widespread pattern of butterfly communities to become dominated by species preferring closed habitats as a result of a general phenomenon of vegetation encroachment. The Pyrenean study quantified the role of both abiotic and biotic factors on plants and herbivorous insects, and provided evidence of the effects of livestock exclusion on ecosystems during a short period of two years. In my last chapter, I unraveled how butterfly assemblages have responded to climatic and habitat drivers by using several ecological indicators. Long term monitoring data indicates how in mountain regions butterfly communities are changing towards more thermophilous and generalist species, but still act as a biodiversity reservoir, as population trends there are not so negative. I conclude that Mediterranean butterflies respond differently across climatic regions, and that a combination of both climatic and landscape factors must be considered to explain butterfly population responses.


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