Ant Diversity and Community Composition in Alpine Tree Line Ecotones
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Department of Botany & Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria
2
Institute for Alpine Environment, Eurac Research, Viale Druso 1, 39100 Bolzano, Italy
3
Department of Ecology, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria
*
Author to whom correspondence should be addressed.
Insects 2021, 12(3), 219; https://doi.org/10.3390/insects12030219
Submission received: 18 September 2020
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Revised: 9 February 2021
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Accepted: 27 February 2021
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Published: 4 March 2021
(This article belongs to the Collection Insects in Mountain Ecosystems)
Simple Summary
Alpine grasslands are among the few terrestrial habitats not obviously dominated by ants. Yet few studies have addressed how ant communities change along tree-line ecotones on mountains. We combined five survey methods to assess ant assemblages along the tree line at five mountains in the south-central Alps of Italy. Ant species richness peaked directly at the tree line, but this was not due to a mixing of forest with grassland species. In subalpine forest and at the tree line, ant assemblages were dominated by mound-building red wood ants. Community composition and functional species traits indicated competition as a potential effect of community assembly in subalpine forest. Further, habitat features such as elevation, dwarf shrub cover, and the extent of a soil humus layer shaped species composition of ant communities around the tree line.
Abstract
Ants are crucial for the functioning of many terrestrial ecosystems, but detailed knowledge of their ecological role is often lacking. This is true for high mountains where a steep environmental gradient exists from mountainous forest, densely populated by ants, to grassland habitats above the tree line, harboring a sparse ant community. We assessed ant communities in and around the tree line ecotone on five slopes in the southern-central Alps, focusing on their species diversity, community composition, and functional dimensions. Species richness and functional diversity were highest directly at the ecotone. Ant community composition was shaped by elevation and shrub cover. Further, the abundance of the dominant mound-building red wood ants (Formica s. str.) influenced the community composition of the subordinate species. We conclude that over the tree line ecotone a shift in predominance from biotic limitations in the forest to abiotic filters in the alpine environment takes place.
