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Universidad de Buenos Aires (2014)

Interacciones tróficas entre dos especies simpátricas de hormigas cortadoras y el ensamble de plantas en el Monte central

Nobua Behrmann, Beatriz E.

Titre : Interacciones tróficas entre dos especies simpátricas de hormigas cortadoras y el ensamble de plantas en el Monte central

Interactions among two sympatric species of leaf-cutter ant and the plant assemblage in the Monte Desert

Auteur : Nobua Behrmann, Beatriz E.

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor de la Universidad de Buenos Aires en el área de Ciencias Biológicas 2014

Résumé
Though water availability is considered the main factor regulating desert plant communities, interactions with herbivores may also play an important role in arid ecosystems. Herbivore’s guild in the Neotropics is characterized by the absence of big ungulates, and the presence of leafcutter ants. These ants interact in diverse ways with the plant community, generating changes in its dynamics and composition. The goal of this work was to analyze the reciprocal effects among plants and leaf-cutter ants in the central portion of the Monte desert, and particularly the possible consequences of ants’ activity on the structure and dynamics of desert plant communities. To do so, I studied different aspects of Acromyrmex lobicornis and Acromyrmex striatus’ trophic ecology. Both ant species actively forage from spring to autumn, but A. lobicornis is mostly noctunal, while A. striatus is exclusively diurnal. In general, A. lobicornis forages at lower temperatures than A. striatus, and doesn’t overlap in its optimal foraging temperatures, which might relate to differences in their thermal tolerance ranges or certain degree of avoidance to each other. Both species show a generalist and opportunist diet and harvest a high percentage of the available plants. Diet composition and degree of selectivity mostly depends on seasonal and inter-annual variations of resource availability. At the colony level, A. lobicornis harvests much more vegetation than A. striatus, though this difference can’t be found at the population level because A. striatus colonies are more abundant. Each species can harvest 70–72 Kg/ha·year, or, among both of them, 20% of primary productivity in the study area. These ants also harvest a large amount of fruits and can act as seed dispersers. In the case of the shrub Condalia microphylla, they not only move the seeds far away from the parental plant and towards favourable microsites, but also they cause the dispersed seeds to germinate more often and faster than the seeds that weren’t manipulated by the ants. This study shows that in desert ecosystem interactions between leaf-cutter ants and plants are frequent and intense, and can play an important role in the dynamics of desert plant communities.

Mots clés : ECOLOGIA DE COMUNIDADES ; INTERACCIONES PLANTA-ANIMAL ; DESIERTOS ; HERBIVORIA ; DISPERSION DE SEMILLAS ; ACROMYRMEX ; FORRAJEO ; IMPACTO ; COMMUNITY ECOLOGY ; ANIMAL-PLANT INTERACTIONS ; DESERT ; HERBIVORY ; SEED DISPERSION ; ACROMYRMEX ; FORAGING ; IMPACT

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Page publiée le 26 février 2016, mise à jour le 3 juillet 2017