Padrões globais na estrutura e fragilidade de redes planta-herbívoro
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2015-03-20
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Universidade Federal de Goiás
Resumo
The intensification of land use due to human activities in natural environments has led to various
consequences to biodiversity, ranging from local extinction of native species and colonization of by
exotic and invasive ones to the complete conversion of ecosystems in to anthropic landscapes. Among
the different biodiversity components that can be influenced by human habitat modification are the
ecological interactions between insect herbivores and their host plants, which together represent 75%
of the known diversity of terrestrial species. In this context, the objective of my thesis was to
investigate global patterns in the structure and fragility of plant-herbivore networks. Specifically, I
sought to answer as the intensification of land use and the dominance of exotic host plant species
influence the structure and fragility of interaction networks of insect herbivores and host plants, and
also I investigate whether there latitudinal gradient in the structuration of these interactions. I
compiled 90 local plant-herbivore networks distributed worldwide, spanning different taxonomic
groups of plants and insects and several feed guilds of herbivores. The main results of my analyses
show that land use intensification and the dominance of exotic host plant species influence different
aspects of plant-herbivore networks, such as species richness and taxonomic distinctness (a proxy to
phylogenetic diversity) of herbivore species and the structure and fragility of interactions. Another
recurrent result was that, when networks composed exclusively of endophagous herbivores were
analyzed separately from those composed exclusively by exophages, only the networks of endophages
had consistent effects of the land use intensity and proportion of exotic host plant species. Altogether,
land use intensification surprisingly increases network specialization by decreasing connectance and
nestedness, and increases modularity; while the increase in the proportion of exotic hosts had opposite
effects. Possibly these changes in the network structure are due to loss proportionally higher of
species with many interactions (i.e., generalists) in relation to species with few interactions (i.e.,
specialists). As a consequence of these changes in the network connectivity, land use intensification
decreases the robustness of plant-herbivore networks, while the proportion of exotic host plant species
increases. Therefore, networks located in habitats with higher land use intensity tend to be less robust
that networks in more pristine habitats, which is a very intriguing result that goes in the opposite
direction of most of the literature on ecological networks. Controling the antropic effects that can act
on the networks, my results show that plant–herbivore networks are structured independently of
latitude, suggesting that the factors that influence the interactions between host plants and insect
herbivores are latitudinally invariant. The results and patterns found emphasize the important
contribution of this thesis to the understanding of plant-herbivore networks in the context of human
disturbances in natural habitats.
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ARAÚJO, W. S. Padrões globais na estrutura e fragilidade de redes planta-herbívoro. 2015. 176 f. Tese (Doutorado em Ecologia e Evolução) - Universidade Federal de Goiás, Goiânia, 2015.