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Contrasting effects of land use intensity and exotic host plants on the specialization of interactions in plant-herbivore networks.

de Araújo WS, Vieira MC, Lewinsohn TM, Almeida-Neto M - PLoS ONE (2015)

Bottom Line: When we analyzed networks composed exclusively of endophagous herbivores separately from those composed exclusively of exophagous herbivores, we found that only endophages showed a consistent change in network specialization at higher land use levels.Altogether, these results indicate that land use intensity is an important ecological driver of network specialization, by way of reducing the local host range of herbivore guilds with highly specialized feeding habits.However, because the effect of land use intensity is offset by an opposite effect owing to the proportion of exotic host species, the net effect of land use in a given herbivore assemblage will likely depend on the extent of the replacement of native host species with exotic ones.

View Article: PubMed Central - PubMed

Affiliation: Programa de Pós-Graduação em Ecologia e Evolução, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, Goiás, Brazil; Laboratório de Interações Ecológicas e Biodiversidade, Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, Goiás, Brazil.

ABSTRACT
Human land use tends to decrease the diversity of native plant species and facilitate the invasion and establishment of exotic ones. Such changes in land use and plant community composition usually have negative impacts on the assemblages of native herbivorous insects. Highly specialized herbivores are expected to be especially sensitive to land use intensification and the presence of exotic plant species because they are neither capable of consuming alternative plant species of the native flora nor exotic plant species. Therefore, higher levels of land use intensity might reduce the proportion of highly specialized herbivores, which ultimately would lead to changes in the specialization of interactions in plant-herbivore networks. This study investigates the community-wide effects of land use intensity on the degree of specialization of 72 plant-herbivore networks, including effects mediated by the increase in the proportion of exotic plant species. Contrary to our expectation, the net effect of land use intensity on network specialization was positive. However, this positive effect of land use intensity was partially canceled by an opposite effect of the proportion of exotic plant species on network specialization. When we analyzed networks composed exclusively of endophagous herbivores separately from those composed exclusively of exophagous herbivores, we found that only endophages showed a consistent change in network specialization at higher land use levels. Altogether, these results indicate that land use intensity is an important ecological driver of network specialization, by way of reducing the local host range of herbivore guilds with highly specialized feeding habits. However, because the effect of land use intensity is offset by an opposite effect owing to the proportion of exotic host species, the net effect of land use in a given herbivore assemblage will likely depend on the extent of the replacement of native host species with exotic ones.

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Path analyses of proportion of monophages from plant-insect networks of (A) all herbivores, (B) endophages, and (C) exophages.For details and explanations, see legend for Fig. 3.
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pone.0115606.g004: Path analyses of proportion of monophages from plant-insect networks of (A) all herbivores, (B) endophages, and (C) exophages.For details and explanations, see legend for Fig. 3.

Mentions: The path models explained 27%, 70% and 18% of the variation in residual connectance considering all networks, only plant-endophage networks and only plant- exophage networks, respectively (Fig. 3). The three path models showed good fit to the data (Table 1). The models also explained 15% (all networks), 41% (endophages only), and 8% (exophages only) of the variation (Fig. 4) in the proportion of monophagous herbivores.


Contrasting effects of land use intensity and exotic host plants on the specialization of interactions in plant-herbivore networks.

de Araújo WS, Vieira MC, Lewinsohn TM, Almeida-Neto M - PLoS ONE (2015)

Path analyses of proportion of monophages from plant-insect networks of (A) all herbivores, (B) endophages, and (C) exophages.For details and explanations, see legend for Fig. 3.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4286214&req=5

pone.0115606.g004: Path analyses of proportion of monophages from plant-insect networks of (A) all herbivores, (B) endophages, and (C) exophages.For details and explanations, see legend for Fig. 3.
Mentions: The path models explained 27%, 70% and 18% of the variation in residual connectance considering all networks, only plant-endophage networks and only plant- exophage networks, respectively (Fig. 3). The three path models showed good fit to the data (Table 1). The models also explained 15% (all networks), 41% (endophages only), and 8% (exophages only) of the variation (Fig. 4) in the proportion of monophagous herbivores.

Bottom Line: When we analyzed networks composed exclusively of endophagous herbivores separately from those composed exclusively of exophagous herbivores, we found that only endophages showed a consistent change in network specialization at higher land use levels.Altogether, these results indicate that land use intensity is an important ecological driver of network specialization, by way of reducing the local host range of herbivore guilds with highly specialized feeding habits.However, because the effect of land use intensity is offset by an opposite effect owing to the proportion of exotic host species, the net effect of land use in a given herbivore assemblage will likely depend on the extent of the replacement of native host species with exotic ones.

View Article: PubMed Central - PubMed

Affiliation: Programa de Pós-Graduação em Ecologia e Evolução, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, Goiás, Brazil; Laboratório de Interações Ecológicas e Biodiversidade, Departamento de Ecologia, Instituto de Ciências Biológicas, Universidade Federal de Goiás, Goiânia, Goiás, Brazil.

ABSTRACT
Human land use tends to decrease the diversity of native plant species and facilitate the invasion and establishment of exotic ones. Such changes in land use and plant community composition usually have negative impacts on the assemblages of native herbivorous insects. Highly specialized herbivores are expected to be especially sensitive to land use intensification and the presence of exotic plant species because they are neither capable of consuming alternative plant species of the native flora nor exotic plant species. Therefore, higher levels of land use intensity might reduce the proportion of highly specialized herbivores, which ultimately would lead to changes in the specialization of interactions in plant-herbivore networks. This study investigates the community-wide effects of land use intensity on the degree of specialization of 72 plant-herbivore networks, including effects mediated by the increase in the proportion of exotic plant species. Contrary to our expectation, the net effect of land use intensity on network specialization was positive. However, this positive effect of land use intensity was partially canceled by an opposite effect of the proportion of exotic plant species on network specialization. When we analyzed networks composed exclusively of endophagous herbivores separately from those composed exclusively of exophagous herbivores, we found that only endophages showed a consistent change in network specialization at higher land use levels. Altogether, these results indicate that land use intensity is an important ecological driver of network specialization, by way of reducing the local host range of herbivore guilds with highly specialized feeding habits. However, because the effect of land use intensity is offset by an opposite effect owing to the proportion of exotic host species, the net effect of land use in a given herbivore assemblage will likely depend on the extent of the replacement of native host species with exotic ones.

Show MeSH