Diversity and network structure of invertebrate communities associated to Heliconia species in natural and human disturbed tropical rain forests

Changes in the core species of the ant-plant network of oak forest converted to grassland: replacement of its ant functional groups

Land-use change in terrestrial environments is one of the main threats to biodiversity. The study of ant-plant networks has increased our knowledge of the diversity of interactions and structure of these communities; however, little is known about how land-use change affects ant-plant networks. Here we determine whether the change in land use, from native oak forest to induced grassland, affected the network properties of ant-plant networks in a temperate forest in Mexico. We hypothesize that the disturbed vegetation will be more nested and generalized due to the addition of generalist species to the network. The oak forest network comprises 47 plant species and 11 ant species, while the induced grassland network has 35 and 13, respectively. Floral nectar was the resource used most intensely by the ants in both vegetation types. The ant-plant network of the induced grassland was significantly more nested and generalist than that of the oak forest; however, none of the networks were nested when considering the frequency of interaction. In both vegetation types, the ants were more specialized than the plants, and niche overlap was low. This could be related to the dominant species present in each type of vegetation: Prenolepis imparis in the oak forest and Camponotus rubrithorax in the grassland. The central core of cold climate ant species in the oak forest was replaced by a central core of subordinate Camponotini and tropical specialists in the induced grassland. These results suggest that the increase in nestedness and generalization in the grassland may be related to the loss of the cold climate specialists from the core of the oak forest network. Our findings provide evidence that land-use change increases the level of generalization in the ant-plant interaction networks of temperate forests.

Diversity metrics of spider communities associated with an understorey plant in tropical rain forest fragments

Human activities change the biodiversity of ecological communities in at least three dimensions: ecologically, taxonomically and functionally. Gathering information on these three dimensions allows the improvement of biodiversity assessments and the increased understanding of anthropogenic impact on natural communities. In this study, we analysed the spider community associated with the tropical plant Heliconia aurantiaca in two contrasting habitat types: continuous forest and forest fragments in south-eastern Mexico. We examined the foliage, stems and bracts of H. aurantiaca individuals in both habitats. We categorized each spider species according to its behavioural and functional traits. We analysed ecological diversity using Hill numbers, taxonomic distinctness and functional diversity using the FRic index. Overall, we collected a total of 110 spiders, of which 44 individuals from 29 species were found in continuous forests, with 66 individuals from 36 species in forest fragments. We found greater ecological diversity in continuous forest than in fragments. In contrast, we found lower functional diversity in continuous forest than in fragments. Taxonomic diversity showed no significant difference between habitats. Forest fragmentation affected the biodiversity of spiders by disrupting species composition and function, which may lead to other ecological changes such as predator–prey interactions and other aspects of ecosystem functioning.

Unravelling Darwin's entangled bank: architecture and robustness of mutualistic networks with multiple interaction types

Trying to unravel Darwin's entangled bank further, we describe the architecture of a network involving multiple forms of mutualism (pollination by animals, seed dispersal by birds and plant protection by ants) and evaluate whether this multi-network shows evidence of a structure that promotes robustness. We found that species differed strongly in their contributions to the organization of the multi-interaction network, and that only a few species contributed to the structuring of these patterns. Moreover, we observed that the multi-interaction networks did not enhance community robustness compared with each of the three independent mutualistic networks when analysed across a range of simulated scenarios of species extinction. By simulating the removal of highly interacting species, we observed that, overall, these species enhance network nestedness and robustness, but decrease modularity. We discuss how the organization of interlinked mutualistic networks may be essential for the maintenance of ecological communities, and therefore the long-term ecological and evolutionary dynamics of interactive, species-rich communities. We suggest that conserving these keystone mutualists and their interactions is crucial to the persistence of species-rich mutualistic assemblages, mainly because they support other species and shape the network organization.

Interaction intimacy of pathogens and herbivores with their host plants influences the topological structure of ecological networks in different ways

•

PREMISE OF THE STUDY

Over the past two decades an interest in the role that plant-animal mutualistic networks play in the organization and dynamic of biodiversity has steadily risen. Despite the ecological, evolutionary, and economic importance of plant-herbivore and plant-pathogen antagonistic relationships, however, few studies have examined these interactions in an ecological network framework.•

METHODS

We describe for the first time the topological structure of multitrophic networks involving congeneric tropical plant species of the genus Heliconia (Heliconiaceae, Zingiberales) and their herbivores and pathogens in the state of Pernambuco, Brazil. We based our study on the available literature describing the organisms (e.g., insects, mites, fungi, and bacteria) that attack 24 different species, hybrids, and cultivated varieties of Heliconia.•

KEY RESULTS

In general, pathogen- and herbivore-Heliconia networks differed in their topological structure (more modular vs. more nested, respectively): pathogen-Heliconia networks were more specialized and compartmentalized than herbivore-Heliconia networks. High modularity was likely due to the high intimacy that pathogens have with their host plants as compared with the more generalized feeding modes and behavior of herbivores. Some clusters clearly reflected the clustering of closely related cultivated varieties of Heliconia sharing the same pathogens.•

CONCLUSIONS

From a commercial standpoint, different varieties of the same Heliconia species may be more susceptible to being attacked by the same species of pathogens. In summary, our study highlights the importance of interaction intimacy in structuring trophic relationships between plants and pathogens in the tropics.