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Tropical rain forest fragmentation affects biotic interactions in distinct ways. Little is known, however, about how fragmentation affects animal trophic guilds and their patterns of interactions with host plants. In this study, we analyzed changes in biotic interactions in forest fragments by using a multitrophic approach. For this, we classified arthropods associated with Heliconia aurantiaca herbs into broad trophic guilds (omnivores, herbivores and predators) and assessed the topological structure of intrapopulation plant-arthropod networks in fragments and continuous forests. Habitat type influenced arthropod species abundance, diversity and composition with greater abundance in fragments but greater diversity in continuous forest. According to trophic guilds, coleopteran herbivores were more abundant in continuous forest and overall omnivores in fragments. Continuous forest showed a greater diversity of interactions than fragments. Only in fragments, however, did the arthropod community associated with H aurantiaca show a nested structure, suggesting novel and/or opportunistic host-arthropod associations. Plants, omnivores and predators contributed more to nestedness than herbivores. Therefore, Heliconia-arthropod network properties do not appear to be maintained in fragments mainly caused by the decrease of herbivores. Our study contributes to the understanding of the impact of fragmentation on the structure and dynamics of multitrophic arthropod communities associated with a particular plant species of the highly biodiverse tropical forests. Nevertheless, further replication of study sites is needed to strengthen the conclusion that forest fragmentation negatively affects arthropod assemblages.

The analysis of species diversity has benefited from multiple methodological approaches that are changing not only the way we measure biodiversity, but also our general conceptualization of it. We review the concepts and methods for measuring species diversity, including a report on how species diversity has been measured in tropical ecosystems, and summarize current methodological approaches that can be used to achieve more comprehensive analyses of species diversity. We reviewed papers dealing with species diversity published in Biotropica over the last 28 yr. Most of the studies were carried out in the Neotropics. The most popular methods for reporting alpha diversity were species accumulation curves, rarefaction curves, and the Shannon-Wiener index, while beta diversity assessments mainly relied on the Sørensen, Jaccard or Bray-Curtis indices. We offer a general framework for comprehensive biodiversity assessments that includes the alpha and beta components, and taxonomic, functional, and phylogenetic dimensions. We briefly describe the conceptual background, relevant methods, and examples of the components, and dimensions described in this framework. To improve our knowledge of tropical biodiversity and its regulatory processes, we encourage researchers to carry out more complete assessments, and to take advantage of the wide variety of methods available; methods that are perhaps especially useful in human-disturbed and human-managed landscapes.Abstract in Spanish is available with online material.