Temporal changes in the structure of a plant-frugivore network are influenced by bird migration and fruit availability

Abstract

Background. Ecological communities are dynamic collections whose composition and structure change over time, making up complex interspecific interaction networks. Mutualistic plant–animal networks can be approached through complex network analysis; these networks are characterized by a nested structure consisting of a core of generalist species, which endows the network with stability and robustness against disturbance. Those mutualistic network structures can vary as a consequence of seasonal fluctuations and food availability, as well as the arrival of new species into the system that might disorder the mutualistic network structure (e.g., a decrease in nested pattern). However, there is no assessment on how the arrival of migratory species into seasonal tropical systems can modify such patterns. Emergent and fine structural temporal patterns are adressed here for the first time for plant-frugivorous bird networks in a highly seasonal tropical environment.Methods. In a plant-frugivorous bird community, we analyzed the temporal turnover of bird species comprising the network core and periphery of ten temporal interaction networks resulting from different bird migration periods. Additionally, we evaluated how fruit abundance and richness, as well as the arrival of migratory birds into the system, explained the temporal changes in network parameters such as network size, connectance, nestedness, specialization, interaction strength asymmetry and niche overlap. The analysis included data from 10 quantitative plant-frugivorous bird networks registered from November 2013 to November 2014.Results. We registered a total of 319 interactions between 42 plant species and 44 frugivorous bird species; only ten bird species were part of the network core. We witnessed a noteworthy turnover of the species comprising the network periphery during migration periods, as opposed to the network core, which did not show significant temporal changes in species composition. Our results revealed that migration and fruit richness explain the temporal variations in network size, connectance, nestedness and interaction strength asymmetry. On the other hand, fruit abundance only explained connectance and nestedness.Discussion. By means of a fine-resolution temporal analysis, we evidenced for the first time how temporal changes in the interaction network structure respond to the arrival of migratory species into the system and to fruit availability. Additionally, few migratory bird species are important links for structuring networks, while most of them were peripheral species. We showed the relevance of studying bird–plant interactions at fine temporal scales, considering changing scenarios of species composition with a quantitative network approach.

Seed‐dispersal networks respond differently to resource effects in open and forest habitats

“…This finding is consistent with the global meta-analysis that found that network specialization increased with decreasing resource availability at high latitudes (Schleuning et al 2012). Patterns of increasing specialization with decreasing resource availability can be explained by changes in frugivore behavior and frugivore specialization on specific, predictable resources (Ramos-Robles et al 2016, Dalsgaard et al 2017). The relationship was reversed on plots with high habitat structure.…”

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

“…However in a more recent analysis an updated version of this Atlantic forest network was nested using a binary measure (Vizentin-Bugoni et al, 2016) Bascompte et al (2003) suggest that increases in the number of species in networks might result in greater nestedness. Sebastian-Gonzalez et al (2015) confirmed this increase in nestedness with greater number of species, but other studies found no such effect (Cuartas-Hernandez & Medel, 2015) or even reduced nestedness with increased number of species (Ramos-Robles, Andresen & Diaz-Castelazo, 2016). Indeed, when we reduced the network to only include species and observations that resulted in “legitimate” flower visits, we found nestedness values were lower although the network was still more nested than expected.…”

Combining plant–frugivore networks for describing the structure of neotropical communities

“…A high resource richness may be the cause of a low niche overlap between frugivores, because seeddispersal systems are known to be the less specialised compared to other types of mutualism such as plant-ant and plant-pollinator interactions (Blüthgen et al 2007). High fruit species richness reduces the overlap between the diets of frugivores because it reduces interspecific competition (Ramos-Robles et al 2016).…”