The individual‐based network structure of palm‐seed dispersers is explained by a rainforest gradient

Abstract

ECHow species interactions change in space and time is a major question in ecology. In tropical forests, plant individuals share mutualistic partners (pollinators or seed dispersers), yet we have little understanding of the factors affecting these individual interaction patterns. We used a seed dispersal individual-based network describing interactions between individuals of a palm species and bird species to investigate how intrinsic and extrinsic characteristics of individual plants influence the network structure. We evaluated if average canopy height, number of fruits, distance to forest gap and habitat type influence the role of palm individuals in the network. From 102 palms, 62 individuals had their seeds dispersed at least once: 17 individual palms in the restinga, 15 in the lowland and 30 in the pre-montane habitat. Twelve bird species were recorded dispersing Euterpe edulis seeds. No palm characteristics influenced interaction patterns in the network, characterized by the level of centrality of each palm. At the network level, modularity with qualitative data was reproduced by the null models which consider the variation in the number and distribution across interactions. Three of the seven identified modules were associated with a particular habitat. Indeed, habitat type explained 50% of network modularity. Habitat association with modularity was driven by differences in species composition across habitats. Palm individuals did not differ greatly in central positions, indicating that bird species are not selecting palm individuals by their characteristics. When using the weighted network, modularity level was higher than expected by the number of interactions, and frequency of interactions was positively correlated with canopy height. Our results suggest that the organization of this individual-based network is mostly driven by habitat type. We hypothesize that extrinsic characteristics, such as habitat type, may affect the network organization of populations of sessile organisms with potentially unanticipated consequences to ecological and evolutionary dynamics.

The turnover of plant–frugivore interactions along plant range expansion: consequences for natural colonization processes

“…Previous research has also shown that module composition in individual-based seed dispersal networks is influenced by habitat preferences. For instance, Friedemann et al [ 20 ] found a consistent trend in the modular structure of neotropical palm-seed dispersal networks along an elevational gradient of rainforest habitats. In a similar framework, studying the Brazilian pepper, Vissoto et al .…”

“…Although this species interacts with all the focal plants in the study, T. philomelos dispersed seeds mainly from the colonization front (MAR = 8%, OJI = 27%, COL = 65%). The song thrush, which interacts with plants from the three modules and the three stands, may be identified as a module-connector (electronic supplementary material, figure S8) as reported for similar thrush species in individual-based seed dispersal networks [ 16 , 20 ]. The preference of song thrush for individuals from the colonization front shows that this species is able to adapt to different landscapes, especially isolated plant configurations and stands outside the juniper forest.…”

“…A particular plant species is typically represented by individual plants, whereas animals can be represented either by individuals (individual-individual interactions) or species (individual-species interactions). Previous research has shown that this individual scale is a powerful approach for examining various issues in seed dispersal interactions, such as intraspecific specialization-generalization processes [16][17][18], fitness consequences [17,19] and network configurations [20]. Intraspecific variability in interactions between plants and seed dispersers can arise from various intrinsic and extrinsic drivers.…”

“…For example, Vissoto et al [ 16 ] documented distinct subsets of individual plants forming modules with frugivorous species, based on their use of different habitats by the animals. In a similar approach, Friedemann et al [ 20 ] found that, along a gradient of rainforest habitats, the modular clustering between frugivores and individual palms was largely due to habitat context rather than individual plant traits. Whether the organization of mutualistic interactions during natural plant expansion follows consistent, generalizable patterns remains unknown [ 25 ].…”

Importance of species traits on individual-based seed dispersal networks and dispersal distance for endangered trees in a fragmented forest

“…Therefore, for many plant species, especially endangered species, it is necessary to focus on the functional traits of the partners interacting with them and the structural characteristics of the interaction network to better understand the interaction process and employ better management strategies. However, the structure of these individual-based networks and their driving factors are poorly understood ( Friedemann et al., 2022 ).…”