Spatial structure of an individual‐based plant–pollinator network

Abstract

The influence of space on the structure (e.g. modularity) of complex ecological networks remains largely unknown. Here, we sampled an individual‐based plant–pollinator network by following the movements and flower visits of marked bumblebee individuals within a population of thistle plants for which the identities and spatial locations of stems were mapped in a 50 × 50 m study plot. The plant–pollinator network was dominated by parasitic male bumblebees and had a significantly modular structure, with four identified modules being clearly separated in space. This indicated that individual flower visitors opted for the fine‐scale division of resources, even within a local site. However, spatial mapping of network modules and movements of bumblebee individuals also showed an overlap in the dense center of the plant patch. Model selection based on Akaike information criterion with traits as predictor variables revealed that thistle stems with high numbers of flower heads and many close neighbours were particularly important for connecting individuals within the modules. In contrast, tall plants and those near the patch center were crucial for connecting the different modules to each other. This demonstrated that individual‐based plant–pollinator networks are influenced by both the spatial structure of plant populations and individual‐specific plant traits. Additionally, bumblebee individuals with long observation times were important for both the connectivity between and within modules. The latter suggests that bumblebee individuals will still show locally restricted movements within sub‐patches of plant populations even if they are observed over a prolonged time period. Our individual‐based and animal‐centered approach of sampling ecological networks opens up new avenues for incorporating foraging behaviour and intra‐specific trait variation into analyses of plant–animal interactions across space.

Geographical variation in mutualistic networks: similarity, turnover and partner fidelity

“…Others have also distinguished between species-driven interaction turnover and rewiring [9,15], but because species-driven turnover was the main contributor, we further partitioned it into pollinator-, plant-and pollinator þ plant-driven (figures 1 and 3). Along the entire gradient, pollinator-driven turnover accounted for a larger fraction of the overall species-driven turnover than that of plants, which probably is an effect of (i) the initial selection of sites based on their vegetational similarity, (ii) the plant-centred sampling protocol where we observed plants for pollinators and not vice versa [42,43], (iii) the higher diversity of pollinators compared with plant species, and (iv) the perennial lifestyle of plants versus the annual lifestyle of the pollinators. Thus, pollinator species probably fluctuated more in abundance and diversity, and consequently accounted for more of the observed interaction turnover.…”

Increasing modularity when downscaling networks from species to individuals

“…A modular structure is derived from constraints in the interactions. Modularity in different kinds of network is indeed associated with a variety of ecological factors and explanatory processes (Bascompte and Olesen in press), such as: 1) convergence in pollination syndromes (Danieli‐Silva et al ); 2) phylogeny and body mass in food webs (Rezende et al ); 3) trophic specialization and host range selection in plant–herbivore interactions (Prado and Lewinsohn ); 4) species phenology in plant–pollinator networks (Bosch et al , Martín González et al ); 5) species niche organization and diet in food webs (Guimerà et al ) and 6) spatial or habitat segregation (Fortuna et al , Dupont et al ). However, the degree of modularity and the number of modules in a network can be constant over time‐ cumulative periods (Dupont and Olesen ).…”

“…Third, we discuss the drivers of modularity in i–sp networks and the underlying mechanisms influencing the distribution of individuals across modules. As only a few pollination networks have been studied at the individual level (see Dupont et al , and Gómez and Perfectti for single species network approaches), the ecological factors causing modularity at this level are poorly known. Specifically, we focus upon pollen resource affinity among individuals and phenology as drivers of module composition.…”

Spatial population structure of rare orchid species in rich fens in the central part of Murmansk oblast

“…Original studies on the level of aggregatedness and types of aggregations in plant populations have provided a basis for formulating the concept of elementary demographic unit (Zaugol'nova, 1994). The spatial organization of populations has received increasing attention in recent studies on heterogeneity of habitats, consortive relationships between plants and animals, and development of conservation measures for rare and endemic species (Luzuriaga et al, 2006;Getzin et al, 2008;Dupont et al, 2014). However, there are only a few publications dealing with certain features of spatial structure in populations of individual orchid species (Kull, 1995;Kaitala and Kull, 2002;Brzosko et al, 2002;Fardeeva et al, 2010; Fardeeva, 2013).…”