Abundance drives broad patterns of generalisation in plant–hummingbird pollination networks

Abstract

Abundant pollinators are often more generalised than rare pollinators. This could be because abundant species have more chance encounters with potential interaction partners. On the other hand, generalised species could have a competitive advantage over specialists, leading to higher abundance. Determining the direction of the abundance–generalisation relationship is therefore a ‘chicken‐and‐egg’ dilemma. Here we determine the direction of the relationship between abundance and generalisation in plant–hummingbird pollination networks across the Americas. We find evidence that hummingbird pollinators are generalised because they are abundant, and little evidence that hummingbirds are abundant because they are generalised. Additionally, most patterns of species‐level abundance and generalisation were well explained by a null model that assumed interaction neutrality (interaction probabilities defined by species relative abundances). These results suggest that neutral processes play a key role in driving broad patterns of generalisation in animal pollinators across large spatial scales.

Frugivore species maintain their structural role in the trophic and spatial networks of seed dispersal interactions

“…The level of modularity and generalism in mutualistic interactions and habitat use may be strongly influenced by species abundance (e.g. Fort, Vázquez, & Lan, 2016;García, Martínez, Stouffer, & Tylianakis, 2014;Simmons et al, 2019) and body size (e.g. García et al, 2014;Palacio, Valderrama-Ardila, & Kattan, 2016;Wheelwright, 1985).…”

Including rewiring in the estimation of the robustness of mutualistic networks

“…Abundance (A): the probability of one species rewiring to another partner is proportional to the relative abundances of the surviving species in the other trophic level, so that a species has higher probability of rewiring its interactions to abundant rather than rarer partners. This assumes that chances of encounter (and subsequent interaction) are governed by species’ relative abundances, which is often the case in pollination networks (Simmons et al, ; Vázquez, Bluthgen, et al, ; Vizentin‐Bugoni et al, ).…”

Niche and neutral processes leave distinct structural imprints on indirect interactions in mutualistic networks

“…The second type of motif produced by neutral processes is complete and asymmetric complete motifs which have many links, providing many possible pathways through which indirect effects can flow (motifs 6, 11, 12 and 16). This likely results from the neutral model's lack of consideration of ‘forbidden links’ (Canard et al., 2014; Jordano, 2016b): as long as two species are of sufficiently high abundance, they are able to interact, resulting in more pathways (Simmons, Vizentin‐Bugoni, et al., 2019). This is in contrast to niche‐based processes, where poor morphological matches or low temporal co‐occurrence would prevent some interactions from being formed.…”