Multilayer networks reveal the spatial structure of seed-dispersal interactions across the Great Rift landscapes

Abstract

Species interaction networks are traditionally explored as discrete entities with well-defined spatial borders, an oversimplification likely impairing their applicability. Using a multilayer network approach, explicitly accounting for inter-habitat connectivity, we investigate the spatial structure of seed–dispersal networks across the Gorongosa National Park, Mozambique. We show that the overall seed–dispersal network is composed by spatially explicit communities of dispersers spanning across habitats, functionally linking the landscape mosaic. Inter-habitat connectivity determines spatial structure, which cannot be accurately described with standard monolayer approaches either splitting or merging habitats. Multilayer modularity cannot be predicted by null models randomizing either interactions within each habitat or those linking habitats; however, as habitat connectivity increases, random processes become more important for overall structure. The importance of dispersers for the overall network structure is captured by multilayer versatility but not by standard metrics. Highly versatile species disperse many plant species across multiple habitats, being critical to landscape functional cohesion.

Reshaping our understanding of species’ roles in landscape‐scale networks

“…However, plant‐based habitat distinctions may not equate to distinct animal communities (Timóteo et al . ). Here, pollinators represent a large proportion of habitat connectors, meaning that these species forage in multiple habitats; this mobility could impact ecosystem stability (Rooney et al, ).…”

Interdomain ecological networks between plants and microbes

“…For example, the terrestrial forest ecosystems perform many ecosystem services, such as carbon sequestration, nutrient cycling and harbouring biodiversity; however, these essential functions are accomplished not by individual species, but by the mutual relationships between various macroscopic and microscopic species. Such relationships among different macroorganism kingdoms have been intensively observed and studied for decades, including plant–insect interactions (Barbour et al, ; Coux, Rader, Bartomeus, & Tylianakis, ), plant–bird interactions (Montesinos‐Navarro, Hiraldo, Tella, & Blanco, ; Timoteo, Correia, Rodriguez‐Echeverria, Freitas, & Heleno, ) and fauna prey–predator interactions (Gibert & DeLong, ; Ushio et al, ). However, such relationships among different domains/superkingdoms in above–belowground ecosystems, especially between multiple plants and various microorganisms (bacteria and archaea), remain elusive (Swenson & Jones, ).…”

Seeing the forest for the trees: Putting multilayer networks to work for community ecology

“…If inter‐layer edge strength is much greater than intra‐layer strengths, inter‐layer processes dominate the community and determine structural properties and vice versa (Pilosof et al, ). In Gorongosa National Park, seed‐dispersal modules become habitat‐specific when the inter‐layer weighting is small relative to intra‐layer weights; however, when inter‐layer weightings were large, landscape‐level groupings of plant–disperser interactions emerged (Timóteo et al, ). These results naturally suggest that when layers (in this case, habitats) are considered to be distinct ecological units, species interactions become grouped by those, often arbitrary, borders.…”

“…When inter-layer edges have been used, they are often uniform (Kéfi, Miele, Wieters, Navarrete, & Berlow, 2016;Timóteo, Correia, Rodríguez-Echeverría, Freitas, & Heleno, 2018). The strength of uniform inter-layer edges is an assumption about the interdependence of layers.…”