Network modularity influences plant reproduction in a mosaic tropical agroecosystem

Abstract

Biodiversity influences ecosystem function, but there is limited understanding of the mechanisms that support this relationship across different land use types in mosaic agroecosystems. Network approaches can help to understand how community structure influences ecosystem function across landscapes; however, in ecology, network analyses have largely focused on species–species interactions. Here, we use bipartite network analysis in a novel way: to link pollinator communities to sites in a tropical agricultural landscape. We used sentinel plants of Brassica rapa to examine how the structure of the community network influences plant reproduction. Diptera was the most common order of flower visitors at every site. Syrphidae visits were the strongest contributor to the number of fertilized pods, while visits by Syrphidae, Hymenoptera and Lepidoptera had the strongest effect on the number of seeds per pod. Sentinel pots at forest sites were visited by more unique species (i.e. species with higher d′ ) than sites in other land uses, and dairy sites had more visitors that were common across the network. Participation coefficients, which indicate how connected a single node is across network modules, were strong predictors of ecosystem function: plant reproduction increased at sites with higher participation coefficients. Flower visitor taxa with higher participation coefficients also had the strongest effect on plant reproduction. Hymenoptera visits were the best predictor for participation coefficients but an Allograpta sp. (Diptera: Syrphidae) was the most influential flower visitor species in the landscape network. A diverse insect community contributed to plant reproduction and connection among nodes in this system. Identifying the ‘keystone’ flower visitor species and sites that have a strong influence on network structure is a significant step forward to inform conservation priorities and decision-making in diverse agroecosystems.

Species–habitat networks elucidate landscape effects on habitat specialisation of natural enemies and pollinators

“…1c), generally hindering the evolution of specialisation also in the long term (Poisot et al ., 2011). Against this background, network topological metrics such as modularity or connectance can capture these community‐level changes in specialisation (Delmas et al ., 2019), which, in turn, can have consequences on ecosystem functioning (Saunders and Rader, 2019). Analogously, species‐level specialisation metrics (Poisot et al ., 2012) computed across multiple networks can elucidate interspecific and intraspecific variation in habitat use (Fig.…”

Don’t forget the flies: dipteran diversity and its consequences for floral ecology and evolution

“…For example, different syrphid fly species vary in their pollen transfer effectiveness and interplant movement patterns when visiting flowers of common mustards (Brassica spp. ; Gervasi and Schiestl 2017;Jauker and Wolters 2008;Rader et al 2013;Saunders and Rader 2019). Behavioral experiments reveal that small, yellow-colored floral markings (akin to anthers with yellow pollen) release innate proboscis extension behavior in flower-naïve syrphids (Lunau and Wacht 1994).…”

“…Nevertheless, these flies frequently visit non-mimetic flowers seeking more conventional nutritious rewards and are becoming more appreciated for their importance as pollinators (Orford et al 2015). At a landscape scale, calyptrate flies are more prevalent flower visitors and pollinators in habitats where their life cycles are enhanced by human activities, such as dairy farms and livestock pens (Saunders and Rader 2019). Calyptrate flies often are observed to be numerically dominant flower visitors in high altitude and/or high latitude biomes worldwide (rev.…”

Peer Review #1 of "Improving insect conservation across heterogeneous landscapes using species–habitat networks (v0.1)"

“…Managing multiple habitats for the conservation of multiple species can be challenging. Recently, it has been proposed to adapt network tools to describe such complex spatial interactions (Hackett et al, 2019;Marini et al, 2019) and to use the resulting species-habitat networks and their metrics to improve conservation of species at the landscape scale (Nardi et al, 2019;Pompozzi et al, 2019;Saunders & Rader, 2019;Lami et al, 2020). First, topology metrics can inform on the architecture and the emerging properties of the whole species-habitat network.…”