Improving insect conservation across heterogeneous landscapes using species–habitat networks

Abstract

Background One of the biggest challenges in conservation is to manage multiple habitats for the effective conservation of multiple species, especially when the focal species are mobile and use multiple resources across heterogeneous protected areas. The application of ecological network tools and the analysis of the resulting species–habitat networks can help to describe such complex spatial associations and improve the conservation of species at the landscape scale. Methods To exemplify the application of species–habitat networks, we present a case study on butterflies inhabiting multiple grassland types across a heterogeneous protected area in North-East Italy. We sampled adult butterflies in 44 sites, each belonging to one of the five major habitat types in the protected area, that is, disturbed grasslands, continuous grasslands, evolved grasslands, hay meadows and wet meadows. First, we applied traditional diversity analyses to explore butterfly species richness and evenness. Second, we built and analyzed both the unipartite network, linking habitat patches via shared species, and the bipartite network, linking species to individual habitat patches. Aims (i) To describe the emerging properties (connectance, modularity, nestedness, and robustness) of the species–habitat network at the scale of the whole protected area, and (ii) to identify the key habitats patches for butterfly conservation across the protected area, that is, those supporting the highest number of species and those with unique species assemblages (e.g., hosting specialist species). Results The species–habitat network appeared to have a weak modular structure, meaning that the main habitat types tended to host different species assemblages. However, the habitats also shared a large proportion of species that were able to visit multiple habitats and use resources across the whole study area. Even butterfly species typically considered as habitat specialists were actually observed across multiple habitat patches, suggesting that protecting them only within their focal habitat might be ineffective. Our species–habitat network approach helped identifying both central habitat patches that were able to support the highest number of species, and habitat patches that supported rare specialist species.

Different types of semi‐natural habitat are required to sustain diverse wild bee communities across agricultural landscapes

“…In the survey conducted in 2020, wild bees were, analogous to the 2014 survey, sampled along 2 m wide transects in the same five major habitat types. However, a 1 km transect was subdivided into sections proportional to the amount of these different habitat types in a landscape (similar to Cappellari & Marini, 2021). These sections were randomly placed in different patches of the corresponding habitat types in each landscape (including flowering crops, not analysed here).…”

“…To assess complementarity of habitats in flower species composition (pooled sampling rounds), we further calculated functional complementarity as the total branch length of a dendrogram based on qualitative differences in flower species assemblages between habitats (Devoto et al, 2012). To investigate whether bee community composition differs across habitat types, we assessed network modularity (Cappellari & Marini, 2021). In modular networks, certain bee species and habitats share more links than others and thereby form modules (Olesen et al, 2007).…”

“…Even though this analysis cannot make any direct inference about the factors determining a species' association to a particular habitat, it evaluates if a species is using mainly one particular or several habitat types (and which). This can be especially useful to develop targeted conservation measures (Cappellari & Marini, 2021).We would like to note, however, that as almost inevitably in most studies assessing pollinator species composition across habitats, under-sampling could lead to an overestimation of uniqueness, which therefore needs to be interpreted with adequate caution. However, our analyses suggest that sampling completeness and coverage was satisfactory in our highly replicated study across 25 agricultural landscapes.…”