Grassland-to-crop conversion in agricultural landscapes has lasting impact on the trait diversity of bees

Abstract

Context Global pollinator decline has motivated much research to understand the underlying mechanisms. Among the multiple pressures threatening pollinators, habitat loss has been suggested as a key-contributing factor. While habitat destruction is often associated with immediate negative impacts, pollinators can also exhibit delayed responses over time. Objectives We used a trait-based approach to investigate how past and current land use at both local and landscape levels impact plant and wild bee communities in grasslands through a functional lens. Methods We measured flower and bee morphological traits that mediate plant–bee trophic linkage in 66 grasslands. Using an extensive database of 20 years of land-use records, we tested the legacy effects of the landscape-level conversion of grassland to crop on flower and bee trait diversity. Results Land-use history was a strong driver of flower and bee trait diversity in grasslands. Particularly, bee trait diversity was lower in landscapes where much of the land was converted from grassland to crop long ago. Bee trait diversity was also strongly driven by plant trait diversity computed with flower traits. However, this relationship was not observed in landscapes with a long history of grassland-to-crop conversion. The effects of land-use history on bee communities were as strong as those of current land use, such as grassland or mass-flowering crop cover in the landscape. Conclusions Habitat loss that occurred long ago in agricultural landscapes alters the relationship between plants and bees over time. The retention of permanent grassland sanctuaries within intensive agricultural landscapes can offset bee decline.

Functional traits of carabid beetles reveal seasonal variation in community assembly in annual crops

“…In our study, we measured continuous morphological traits on our sampled individuals. We found that carabid species, traits in arable field communities differentiate along three main dimensions of functional specialization, similar as previously shown for other taxa (Le Provost, Badenhausser, Le Bagousse-Pinguet, et al, 2020).…”

“…Dispersal-related traits might be filtered by landscape spatiotemporal structure. It has been previously shown that long-term land-use change to more intensive agricultural landscapes has impoverished the functional diversity of mobility traits in carabid assemblages (Le Provost, Badenhausser, Le Bagousse-Pinguet, et al, 2020), and selected species with higher dispersal abilities and tolerance against agricultural disturbances (Turin & Den Boer, 1988). Secondly, in some species, macropterous individuals do not necessarily possess functioning flight muscles and are therefore incapable of flight (Desender & Turin, 1989; Nelemans, 1987), at least at certain periods of their life cycle (Van Huizen, 1977).…”

“…The same 13 species were among the most abundant species in each year of the study: Poecilus cupreus (32.8 %), Brachinus sclopeta (19.0 %), Anchomenus dorsalis (13.6 %), Calathus fuscipes (4.3 %), Nebria salina (4.2 %), Brachinus crepitans (4.1 %), Pterostichus melanarius (2.4 %), Harpalus dimidiatus (2.2 %), Harpalus distenguentus (1.5 %), Amara consularis (1.4 %), Pseudoophonus rufipes (1.3 %), Microlestes minutulus (0.6 %), and Microlestes maurus (0.4 %). Morphological traits were measured on these 13 selected dominant species according to standardized protocols (Le Provost, Badenhausser, Le Bagousse-Pinguet, et al, 2020). Twelve individuals per species and per sex from our local species collection were measured.…”

“…On each individual, we measured three sets of traits related to body size, movement ability, and resource acquisition that describe leading dimension of forms and functions in arthropods (Le Provost, Badenhausser, Le Bagousse-Pinguet, et al, 2020; Moretti et al, 2017). Body size is an important trait related to metabolic rate (Brown et al, 2004) and thermoregulation (Uvarov, 1977).…”

“…However, carabid beetle community structure has been shown to vary among different crop types (Eyre et al, 2013; Marrec et al, 2015). For instance, grassland habitat may offer stable habitat over time within agricultural landscape, and has been shown to promote functional diversity for plants and arthropods (Le Provost, Badenhausser, Le Bagousse-Pinguet, et al, 2020; Le Provost, Badenhausser, Violle, et al, 2020; Le Provost et al, 2017). In addition, carabid beetles may be sufficiently mobile (Ribera et al, 2001) to develop temporal strategy of habitat use, especially in response to seasonal environmental changes such as crop rotations (Holland et al, 2009; Marrec et al, 2015; Thomas et al, 2001).…”