Crop heterogeneity is positively associated with beneficial insect diversity in subtropical farmlands

Abstract

Increasing crop configurational heterogeneity—smaller crop fields with more field margins—has been repeatedly found to support farmland biodiversity. But research on compositional crop heterogeneity—the number and evenness of crop types—has usually shown only weak effects. However, much of this research has been conducted in large‐scale temperate agroecosystems. We examined smallholder subtropical agroecosystems in southern China to assess the effects of crop heterogeneity on beneficial insect biodiversity. In addition to pollinators (bees, apoid and vespid wasps, and butterflies), we studied dung beetles and dragonflies/damselflies, which are not usually considered in cropland heterogeneity studies, but are abundant in these multi‐functional agroecosystems. We sampled these taxa in 468 transects placed inside 52 farms across three seasons (summer, spring and winter), collecting data on 27,245 insects belonging to 160 species. We found a strong positive effect of crop compositional heterogeneity (measured by Shannon–Wiener index) on dung beetle and dragonfly/damselfly diversity. Bee/wasp and butterfly diversity, conversely, was positively affected by crop configurational heterogeneity (measured by cumulative field margin length). Field margin type, categorized by the structure of the dominant crop types, was consistently an important explanatory variable, with weedy margins having high insect diversity. The presence of a vegetable crop on one side of the field margin, compared to non‐vegetable monocultures on both sides, increased diversity in 3/4 taxon‐season comparisons made for rice and 6/9 comparisons made for sugarcane or corn. Synthesis and applications. We demonstrate that crop compositional heterogeneity can support insects that respond to differences among crop types, including taxa that play a key role in nutrient cycling (dung beetles) and natural pest control (dragonflies/damselflies). Incorporating structurally diverse crops into monoculture Asian agroecosystems can reduce the adverse effects these intensive systems have on beneficial insects, and increase crucial ecosystem services.

Effects of Traditional Orchard Abandonment and Landscape Context on the Beneficial Arthropod Community in a Mediterranean Agroecosystem

“…On the other hand, in the traditional orchards located in areas with a low percentage of semi-natural habitats, the studied groups may be limited by management practices and the scarcity of alternative resources. This trend is observed despite the high crop heterogeneity and small field size, following the general pattern of European studies where other variables such as landscape complexity are of greater relevance ([ 108 ] and references therein). However, as the percentage of semi-natural habitats increases, these limiting capacities become available in the surrounding area, thus allowing the communities of the study groups to thrive and spill over from these unmanaged habitats and successfully exploit the resources (especially prey or hosts and floral resources during the blooming period and spring) that traditional orchards provide [ 32 , 42 , 109 , 110 , 111 ].…”

Crop and landscape heterogeneity increase biodiversity in agricultural landscapes: A global review and meta‐analysis

“…However, our taxonomic order level analysis suggested that some pollinators, such as Hymenoptera and Diptera, benefited from configurational heterogeneity more than compositional heterogeneity in crop fields. As these groups are comprised of flying insect pollinators, they can exploit resources from various cover types within the landscape, and thus the connectivity between different fields may be more important to support their cross‐habitat movements, rather than a particular cover type (Hass et al., 2018; Priyadarshana et al., 2021; Tscharntke et al., 2012). In contrast, for Coleoptera and Araneae, the compositional heterogeneity component was more important than configurational heterogeneity.…”

“…In contrast, for Coleoptera and Araneae, the compositional heterogeneity component was more important than configurational heterogeneity. As these groups are comprised of predators with low mobility, they may benefit from particular habitat types within the landscape (Aviron et al., 2005; Boetzl et al., 2020; Kromp, 1999; Martin et al., 2016; Priyadarshana et al., 2021). For example, ground beetles and spiders may utilize certain crop fields for hunting when pest populations are high, and move into nearby field margins to forage as the crops senesce, highlighting the importance of temporal crop dynamics and semi‐natural habitats (Aviron et al., 2005; Bianchi et al., 2006; Gallé et al., 2018; Sotherton, 1984).…”

“…Promoting spatial heterogeneity through habitat diversity and connectivity between crop and non‐crop cover types within the landscape (i.e., landscape heterogeneity) has been suggested as a valuable approach (Fahrig et al., 2011). Recently, ecologists also have started testing whether increasing spatial heterogeneity of the crop mosaic itself, through increased crop diversity and connectivity between crop fields (i.e., crop heterogeneity), while keeping the area of non‐cropped land constant, could increase biodiversity (Alignier et al., 2020; Bertrand et al., 2016; Collins & Fahrig, 2017; Fahrig et al., 2015; Hass et al., 2018; Priyadarshana et al., 2021; Sirami et al., 2019).…”

“…We predicted they would benefit from landscape heterogeneity more than crop heterogeneity (Figure 1c). Conversely, less mobile small‐bodied taxa, such as many invertebrates, may benefit from diverse cover types within their typically smaller home ranges (Cano et al., 2022; Hass et al., 2018; Maurer et al., 2022; Priyadarshana et al., 2021; Zurbuchen et al., 2010). Bees, spiders and beetles, for example generally have home ranges <0.5 km 2 (Loreau & Nolf, 1993; Seer et al., 2015; Zurbuchen et al., 2010), but large‐bodied bees might exhibit larger foraging ranges (Greenleaf et al., 2007).…”