Declining Abundance of Coccinellidae (Coleoptera) Among Crop and Prairie Habitats of Eastern South Dakota, USA

Lady (= ladybird) beetles (Coleoptera: Coccinellidae) provide agroecosystem services as major predators of aphids and other pests of field crops. Several native coccinellids in North America have declined in association with the introduction of invasive species of lady beetles. In particular, populations of three native species declined drastically (Coccinella transversoguttata richardsoni) or effectively disappeared (Coccinella novemnotata, Adalia bipunctata) from agricultural landscapes in eastern South Dakota, U.S.A., following establishment of an invasive coccinellid (Coccinella septempunctata) in the 1980s. Since then, two other non-native coccinellids (Harmonia axyridis and Hippodamia variegata) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous coccinellid guild is lacking. This paper summarizes long-term results from 14 years (2007–2020) of sampling coccinellids by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,338 aphidophagous coccinellids comprising 10 species were sampled. Two invasive species (Coc. septempunctata, Har. axyridis) were the third- and fourth-most abundant species, respectively. The seven most abundant species constituted 99% of all coccinellids sampled and were recorded from all six habitats. However, coccinellid species ranged considerably in their evenness of habitat use, resulting in differences in rank abundance among habitats. Coccinellid assemblages were similar for alfalfa and winter wheat, but not for other habitats, which possessed distinct coccinellid assemblages based on rank abundance. Annual abundance of coccinellids varied considerably within habitats, but declining trends were evident from significant negative regressions in annual abundance for adult and immature coccinellids in corn and adults in soybean. As a group, native adult coccinellids showed a significant declining trend in corn but not in other habitats, whereas trends for non-native adult coccinellids were non-significant in all habitats. Sample rates of coccinellids in alfalfa, spring grains, and corn in this study were 74, 26, and 6%, respectively, compared to that of a previous study from the region, further indicating substantial decreases in coccinellid abundance. Possible explanations and implications for observed patterns in coccinellid diversity and individual species abundances in field crops and restored prairie of eastern South Dakota are discussed with respect to prey, agronomic trends, and landscape factors.

Pore architecture and soil carbon accrual in soils under monoculture switchgrass vs. prairie soils

<p>Bioenergy crop cultivation is suggested as one of the promising options to increase soil organic carbon (SOC) stock, and thereby sequester atmospheric carbon dioxide. Yet, the increase in SOC varies greatly depending on the cropping system, with high plant diversity in particular appearing to be positive for carbon storage. This is recently linked to, among other things, the formation of a pore architecture favorable for microbial function and the storage of microbial degradation products. However, little is known about whether this observation holds true for a wide range of soil textures. Therefore, the objective of this research was to compare the abundance of pores with different sizes and SOC contents in soils with contrasting texture and plant diversity. Soil cores and surrounding soil samples were taken on seven long-term field experiments of monoculture switchgrass and restored prairie sites in Michigan, USA. In addition to texture and SOC analyses in disturbed soil samples, undisturbed cores with a diameter of 5 cm were scanned by micro-computer tomography (µCT) at a resolution of 18 µm. These will be used to analyze pore characteristics.</p><p>such as pore size distribution.</p><p>Results reveal, in highly sandy soil, high plant diversity was less effective to form narrow mid-size pores, and thus did not enhance SOC, while numerically higher SOC contents were observed in the restored prairie of less sandy soil, having higher abundance of mid-size pores compared to the monoculture. In conclusion, in the highly sandy soil, restored prairie with plant diversity was less effective to form pores in the mid-size range, and thus it couldn’t enhance the capability of C sequestration.</p>

Drivers of ecosystem metabolism in restored and natural prairie wetlands

Elucidating drivers of aquatic ecosystem metabolism is key to forecasting how inland waters will respond to anthropogenic changes. We quantified gross primary production (GPP), respiration (ER), and net ecosystem production (NEP) in a natural and two restored prairie wetlands (one “older” and one “recently” restored) and identified drivers of temporal variation. GPP and ER were highest in the older restored wetland, followed by the natural and recently restored sites. The natural wetland was the only net autotrophic site. Metabolic differences could not be definitively tied to restoration history, but were consistent with previous studies of restored wetlands. Wetlands showed similar metabolic responses to abiotic variables (photosynthetically active radiation, wind speed, temperature), but differed in the direct and interactive influences of biotic factors (submersed aquatic vegetation, phytoplankton). Drivers and patterns of metabolism suggested the importance of light over nutrient limitation and the dominance of autochthonous production. Such similarity in ecosystem metabolism between prairie wetlands and shallow lakes highlights the need for a unifying metabolic theory for small and productive aquatic ecosystems.

Evolution in novel environments: do restored prairie populations experience strong selection?

When populations colonize new habitats, they are likely to experience novel environmental conditions, and as a consequence may experience strong selection. While selection and the resulting evolutionary responses may have important implications for establishment success in colonizing populations, few studies have estimated selection in such scenarios. Here we examined evidence of selection in recently established plant populations in two prairie restorations in close proximity (< 15 km apart) using two approaches: 1) we tested for evidence of past selection on a suite of traits in two Chamaecrista fasciculata populations by comparing the restored populations to each other and their shared source population in common gardens to quantify evolutionary responses and 2) we measured selection in the field. We found evidence of past selection on flowering time, specific leaf area, and root nodule production in one of the populations, but detected contemporary selection on only one trait (plant height). This demonstrates that while selection can occur in colonizing populations, resulting in significant evolutionary responses in less than 6 generations, rapid evolutionary responses may be weak in even nearby populations sown with the same source population. Because contemporary measures of selection rarely predicted observed evolutionary responses, it also suggests that selection likely differs over the early stages of succession that characterize young prairies.

The Limits to Adaptation in Restored Ecosystems and How Management Can Help Overcome Them

Adaptation drives the diversity of form and function observed in nature and is key to population persistence. Yet, adaptation can be limited by a lack of genetic variation, trade-offs, small population size, and constraints imposed by coevolving interacting species. These limits may be particularly important to the colonizing populations in restored ecosystems, such as native prairies restored through seed sowing. Here, we discuss how constraints to adaptation are likely to play out in restored prairie ecosystems and how management decisions, such as seed mix composition, prescribed fire, and strategic site selection, might be used to overcome some of these constraints. Although data are still limited, recent work suggests that restored prairie populations likely face strong selection and that promoting the potential for adaptation in these systems may be necessary for restoring populations both now and in the face of further global change.