Meta-analysis: Higher plant richness supports higher pollinator richness across many land use types

Authors: KRAL-O'BRIEN, KATHERINE - North Dakota State University; O'Brien, Peter; HOVICK, TORRE - North Dakota State University; HARMON, JASON - North Dakota State University

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2020
Publication Date: 1/16/2021
Citation: Kral-O'Brien, K.C., O'Brien, P.L., Hovick, T.J., Harmon, J.P. 2021. Meta-analysis: Higher plant richness supports higher pollinator richness across many land use types. Annals of the Entomological Society of America. 114(2):267-275. https://doi.org/10.1093/aesa/saaa061.
DOI: https://doi.org/10.1093/aesa/saaa061

Interpretive Summary: Pollinators, including bees, butterflies, and moths, are beneficial for more than 75% of global crop species, and they perform critical pollination services that help maintain diverse plant populations in natural systems. However, pollinators are declining worldwide due to many forces of global change, especially land conversion. Large amounts of land have been converted from natural systems, such as grasslands or woodlands, to agriculture to meet the ever-increasing demand for food, fuel, and fiber. This conversion decreases not only the overall amount of pollinator habitat but also the number of different plant species that are present in the remaining habitat. These changes in habitat have the potential to affect pollinators and, subsequently, their capacity to support long-term resilience and sustainability of both agricultural and native systems. We combined the results of 60 published studies to perform a meta-analysis examining the relationship between the number of pollinator species and the number of plant species found at a diverse group of research locations. We found that the number of pollinator species was higher when the number of plant species was higher. This relationship was the same among all types of pollinators, including bees, butterflies, and moths, as well as all types of land use, including agriculture, grasslands, and woodlands. These findings suggest that land managers can increase the number pollinator species by increasing the number of plant species, using strategies like planting different species or managing existing land with tools like grazing or fire. However, the number of pollinator species did not increase in some studies with the addition of plant species, which highlights the importance of proper plant species selection. Overall, this meta-analysis indicates that increasing the number of different plant species present at a site will likely increase the number of pollinator species, even in areas with low biodiversity. Thus, these findings are important to researchers and land managers aiming to increase pollinator species by providing support for a consistent, broadly applicable strategy: increase the number of different plant species present.

Technical Abstract: Global biodiversity declines are attributed to many factors including landscape fragmentation and vegetation homogenization. These patterns may be exacerbated by the intensification of agroecosystems, as management to meet increasing demand for food, fuel, and fiber often comes at the cost of biodiversity and subsequent ecosystem functions and services. Conserving biodiversity will be necessary to create sustainable agroecosystems capable of optimizing both production and services such as pollination. We conducted a meta-analysis to examine the relationship between plant species richness and pollinator species richness to determine if higher plant species richness supports higher pollinator species richness, especially in areas prone to biodiversity losses. We found pollinators, including bees, butterflies, and moths, responded positively to increasing plant species richness, irrespective of location or land use, suggesting the capacity to increase pollinator richness through management strategies that increase plant species richness. However, we found pollinators in manipulated studies did not consistently respond to increasing plant species richness despite the overall positive relationships in observational and experimental studies, highlighting the importance of plant selection when making management decisions aiming to improve pollinator richness. Additional studies in regions such as Africa and South America will help fill in latitudinal gradients and provide greater coverage necessary to make more precise patterns. Improving plant species richness or taking proactive approaches to restore plant species richness will likely increase pollinator richness and be beneficial in agroecosystems to support necessary biodiversity.