A Guide to 23 Global Syntheses of Plant Diversity Effects: Unpacking Consensus and Incongruence across Trophic Levels

Flower diversity on organic farms increases invasive ants rather than non‐invasive natural enemies

“…Fire ants were the only significant environmental predictor of predator evenness, having a negative influence (albeit a weak relationship that might sharpen with more comprehensive ant sampling in future studies). Despite our predictions and a large body of work supporting positive links between natural enemies and non-crop diversity(Holmes & Blubaugh, 2023), all plant diversity metrics we examined had neutral or negative impacts on non-invasive predators, perhaps due to the disruptive influence of fire ants.…”

“…In contrast, flowers tend to grow farther away from focal crops at field borders, providing nectar and pollen for more mobile natural enemies (Albrecht et al, 2021). Plant diversity at more intimate spatial proximity to crop plants typically has stronger effects on natural enemy attraction (Albrecht et al, 2021;Andow, 1991;Holmes & Blubaugh, 2023;Letourneau et al, 2011), but in our invader-dominated predator community, neither source of plant diversity increased native predators.…”

“…Plant diversity often strengthens predator diversity and biological control, yet varying outcomes across studies still preclude highly specific and accurate planting recommendations for farmers (Holmes & Blubaugh, 2023). Community evenness might be a more reliable metric linking natural enemy diversity , plant F I G U R E 2 Relationships between non-invasive predator evenness and fire ant abundance (a), floral richness (b) and weed richness (c) estimated at the family level on zucchini plantings at 37 organic farms.…”

Organic compost belowground and floral diversity aboveground interactively shape beneficial insects in urban gardens

“…Natural suppression of crop pests is simultaneously determined by ‘top‐down’ factors like diverse non‐crop habitats that enhance natural enemies (Holmes & Blubaugh, 2023), alongside ‘bottom‐up’ factors like organic soil amendments and beneficial microbes that enhance plant growth and herbivore resistance (Alyokhin et al., 2020; Han et al., 2022; Pineda et al., 2017). Separate and fruitful lines of research characterize how diversification aboveground and belowground might shape biological control, but integrating both tactics will be key for transforming intensely managed crop monocultures into the regenerative systems that will be necessary for the optimization of crop productivity alongside environmental stewardship (Bellone et al., 2023; Deguine et al., 2021).…”

“…Flowering plants and impervious surfaces both seem to be key in predicting biocontrol services in urban environments, having positive and negative influences, respectively (reviewed in Arnold et al., 2019; Lin et al., 2015). However, floral resources can still fail to attract beneficial insects to urban gardens (Lowenstein et al., 2017; Matteson & Langellotto, 2011), suggesting there is much nuance yet to unpack about other ecological variables that shape context‐dependent impacts of aboveground diversity on insect food webs (Holmes & Blubaugh, 2023).…”