By Lauren Snyder
Hannover, Germany (July 5, 2021)—Farmers have long relied on predatory insects to control insect pests in their fields, but global declines in biodiversity threaten these services, as habitats with little biodiversity are often weak providers of ecosystem services. Researchers often use the number of species (species diversity) as a proxy for measuring biodiversity and predicting the strength of ecosystem services, but a clear link between predator species diversity and insect pest control remains elusive—previous studies have found positive, negative, and neutral relationships. Now, in a new study in the journal Ecological Applications, Cornell University researchers led by Ricardo Perez-Alvarez, a former doctoral student in the lab of professor Katja Poveda, and now postdoctoral researcher in the group of Zoological Biodiversity at the Leibniz University of Hannover demonstrates that measuring the functional traits (e.g., physical or behavioral characteristics) of a predator community is a more effective way of characterizing biodiversity and predicting the strength of pest control services. Specifically, the authors show that the variation in body size of the local predator community is a key indicator of pest suppression. Moreover, they demonstrate the diversity of predator body sizes, and therefore the strength of pest control services, varies in response to the type of habitat surrounding a farm.
While ecologists are increasingly using functional traits to predict the strength of pest control services in agriculture, the majority of studies have been conducted in highly controlled, simplified environments that do not accurately capture conditions on working farms spread across diverse landscapes. “More and more we are understanding that the type of habitats surrounding a farm—what we call landscape composition—can impact the strength of pest control services, so our goal was to understand how predator trait diversity influences pest control in real world conditions,” Perez-Alvarez says.
“We were particularly interested in predator body size because body size can tell you a lot about an organism. For example, the size of an animal can tell you how much energy it needs to survive, which in turn is associated with other attributes such as its ability to move across the landscape, how fast it grows, and its ability to produce offspring. Measuring body size is an easy way to collapse multiple characteristics of an organism into a single trait,” Perez-Alvarez said.
To determine how landscape composition affects the body size structure of predator communities, and how these changes affect pest suppression on working farms, the research team studied naturally occurring predatory ground beetles on 11 farms in the Finger Lakes Region of New York State, USA. The team selected farms surrounded by high and low levels of agriculture, and used sentinel prey to measure predation rates directly in the field.
The study found that larger ground beetles were more effective at controlling insect pests than their smaller counterparts, and that simplified landscapes—landscapes with a lot of agriculture—tended to have larger beetles compared to landscapes with less agriculture. Interestingly, previous studies looking at the effect of landscape composition on different insect groups such as bees and butterflies showed that simplified landscapes favored smaller body sizes. Perez-Alvarez and colleagues show ground beetles respond differently, which highlights the importance of evaluating how different kinds of insects respond to changes in landscape composition. In addition, these findings suggest that the previously reported variation in the relationship between predator diversity and pest control may be at least partially explained by variation in landscape composition.
However, the number of large individuals in a predator community did not fully explain the magnitude of pest control in this study. Rather, pest control was strongest in predator communities with an even representation of small and large predators. In other words, while large predators give a boost to pest control, having a diversity of predator sizes is also important. One reason could be that large and small predators use different resources and therefore compete less with one another, leading to strengthened pest control.
“Conservation programs often have limited budgets, so understanding the key players in an ecosystem is critical to effectively target our efforts. At the same time, our study clearly underscores the need to conserve predator communities with diverse traits. If we concentrate conservation efforts on one key species, we may be ignoring other species that are vital to the overall services we are trying to promote,” explains Perez-Alvarez.
Co-authors include Katja Poveda, professor of entomology at Cornell University; Heather Grab, lecturer in the School of Integrative Plant Science at Cornell University; and Anthony Polyakov, a recent graduate of the Department of Entomology at Cornell University. The study was funded by the National Institute of Food and Agriculture at the United States Department of Agriculture.
Original Publication: Ricardo Perez-Alvarez et al, Landscape composition mediates the relationship between predator body size and pest control, Ecological Applications (2021). doi.org/10.1002/eap.2365
Lauren Snyder holds a doctorate in agroecology from Cornell University and is a freelance science communicator based in Hannover, Germany. Email: laursnyder@gmail.com
