Predator–prey interactions in a ladybeetle–aphid system depend on spatial scale

Abstract

The outcome of species interactions may manifest differently at different spatial scales; therefore, our interpretation of observed interactions will depend on the scale at which observations are made. For example, in ladybeetle–aphid systems, the results from small‐scale cage experiments usually cannot be extrapolated to landscape‐scale field observations. To understand how ladybeetle–aphid interactions change across spatial scales, we evaluated predator–prey interactions in an experimental system. The experimental habitat consisted of 81 potted plants and was manipulated to facilitate analysis across four spatial scales. We also simulated a spatially explicit metacommunity model parallel to the experiment. In the experiment, we found that the negative effect of ladybeetles on aphids decreased with increasing spatial scales. This pattern can be explained by ladybeetles strongly suppressing aphids at small scales, but not colonizing distant patches fast enough to suppress aphids at larger scales. In the experiment, the positive effects of aphids on ladybeetles were strongest at three‐plant scale. In a model scenario where predators did not have demographic dynamics, we found, consistent with the experiment, that both the effects of ladybeetles on aphids and the effects of aphids on ladybeetles decreased with increasing spatial scales. These patterns suggest that dispersal was the primary cause of ladybeetle population dynamics in our experiment: aphids increased ladybeetle numbers at smaller scales because ladybeetles stayed in a patch longer and performed area‐restricted searches after encountering aphids; these behaviors did not affect ladybeetle numbers at larger spatial scales. The parallel experimental and model results illustrate how predator–prey interactions can change across spatial scales, suggesting that our interpretation of observed predator–prey dynamics would differ if observations were made at different scales. This study demonstrates how studying ecological interactions at a range of scales can help link the results of small‐scale ecological experiments to landscape‐scale ecological problems.

Caterpillar movement mediates spatially local interactions and determines the relationship between population density and contact

“…Spatially local interactions can influence ecological processes including disease, predation, and resource competition [ 28 ], and other authors have also found that movement is a key determinate of how local interactions scale up to population-level effects (eg. [ 52 , 54 , 64 ]). Our results further illustrate how understanding the relative scales of habitat heterogeneity and animal movement is critical to determining how spatially local interactions impact ecological dynamics.…”

Generalist Predators Shape Biotic Resistance along a Tropical Island Chain

“…Also, in order to ascertain the exact extent of predator-mediated population suppression, we need to step beyond our current ‘snap-shot’ survey and conduct season-long combined assessments of mealybug and predator populations. In A. lopezi -colonized fields, biological control activity proved comparatively stable across a range of CAM densities and strongly responsive to predator density, especially at plant level (e.g., [ 82 ]). Meanwhile, a strong regulatory effect of A. lopezi (as demonstrated through multi-year population studies; [ 34 ]) is evident in the consistently high level of P. manihoti suppression across islands and its cascading impacts on predator abundance.…”

Modelling the effects of field spatial scale and natural enemy colonization behaviour on pest suppression in diversified agroecosystems

“…The effects of patch size on predator/parasitoid colonization, and how differences in within-field foraging behavior (e.g., directed vs. diffusive) can interact with habitat scale and patterning, are increasingly well documented (Karevia, 1985;Olson et al, 2000;Arditi et al, 2001;Banks and Yasenak, 2003). More recent work using a stochastic metacommunity approach parameterized with salt marsh field data similarly demonstrates that aphid suppression by ladybird beetles diminishes at larger spatial scales due to reduced prey-taxis (Lin & Pennings, 2018). Bianchi et al (2017) highlighted the importance of landscape spatial scale, using a mass-action perspective to demonstrate the need for careful attention to habitat management for natural enemies while being mindful of predator dispersal abilities.…”