Interactions between plants and herbivores do not occur in a vacuum. The presence, identity, and density of neighboring plants can significantly decrease (or increase) herbivore performance and preference, a phenomenon known as associational resistance (or susceptibility). Neighboring plants can also ameliorate harsh abiotic conditions, resulting in positive plant-plant associations that affect not only individual growth and survival, but also landscape-scale vegetation patterns. Research in this area aims to link the effects of plant-plant interactions across scales, from individual plant phenotype to whole ecosystem patterns of plant abundance and diversity. Examples of research in this area can be found below:
Positive interactions between plants--including the inhibition of herbivores by neighbors ("associational resistance") are particularly common in physically stressful ecosystems like African savannas. Using a series of small-scale experiments, we showed that growing in close proximity to spiny Acacia trees not only reduces browsing damage on understory plants, but also allows them to decrease investment in their own defenses and increase investment in growth and reproduction. In contrast, we found that plants growing in abandoned cattle corrals and experimentally cleared plots, both of which attract herbivores, invest significantly more in defense than conspecifics growing among neighbors. Collectively, these results suggest that plant-plant interactions cause consistent differences in herbivore pressure across the landscape, with parallel patterns of plant defense investment at the same scale.
Plant-plant interactions are invoked as a near-universal mechanism behind vegetation spatial patterns, which are ubiquitous in nature. However, these interactions alone cannot explain the complex patterns observed in many landscapes, particularly those with regularly spaced social insect colonies. Using a combination of field surveys and theoretical models, we showed that both plant-plant interactions and antagonistic interactions between neighboring termite colonies are necessary to create the patterns we observed in Kenyan savannas, as well as those found in the famous fairly circle landscapes of Namibia.
Relevant publications:
Relevant publications:
- Bonachela, JA, RM Pringle, E Sheffer, TC Coverdale, JA Guyton, KK Caylor, SA Levin and CE Tarnita. Termite mounds can increase the robustness of dryland ecosystems to climatic change. 2015. Science 347: 651-655.
- Coverdale, TC, TR Kartzinel, K Grabowski, RK Shriver, AA Hassan, JR Goheen, TM Palmer and RM Pringle. Elephants in the understory: opposing direct and indirect effects of consumption and ecosystem engineering. 2016. Ecology 97: 3219-3230.
- Coverdale, TC, JR Goheen, TM Palmer, and RM Pringle. Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants. 2018. Ecology 99: 1724-1736.
- Tarnita, CE, JA Bonachela, E Sheffer, JA Guyton, TC Coverdale, RA Long and RM Pringle. A theoretical foundation for multi-scale regular vegetation patterns. 2017. Nature 541: 398-401.
- Coverdale, TC, IJ McGeary, RD O’Connell, TM Palmer, JR Goheen, M Sankaran, DJ Augustine, AT Ford, RM Pringle, and CE Tarnita. 2019. Strong but opposing effects of associational resistance and susceptibility on defense phenotype in an African savanna plant. Oikos 128:1772-1782.