Specialist herbivores under climatic warming: Bottom-up and top-down regulation and trophic chain stability







Biodiversity and food production are ecosystem services challenged by climatic warming via range shifts of species, phenological changes in crop growth and growing demand for agricultural land. Both natural and agroecosystems have to be made more resilient towards abiotic changes that might harm their ecosystem functioning. In food webs, sensitivity to climate change has been evidenced to increase by trophic level. In addition, specialist species are less adapt to environmental disturbance than generalists, and show often higher habitat dependence and reduced mobility. Climatic warming and abiotic changes such as summer heat waves may thus disturb in particular specialised trophic interactions and alter dynamics of herbivores and their predators and parasitoids in spesialised systems. This project aims to examine how temperature variation and extremes predicted for the near future affect specialised tritrophic system stability. It focuses on studying the role of cascading ecological effects bottom-up and top-down in the trophic web and mediated by herbivorous arthropods. One of the goals is to compare how pest herbivores and their natural enemy life cycles and their comparative dynamics as a whole respond to temperature changes. Potential of higher diversity at lower trophic levels (plants as primary producers) to buffer system stability towards temperature change and for sustaining biological pest control by natural enemies is hypothesized. Using Brassica sp. plants, Pieris sp. herbivores and their specialist natural enemies (Cotesia sp. parasitoids) as a model system, herbivore-natural enemy dynamics in relation to temperature and agricultural diversity will be studied using long-term observational data and targeted field and growth chamber experimentation. The results aid in understanding regulation mechanisms of specialised trophic cascades and hope to reveal means for improving resilience towards abiotic change in Finnish natural and agroecosystems. The project runs from 1.9.2012 to 31.10.2015 and is funded by the Academy of Finland (Post doctoral researcher´s project).