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Institut de Recherche sur la Biologie de l'Insecte

UMR 7261 Faculté des Sciences et Techniques

Avenue Monge, Parc Grandmont  

37200 TOURS (France)

Current research

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Many studies have shown the ecological impact of the climate change that has occurred this past century. Some species are shifting their geographic distributions while others are prone to extinction. Nevertheless, the mechanisms through which climate variations and climate change influence individuals and populations still remain blurred. This lack of knowledge on the mechanisms in play handicaps severely our ability to predict accurately the ecological impacts of global change. Moreover, the greatest challenge to reliably predict the effects of global change on ecosystem processes and community structures is to determine how abiotic and biotic context alters the direction and magnitude of the global change effects on biotic interactions.

Our aim is to assess quantitatively the net effect of climate change on every single species in a multitrophic system, considering both direct and indirect influences. A key step in the search for higher prediction power is to understand how the microclimate of species is working, and to assess the magnitude of the micro-climatic change as induced by the macro-climatic change. We want to develop a biophysical approach, which consists in building the heat budget of organisms (Fig. 1) to compute microclimate temperature and body temperatures of ectotherms from climatic variables taken at the regional scale. Then, the biophysical model could be connected to physiological models and population dynamics allowing us to forecast the ecological effects of climate change.

We study the following tri-trophic system: the red spider mite (Panonychus ulmi), feeding on leaves of the apple tree, and a phytoseiid predatory spider mite (Typhlodromus pyri). This system is of socio-economical importance due to the impact of the red spider mite in agro-systems and the use of phytoseiids as a biological control agent. We expect the thermal biology of the acarids to be tightly related to leaf temperature as they live within the leaf boundary layer. The indirect effects of climate change on the red mite, through the impact on the plant, might therefore be substantial.

Figure 1. The heat budget of an ectotherm combines any kind of heat exchange between the organism and its environment to compute the body temperature (TB). Here, the insect receives energy from solar radiation (Qrad), as well as thermal radiation from the atmosphere (QTa). Solar (reflection) and thermal (emission) radiation are sent from the environment like the ground surface (Qgr). The insect body emits itself thermal radiation (QT) proportionally to its TB. Heat is exchanged with ambient air through (forced) convection (Qconv), and heat can be conducted between the insect and the ground surface (Qcond). Finally, heat could be lost during evapotranspiration (Qevap). When TB reaches

The project started very recently. The first step consists in investigating the response of spider mites to the thermal heterogeneity of a leaf surface: do spider mites move over leaf surface in response to leaf temperature variations? Does the red spider mite respond to leaf temperature variations differently when the predator is present?

Then, we are developing the biophysical model which integrates biotic interactions and the cascading spatial scales, from the regional scale down to a tree canopy, a leaf surface and the scale at which the spider mites are living in. This biophysical model combines several sub-models one after another (Fig. 2).

Figure 2. Our conceptual approach: combining different models to predict population dynamics of mites from climatic variables taken at the regional scale. The cascade of model considers the microclimatic quality. This biophysical model allows to cross spatial scales (region down to canopy and leaf), as well as functional (from individuals to populations) and trophic scales (plant, herbivore and predator).

We are planning to connect the biophysical model to a model of population dynamics of spider mites. This integrative model will allow us to predict population fluctuations within a tree canopy as function of temperature variation within microclimates. We also plan to get long-term continuous measurements of body temperatures, together with demographic and microclimatic recordings, in apple orchards in the field. These data will be useful to test model predictions.

Sylvain Pincebourde
Jérôme Casas
Christelle Suppo
Fabrice Vannier
Robin Caillon

Sylvain Pincebourde. J. Casas. Christelle Suppo Magal. Fabrice Vannier. Robin Caillon.

Pincebourde S. & Woods A. H. (2012). Climate uncertainty on leaf surfaces: the biophysics of leaf microclimates and their consequences for leaf-dwelling organisms. Functional Ecology 26, 844-853.

Pincebourde, S., Sanford, E., Casas, J., & Helmuth, B. (2012). Temporal coincidence of environmental stress events modulates predation rates. Ecology letters, 15, 680–8.

Pincebourde S., Sinoquet H., Combes D. & Casas J. (2007). Regional climate modulates the canopy mosaic of favourable and risky microclimate for insects.

Journal of Animal Ecology 76, 424-438.

Pincebourde and Woods FE2012.pdf Pincebourde et al. Ecology Letters 2012-supp.pdf Pincebourde et al_JAE 2007.pdf Climate Change and Trophic Cascades