"An approach to holistic ecological risk assessment: Food web responses to a warmed climate as a case study"
Abstract There is ample evidence on the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The Earth's climate has warmed by approximately 0.6 oC over the past 100 years. IPCC has projected the mean global surface air temperature to increase by 1.4 oC to 5.8 oC from 1990 by 2100, with the magnitude of the increase varying both spatially and temporally. Coastal ocean temperature increases are expected to be slightly lower than the IPCC projected increases for land, but still are expected to rise measurably. Responses by individual species to climate change may disrupt their interactions with others at the same or adjacent trophic levels, as well as their metabolic and reproductive processes. The inevitable uncertainties and ambiguities and highly complex dynamics associated with ecosystems present considerable challenges when assessment of potential ecological risks is attempted. The objective of this study is to examine robustness of ecosystems under a warmer climate (?). Specifically, whether the persistence of species in food-webs will be reduced by an increased metabolic rate expected under a warmed climate will be examined. In this study, two target food webs, the marine food web and the terrestrial food web, are studied. The theory of trophic interactions, competition among producer species by synthesizing nutrient-dependent growth of producer species, and one of food-web structure models, the niche model are used. Temperature is assumed as one of the primary factors to affect metabolic rate through various mechanisms. Three climate scenarios are studied: the best scenario with a minimal increase in global temperature of 1.4 oC, an average scenario with an average increase in global temperature of 3.6 oC, and the worst scenario with a maximum increase in global temperature of 5 oC. Three different types of climate are considered: the tropical climate, the temperate climate, and the Arctic/Antarctic climate. A computer simulation tool combining a nonlinear bioenergetic model of complex ecological networks with a food-web structure model is used to simulate food-web responses to metabolic rate for marine and terrestrial food webs. A thirty-species food web is assumed for every single simulation. Major outputs from simulations include species richness, connectance, links per species, and percentages of top, intermediate, and basal species in a food web. These properties in the two target food webs under each climate scenario in each type of climate are simulated and compared. The outcome of this study should help understand ecological risks associate with climate change.