Amplified temperature dependence in ecosystems developing on the lava flows of Mauna Loa, Hawai'i

Abstract

Through its effect on individual metabolism, temperature drives biologically controlled fluxes and transformations of energy and materials in ecological systems. Because primary succession involves feedbacks among multiple biological and abiotic processes, we expected it to exhibit complex dynamics and unusual temperature dependence. We present a model based on first principles of chemical kinetics to explain how biologically mediated temperature dependence of ''reactant'' concentrations can inflate the effective temperature dependence of such processes. We then apply this model to test the hypothesis that the temperature dependence of early primary succession is amplified due to more rapid accumulation of reactants at higher temperatures. Using previously published data from the lava flows of Mauna Loa, HI, we show that rates of vegetation and soil accumulation as well as rates of community compositional change all display amplified temperature dependence (Q10 values of Ϸ7-50, compared with typical Q10 values of 1.5-3 for the constituent biological processes). Additionally, in young ecosystems, resource concentrations increase with temperature, resulting in inflated temperature responses of biogeochemical fluxes. Mauna Loa's developing ecosystems exemplify how temperature-driven, biologically mediated gradients in resource availability can alter the effective temperature dependence of ecological processes. This mechanistic theory should contribute to understanding the complex effects of temperature on the structure and dynamics of ecological systems in a world where regional and global temperatures are changing rapidly.ecosystem development ͉ metabolic theory of ecology ͉ primary succession ͉ Q 10 ͉ elevation B iological metabolism-the uptake, transformation, and allocation of energy and materials by living things-shapes ecological phenomena (1). The metabolic theory of ecology has identified body size and temperature as critical variables driving metabolic rates and, thereby, ecological processes such as photosynthesis, respiration, population growth, and secondary succession (1-3). Through such processes, biological metabolism largely controls global cycles of carbon and nitrogen.Primary succession-the development of ecosystems on new substrates such as lava flows, sand dunes, or land exposed by receding glaciers-is a complex process involving the accumulation of carbon and nutrients in biomass and soil and the concurrent assembly of a diverse biotic community (4, 5). It is driven by multiple interacting processes, including substrate weathering, primary production, soil formation, and colonization and subsequent turnover of plant, animal, fungal, and microbial species. Most of these processes are mediated by organisms whose biological function exhibits clear temperature dependence (1). It is known that temperature affects the rate of primary succession (4, 6-9). Not well understood, however, is how the multiple ecological processes interact to affect the overall rate of ecosystem development and to determine...

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