Considering plant structure in models of plant growth and development

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    ABSTRACT: The sensitivity of the North Atlantic thermohaline circulation to the input of fresh water is studied using a global ocean circulation model coupled to a simplified model atmosphere. Owing to the nonlinearity of the system, moderate changes in freshwater input can induce transitions between different equilibrium states, leading to substantial changes in regional climate. As even local changes in freshwater flux are capable of triggering convective instability, quite small perturbations to the present hydrological cycle may lead to temperature changes of several degrees on timescales of only a few years.
    Nature 11/1995; 378:145-149. · 38.60 Impact Factor
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    ABSTRACT: During the next 50 years, which is likely to be the final period of rapid agricultural expansion, demand for food by a wealthier and 50% larger global population will be a major driver of global environmental change. Should past dependences of the global environmental impacts of agriculture on human population and consumption continue, 10(9) hectares of natural ecosystems would be converted to agriculture by 2050. This would be accompanied by 2.4- to 2.7-fold increases in nitrogen- and phosphorus-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems, and comparable increases in pesticide use. This eutrophication and habitat destruction would cause unprecedented ecosystem simplification, loss of ecosystem services, and species extinctions. Significant scientific advances and regulatory, technological, and policy changes are needed to control the environmental impacts of agricultural expansion.
    Science 05/2001; 292(5515):281-4. · 31.03 Impact Factor
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    ABSTRACT: We analyzed three models of tritrophic interactions among hosts, parasitoids, and hyperparasitoids. In their deterministic versions, all models can produce dynamics in the form of a torus, in which there are both short-term cycles and long-term cycles of tens or hundreds of generations. To investigate whether similar long-term patterns can occur when there is environmental variability, we produced stochastic versions of the three models. Long-term population fluctuations occurred over a wider range of parameter values in the stochastic models than in the deterministic models. This suggests that long-term population fluctuations are plausible features of natural tritrophic systems. We use this example to argue that characterizing nonlinearities should not be the sole objective when analyzing stochastic population dynamics. The long-term dynamical patterns produced by our stochastic models can be investigated using linear techniques to quantify the patterns of density dependence in the multispecies system. These techniques identify long-term patterns as near-random-walk dynamics occurring concomitantly with short-term quasi-cyclic dynamics in the three-dimensional three-species system. Interpreting stochastic population dynamics in terms of patterns of density dependence makes it possible to identify the potential for long-term population fluctuations in the absence of very long-term data sets.
    Ecology 04/1998; 79(3):1039-1052. · 5.18 Impact Factor

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Jun 1, 2014