![]() For example, extreme events change high or low temperature regimes and exacerbate moisture limitations from a state of stress to one of disturbance, because their physiological effects change from reduced productivity to mortality. ![]() However, the potential ecological importance of climatic variability has also been recognized. Work on climatic variability has indicated that anomalies (in climatology, the difference from average) in one direction could be balanced by anomalies in the other direction. We use a spatially explicit, two-species, agent-based model (derived from an earlier model of alpine treeline in the Rocky Mountains, USA) with contrasting gradients of change in the relative strength of competition and facilitation to simulate responses of an ecotone to climatic variability. We aim to examine how different hypothesized modes of plant interaction alter ecological response to changing climatic variability. , and 2) recognition of climatic variation. Current theory is rooted in ideas on frequency dependent population processes such as competition, but ideas based on facilitation may provide new insights necessitating 1) the need to incorporate interactions among organisms in species distribution models, e.g. Thus, the ecological impacts of climatic variability requires research, specifically on how climate variability will affect population processes, and how to apply basic ecological theory to understand community responses to climate change. Interactions are more diverse and more interwoven than previously conceived, and their quantification will be necessary to move beyond simplistic species distribution models.Īs the global climate changes, shifts in climatic variability, including extremes, could have ecological consequences at least as great as would result from changes in mean temperature and precipitation. ConclusionsĮcotone responses are determined by the differences in slopes of the species response to the environment near their point of intersection and further changed by whether neighbor interactions are competitive. The memory embedded in the size-mediated model does not appear to buffer extreme events because the interactions between the two species within their shifting ecotone determine the outcomes. In the size-mediated model the competitive species advances farther along the stress gradient at the expense of the second species. ![]() With climate amelioration, the spatial pattern at the ecotone shows an advance of both species into what had been a higher stress area, but with less density when variation increases. The interactions included in both models of the stress gradient hypothesis similarly reduce the effects of increasing climatic variability. Because the size model includes system memory, it is expected to buffer the effects of extreme events. The environment undergoes progressive climate change and increases in variability. The simple model has two hierarchically competitive species on a single environmental gradient. Two instantiations of the stress gradient hypothesis, simple stress and a size-mediated model, are represented in a spatially explicit agent based simulation of an ecotone derived from observations of Abies lasiocarpa, Picea engelmannii, and Pinus albicaulis in the northern Rocky Mountains. The response will depend on interactions among individuals along environmental gradients, further affected by stress gradient effects. Variability added to directional climate change could have consequences for ecotone community responses, or positive and negative variations could balance.
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