System Ecology Ecosystem and Communities

The leading question in desert ecology is whether aridity alone can explain all aspects of biological systems. If so, desert environments could be understood simply by characterizing the harsh, abiotic environmental factors that prevail in desert systems. Thus, desert systems do not follow the typical ecosystem view and can be described as simplified systems that react to discrete rain events (triggers) by short-term growth production (pulse), interspersed by long-term storage of organic material (seeds, roots, and stems - reserves). This pulse-reserve conceptual desert model is clearly too simplistic; however, it provides an important framework for the description of major ecological components of deserts.

In contrast to this basic view of deserts, two major alternative hypotheses have been developed in regard to the driving factors defining communities and populations in deserts. One hypothesis states that only the primary producers are water limited and all other trophic levels (consumers) are determined by the magnitude of this water-dependent primary production. Another hypothesis postulates that water shortage affects organisms only individually and has no direct effect on higher-order species interactions. According to this view, aridity effects on ecosystems and communities are rather the indirect outcomes of direct physiological and behavioral responses of individual organisms (and their populations) to scarcity of water. Despite the fact that the temporal and spatial lack of water is clearly the driving force behind the individual ecologies of desert species, current research makes it clear that species interactions, including both negative and positive ones, can be strong in deserts. The following sections strive to provide a brief summary of the types of interactions typical to deserts.

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