Hot desert ecosystems: an integrated view.

Examines the nature of sources of spatial variation in concentration and availability of water and food, which have greater consequences in deserts than in richer biomes. There is no single optimal adaptive strategy for desert plants or animals: a great diversity of life forms uses water and food resources in different ways in space and time. Two subsystems coexist in deserts: a spatially large and temporally long-lasting system of low production and low energetic reward, and a system where the energetic reward is high but difficult to find in space and/or time. Consequently, two major directions of adaptation in desert organisms are adaptation for better use of episodic resources vs. adaptation for better use of poor resources. Behavioural plasticity and wide geographical and habitat ranges are typical features of desert organisms. There is a tendency for competition to decrease towards more extreme environmental conditions; in turn this helps to explain, for example, the large number of relict species. -P.J.Jarvis