The objective of this chapter is to discuss the dynamic behavior of the biotic components of arid ecosystems in relation to water and energy flow between and within seasons. The growth responses of the different plant species occupying adjacent ecosystems in a watershed will be related to water availability and to heat energy levels. Growth and behavioral responses of groups of animals with contrasting adaptations to changing conditions of food and water availability will be discussed. Plant and animal litter redistribution and decomposition patterns will be discussed with respect to patterns of energy flow and climatic variation. Finally, general conclusions about desert ecosystem dynamics with respect to short-term water and energy flow will be stated.