Mutualism : A Factor in Ecological Succession Through its Influence on Nutrient Resource Ratios

Abstract

Changing resource availabilities and requirements are an important factor in successional sequences. In aggrading ecosystems beginning on bare rock. carbon may be the first limiting resource. In secondary succession. nitrogen usually is the first nutrient element which ceases to become limiting. and on nutrient poor soils. it is followed by sulfur. and then phosphorus. In degrading ecosystems. the sequence may be reversed. The changes in resource abundance during aggradation come about in part through the influence of microbial activity. Microbes depend on the autotrophs for their energy supply. while autotrophs depend on microbes for their nutrient supply. This mutualistic relationship appears to be an important regulator of ecosystem function. and of ecological succession on nutrient poor soils. Mutualism as well as competition is important in succession. Plant communities change the resource base upon which they survive through mutualistic interaction with microbes. The changing resource base in turn causes a change in the plant communities which depend on the resources. When a series of these interactions begins on a nutrient-poor substrate. the ratio of resources often changes in a regular and predictable sequence. The resultant change in plant communities may be considered to be succession.