Algal Succession in a Hot Spring Community

Abstract

Algal samples from a hot spring in Yellowstone National Park, Wyoming, were taken at 10 temperature intervals, 10 m apart, from 57.2 C downstream to 45.7 C, and then the entire visible was removed. Sampling was continued at the same intervals during the 1st, 3rd, 5th 7th-week successional stages. No successional stage had more than 17 species but four species were noticeably the dominants in the descending order of: Synechococcus lividus, Mastigocladus laminosus, Phormidium laminosum and P. angustissimum. These dominants comprised 94.56%o of the frequency and 70.69% of the volume in the climax community, increasing to 97.37% of the frequency and 91.77% of the volume in the 1st week seral stage. The four dominants alone were sampled at the highest temperature interval in the climax but only two were present in the lst-week seral stage at the same temperature interval. Other species entered the as the water cooled in all seral stages. The minor species reappeared in the lst-week seral stage at a mean temperature 2.23 C lower than in the climax community. The uniform conditions in the hot spring environment, and the uniformity of the (blue green algae) created a situation paradoxical with the competitive exclusion principle by which hierarchal order and diversity were maintained during the seral stages. progressed without the changing the environment, and without being affected by changing external factors. The combined actions of individual populations, each in exponential growth, may have been responsible for the overshooting the carrying capacity of the environment for diversity before returning to the carrying capacity of the climax community. INTRODUCTION Community succession is one of the oldest of ecological concepts and has numerous interpretations resulting from varied field studies and, more recently, ecological models. An interpretation by Clements (1905, 1916) considered the as a single entity that develops, as would an organism, to maturity. This organismic interpretation of succession has been embraced by numerous ecologists for its apparen.t logic, ease of comprehension and the status of its advocate. Clements believed that succession was an orderly process in which a progressed to a more complex and that all successional stages in a region would culminate in one monoclimax. From Clements' aspect community and succession concepts were lineal descendants of a long tradition of natural philosophy which held that there were design, purpose and unity in nature and that these required a holistic approach to their understanding (McIntosh, 1980). Gleason (1926), as perhaps the most prominent early ecologist to reject Clements' interpretation of succession, considered succession to be an ecological process of the mass effect of individual plants acting within the the core of the individualistic concept of succession. The long span of time involved in successional studies has been a disadvantage in studying the process on one site (McIntosh, 1980). Henry and Swan (1974) believed that one generation of white pine can dominate a forest for 200-250 years before other species begin replacing them. Gleason (1927) wrote that, Succession in general is very slow, and the vegetational history of any particular habitat is more apt to be measured in thousands of years, or even in tens of thousands, than in centuries or decades. Because of this slow rate of terrestrial succession and because meteorological records at the time (1927) extended less than a century, Gleason further stated that a studied might actually be in retrogression. Hot spring communities offer an excellent 1 This study was supported in part by the Grants and Research Funding Committee, Southeast Missouri State University.