Population Structure and Biomass Production by a Stream Salamander

A life-table based on collections from a population of Desmognathus fuscus in Gaston Co., North Carolina, is presented. An estimate based on the weight of captured individuals predicts that salamanders from each clutch will provide 17.5 g of salamander biomass to other community predators and decomposers, or an average of 1.8 g per year. Population density is estimated to be between 0.4 and 1.4 salamanders per square meter of stream bed. The corresponding average annual production would then fall between 0.1 and 0.3 g/m2 of stream bed. INTRODUCTION Measures of the importance of populations of a particular species in a particular community are usually based on abundance and size of the individuals of the species. When these measures are used to define the importance of plant species, the information gained is of considerable value, for the physical structure of the community can be derived from them. The same inforrmation about an animal species, however, does not define a particular structure. A more interesting measure of the importance of an animal species in its community would be an estimate of the annual production of the pop'ulation of that species. The resulting figure can then be compared with the production of the community as a whole or with that of populations of other species. This paper will present an estimate of the biomass production rate of the stream salamander, Desmognathus fuscus. A population of D. fuscus in Gaston Co., North Carolina, was sampled in five spring collections during 1961 and 1962. The data obtained from these collections are presented graphically in Fig. 1. POPULATION STRUCTURE The initial step in the technique of production estimation which will be utilized in this paper is the derivation of a life-table for the population. The life-table gives the rate at which animals in different age classes are dying, or contributing their biomass to the community. When these rates are multiplied by the weights of the animals in these age groups, the desired rates of biomass production are obtained. The life-table derived from the data in Fig. 1 is given in Table 1. The construction of this table follows the directions of Birch (1948), and the example of Organ (1961) for salamanders of the genus Desmognathus. The remainder of this section is a description of the construction of the life-table. 1 Present address: Department of Zoology, University of Washington, Seattle, Washington 98105.