The effect of invasion rate, species pool, and size of area on the structure of the diatom community.

Abstract

what effect altering the invasion rate had on the structure of the community. The third series of experiments was a comparison of the structure of diatom communities in structurally and chemically similar streams on the island of Dominica and in the United States. The temperature of the water in the two rivers was similar when the studies were made. Methods and Procedures.--In order to carry out the first series of experiments, duplicate smnall glass squares 9 mm2, 36 mm2, and 625 mm2 were each erected on a small plastic pedicel about 10 mm in length which was fastened onto a glass slide. These glass slides were placed in plastic boxes which were opened so that the current would pass across the glass squares, giving sirmilar conditions for the attachment of the diatoms across the surface. Having the current strike the slides would have created strong, uneven current patterns. The slides were p]aced in clean boxes each day and the pedicels and slides carefully cleaned. This was to minimize the chance that diatoms from sources other than the passing water might invade the glass squares on the ends of the pedicel. The experimental design was to simulate the invasion of species from distant sources onto islanids of varying size ranges. These slides were placed in the flowing water from a spring (Roxborough Spring) and in a eutrophic stream (Ridley Creek). Previous studies had shown that the total number of species in Roxborough Spring in the area studied was about 60 at any onie time, and in Ridley Creek about 250. It should be noted that the chemical characteristics of the water and the temperature were more variable in Ridley Creek than in Roxborough Spring. Since the spring has a deep source, the chemical characteristics and temperature of the water in it remain almost constant, over long perio(ds of time. The seconid series of experiments was designed to simulate what might happen if the invasioni rate were lowered as hapiperis onl. an islanid fairly distanit from a