โ Scribed by H. B. N. Hynes; W. D. Williams
No coin nor oath required. For personal study only.
WILLIAMS (1962a, 1962b) has shown that there is reason to believe that Asellus meridianus RAC. and Asellus aquaticus (L) ., two species of isopods which are widely distributed in Britain and parts of Europe, and hereafter referred to as M and A respectively, occupy very similar ecological niches in Britain; and that the latter is replacing the former by competitive exclusion . Laboratory experiments designed to show that the presence of one species affected the survival and abundance of the other were not conclusive (WILLIAMS 1963), and they had to be discontinued when WILLIAMS left Britain for Australia . The present paper describes further experiments, carried out by HYNES in Liverpool, England, in consultation with WILLIAMS .
Seventy five aerated jars were set up in an unheated aquarium in December 1960 . The jars were in two series : 15 were small (9 cm in diameter) and contained half a litre of tap water, and 60 were large (14 cm in diameter) and contained 12 1 of tap water . The bottom of each jar was covered with a 1 cm layer of calcareous sand and to each were added about 20 autumn-shed elm leaves .
The large jars were themselves divided into four classes . Fifteen
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