“…The study on the problem of the influence of toxicants both on the growth of one population and on the competition of two species for a critical nutrient has received considerable attention in the past decades (see, e.g., [1,2,5,11,13,21,22,18,19,20,1374 HUA NIE, SZE-BI HSU AND JIANHUA WU 28,30,31]). Particularly, there has been a lot of interest in the so called allelopathic competitions between species (see, e.g., [2,5,16,21,22,18,24,28]).…”