DO NUTRIENT-COMPETITION MODELS PREDICT NUTRIENT AVAILABILITIES IN LIMNETIC ECOSYSTEMS

Recent theory on resource competition, predicated on the importance of hypothesized trade-offs between minimum requirements for nutrient res ources, predicts that there should be negative correlations between th e supply rate of major limiting nutrients and the availability of at l east some secondary nutrients and/or among the availabilities of diffe rent limiting nutrients. However, an analysis of four data sets from l arge-scale surveys of lakes shows mostly positive correlations among t he availabilities and supplies of nutrients. In contrast, a fifth data set, obtained in an area of high acidification, does show several imp ortant negative correlations that are consistent with the nutrient com petition models. Further analyses suggest two possible explanations fo r the preponderance of positive correlation. Negative correlations bet ween nutrients and light indicate that an important trade-off among sp ecies regulating phytoplankton may involve low light requirements vers us low nutrient requirements. The existence of negative correlations i n nutrient availabilities in acidic lakes (where herbivory appears les s important than in buffered lakes) also suggests that another importa nt trade-off may involve an ability to minimize loss rates (especially due to grazing) versus an overall ability to exploit nutrient resourc es.