PARENT SESSION
Oral Session #27: Aquatic Ecology: Lake structure and function. Presiding: L.A. Hansson.
Tuesday, August 7, 2001. 8:00 AM to 11:30 AM. Hall of Ideas I.

The relative importance of resource limitation and predator limitation in 10 Michigan lakes of varying productivity.

Darcy, Tara¹, ¹

ABSTRACT- Few studies have addresssed how the relative importance of resource limitation and predator limitation may vary along a gradient of productivity. To address this question, I conducted an experiment in 10 southwest Michigan lakes that vary widely in productivity, ranging in total phosphorus levels from 9.8 g/L to 122.8 g/L. Benthic algae (primary producers) were the focal trophic level in the experiment. Benthic algal communities were established on clay pots in situ for 30 days prior to the beginning of the experiment. After peak biomass of benthic algae was reached, I manipulated resource levels (addition of N and P versus ambient nutrients to the interior of the clay pot) and predators (removal of grazers versus ambient grazers) in a 2x2 factorial design. Benthic algae were sampled from the clay pots 6 days later to measure algal biomass [chlorophyll a(chl a)], mat chemistry (%C, %N, and %P), and community composition (genera). I calculated algal growth rates in each of the four treatments as the difference in the natural logarithms of chl a values on day 0 and day 6. Strengths of resource limitation and predator limitation in each lake were estimated as the difference in algal growth rates between control and resource addition treatments, and the difference between control and predator removal treatments, respectively. Results indicate that resource limitation of benthic algae tends to be stronger than predator limitation in most systems, and the amount of resource limitation remains relatively constant regardless of the overall productivity of the lake. Predator limitation tends to decrease as the productivity of the lake increases, but the relationship is not significant.

KEY WORDS: limitation, productivity, benthic algae, lakes