From laboratory experiments, it has been suggested that visually guided fee
ding, chemical and mechanical perception of increased ingestion rate (inclu
ding perception of hunger and satiation), and odors associated with algae h
elp Daphnia in tracking food gradients. To test the ability of Daphnia to f
ind food in the field, suspended yeast, suspended clay. or control water wa
s pumped into a localized point in the littoral zone of Lake Myravann (Berg
en, Norway), Daphnia longispina and Daphnia pulex, the most numerous zoopla
nkton species in the experimental area, aggregated in areas of yeast input
but not when adding suspended clay or control water. Thus, Daphnia is able
to evaluate the patches both quantitatively and quatitatively, possibly thr
ough perception of increased ingestion rate and odor, while light scatterin
g is indicated to be unimportant. This is the first experiment to demonstra
te that Daphnia is able to find patches of food under natural conditions.