Data from: Predation and the formation of multicellular groups in algae

Background: The evolution of multicellular organisms must, at some point,
have involved the congregating of single-celled organisms. Algal species
exist that sometimes live in groups and sometimes live as single cells.
Understanding the conditions that lead to algal assemblage in such cases
may cast light on the selective forces that favour multicellularity.
Hypothesis: Forming groups could defend algae against predation if
predators are unable to engulf large-sized entities. Organisms: Three
algal prey (Chlorella sorokiniana, Chlorella vulgaris, and Scenedesmus
obliquus) and three predators (Ochromonas spp., Tetrahymena thermophila,
and Daphnia magna). Methods: We tested the tendency to aggregate in all
nine different prey–predator combinations. Results: At least two of the
predators, Ochromonas and Daphnia, were significant predators because
their presence decreased algal density. In all nine combinations, adding
the predator species led to the formation of algal groups. In three
combinations, adding merely products of the predators in the absence of
the predators themselves stimulated group formation.