Data from: Competition between mixo- and heterotrophic ciliates under dynamic resource supply

The outcome of species competition strongly depends on the traits of the
competitors and associated trade-offs, as well as on environmental
variability. Here we investigate the relevance of consumer trait variation
for species coexistence in a ciliate consumer – microalgal prey system
under fluctuating regimes of resource supply. We focus on consumer
competition and feeding traits, and specifically on the consumer’s ability
to overcome periods of resource limitation by mixotrophy, i. e. the
ability of photosynthetic carbon fixation via algal symbionts in addition
to phagotrophy. In a 48-day chemostat experiment, we investigated
competitive interactions of different heterotrophic and mixotrophic
ciliates of the genera Euplotes and Coleps under different resource
regimes, providing prey either continuously or in pulses under constant or
fluctuating light, entailing periods of resource depletion in fluctuating
environments, but overall providing the same amount of prey and light.
Although ultimate competition results remained unaffected, population
dynamics of mixotrophic and heterotrophic ciliates were significantly
altered by resource supply mode. However, the effects differed among
species combinations and changed over time. Whether mixotrophs or
heterotrophs dominated in competition strongly depended on the genera of
the competing species and thus species-specific differences in the minimum
resource requirements that are associated with feeding on shared prey,
nutrient uptake, light harvesting and access to additional resources such
as bacteria. Potential differences in the curvature of the species’
resource-dependent growth functions may have further mediated the
species-specific responses to the different resource supply modes.
Overall, our study demonstrates that genus- or species-specific traits
other than related to nutritional mode may override the relevance of
acquired phototrophy by heterotrophs in competitive interactions, and that
the potential advantage of photosynthetic carbon fixation of
symbiont-bearing mixotrophs in competition with pure heterotrophs may
differ greatly among different mixotrophs, playing out under different
environmental conditions and depending on the specific requirements of the
species. Complex trophic interactions determine the outcome of
competition, which can only be understood by taking on a multidimensional
trait perspective.