Mixotrophs combine resource use to outcompete specialists: Implications for aquatic food webs

J Tittel, V Bissinger, B Zippel, U Gaedke, Elanor M Bell, A Lorke, N Kamjunke

Research output: Contribution to journalArticlepeer-review

184 Citations (Scopus)

Abstract

The majority of organisms can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such "mixotrophy" is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, and the benefits must outweigh these costs. In accordance with mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light, mineral nutrients, and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724). Here, we demonstrate the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake mixotrophs reduced prey abundance steeply. The data suggest that, as a consequence, grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from competition with and losses to higher grazers. Furthermore, the mixotrophs structured prey abundance along the vertical light gradient, creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient-poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments.
Original languageEnglish
Pages (from-to)12776-12781
Number of pages6
JournalP NATL ACAD SCI USA
Volume100
Issue number22
DOIs
Publication statusPublished - 2003

Keywords

  • OLIGOTROPHIC LAKE
  • DYNAMICS
  • INTERSPECIFIC COMPETITION
  • ACIDIC MINING LAKE
  • NANOPLANKTON
  • SARGASSO SEA
  • DEEP CHLOROPHYLL MAXIMUM
  • MEDITERRANEAN SEA
  • PICOPLANKTON
  • PHYTOPLANKTON COMMUNITY

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