Use of non-limiting substrates to increase size; a generic strategy to simultaneously optimize uptake and minimize predation in pelagic osmotrophs?
Article first published online: 28 APR 2005
Volume 8, Issue 7, pages 675–682, July 2005
How to Cite
Thingstad, T. F., Øvreås, L., Egge, J. K., Løvdal, T. and Heldal, M. (2005), Use of non-limiting substrates to increase size; a generic strategy to simultaneously optimize uptake and minimize predation in pelagic osmotrophs?. Ecology Letters, 8: 675–682. doi: 10.1111/j.1461-0248.2005.00768.x
- Issue published online: 28 APR 2005
- Article first published online: 28 APR 2005
- Editor: Peter Morin Manuscript received 17 November 2004 First decision 29 December 2004 Manuscript accepted 7 March 2005 Exceeds normal length
- cell size;
- food webs;
- life strategies;
- trophic niches
Coexistence of two organisms competing for the same nutrient is possible if one is an ‘uptake’, and the other a ‘predation defence’ specialist. In pelagic food webs this principle has been linked to cell size. Small osmotroph cells, with their high surface : volume ratio, have been argued to be uptake specialists, while larger osmotrophs avoiding the intense grazing pressure from small protozoan predators might represent ‘predation defence’ specialists. This may seem like an obligatory trade-off situation that necessitates a choice of either being small or being large, and thus being potentially dominant in oligotrophic or in eutrophic environments, respectively. However, in a more precise form, the theory for nutrient diffusion states that it is the ‘surface : cell requirement of limiting element’ ratio, rather than the ‘surface : volume’ ratio, that is important. The distinction is crucial, since it opens up the possibility of there being life strategies that use a non-limiting element to increase size. Hypothesized to maximize uptake and predator defence simultaneously, such strategies should be particularly successful. We suggest that this strategy is exploited by osmotrophs with different size and physiology, such as heterotrophic bacteria, unicellular cyanobacteria and diatoms. Since the strategy implies a shift in organism stoichiometry, the biogeochemical implications are strong, illustrating the tight relationships between physical micro-scale processes, organism life strategies, biodiversity, food web structure, and biogeochemistry.