Complete compensation in Daphnia fecundity and stage-specific biomass in response to size-independent mortality

Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Journal of Animal Ecology (Impact Factor: 4.5). 03/2010; 79(4):871-8. DOI: 10.1111/j.1365-2656.2010.01679.x
Source: PubMed


1. Recent theory suggests that compensation or even overcompensation in stage-specific biomass can arise in response to increased mortality. Which stage that will show compensation depends on whether maturation or reproduction is the more limiting process in the population. Size-structured theory also provides a strong link between the type of regulation and the expected population dynamics as both depend on size/stage-specific competitive ability.
2. We imposed a size-independent mortality on a consumer-resource system with Daphnia pulex feeding on Scenedesmus obtusiusculus to asses the compensatory responses in Daphnia populations. We also extended an existing stage-structured biomass model by including several juvenile stages to test whether this extension affected the qualitative results of the existing model.
3. We found complete compensation in juvenile biomass and total population fecundity in response to harvesting. The compensation in fecundity was caused by both a higher proportion of fecund females and a larger clutch size under increased mortality. We did not detect any difference in resource levels between treatments.
4. The model results showed that both stages of juveniles have to be superior to adults in terms of resource competition for the compensatory response to take place in juvenile biomass.
5. The results are all in correspondence with that the regulating process within the population was reproduction. From this, we also conclude that juveniles were superior competitors to adults, which has implications for population dynamics and the kind of cohort cycles seen in Daphnia populations.
6. The compensatory responses demonstrated in this experiment have major implications for community dynamics and are potentially present in any organisms with food-dependent growth or development.

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Available from: Karin A Nilsson
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    • "Theoretical models of varying complexity, from stagestructured to fully size-structured consumer-resource models, suggest that single-generation cycles are to be expected whenever intraspecific competition is asymmetric, with small individuals being competitively superior over large ones in exploiting the common resource (de Roos and Persson 2003). Accordingly, recruit-or juvenile-driven generation cycles have been observed in fish species, including roach (Rutilus rutilus) and vendace (Coregonus albula; Persson and de Roos 2006), as well as in Daphnia (McCauley et al. 1999; Nilsson et al. 2010). The similarity between different types of population models as well as the corresponding empirical data suggests that these effects of intraspecific competition on population dynamics reflect a general characteristic of size-structured populations. "
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