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Complete compensation in Daphnia fecundity and stage-specific biomass in response to size-independent mortality
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Wageningen IMARES, PO Box 68, 1970 AB IJmuiden, the Netherlands.
2010 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 79, no 4, 871-878 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
John Wiley & Sons, Inc , 2010. Vol. 79, no 4, 871-878 p.
Keyword [en]
biomass compensation, biomass model, compensatory response, Daphnia pulex, harvesting, population dynamics, population regulation, regulatory mechanisms, size dependence, stage structure
URN: urn:nbn:se:umu:diva-35812DOI: 10.1111/j.1365-2656.2010.01679.xISI: 000278399300017OAI: diva2:349273
Available from: 2010-09-21 Created: 2010-09-06 Last updated: 2010-09-24Bibliographically approved
In thesis
1. Effects of size-dependent predation and competition on population and community dynamics
Open this publication in new window or tab >>Effects of size-dependent predation and competition on population and community dynamics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Most animals grow substantially during their lifetime and change in competitive ability, predatory capacity and their susceptibility to predation as they grow. This thesis addresses the implications of this on regulation and dynamics within populations as well as between population interactions.

In size-structured populations either reproduction or maturation may be more limiting. If juveniles are competitively superior, the competitive bottleneck will be in the adults and reproduction will be limiting. Mortality will in this case result in overcompensation in juvenile biomass through increased reproduction. Compensation in biomass was demonstrated in Daphnia pulex populations subjected to size-independent mortality, where juvenile biomass did not decrease when a substantial harvest was imposed due to increase per capita fecundity. This supported that juveniles were superior competitors and that population cycles seen in Daphnia are juvenile-driven.

Compensatory responses in biomass may lead to that predators facilitate eachothers existence by feeding on a common prey, a phenomenon coined emergent facilitation. In an experimental test of the mechanism behind emergent facilitation it was demonstrated that the invertebrate predator Bythotrephes longimanus was favoured by thinning of its prey Holopedium gibberum. The thinning mimicked fish predation and targeted large individuals while Bythotrephes preferrs small prey.

Size dependent predation also occurs within populations, i.e. cannibalism, were large individuals feed on smaller conspecifics. Two populations of the common guppy (Poecilia reticulata) originating from different environments were demonstrated to differ in cannibalistic degree. Cannibalism was also affected by the presence of refuges and females and juveniles from one population were better adapted to structural complexity than the other.

The effects of these differences in cannibalism on population regulation and dynamics were studied in long term population experiments. Both populations were regulated by cannibalism in the absence of refuges, and displayed cannibal-driven cycles with suppression of recruitment and high population variability. The presence of refuges decreased density dependence and population variability and harvesting of large females in the absence of refuges led to population extinctions in the more cannibalistic population. The less cannibalistic population had higher population biomass and stronger density-dependence in the presence of refuges. When refuges were present, cohort competition increased and cycles with short periodicity were seen.

Large individuals were not only cannibals, but could successfully prey on other species. Small and large guppies were allowed to invade resident populations of Heterandria formosa. Small invaders failed while large invaders succeeded as predation from large invaders broke up the competitive bottleneck that the resident population imposed on juveniles of the invader. 

Place, publisher, year, edition, pages
Umeå: Institutionen för ekologi, miljö och geovetenskap. Umeå universitet, 2010. 34 p.
size-structure, cannibalism, resource competition, predation, emergent facilitation, population regulation, population dynamics, overcompensation, density-dependence, cycles
Research subject
Animal Ecology
urn:nbn:se:umu:diva-35686 (URN)
Public defence
2010-10-15, Kemi- biologihuset, KB3B1, Umeå universitet, Umeå, 10:00 (English)
Available from: 2010-09-24 Created: 2010-08-31 Last updated: 2014-01-27Bibliographically approved

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Nilsson, Karin A.Persson, Lennart
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