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Refuge availability and within-species differences in cannibalism determine population variability and dynamics
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.
2013 (English)In: Ecosphere, ISSN 2150-8925, Vol. 4, no 8, 100- p.Article in journal (Refereed) Published
Abstract [en]

Theoretical studies show that both cannibalism and intraspecific resource competition can have major effects on population dynamics. Cannibalistic intensity, offspring size, harvesting and refuge availability are important factors affecting the interplay between cannibalism and competition. We studied two populations of the common guppy (Poecilia reticulata) that differed in their cannibalistic voracity as well as offspring size. We manipulated the availability of refuges for juveniles and harvesting intensity of large adults to investigate how these factors influenced the dynamics of the two populations. Overall population dynamics was mainly affected by the origin of the founder populations and the presence of refuges. The population with a higher cannibalistic propensity and smaller offspring exhibited higher population variability, and the presence of refuges reduced cannibalism and stabilised the dynamics in both populations. Harvest of large cannibalistic females destabilised the dynamics and caused extinctions of several populations without refuges. Both populations displayed cannibal-driven cycles with repression of recruitment when no refuges were present. Cycle periods were shorter with refuges present and the dynamics were more cohort like with synchronised peaks in density of vulnerable juveniles and cannibals. We suggest that increased number of refuging juveniles led to intensified resource competition in the population. The harvest yield was low in the refuge treatments as few females grew large due to resource competition, leading to a small impact of harvesting in these treatments.

Place, publisher, year, edition, pages
Washington: Ecological Society of America , 2013. Vol. 4, no 8, 100- p.
Keyword [en]
cannibalism, coefficient of variation, competition, extinction, guppy, harvest, Poecilia reticulata, population dynamics, refuges, structural complexity
National Category
URN: urn:nbn:se:umu:diva-84804DOI: 10.1890/ES13-00105.1ISI: 000327379400009OAI: diva2:691295
Available from: 2014-01-27 Created: 2014-01-20 Last updated: 2014-01-27Bibliographically 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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