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    The Nile perch invasion in Lake Victoria: cause or consequence of the haplochromine decline?

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    Author
    van Zwieten, P.A.M.
    Kolding, J.
    Plank, M.J.
    Hecky, R.E.
    Bridgeman, T.B.
    MacIntyre, S.
    Seehausen, O.
    Silsbe, G.M.
    Date
    2016
    Permanent Link
    http://hdl.handle.net/10092/13005

    We review alternative hypotheses and associated mechanisms to explain Lake Victoria’s Nile perch takeover and concurrent reduction in haplochromines through a (re)analysis of long term climate, limnological and stock observations in comparison with size-spectrum model predictions of co-existence, extinction and demographic change. The empirical observations are in agreement with the outcomes of the model containing two interacting species with life-histories matching Nile perch and a generalized haplochromine. The dynamic interactions may have depended on size related differences in early juvenile mortality: mouth-brooding haplochromines escape predation mortality in early life stages, unlike Nile perch that have miniscule planktonic eggs and larvae. In our model predation on the latter by planktivorous haplochromine fry act as a stabilizing factor for co-existence, but external mortality on the haplochromines would disrupt this balance in favor of Nile perch. To explain the observed switch, mortality on haplochromines would need to be much higher than the fishing mortality that can be realistically re-constructed from observations. Abrupt concomitant changes in algal and zooplankton composition, decreased water column transparency, and widespread hypoxia from increased eutrophication most likely caused haplochromine biomass decline. We hypothesize that the shift to Nile perch was a consequence of an externally caused, climate triggered, decrease in haplochromine biomass and associated recruitment failure rather than a direct cause of the introduction.

    Subjects
    Lakes
     
    Eutrophication
     
    Predator-prey interaction
     
    Invasive species
     
    Climate change
     
    Field of Research::06 - Biological Sciences::0602 - Ecology::060204 - Freshwater Ecology
     
    Field of Research::07 - Agricultural and Veterinary Sciences::0704 - Fisheries Sciences::070402 - Aquatic Ecosystem Studies and Stock Assessment
     
    Field of Research::05 - Environmental Sciences::0501 - Ecological Applications::050101 - Ecological Impacts of Climate Change
     
    Field of Research::05 - Environmental Sciences::0501 - Ecological Applications::050103 - Invasive Species Ecology
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