Evolutionary and plastic rescue in multitrophic model communities

Under changing environmental conditions, intraspecific variation can potentially rescue populations from extinction. There are two principal sources of variation that may ultimately lead to population rescue: genetic diversity and phenotypic plasticity. We compared the potential for evolutionary rescue (through genetic diversity) and plastic rescue (through phenotypic plasticity) by analysing their differential ability to produce dynamical stability and persistence in model food webs. We also evaluated how rescue is affected by the trophic location of variation. We tested the following hypotheses: (i) plastic communities are more likely to exhibit stability and persistence than communities in which genetic diversity provides the same range of traits. (ii) Variation at the lowest trophic level promotes stability and persistence more than variation at higher levels. (iii) Communities with variation at two levels have greater probabilities of stability and persistence than communities with variation at only one level. We found that (i) plasticity promotes stability and persistence more than genetic diversity; (ii) variation at the second highest trophic level promotes stability and persistence more than variation at the autotroph level; and (iii) more than variation at two trophic levels. Our study shows that proper evaluation of the rescue potential of intraspecific variation critically depends on its origin and trophic location.     

The use of integrated constructed wetlands (ICW) for the treatment of separated swine wastewaters

Haplochromine cichlids used to be the main prey of the introduced Nile perch, Lates niloticus, in Lake Victoria. After depletion of the haplochromine stocks at the end of the 1980s, Nile perch shifted to the shrimp Caridina nilotica and to a lesser degree to its own young and the cyprinid Rastrineobola argentea. In the present study, we investigated the Nile perch diet in the northern Mwanza Gulf after resurgence of some of the haplochromine species and compared it with data collected in the same area in 1988/1989. It became clear that haplochromines are again the major prey of Nile perch. The dietary shift from invertebrate feeding (shrimps) to feeding on fish (haplochromine cichlids) occurs at a smaller size than it did when Nile perch were taking primarily dagaa and juvenile Nile perch as their fish prey. The apparent preference for haplochromines as prey has reduced the degree of cannibalism considerably, which may have a positive impact on Nile perch recruitment.