Trophic relationships inside the lake Nakuru during two different phases. Journal Article: Moreau, J, K. Mavuti and T. Daufresne (2001) A Synoptic Ecopath model of biomass flows during two different static ecological situations in Lake Nakuru (Kenya) Hydrobiologia Volume 458, 63-74.
Nakuru lake is situated in the Gregory rift in Kenya. • Sudden changes in physico-chemical characteristics. • Studied by a group of German Scientists: E. Vareschi, J. Jacobs . • No ‘normal’ lake Nakuru: constant changing, unpredictable pattern.
Two successive Phases • 1972-1973: High water level – High productivity of all trophic components. • 1974-1975: Period of low productivity. • 1976-1978: Period of recovery. • Using the ECOPATH model tried : 1)to provide model representations corresponding to the two critical periods. 2) See what impact the changing of the biomass of a main group has on the lake. 3) Approach the general pattern of changes.
Ecopath: Free ecosystem modelling software • comprises species of common physical habitat, similar diet, and life history characteristics into ‘’boxes’’. • They assumed that in each of the two periods the ecosystem was near equilibrium conditions. • All key data were obtained from published literature on the lake itself ( mostly from E. Vareschi, J Jacobs studies).
Groups used in Ecopath • Pelicans , Minor birds,Greater Flamingos, lesser Flamingos. • Rotifers, Zoobenthos, Heteroptera, Copepods. • CyanobacteriumS.Platensis,, nanoplakton, benthic algae, detritus.
Some Results • Codependence between living communities. • Pelicans population stable • Decrease of the population of S. Platensisin 1974 the cause of lesser flamingos migration. • Collapse of copepods the cause of greater Flamingos migration. • The collapsing of S.Platensis in 1974 the cause of the increase in benthic algae, detritus and nanoplakton • In late 1974, increase of benthic algae and detritus the cause of zoobenthos development and return of greater flamingos.
Transfer efficiencies very similar in both phases. • Global trophic Structure remains similar despite the changes of abundance of the various groups between the two phases. • This partly explains the survival of Lake Nakuru ecosystem. • Reason of sudden collapse of S. Platensis and Copepods not clear. • The reasons of the spectacular changes not only physicochemical but also Biological. • Lake Nakuru is STILL CHANGING!!!