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Paradox of the Cichlids T.Janzen & R.S.Etienne Community and Conservation Ecology Group, University of Groningen Introduction The young age and high diversity of the cichlids in the three African rift lakes has amazed biologists, ecologists and evolutionary researchers for many years. Lake Tanganyika is deeper, older, and has a more complex bathymetry than the other two lakes. Ecological and evolutionary theory tells us that it should have the most species of the three lakes, but it has the fewest. Why? Lake Victoria Lake Lake Malawi Tanganyika Age (My) 0.25-0.75 3–5 9 – 12 # Species ~700 ~700 ~250 68 635 29 600 32 893 83 m 706 m 1 471 m Area (km2) Water height Depth Million years ago Proposed lake level of Lake Tanganyika Existing theory ignores external factors •Lake Age Differences in age could promote diversity by granting more time for speciation to act, but it also grants more time for extinction to occur. •Water level fluctuations Over the history of the three lakes water level changes have not been rare instances, but rather recurring phenomena. Frequent changes of water level could promote diversificiation by changing lake size. •Bathymetry Lake Tanganyika is the deepest of the three lakes and consists of three sub-basins that cause the lake to split up when water levels are low. Interaction between the water level and the bathymetry could therefore promote allopatric speciation. Research questions •How do external factors influence biodiversity? •How do allopatric and sympatric speciation interact during adaptive radiation? •What is the influence of bathymetry on the differences in biodiversity in the rift lakes? •Is sexual selection stronger in lake Malawi compared to lake Tanganyika? picture courtesy Jen Reynolds Approach To answer these questions we will make use of spatially explicit individual based simulations. We will develop a general model assessing the influence of environment size, environment shape and environment stability on biodiversity. Using this general model we will be able to make predictions on the african rift lake system, incorporate specifics of the african rift lakes and make accurate predictions about current biodiversity estimates.