Changes in life-history traits during community assembly.
Wolnowska, Izabella *,1, Caceres, Carla1, 1 University of Illinois at Urbana-Champaign, Urbana, IL
ABSTRACT- Plankton ecologists have recently discovered a way to couple a description of past events with experimental tests of the mechanisms underlying the observed patterns. Diapausing eggs of zooplankton can accumulate in large numbers in lake sediments, where they remain viable for decades. When these eggs are removed from the lake and hatched in the laboratory, they provide a living link to past populations and communities. Dozens of lakes in east-central Illinois, USA, were formed within the past century when strip-mining created new basins. We are using the sediment record of these lakes to address questions regarding how genetic diversity, life-history variation and interspecific interactions influence the persistence ability of populations, and consequently, the development of planktonic communities. Sediment cores extending to the formation of each lake have been collected from 8 lakes, and often show clear patterns of species replacement in the cladoceran assemblage through time. In Sportsmans Lake the herbivorous cladoceran Daphnia ambigua invaded early but was later replaced as the dominant species by larger-bodied daphniids. Here, we address life-history variation in Daphnia ambigua, from the time of its colonization of the lake to present. Ten clones were isolated from the water column of Sportsmans Lake as well as three different depths in the sediment. For each of the 40 clones, we conducted abbreviated life tables and juvenile growth rates to quantify key life-history traits. Juvenile growth rate varied over the four time periods; many early colonists were smaller and grew more slowly than did more recent clones.
Key words: life history traits, lakes, Daphnia
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