Fluctuations In Lifespan And Reproduction Rates Of "Daphnia" Based On Different Environmental And Nutritional Conditions

1513 words - 6 pages

Daphnia are small animals. They are plankton to be precise and they are a major component in the food chain in freshwater environments such as lakes, ponds, rivers, swamps and even in some acidic swamps. Mostly fishes and amphibians such as; toads and frogs feed on them. Hence their rate of growth and reproduction is of a high importance for the reproduction and survival rate of the above mentioned species. In terms of their biological taxonomic unit they belong to the kingdom Animalia, phylum Arthropoda, subphylum Crustacea, class Branchiopoda, order Cladocera, family Daphniidae and genus Daphnia.Daphnia reproduce sexually and parthenogenetically (Sterner, 1998). Parthenogenesis is the asexual reproduction of a species from females only. The females reproduce more females from their unfertilized eggs. No males are available in a parthenogenetic reproduction. Men are only produced for sexual fertilization only, which will help to introduce more variability in the gene pool of the species via sexual reproduction. After the males fertilize the eggs, they die. Sexual reproduction is performed in mid autumn were the conditions for such reproduction is the best (Sterner, 1998). The peak season of Daphnia’s asexual/ parthenogenetical reproduction starts from mid spring to late summer (Sterner, 1998). The sexual fraction of Daphnia’s population ranges between a minimum of 3.0% to a maximum 8.0% of the total population all year around. Hence, the species is considered to be a parthenogenetic species (Hülsmann and Weiler 2000).The rate of survival and the rate of reproduction of Daphnia are highly influenced by the fluctuations and changes that occur in the environmental conditions of their surrounding habitats (Hülsmann and Weiler 2000). Three of the most influential environmental conditions that easily alter these rates are; “lake-origin and food concentration”, “predation by other organisms” and “temperature” (Hülsmann and Weiler 2000).Out of the three factors mentioned above, “predation by other organisms” has the lowest effect on the rate of survival and the rate or reproduction of Daphnia as concluded by the results of the experiment that was conducted by Sterner (Sterner, 1998). The most important factor is “lake-origin and food concentration” followed by the second relevant factor, namely the change in the “temperature” of the environment of Daphnia (Sterner, 1998). Daphnia are mostly filter feeder that feed on algae, small organic particles and smaller organisms like rotifers and bacteria. Their food supply is directly proportional to the “primary production” of the aquatic environment that they are living in (Sterner, 1998). In order to determine the rates of survival and reproduction of Daphnia under different food concentrations, a “starvation-experiment” was conducted on two different taxons of Daphnia; Daphnia Hyaline and Daphnia Galeata...

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