The Effects of Population Density on the Reproduction and Survival of Daphnia Magna
Abstract
The population dynamics of Daphnia magna are observed under three different conditions; low, medium, and high density. The effects of different population densities on the survivorship and reproduction of Daphnia are observed over a two-week period within a lab environment. Over the two week period, the numbers of parent Daphnia alive and dead are recorded daily, along with the amount of offspring produced each day. From the main parameter investigated, the net reproductive rate, the results of the experiment support that higher densities result in less successful reproduction and decreased fecundity. Values for the instantaneous growth rate of the populations also suggests that low and medium density populations allow for greater growth rates than high density populations. The results indicate that greater resource availability is directly related to higher fecundity, but that medium density populations can have similar growth rates despite a much smaller birth rate.
Introduction
In any population, birth rates, mortality rates, immigration, and emigration determine whether the population’s numbers will increase, decrease, or remain the same. Factors that can have great effects on both fecundity and mortality rates can include density-dependent mechanisms (those that have a greater influence on population dynamics as population densities remain high) and intraspecific competition (occurs when members of the same species compete for resources). The objective of our experiment is to determine the effect that population density has on both the survival and reproduction of lab-grown Daphnia magna. Because the experiment was done in a controlled lab environment, immigration and emigration of individuals can be ignored. This study will address how certain variables, such as net reproductive rate and instantaneous rate of growth, change with respect to three different population densities of Daphnia. The ecological hypothesis of this experiment
The population dynamics of Daphnia magna are observed under three different conditions; low, medium, and high density. The effects of different population densities on the survivorship and reproduction of Daphnia are observed over a two-week period within a lab environment. Over the two week period, the numbers of parent Daphnia alive and dead are recorded daily, along with the amount of offspring produced each day. From the main parameter investigated, the net reproductive rate, the results of the experiment support that higher densities result in less successful reproduction and decreased fecundity. Values for the instantaneous growth rate of the populations also suggests that low and medium density populations allow for greater growth rates than high density populations. The results indicate that greater resource availability is directly related to higher fecundity, but that medium density populations can have similar growth rates despite a much smaller birth rate.
Introduction
In any population, birth rates, mortality rates, immigration, and emigration determine whether the population’s numbers will increase, decrease, or remain the same. Factors that can have great effects on both fecundity and mortality rates can include density-dependent mechanisms (those that have a greater influence on population dynamics as population densities remain high) and intraspecific competition (occurs when members of the same species compete for resources). The objective of our experiment is to determine the effect that population density has on both the survival and reproduction of lab-grown Daphnia magna. Because the experiment was done in a controlled lab environment, immigration and emigration of individuals can be ignored. This study will address how certain variables, such as net reproductive rate and instantaneous rate of growth, change with respect to three different population densities of Daphnia. The ecological hypothesis of this experiment
Cited: Ban, S., Tenma, H., Mori, T., and Nishimura, K. 2009. Effects of physical interference on life history shifts in Daphnia pulex. Journal of Experimental Biology 212: 3174-3183. Cox, E.J., Naylor, C., Bradley, M.C., and Calow, P. 1992. Effect of differing maternal ration on adult fecundity and offspring size in laboratory cultures of Daphnia magna Straus for ecotoxicological testing. Aquatic Toxicology 24: 63-74. Luerling, M., Roozen, F., Van Donk, E., and Goser, B. (2003). Response of Daphnia to substances released from crowded congeners and conspecifics. Journal of Plankton Research 25: 967-978. Nandini, S., S.S.S. Sarma, and Ramirez-Garzia, P. 2000. Life table demography and population growth of Daphnia laevis (Cladocera, Anomopoda) under different densities of Chlorella vulgaris and Microcystis aeruginosa. Crustacaena 73: 1273-1286. Preuss, T.G., Hammers-Wirtz, M., Hommen, U., Rubach, M.N., and Ratte, H.T. (2009). Development and validation of an individual based Daphnia magna population model: The influence of crowding on population dynamics. Ecological Modelling 220: 310-329. Yurista, P.M., and W.J. O’Brien. (2001). Growth, survivorship and reproduction of Daphnia middendorffiana in several Arctic lakes and ponds. Journal of Plankton Research 23 :733-744.