Non-linear Zooplankton Models

The summer is over, and classes have started again.  l can say with certainty that I had a productive and enjoyable summer in Williamsburg.

This summer, we began working with a new, non-linear model for the Acartia tonsa population in the Chesapeake Bay. The model is shown below.


My goal for this summer was to find biologically realistic parameters for this model, so that we could conduct relevant analysis on the model.  I combed the literature to find parameters or data that I could use to calculate parameters. I was most interested in finding data to calculate the grazing rate on phytoplankton, cannibalism rate, and prey choice. I also found the non-predatory mortality rate and an estimate of the carrying capacity for the phytoplankton.  Unfortunately the actual process of finding the parameters was not very interesting to tell about, because it mainly involved reading many papers and performing data fits in MATLAB. To give you some idea, the figure below shows a year’s worth of abundance of phytoplankton.  This figure was used to estimate the carrying capacity in the Chesapeake Bay.


Using data from a paper looking at the cannibalism rates of A. tonsa, I found the prey choice to be around.98, which suggests that the zooplankton spend most of their time cannibalizing the young rather than grazing on phytoplankton. But because this data set lacked information on the phytoplankton grazing rates, I am a little skeptical of these results.

I would still like to estimate the growth rate of the phytoplankton, and I am interested in conducting my own experiments to better study the prey choice between grazing on phytoplankton and cannibalism of the younger stage classes.



  1. Presumably older zooplankton prefer to cannibalize younger zooplankton because animals have a higher caloric density than phytoplankton. This would allow the zooplankton to grow faster as well as require them to spend less time feeding. However, the young zooplankton must be getting energy from somewhere, presumably by eating phytoplankton. It would be interesting to examine how the rates of phytoplankton grazing and cannibalism differ between younger and older zooplankton. It is also interesting that cannibalism is such a predominate strategy because it would be more risky than phytoplankton grazing. Plants don’t fight back when they are being eaten whereas eating other animals could be a risky endeavor. However, if older zooplankton are large enough to cannibalize younger zooplankton with little risk of injury, then cannibalism would be the most effective feeding strategy.