PhytoZoo: Phytoplankton-Zooplankton Interaction Model (v1.0)


(c)Ferdi Hellweger, Northeastern University, Boston.

NOTE: The applet requires Java 1.4.1 or higher. It will not run on Windows 95 or Mac OS 8 or 9. Mac users must have OS X 10.2.6 or higher and use a browser that supports Java 1.4. (Safari works, IE does not. Mac OS X comes with Safari. Open Safari and set it as your default web browser under Safari/Preferences/General.) On other operating systems, you may obtain the latest Java plugin from Sun's Java site.

QUICK START: Click setup (may have to hit it twice), then go.



This model illustrates the interaction of phytoplankton and zooplankton in a lake. The phytoplankton (green dots) are little plants that float around in the water due to turbulence. They also grow by a process called photosynthesis, which is continuous here because there is plenty sunlight and nutrients. The zooplankton (black “monsters”) are little animals that move around and eat the phytoplankton. The zooplankton also die periodically.

At the beginning of the simulation, there are not many zooplankton, and as a consequence, the number of phytoplankton increases rapidly. However, as the food source for the zooplankton increases, their number starts to increase as well. After some time, there are enough zooplankton to significantly reduce the number of phytoplankton. This, in turn, means less food available for the zooplankton and their numbers starts to decrease due to death. Now that the zooplankton number is lower again, the phytoplankton don’t get eaten that much, so their number increases again. The cycle continues from the beginning.

Note: The model is based on basic predator-prey interaction models. However, to prevent an artifact known as "numerical extinction" (due a limited number of agents), the agent numbers for the phytoplankton and zooplankton are prevented from going to zero.


This model was created by Ferdi Hellweger using NetLogo by modifying an existing sample model in the NetLogo model library. Here are the relevant NetLogo references:

Wilensky, U. & Reisman, K. (1999). Connected Science: Learning Biology through Constructing and Testing Computational Theories -- an Embodied Modeling Approach. International Journal of Complex Systems, M. 234, pp. 1 - 12. (This model is a slightly extended version of the model described in the paper.)

Wilensky, U. & Reisman, K. (in press). Thinking like a Wolf, a Sheep or a Firefly: Learning Biology through Constructing and Testing Computational Theories -- an Embodied Modeling Approach. Cognition & Instruction.

Wilensky, U. (1998). NetLogo Wolf Sheep Predation model. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

Here is the source code: PhytoZoo.nlogo

Here is a reference to learn more about phytoplankton and zooplankton and their interaction:

Chapra, S. C. 1997. Surface water-quality modeling. McGraw-Hill, Boston.

Here is a link to Ferdi's homepage:

Ferdi Hellweger Homepage