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Peer Review




Overall Numeric Rating:

4 stars
Content Quality: 4 stars
Effectiveness: 5 stars
Ease of Use: 4 stars
Reviewed: Aug 12, 2001 by Biology Editorial Board
Overview: "Grass World" is an ecological simulator from Yale University?s Center for Computational Ecology. The program uses Gecko, an individual-based simulator for modeling ecosystem dynamics. The Grass World models are of an essentially flat system featuring a three-level food chain: plants that use sunlight and soil nutrients, herbivorous grasshoppers, and carnivorous spiders. Organisms are represented by dynamic spheres that represent space occupancy and interaction with the model ecosystem. The size of an organism is defined by the radius of the sphere, which can be viewed either as a two-dimensional circle, or as a three-dimensional sketch of the sphere. Menus besides the model provide discussion, exploration, help and references. Top menu buttons enable the user to vary scenarios, parameters, and steps throughout the simulation. Graphical representations, using Java Applets, allow visualization of scaled biomass and population size.
Type of Material: Simulation
Technical Requirements: HTML with Java Applet
Target Student Population: Advanced College or Graduate

Evaluation and Observation

Content Quality

Rating: 4 stars

Quality of Content: (4.60) (4.25) = Rounded to 4.4

  • Clearly laid out and organized.

  • Material complete.

  • Accurate with excellent references to justify simulations.

  • Good use of simulation with text annotations available in side menu.

  • Graphics are straightforward.

Concerns: None

Potential Effectiveness as a Teaching Tool

Rating: 5 stars

Potential Effectiveness as a Teaching Tool: (4.50) (4.50) = Rounded to 4.5

  • Great resource for ecosystem modeling.

  • Graphics are good, but could be converted to 3-D to make more engaging for

  • Site provides two scenarios with directions on how to set the simulation,
    as well as questions to answer.

  • Ability to vary animations enriches the learning experience.

  • Excellent use of discussion, help, and references in side menu.


  • May be too complex for beginning college students.

Ease of Use for Both Students and Faculty

Rating: 4 stars

Usability: (4.25) (4.20) = Rounded to 4.2

  • Visualization through the three-dimensional representation of the simulation
    is very helpful in understanding the simulator.

  • Easy to navigate.

  • Simulation can be controlled with pause and restart buttons.

  • Average speed, but good for Java Applet.

  • No major bugs or defective links.


  • A default simulation begins upon entering the site with Population and Scaled Biomass graphs overlaying the main screen. This may confuse first-time users.

Features of Excellence:

  • Side menus contribute excellent documentation of the simulation.

  • Top menus provide good co ntrol of animations and variation of simulations.

  • Emphasizes graphical interpretation of data.


  • Animations might be more engaging with 3-D graphics.

  • Additional links providing basic information about ecosystem modeling would better prepare some students for experiencing the simulation.

  • Additional assignments would be useful.

Overall Rating: (4.38) Rounded to 4.4