Community Assembly Lab

Community Assembly Lab

David Bishop and Tad Fukami

Background

Ecological communities are not created instantly, but are constructed through repeated invasions of species. This process is known as "community assembly" (see Drake 1991). With different scenarios of community assembly, the resulting community structure can look different even under a similar set of environmental conditions (see Sutherland 1974). For example, different sequences of invasions can produce alternative species compositions. Such effects of invasion sequence are important to understanding why communities we see today look as they do: it may not be sufficient to study community structure at present, but we may also need to know the history of community assembly.

Outline of this lab

In this lab, we will have three algal species that compete over nutrients. They are green algae (GREEN), blue algae (BLUE), and red algae (RED). These species have been set to differ in two characteristics, "cost of living" and "prey value." We will manipulate invasion sequence of these species. Your task is to observe whether different sequences of invasions produce different community structures and, if they do, discuss possible ecological explanations for the production of alternative community states.

In addition, we will pay close attention to the variation among replicates of the same sequence. You may find some sequences deterministic and others indeterministic. By deterministic, we mean that that sequence always results in the same species composition. By indeterministic, we mean that the same sequence lead to different compositions each time the simulation is run.

Start Up

Run EcoBeaker and open the situation file entitled "community assembly"

Click on GO in the control panel box. After 300 days have passed click STOP. The table on the right of your monitor shows you how many individuals of each species are present at 300 days. The graph above gives you the same information.

Currently all the three algal species are introduced at day 50. In the next section, you will change the order each species is introduced by changing the numbers in the box.

Click on the RESET button. Read all instructions carefully. As you go through the lab, record all data in your notebook.

The Lab

First sequence: Red, Blue, Green

By changing the numbers in the box, set RED to be introduced at day 50, BLUE at day 100 and GREEN at day 150.

Click START and let it run for 300 days. After 300 days click STOP and record number of each species present.