Fossil Competitive Exclusion Activity

I use this activity as a lab with my invertebrate paleontology course, which is an upper level undergraduate course. That said, this could also be used to discuss the role of competition in any paleo course, or a historical geology course.

Going into this activity, I would want students to have a basic understanding of concepts like competition and niche partitioning. I would also want students to be at least familiar with what corals and bryozoans are, as well as, more generally, what it means to be an encrusting colonial organism.

This activity is one of many weekly labs that relate back to the topics being covered that week. Since this is being used in my invertebrate paleontology course, we complete this activity after learning about bryozoans.

The overall goal is to get students to understand the reasons why different competitive interactions occur between these encrusting organisms, and, more broadly, for them to think about how competition works within ecology (especially for sessile colonial organisms). By introducing students first to the fossil examples of competitive interactions, students can then see how their simulation ends up recreating scenarios that result in these overgrowth/competitive interactions between colonies.

By comparing their simulation to real world data, students can think critically about how we build models and how we can improve/alter the models that we have. Also, more broadly, the structure of the simulation can illustrate the importance of deterministic versus stochastic mechanisms in natural history. The simulation is set up for cheilostomes to win (fitting with the data from overgrowth patterns), but the random nature of the starting location of the colony on the board, as well as the choices individual students make as they grow the colony, highlights the role that contingency and history play in the outcomes of these types of competitive interactions.

Looking at specimens of fossils and interpreting overgrowth patterns can help build spatial thinking skills. Also, this is a group activity that requires working in groups competitively but civilly.

To complete this activity, you will need vinyl mats with hexes on them. Size can vary depending on how long you want the activity to take, but I use 26x23.5 inches. You will need one mat for every 5 students. You will also need colored markers that are designed to draw on vinyl mats. Chessex sells both mats and markers for drawing on said mats (available on Amazon). Finally, you will also need a round thin object with a diameter of around 1.5 to 2 inches which students will use as their initial larvae token for throwing onto the mat (you could use a milk bottle top, a large coin, a POG slammer, etc.).

The write-up for the main activity is attached as supporting material. Below is a short overview of how the activity plays out.

After an introduction that describes the three main types of competitive interactions between encrusters, the simulation starts with groups of five taking turns throwing their round object token onto the mat (their free swimming larvae). Where ever the object lands will be the site of their new colony. Each player will start with a colony of 7 hexes, so when the object lands, have students shift their token so that it is centered around the nearest cluster of 7 hexes. The student will then use their colored marker to draw a perimeter around the 7 hexes that it touches to form their initial colony. Once every player has determined where their colony begins, they then grow their colony following the rules of the activity. Growth is represented by students drawing borders around new hexes in their color. The activity ends when all available space has been occupied. Players then count their spaces to determine who won. Students will then answer questions about the results of their simulation.

Competitive Exclusion Activity (Microsoft Word 2007 (.docx) 885kB Oct8 26)

Students often struggle with visualizing overgrowth on the pictures of real fossils. It can be helpful to let students know that "standoff" means that there is no evidence of one colony growing over the other. This can mean that the two colonies meet along a margin, or that there is a space between the two colonies where neither colony can successfully grow. Whereas overgrowth literally involves one colony growing over the top of the other. Because the questions all involve 2d images, it can make it a bit difficult for students to see the overgrowth patterns on the top two images.

Second, make sure that students follow the overgrowth rules in the simulation. These rules are not necessarily scientifically accurate, but they are written so that the simulation ends in a timely manner. Without limiting overgrowth to just the margins of a colony, players could end up extending the time of the simulation in an unmanageable way. By limiting overgrowth to just the outer margins of any bryozoan colony, you get to the point where no one can grow any further much faster, which is essential to completing the lab within a roughly 2-hour time window.

The "coral" player is not based on any specific species of coral, but is in the game to give an example of an encrusting organism that prevents other colonies from growing near it. This should result in standoff boundaries between the coral player and the bryozoan players.

The bonus points towards their lab grade are put in place both to inspire a bit of competition, but also to balance a game that is intentionally unfair. Cheilostomes grow faster and act first, meaning they should take up the most space. By doubling the extra bonus points cyclostome players receive, this gives students an incentive to try hard to win, despite the odds clearly being stacked against them (and it can cushion the loss).

The final three questions of the activity are what I weigh most heavily in my grading. These questions ask the students to compare the results of their simulation to the real world data. In these questions, students are asked how their simulation did (or did not) fit within the expectations of the real overgrowth patterns. And if there are any deviations, they are asked to explain why this might occur. A good sign that students are understanding the concepts will be if they mention that bryozoans probably do not plan out their competitive interactions in the same way humans might, and that they certainly are not making cross-species alliances.

The PRI has an amazing Digital Atlas of Ancient Life, which is an excellent resource for all things paleo. For context on cheilostomes and cyclostomes, here is a link to their overview on bryozoans.
https://www.digitalatlasofancientlife.org/learn/bryozoa/