Note: This was posted by WillW in the other class-might be helpful as we did not assign a scribe that day.
The Isle Royale simulation in class points out the significance of free population growth, the presence of predators, and the availability of food in an ecosystem. The three simulations that we did focus on each of these and their effects on the populations of moose and wolves.
This exercise focused on the population of moose when there are no predators present. We ran the simulation for about fifty years. The resulting graph looks similar to an S curve with a slight rise and fall before it reaches carrying capacity. This is an example of a population overshooting its carrying capacity, which then results in a dieback, also called correction, in the population until the carrying capacity is achieved.
A couple important things to note.
1 – A population grows fastest when it is medium sized.
2 – No population can sustain a J curve indefinitely. There is always a carrying capacity.
3 – The moose overshoot their carrying capacity because they have no natural predators. The dieback is then caused by the resulting food shortage when the moose are placed in direct competition with each other.
4 – The point of greatest population growth is called the inflection point.
In this exercise, wolves were introduced to the island.
This graph shows the relationship in population size between prey and predators, as highlighted by this exercise. There is a sinusoidal relationship between the populations because they rely on each other. The average moose population greatly decreases with the presence of predators. However, the moose that are present in this exercise are generally healthier than those from the first exercise. This is because they have less intraspecies competition for food.
This exercise explored how the length of the growing season effects the wolf and moose populations. We saw that when there was a short growing season, both populations declined in numbers. This was expected, because a smaller growing season means less food for the moose, which leads to less for the wolves.
When the growing season was longer, there was a larger supply of food available for the moose. This led to a spike in the numbers of moose, followed shortly by a increase in the number of wolves. However, both animals eventually became extinct. This is the paradox of enrichment. This is when both the moose and the wolves overshoot their carrying capacity. The unchecked growth of moose leads to surpassing their K. When the food runs out, the combined force of little food and increasing wolf population causes the moose to go extinct. This causes the wolves to go extinct because there is no food left for them.
This is the link to the Isle Royale study home page if you have any questions:
*Yes, check out the site if you have a moment-you can click on an interactive graph with the real data from Isle Royale-interesting and more complex than the simulation. -Mr. W