Relative Size

The model may suggest how the relative populations of rabbits and foxes compare with each other.

Observe the predictions of the model for values in these ranges:

Initial # rabbits (R) between 50 and 200
Initial # foxes (F) between 50 and 200
Rabbit birth rate (B) between .04 and .07
Fox death rate (D) between .04 and .07

Question 3: In the model, is one population (rabbits or foxes) always larger or smaller than the other?
The populations will fluctuate as rabbits get eaten by foxes and the fox population grows, the rabbit population will decrease and as foxes die of natural causes or a lack of avaliable food, the rabbit population will increase as the fox population decreases. Sometimes the populations of each species will be pretty even with each other but the exact number of animals in each species will not be equal and one population will always be larger or smaller than the other depending upon which population has the upperhand. There is not one species (rabbits are foxes) alone that tends to be larger or smaller in population. The size of each species fluctuates adn demonstrates that the rabbits population can outweigh the fox population and vice versa depending on the predator/prey relationship changes.

-While the population fluctuates as described, the rabbit population tends to be larger-but also more inconsistent-than the foxes. The foxes have a more steady population, but their population determines the rabbits population. It is not an issue of which species has the "upperhand" because it is a Predator-Prey model, demonstrating a species' dominance and ability to determine the population of another species through hunting. It is a perfect example of "Survival of the Fittest," within the rabbit and fox populations. For the rabbits-whoever can escape the foxes, and for the foxes-whoever can capture the rabbits, will unequivocally be the ones who survive. To answer the initial question-Neither the rabbits nor foxes are always larger or smaller.-

Question 4: Does this prediction make sense? Why might the populations behave like the model suggests? Or why not?
This prediction does make sense due to the obvious fluctuations represented in this model. The populations of foxes and rabbits depend on each other, because the foxes find nourishment through the rabbits. On the other hand the rabbit’s population is effected by the number of foxes that pose a threat. Populations may fluctuate similarly to the model’s predictions; however, I believe that these differences may be more mutual. In any environment, organisms must keep other’s populations in check. For example, foxes become much more susceptible to disease when populations are high. Despite the assumption that the island can sustain the rabbits with more than enough food, no island in the world has an unlimited amount of food. Therefore, the population of rabbits must also not exceed the amount of nutrients available on the island. In conclusion, these populations may balance each other as shown in the model, due to their dependence on each other, as well as their environment.

Question 5: What does this have to do with a concept from Ecology called the "Ecological Pyramid"?
This model clearly demonstrates the "Ecological Pyramid of Productivity". The pyramid helps define something similar to the food chain, however, productivity pyramids pay attention to the energy flowing through the food chain. Pyramids of Productivity show the rate of production over time, instead of at a specific time. A rule of an ecosystem is that the most energy must be located in the lower trophic levels (in this case, the rabbits) which allows for those organisms to maintain a stable population while still feeding the animals of the high trophic levels (in this case, the foxes). Referring to the model, we can see that there are always more rabbits than foxes. Moreover, the amount of primary produces is greater than the amount of primary consumers, while the number of each becomes larger as time progresses.

NOTE: Until April 17, please answer only one of the unanswered research questions. If you have an original contribution to make on a question someone else already has answered, you may include it at any time.

page revision: 22, last edited: 24 Apr 2008 18:18