The final step in model building is to compare the model's predictions with experiment. We need to find experimental observations that help evaluate our model.
Question 21: What kind of information can you find on the web or in the Library databases about real systems that may be described by this model?
- What real populations have been studied that may be described by the model?
- What kind of animals, plants, or other organisms were involved?
- Where were the located?
When searching the web for real systems that may be described by the Rabbit/Fox predator-prey model I was surprised by the number of hits I received. Not only are there predator/prey interactions, but there are also herbivore-plant, and parasite-host interactions. All of these interactions play a huge role in the movement of energy through various food chains. Our class has focused on the Predator-Prey cycle. There are many simple cycles that can be studied especially in the boreal forest and turdra. Many organisms (that are prey) often have a special defense mechanism that helps them protect themselves from predators. A real system that has been studied is that of prickly pear cactus and the cactus moth in Australia. The prickly pear cactus is a native South American cactus. When introduced to Australia it caused much of the land to become barren or unable to farm. The Australian moth fed on the cactus which kept it under control. Years passed and it was observed that both the cactus and moth were rare. Therefore, one would assume that once the prickly pear cactus was rare the moth became rare as well because its food source was on the decline. This example closley follows the relationship we discovered by making our Predator-Prey model system.
There is a nontypical example which involves fishery discards of dead organisms and its effect on other sea life. Studies in Australia observed the increase in fishery discards and its ability to effect other sea life, predator/prey relationships, and struggle for avliable resources. Studies have confirmed that increases in discards have a negative impact of some species and a positive impact on others, such as scavengers. The predator/prey relationship is evident with the relationship between scavengers and fishery discards considering that the increase in fishery discards causes an increase scavengers and the predator/prey model would most likely be an appropriate description of the relationship. Although, the increase in discards effect most populations in a negative way, those predators of waste materials in the sea will most likely have a predator/prey relationship with the fishery discards that can be appropriately described by the model in this project.
I was able to find information about the predator-prey model in the library database. I began my search in ScienceDirect, because this information deals directly with animals, and typed in the keywords: real populations in predator-prey model. This database gave me numerous articles dealing with the predator-prey model, but the article that I found to be the most interesting dealt with Lion, wildebeest and zebra and these observations took place at Kruger National Park, South Africa. This model is very similar to the predator-prey model dealing with rabbits and foxes because the lion can be compared to the fox as the predator, and the wildebeest and zebra can be compared to the rabbit as the prey. The model also included the following assumptions:
- For the traditional predator–prey models it is assumed that only two species are present in the interaction situation and that food is plentiful for the prey species.
- All exterior factors that may affect the dynamics of these species, such as droughts, fires and epidemics, are assumed to be stable for the period under discussion, or at least have a similar effect on the interacting species.
- We prefer to use continuous models since the populations are large enough, no distinction is made between age groups of a species, and continuous models in this case are much more accurate in describing the population variations over time than their discrete counterparts.
- Throughout the exercise, all results indicate population sizes measured in thousands. The population densities are indicated on the vertical-axis, and time on the horizontal-axis in all figures.
- Accurate census numbers for lion in the region over this period are not available, but officials roughly estimate that 300–700 lion, sustained by migration, were present in the area at any given time, depending on prey availability. We assume an initial population of 500 lion throughout the exercise.
In the end this model made some of the same predictions as the rabbit-fox model. As the lions began to die from natural causes, the wildebeest and zebra population began to increase. Also the three graphs for the lion, wildebeest and zebra followed similar patterns and indicated that over time the populations of the species showed smaller fluctuations and began to stabilize.
If you answer this question, please include references to the web sites or databases.
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