A study of population demands on the energy supplies in an ecosystem
On page 20-23, you will be studying how the increase of a population in a highly fictitious prairie environment consumes the available energy. I say highly fictitious because the growth of the population is not real. But that's not the point. The point is to see how the increase of the population size puts more pressure on the consumption rate of the carry capacity of the environment.
The data should look something like this.
The data should look something like this.
You will notice that as the population increases, the amount of available energy is diminished. On the following day we will discuss the implications of this phenomena in our class discussion of "Population Dynamics".
On this day we examine both of these graphs and apply it to the real life - with the understanding that the graph pertaining to the prairie system is highly manipulated. (Critters don't populate like that - and there really is no predation in this example). Nevertheless, it does serve to explain many aspects of how a population size puts demands and stresses on the environment.
For instance, if we were to replace the prairie system with a cow pasture - it may make more sense. If I had 10 acres of field grasses to raise cattle, how many cows could it support? 1 cow would be just fine. But what about 5? I'm sure it would be equally just fine. But what about 15 or more? There comes a point where the grasses on the field cannot keep up with the demands and rates of consumption. Eventually, a few things start to happen on the field that we begin to witness.
For instance, if we were to replace the prairie system with a cow pasture - it may make more sense. If I had 10 acres of field grasses to raise cattle, how many cows could it support? 1 cow would be just fine. But what about 5? I'm sure it would be equally just fine. But what about 15 or more? There comes a point where the grasses on the field cannot keep up with the demands and rates of consumption. Eventually, a few things start to happen on the field that we begin to witness.
- Starvation: There's not enough grass to go around. In fact since many of the grasses can't grow back fast enough, many cows start to pull up the roots. This leads us to #2.
- Overgrazing: When cows eat (or "graze") more (another word for "over") than what can grow back, it puts stress on the field, and the field can no longer support the critters who depend on it.
Let's assume that a cow can consume 10 square meters a day of grassland area in a pasture.
Since the field can only handle a certain amount of cattle on it, we have what we call a limiting factor. A limiting factor is a variable in the environment that limits or slows the growth of an organism's growth or activities. These variables can be space, food or shelter. (Here is a resource that talks more about limiting factors and human impact).
This is why a predator pray relationship is highly important. It's one of the ways nature keeps the populations in check, or balance. If you will notice, in the Wolf v. Elk population graph, you may have noted that there were two columns as to why elk would leave the population - that is... death through predation or death through starvation. This, of course, adversely affects the elk population. But also note that as the wolf population grew after being re-introduced, the elk population eventually got to a point where it was no longer consuming more than the environment could handle - in other words, they were no longer starving. It's really a matter of ecological economics. I loosely coin the phrase after the basic study of economics, or the study of supply and demand. Meaning - the environments ability to provide food (supply) and the population of critters that can be supported by the food supply (demand).
This is why a predator pray relationship is highly important. It's one of the ways nature keeps the populations in check, or balance. If you will notice, in the Wolf v. Elk population graph, you may have noted that there were two columns as to why elk would leave the population - that is... death through predation or death through starvation. This, of course, adversely affects the elk population. But also note that as the wolf population grew after being re-introduced, the elk population eventually got to a point where it was no longer consuming more than the environment could handle - in other words, they were no longer starving. It's really a matter of ecological economics. I loosely coin the phrase after the basic study of economics, or the study of supply and demand. Meaning - the environments ability to provide food (supply) and the population of critters that can be supported by the food supply (demand).
Overgrazing
Concepts to understand
Ecological Economics:
Economics - the study of supply and demand in the market place. This lesson is to explain the energy supply and demand on an ecosystem.
Carry Capacity: An areas ability to support life.
Limiting Factor: The factor that limits an areas ability to support life.
Economics - the study of supply and demand in the market place. This lesson is to explain the energy supply and demand on an ecosystem.
Carry Capacity: An areas ability to support life.
Limiting Factor: The factor that limits an areas ability to support life.
The importance of Preditors
The second graph that we worked on in class is the predator prey relationship between the wolves and the elk. It should look like this. We'll discuss this more on our next day - Population Dynamics.