La Cienega Project
Organ Pipe Cactus National Monument

Population Studies

A population is the number of individuals of a certain species found in a certain area. For example, the total number of people in Ajo, is a population. The total number of C. eremus in Quitobaquito is a population too. But when you look at these two populations, you will find some very big differences.

When ecologists look at populations they want to know two basic things.

1) How long does an animal live?
2) How often does it reproduce?

If these two questions are answered, most animals can be grouped into one of three kinds of populations as you can see in the graph to the left.

Type I populations tend to live for a long time and reproduce slowly. Only a few babies are born in an individual's lifetime. The babies that are born usually survive because they have stong ties to their parents and are taken care of past birth. Because of this, you will find lots of individuals of lots of different ages. Humans fit into this curve. Most of us live to an age where we are capable of reproducing. Many of us will live to be near 70 years old, or older. However, after 70, there are relatively few of us still around.

Type III populations are the opposite, very short lived and reproduce very quickly. Our Quitobaquito Pupfish are considered a type III population. If you surveyed the population you would see mnay more young, baby fish than old mature ones. Lots of baby fish (fry) don't survive at all because their parents do not care for them once the eggs are layed. The strategy here seems to be have as many babies as you can, and hope some of them live long enough to reproduce.

Type I populations tend to be very stable. There are usually no large spikes or drops in the total number of individuals. If there is a dramatic decrease on a population, a disease or natural disaster for example, it is difficult for type I populations to recover. If a type I species is considered threatened or endangered, each individual matters.

Type III populations are not stable. They can over-populate an area quickly and then die-off due to a lack of resources. Once resources become plentiful again, they quickly re-populate the area. In Quitobaquito 10,000 fish live quite well, but if the water level drops there will be a dramatic decrease in numbers. If we get a good storm and the water level comes back up, the fish that survived the drought will have more babies and the population will increase again. When a type III species is considered endangered or threatened, it is usually related to amount of resources available to the fish. The species will usually recover if there is suitable habitat available. So, in the case of a type III, preserving each individual animal is not as important as protecting suitable habitat.

In Quitobaquito, it is the habitat that we are concerned about. If our drought continues, or if something happened to the spring, all Quitobaquito pupfish habitat would be lost. Even if we could recover the habitat, the fish could not repopulate the spring if they go extinct. Why then is La Cienega so important to the survival of the pupfish C. eremus?