How Do Ecosystems Change Over Time?

Remember that a change in gene frequency in a population over the course of years is evolution. Explain that the genetic differences of organisms within a species increases the chances that at least some members of a species will survive under changing environmental conditions.

Ecosystems and Evolution

In biology, we talk about organisms alone and in groups. So far, we’ve been concerned mainly with individual organisms, which together form populations. Those populations of organisms combine with other populations in order to form communities, and those communities come together with abiotic factors to form entire ecosystems. As we’ve already seen, those ecosystems can be grouped together as a biome when they exhibit similar climates. So, when we study ecosystems and evolution, we are concerned with how the populations in those communities change.

When you look at a population of humans, there are always certain similarities and differences that you notice. For instance, skin color, hair type and color, eye color, average height are all genetic characteristics that are the easiest to notice about people. Biologists don’t just study humans; we study all sorts of living things.

Imagine that you were looking in a field of butterflies: you see thousands that have yellow and black coloring and also a few dozen that have blue and black coloring. You also notice that there are hundreds of birds hunting the butterflies. Before we look at the behavior of the birds, we can make a conclusion about the gene frequency of the yellow color among the butterflies. Specifically, we can say that the gene frequency of yellow is around 99%, because 99% of the butterflies have yellow instead of blue. Similarly, we can say that the gene frequency of blue is about 1% for this population of butterflies.

Gene frequency, or the percentage of individuals in a population that have a certain characteristic, is a way to measure evolution. Going back to the butterflies and the birds, you notice that the birds are only hunting the yellow and black butterflies. For some reason, they are leaving the blue and black butterflies alone. You leave and come back a week later to the same field to find that there are only a few hundred butterflies; what’s more, half of them are now blue and black butterflies!

This is an example of evolution – in this case, the population of butterflies has changed. The gene frequency of yellow coloring has decreased to about 50% because of changing environmental conditions. What were the “changing environmental conditions”? The birds that were hunting the butterflies made the change in the butterfly population. Even though the total number of butterflies has decreased, the blue and black butterflies are surviving better because of the hunting patterns of the birds.

We have seen that there are many factors that go into making a biome: temperature, precipitation, animals, plants, mountains, rivers, oceans, etc. All of these factors affect the evolution of the living things within the biome.

Questions

What is the biotic relationship between the yellow and black butterflies and the blue and black butterflies that feed on the same plants? Explain.
What is the biotic relationship between the butterflies and the birds? Explain.
Calculate the gene frequencies if there were 150 yellow and black butterflies and 100 blue and black butterflies in the field.
List at least two reasons that the birds could be only eating the yellow and black butterflies.
Predict what would happen if the climate became mostly cloudy, changing the birds' vision so that both types of butterflies appear to be the same. What type of interaction is this, in terms of biotic and abiotic factors?
Consider the Rockefeller Park ecosystem. Inside the ecosystem, among other things, are bushes, trees, and rabbits.
- Come up with any genetic characteristic for the rabbits that has two forms (in the butterfly example, this was the yellow and blue colors). This can be something like the color of fur, type of nose, length of ears, etc.
- Come up with genetic frequencies for these two forms, as percentages. Keep in mind that all percentages need to add up to 100%.
- What do you think will happen to these gene frequencies if snakes are introduced to Rockefeller Park? Assume that evolution will happen, and list the gene frequencies after the snakes are introduced.