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Tropical Evolution

On this page we will learn why evolution in the tropics seems to be occuring at a faster rate than in the temperate climates.



The Big Question:

Is evolution in the tropics occurring at a faster rate than evolution in the temperate areas?

This is a good question based on the observation that there are quite a few more species in the tropics than in the temperate zones. In fact, we are talking about a scale of more than 10 times the number! So how come we have so many species in the tropics? There are a few different theories that attempt to explain this as I will briefly review.

Tropics are older and the climate more stable
It is true that seasons change less in the tropics. Temperatures vary less and thus, animals need to have fewer adaptations for extreme weather. We also know that during the ice-ages, large sheets of ice covered a huge part of northern North America. However, it is difficult to test this theory because it is mostly historical in bases and can not be proven. Besides, who is to say that the climate in the tropics didn’t change in the last ice age.

High level of Competition between species.
This theory states that in the past the competition for resources in the tropics was extremely intense. Because of this, species began to evolve into specialists so that only they could occupy their individual niche. This theory is also a bit difficult to prove though, because how does one prove that competition occurred in the past!

Suppose you do have several competing creatures. If one is a bit better at competing it will soon become the only species. At some point it may become 99 percent of the population. The only thing that could prevent it from taking over is a bit of top-down control – predators. Predators will choose the most obvious species to eat first (the one with 99 percent of the population). Thus, the less abundant species will be able to stay in the population, and the species diversity increased.

High Productivity
The tropics receive more sunlight than the rest of the world. They also receive steady light throughout the year whereas temperate areas have pronounced winters. Thus, the tropics can grow more plant biomass. It has been hypothesized that this high plant biomass contributes to high numbers of insects that eat them, which translates into (say) birds that eat them, to (say) eagles that eat them … etc. The point is that there is more energy in the system that flows up the food chain.

Text by Rob Nelson

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