Tropical rainforests are some of the most biodiverse places on Earth. There are more numbers of birds, mammals, plants, insects in regions like this. It is not just abundance of it, it is how many different species we find in a given area. But why is that?
It might seem obvious or even like a silly question, but more you think about it the weirder it gets. Because life has shown it can succeed pretty much anywhere, from the top of highest mountains to the bottom of the ocean. But Eart’s most biodiverse places are always regions like this, tropical rainforests.
One reason why is that rectangular projection of Earth (AKA normal map) lies to us. Rectangular projections are distortions of a sphere that make the poles look bigger and the tropics look smaller than they really are. When in reality, the tropics contain about 40% of the area on earth. Unsurprisingly, a large area usually have more species. In less than half a square kilometre in the Amazon, we can find as many tree species as we find in four million square kilometres of temperate forest. Species here are at a higher density, there must be something special about tropical ecosystems.
Climate is one factor. When we look at plant fossils and where they are found at different times in Earth’s natural climate history, tropical forests are older than temperate forests, they had more time to become rich. But just because tropical regions don’t have cold winter and they survive the last ice age does not mean it’s easy to survive here. There are dry and wet seasons, there is competition for the resource, no matter what kind of organism you are, there is a lot of stuff that wants to eat you.
On average the tropics are warm and they get plenty of water. This part of the Earth gets average solar radiation through the year. Which means that plants and the animals they support get more energy, they are more productive.
But this still only explains why there is more life, not why so many different kinds of life.
If you have got a pizza, more people can get a slice if you cut it up into a thousand tiny ones vs just a few. In an ecosystem, we call it NICHES, the habitat and condition that one organism needs to flourish and here in the rainforest, there is a lot of slices. Organisms that live at higher latitudes have to be more adaptable and be able to handle lots of different conditions.
Life is more stable in the tropics. Near the equator, there is essentially the same number of hours in day and night no matter what month it is. Let’s say you are a bard that eat insects or you are a bat. You got the same number of hours to do your feeding. The birds get the day shift, the bats get the night shift. You get that niche evenly. That wouldn’t work at higher latitudes and more temperate climates. There is simply just too much change, too much disruption for these species to keep track of. This might explain a reason why more species coexist near the equator.
The Tropics are crowded, so the competition for resources is extreme. That competition drives organisms to specialize. But because climate and seasons are more stable that specialization isn’t as risky more species less area.
Above theories are really good at explaining why there are so many species in the rainforest. But there is one more question which above Theory has not answered. Question is Beginning of our Story, where those species come from? It’s might be possible that evolution is actually working on overdrive here near the equator, the speciation, the creation of new species by various natural forces, actually happens faster near the equator.
Each generation of living things gather changes, mutations, some are good, some are bad, some are nither. But it isn’t until those changes are passed on to next generation that natural selection and time can do their thing. The reason that bacteria are so good at adapting is that they reproduce quickly, They have more generations in less time.
The same thing happens here in the rainforest. Plants and Animals grow up faster, they can have more generations. This drives competition, this is what forces plants and animals to specialize in all of the amazing ways that we have seen. This theory that evolution happens faster near the equator, finally ties together ideas of time, area and energy to explain the origin of biodiversity.
There is an idea that says the tropics are so well suited to the creation of new species that it is like an engine for biodiversity. There is another idea say that this area so rich and productive for plants and animal and the climate is so stable that species don’t go extinct so fast. More species are born here and species live longer here, the tropics are both a cradle and a museum.
Scientists even think that over many many years species from places like this go and seed biodiversity throughout the rest of the world. This is why it is so important to protect the rainforest to preserve life’s cradle and museum. We should keep it from being cut up because more area means more species. To keep the climate from changing to keep this place stable and rich for life.
Biology still has not answered one of it’s most basic questions How Many Species Are There?
EO Wilson once wrote that “unlike the rest of science, the study of biodiversity has a time limit.” If species begin to go extinct faster than we can describe them then we might never know how much life Earth has to offer.