Question: How do we explain the cast array of different plants in the rain forests of our planet, when natural selection and competition would suggest that there should really be only a few species that have out competed the other species? Is it because the pressures are less due to the abundance of resource?

Haihan Tan answered on 30 Dec 2013:

Good question!

“Is it because the pressures are less due to the abundance of resource?” – Yes, this may be a reason in certain situations, for example if a tree falls and allows a window of sunlight through to the undergrowth. And rainforests are indeed places that are originally rich in resources. But ultimately competition does increase if and when resources start to get scarce.

Another way you might look at this is to think of the rainforest not as a single environment, but as a patchwork of different micro-environments in which different species live. Often different species have slightly different resource needs, so there are different pockets (“niches”, in ecology-speak) in which different species can thrive.

Also, many plant species may also depend on one another in certain ways. This kind of mutualism is another reason for multiple co-existing species.

Competition is ever-present, but there are “tricks” to get around it somehow, so to speak. There is unfortunately no catch-all answer but hope this gives a starting point for consideration!