Expert: Dana Krempels, Ph.D. - 9/9/2008

Question
How did animal and/or plant life develop in lakes that have no access to rivers or oceans - such as a closed lake on top of a mountain?

Answer
Dear Lisa,

There are some closed bodies of water that don't have much in the way of large flora and fauna.  But there are many different forms of life that can travel via diaspora such as environmentally-resistant resting spores that can travel for thousands of miles on the wind and end up in the most unlikely places.  These can grow and--in isolation from their ancestral population--change genetically over generations to become different from the original source population.  

Insects can fly, seeds can travel by air, and even *fish* can be transported if they are dropped by birds who have captured them and then lose their grip (which happens more than you might think).  Humans are a major source of transport for many species that otherwise would not be able to pioneer/invade new habitats.

The closed lakes on mountaintops that have animals and plants in them didn't get them via evolution of these life forms from non-living matter.  Ancestral individuals were transported to these lakes in various ways, and--if they were successful--their descendants live there today, evolving in isolation from their original source population.  Evolution like this is generated via a phenomenon known as Genetic Drift--the evolution of populations due to isolation and small population size.

Hope that helps.

Dana