Saturday, March 2, 2013

So you slept through science class, part 5–Biodiversity!

We often hear about protecting “biodiversity,” but what does that term really mean?  Biodiversity is the way that scientists determine which species are found in ecosystems.  The scientists try to answer two questions:

  1. How many different species are in this particular ecosystem?
  2. What is the relative abundance of the species found in the ecosystem?

So let’s start with the basics – what is a species?  A species is a group of organisms able to breed successfully and produce fertile offspring over several generations.  Dogs are a species; monarch butterflies are a species; willow oak trees are a species. 

When scientists want to determine the biodiversity in an ecosystem, the first number they need is the number of species.  Many methods exist for counting species.  In the case of plants, scientists can count the number of different species in a set area (1 meter square; 1 mile square) and perhaps extrapolate the number out to a large area, depending on the distribution of the plants.  Since animals can move around, methods for counting them are a little different.  For animals that live in the open, like the arctic, herds of animals can be counted from planes.  I counted butterflies for my dissertation by walking “transects” or paths to count individuals.  More “shy” animals, might be caught and recaptured to calculate a species number.

The second step in the process of determining biodiversity is figuring out the relative abundance of the various species.   Two forest stands with 100 trees of 5 different species don’t necessarily have the same relative abundance.  One forest stand could have 96 trees of species 1, and 1 tree each of species 2,3,4, and 5, and have very different relative abundance from the other forest stand with 20 trees of each species. 

Once scientists have both species numbers and relative abundance, they combine these numbers to determine biodiversity.  What’s the goal?  In biological conservation, the healthiest ecosystems are considered the ones with the greatest biodiversity.  This biodiversity is said to give the ecosystem the best resilience to change and shocks.  Just like the old adage says, “Don’t put all your eggs in one basket,” a diverse assortment of species helps to sustain life in an ecosystem.  Do we expect all ecosystems to have the same biodiversity?  No.  Tropical ecosystems and aquatic ecosystems, such as coral reefs, have very high biodiversity, while others have fewer species.  Just as we greenmomsters try to maximize the individual potential of each of our kids, the conservation goal in ecosystems is to see each one maximize its expected biodiversity.

So there it is, biodiversity in a nutshell.  Next science class, we’ll talk about how land managers are trying to apply this concept in the real world.

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