Monday, January 21, 2013

What is biological diversity and why do we have it?

Back in November, before the holiday feeding frenzy got me writing mostly about food and exercise (2 of my favorite subjects!), I introduced some basics of genes and genetic expression, the basis of all life (yes, you too!).

so true!  image: Funny Pictures blog
I know, these subjects don't tempt in quite the same way as Christmas cookies...but while you are what you eat, even this depends hugely on what your genes dictate, so they're worth revisiting.

Genes, brief review

Genes are units of DNA inherited from our parents that carry information that determines our physical traits, which, in turn, affect our relative fitness (our ability to survive and reproduce compared to others) in a given environment.

image: Hudson Alpha
Each cell in our body contains over 20,000 genes, and tiny changes to just one of them can cause variation among individuals, even in the same species.

We humans display a range of countless features: hair curliness, dimples, skin and eye color, height, voice clarity, toe length, and running speed, to name just a few.

And that's just within our single species! What about the others?

Species diversity

As you might guess, variability in the expression of many individual genes leads to even greater variability among the different animals and plants that are made up of those genes. My last post showed some of the incredible beauty and variety found in just 4 groups of insects.

In fact, scientists have identified roughly 1.3 million species, but they estimate there are far more that remain undescribed. These are the species that haven’t been found yet, haven’t been catalogued, or are actually different than what we think they are.

tarantula neighbor in Costa Rica
sponge with other marine inverts
photo: Peter Southwood
Most of the world’s species are small invertebrates (they have no backbone), such as earthworms, arthropods (e.g. insects, spiders, lobsters...), sponges, starfish, and protozoans (single-celled micro-organisms). Even within this group, arthropods rule.

Scientists who recently surveyed sections of a single rainforest reserve in Panama estimate that 25,000 arthropod species live in the 6,000 hectare (15,000 acre) reserve. Yes, four times more arthropods live in that reserve than there are mammals on earth.

This means that you could find 300 species of arthropod for every mammal species, 83 for each bird species, and 20 for each plant species! In other words, most living things on earth (minus single-celled creatures) are arthropods.

What's your favorite arthropod?

Next post alert: Why you should care about biodiversity!


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