Biodiversity – term coined in 1980’s to refer to
Biological diversity, a concept already developed in the 1950’s
Lots of definitions, but perhaps simplest one is
“Species richness and relative species abundance in space and time”
Hubbell (2001)

Note that this definition is NOT limited to species richness , or simply the number of species in an area or sample.
It also incorporates the notion of the relative EVENNESS of distribution of the abundance of organisms

The idea here is this: If you go out into a corn field and see nothing but corn and a few blackbirds, and very many of them, you will conclude that this environment is not very diverse, even if there are a number of rare and less obvious animals and plants there. On the other hand, if you go into a tropical forest and see that almost every other tree or insect you look at is different, you will conclude that this environment IS diverse. IT is NOT just that there are more species there, but also that you keep seeing new ones each time you sample the forest.

Species richness
Species accumulation curve

Relative abundance of species:
RARITY and COMMONNESS
If one takes a sample of individuals (or encounters them in the field)
How often does one encounter species A versus species B?
Potential problems:
Biases in sampling methods
Variation in space and time

OK, so far we have been talking about describing diversity in one area
This is what we refer to as alpha diversity
How much does the composition of species differ between areas?
This we refer to as beta diversity or faunal turnover
And how does this add up to the global diversity of organisms?
This we refer to as gamma diversity

There are other ways to categorize diversity too, that could be useful.
For instance, ecological diversity (diversity of different ecological roles)
Phylogenetic diversity (diversity of major organismal lineages)
Interaction diversity (diversity of interconnected interactions in food webs)

How do these different types of diversity relate to conservation?
Well, just think about these questions:
Chris mentioned earlier that tropical rain forests contain more different species than coral reefs, but that coral reefs contain more MAJOR KINDS of organisms. Does that add to the value of coral reefs?
What if the only representative of a major group happens to be found in an area you are considering preserving…?

Another question:
Let’s say you have four Caribbean coral reefs already set side as preserves, and two mangrove forests and 3 rocky temperate shorelines. You have the opportunity to purchase and set aside two more areas, but what you have available are:
3 more Caribbean coral reefs
2 mangrove forests
2 rocky temperate shorelines
2 deep-sea vents
2 seagrass estuaries
2 South Pacific lagoons
What do you choose?