Biodiversity, a contraction of the phrase "biological
diversity," is a complex topic, covering many aspects ofbiological variation. In popular usage, the word
biodiversity is often used to describe all the
species living in a particular area. If weconsider this area at its largest scale - the entire world -
then biodiversity can be summarized as "life on earth." However,scientists use a broader definition of biodiversity, designed to
include not only living organisms and their complexinteractions, but also interactions with the abiotic
(non-living) aspects of their environment. Definitionsemphasizing one aspect or another of this biological variation
can be found throughout the scientific and lay literature (see
Gaston, 1996: Table 1.1 ). For the
purposes of this module,
biodiversity is defined as:
the variety of life on Earth at all its levels, from genes to
ecosystems, and the ecological and evolutionary processes thatsustain it.
Genetic diversity is the “fundamental currency of
diversity” (
Williams and
Humphires, 1996 ) that is responsible for variation
between individuals, populations and species. Therefore, it isan important aspect of any discussion of biodiversity. The
interactions between the individual organisms(
e.g. , reproductive behavior, predation,
parasitism) of a population or community, and theirspecializations for their environment (including ways in which
they might modify the environment itself) are importantfunctional aspects of biodiversity. These functional aspects can
determine the diversity of different communities and ecosystems.
There is also an important spatial component to
biodiversity. The structure of communities and ecosystems(
e.g. the number of individuals and species
present) can vary in different parts of the world. Similarly,the function of these communities and ecosystems
(
i.e. the interactions between the organisms
present) can vary from one place to another. Differentassemblages of ecosystems can characterize quite diverse
landscapes, covering large areas. These spatial patterns ofbiodiversity are affected by climate, geology, and physiography
(
Redford and Richter, 1999 ).
The structural, functional, and spatial aspects of biodiversity
can vary over time; therefore there is a temporal component tothe analysis of biodiversity. For example, there can be daily,
seasonal, or annual changes in the species and number oforganisms present in an ecosystem and how they interact. Some
ecosystems change in size or structure over time(
e.g. forest ecosystems may change in size
and structure because of the effects of natural fires, wetlandsgradually silt up and decrease in size). Biodiversity also
changes over a longer-term, evolutionary, time-scale. Geologicalprocesses (
e.g. ,
plate tectonics ,
orogenesis , erosion), changes in
sea-level (marine transgressions and regressions), and changesin climate cause significant, long-term changes to the
structural and spatial characteristics of global biodiversity.The processes of natural selection and species evolution, which
may often be associated with the geological processes, alsoresult in changes to local and global flora and fauna.
Many people consider humans to be a part of nature, and
therefore a part of biodiversity. On the other hand, some people(
e.g. ,
Redford and
Richter, 1999 ) confine biodiversity to natural variety
and variability, excluding biotic patterns and ecosystems thatresult from human activity, even though it is difficult to
assess the "naturalness" of an ecosystem because human influenceis so pervasive and varied (
Hunter,
1996 ;
Angermeier, 2000 ;
Sanderson
et
al. ,2002 ). If one takes humans as part of
nature, then cultural diversity of human populations and theways that these populations use or otherwise interact with
habitats and other species on Earth are a component ofbiodiversity too. Other people make a compromise between totally
including or excluding human activities as a part ofbiodiversity. These biologists do not accept all aspects of
human activity and culture as part of biodiversity, but they dorecognize that the ecological and evolutionary diversity of
domestic species, and the species composition and ecology ofagricultural ecosystems are part of biodiversity. (For further
discussion see the modules on
Human
evolution and
Cultural
Diversity ; in preparation.)
