WHAT IS BIODIVERSITY?
Loss of Species
By the early 1980s, scientists around the world
had begun to recognize that species extinctions were occurring on a global
scale. The rate of these extinctions rivaled, or surpassed, those of the
Cretaceous period 65 million years ago when many species,
including the dinosaurs became extinct. The crisis facing species today differs in one
fundamental way from any other extinction events: all other cases of mass
extinction throughout global history have come about as the result of
climatic change, a natural geological change or some cataclysmic event.
The present crisis, however, is being driven by human influences.
Throughout the 1980s and early 1990s, the scientific community, the media,
the public, and governmental agencies worldwide began working
to preserve the biological diversity of terrestrial systems. Issues
such as deforestation of tropical forests, overdevelopment,
overexploitation of species, pollution, habitat loss, invasions by
introduced species, and other issues which addressed habitat preservation
and conservation were brought into public focus. However, maintaining the biological diversity of marine
and estuarine systems was largely overlooked throughout the 1980s, even
though it was generally accepted that marine systems are far more species
rich and have greater ecosystem diversity than terrestrial systems.
Representatives from 32 of the
33 known animal phyla can be found in ocean and coastal waters. Of these, 15 phyla occur
exclusively in estuarine or marine environments.
The vast wealth of life on earth is unified by a
common strand: DNA. All living things owe their forms and functions to the
molecular makeup of their DNA. But perhaps more intriguing than life's
unity is its immense diversity. Biological diversity - biodiversity - is
one of the central themes of conservation. But what exactly is biological
diversity, and why should we be concerned about preserving it? Simply put,
biodiversity may be defined as the measure of how healthy our ecosystems
are. Healthy ecosystems support high biological diversity;
while stressed or highly disturbed ecosystems do not. When we
consider biodiversity as a whole, we are actually addressing 3 main
components: genetic level biodiversity, species richness and ecosystem
Genetic Level Biodiversity:
The term "genetic diversity" is the
most fundamental level of biodiversity, and refers to the degree of
variation in all the genes for all individuals within a species. Here we
will define a species as a group consisting of all the collected populations of morphologically similar organisms which are able to
interbreed with one another. A population is defined as consisting
of all the individuals of the same species within a defined geographical area,
for example, the Indian River Lagoon.
Within a species, it is theoretically possible
for any individual to breed successfully with any other individual of the
species. However, populations,
tend to remain somewhat separated from each other. Thus, there is a higher
probability that an individual within a population will select a mate from
the same population. Within a large population, the effect of
geographic separation of populations, which often results in reduced genetic
mixing, is small. However, within small populations, there can be a tendency
toward reduced genetic diversity among members of that population. Over
long periods of time, this can lead to geographically separated
populations diverging genetically, each population having its own set of
genetic adaptations which allow it to live optimally within a particular habitat.
This genetic divergence is the basis for
evolution. Populations having greater genetic diversity are far better
equipped to cope with environmental change and go on to reproduce
successfully than populations with low genetic diversity. Populations with
low genetic diversity can become so well adapted to local conditions that any
environmental disturbance may be enough to reduce their numbers
dramatically, or even destroy them entirely. Thus, in thinking about
preserving biodiversity, one must consider that each population within a
species may have some unique set of genetic adaptations that could
potentially assist the entire species in overcoming environmental, or
human influenced challenges to its survival.
This term, quite simply, is the measure of the
number of species which occur within a particular taxonomic level (i.e.,
genus level, family level, etc.) in a
geographic area. In marine ecosystems, species diversity tends to vary
widely depending upon latitudinal and longitudinal location.
Along a latitudinal gradient, species
diversity tends to increase toward tropical areas. Within tropical areas, species diversity tends to increase
along a longitudinal gradient, with more species being found toward the
Indo-Pacific region around northeastern Australia, Indonesia and the
Philippines. There is a moderate amount of species diversity in the
eastern Pacific and western Atlantic oceans, with lowest species diversity
found in the eastern Atlantic.
Ecosystems are the collection of all the plants and
animals within a particular area, each differing in species composition, physical
structure and function. Even within highly diverse ecosystems, these
elements can differ widely. For example, most estuarine ecosystems, especially salt
marshes, generally have high primary production. Coral reefs, an entirely
different type of ecosystem, must rely on the efficient recycling of
nutrients in order to maintain high productivity. Deep sea ecosystems,
while rich in species, have no primary production because sunlight does
not penetrate such vast depths.
The factors which threaten biodiversity in
estuaries and in the oceans are generally the same as those which affect
biodiversity in terrestrial systems: overexploitation, physical alteration of habitat
areas, alien species introductions, and changes in atmospheric composition. Many
threats to the survival of life in the oceans (i.e., siltation, nutrient
loading, pollution of air and water by toxic chemicals, etc) can originate on
land. Also threatening marine ecosystems, particularly coastal and
estuarine systems, is the continuous increase in the size of human
populations, wasteful resource consumption, lack of knowledge, and poor
management. Habitat degradation which occurs as the result of these problems,
inevitably leads to loss of species from an ecosystem, and thus, a loss of
The Solution: Preserving Biodiversity
In order to insure biological diversity in
both marine and terrestrial systems, we must finally recognize the fact that our natural resource base,
our economic development, our food, our medicine, our clothing, the air we
breathe, indeed our very existence on this planet is dependent on the life
around us. In preserving biological diversity, we are simply insuring our
own continued prosperity and survival.
Norse, Elliot A. 1993. Global Marine Biological
Diversity: A Strategy for Building
Conservation Into Decision Making. Island Press, Washington, D.C. 384 pp.
Thorne-Miller, Boyce, and J. Catena. 1991. The
Living Ocean: Understanding
and Protecting Marine Biodiversity. Island
press, Washington D.C.180 pp.
Report by: K. Hill,
Smithsonian Marine Station
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Page last updated: Aug. 1, 2001