What is biodiversity?  It is a term coined from two words:  biological and diversity.  It describes the variety within and among living organisms, and the communities or ecosystems in which they live.  Specifically, biodiversity refers to biological and ecological variety at three different levels, including the interrelationships among these levels:

1.  The variety of genetic material within a species.

2.  The variety of species within an ecosystem.

3.  The variety of ecosystems within a region.

In an ecosystem, all of the organisms that make up the numerous species interact directly or indirectly with each other and with their surrounding nonliving environment.  For an ecosystem to function properly, is this complexity necessary?  Is there a reason why ecosystems evolved such elaborate relationships among life forms?  The answer to these questions is yes.  We will use cetaceans (whales, dolphins, and porpoises) as an example to explain why this is true.  First, however, let us explore why biodiversity is so important in the natural world.

Levels Of Diversity
Genetic	Allows species to adapt to changes within their community.  A community is an association of different species living together in the same area and the interactions of those species.   For example, imagine that a disease invaded a population of dolphins somewhere in a given area of the ocean.  If the entire population of dolphins shared the same genetic composition, the population would likely be destroyed.  If the dolphin population was genetically diverse, however, some individuals might be resistant to the disease and the population as a whole would survive.  In other words, genetic diversity retains options.
Species	Is an indication of the biological wealth of an ecosystem.  Each species uses a different part of the ecosystem for survival and function together to form food chains, food webs, etc.  Like genetic diversity, the more variety there is, the more the community can withstand change.
Ecosystem	Results from and contributes to genetic and species diversity within a community.  This is like a food web in which organisms develop and grow because of the presence of other organisms.  This produces many different kinds of marine ecosystems, i.e., intertidal, coastal, open-ocean, etc.  Ecosystem diversity, therefore, provides flexibility.  For example, if an oil spill occurred along a coastline, the oil may meet a natural barrier created by offshore currents which may keep the oil confined to only one area.  Consequently, not all ecosystems would be affected.

Importance Of Biodiversity
Biological diversity, whether on land or in the sea, is much like economic diversity in a city.  If a city’s economy depended solely on one company for example, say a lumber company, the city’s economic health would depend on the fluctuating demand for wood.  If its economy was more diversified, the city would be more flexible and less vulnerable to change.  When wood was in less demand, therefore, the city could sustain itself with other economic options.  The same concept applies to the environment.

Staying with the better known forest ecosystem, another example is planting the same species of trees in a clear-cut area.  In the past, many lumber companies harvested large sections of forest habitat by cutting down all the tress and leaving the area devoid of plant life.  This still occurs but there is a tendency now to replant the area with saplings for future harvest.  The good news is that replanting a clear-cut area is becoming common practice.  The bad news is that only one or two species of trees are used.  Science is now finding that planting one tree species is not nearly as effective in creating a productive ecosystem as planting a variety of trees.  This is like you always eating the same thing at each meal.  You would not have a balanced diet and eventually your health would suffer.  Consequently, your quality of life would be inadequate.  The environment works in much the same way.  Without a wide diversity of organisms, the quality of the environment suffers, and so does its “health.”  Its ability to withstand change would be impaired.

The point here is that biodiversity acts as a buffer to allow “life” to adapt to a constantly changing environment.  A wide variety of organisms, therefore, is important for producing a “healthy” ecosystem.  Biodiversity and its resulting complexities are necessary for an ecosystem to function properly.
 

Cetaceans And Biodiversity
What does biodiversity have to do with cetaceans?  Like all other life forms, cetaceans are part of an ecosystem.  Through their existence and doing whatever cetaceans do, they contribute to the “health” of an ecosystem.  Whether it is harvesting food or supplying oxygen to the atmosphere, human beings and other organisms depend on the marine environment (along with numerous other ecosystems) to keep them alive.

Like other forms of life, cetacean species are showing signs that their existence is threatened by human activities (Leatherwood et al. 1983), mostly through the destruction of their habitat.  A clear-cut area is an obvious sign that the terrestrial environment has been disturbed.  For the marine environment, signs of disruption may not be so obvious.  You may go to the coastline and see a vast amount of water but that does not mean the ecosystem is intact.  Populations of cetacean species are becoming decimated.  Their numbers are so low that they are either threatened, endangered, or at risk of entering these two categories.

The point here is that if cetacean species began to disappear (extinction), the marine ecosystem will start to fall apart.  At that point, the lives of human beings and other living organisms are threatened.  We are dangerously close to the beginning of this process.
 

What Would Happen If Cetaceans Disappeared?
Do you know how many cetacean species exist?  Currently, there are at least ten living species of baleen whales and 65 or more living species of toothed whales (Leatherwood et al. 1983).  This is quite a variety of marine mammals.  From an extremely practical approach, perhaps the disappearance of one or only several cetacean species would still leave the marine environment intact.  This, however, is not the case.  At least one third or more of all cetacean species are at risk of becoming endangered.  Because of pollution and habitat destruction, cetaceans are not the only marine organisms at risk of disappearing.  In short, the world has reached a biological diversity crisis, both on land and in the sea.

What would happen if cetacean species began disappearing from the marine ecosystem?  Under “normal” circumstances, biological communities reach an equilibrium in which all of their elements become adjusted to each other.  Mechanisms within the communities help maintain relative stability when changes occur, such as fluctuation in population numbers, etc.  This stability usually allows each species to live efficiently and in relative harmony with the other species in their community, even though they may compete for the same basic resources.

When a sudden change occurs or if a species is removed from the community, the ecosystem becomes disrupted.  The greater the change and the more significant the species (or any other element), the more disruption there will be in the entire system (Mech 1970).  Therefore, if cetacean species (or any other) began disappearing from the marine environment, the expected changes would be at least the following:

1.  A sudden takeover of a few species to the detriment of several others.

2.  Decreased efficiency and vigor of some species.

3.  Greater fluctuations in the numbers of various species.

4.  A decrease in the general stability of the community.

Because of their activities, human beings are creating unstable ecosystems which are becoming less capable of dealing with changes, i.e., pollution and habitat destruction.  Decreasing cetacean populations are only one of many symptoms that indicate human activities are affecting biodiversity in the marine environment.
 

References

Leatherwood, S., Reeves, R. R. & Foster, L.  1983.  The sierra club handbook of whales and dolphins.  San Francisco:  Sierra Club Books.

Mech, L. D.  1970.  The wolf:  the ecology and behavior of an endangered species.  Garden City, New York:  The Natural History Press.