WE KNOW HOW MANY KINDS OF ANIMALS THERE ARE? (Part 1 of 2)
by Whit Gibbons
October 28, 2002
How many kinds of animals are there? The answer is one of the most evasive
in conservation ecology. The question has often been asked, but seldom
satisfactorily answered even for particular wildlife refuges, national
parks, and coastal islands that have distinct boundaries, not to mention
the tropics in general or the entire planet. The estimated number of
species has ranged from a few million for the world to more than a tenth
of a billion just in the oceans.
Biologists disagree on how many animals exist in the world, or even
in a defined geographic region, for many reasons. One complicating issue
is whether a particular species or other identifiable group of organisms
represents one kind or several different kinds.
The endangered Perdido Key beach mouse is an example of how naming animals
can become an issue. Surviving populations of the small, sand-burrowing
mouse exist naturally in Gulf State Park, Baldwin County, Alabama, and
in part of the Gulf Islands National Seashore, Escambia County, Florida.
However, the beach mouse belongs to a more common species known as the
oldfield mouse that has a much wider geographic range, covering much
of the Southeast. So why is anyone worried about this "species"?
Why do we need to be concerned about extinction of a species when in
most places it is doing fine?
The matter of defining how many kinds of mice are represented by the
species becomes even more convoluted. Consider that, in addition to
the mainland oldfield mouse and the Perdido Key beach mouse, the species
comprises other distinguishable groupings of beach mice, including the
Alabama beach mouse and, in Florida, the Santa Rosa, Choctawhatchee,
and St. Andrews beach mice. Consequently, even though none of the several
populations of beach mice have evolved sufficiently to become separate
species from the oldfield mouse, each beach group is distinctive.
Part of the politics of conservation is making a convincing argument
that a species can be endangered in one part of its range but not another.
After all, if a species is thriving in one region, how can we say the
species is endangered? Wouldn't the species be either all right from
an environmental perspective or not all right? Fortunately, the Fish
and Wildlife Service (FWS) solved that conservation conundrum several
years ago by designating some species as officially endangered or threatened
in one part of their geographic range although the same species might
be doing well elsewhere.
By being recognized as ecologically distinct from the mainland oldfield
mouse and less likely to persist, some of the beach mice were given
endangered species status by the FWS. Much of beach mouse behavior remains
similar to that of mice on the mainland, including a tendency to be
primarily nocturnal and to dig underground burrows for protection. Part
of the distinction of beach mice when compared to their mainland counterparts
is that their pelage is a lighter color, being almost white in some
of those from Santa Rosa Island. Presumably this change in coat color
is a product of natural selection, in that mice with dark coats on a
sandy beach would be more obvious to night predators such as owls. Hence,
genes that favored light-colored mice would have a higher probability
of being passed down to the next generation than genes that made a mouse
In a philosophical debate about whether beach mice, as members of an
otherwise common species, should be protected, the issue arises of how
many kinds of mice are represented. Conservationists might argue that
beach mice are different kinds of animals from each other and from mainland
oldfield mice. An equally convincing argument might be made that all
of them are the same kind of animal because they are the same species,
although their habitats and environmental requirements differ. The question
has no perfect answer from a conservation perspective. Also, it seems
unlikely that even mammalogists will ever fully agree on the designations
of how many kinds of "oldfield/beach" mice there are, let
alone how many kinds of mice exist in the world.
week: How Do We Count Animals We Cannot See?)
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