In Africa, U.S. grants also support African elephant populations. Big critters need to rid themselves of huge amounts of body heat; elephants may cover themselves with dirt to control solar heating. U.S. Fish & Wildlife Service.
If you're getting the idea that big animals are prone to extinction, we should point out that plenty of small critters went ka-bunga during cataclysmic die-offs in the distant past. But during the recent extinctions, larger critters were indeed losing critters.
All this emphasis on size raises an interesting question: Why do some animals get big, and what advantages and disadvantages does size confer?
One
major group of advantages stems from food efficiency -- on miles per gallon,
if you wish. Because a big animal has a lower surface-to-volume ratio
than a small one, it loses less heat to the surroundings and so needs
to produce less energy to maintain its body warmth. Pound for pound, a
mammoth needs less grub than a deer (to say nothing of a hummingbird)
to stay in business.
But it's not simply a matter of surface-to-volume ratio. As University of Wisconsin-Madison zoologist Warren Porter notes, large animals also have a thicker "boundary layer" -- static air that slows heat removal. That is one reason why many large animals seek shade or water (beach umbrella or swimming pool, sir?) in the hottest part of the day.
Is small beautiful?
How else does size play into the survival equation
for animals? It largely comes down to essentials like warmth, food and
sex. Large animals:
generally
live aboveground. "If you're small, you go below the ground, you never
look at temperatures colder than 32 ° F," says Porter, who adds that
even in the tundra, body heat warms burrows above the freezing point.
must
dispose of more waste heat. Animals above a certain size, Porter says,
"will cook" because they cannot dump waste heat. While whales and walruses
suffer this limitation, they live in cold water that removes great amounts
of heat -- one reason they get so big.
have
longer life spans, and need less energy, on average, to grow.
take
longer to reproduce, limiting their rate of population growth. On the
other hand, quick reproduction and short lifespans help small organisms
adapt to circumstances -- explaining why insects and microbes
evolve resistance to pesticides and drugs.
make
more awesome predators, and tougher prey for carnivores.
tend
to be clumsy. Elephants can walk long distances on those long legs, but
if they tried to jump they would break those legs, Porter says. (Bitty
critters, on the other hand, can spin
spider webs and even walk
on water!)
As you can see, this quick-and-dirty list fails to fully explain the extinction of certain animals and the sparing of others. It's the old biological paradox: While elephants squash fleas, fleas respond by sucking elephant blood.
We can only report that we're happy that the school bus-sized crocodile chose to walk into the history books long before humans began to wait for school buses!
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