Animal families with the most diversity also have widest range of size

Mar 17, 2009
Size comparison of (L-R) Blue Whale, human, Brachiosaurus, Giraffe. | Jomegat, Wikimedia Commons

(PhysOrg.com) -- Somewhere out there in the ocean, SpongeBob SquarePants has a teeny-tiny cousin and a humongous uncle.

That's just what one would expect from a new analysis of body sizes across all orders of animal life that was conducted by researchers at the National Center (NESCent), in Durham, N.C. and the University of North Carolina, Chapel Hill.

Researchers Craig McClain and Alison Boyer created a giant database on body sizes across all orders of animal life and found that phyla -- families of animals grouped together by a similar body plan -- with the greatest of were also those with the largest range of body sizes.

The sponges, Poriferans, were found to have some of the greatest diversity of both and species, ranging from microscopic to the size of an automobile. Molluscs (snails, squid, clams, chitons), and Arthropods (crabs, insects, lobsters, copepods) also showed great diversity. So did our family, the Chordates, which ranges from a half-inch fish in the swamps of Borneo to the truly leviathan 100-ton , with all the fishes, birds and mammals in between.

On the one hand, it may seem obvious that diversity in size and diversity in species go together, acknowledges marine biologist McClain, assistant director of science at NESCent. But it also says something a little more subtle about how new species arise and adapt to all the available niches in the environment.

"This really comes down to understanding the on Earth," McClain said.

The group's findings appear online in . The research was conducted in part at the Monterrey Bay Aquarium Research Institute, funded by the David and Lucile Packard Foundation, and the Smithsonian National Museum of Natural History. NESCent is a National Science Foundation collaboration of Duke, UNC and N.C. State that is housed in buildings Duke leases.

The Blue Whale, incidentally, is the largest animal ever, but the Chordate group doesn't boast the smallest. That distinction belongs to animals with names like mud dragons, brush heads, jaw worms, stomach hair worms and water bears that are so small they live between individual grains of sediment in the ocean. But this smallest group's range doesn't reach up to the largest body size.

This is a pattern that repeated itself several times in the data, McClain said. There are apparently physical limits to the range of sizes that can work for some body plans. In worms, for example, it is impossible to slither along if the girth and weight become too large. (The largest worm, Riftia pachyptila, from deep-sea vents, doesn't move.)

Within the range of sizes that works for a given body plan, evolution creates new species and new sizes, McClain said. What this sweeping analysis hasn't solved is the riddle about how different body sizes emerge. One theory says that body sizes arise through random natural variation. A second says that size diversity is driven by the availability of unused niches in the environment.

The finding also points to areas where more species might be waiting to be discovered. For example, the little-studied priapulid worms (aka "penis worms") have only 16 species on the books, but with a very large range in size. McClain's guess is that there may be more undiscovered species within that range of sizes. "There are groups that definitely don't have a lot of people studying them," he said.

Knowing something about a body plan's size constraints also might allow for a ballpark estimate of its number of species, McClain said.

Source: Duke University (news : web)

Explore further: How ferns adapted to one of Earth's newest and most extreme environments

add to favorites email to friend print save as pdf

Related Stories

World's smallest snake found in Barbados

Aug 03, 2008

(PhysOrg.com) -- The world's smallest species of snake, with adults averaging just under four inches in length, has been identified on the Caribbean island of Barbados. The species -- which is as thin as ...

Zombie worms found in Britain's North Sea

Oct 19, 2005

So-called zombie worms that feed on bones of dead whales have reportedly been found in England's North Sea. Scientists say the worms belong to a new class of marine organism that scavenges whale carcasses, The Independent rep ...

New study reveals hidden neotropical diversity

May 15, 2008

Evidence of physically similar species hidden within plant tissues suggest that diversity of neotropical herbivorous insects may not simply be a function of plant architecture, but may also reflect the great age and area ...

Which Carnivores Kill Other Carnivores

Mar 17, 2006

Ecologists used to think of prey as the most important factor governing the structure of predator communities. However, over the past twenty years, they have increasingly recognized the importance of interspecific killing ...

A unique marine symbiosis is studied

Sep 23, 2005

A symbiosis of bacteria and a marine worm found by Monterey Bay, Calif., researchers is believed the only one solely using marine mammals for nutrition.

When animals evolve on islands, size doesn't matter

Nov 07, 2007

A theory explaining the evolution of giant rodents, miniature elephants, and even miniature humans on islands has been called into questions by new research published today in Proceedings of the Royal Society B: ...

Recommended for you

User comments : 0