Sydney, Jan 29 (IANS) Animals at high latitudes grow better than their counterparts closer to the equator because higher-latitude vegetation is more nutritious, says a new study.
The report presents a novel explanation for Bergmann’s Rule, the observation that animals tend to be bigger at higher latitudes.

Ever since Christian Bergmann made his observation about latitude and size in 1847, scientists have been trying to explain it.

The traditional explanation is that body temperature is the driving force. Because larger animals have less surface area compared to overall body mass, they don’t lose heat as readily as smaller animals.

That would give big animals an advantage at high latitudes where temperatures are generally colder.

But biologist Chuan-Kai Ho from Texas A&M University wondered if there might be another explanation. Might plants at higher latitudes be more nutritious, enabling the animals that eat those plants to grow bigger?

Accordingly, Ho along with colleagues Steven Pennings and Thomas Carefoot from the Universities of Houston British Columbia, respectively, devised lab experiments.

They raised several groups of juvenile planthoppers on a diet of cordgrass, which was collected from high to low latitudes.

Ho and his team then measured the body sizes of the planthopppers when they reached maturity. They found that the planthoppers that fed the high-latitude grass grew larger than those fed low latitude grass.

The researchers performed similar experiments using two other plant-eating species — grasshoppers and sea snails.

“All three species grew better when fed plants from high versus low latitudes,” Ho said.

“These results showed part of the explanation for Bergmann’s rule could be that plants from high latitudes are better food than plants from low latitudes.”

Although this explanation applies only to herbivores, Ho explained that predators might also grow larger as a consequence of eating larger herbivores, said a Texas A&M release.

“We don’t think that this is the only explanation for Bergmann’s rule,” Ho added. “But we do think that studies of Bergmann’s rule should consider ecological interactions in addition to mechanisms based on physiological responses to temperature.”

These findings are slated for publication in the February issue of The American Naturalist.