Size is not everything

Size is not everything

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Brazilian biologist says that, besides the absolute weight, the concept of megafauna must take into account the relative impact of the animal on its ecosystem.

Megafauna can be translated as "the set of giant animals".

Although this definition may include dinosaurs, the term is most commonly used to refer to all large prehistoric animals that coexisted with the human species and disappeared at the end of the last Ice Age.

According to a Brazilian biologist, it is not just the size of an animal that must be taken into account when including it as a representative of the so-called megafauna. It is also necessary to analyze the context in which he lives and the extent of his impact on this environment. A terrestrial mammal of a few pounds which, in absolute terms, is considered midsized or even small should be regarded as a specimen of megafauna if the impact of its presence on a small ecosystem, such as an island, is similar on a scale. relative, to the repercussions of much larger animals from larger ecosystems.
In other words, to be considered a member of the megafauna, an animal does not necessarily have to be large and heavy, but the impact on its location must be. "The medium-sized fauna of one ecosystem is the megafauna of another ecosystem," says biologist Mauro Galetti of Rio Claro State University (Unesp), who defends this relativistic view of the concept of megafauna in a scientific paper written with American Dennis M. Hansen of Stanford University and published in the journal Science.

The classic definitions of megafauna concern continental animals and advocate that animals weighing more than 44 kilograms or, according to other authors, just over one ton can be accommodated in this category.

"But in the context of an island, a 15-kilogram dodo could be seen as a gigantic animal," comments Galetti. Extinct 200 years ago, the dodo (Raphus cucullatus) was a flightless bird that lived in Mauritius, a small Indian archipelago, measuring about one meter.
The term magafauna refers almost instantaneously to the history of extinction in various parts of the world of huge terrestrial vertebrates between 50,000 and 10,000 years ago. In South America, large mammals have disappeared, such as giant terrestrial sloths and gonphotteries (Stegomastodon superbus), a type of mastodon of about 7,500 kilograms. Large plant-eating animals are seen as important in an ecosystem because they help to disperse seeds of large fruits and play a decisive role in maintaining species biodiversity and the genetic flow of a region.

If one large animal goes extinct in a given locality and another, albeit smaller, cannot assume its ecological role in that ecosystem - for example, it can no longer carry the seeds that the other carried - there will be an impoverishment of the flora and fauna. local fauna.

From tons to pounds - The problem is that historically everything that is big is being wiped off the face of the earth.

"There is a shrinkage in the size of frugivorous animal species," comments Galetti, a scholar on the issue of seed dispersal in Brazilian biomes.

On the islands, this trend is even more pronounced than on dry land.

To illustrate this issue, the Unesp researcher and his Stanford colleague analyzed what happened to large fruit-eating animals in three distinct types of ecosystems: in continental areas (especially in South America), on a continental island (Madagascar, near East African coast) and an oceanic island (Mauritius). They found that the difference in weight between the largest extinct vertebrate that ever lived in these places and the largest animal still inhabiting these points on the globe is much larger on the islands than on the continent. "In South America, this difference is of the magnitude of one order and on some islands two or three orders," said Galetti, who did a science study at Stanford as a New Frontiers postdoctoral fellow. , from FAPESP.
The numbers that show what was said. The largest mammal living in South America was the 7.5-tonne gonfottery. Today is the tapir, with about 300 pounds. In Madagascar, always remembered as an ecological sanctuary, the largest animal in the past was the elephant bird (Aepyornis maximus), an extinct species of up to 450 kilograms. It is currently a 10-pound tortoise (Astrochelys radiata). The heaviest animal to have ever walked around Mauritius was a 100-pound tortoise (Cylindraspis triserrata). It is now the bat of the species Pteropus niger, also called the flying fox, which weighs just over half a kilo. It should be noted that the extinction of the largest animals on these islands is a more recent process (of the last 2,000 or 3,000 years) than in South America. In environmental terms, the disappearance of the largest animals can have a greater impact on island lands than on the continents because there are usually fewer species on them that can assume the ecological role of extinct ancestors. On the continents, even with the disappearance of megafauna and the shrinking of larger specimens, there is a greater degree of ecological redundancy between species and more animals can play the role of others.
But the years may be counting on the ability of continents to harbor relatively small animals compared to the classic megafauna, but large enough to assume the ecological role of larger ancestors. The scientists from Unesp and Stanford made a projection for the future that was not very encouraging. If all the endangered species of frugivorous animals actually disappear in the coming years, the extremely radical shrinking of island fauna will be repeated with the same intensity on the continents. If this really materializes, the largest fruit-eating animal in South America will be the guariba (Alouatta seniculus), a mere 9-pound primate, 840 times lighter than the extinct gonfoterium. Unfortunately, in this hypothetical future scenario, the situation on the islands turned out to be even more distressing. In Mauritius, the largest animal will be a bird of only 9 grams, according to the survey.

Adapted from: Research Magazine Fapesp- 03/04/09

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