Hunting is altering the natural evolution of animals with horns or fangs

Hunting, whether legal or poaching, is disrupting the order of things in nature.

By preying on the animals with the biggest horns or tusks, it causes an artificial selection pressure that is replacing natural selection: Animals that for millions of years have thrived on their biggest antlers or huge canines are now more likely to die to death. hands of humans before passing on their genes to the next generation.

This has led to more and more tuskless elephants or goat-dominant males with smaller defenses.

The ecological consequences of such a tipping are yet to be determined.

One of the most intrusive forms of humans in animal life is trophy hunting, where what matters is some characteristic feature of the game, such as the size of its defenses.

Throughout colonial times, Westerners traveled to Africa to hunt two of its most imposing animals, elephants and rhinos.

As with deer and goats in the north, the larger their tusks or horn, the more prized the game.

Out of ego, fame or who knows why, the hunters wanted to be immortalized photographed next to the downed animal, as was shown by the emeritus king on his safari in Botswana or the former president of the United States, Theodore Roosevelt a century earlier (see image below).

These photographs have served a group of researchers to verify that the rhinoceros horn has not stopped shrinking since the end of the 19th century.

Thanks to a database dedicated to these animals, they were able to collect and analyze 4,441 images, a third of them photographs.

Nearly a hundred are shot specimens (most of them have their hunters next to them).

the oldest are from 1886 and in the five remaining rhinoceros species they have observed the same trend.

Those photographed in the 1990s (there are no more recent images) have a smaller tusk than those hunted 100 years earlier.

There is no longer trophy hunting for these animals, it was killing these species.

At the beginning of the 20th century, a population of 500 was estimated.

000 rhinos of three different species in Africa (Asian populations were much smaller).

In the eighties, the population was already a few thousand and one of the species can already be considered extinct.

But, as the authors of the research recall, there is still poaching, so the shrinkage will continue its process.

The researcher Oscar Wilson, co-author of the work with the images of rhinos while working at the University of Cambridge (United Kingdom), recalls that a change in the size of the horns has consequences.

"We can't know exactly what will happen, but rhinos use them to defend their territory or attract a mate, so we think decreasing horn size is likely to have some impact on how they'll be able to do these things." .

And there is another possible effect that he fears: "We are also concerned that [the shrinkage] will lead poachers to shoot a greater number of rhinos to obtain the same volume of horn, thus killing more rhinos," adds the now researcher. at the University of Helsinki.

Shortly after leaving the US presidency, Theodore Roosevelt went on a trip to Africa to fund the projected Museum of Natural History.

In one year and only two species of rhino, he and his son killed 106 animals.Kermit Roosevelt (United States Library of Congress)

Wilson's work, based on photographs, has not allowed them to calculate the exact percentage reduction in the size of the rhino's defenses.

But there are very specific data on elephants.

At the end of 2021, the journal

published one of the most ambitious papers on a phenomenon already observed by ecologists, but until then considered anecdotal or circumstantial: more and more elephants are being born without tusks.

Like rhinos and other large herbivores, elephants are so important to the entire system that scientists call them ecosystem engineers, for their ability to modify the landscape.

For this reason, the fact that more and more elephants are born without tusks will have consequences.

The

study is based on almost 50 years of observations of an elephant population that has suffered like few others and still suffers from poaching to remove their tusks.

At the beginning of the 1970s, there were about 2,500 proboscidia in the Gorongosa National Park (Mozambique).

But in 1977 a civil war broke out in the country.

The park was a war zone and both sides used the ivory to finance themselves.

At the end of the conflict, in 1992, there were barely 200 copies left.

But park curators and researchers from Princeton University (United States) noted another fact: before the war, only 18.5% of calves were born without tusks.

After finishing, the percentage was 50.9%.

Tusks suddenly became a problem, when in natural circumstances they are very useful organs for elephants."

Brian Arnold, researcher at Princeton University, United States

Princeton researcher Brian Arnold said in a note that "tusks suddenly became a problem, when in natural circumstances they are very useful organs for elephants."

In addition to their defensive function, animals also use them for food.

In fact, they observed that the specimens without their canines have a different diet.

"Specifically targeting the fanged females gave the fanged females a huge competitive advantage," adds Arnold.

It is not known how widespread the phenomenon observed in the Gorongosa is.

Another study published a few years ago with data from parks in Zambia, which shares a border with Mozambique, observed that the proportion of elephants born without tusks went from 10.5% in 1969 to 38.2% 30 years later.

However, in parks located further north, such as those in Kenya, they have not detected changes in the proportion of tuskless calves, according to George Wittemyer, a researcher at Colorado State University (United States), who has spent more than 20 years studying elephants and the dangers that threaten them in the Samburu and Buffalo Springs National Reserves in northern Kenya.

On the consequences of a life without fangs on his survival,

Wittemyer recalls that "Asian elephants have been selected by humans until the females have ceased to have tusks and there they are still."

Another different thing is its ecological impact: “We can say that they will survive without the fangs.

But this could upend behavioral and ecological interactions,” she concludes.

In the northern hemisphere, the shrink has been fattening the goats.

One of the first to observe it was the ecologist at the University of Alberta (Canada) David Coltman.

In 2003 he published a paper on the status of a population of mountain mouflon, a mighty horned bovid native to North America.

Under the impact of hunting, the antlers of males shrank by almost 30% between 1973 and 1996, when hunting was banned in the region because very few legal-sized rams remained.

As Coltman recalls, “big horns are generally held by higher quality individuals, so we suspect that taking larger horned rams may make a population less viable.”

In fact, several works have shown that the size of the antlers is related to a higher sperm quality and, in generating a better heritable physical condition.

"We have also seen that large horns in females may be related to greater reproductive success, so hunting may have additional indirect effects on females."

Mountain goats in various areas of Spain have reduced their horns in recent decades.

The same phenomenon has been observed in other species of bovids from other parts of the world, such as mouflons from the Rockies or chamois from the AlpsMathieu Sarasa

The phenomenon has been observed in other bovid species, such as chamois and, in Spain, in the ibex.

The ecologist from the University of Jaén Jesús Mª Pérez has spent two decades studying the impact of trophy hunting on various species of mountain ungulates.

In a study published in 2011, they observed that the average length of the horns of the ibex in the area of ​​the Cazorla, Segura y Las Villas Natural Park had decreased by 15.4% between 1975 and 1985. While, in the case of the Atlas mouflon (a North African species introduced into Spanish hunting grounds), the dimensions of its antlers decreased by 10.9% between 1980 and 1991. It must be taken into account that maturity in both species and, therefore, , the size of their horns is not reached until they are 10 years old in the ibex and eight years old in the mouflon.

Large horns are held by higher quality individuals, so we suspect that taking rams with larger horns may make a population less viable."

David Coltman, ecologist at the University of Alberta, Canada

“In the Sierra Nevada we rarely see large old animals anymore.

Either they are very well hidden or they have already been hunted.

In fact, many researchers warn that the animals are being hunted earlier and earlier”, says the ecologist from the University of Jaén.

But he isn't sure about the long-term effect of hunting on antler size, and, he says, there is no consensus among scientists.

"For some, it is an evolutionary response, but others say that evolution is slower."

Determining the extent of the hunting impact is the key.

Is it just a demographic hit limited to the physical elimination of the bearers of the greatest defenses or does it have evolutionary consequences and the following generations will have smaller ones?

Marco Festa-Bianchet is director of the department of biology at the University of Sherbrooke (Canada) and has spent years studying the impact of hunting in caprines, but also among deer.

“To my knowledge, there is no evidence in deer.

Obviously, there are some cases of demographic effects, if all the big ones are eliminated, only the small ones will remain, but there is no evidence, as far as I know, of an evolutionary effect.

In fact, in the case of mouflons from the Canadian mountains, the latest work published by David Coltman with data from the last 20 years shows that "the growth of the horns stopped decreasing with the cessation of hunting and would be showing some signs of recovery.

Yet in 2020, 30 years after the end of the civil war in Mozambique, a third of Gorongosa elephants are still being born without tusks.

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