The beasts of prey, fish, and birds at the top of the food chain are in distress. Over the past 100 years, the number of large predators in the world has declined by more than 90%. Scientists are trying to understand why this happens and how it affects the Earth's ecosystem
For a long time, and especially actively in the last 100 years, man mastered and, in fact, destroyed the natural habitats of large predators. Lions, sharks, eagles (and this is not a complete list) were on the verge of extinction.
The brown bear, whose subspecies were widespread throughout Europe, Asia, America and even northern Africa, is now largely exterminated. The Californian grizzly bear, the Mexican brown bear, the African bear have disappeared, and the Apennine one can be counted almost on one hand.
The fate of tigers in the forests of Asia is deplorable, the lions are in a slightly better position, but their number has become much smaller in recent decades. In some places on the planet, there are so few predators that they have lost their natural significance, and this negatively affects ecosystems, endangering the existence of food chains and ecological balance on the planet.
Countdown
To top it off, a thorough analysis of the current situation is impossible due to the lack of sufficient statistical data.
The number of many species began to decline rapidly, and some became extinct long before the appearance in the middle of the last century of modern ecological theories, more advanced methods of field research and accounting of animals in the natural environment.
And yet there is a way out of this seemingly hopeless situation. Scientists decided to go from the opposite and began to study the response of individual ecosystems to the artificial colonization of previously extinct animals and, in particular, large predators. One successful example of this approach is Yellowstone National Park, an international biosphere reserve in the northern United States.
If in 1995 three dozen wolves were not brought here from Canada, which disappeared from the local forests in the 20s of the last century, the local poplars would have died completely. Scientists have been able to trace the relationship between a sharp decline in predators and balance in the ecosystem.
The multiplying army of wapiti deer destroyed the leaves, bark and shoots of poplars and willows. Because of their voracity, beavers began to leave Yellowstone Park and other parts of the Rocky Mountains, for which willow bark is their main food. When the beavers stopped building dams, the reservoirs they created dried up, which, in turn, contributed to additional dynamics in the landscape, all kinds of animals and birds settled around them, and accordingly, the biological diversity increased.
Canadian "settlers" began to multiply rapidly, and within a few years the first signs of recovery were outlined in Yellowstone. Wolves slightly thinned the population of voracious wapiti, and the rest had to change their behavior, and at the same time the places of harvest. If before they gnawed all the trees in a row, now they began to avoid steep slopes, flooded forests and dense thickets, from where it would be difficult to get their feet away from their pursuers.
Now, even on the plains, where everything can be seen from afar, the deer still take a long look at the terrain. Caution not only saves their lives, it also limits the time of their meal - to the great happiness for willows and poplars, and therefore, beavers, birds and other inhabitants, because now the trees will be able to get stronger and grow much higher than the reach of deer. There are more beavers, birds and trees, small orderlies of the forest.
After wolf meals, crows, eagles and coyotes get the long-awaited carrion, and this helps them survive in harsh winters. Without wolves, the number fell in winter is more unpredictable for animal nurses: relatively few deer and other animals die in mild winters.
The Feeding Wolf
With global warming, climatologists predict more mild winters, but scavengers living in the neighborhood of wolves are provided with food all year round. Thus, they have a much better chance of adapting to new conditions. On the other hand, wolves will inevitably push coyotes out. Today, the latter have already become half as much, and in the main habitats of wolves, it has generally dropped to 10% of the previous figure. The fact is that for a wolf, a younger brother is an unwanted competitor. Mating season is a particularly dangerous period for coyotes, when a wolf can easily sniff out a coyote's burrow with cubs. And as the number of coyotes decreases, the number of populations of animals that are not of interest to large predators increases.
But it is difficult to predict all the consequences. As coyotes disappeared from the bushy areas in the Los Angeles suburbs, control of the territory passed to the domestic cats. The change of power has led to a sharp decline in the number of small birds. In West Texas, things are a little different: when coyotes were removed from the experimental territories, a war for food broke out between 12 species of rodents. A year later, in accordance with the principle "there should be only one left", one remained. The sacciform mouse proved to be the most resilient and adaptable rodent.
Redistribution at sea
Over the past 100 years, the number of large sharks in the oceans has decreased by more than 90%. The situation is no better with large tunas and other predatory fish that occupy the top of the food chain. This entails changes in the lives of other animals.
Between 1970 and 2005, between 90 and 99% of large sharks disappeared off the east coast of the United States. Their main diet consists of smaller brothers and stingrays, which immediately bred heavily.
In some areas of the Baltic Sea, the decline in the number of dominant predatory fish, pike and perch, affected the state of the entire ecosystem, which led to the growth of some species of algae. The reason is that the lack of predators leads to a sharp increase in the number of smaller fish such as sticklebacks, and this, in turn, intensively exterminates small crustaceans that feed on algae, and they immediately begin to overgrow.
In the Black Sea, the situation is even more depressing. In the 1970s, over-catching of dolphins and large predatory fish led to a spike in the number of small fish that feed on crustaceans. The decrease in the number of crustaceans feeding on algae led to a massive growth of algae, and the absence of large fish provoked a massive capture of small fish. As a result, a large ecological niche was empty, which in a short time was filled with useless jellyfish.
No sharks, no balance
In the northwestern Atlantic Ocean, stingrays are unexpectedly free. In the absence of sharks, their main "consumer", they are at the top of the food chain. For some period of time, their number increased by 9% per year, and today there are already more than 40 million individuals.
Such a horde can completely devour all American scallops, an ecologically and economically important species for many regions. Only in Chesapeake Bay in the eastern
United States, stingrays eat at least 840 thousand tons of mussels in just 100 days in the bay. The commercial catch of scallops in the bay has dropped to several tons per year.
Overfishing has led to the disappearance of large sharks and other fish at the top of the food chain from tropical coral reefs. The golden time has come for small fish and sea stars, which in coral reefs usually become prey for predators, keeping their numbers within the framework necessary for ecological balance. In several locations, the absence of predators has apparently contributed to the increase in coral-eating starfish, which has severely reduced the population of reef-building corals.
The threat loomed not only over sharks, but also over other marine predators. "Environmental supervision"
sea otters have been carrying sea otters for a long time in the northern part of the Pacific Ocean. Algal forests, home to juvenile fish and other marine animals, can reach significant heights, unless the sea urchins are feeding on the stems. Without the control of the sea otters, sea urchins devour vast amounts of algae, often destroying entire forests.
Sea otters were almost completely exterminated in the 19th century by fur hunters. They managed to revive thanks to the settling of otters near the western coast of Canada and the United States.
Algal forests dampen the shock of waves, protect the shores from erosion, and make it possible for nutrient-rich particles to sink to the seabed. Photosynthesis in algal forests is three to four times more active, which favorably affects the state of higher representatives of the food chain. The living conditions of mussels in such forests are much better, and some species of fish are found here ten times more often.
Feathered under threat
The uncontrolled trapping and destruction of the natural habitat also had a disastrous effect on the feathered predators - eagles, hawks, falcons and owls in many European countries. The decline in populations is now observed in those parts of the world where traditionally birds had enough game and space. In Burkina Faso, Mali and the Republic of Niger (West Africa), the number of 11 large eagle species has decreased from 86% to 98% in 30 years. Outside protected areas, as well as in Botswana (South Africa), the number of birds of prey is 40% lower than inside protected areas.
Biologists have noticed that in the Italian Alps, the habitats of the goshawks and four species of owls are characterized by a greater variety of trees, butterflies and small birds compared to those forests where hawks and owls are absent or too few of them.
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Available data indicate that species diversity significantly affects the ability of an ecosystem to withstand natural and anthropogenic destruction, as well as self-repair.
Biologists are comprehensively investigating how the absence of large predators affects food webs on land, in the sea and in the air. Obviously, the consequences are somehow determined by the characteristics and composition of each individual ecosystem. Often, the disappearance of a large predator affects only the next link in the food chain. Sometimes this affects the existence of both medium-sized predators and herbivores, as well as plants and even small algae.
Let's hope that through joint efforts, the scientific community will be able to find a solution to this ecological puzzle, which, in turn, will be embodied in a concrete plan for the artificial colonization of strategically important regions by predators.
Science Illustrated 2011