People can purse prey at high speed with cars and airplanes. Use of powerful boats and better nets means people can access deep oceans where our bodies would not survive. Better weapons mean that hunting and fishing are relatively safe activities, at least compared with animal hunts. The human species was able to become a superpredator through technology, which has allowed us to escape the limits usually found in predator-prey relationships. But due to fishing pressures, they currently begin breeding at four-and-a-half years old and produce fewer offspring. Cod, for instance, can live for more than two decades and usually start breeding around six years old. Removing those fish dials back the reproductive capabilities of the population, and it can also affect the evolution of a species. Old, large fish tend to produce the most offspring, sometimes hundreds of thousands of eggs in a single year. This chart shows that the rates at which humans exploit land mammals and marine fish vastly exceed the impacts of other predators.īut this practice can have ramifications for a population, Darimont said, especially among fish. “Those juveniles then grow to become adults available for harvests in the future,” he said. Also, most fisheries and wildlife management schemes specifically call for adults to be harvested, because in theory it frees food and other resources for juveniles, lead author Chris Darimont of the University of Victoria noted at the teleconference. When processed, older animals provide more meat for the effort. Humans target adult animals for many reasons. Humans take a median of 14 percent-and as much as 80 percent or more in extreme cases. Marine predators harvest about 1 percent of adult biomass each year. In the oceans, the situation is even more dramatic. But the harvest of adult carnivores by humans was nine times that of other large carnivores, which were mostly killing each other through competition. In some cases, such as with herbivores on land, they found that humans kill adult prey at about the same rate as non-human predators do. Eventually, he and his colleagues gathered more than 2,200 data points on 399 prey species from every ocean and all the continents except Antarctica. Inspired by this ecological disconnect, Reimchen began collecting data from other studies that had looked at predators, including humans, and the characteristics of the prey they were consuming. “This situation contrasted dramatically with the commercial fishing I observed in adjacent marine waters, which were taking from 40 to 80 percent of the biomass of salmon and herring, and then predominantly the reproductive-age classes,” Reimchen recalled at a telephone press conference held on Wednesday. This was because the predators overwhelming consumed fry, juveniles and sub-adults, eating only 5 percent of the reproductively valuable adults each year. Despite the number of predators, the stickleback population remained steady. There, 22 species of trout, loons and other predators fed on stickleback fish. The new study got its start back in the 1970s, when Thomas Reimchen of the University of Victoria was studying predator-prey interactions in a remote Canadian lake. “Depleting the capital is risky, particularly in long-lived, late-maturing organisms.” “Adult individuals provide the ‘reproductive capital’ of a population, akin to the financial capital in a bank account or retirement fund,” Dalhousie University biologist Boris Worm notes in a commentary that accompanies the study, published today in Science. Humans, by contrast, are far more likely to be killing big strapping adults, particularly among carnivores on land and fish in the ocean. Across the animal world, predators focus their efforts on juveniles. The human species really is unlike any other predator on the planet, especially when it comes to our choice of prey.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |