<P> As animals at the summit of the food chain, bears do not have many predators . The most important are humans, and as they started cultivating crops, they increasingly came in conflict with the bears that raided them . Since the invention of firearms, people have been able to kill bears with greater ease . The tiger is the only four - legged predator that regularly preys on adult bears, including brown bears, sloth bears, Asiatic black bears, and sun bears . </P> <P> Bears are parasitized by eighty species of parasites, including single - celled protozoans and gastro - intestinal worms, and nematodes and flukes in their heart, liver, lungs and bloodstream . Externally they have ticks, fleas and lice . A study of American black bears found seventeen species of endoparasite including the protozoan Sarcocystis, the parasitic worm Diphyllobothrium mansonoides, and the nematodes Dirofilaria immitis, Capillaria aerophila, Physaloptera sp., Strongyloides sp. and others . Of these, D. mansonoides and adult C. aerophila were causing pathological symptoms . By contrast, polar bears have few parasites; many parasitic species need a secondary, usually terrestrial, host, and the polar bear's life style is such that few alternative hosts exist in their environment . The protozoan Toxoplasma gondii has been found in polar bears, and the nematode Trichinella nativa can cause a serious infection and decline in older polar bears . Bears in North America are sometimes infected by a Morbillivirus similar to the canine distemper virus . They are susceptible to infectious canine hepatitis (CAV - 1), with free - living black bears dying rapidly of encephalitis and hepatitis . </P> <P> In modern times, bears have come under pressure through encroachment on their habitats and illegal trade in bear parts, including the Asian bile bear market, though hunting is now banned, largely replaced by farming . The IUCN lists six bear species as vulnerable; even the two least concern species, the brown bear and the American black bear, are at risk of extirpation in certain areas . In general these two species inhabit remote areas with little interaction with humans, and the main non-natural causes of mortality are hunting, trapping, road - kill and depredation . </P> <P> Laws have been passed in many areas of the world to protect bears from habitat destruction . Public perception of bears is often positive, as people identify with bears due to their omnivorous diets, their ability to stand on two legs, and their symbolic importance . Support for bear protection is widespread, at least in more affluent societies . Where bears raid crops or attack livestock, they may come into conflict with humans . In poorer rural regions, attitudes may be more shaped by the dangers posed by bears and the economic costs they cause to farmers and ranchers . </P>

Where does the term bear market originate from