Hunting is claimed to give resource managers an important tool in managing populations that might exceed the carrying capacity of their habitat and threaten the well-being of other species, or, in some instances, damage human health or safety.[citation needed] However, in most circumstances carrying capacity is determined by a combination habitat and food availability, and hunting for 'population control' has no effect on the annual population of species.[citation needed] In some cases, it can increase the population of predators such as coyotes by removing territorial bounds that would otherwise be established, resulting in excess neighbouring migrations into an area, thus artificially increasing the population. Hunting advocates[who?] assert that hunting reduces intraspecific competition for food and shelter, reducing mortality among the remaining animals. Some environmentalists assert[who?] that (re)introducing predators would achieve the same end with greater efficiency and less negative effect, such as introducing significant amounts of free lead into the environment and food chain.