I'm trying to build a species that's exclusively carnivorous, and its favored prey is humans. The species is a mammalian ambush predator, probably with a build similar to a big cat such as a tiger, though I'm also drawing some inspiration from classic dragon lore. It has magical origins and reproduces slowly. Its habitat is a rainy, subarctic coniferous forest similar to the west coast of Canada, at such a latitude that winters are much darker than summers, which may mean that it does a lot of its hunting in winter. The humans in this setting are fairly advanced hunter-gatherers: the environment is productive enough that people can be semi-sedentary, similar to west-coast First Nations like the Haida and Tlingit, though some also practice part-time reindeer herding like the Sami or some groups in northern Asia.

I want this critter to be common enough and hungry enough that humans generally have to be wary of it when they venture into the woods. As far as size, at its smallest it should be at least as big as the average human and a decent challenge for a single warrior. It is difficult to kill, and although it's mammalian, like a reptile, it keeps getting bigger the longer it lives, and I'd like to see some legendary individuals get to draconic proportions. But how big and how common can I make this thing before my human population can no longer survive under its predation?

I've seen the rule of a 1:10 predator-prey ratio by biomass, but the 10 should represent how much prey is actually consumed, not the size of the prey's population (a tiger can eat up to 10x its own weight annually), and I'm not sure how large a percentage of a human population (which will still also face some mortality from ordinary causes like old age, injury, disease, and human violence) can be eaten by a predator before that population can no longer reasonably replace itself.

I'm trying to build a species that's exclusively carnivorous, and its favored prey is humans. The species is a solitary mammalian ambush predator, probably with a build similar to a big cat such as a tiger, though I'm also drawing some inspiration from classic dragon lore. It has magical origins and reproduces slowly. Its habitat is a rainy, subarctic coniferous forest similar to the west coast of Canada, at such a latitude that winters are much darker than summers, which may mean that it does a lot of its hunting in winter. The humans in this setting are fairly advanced hunter-gatherers: the environment is productive enough that people can be semi-sedentary, similar to west-coast First Nations like the Haida and Tlingit, though some also practice part-time reindeer herding like the Sami or some groups in northern Asia.

I want this critter to be common enough and hungry enough that humans generally have to be wary of it when they venture into the woods. As far as size, at its smallest it should be at least as big as the average human and a decent challenge for a single warrior. It is difficult to kill, and although it's mammalian, like a reptile, it keeps getting bigger the longer it lives, and I'd like to see some legendary individuals get to draconic proportions. But how big and how common can I make this thing before my human population can no longer survive under its predation?

I've seen the rule of a 1:10 predator-prey ratio by biomass, but the 10 should represent how much prey is actually consumed, not the size of the prey's population (a tiger can eat up to 10x its own weight annually), and I'm not sure how large a percentage of a human population (which will still also face some mortality from ordinary causes like old age, injury, disease, and human violence) can be eaten by a predator before that population can no longer reasonably replace itself.