Runoff with a high sediment load. Watershed area is overgrazed. Photograph was taken during a small thunderstorm event. Bears versus rattlesnakes might be an example. Furthermore, we tolerate some species around us more than others, i.e., it is okay to have birds in the city but probably not a large population of alligators or poisonous snakes.
Some species do better than others in proximity to humans.
Although difficult to map, there are certain patterns to species' distribution. Although humans are very adept at modifying their environment, physical influences such as topography, environmental hazards , climate, water and other natural resources , and proximity to transportation routes has a large influence on where we live and what we do. Human settlement Physical influence of city location uniform spacing indicates broadly distributed resources clustered spacing indicates resource concentrations linear spacing indicates natural transportation routes such as rivers, base of mountain ranges, etc. A large city in an otherwise sparsely settled area may indicate that although the region may be inhospitable, the city serves some other purpose unrelated to the surrounding area. Las Vegas, Nevada is a good example.