Population growth near protected areas threatens the capacity of such areas for biodiversity conservation. Protected areas may even encourage growth by providing economic benefits that attract migrants. Consequently, understanding the relationships between human demographics and biodiversity is important for conservation. We studied a community-governed Wildlife Management Area bordering the Selous Game Reserve in Tanzania, set up to benefit local people and the subsistence rural economy. Annual population growth in this area is 5%. We used a combination of ecological and socio-economic surveys to determine the causes of this growth and its effect on wildlife in the Wildlife Management Area. One-third of local people interviewed were immigrants to the area. Population growth appeared to be unrelated to the protected area; instead an increasing proportion of immigrants cited readily available land as their reason for moving. Pastoralism was associated with fewer signs of large grazing mammals and elephants Loxodonta africana and agriculture was associated with fewer signs of elephant and buffalo Syncerus caffer but more signs of other ungulates. Few residents were aware of the Wildlife Management Area and few received any benefits from wildlife and therefore had little reason to conserve it. This situation is attributable to poor management of the Wildlife Management Area. Detrimental effects of human activity could spread to the Selous Game Reserve if population growth continues. However, natural resources could benefit residents if properly managed. Interactions between human demographics and protected areas are complex and may be best managed on a case-by-case basis.