Whether ecotourism actually aids in the conservation of endemic and threatened species has been highly debated. Many argue that the impacts of tourism are too detrimental and intrusive to allow for populations to proliferate, particularly in regards to sensitive and rare species (Kurger 2005, Isaacs 2000). Case studies of ecotourism have revealed both positive and negative effects.

An example of a positive effect was seen in Nevin and Gilbert (2005) in their study on brown bears within British Columbia. They  observed the effects of ecotourism on the demographics of brown bears. They noted that human presence from ecotourism resulted in a displacement of large males, but not subordinate males, females, or cubs (Nevin and Gilbert 2005).

Three brown bears examining a stream in hopes of catching some fish.

This created refuge and increased feeding opportunities for subordinate age and sex classes (Nevin and Gilbert 2005).  These opportunities were hypothesized to potentially increase population productivity due to the strong positive correlation between mean female mass and litter size (Nevin and Gilbert 2005). Improvement from past management strategies, and unexpected positive outcomes of ecotourism have allowed for positive impacts within ecosystems beyond initial conservation goals.

Common negative effects of ecotourism were frequently related to stress, increased susceptibility to disease, and decreased biological functioning. A specific example of this is the Amazonian Lake hoatzins (Opisthocomus hoazin) pictured below, who had significantly lower chick survival rate in nesting areas exposed to tourists, as well as lower average body weight and a stronger hormonal response rate to stress stimulus than unexposed birds (Müllner et al 2004).

The Amazonian Lake hoatzins (Opisthocomus hoazin), who in ecotoursim reserves in Costa Rica has been negatively effected by the presence of ecotourism.