Our results strongly suggest that the long-term presence of a research area is an effective way to protect wildlife populations. Its presence was found to be a strong predictor of wildlife population densities, especially for threatened or over-harvested species. Although we cannot control for all influential factors (e.g. total annual budget and conservation activities), it still appears that the mere presence of researchers is sufficient to generate a positive impact on wildlife populations in the vicinity.
It could be argued that our results may be an artefact of placing research stations in areas of high wildlife abundance. The initial choice of the location of the first research project within TNP was made after confirmation of the presence of a healthy chimpanzee population, but selected mainly for logistical reasons (e.g. access to roads and existing infrastructure; [13
]). Furthermore, analyses by Hoppe-Dominik et al
] of long-term data on wildlife density and distribution for four areas of the TNP indicate that another area of the park (the southeast) also contained high large mammal density at the time the first research project was established (see the electronic supplementary material, figure S3). Moreover, their results demonstrate that only two areas of the park did not suffer a decrease in their animal density between 1977 and 2004, areas where there was a research and tourist presence. This further corroborates our results that demonstrate the positive influence of the presence of a research area on wildlife protection.
Researchers can also have negative effects on wildlife within protected areas, notably by increasing the likelihood of disease transmission between humans and wildlife, which applies especially to apes [19
]. These problems should be addressed to the best of our abilities in order to reduce the potential negative impact of our presence [20
]. Nonetheless, the positive impacts still appear to outweigh the negative ones [19
]. Regular monitoring of wildlife populations and their threats can help conservationists to respond rapidly to population declines. Unfortunately, such a programme is currently being implemented in only a few African national parks [2
We demonstrate that in addition to obtaining information on population status, wildlife monitoring can also be a simple means by which to measure the success of conservation actions. As such, systematic evidence-based methods should be put into use more widely, in particular to evaluate park management efficiency, as well as conservation activities of individual practitioners.
Finally, it should be emphasized that the positive effect of the presence of researchers or conservationists will only be a temporary one, unless sustained over a long period of time. For instance, a conservation organization was present at Marahoué National Park (Côte d'Ivoire) between 1998 and 2002, during which time the park was well-preserved. Shortly after the departure of the organization, this park suffered major human encroachment, resulting in a 93 per cent decrease in forest cover [6
]. This exemplifies the importance of long-term commitment by research and conservation projects to ensure the continuous beneficial effect of their presence for wildlife populations and their habitats.