Lions have suffered dramatic population and geographic range collapse owing to human activities. They now occur in less than 30% of their historic range and total numbers have fallen by 70% to 33,000 since 1980. Retaliatory killing in the wake of livestock depredations, habitat loss and fragmentation, and prey loss are the three main factors responsible for these declines. As bad as things are, the problem is only worsening.

Prof. Craig Packer (U. Minnesota) organized a host of scientists and managers who studied lion populations across 11 African nations and 42 protected areas, including me and my colleagues. Each of us furnished population trends over at least 8 years and details of the area's management budgets; some areas were enclosed by fences (black symbols) and others were not (red).

The most remarkable finding was the effect of expenditures needed to manage the reserves. $500 per km2 per year permitted a fenced reserve to maintain lions near 80% of capacity. Four times(!) as much money was needed to maintain an unfenced population at only half its capacity.

There are many reasons to be unhappy with these results, but the study’s conclusions seem inescapable. Despite their detrimental effects on gene flow and migratory species, fences are effective both in containing large predators--protecting surrounding communities from their depredations--as well as in excluding human and livestock encroachment and resource extraction (via bushmeat and grazing) from reserves. Fencing reserves requires substantial capital investment and entails additional management expenditures to ensure outbreeding, etc. However, it may represent the only means to protect a growing African population from large and dangerous predators, and vice versa!

To read more about this work, read our recent article:

Packer, C. et al. (numerous co-authors including BDP). 2013. Conserving large carnivores: Dollars and fence. Ecology Letters article supplemental material