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Drug lord Pablo Escobar imported 4 Hippopotamuses (Hippopotamus amphibius) onto his private estate in Colombia in the 1980s. Since his arrest and assassination, the hippos have escaped the confines of the property and have begun to reproduce in the wild of Colombia. They now number approximately 60 individuals. The presence of such a large, and possibly dangerous, species in a new habitat raises several moral and ecological questions and dilemmas. It is unknown what effect these animals may have on their new environment, or the threat that they pose to the people living near them. In an effort to mitigate possible risks to the environment and local populations the Colombian government initiated an effort to castrate all males in the herd. However, it is unlikely that these efforts will be very effective in curbing the population growth of the animals. South America lost most of its large species of animals during the Quaternary Extinction and it is possible that the hippos are filling a gap that still exists in the ecology of the continent. The rewilding efforts occurring around the world aim to restore and protect natural processes and habitats by introducing (or reintroducing) apex predators or keystone species. Perhaps further research could shed light on possible positive influences that the Hippos have on the South American environment and responsible ways to avoid risks to local populations.

The Late Quaternary witnessed a dramatic wave of large mammal extinctions, that are usually attributed to either human hunting or climatic change. We hypothesized that the large mammals that survived the extinctions might have been endowed with larger brain sizes than their relatives, which could have conferred enhanced behavioral plasticity and the ability to cope with the rapidly changing Late Quaternary environmental conditions. We assembled data on brain sizes of 291 extant mammal species plus 50 more that went extinct during the Late Quaternary. Using logistic, and mixed effect models, and controlling for phylogeny and body mass, we found that large brains were associated with higher probability to survive the Late Quaternary extinctions, and that extant species have brains that are, on average, 53% larger when accounting for order as a random effect, and 83% when fitting a single regression line. Moreover, we found that models that used brain size in addition to body size predicted extinction status better than models that used only body size. We propose that possessing a large brain was an important, yet so far neglected characteristic of surviving megafauna species.

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