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 61 snakes DHJanzen100723.jpg high resolution
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To return to the question of why there is a noticeable difference in the general abundance of snakes and lizards (and it turns out, ground-nesting birds and small mammals) between tropical Africa and the neotropics. In short, the high generation of herbivorous megafauna cadavers in the African tropics is sustaining a huge fauna (and many species) of medium to small carnivores. To the mongooses, jackals, and storks may be added baboons, hawks, eagles, cats, and all the juveniles of the large predators. ALL of these animals have their populations maintained at a much higher density than could be supported by any community of small prey, by the fact that each of the predators can turn to those carcasses for a snack, for insects, for food during the times of low prey density. Put another way, when the small prey density falls in the neotropics (due to disease, drought, or just predator-prey cycles), the coyote has only fruit to turn to, and if there is none, its adults get thin and the kids die. When the same happens in the African tropics, the jackal can turn to those ever-present carcasses for starvation food. Now multiply this by hundreds of species of small predators spread over millions of years of evolution. The outcome is incredible crypsis in the lizards (e.g., chameleons) and a very high ratio of snakes that are defensively very poisonous to large mammals (e.g, mambas, kraits, cobras). In Africa, one would never think of picking up an unidentified large snake like this, while in the neotropics, it is standard practice. Another outcome is that the only reliable place to find snakes and lizards is either in large rock outcrops (with holes down which they can dive when pursued) and in villages (where people keep down the density of predators). What happened when the Pleistocene herbivores, which surely must have been as dense if not more in their respective habitats as were the African herbivores when the Europeans arrived, were taken off the scene. Most of the zoo of small carnivores seen today in Africa must have been a consequential loss. Our current coyotes, raptors, small cats, foxes, etc. are but a pale shadow of what was (to say nothing of the giant fusions and other scavengers that also went with the loss of the Pleistocene herbivores). And, relieved of this carnivory, the neotropical lizard, snake, mouse and ground-nesting bird community must have blossomed. To visualize this, just imagine what would happen if a troop of baboons or meercats (a kind of social mongoose) were to be turned loose in Mexico or Costa Rica. For a week, they would be fat and gorged on the many small vertebrates that dot the countryside. And the next week they would be starving - those that would survive would mostly do it by shifting their diet to far more frugivory than is the case in Africa. |
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