Altogether, it takes seven years for the wildebeest bones to fully disintegrate, releasing nutrients like phosphorous and carbon into the river. This slow decomposition, while unpleasant to smell, is crucial for the Mara River ecosystem, sustaining microbes, insects, and fish, as well as large scavengers. In the past, river ecologists had assumed that high levels of dissolved carbon from rotting corpses are unhealthy and unnatural for rivers. But the researchers found that protected parks actually have more dissolved carbon their rivers compared to unprotected ones, suggesting that less human influence can sometimes mean more putrid rivers.
Unfortunately, there are few ecosystems that can directly compare to the Mara. That’s because humans have disrupted nearly every large herbivore migration on the planet, and continue to kill off these key animals faster than they can kill themselves. It’s practically impossible for human biologists to get an accurate sense of what ecosystems looked like before the loss of large animals, because, according to many paleoecologists, humans have been wiping out large animals since the prehistoric migrations out of Africa.
The human migration across the Bering Strait into the Americas 15,000 years ago was followed by the extinctions of American mammoths and mastodons, giant ground sloths, sabre-tooth cats and giant armadillos. Other continents also suffered losses. When humans first landed in Australia 60,000 years ago, they would have encountered 500-pound kangaroos, 10-foot-tall flightless birds, wombat relatives the size of rhinoceroses, and monitor lizards that grew to over 20 feet long. By 45,000 years ago, all of those species were gone.