The lionfish, is a fierce predator. It is native to ranges in the Pacific Ocean and is one of the many invasive species brought the to American continent by humans or human travel. Like so many species who find themselves without any natural predators or competition, it has succeeded vociferously. The species was likely introduced to the Caribbean in the 1980s. Since then, populations have skyrocketed and spread as far south as Brazil and as far north as Delaware as of 2014. The lionfish’s success, however, comes at the incredible detriment and destruction of natural reef systems in the Atlantic, increasing worries of a trophic cascade that would reduce diversity in Atlantic reef systems by, some estimate, eighty percent. Lionfish reproduce at astounding rates, and a major study demonstrated that one adult lionfish reduced the population of young fish and crustaceans by 79% within five weeks.
The lionfish doesn’t need to kill all the fish and destroy every coral to cause a full collapse. It only needs to weaken the ecosystem enough for it to collapse under its own weight. There is another lionfish of sorts. One who is far more damaging and far more widespread.
A major extinction event has been occurring over the past 100,000 years or so. Some scientists argue for more others for less. It is referred to as the sixth extinction, the Anthropocene Extinction, the Holocene extinction, and other names besides. There is no agreement on when exactly it begins, or which species perished due exclusively to human activity and which were weakened by a number of factors of which humans were only one. Nonetheless, these different names indicate that it is, largely, of human origin, and an event which has only been rivaled in five previous major extinction events–the most well-known of which obliterated the dinosaurs at the end of the Cretaceous period. I do not wish to discuss major extinction events in this post (perhaps another), but instead only draw a parallel between the lionfish and the human,
History is writ in stone. Or at least it can be discerned from stones and what study of the fossil record tells us is that as humans turn up, megafauna begin to decline and disappear. What are megafauna? In short, they are large animals (generally anything larger than a deer).
To give a specific example, the Moa were prolific on the island of New Zealand a little less than 800-years ago. There were nine species of Moa in total, ranging in height from 4-feet to 12-feet. Estimates place these birds on New Zealand as far as 60-million years back, where they lived and flourished, evolving into separate, but similar, species. The Moa were the dominant herbivores on the north and south islands, and their only natural predator was the Haast Eagle, who preyed on them from the sky. The Moa’s 60-million year reign, however, was brought to an abrupt end at the arrival of the Maori (around the year 1300). The Moa were hunted into extinction within an approximate 100-year span. Maori midden heaps suggest that the birds made for easy prey and were barbecued by the dozens. 60-million years of successful adaptation brought to an abrupt halt.
Fossil records show that similar megafaunal extinctions occur wherever humans turn up–Australia 50,000-years ago, North America, 100,000 years ago, etc. While the Moa’s case is unique in that it is almost certainly human overkill (much like lionfish overkill) that caused the creature’s extinction, the correlation with the arrival of humans and the decline in megafaunal lifeforms is too concrete to ignore. Large species such as the giant ground sloth, the diprotodon, the giant polar bear, the sardinian giant otter, well known species such as the woolly mammoth and saber-toothed tiger, along with the giant marsupials of Australia all began their decline shortly after humans arrived. Humans are not likely only cause for the extinction of these species–many suffered sweeping changes in climate and environment while humans began their hunt– but humans are one of the causes and possibly the major cause. As with the lionfish, the species need not be completely destroyed to cause an extinction; rather, the ecosystem need only be fractured and stressed for species to fall apart all on their own.
Most megafaunal species are just that: large. In many cases, very large. There are some advantages associated with being large, the most important of which is: only the very desperate hunt you. Size is what allows elephants, rhinos, hippos, and giraffes to graze rather contentedly without worrying much over predators. However, one of the disadvantages of being large is that it takes much longer for offspring to mature. Thus gestation periods and life-cycles are greatly extended. It takes, on average, 645-days for an African elephant to give birth and fertile females only give birth every 3-6 years. An elephant won’t be independent until age 15 and won’t be fully grown until age 20-25. This means that any reduction in population takes a long time to rebound. In other words, mega-fauna are uniquely vulnerable to persistent hunting because their populations, when stressed, struggle to rebound quickly. In fact, for many, a quick rebound or adaptation is an impossibility.
Furthermore, with reduced populations the increase of inbreeding means that the species will likely suffer genetic defects and abnormalities. Meaning, if the population drops below a certain number (some argue 10,000 for large mammals) then it will likely collapse due to lack of genetic diversity.
Again, to cause an extinction, the species doesn’t need to be destroyed outright, only fractured and stressed. We are the lionfish who put many large animals (megafauna) under continued duress for various reasons. The weight of history cannot be disguised or dismissed despite claims to the contrary and it has weighed too heavily in our favor. If we do nothing to curb background extinction rates we could see the continued disappearance of species on whom we depend. We have seen this story play out with the Dodo and many others. Large animals are always the first to disappear in an ecosystem and they have been disappearing for a very long while. They are earth’s canary in the coal mine. How many canaries need to die before we get the message?