Isle of Dwarves and Giants: Ecology of Bermuda
Since life first invaded the land, islands have served as worlds in miniature, disconnected from the mainland’s ferocious competition. From the dwarf dinosaurs of Hatzeg to the giant lemurs of Madagascar and the flightless birds of New Zealand, they have allowed the few who reach them to evolve into forms alien to the rest of the world. Of course, the vast majority of island biodiversity would disappear in the face of human colonization. The inhabitants had lost their fear of outsiders, and were easy targets for explorers in need of food.
During the course of the Regression, many islands, particularly smaller, more isolated ones, would lose contact with the outside world. While many would simply revert to a more tribal lifestyle, a few isles would prove unable to support their stranded human inhabitants. People would fight each other over scraps of food and drinkable water. When those finally dried up, the few remaining survivors would succumb to hunger and dehydration. And when the last inhabitant of the island passed, the microsphere would return to the wild. In most cases, however, it would not be the surviving native species that would claim the islands, but instead the creatures man brought with him. Livestock, pets, pests, and introductees would find a blank slate for them to adapt to. While many would be unable to survive without human settlement, a few managed to hold on.
A good example of the trends listed above is Bermuda. 768 miles from the mainland, before settlers arrived, it was a home to unique island birds, such as flightless ducks, Bermuda towhees, and a unique species of tortoise. After humans arrived and colonized the island, only a handful of endemic species, such as the Bermuda petrel, longnose skink, and Bermuda ant survived. And after humans died out, the introduced species began to proliferate.
Another trend that Bermuda exhibits is Foster’s rule. The general idea is that, on islands, large animals will generally get smaller while small animals will generally get larger. The reason is twofold. For one, resources. Large animals require more food to survive, and since islands are, by definition, smaller than continents, there’s less food than on the mainland. Thus, it’s more efficient to be smaller and require fewer resources. By contrast, smaller animals can afford to grow larger to meet the capacity of their environment. The second part is competition and predators. Islands tend to lack the common predators and competitors, allowing island species to not have to worry about being eaten or having to fight for food as much.
900 years later, Bermuda is a very different place. No human has set foot on the island in nearly 800 years, sans the occasional shipwrecked human who doesn’t last very long. Florally, it's a mix of species native to the island (such as the Bermuda cedar and Bermuda sedge) and introduced species. A similar story is found in the invertebrate fauna. By contrast, Bermuda has no native amphibians, though introduced cane toads and Antilles coqui have naturalised with the island’s fauna.
A more interesting development can be seen in reptiles. Most notably, introduced Jamacian anoles are showcasing a very common trend among insular anoles. Like in the Caribbean, anoles are converging on a specific set of ecomorphs. While not enough time has passed for speciation, the different ecomorphs are much more likely to breed with themselves than other ecomorphs; in a few thousand or hundred thousand years, its likely true speciation will occur. Crown giants are, as the name suggests, relatively large anoles that live in the highest portions of trees. They jump from tree to tree and can eat smaller lizards and even birds eggs. Trunk-crown are much smaller and live on the uppermost trunk and lower canopy. Short legs and large toes allow them to climb with ease. On Bermuda, trunk-crown are the most basal, as the ancestral Jamacian anole was of this ecomorph. Finally, trunk-ground anoles live on the lower trunk and nearby rocks. These are the least colorful of the ecomorphs present. While there are several other anole ecomorphs, none have developed on Bermuda just yet. Still, it serves as a fascinating display of convergent evolution.
Birds, meanwhile, have fewer stand-out differences. Smaller birds, like sparrows and cardinals, have grown slightly larger, while larger birds, like crows and owls, have shrunk somewhat. The most notable change is among chickens. They are noticeably larger than mainland breeds, and roosters have more vibrant feathers and combs. This is likely a response to the relative lack of predators, allowing males to dedicate more resources to extravagant displays.
The most dramatic change, however, is the presence of land mammals. Before the Europeans, the only mammals found were marine mammals and a handful of bats. Now, eight terrestrial mammals call Bermuda home.
Three of the eight are rodents, all of them nearly double their ancestor’s size. House mice are most common in the grassier parts of the island, nibbling on seeds and blades of grass. They play an important role in these ecosystems, serving as prey for larger predators. Brown rats, meanwhile, are the most carnivorous of the rodents present; their incisors make short work of land crabs and other invertebrates, and sometimes even take small lizards and frogs. They are still omnivorous, though, and readily eat seeds. Black rats have begun to move up into the trees. With no squirrels introduced, they form a very rough approximation of their niche. This makes them in close proximity to owls, who make up a large portion of their diet.
Often considered rodents, rabbits are also found in Bermuda during the New Medieval age. They are most common in more open areas, grazing on grass for most of their food. Interestingly, they have adapted to the relative lack of resources; while not deviating too much in size, they produce a noticeably smaller litter than most leprids, most likely an adaptation to avoid overpopulation. To compensate for fewer offspring, mothers devote more energy to caring for their kits, ensuring more survive to adulthood.
Cats, ever the adaptable hunter, are thriving on the island. Indeed, very little has changed from their domestic ancestors aside from a selection towards a brown tabby coat to better blend in. They are more common in forested parts. Despite their larger size, cats are still the primary predator of the island’s rodent population.
The last three mammals are arguably the strangest animals on the island. All of them are considerably smaller than their domestic ancestors, and behave quite differently.
The first is the Bermuda dwarf pig. At 18 inches tall and weighing no more than 150 pounds at maturity, they are among the smallest pig breeds in the world. Their coat is commonly bristly, and usually a brown to blend in with the foliage. Piglets have re-evolved the stripes found on wild boar. Their diet is very varied, incorporating fruits, nuts, tubers, insects, small vertebrates, and even carrion; indeed, the event that brings the most amount of pigs, or indeed any animal that incorporates meat into its diet, together is the washing ashore of a whale carcass. While wild boars are known for their ferocity, dwarf pigs are very flighty, their size making them common prey items for Bermuda’s larger predators.
The predator that preys the most on dwarf pigs is the Bermuda wild dog. With the wildly different breeds that formed their ancestors, it can be somewhat difficult to generalize their physical attributes. Their coats are usually short, but the patterns on them range wildly, from solid colors to patches, spots, saddlebacks, and just about any pattern modern breeds have. Broadly speaking, adults range in size 24 inches tall and weigh 43 pounds to 14 inches tall and weigh 10 pounds; most are around 18 inches tall and weigh 22 pounds. This puts them, on average, the size of a red fox, which is a fairly apt comparison. They are omnivores with a carnivorous bend, preying on rodents, rabbits, ground birds, and dwarf pigs, while also eating berries, fruit, and even some grains. Bermuda wild dogs are less social than domestic dogs, a byproduct of fewer resources making large packs infeasible. Pairs are monogamous, often hunting together. Still, there are a few occasions that bring a large number of dogs together, namely large carcasses washing ashore, and the calving season of the last mammal.
The Bermuda dwarf cattle is the largest land animal on the island. While a giant compared to the other animals of the island, it is positively puny compared to most cattle breeds; the best reference would be the Dexter cattle, with the height of a large dog and the weight of a large boar. They are also the rarest animal, with there only being 200-400 individuals at any given time. Their diet incorporates a relatively large amount of browse, at least when compared to most cattle. Bulls sport relatively large horns, comparable in size to a more standard-sized breed. This is a reflection of their behavior. While most island species become more docile with fewer predators, the scarcity of resources and cows, combined with nothing that can consistently hunt them, has made bulls incredibly aggressive, especially during mating season. Fights between bulls are brutal, often leaving the loser dead. Indeed, few males die of old age, and those who do have the scars of a true survivor. Also, while adults are virtually free of predators, calves are sometimes picked off by large groups of wild dogs.
Despite being the largest mammalian carnivore on the island, wild dogs aren’t the apex predator. That title belongs to a colonizer that arrived a mere 500 years ago. Golden eagles can, and do, hunt every creature on the island except adult cattle. They roost in large trees and on rocky outcroppings, away from most potential egg thieves.
Bermuda, despite being a unique glimpse of an ecosystem deprived of humans, it is almost certainly not one to last. While the ships of the United States or the State of Louisiana have not yet mastered open ocean travel, it seems inevitable that, sooner or later, humanity will someday rediscover Bermuda. And when that day comes, it will spell the end of the unique life that calls the island home. They will join the likes of the moa and the dodo and the large marsupials of Australia as insular victims of human colonization. But until that day, Bermuda will be a bizarre world, unlike anything around today.