In the first part of my island biogeography post, I talked about how animals got to islands, giants, dwarves, copycats, and adaptive radiation (I suggest clicking this link if you need a refresher). Now in part 2, I will talk about one of the downsides that animals living on islands face: vulnerability to a variety of threats. Just a warning: I will be talking about touchy subjects including climate change and feral cats in this post, which I have learned from experience is a subject people do not like to talk about and often ends in a fight. Please keep it civil in the comments, otherwise I may have to delete some comments on the subject.
There are examples of how fragile island ecosystems are present in the fossil record long before humans evolved. One such is of one of the many islands bathed in the azure waters of the Tethys Seaway during the Jurassic Period that would one day become the bedrock of Europe. As I mentioned last time, animals living on islands that are normally larger on the mainland are smaller due to constraints of space and resources, and this was no different for the Lagenberg quarry in Germany. Dinosaur fossils found there are mostly of dwarf taxa found elsewhere in Portugal, Africa, and North America such as an island species of the megalosauroid Torvosaurus, diplodocoids, stegosaurs, several indeterminate theropods, and a miniature brachiosaur known as Europasaurus, which was found in a large assemblage which suggests that a herd of these tiny sauropods drowned en masse and were scavenged by crocodilians and fish as evident by tooth marks on the fossils. About 35,000 years after the sediments of the drowning incident were deposited, a series of large tracks suggesting the formation of a landbridge which led to a faunal overturn of the site. The resident Torvosaurus has been estimated to be 13 feet in length, whereas the arriving theropods were estimated to be between 23 and 26 feet long if reconstructed as a relative of Allosaurus, which had been found in North America, Portugal, and possibly East Africa. It's possible that the creators of the tracks hunted the mini dinosaurs, who stood no chance against the larger invaders, to extinction. Sound familiar?
What first made the wildlife of the Galápagos islands recognized around the world was not for Charles Darwin's observations on natural selection, but as a food source. Pirates would use the islands as a hideout from Spanish naval forces while stalking the oceans to plunder cargo ships laden with riches from the Spanish colonies in the Americas sailing to Europe. The islands didn't have much mineral use to the pirates, but instead they served as a limited but substantial source of fresh water for the pirates and more importantly as a source of food. If you guessed that pirates hunted the tortoises for food, you would be correct. Giant Tortoises were a preferred source of food for sailors, pirates, and whalers because they were docile and large enough to feed several crew members. Ship crew members would often capture as many tortoises as they need and bring them aboard to kill later; seabirds and sea lions were often slaughtered on the beaches. Intensive harvesting would take a heavy toll on tortoise numbers, whose late age of reproductive maturity and low likelihood of hatchlings surviving could not keep up with the pressure of hunting.
The animals of the Galapagos weren't the only ones to fall victim to the appetites of sailors, as one of the most famous extinct animals in written history (second only to mammoths if cave paintings count as writing) was also a soft target for hungry seafarers, I'm of course talking about the Dodo. Pop culture has painted a picture of this island inhabitant as so slow and dumb, it was destined for extinction, but the reality about this giant is much different. Comparisons of brain size to body size leads scientists to conclude that Dodos were actually fairly smart, and depended more on smell than sight to find the abundant fruit on the island, supplemented with small land vertebrates and shellfish. Dodos weren't dumb, they had lost all adaptations to avoid predators because there were none on their island home of Mauritius until humans arrived and exploited them as a source of fresh meat like with the tortoises of the Galapagos
When pirates, whalers, and sailors arrive on islands such as Mauritius or the Galápagos, they often introduce livestock such as sheep, goats, and pigs to provide an additional source of food for when they pass through the areas in addition to the native mammals, seabirds, tortoises and/or Dodo. However, introducing such herbivores to an island can have disastrous effects as they trample and browse on native plants down to the roots if not properly contained, preventing the plants from regrowing.
One of the most widespread introduced species on islands is one that was not intentionally released by humans. Rats and ants have found their way to many island groups as stowaways on ships and plants, and with no predators on the islands, they rapidly spread upon making landfall. In large swarms, Little Fire Ants (Wasmannia auropunctata) drive native insects out of forest habitat and attack ground nesting birds and reptiles which have no enemies. Rats are particularly dangerous for native birds because they prey on nests, eating the eggs and chicks as well as the adults and competing with them for food. To protect their sugarcane crops, plantation owners introduced Small Indian Mongooses (Herpestes javanicus) from India to Molokai, Maui, and Oahu and have since spread to every Island except Lanai and Kauai, hoping they would prey on the rats. This did not go as planned because the rats are mostly nocturnal while the mongooses are diurnal and instead targeted the eggs and hatchlings of native ground-nesting animals instead such as chickens, francolins, and Hawaiian Geese. Goose numbers were around 25,000 when Europeans first arrived in Hawaii in 1778, but by the 1950s, they had been reduced to 30
As if two introduced mammalian predators wasn't enough for Hawaii's endemic birds to deal with, they also have to battle mosquitos that transmit deadly diseases such as Avian Malaria. It results when a blood-borne parasite, Plasmodium relictum, is transmitted from infected birds to healthy birds by mosquitoes under suitably (warm) temperatures. Once infected, many birds die. Thus, the introduction of mosquitoes made it possible for native birds to become infected, given that a reservoir of disease was present, such as invasive birds like the Japanese White-eye and Red-billed Leiothrix. It's estimated that P. relictum has caused the extinction of a third of the 55 species of Hawaiian Honeycreepers present when Europeans arrived. The survivors retreated to higher elevation forests where cooler temperatures inhibited the growth of the parasite, but many fell victim to the disease...
If the idea of an entire island disappearing underwater sounds ridiculous, guess what: it actually happened! East Island is a low-lying islet surrounded by shallow reefs in the French Frigate Shoals, part of the Northwest Hawaiian Islands, and one of the most important nesting sites for Green Sea Turtles in Hawaii, most of which were born on the island. East Island recently made news when storm surge by Hurricane Walaka washed away most of the island, leaving a 150 foot sliver behind. While the reduction in size of East Island has not directly been linked to anthropogenic climate change, it it contributes to the strength and frequency of hurricanes like the one that overtook the island. Part of the theory that hurricanes will become more frequent and stronger is because warmer water provides more energy to feed them, which has been reinforced by computer simulations that produce more intense storms with rising ocean temperatures. To quote an article from the New York Times: “This is probably a forebear of things to come.”
Tropical storms often have massive impacts on tropical islands, and none were nearly as damaging as Hurricane Iniki in 1992 (around the same time Jurassic Park was filmed and may have inspired "Hurricane Clarissa" from The Lost World novel, Steven Spielberg even included footage of the storm making landfall in the associated scene when Dennis Nedry shuts down the parks security system and the Tyrannosaurus escapes). Iniki made landfall on the south-central portion of Kauaʻi, bringing its dangerous inner core to the entire island. Storm surges reached 6 feet high in most parts of the island, sometimes reaching 18 feet with waves as high as 35 feet causing a debris line more than 800 feet inland. Thousands of homes on Kauai were either damaged, destroyed, or lost completely. Agriculture was also heavily impacted by Iniki. Though much of the unharvested sugar cane crop was severely damaged, tender tropical plants like bananas and papayas were destroyed and fruit and nut trees were uprooted or damaged. On the island, one person died when struck by debris, while another lost her life when a portion of her house fell on her. Offshore, two Japanese nationals died when their boat capsized. The Kauai Nukupu'u was abundant until the 1800s when clearing of forests for agriculture destroyed much of its habitat and forcing them to take refuge in the Alakai plateau along with many of the other endemics. The damage caused to the island by Iniki may have led to the nukupu'u's extinction, as they were not seen after 1996.
I added this video of a Kaua'i O'o singing at the end mainly to show how great the impact of humans is on island endemics. One of the few recordings of a Kauai O'o is of the last male alive at the time singing for a mate that will unfortunately never come. "Now his voice is gone"
To end on a good note, I should mention that all hope is lost for island biodiversity, as there are many I've done lots of research on conservation groups whose work focuses on islands, and here are some of my favorites:
The YB Odyssey Facebook Page
My Flickr site
Leica Nature Observation Blog
Young Birders of the Round Table
crazed4birds (Drew Beamer)
Blue Ridge Birding (Max Nootbaar)
Whimbrel Birders Club
The Eyrie (ABA Young Birders)
The Birding Place (Aidan Place)
Lost In Nature (Jared Gorrell)
Bird Boy Canada (Ethan Denton)
Prairie Birder (Charlotte Wasylik)
Wing Tips (Tessa Rhinehart)
Soar Birding & Nature Tours (Noah Kuck)
Setophaga dominica (Oscar Wilhelmy)
Is yours not featured? Let me know