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Island biogeography Peter Shaw Introduction The aim of today’s lecture is to introduce you to some of the strange biodiversity found on remote oceanic islands, to explain why so many of these species are endemic and so greatly endangered, and to introduce of islands system (Easter island) as a parable of unsustainable development. Examples of island ecosystems Today I am interested in systems which are old and highly remote. The largest collection of these occur in the pacific: the Hawaiian archipelago, Easter Island, Lord Howe Island, the Galapagos... The Indian ocean has the Mascarene islands, Aldabra, Round island... The Atlantic has but few - St Helena, Tristan de Cunha. Even the Mediterranean had its island endemics, on Cyprus, Mallorca and others. Colonisation A new volcano emerges from a mid-oceanic hotspot. Sea level changes expose a new Coral atoll. How does live get there? Fly or float! Earliest colonisers usually come in on the wind seeds of plants, insects, eventually a few exhausted birds. Spiders fly in too. Other organisms raft in: a few plants (coconuts, the sea bean) have seeds adapted to float in sea water and germinate on remote beaches.. Rafting Is the technical name for the process by which non-flying animals end up marooned on remote islands. Mammals do not raft well (humans excepted), but reptiles do. A python was found on Krakatoa within a year of its eruption. The Fijian iguana Brachylophus vitiensis is most closely related to iguanas found in the Carribean. Its ancestor must have rafted across the pacific before the 2 Americas collided. What colonisers find: Is a pristine, predator-free system where the problems of survival are mainly physical. There are few or no competitors, and many vacant ecological niches. The processes of evolution work rapidly under conditions like this - aberrant/odd individuals are more likely to survive than on the mainland, and may found an entire new lifestyle - hence species. Remote islands routinely contain endemic species - the more remote the island, the more endemics. What you end up with: Is a community which has been assembled haphazardly from a few colonising species, often with species feeding on unusual foods or growing in odd ways. A general truism relates species number to island size: for a given level of remoteness, bigger islands have more species: S A S = C Az S = Species richness C = a constant for a given system A = area z = a scaling constant, typically 0.1-0.35 This means 10* area = 2* species (roughly). 3 reasons: Small Why endemics? genetic input (the founder effect). Entire populations have the genetic make-up of the founding couple. Isolation - no connection with mainland gene pool to dilute changes. Unusual selection pressures. NOT no selection pressures, but very different to mainland life with diseases and predators. Given these conditions, evolution can act rapidly. Wallabies released on Hawaii in 1910 already have such different colour, size and enzyme polymorphisms to Tasmanian populations that they deserve status as a new species. Endemism Remote islands contribute to biodiversity out of all proportion to their area, due to their endemic species. Even in the UK, 2 of our native mammals are island endemics: the Skomer vole and the St Kilda vole. Hawaii is especially famous for endemics (91% of its native species). The whole genus of Hibiscadelphus (6 spp. of plant) is 14 individuals in the wild. Half the birds listed as endangered in the whole of the US are in Hawaii. Features of isolated island endemics 1: Size changes Birds and insects may become giant and/or flightless. (Giant Earwig of St Helena, Dodo of Mauritius, elephant bird of Madagascar, Flightless rails all that used to be all over the Pacific - now confined to Henderson island). Mammals if present may become dwarf: Cypress had pygmy hippos. Mallorca had an endemic dormouse and an elephant, both about the same size! Komodo dragons evolved to predate pygmy elephants. Tortoises where present become giant Galapagos and Aldabra. Features of isolated island endemics 2: Lifestyle changes The Laysan finch looks like a sparrow, but lives like a vampire bat, sucking blood from albatrosses. Galapagos finches have evolved to use cactus spines as a tool. Hawaii has a caterpillar which catches flying insects. In Hawaii Lobelias are giant trees. A Seychelles tree Pisonia grandis has large sticky flowers which catch nestling terns. The tree benefits from their nutrients as they decay carnivorous flowers. Features of isolated island endemics 3: Vulnerability Almost all island endemics are automatically a conservation worry due to small geographical range. In addition: They have no fear of predation. They tend to be K selected - few large offspring. They have no tolerance of disease. Predation It is quite normal for wild birds in remote systems to see humans as useful landing posts! This lack of fear reflects evolutionary heritage, but is a disaster in terms of survival. A consistent pattern is that remote islands used to hold giant flightless birds, until humans arrived. Geese in Hawaii Moas in New Zealand Kakapos in New Zealand Giant owls in the bahamas. It seems clear that in many cases we simply ate the species to extinction. RIL: BiowarfareChatham Island Black Robin Far worse damage was done by the species we introduced.One Rats, cats, goats are of the rarestpigs birdsand in the the worst, but world. deer, ferrets and on possums are It once lived Pitt, also causing damage Mangere in andNew LittleZealand. Mangere Islands. Cats cat exterminated One lighthouse keeper’s brought the home species onofPitt and Mangere island one entire population the Chatham so by the turn of the robin PetroicaIsland, traversi home, dead, one by century only about 25 pairs one! (a 2nd popn survived - now 100 birds remained. descended from 1 female) The destruction ofRats forest on Little Mangere coupled with swim ashore fromIsland, shipwrecks, andthe arelow breeding rate, destructive predators of ground-nesting caused the numbers to decline even further. To prevent extinction birds. Removing rats from the Isle of Maythe 7 birds surviving involved 2 tons of warfarin. Saving the dark in 1976-77 were moved the larger Mangereinvolved Island. In spreading 1980 an heraldtopetrel in Pitcairn 2 intensive management tons of brodifacoum on a 65ha island. plan was started to save the Black Robin from extinction. The biggest single killer of native Hawaiian birds came from one barrel of water thrown overboard in the 1880s. This introduced mosquitos, which vectored avian malaria. Now the surviving endemic birds are in high, cold mosquito-free forests. Almost all bird life on Guam has been wiped out by the introduction of a Solomon-island bird eating snake Boiga irregularis, which stowed away with the US military. Woods are now full of spiders webs, as there are no birds to eat spiders or snap their webs. Goats! Trochetiopsis ebenus St Helena ebony - once widespread on St Helena. 16th century goats destroyed the forest, and the world population is 2 bushes on one remote cliff. Are the bane of island endemic plants. They eat anything, climb well, and are hard to kill. Worse, they were deliberately released onto remote islands in previous centuries - for food for shipwrecked sailors. 26% of all island endemic plants in the IUCN red data book are mentioned as threatened by goats. In destroying vegetation, they endanger animals too - starving out tortoises etc. Ways to kill goats: Shoot them. They soon get the hang of this one - use a helicopter. Poison them - paint toxins such as compound 1080 onto target foliage. (This works well at first, but as the population falls and bushes come back this ceases to be effective). The Judas goat technique: release sterilised goats onto the island, fitted with radio collars. They will home in on the wild goats, and lead hunters to them. Don’t stop! Pinta island (Galapagos) had 10,000 goats. These were hunted down to 3 animals, then left. 12 years later there were 20,000 goats, albeit very inbred. In Hawaii one of the threats to native forest comes from pigs. These disturb the soil, damaging the roots of native Metrosideros trees and allowing in seedlings of Myrica - an alien nitrogen fixer. Attempts to control these pigs give me 2 sharply contrasting stories: Fences. Conservation workers try to isolate pigs from an area by putting up a fence - but a determined pig is very hard to keep out. The most determined research on pig-proof fences comes from the growers of illegal Cannabis plantations, who still come along some days to find a pig looking vague but contented, among the squashed remains of a year’s harvest… Nooses: The best control measure is simply to lay nooses at neck height along forest trails, and return for the decaying remains every few weeks... Easter Island (Rapanui) The colonisation of Easter island is one of the great achievements of human pre-history. What happened next is a warning. Around AD 400 a canoe carrying Polynesians arrived on Easter Island after a sea voyage of at least 2000 miles. They found a wooded volcanic island. 1000 years later a unique, complex culture had developed. The trees were all gone, used for boats fuel and for moving Moai (giant statues). No trees = no boats Once the trees were gone, the islanders were isolated and stuck. They destroyed the seabird colonies, then the bird colonies on swimmable offshore islands, then underwent a population crash., c. 10,000 -> 4000 in c. 50 years. The crash phase was marked by incessant tribal warfare. Hens were kept in heavily re-inforced stone houses, families hid in caves, cannibalism was routine. This phase left the island with people, chickens, a few domestic plants - and nothing else. Wild biodiversity was all but destroyed. Then Europeans came - we took many slaves, introduced smallpox, and reduced the native population to double figures.