Lecture 5 Insular Gigantism and Dwarfism-island biogeography

1. Lecture 5 Insular Gigantism and Dwarfism-island biogeography • Island giants are aplenty: Komodo has its dragons. Madagascar has its giant hissing cockroach. Until about 1,000 years ago, New Zealand had its colossal bird, the moa. • Of dwarves, the world has witnessed everything from foxes, rabbits, and snakes that are smaller than their mainland counterparts, to that ultimate oxymoron(矛盾）, the pygmy mammoth, which once existed in various forms from California's Channel Islands to Wrangel Island in the Siberian Arctic

2. Why does this happen? • What factors encourage a species to alter its dimensions on islands? • What, in short, determines whether a creature will get Brobdingnagian or Lilliputian?

3. insular gigantism Giant Weta Japanese Spider Crab Elephant Bird Giant Isopod

4. Giant Isopod in in cold, deep waters of the Atlantic  a good example of deep-sea gigantism

6. 3-foot, 22-lb rabbit East Timor Giant Rat Galapagos Giant Tortoise

7. Komodo Dragon Komodo Dragon Giant moe Giant Squid

8. Insular Dwarfism

9. Little People of Flores

10. Could a tiny sub-species of in the genus Homo have co-existed in Indonesia with humans as recent as 12,000 years ago? • First dubbed a “hobbit-like human ancestor”, it was soon discovered that Homo floresiensis was in fact its own species, standing just three feet tall, about the height of a modern human toddler. Nine skeletons were found in Flores, Indonesia in 2003 • The team that discovered H. floresiensis believe the species is an example of insular dwarfism, with their growth restricted by a limited choice of food on the island

11. Dwarf Elephants • prehistoric dwarf elephants evolved to be much smaller than modern elephants due to their insularity on islands around the world including Crete, Cyprus, Timor and the same island of Flores, Indonesia where pygmy human relatives were found • dwarf elephants really were small: the Cyprus dwarf elephant likely weighed around 440 pounds

12. THE ISLAND RULE • The table reveals some interesting  trends ：Rodents tend toward gigantism, while carnivores, lagomorphs (兔形类，rabbits and hares), and artiodactyls (偶蹄类，deer, hippos, and other even-toed ungulates) are more likely to become dwarfed. • Overall, amongst mammal species that colonize islands, big ones have a tendency to shrink while small ones are apt to enlarge. • Biologists have come to call Foster's generalization the "island rule." Evolution of Mammals on Islands." Nature 202: 234-235 (18 April 1964).

13. Giants and dwarfs Three hypothesis for gigantism of island species (Schwaner & Sarre 1988) ①Predation hypothesis: either there is selective release if no predation occurs or there is selective advantage to escape a window of vulnerability ②Social-sexual hypothesis: due to high densities that occur among island populations, intraspecific competition among males and females selects for larger body size ③Food availability hypothesis: increase in the mean and variance in food supply/demand ratio selects for giants

14. 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.

15. 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.

16. 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.

17. 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.

18. Biowarfare • Far worse damage was done by the species we introduced. Rats, cats, pigs and goats are the worst, but deer, ferrets and possums are also causing damage in New Zealand. • One lighthouse keeper’s cat brought home one entire population of the Chatham island robin Petroica traversi home, dead, one by one! (a 2nd popn survived - now 100 birds descended from 1 female) • Rats swim ashore from shipwrecks, and are destructive predators of ground-nesting birds. Removing rats from the Isle of May involved 2 tons of warfarin. Saving the dark herald petrel in Pitcairn involved spreading 2 tons of brodifacoum on a 65ha island.

19. 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.

20. Island Biogeography Definition: A subdivision of biogeography that relates the manner in which species distributions are influenced and restricted by “islands.” The “island” is any area of habitat surrounded by an inhospitable matrix to the species occurring on that island. Image credit: http://www.okstate.edu/artsci/botany/bisc3034/lnotes/islands.htm

21. Types of Islands

22. Continental Islands: Formed on continent; may have formerly been connected to mainland by land bridge: Island Current Sea Level Former Sea Level Continent Submerged Land Bridge Continental Shelf

23. Examples of Continental Islands British Isles California Channel Islands Block Island, Nantucket, Martha’s Vineyard

24. British Isles: Land mass is part of European continent. During the last ice age, Britain was connected to Europe by a plateau called Doggerland. Doggerland Source: New Scientist, 8 Nov. 2008

25. As Ice Age ended, rising sea level flooded Doggerland and formed English Channel. Dogger Bank, an upland area of Doggerland, outlined in red. North Sea England France

26. California Channel Islands:Group of eight islands off the California coast; during last ice age, some were connected to mainland by land bridge.

27. B. Oceanic Islands: Never connected to continent; usually formed by volcanic activity and isolated from continent by deep ocean. Oceanic Island Current Sea Level Former Sea Level Continental Shelf Undersea Volcano Sea Floor

28. Examples of Oceanic Islands • Iceland • Japan • Aleutians • Bermuda • Caribbean Islands • Hawaiian Islands • South Pacific Atolls • Et al.

29. Many Caribbean islands were formed by volcanic activity at subduction zone.

30. Virtual Islands • Isolated communities separated via some sort of barrier • Ex. Sky Islands (southeastern Arizona/ southwestern New Mexico) • Ex. Discontiguous habitats created via fragmentation • Ex. Caves!

33. Islands are important natural laboratories for the study of biogeography, ecology, population genetics, evolutionary biology, etc.

34. Early naturalists (e.g., 16th-18th centuries) exploring isolated islands noted new types of plants and animals, which were often distinctive for each island or island groupFor several centuries, scientific focus was on cataloging the diversity of island organisms

35. Darwin observed dozens of animal species unique to the Galapagos

36. …including 13 species of Galapagos Finches

37. 1859 - Publication of “On the Origin of Species” Darwin speculated on possible means by which organisms colonized islands and evolved into new species (e.g., Galapagos finches)

38. Species-Area Relationship and Size

39. Isolation and Species Area

40. Species Isolation

41. Species Isolation

42. Species Turnover

43. Species Turnover

44. Island Size Richness = island size and distance from mainland • Small islands • Less habitat • Smaller populations • Higher rates of extinction (intra,inter-specific competition)

45. Island Distance Richness = island size and distance from mainland • Distant islands • Lower rates of colonization • However, this does depend on dispersal mechanism of the species!

46. Dispersal vs. Vicariance Hypotheses Dispersal Hypothesis: Species originated in one area and dispersed to other areas. Vicariance Hypothesis: Areas were formerly contiguous, and were occupied by a common ancestor. Speciation occurred once barriers arose.

47. “Theories, like islands, are often reached by stepping stones…” MacArthur and Wilson (1967)

48. Theory of Island Biogeography MacArthur and Wilson (1963): The number of species of a given taxon that become established on an island represents a dynamic equilibrium controlled by the rate of immigration of new species and the rate of extinction of previously established species. Image Credit: http://www.sscnet.ucla.edu/anthro/faculty/arnold/california-lab.htm

49. Formation of a New Island • Island of Krakatau • Massive volcanic eruption in 1883. • Destroyed two-thirds of island. Also, eradicated life on neighboring islands of Rakata, Sertung, and Panjang.

50. Formation of a New Island • 1930, a new island was formed from volcanic activity (Anak Krakatau). • Recolonization studies: • Nine months after 1883 eruption: first colonist of Rakata was a spider. • 1896, 11 species of ferns and 15 species of flowering plants. 16 species were dispersed by wind and another 8 by sea.