II. Island Biogeography

Transcription

1 II. Island Biogeography Start March 18, 2013

2 III. Island Biogeography Biogeography: The study of the distribution of organisms in space and time.

3 Biogeography looks at four fundamental processes: 1. Dispersal: Movement of organism(s) from a point of origin (= location of source, or ancestral, population) to a new location. 2. Colonization: Organism reaches new location, survives, reproduces, and establishes new population. 3. Extinction: Species is eliminated from a particular area (i.e., no more reproducing individuals present); species may survive elsewhere, and may re-colonize area where it went extinct. 4. Evolution: Surviving population in a particular area undergoes change(s) in frequency of gene alleles; may result in altered phenotype, and, given sufficient time, possibly the formation of new species (= speciation).

4 Island In very general terms, an island is an area of suitable habitat surrounded by an expanse of unsuitable habitat.

5 An island can be a land mass surrounded by water (stream, lake or ocean); coral reef surrounded by expanse of water without reefs; Isolated terrestrial habitat amid a larger land mass, such as a - mountain top; - forest remnant surrounded by cleared land; - water-filled tree hole in forest

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

7 Early naturalists (e.g., 16 th -18 th centuries) exploring isolated islands in remote regions noted new types of plants and animals; often distinctive for each island or island group. For several centuries, scientific focus was on cataloging the diversity of island organisms.

8 1835 Voyage of the H.M.S. Beagle Charles Darwin observed dozens of animal species unique to the Galapagos islands off Ecuador.

9 including 13 species of Galapagos Finches What Darwin Saw Video

10 Publication of On the Origin of Species Darwin speculated on possible means by which organisms à colonized islands, and à evolved into new species (e.g., Galapagos finches) On the Origin of Species (can be downloaded in various formats)

11 Darwin hypothesized that the 13 species of finches may have evolved from a single ancestral species from the mainland.

12 Eruption of Krakatau (Krakatoa), a volcanic island in Indonesia (Aug ). Subject of first substantive scientific study of a volcano.

13 Krakatau is a volcanic island in the Sunda Strait, between Java and Sumatra

14 Aug. 27, 1883, am: A massive eruption blew away half of Krakatau; remaining portion (Rakata volcano cone) plus three neighboring islands left covered with meters of pumice and ash (= a sterile landscape?). Verlaten Island Anak Krakatau (volcano) Lang Island Rakata (volcano) Krakatau Island

15 Rakata and adjacent islands formed a laboratory for study of island colonization and tropical succession: May first researchers reach the islands; find only a spider in a crevice on the south side of Rakata." October grass shoots growing on Rakata."

16 Botanists, and later zoologists, begin monitoring colonization of Rakata: nine species of flowering plants present on beaches; species of flowing plants present; development of coastal forest provided seeds and fruits for colonizing bats and birds; ferns (with spores that can be dispersed by wind) were first colonizers away from the coast;

17 species of flowing plants and 13 species of birds present; species of birds present; but, at least 5 bird species present in early 20 th century were now extinct on Rakata;

18 ~ 50% of inland plant species on Rakata in 1897 have become extinct; however, since 1934, 16 additional families of higher plants have colonized.

19 colonization by new plant species was initially high, then dropped as available space became occupied by pioneer species; immigration rate then increased as developing forests created new habitat (= potential new ecological niches); as forests replaced grasslands, insects and birds dependent on grasses became extinct on island.

20 Biogeographical lessons from Krakatau: Composition of plant and animal communities at any given time reflects colonization local extinction succession disturbance

21 Recent studies* have re-evaluated ecological succession and extinctions on Rakata and adjacent islands since 1883: Most plant extinctions have been species introduced by people, and rare or ephemeral species; Few naturally colonizing and established species have become extinct. * Whittaker, R.J. et al GeoJournal 28.2: Whittaker, R.J. et al. 2000, J. Biogeograpy 27(5):

22 Anak Krakatau is still active: Video of Anak Krakatau eruption (music by Jimmy Buffet):

23 More recently, island biogeographers have begun focusing on patterns and mechanisms of evolution of island flora and fauna. Dr. Koning will discuss this stay tuned

24 Types of Islands

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

26 Examples of Continental Islands 1. Greenland 2. New Guinea 3. British Isles 4. California Channel Islands 5. Block Island, Nantucket, Martha s Vineyard

27 This slide not shown in class Greenland World s largest island; part of North American Continent Nunavut Territory Greenland Iceland Quebec North American Continental Shelf

28 This slide not shown in class New Guinea World s second largest island; Part of Sahul Continent with Australia and Tasmania, et al. New Guinea Sahul Continental Shelf Australia Torres Strait Bass Strait Tasmania

29 This slide not shown in class 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

30 This slide not shown in class As Ice Age ended, rising sea level flooded Doggerland* and formed English Channel. England North Sea Dogger Bank, an upland area of Doggerland, outlined in red (15-36 m deep). France * From the Dutch dogge = cod-fishing boat

31 This slide not shown in class California Channel Islands: Group of eight islands off the California coast; during last ice age, some were connected to mainland by land bridge.

32 Continental Islands: Two Special Cases 1. Eroded limestone islands of the Bahamas and Bermuda: Rising sea level and wind eroded parts of San Salvador and Bermuda, leaving many small, erosion-resistant islands (= cays* in the Bahamas). * Pronounced keys

33 Cays on the horizon (arrow) were once part of San Salvador; still part of San Salvador continent (San Salvador Bank).

34 San Salvador s offshore cays

35 Several of these cays have relict populations of an endangered lizard (San Salvador Rock Iguana, Cyclura rileyi) that is now rare on San Salvador itself.

36 Bermuda is a collection of ~180 limestone islands, many formed by erosion of a larger aeolian limestone mass ( continent ).

37 Continental Islands: Two Special Cases 1. Eroded limestone islands of the Bahamas and Bermuda 2. Barro Colorado Island, Panama Canal

38 Barro Colorado Island (BCI): A 1500 hectare remnant of lowland moist forest in the middle of the Panama Canal; managed by the Smithsonian Institute as a tropical research site.

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

40 Examples of Oceanic Islands Volcanic Origin Iceland Aleutians Hawaiian Islands Antilles Bermuda Western Pacific atolls Non-Volcanic Origin Bahamas Belize atolls and Barrier Reef cays Great Barrier Reef Islands New Zealand Madagascar

41 Dispersal to Oceanic Islands Terminology Disseminule: Life stage or form of organism that can be disseminated, i.e., dispersed to a new location, such as an island.

42 Disseminules include: Spores (fungi, ferns, mosses, bacteria, protists) Plant seeds, seedlings, fruits, branches Intact plant (or seeds) in mass of soil Animal fertilized eggs, larvae, juveniles, adults

43 Dispersal to Oceanic Islands Terminology Disseminule: Life stage or form of organism that can be disseminated, i.e., dispersed to a new location, such as an island. Propagule: Colonizing unit = minimum number of individuals (disseminules) capable of colonizing an island.

44 Dispersal to Oceanic Islands Successful colonization may require more than the minimum number of propagules; that is Propagules and their offspring must survive and thrive to populate an island; Successful colonization may require multiple attempts.

45 Propagules include: Spores (bacteria, fungi, ferns, mosses, protists) Plant seeds, seedlings, fruits, branches or intact plant bearing fruit - must be capable of producing a new individual. Animal fertilized eggs, inseminated female, or group of animals including at least one male and one female.

46 Dispersal to Oceanic Islands More Terminology: Sweepstakes Route: Long distance dispersal depends on random events. Animals and plants don t intentionally seek out islands to colonize; Only a tiny fraction of source population will be dispersed; Many (probably most) disseminules will not survive the journey to the island.

47 Dispersal to Oceanic Islands Terminology (continued) Sweepstakes Route: Long distance dispersal depends on random events. Island-Hopping: Organisms may disperse over long distances by moving from one island to another.

48 Long-distance dispersal by island hopping: Source Pop. The thickness of the arrows is proportional to the number of successful dispersal events.

49 Agents / Mechanisms of Dispersal Organisms arrive at oceanic islands by air or by sea, naturally or by human intervention.

50 Aerial Transport Wind: Very small, light disseminules à carried aloft by winds à may be dispersed long distances. Examples: Microbes in water droplets (including coral pathogens!) Spores, seeds with hairy filaments Small insects and spiders (aided by silk parachute )

51 Wind: Aerial Transport Insects, birds, bats may fly directly to island, or be blown off course by strong winds à land on an oceanic island Winds generate ocean currents à may transport organisms by sea.

52 Ocean Transport Drifting: -marine plankton (algal gametes; seagrass seeds; coral planulae; other invertebrate larvae; fish larvae) -floating plant seeds or fruits (e.g., morning glory seed; coconuts) -floating lizard eggs (allowed colonization of some Bahamian islands after hurricanes)

53 Rafting: Ocean Transport Logs or large chunks of soil with rooted plants, and possibly animals, may wash away from land during storms drift in ocean for days or weeks, eventually arrive at an island.

54 Examples of Dispersal by Rafting 1969 floating island of soil and vegetation (~13 meters across, with dozens of trees up to 12 meter tall) drifted 60 km away from Cuba in 11 days; could have reached an island?

55 Examples of Dispersal by Rafting 1995 Following two hurricanes, mass of logs and uprooted trees (some > 10 meters long) came ashore on Caribbean island of Anguilla. Logs carried at least 15 green iguanas (males and females) from Guadeloupe, 250 km away. Within 2 years, green iguanas were established on Anguilla.

56 Some Small Mammals May Have Reached Madagascar by Rafting Source: John Kricher, A Neotropical Companian (2 nd ed.), Princeton Univ. Press, 1999

57 Marine Organisms May Be Transported by Biotic Rafts Tree Trunk Macroalgae Thiel and Gutow (2005) Oceanogr. Mar. Biol. 42:

58 Some Marine Organisms Transported by Abiotic Rafts Volcanic pumice = Floats; colonized by microalgae and invertebrates Thiel and Gutow (2005) Oceanogr. Mar. Biol. 42:

59 2011 Tohuku Earthquake Tsunami: Dispersal by Rafting on Man-made Debris Marine organisms transported to North American shores; Not clear if any terrestrial organisms have colonized islands

60 Ocean Transport Swimming: Fish and other aquatic animals may be able to swim long distances, esp. if aided by ocean currents à Islands (or coastal areas) - Crocodiles are thought to have reached N. American by swimming across the Atlantic (> 2800 km) 7 mya Some terrestrial animals (e.g.,elephants) may be able to swim short distances (e.g., a few km) à reach islands.

61 Open, or deep, water may be a barrier to dispersal Wallace s Line was originally developed by Alfred Russel Wallace based on the distribution of terrestrial mammals and birds: West of Line: Species from tropical Asia; East of Line: Species from Australia and New Guinea Source: John Kricher, A Neotropical Companian (2 nd ed.), Princeton Univ. Press, 1999

62 PLATE 1-1 (a) CHARLES DARWIN (b) ALFRED RUSSEL WALLACE Source: John Kricher, A Neotropical Companian (2 nd ed.), Princeton Univ. Press, 1999

63 Dispersal Mechanisms Continued

64 Global Wind Patterns Result of differential: Heating (0, 60 Lat.) à warm air rises à low pressure Cooling (30, 90 Lat.) à cool air sinks à high pressure Pressure differences à Winds Rotation of earth (Coriolis Effect) à alters wind patterns High Pressure Low Pressure

65 Ocean Surface Currents: Clockwise in N. hemisphere, Counterclockwise in S. hemisphere; Due to differential heating (0-5 Lat.) and cooling (60 Lat.), global wind patterns, Coriolis Effect

66 Prevailing winds and ocean currents determine major routes of dispersal by air and sea Dispersal routes can be altered by Seasonal changes in prevailing winds or currents (e.g., winter vs summer) Local patterns of wind and currents (e.g., around land masses)

67 Major Caribbean Currents

68 Major Caribbean Currents Florida Current Florida Current Flow: Summer Late Fall-Winter

69 Major Caribbean Currents Florida Current Antilles Current Antilles Current Flow: Summer Winter

70 Major Caribbean Currents Florida Current Antilles Current Caribbean Current Caribbean Current Flow: Summer Winter

71 Another Dispersal Mechanism: Hitchhiking: One disseminule transports another disseminule Examples: Small, sticky seeds or fruits, or small invertebrates, carried by birds (or bats) - attached to feathers (or fur) - in mud on their feet - seeds, or invertebrate eggs, may be carried in a bird s gut Parasites carried in, or on, their host

72 Case Study: Plant Dispersal to the Galapagos Islands

73 Case Study: Plant Dispersal to the Galapagos Islands Galapagos flora came from S. America via an estimated 378 colonization events: 60% via birds (hitchhiking) 31% via wind 9% via drifting in ocean currents Refer to article, Chance Dispersal, by S. Carlquist

74 Protoadaptations for Dispersal Anatomical and/or physiological traits that enable organism to be dispersed (e.g., to an oceanic island). Examples: Very small size may aid wind dispersal or hitchhiking Larger size may aid long-distance swimming or drifting Resistance to (or tolerance of) desiccation (due to salt water; lack of freshwater) prolonged exposure to very warm, or very cold, ocean water Prolonged exposure to intense sunlight Sufficient energy reserves (and/or low metabolic rate) for prolonged ocean journey

75 Protoadaptations for Dispersal Oceanic islands usually lack native terrestrial mammals and amphibians due to stresses associated with ocean travel. Native: Organism that arrived by natural means - no human intervention. Reptiles, birds, bats, insects, and molluscs are common native inhabitants of oceanic islands. Why?

76 Colonization of Oceanic Islands Colonization of island usually requires different traits than the ones that permitted dispersal to the island (e.g., rapid population growth rate). Some (probably most) organisms reaching an island will not be successful at colonizing it.

77 Pioneer Plant Species Effective colonizers of a newly-formed island May alter the environment in such a way as to facilitate subsequent colonization by other organisms The result is ecological succession: A change in the plant and animal communities over time.

78 Fate of Colonizing Organisms Refer to Handout