Continental vs. Oceanic Islands. Island Biogeography. Islands Continental/Oceanic. Problems/ Issues Access/Isolation Habitat Hazards

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1 Dr. Barbara Holzman Island Biogeography Islands Continental/Oceanic Problems/ Issues Access/Isolation Habitat Hazards Theory of Island Biogeography MacArthur and Wilson Problems w/ theory Natural Reserve Planning Continental vs. Oceanic Islands Continental islands Continental islands are bodies of land that are connected by the continental shelf to a continent. That is, these islands are part of an adjacent continent and are located on the continental shelf of that continent. Ex. Greenland, Barbados, Trinidad, Sicily, Sumatra, New Guinea, Tasmania. 1

2 Oceanic Islands islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands. Volcanic islands Volcanic islands are built by volcanoes, not geologically part of any continent. One type of volcanic island is found in a volcanic island arc. These islands arise from volcanoes where the subduction of one plate under another is occurring. Ex. Mariana Islands, Aleutian Islands, Tonga, etc. Another type of volcanic island occurs where an oceanic rift reaches the surface. Ex. Iceland. The last type of volcanic island are those formed over volcanic hotspots. A hot spot is more or less stationary relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Ex. Hawaiian Islands, Concepts/Issues 1) Nature of the island biota How does it differ from the source area(s)? What is the nature of the immigrants that allowed them to reach and colonize the island? 2

3 2) Identify and quantify the factors that control: - Rate at which new species reach an island - Rate at which species become extinct on an island - Number of species an island can support 3) Process of evolutionary change by which an island becomes an integrated ecosystem - Each organism adapted to physical and biological aspects of its life on the island - Occupation of niches Islands and Colonization Factors: Dispersal abilities of immigrants Galapagos Islands: 60% by bird, 30% by wind, 9% drifted by sea Diversity of habitats: less than 9 hectares = BEACH/ latitude, elevation, etc. Isolation -- How far from source? How rich is source? Hazards Hurricanes, volcanoes, humans Ability to adapt gene pool founder effect small population w/ little genetic variability 3

4 Number of Species and Area (reptiles/amphibians) Island Area and Diversity (flora) Island Area and Diversity 4

5 Founder Effect Founder effect and bottlenecks Tiburon Island, Mexico Elephant seals Q. Victoria Hemophilia Amish (extra digit) 5

6 Evolution Unchecked Gigantism: Giant tortoise, Elephant bird, Komodo dragon, Dwarfism: Mouse lemur, pygmy mammoth, Madagascar kingfisher Channel Islands Fox weighs approximately 1.8 kilograms smallest fox species in the United States predators: golden eagles, humans Urocyon littoralis Loss of flight 6

7 Relics Published in 1967 Theory of Island Biogeography Number of species on an island depends on a number of factors: area (topography assumed) diversity of habitat accessibility to colonists richness of source I.B. add equilibrium between rate of colonization by new species and extinction of existing species 7

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9 Equilibrium predicted S=CA Z S = number of species A= area C= Modes of dispersal Rates of immigration and extinction History of Rakata higher plant flora since

10 Effect of Distance From the Mainland: Near Islands have a higher rate of colonization Near Islands have a higher equilibrium number of species Effect of Island Size: Large Islands have a higher equilibrium number of species 10

11 Problems with the IB Theory Its applicability to all organisms is in question Simply looking at physical characteristics is limited (i.e. area/isolation) Equilibrium can only be maintained in a constant environment (not with climatic disturbances/ envir. changes/ humans) Quantitative attempt simplifies process Where Can We Find "Islands"? Oceanic Islands Arise from volcanic activity; Galapagos and Hawaii Continental Islands Islands that were once contiguous with the mainland; Aleutians/Channel Islands Agricultural Fields Caves Fragmented Forests Mountaintops Hosts (Parasites see hosts as islands) Ponds/ Streams Cities (fragmented landscapes) Application of Island Biogeography The Theory of Island Biogeography has been used in the creation of nature reserves, designing habitat and determining the number of species a habitat can viably carry. Although there are many shortcomings of the quantitative nature of the theory, some of this work has been helpful. Nature Reserves Design of nature reserves can lead to problems How big is big enough? SLOSS 11

12 SLOSS: Single large or several small??? Single large Several small Connectivity Application of Island Biogeography To "Habitat Islands" Habitat diversity confounds affects of area "Edge Effect" on habitat islands Degree of Isolation in habitat islands may be difficult to assess Corridors Roadless Areas between Yellowstone and Grizzly Park 12

13 Why Do We Care About Island Biogeography? "Insularity is a universal feature of Biogeography." - (MacArthur and Wilson ) Applicability of Island Biogeography Models to other "Islands" Island Biogeography and evolution can lead to endemic species Conservation Biology Fragmented Landscape High number of Island Endemics 34% of US listed species are from Hawaiian Islands or Puerto Rico Island Biogeography Islands Continental/Oceanic Problems/ Issues Access/Isolation Habitat Hazards Theory of Island Biogeography MacArthur and Wilson Problems w/ theory Natural Reserve Planning Assignment 13