Island biogeography What controls the number of plant and animal species on this island? Does size matter? Isolation? Habitat variation? Environmental history? Island in the Bay of Fundy
Species - area relationships Johann Reinhold Forster (1729-98) served as a botanist with Captain Cook. After exploring the islands of the southern Pacific he observed: “Islands only produce a greater or less number of species as their circumference is more or less extensive”. Small islands harbour fewer species. The Forsters’ (father & son) collecting specimens in Tahiti
Species-area relationships Arrhenius (1921) “Species and Area” Gleason (1922) “On the relation between species and area”. Ecology, 3. Gleason censused the plants in 240 1m2 plots in an aspen wood in northern Michigan. He found 27 species in total, with an average of 4 species per quadrat.
Species-area relationships Preston (1962) “The canonical distribution of commonewss and rarity”. Ecology, 43. Preston introduced the ‘Arrhenius equation’: S = cAz where S is number of species, A is plot area, and c and z are constants.
Applying the Arrhenius equation to Gleason’s data: z = slope c c = intercept
Variations in value of c e.g. insects plants e.g. mammals
Variations in the value of z real world cases (0.26- 0.33)
What do these have in common? 1 3 2 4
MacArthur and Wilson’s“Theory of Equilibrium Island Biogeography” (1967) = equilibrium species number
Galapagos plant diversity and microclimate: area is a proxy for habitat variability <300 m >500 m
Plant diversity in the south Pacific: is the variability controlled by habitat variation?
Avifaunal diversity in the south Pacific: the effects of distance from PNG
Testing the MacArthur and Wilson theory A. Natural experiments - Krakatau/Rakata
Bird and mammaldiversity on the remnant islands of Krakatau vs. the biodiversity of neighbouring islands Rakata remnants neighbours Rakata
Rakata bird colonization McArthur & Wilson’s equilibrium predictions from nearby islands: 30 bird species 40 yrs to equilibrium; turnover: 1 species/yr. ? Survey dates
Testing the theory:artificial experimentsI: defaunation and colonization Small mangrove islands in the Florida keys
Testing the theory:artificial experimentsII: colonization of artificial substrates Fouling panels
Extending the theory “Insularity is moreover a universal feature of biogeography. Many of the principles graphically displayed in the Galapagos Islands and other remote archipelagos apply in lesser or greater degree to all natural habitats” e.g. mountain-top alpine areas; islands of trees at the arctic treeline, urban parks, lakes, bogs, desert oases, clearcuts, islands of fragmented habitat, and even individual rocks, plants, etc.
Mountain islands • Distribution of alpine tundra ecosystems in BC; an archipelago formed by hundreds of ± discrete islands separated by forest and prairie in the neighbouring valleys.
Vacant urban lots Vacant urban lot, Philadelphia Crowe, L. M. 1979.Lots of weeds: insular phytogeography of vacant urban lots. J. Biogeography 6: 169-181.
Fragmented habitat islands 1830 1882 “the breakup of a large landmass into smaller units would necessarily lead to the extinction or local extermination of one or more species and the differential preservation of others” Alphonse de Candolle, 1855 True for all habitats; e.g. Wisconsin woodlands 1902 1950