Island Biogeography 1

Transcription

1 Island Biogeography 1

2 Island Biogeography 2

3 Island Biogeography Islands of subalpine coniferous forest (black areas) in the American Southwest. Contour lines are the lower edge of montane conifer forest. The Rocky Mountain boreal forest extends northward in Colorado (from Frey et al. 2007). 3

4 Island Biogeography Why study islands? Characterized by isolakon, a principal factor driving evolukonary change. Smaller, perhaps simpler, ecosystems that are usually more tractable in terms of ecological and evolukonary processes operakng within species and communikes. 4

5 Island Biogeography Island biogeography has generally centred on three major approaches: 1. Describe diversity and composikon of island biotas and how they differ from conknental flora and fauna, and the nature of adaptakons that influence dispersal to and colonizakon of islands 2. IdenKfy and quankfy factors that influence rate of dispersal to islands, rates of exknckon on islands, and the numbers and kinds of species islands can support 3. Understand evolukon of communikes in novel environments following colonizakon 5

6 FoundaKons of Island Biogeography The species-area rela;onship 30 S 25 S = ca z one of community ecology s few universal regularikes - Thomas Schoener 1976 Species-area relakonship: S = ca z S = number of species (or richness) A = habitat or island area z = fi]ed parameter (represents slope of the species - area relakonship when plo]ed on log-log scale) c = fi]ed parameter (constant), but can vary substankally across islands or taxa Number of Species (S) A S 30.0 log(s) = log(c) + z[log(a)] A Area (A) 6

7 FoundaKons of Island Biogeography The species-area rela;onship Diversity of conifer and flowering plant genera and endemics in the Pacific islands. Number of genera Island area (km 2 ) More isolated islands are shown as triangles Other islands (circles) show a pa]ern very close to the regression, indicakng high correlakon. 7

8 FoundaKons of Island Biogeography The species-area rela;onship Number of Species Area (hectares) Species-area relakonship for bu]erflies on islands off the BriKsh Isles. A marginally significant 8 relakonship with substankal sca]er (from Dennis & Shreeve 1997)

9 FoundaKons of Island Biogeography The species-area rela;onship Number of resident species (log scale) Birds S = 2.53 A Mammal and Bird Diversity in the Great Basin Mountains Small Mammals S = 1.19 A Area above 2300 m elevakon (km 2 ) (log scale) (from Lomolino et al. 2010, ager Brown 1978) 9

10 FoundaKons of Island Biogeography The species-area rela;onship Number of Species Area (Km 2 ) Species-area relakonship for freshwater fish from North American lakes (triangles) and African lakes (circles). African lakes are much older (>1 million years) than North American lakes (post-glacial; < 10,000 years ago) and have a steeper slope (z) (from Barbour and Brown 1974) 10

11 FoundaKons of Island Biogeography The species-area rela;onship Number of Species Area (Km 2 ) African lakes are much older (>1 million years) than North American lakes (post-glacial; < 10,000 years ago) and have a steeper slope (z) (from Barbour and Brown 1974) The older African lakes have been a center for speciakon parkcularly in the long term historical diversificakon of African Cichlids 11

12 FoundaKons of Island Biogeography The species-area rela;onship ExplanaKons: Larger areas hold more individuals, random sampling of more individuals should result in more species on larger islands Since larger areas hold more individuals, and exknckon is less likely in large populakons, there will be less exknckon on larger islands Target effect: larger islands have a larger shoreline, which leads to higher immigrakon rates (higher chance of intercepkng dispersing individuals) Higher geographic/habitat diversity on larger islands (e.g., elevakon ranges, topographic complexity) Higher likelihood of abiokc disturbance on smaller islands, leading to higher exknckon rates More evolukonary diversificakon on larger islands (more opportunity for within-island separakon of populakons and allopatry) 12

13 FoundaKons of Island Biogeography The species-area rela;onship Sampling larger areas of conknuous habitat Log (Species Richness) OR Log (Area) Small isolated islands have fewer species than similarly sized areas on a conknent. PopulaKons are less likely to be rescued on islands - higher probability of exknckon Sampling islands independently 13

14 FoundaKons of Island Biogeography The species-area rela;onship Number of Species in EnKre Insular Fauna Isolated islands New Guinea Species-area relakonship for pomerine ants of Moluccan and Melanesian islands Insular faunas (#1-24) = samples from isolated islands New Guinea (#25) = sample areas of different sizes in a single landmass Mainland tropical Asia (#26) Area of Island (Miles 2 ) Figure from Wilson 1961, black line added to emphasize slope across insular faunas 14

15 FoundaKons of Island Biogeography The species-isola;on rela;onship Assume that decline in richness results from decline in dispersal with increasing isolakon 30 S S = k 1 e -k 2(I2) Species-isolaKon relakonship: S = k 1 e -k 2(I2) S = number of species (or richness) I = isolakon k 1, k 2 = fi]ed constants Number of Species (S) I S log(s) = k 1 e -k 2(I2) IsolaKon (I) 15 I

16 FoundaKons of Island Biogeography The species-isola;on rela;onship Species-isolaKon relakonship for bu]erflies on islands off the BriKsh Isles. A significant relakonship with substankal sca]er (Dennis & Shreeve 1997) 16

17 FoundaKons of Island Biogeography The species-isola;on rela;onship Sierras Pampeanas, ArgenKna - high elevakon grassland habitats in mountains isolated from the main Andes Figure shows number of high Andean bird species on each mountain island (black) plo]ed against distance to the main Andes (gray) in Central-Western ArgenKna (from Nores 1995) 17

18 FoundaKons of Island Biogeography The species-isola;on rela;onship ExplanaKons: Low immigrakon rates prevent far islands from a]aining equilibrium. Low immigrakon rates lead to a lower number of species at equilibrium. Lower diversity of habitats on isolated islands. Rescue effect: populakons on near islands are less likely to go exknct due to immigrakon from the mainland. 18

19 FoundaKons of Island Biogeography Routes of dispersal in and out of Melanesia followed by the ponerine ants (from Wilson 1959) 19

20 FoundaKons of Island Biogeography E.O. Wilson s Taxon Cycle for Melaniesian ant fauna (Species turnover in ;me) 1) AdaptaKon to marginal habitat on mainland. 2) Cross water gap and establish in marginal habitat on an island. 3) Go exknct, or 4) colonize inner rain forest. 5) Diversify in structured forest habitat. 6) Adapt to marginal habitat, conknue cycle on further islands (Wilson 1959) 20

21 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) Proposed by E.O. Wilson and R.H. MacArthur (1963, 1967) to explain three characteriskcs of island biotas: 1. Species-area relakonship 2. Species-isolaKon relakonship 3. Species turnover (T) Rate T 0 Ŝ P # Species 21

22 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) Proposed by E.O. Wilson and R.H. MacArthur (1963, 1967) to explain three characteriskcs of island biotas: 1. Species-area relakonship 2. Species-isolaKon relakonship 3. Species turnover (T) Rate T S T L Ŝ S 0 P Ŝ L # Species 22

23 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) Proposed by E.O. Wilson and R.H. MacArthur (1963, 1967) to explain three characteriskcs of island biotas: 1. Species-area relakonship 2. Species-isolaKon relakonship 3. Species turnover (T) Rate T N T F 0 Ŝ F Ŝ N P # Species 23

24 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) Two assumpkons of the ETIB: 1. Rate of immigrakon of new species decreases with increasing species on the island. Reaches zero when all species in the source area (P) are on the island. 2. Rate of exknckon increases with increasing number of species on the island. Rate T 0 Ŝ P # Species 24

25 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) As more species arrive, the chance of having deleterious (exknckon-inducing) interackons increases. VariaKon in exknckon/immigrakon probabilikes between species: - Best dispersers arrive quickly, poorer dispersers arrive later and later. - When many species are present, more exknckon-prone species are lost first. Rate T 0 Ŝ P # Species 25

26 The Theory of Island Biogeography the Equilibrium Theory of Island Biogeography (ETIB) Equilibrium predickon: curve # Species Ŝ Time 26

27 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribukons and diversity (e.g., dispersal). 27

28 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribukons and diversity (e.g., dispersal). 2. ConservaKon biology. Relevant to the design of wildlife reserves. Figure depicts different designs for reserves based on a given available area. In each case, the design on the leg is preferred. Scenario (A) is a depickon of the "SLOSS debate is it be]er to have a "single large or several small reserves? Which scenarios can be understood based on the principles of the ETIB? 28

29 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribukons and diversity (e.g., dispersal). 2. ConservaKon biology. 3. The ETIB made testable predickons. e.g., Equilibrium species richness (reached via a convex colonizakon curve). S LN > S LF S SN > S SF T SN > T LN T SF > T LF 29