Island Biogeography 1

Transcription

1 Island Biogeography 1

2 Island Biogeography 2

3 Island Biogeography Islands of Petran subalpine coniferous forest (black areas) in the American Southwest. Contour lines are the lower edge of Petran 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 isolalon, a principal factor driving evolulonary change. Smaller, perhaps simpler, ecosystems that are usually more tractable in terms of ecological and evolulonary processes operalng within species and communiles. 4

5 Island Biogeography Island biogeography has generally centred on three major approaches: 1. Describe diversity and composilon of island biotas and how they differ from conlnental flora and fauna, and the nature of adaptalons that influence dispersal to and colonizalon of islands 2. IdenLfy and quanlfy factors that influence rate of dispersal to islands, rates of exlnclon on islands, and the numbers and kinds of species islands can support 3. Understand evolulon of communiles in novel environments following colonizalon 5

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

7 FoundaLons of Island Biogeography The species- area rela;onship Diversity of conifer and flowering plant genera in the Pacific islands. Number of genera Island area (km 2 ) 7

8 FoundaLons of Island Biogeography The species- area rela;onship Number of Species Area (hectares) Species- area relalonship (note log scale) for bu^erflies on islands off the BriLsh Isles. A marginally significant relalonship with substanlal sca^er (from Dennis & Shreeve 1997) 8

9 FoundaLons 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 elevalon (km 2 ) (log scale) (from Lomolino et al. 2010, afer Brown 1978) 9

10 FoundaLons of Island Biogeography The species- area rela;onship Number of Species Area (Km 2 ) Species- area relalonship 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 higher slope (z) (from Barbour and Brown 1974) 10

11 FoundaLons of Island Biogeography The species- area rela;onship ExplanaLons: Larger areas hold more individuals, random sampling gives more species on larger islands. Since larger areas hold more individuals, and exlnclon is less likely in large populalons, there will be less exlnclon on larger islands. Target effect: larger islands have a larger shoreline, which leads to higher immigralon rates (higher chance of interceplng dispersing individuals). Higher geographic/habitat diversity on larger islands (e.g., elevalon, precipitalon). Higher likelihood of abiolc disturbance on smaller islands, giving a higher exlnclon rate. More evolulonary diversificalon on larger islands (more opportunity for within- island allopatry). 11

12 FoundaLons of Island Biogeography The species- area rela;onship Sampling larger areas of conlnuous habitat Log(Species Richness) OR Log(Area) Sampling islands independently 12

13 FoundaLons of Island Biogeography The species- area rela;onship Number of Species in EnLre Insular Fauna Isolated islands New Guinea Species- area relalonship 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 1 from Wilson 1961, black line added to emphasize Insular faunas 13

14 FoundaLons of Island Biogeography The species- isola;on rela;onship S 30 S = k 1 e - k 2(I2) Assume that decline in richness results from decline in dispersal with isolalon Best to control for island area Species- isolalon relalonship: S = = k 1 e - k 2(I2) S = number of species (or richness) I = isolalon k 1, k 2 = fi^ed constants Number of Species (S) I S log(s) = k 1 e - k 2(I2) IsolaLon (I) 14 I

15 FoundaLons of Island Biogeography The species- isola;on rela;onship Species- isolalon relalonship (note scale and units on both axes) for bu^erflies on islands off the BriLsh Isles. A significant relalonship with substanlal sca^er (Dennis & Shreeve 1997) 15

16 FoundaLons of Island Biogeography The species- isola;on rela;onship Sierras Pampeanas, ArgenLna Number of high Andean bird species on each mountain island (black) plo^ed against distance to the main Andes (gray) in Central- Western ArgenLna Figure 3 from Nores

17 FoundaLons of Island Biogeography The species- isola;on rela;onship ExplanaLons: Low immigralon rates prevent far islands from a^aining equilibrium. Low immigralon rates lead to a lower number of species at equilibrium. Lower diversity of habitats on isolated islands. Rescue effect: populalons on near islands are less likely to go exlnct due to immigralon from the mainland. 17

18 FoundaLons of Island Biogeography Routes of dispersal in and out of Melanesia followed by the ponerine ants (from Wilson 1959) 18

19 FoundaLons of Island Biogeography E.O. Wilson s Taxon Cycle for Melaniesian ant fauna (Species turnover in ;me) 1) AdaptaLon to marginal habitat on mainland. 2) Cross water gap and establish in marginal habitat on an island. 3) Go exlnct, or 4) colonize inner rain forest. 5) Diversify in structured forest habitat. 6) Adapt to marginal habitat, conlnue cycle on further islands (Wilson 1959) 19

20 The Theory of Island Biogeography a.k.a., the Equilibrium Theory of Island Biogeography (ETIB) Proposed by E.O. Wilson and R.H. MacArthur (1963, 1967) to explain three characterislcs of island biotas: 1. Species- area relalonship 2. Species- isolalon relalonship 3. Species turnover (T) Rate T 0 Ŝ P # Species 20

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

22 The Theory of Island Biogeography a.k.a., the Equilibrium Theory of Island Biogeography (ETIB) Proposed by E.O. Wilson and R.H. MacArthur (1963, 1967) to explain three characterislcs of island biotas: 1. Species- area relalonship 2. Species- isolalon relalonship 3. Species turnover (T) Rate T N T F 0 Ŝ F Ŝ N P # Species 22

23 The Theory of Island Biogeography a.k.a., the Equilibrium Theory of Island Biogeography (ETIB) Two assumplons of the ETIB: 1. Rate of immigralon 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 exlnclon increases with increasing number of species on the island. Rate T 0 Ŝ P # Species 23

24 The Theory of Island Biogeography a.k.a., the Equilibrium Theory of Island Biogeography (ETIB) Why are the lines concave? As more species arrive, the chance of having deleterious (exlnclon- inducing) interaclons increases. VariaLon in exlnclon/immigralon probabililes between species: - Best dispersers arrive quickly, poorer and poorer dispersers arrive later and later. - When many species are present, the more exlnclon- prone species are lost first. Rate T 0 Ŝ P # Species 24

25 The Theory of Island Biogeography a.k.a., the Equilibrium Theory of Island Biogeography (ETIB) Equilibrium prediclon: curve # Species Ŝ Time 25

26 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribulons and diversity (e.g., dispersal). 26

27 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribulons and diversity (e.g., dispersal). 2. ConservaLon 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 lef is the preferred one. Which scenarios can be understood based on the principles of the ETIB? Scenario (A) is a depiclon of the "SLOSS debate is a "single large or several small reserves be^er? 27

28 Significance of the ETIB 1. Reinvigorated interest in role of contemporary processes to explain species distribulons and diversity (e.g., dispersal). 2. ConservaLon biology. 3. The ETIB made testable prediclons. e.g., Equilibrium species richness (reached via a convex colonizalon curve). S LN > S LF S SN > S SF T SN > T LN T SF > T LF 28