Galapagos Islands 2,700 endemic species! WHY?

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1 Galapagos Islands

2 Galapagos Islands 2,700 endemic species! WHY?

3 Denali, Alaska Low species diversity. Why?

4 Patterns of Species Diversity Latitudinal Global pattern drivers? Islands (but also mtn. tops, lakes, etc.) Patterns with island size Species-Area curves Patterns with island size & distance Theory of Island Biogeography (Deb s lecture) Predicting species diversity as a function of colonization and extinction rates Metapopulations* Modern extension of island biogeography *not related to diversity

5 Global patterns of species diversity (land plants)

6 Latitudinal diversity gradient: Birds from the new world Gaston & Blackburn (2000) Pattern and Processes in Macroecology.

7 BUT...other features also influence diversity Evolutionary history, habitat heterogenity, species interactions, etc.

8 Why are there latitudinal diversity gradients?! Time:! time since glaciation/major disturbance, which resets diversity! climate stability = more diversification! Area:! global land area dominated by tropics, statistical artifact? boreal 23% tundra 2% tropical 40%! Energy:! Solar input higher, more productivity could allow multiple species to coexist (more action at the base of the food web) temperate 19% subtropical 16% Rosenzweig (1992) Journal of Mammalogy

9 Some exceptions: Some taxa are adapted to life at higher latitudes (e.g. penguins and auks)! Aphids, sawflies, ichneumonids and bees: show peaks at intermediate or high latitudes.

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11 Hotspots ISLANDS AS SPECIAL HOTSPOTS OF DIVERSITY Endemic species are those found only in a single area

12 Island species richness Bigger islands have more species than small islands Species-Area curves # species Documented for diverse taxa Island area Other types of habitat also follow this pattern...island-like (mtn. tops, forest remnants, lakes, etc.)

13 Species richness increases with island AREA Log scale Log scale Rich Glor MacArthur and Wilson (1967)

14 S = c A z c is constant of spp./ area z is the slope Galapagos land plants z = 0.32 (~0.3 most islands)

15 What s z for species-area curves on continental areas? z = 0.17 (~ for land areas) North American birds

16 Species-Area relationship for N. Wisconsin Lakes

17 Island species richness If z ~0.3 on islands, and ~ on land What does that tell us about islands??

18 An extension of this idea: Island biogeography! Dynamic equilibrium theory that explains species richness of islands! Island richness determined by colonization and extinction rates (number of species thru time)! Richness increases with size (more habiats to support more species, less extinction)... decreases with isolation (less likely to be colonized)

19 Species richness decreases with isolation More isolated islands less likely to receive colonists (immigration low)

20 Extinction more likely for small populations (small islands) large small MAINLAND near Colonization more likely for closer islands far

21 Island biogeography

22 Experimental Results Simberloff & Wilson! Species richness on islands returned to levels similar to before defaunation! Closer, larger islands had more species! The precise species identity was not consistent, only the total number of species " Order of colonization and species interactions important for who composes the community! Support for dynamic equilibrium

23 And now for a big mental leap... from diversity to individual population dynamics Meta populations! Collection of subpopulations! Proportion of sites occupied determined by colonization and extinction rates at each site Rana cascadae Number of patches occupied

24 And now for a big mental leap... from diversity to individual population dynamics Meta populations! Collection of subpopulations! Proportion of sites occupied determined by colonization and extinction rates at each site! Connected by individual movement (dispersal between sites provides colonists) Rana cascadae! Individual sites may be colonized in one year and extinct the next! Individual site dynamics are variable, but overall metapopulation can be stable

25 Metapopulation dynamics brown=occupied white=empty

26 Metapopulation dynamics

27 Metapopulation dynamics

28 Metapopulation dynamics

29 Metapopulation dynamics

30 Metapopulation dynamics

31 Classic metapopulation! Subpopulations have independent dynamics and are connected by dispersal! All patches of identical quality (not realistic)

32 Classic metapopulation! Lesson 1: Unoccupied patches or disappearing subpopulations can be rescued by immigration from other patches (Rescue Effect)! Lesson 2: Unoccupied patches are necessary for metapopulation persistence! How would this theory change your recommendation for habitat protection?

33 Mainland-Island metapopulation! 1 area persists indefinitely ( mainland ) and provides colonists to other areas that go extinct! Differences in patch quality

34 Source-Sink metapopulation! In sources, r > 0! In sinks, r < 0! Sinks persist because they are resupplied with individuals from sources! Differences in patch quality

35 Deforestation, in the tropics Islands? And here Will metapopulation theory become more important with increasing fragmentation?

36 Exam #2! Write in the space provided! Think about what you want to say before you start writing! Write legibly... we will stop grading an answer if we can t read it! Read the question carefully no trick questions

37 Exam #2 Results Exam 2 Grade Distribution Mean 73% Max 94% Grade (%)