Learning objectives. 3. The most likely candidates explaining latitudinal species diversity

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1 Lectures by themes Contents of the course Macroecology 1. Introduction, 2. Patterns and processes of species diversity I 3. Patterns and processes of species diversity II 4. Species range size distributions 5. Patterns of species abundance 6. Patterns of species body sizes 7. Energy, species body size and distribution Evolutionary community ecology 8. Community phylogenetics Eco-evolutionary dynamics and co-evolution Rapid evolution Processes at the local scale - competition, apparent competition - predation, herbivory - parasites - mutualism, positive species interactions 1 Learning objectives 1. General patterns of species richness - area, latitude 2. Effects of species and extinction probability 3. The most likely candidates explaining latitudinal species diversity A. Area B. Energy/climate C. Time 4. Palaeontological patterns in latitudinal diversity gradient (LDG) The proces(es) behind the latitudinal diversity gradient At least 30 different hypotheses explaining latitudinal richness gradient have been proposed Willig et al Ann. Rev. Ecol. Syst. 34:273- Species diversity and coexistence 3 Species diversity and coexistence 3 1

2 What may explain latitudinal patterns of species diversity?? Three most likely candidates A. Area B. Energy/climate C. Time Species diversity and coexistence 4 Species diversity and coexistence 4 A. Area hypothesis Tropics has highest species richness because it has the greatest geographical area large areas include species with large range species with large range have larger population sizes species with large range are buffered against extinction species with large ranges may have high allopatric speciation rates (geographic barriers) Terborgh 1975, Rosenzweig 1995 Species diversity and coexistence 5 Species diversity and coexistence 5 Land area relative to latitude Species diversity and coexistence 6 Species diversity and coexistence 6 2

3 A test of the area hypothesis using New World birds Blackburn & Gaston Evolutionary Ecology 11:195- Relationship between area and species richness across regions (biomes) is weak - tropical areas may cause this by spilling over species to extra-tropical areas (out of the tropics-hypothesis) The number of pooled tropical and extra-tropical bird species not related to land area (r 2 = 0.34, n = 7, N.S.) Prediction: excluding tropical species should result in significant association between area and species richness among biomes Species diversity and coexistence 7 Species diversity and coexistence 7 When considering only extra-tropical species, species richness and land area are positively associated (independently of the latitude and productivity of the regions) Species diversity and coexistence 8 Species diversity and coexistence 8 Observations contradicting with area hypothesis - Extratropical biomes together comprise larger area than tropics, yet they have lower number of species Species diversity and coexistence 9 Species diversity and coexistence 9 3

4 What may explain latitudinal patterns of species diversity?? B. Energy hypothesis - The first proposed hypothesis to explain latitudinal diversity gradient (von Humboldt 1808) Higher energy availability in an area provides wider resource base, permitting more species to occur. high amount of energy translates either into one species with very high population size or several species with low population size high amount of energy probably result in higher abundance, which have lower extinction risk Species diversity and coexistence 10 Species diversity and coexistence 10 Measures of energy availability - Primary productivity - Actual evapotranspiration net atmospheric energy balance and water availability - Potential evapotranspiration net atmospheric energy balance independent of water Species diversity and coexistence 11 Patterns of species richness relative to energy availability Species diversity and coexistence 12 Species diversity and coexistence 12 4

5 Species diversity and coexistence 13 Hawkins et al Ecology 84:1608-; Ecology 84: Species diversity and coexistence 14 Species diversity and coexistence 14 Species diversity and coexistence 15 Species diversity and coexistence 15 5

6 Linear vs. hump-shaped energy- species-relationships Hump-shaped relationship - When productivity and its variance are positively correlated suggesting that productive areas cannot maintain high species richness year round Linear relationship - Productivity is stable year round (low variation) and high species richness maintained year round. Chown & Gaston Evolutionay Ecology Research 1: 365- Species diversity and coexistence 16 Species diversity and coexistence 16 Problems with energy hypothesis How energy translates into (more) species? - Association between energy and speciation, mortality and geographic dispersal Energy is associated with many other variables, such as temperature, harshness of climate, etc. Fig. Bird species richness in Britain in 10 km2 squares relative to summer temperature Species diversity and coexistence 17 Species diversity and coexistence 17 Latitudinal variation in the importance of energy and water in explaining species richness Hawkins et al Ecology 84: Species diversity and coexistence 18 Species diversity and coexistence 18 6

7 Latitudinal variation in the importance of energy and water in explaining species richness Hawkins et al Ecology 84: Species diversity and coexistence 19 Species diversity and coexistence 19 How energy can materialize into more species? Wright (1983, Oikos 41: ) proposed a link between species-area and species-energy hypotheses The More Individual Hypothesis : - species-area hyp. a special case of a general species-energy relationship - total no. of individuals on an area is proportional to the total amount of resources or product of area and resource density The More Individual Hypothesis asssumes: - area with greater food resources (energy) should support more individuals - communities with more individuals can support more species above some minimum viable size (=lower extinction rates) Preston 1962 S~ N z S= Species richness N= number of individuals Z = constant Wright s energy hypothesis (More individual hypothesis) * For areas of similar isolation Immigration rate* S small Sl arg e Number of species Low energy High energy Extinction/Speciation rate Species diversity and coexistence 21 Species diversity and coexistence 21 7

8 Correlative tests of the More Individual Hypothesis Araujo Global Ecology and Biogeography 12: 5-12 Gaston & Evans Proc. R. Soc. B 271:1649- Are human population sizes and species richness positively correlated? Are the areas with high human pop. density associated with high bird abundances greater biomass? Species diversity and coexistence 22 Species diversity and coexistence 22 A test for the More Individual Hypothesis Mönkkönen et al GEB 15: Data: - Breeding passerine bird communities in Europe and North America species number and their abundances/area unit - Species were divided to residents, short-distance migrants, and tropical migrants - AET (total, breeding season, and winter) was used as a proxy for energy availability - Energy use of communities was estimated by transforming body sizes to metabolic rates and multiplying them with density of each species Predictions: - Total density and energy use in communities is linearly related to energy availability - Species richness is a positive function of total bird density - If energy affects population densities, resident populations are expected to be related stronger to energy than migratory species Species diversity and coexistence 23 Species diversity and coexistence 23 Body mass and density N cm 0.75 sp. Body mass and energy use 0.75 E cm Pop. density Energy use Body mass Body mass 24 8

9 The data - Breeding bird survey data - Estimate about co-occurring species and their relative density - Productivity data (latitude, longitude, temperature) N 110 N 110 Results: Mönkkönen et al Characteristics of breeding bird communities in Europe North America Species diversity and coexistence 26 Species diversity and coexistence 26 Results: Mönkkönen et al The final model explained about 40% of the density and energy use - Resident density and energy use was best explained by annual AET (50-60% of variation) - For short-dictance migrants, annual AET explained only about 5% of variation Species diversity and coexistence 27 Species diversity and coexistence 27 9

10 Results: Mönkkönen et al In Europe, winter AET explained c. 25% of variation in density and energy use of tropical migrants. However, association was negative. Some other factor more important than productivity Species diversity and coexistence 28 Species diversity and coexistence 28 Results: Mönkkönen et al Number of species is a positive function of density and energy use Species diversity and coexistence 29 Species diversity and coexistence 29 Conclusions - Results are consistent with species-energy theory and with More Individual Hypothesis increasing energy positively associated with density and energy use differences among migratory groups - Increased density and energy use translated into more species - Migratory bird populations limited by non-breeding season Species diversity and coexistence 30 Species diversity and coexistence 30 10

11 Test of the More Individual hyp.- interaction with energy and area Species-Area-hyp Species-energy hyp More Ind hyp Hurlbert & Jetz Am Nat 176 Species diversity and coexistence 31 w z: Slope differs betweeen S-A and S-E hyp. q 0: Interaction betweeen S-A and S-E (slope) Species diversity and coexistence 32 Data - The distribution of 6043 bird species across 110*110 km grid cells (c ) on 107 regions - Species richness was explained by - Energy (net primary productivity, NPP) - Range in NPP - Elevational range - Habitat diversity - Slope of the habitat-area relationship Species diversity and coexistence 33 11

12 Species diversity and coexistence 34 Species richness increase at a faster rate with NPP than with area. Species diversity and coexistence 35 Why energy has stronger effect on species richness than area? Species diversity and coexistence 36 12

13 What may explain latitudinal patterns of species diversity?? C. Time hypothesis - ecological time hypothesis - evolutionary time hypothesis Species diversity and coexistence 37 Species diversity and coexistence 37 Ecological time hypothesis Species richness of an area depends on the time period species have had to colonize or recolonize the area since earlier ecological upheaval. For example, the latest glaciation has been suggested to result in higher rate of extinctions of trees in western Palaearctic due to east-west orientation of barriers. As a result, forest dwelling bird species richness is lower in W. Palaearctic than in Nearctic and east Asia. Mönkkönen & Viro J. of Biogeography 24. Blondel TREE 13. Species diversity and coexistence 38 Evolutionary time hypothesis 1. Time for speciation hypothesis (Tropics as a museum) - Diversification rates are similar in tropics and temperate areas - Tropical clades are older have accumulated higher no. of species than temperate clades 2. Diversification rate hypothesis (Tropics are a cradle/museum) - Speciation rates are higher and/or extinction rates are lower in tropics 3. Out of the tropics Species diversity and coexistence 39 13

14 The present day latitudinal diversity gradient (LDG) is explained by current - climatic variables/energy availability - geographical factors (area) - evolutionary/ecological history Species diversity and coexistence 40 Lessons from the palaeontological data about LDG Marine invertebrates in late Ordovician-Early Silurian ( Ma) Mannion et al Trend Ecol Evol 29 Species diversity and coexistence 41 Dinosaur divetsity in late triassic-cretaceous ( Ma) Species diversity and coexistence 42 14

15 Mammal diversity in North America in early Palaeocene (64-58 Ma) Rose et al Geology 39: No evidence for modern-type LBG - Flat LBG between 35ºN - 63ºN Why? - Early mammals responded differently to climate than extant mammals - Too short evolutionary time after K/Pg mass extinction (66 Ma) - Low seasonality allowed flattened LBG Species diversity and coexistence 43 Onset of Antarctic glaciation Temperature Blue shading= icehouse world Open circle = palaeotemparate peak in LBG Solid circle = polewarddecline in LBG Species diversity and coexistence Modern day LBG evident only from icehouse periods - low extinction rates in tropics - high dispersal into the tropics 2. Temperate peaks in LBG during greenhouse periods - tropics too hot for organisms - High extinction rates - Dispersal out of the tropics 3. Continental drift may also have an effect Species diversity and coexistence 45 15

16 Case study: Evolutionary and ecological processes affecting swallowtail species richness Condamine et al Ecology Letters 15 The effect of - host plant use and shifts - historical biogeography - climate change...on diversification and origin of swallowtails Species diversity and coexistence 46 Species diversity and coexistence 47 Parnassiinae, Temperate Papilioninae, Tropical Species diversity and coexistence 48 16

17 Species diversity and coexistence 49 EOGM = Early Oligocene Glacial Maximum LOWE = Late Oligocene Warming Event MMCO = Middle Miocene Climatic Optimum PPG = Plio-Pleistocene Glaciations = significant diversification Species diversity and coexistence 50 Conclusions - Swallowtails originated in Northern hemisphere during warm climatic conditions - Tropical and temperate clades are equal in age, BUT tropical clade has more species Tropical species has higher speciation rate and/or lower extinction rate Available energy, carrying capacity, time for speciation hypotheses not supported Diversification/extinction rate hypothesis supported Species diversity and coexistence 51 17

18 What has affected diversification rate in swallowtails? 1. Paleoclimates 2.Host plant use and shifts 3. Historical biogeography (dispersal possibilities) Species diversity and coexistence Paleoclimates and Historical biogeography (dispersal possibilities) Changing climatic conditions have shifted the distribution of swallowtails host plants AND Tectonic movements have opened new dispersal routes Swallowtails have followed their host plants - niche conservatism hypothesis - effect of dispersal! Species diversity and coexistence Host plant use and shifts Species diversity and coexistence 54 18

19 Escape-and-radiate hypothesis Ehrlich & Raven Evolution 18 Trait value Prey or host Predator or parasite Time Species diversity and coexistence 55 What causes faster speciation in warmer areas (=tropics)? - Energy - Environmental stability/predictability - Intense interspecific interactions - Population size - Shorter generation lenght - Diverse heterogeneity of the environment Why researchers are trying to find THE FACTOR explaining the diversity patterns? Important to remember - The most likely candidates explaining latitudinal species diversity - Different effect of energy vs. area on species richness - Lessons from the palaeontological LDG data - Peak in LDG varied between temperate and tropical areas between icehouse and greenhouse periods - Higher diversification in tropics - Geographic dispersal, niche conservatism/evolution 19