Biogeography & Biodiversity

1. Biogeography & Biodiversity Chapter 24

2. Ecosystems & Climate Biogeography- study of distributions of organisms The shift from travel notes to surveys to measurements Vegetation structure to climatic conditions Using community structure for inferring climate The switch to using both Units of plant and animal life = Biomes

3. Ecosystems & Climate • Classification of plant types • Candolle (1855) • Divided world into zones based on plant types • Distribution along altitudinal gradient • Merriam (1884)

4. Ecosystems & Climate • Study of animal life distribution followed • F.E. Clements & V.E. Shelford (1939) • Combined plant / animal distribution • Community concept • Introduced biotic unit of Biome • Biogeography

5. Ecosystems & Climate Classification of climate Koppen (1900) Used Candolle’s plant classification Established link between climate and plant distribution

6. Classification themes • Reflect adaptations of the dominant plant forms to regional climate • Abundance of trees, shrubs, and grasses • Leaf types • Relative allocations of carbon above and below ground • Adaptations to moisture, temperature, nutrients

7. Evidence of adaptations • Similar climates producing similar plant forms • Despite evolutionary relatedness of taxa • Covergent evolution • Charles Darwin • Similarities in form & function

8. Terrestrial ecosystems • Classification based on plant forms • Patterns of geographic scale • Most prevalent – equatorial diversity • Diversity highest where productivity is highest • Tropical production / diversity • Altitudinal variation

9. Terrestrial ecosystems Variations in distribution

10. Latitudinal gradients

11. Evapotranspiration gradient AET (actual)

12. Evapotranspiration gradient PET (potential)

13. Altitudinal gradients

14. Ecosystem biomass • Temperature / rainfall • Evapotranspiration rate • Decomposition rate • Nutrient cycling • Biomass allocation • trees / shrubs / grasses • Complex physical structure  biodiversity Major biomes

15. Ecosystem biomass Standing biomass – function of temperature & precipitation

16. Aquatic ecosystems • Linked by water cycle • Classified by physical features • Salt content • Freshwater • Marine • Estuarine • Flow • Lentic • Lotic • Depth profile • Light penetration • Temperature • Dissolved oxygen • Productivity

17. Aquatic ecosystems • Diversity highest equator • Diversity/productivity inversely related • Seasonality • Vertical movement of nutrients • Marine systems • Upwellings determine productivity • Permanent equatorial thermocline • supports higher diversity

18. Diversity Alpha diversity – local community Gammadiversity – within a geographical area (across communities) • Gamma diversity changes occur over geological time • Alpha diversity may change with local habitat disturbance

19. Habitat destruction • Leading cause of species loss • Vegetative losses • Patch habitat • Global tropical rainforest loss • 2.4 acres / second (2 football fields) • 149 acres / minute • 214,000 acres / day (larger than New York City) • 78 million acres / year (larger than Poland) • 137 species becomes extinct every day (50,000 / year)

20. Terrestrial ecosystems revisited • Terrestrial ecosystem classification– vegetative biomass production • Vegetative heterogeneity increases species diversity • Increased production  increased diversity • Diversity generally highest at equator

21. Aquatic ecosystem revisited • Aquatic ecosystem classification – physical features • Seasonality – productivity • Increased production  decreased diversity • Marine vs. freshwater • Diversity generally highest at equator

22. Edge habitats • Edge habitats increase diversity • Marine coastal habitats • Estuaries, bays, lagoons • Tidal influences • Salinity influences • Temperature variations • Terrestrial edge habitats • Increased vertical stratification • Increased species habitat