Biogeography & Biodiversity Chapter 24

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

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

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

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

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

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

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

Terrestrial ecosystems Variations in distribution

Latitudinal gradients

Evapotranspiration gradient AET (actual)

Evapotranspiration gradient PET (potential)

Altitudinal gradients

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

Ecosystem biomass Standing biomass – function of temperature & precipitation

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

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

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

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)

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

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

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