Biogeography Biogeography & &

BiodiversityBiodiversity

Chapter 24

Ecosystems & Climate 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 & ClimateEcosystems & Climate

• Classification of plant types– Candolle (1855)– Divided world

into zones based on plant types

– Distribution along altitudinal gradient

• Merriam (1884)

Ecosystems & ClimateEcosystems & 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 & ClimateEcosystems & Climate

•Classification of climate

–Koppen (1900)–Used Candolle’s plant classification–Established link between climate and plant distribution

Classification themesClassification 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 ecosystemsTerrestrial 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 ecosystemsTerrestrial ecosystems

Variations in distribution

Latitudinal gradientsLatitudinal gradients

Evapotranspiration gradientEvapotranspiration gradient

AET (actual)AET (actual)

Evapotranspiration gradientEvapotranspiration gradient

PET (potential)

Altitudinal gradientsAltitudinal gradients

Ecosystem biomassEcosystem biomass

• Temperature / rainfall – Evapotranspiration

rate– Decomposition rate– Nutrient cycling

• Biomass allocation– trees / shrubs /

grasses

• Complex physical structure biodiversity

Major biomes

Ecosystem biomassEcosystem biomass

Standing biomass – function of temperature & precipitation

Aquatic ecosystemsAquatic 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 ecosystemsAquatic ecosystems

• Diversity highest equator

• Diversity/productivity inversely related

• Seasonality – Vertical movement of nutrients

• Marine systems– Upwellings determine productivity – Permanent equatorial thermocline

• supports higher diversity

DiversityDiversity

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 destructionHabitat 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 Terrestrial ecosystems revisitedrevisited

• Terrestrial ecosystem classification– vegetative biomass production

• Vegetative heterogeneity increases species diversity

• Increased production increased diversity

• Diversity generally highest at equator

Aquatic ecosystem Aquatic ecosystem revisitedrevisited

• Aquatic ecosystem classification – physical features

• Seasonality – productivity

• Increased production decreased diversity

• Marine vs. freshwater

• Diversity generally highest at equator

Edge habitatsEdge 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