Geography of Communities

Communities

• Community as a superorganism (Clement) – highly integrated system

• Gleason – groups of species that happen to be at same place and time

• Either way, there is organization, even predictability

Community Organization: Energetics

• Body mass (size) and trophic status• Basal metabolic rate (m) – energy uptake

and metabolism of animals at restm = cM0.75

Where c = taxonomic-specific constant M = body mass

Larger animal requires more total energy BUT less energy per unit of mass (0.75) than small animal

Can also be applied to plants

Implications of Body Size

• Larger body size = storage potential• Size influences size of environment needed• Patchiness greater at smaller spatial scales

= finer divisions of environment by smaller organisms (explaining why so many tiny species despit advantages of large body)

• Large animals contrained to large geographic range

• Low carrying capacity

Relationship between range and body mass

Community Organization: Energetics

• Energy flow ---- Food chains/webs

• Laws of thermodynamics place limit on complexity of community

• Productive-ecosystem-hypothesis

Communities in Space and Time: Transitions

• Ecotones – transitional areas between habitats

• Coenocline – a gradient of communities through transition in abiotic conditions or habitat

Discrete Communities

Not comm. somespecies replace

GradualReplacement

Indep. sp.No abruptreplacement

Nested,segregated

Hypothetical Coenoclines

Communities in Space and Time: Transitions

• Are community changes causal or independent?

• Whittaker – examined mountain communities• Found evidence of independence (no abrupt

changes)

Communities in Space and Time: Transitions

Yeaton and pine distribution

Communities in Space and Time: Succession

• Sequential changes in community composition over time

• Implications – changes in community composition from– Differences in life history strategies (r vs. K)– Unintentional engineering– Competition

• Clementsian view• Gleasonian view

Terrestrial Biomes

Biogeographic Units

Climatic Regions

Net PrimaryProductivity

Ecosystem Geography

• Examines how processes of production, energy flow, and nutrient cycling influence distribution of ecosystems

• Basis for development of ecoregions