Geographic limits of distribution and species interdependencies.
e.g., biotic effects on physical factors:
Atmospheric oxygen
The role of algae in the PreCambrian
Soil development
Nitrogen-fixing bacteria and mycorrhizal fungi
Communities may be located individually in time and space
Clements (1616)--communities have interlocking species and functions.
Emphasis is on positive correlations in occurrence
Gleason (1917), Whittaker (1975)--communities are shifting associations.
Correlations are often through uncontrolled variable effects.
Biogeographic generalizations about plant and animal associations:
Biomes are large, defined classes, not individuals:
e.g., coral reefs, deserts, tropical rainforests
Life Zones combine latitude and elevation:
e.g., Boreal, Sonoran,
Ecosystems are functional systems of nutrients, energy, producers, consumers, and especially pathways and cycles.
Ecosystems are open, within the biosphere.
Ecologists and biogeographers are both concerned to understand the distribution and abundance of plants and animals.
Ecologists study the structure and functions of communities and ecosystems: energy flow, interactions, abundance.
They often see different species as interchangeable units in trophic systems.
Biogeographers study the geographic distributions and evolutionary changes of organisms in space and time.
Different species are likely to be regarded as unique.
These patterns and processes are much dependent on community ecology.
Biogeography tends to be less reductionist and experimental (and therefore harder to defend), but more historical and evolutionary because of the larger temporal and spatial scales.
GENERALIZATIONS IMPORTANT TO BOTH ECOLOGY and BIOGEOGRAPHY
1) Body Size in relation to energetics:
basal metabolic rate, m = Cm0.75 c varies, but slope exponent is nearly uniform
(Because slope exponent is <1, large animals are more efficient per unit of body weight)
How does this affect:
distribution (resistance to stress?)
division of resources and sympatric species diversity?
numbers of small- and large-bodied species in clades?
range size (in animals)?
body size and biomass in relation to level in food webs?
(contrast predators and parasites)
(note generalization about productivity and species, p103)
2) Generalized spatial patterns
Species distributional responses to
sharp boundaries are sharp
ecotones allow overlap
transitional zones may support specialized species
Five theoretical patterns: Fig. 5.7
Observed patterns were like D (Whittaker 1967): Fig. 5.8
(large plots were averaged)
Pines on west slope of Sierra Nevada show exclusion
within morphological types (Fig. 5.9)
Some communities are highly-evolved
with tight interdependencies and interactions
Keystone species-->strong community effects
some are not predictable (e.g. glaciated regions)
weaker community effects
When do communities exhibit Clements' succession?
When do communities exhibit Gleason's dispersal dominance?
How did plant communities respond to deglaciation?
Environmental catastrophes cause mass extinctions.
Next: Terrestrial and Marine Biomes, pages 110-133