1. Communities
An association of interacting populations
in the same place at the same time
-- have characteristic physiognomy
Ecosystem
A community plus its abiotic environment
-- includes energy flow, biogeochemical
cycling

2. Community Structure Patterns visible in a community including:
-- physiognomy
-- dominant species
-- number of trophic levels
-- number and abundance of species
species richness vs. species diversity

3. What factors determine community structure?
Major Questions
What factors determine community structure?
Why are some communities more resilient to disturbances than others?
A disturbance is any discreet event that removes organisms and opens space for colonization of same or different species

4. Communities as fixed species assemblages
-- C. H. Merriam, 1890s Arizona
-- all interacting species, co-dependent
-- superorganism
-- Life Zone concept

5. Life Zones Alpine Hudsonian Canadian Transition

6. Fig (EFB)

7. Organismic or fixed concept
Continuum concept
Fig (EFB)

8. -- can identify to species by morphology
Fossil Pollen:
-- can identify to species by morphology
-- preserve well in sediment cores from lakes, bogs
-- represent past plant communities
-- can radiocarbon date organic remains in
cores to determine age of communities
Margaret Davis: studied fossil pollen from lake cores
in the eastern U.S.

9. Ice sheet

10. Fig (EFB)

12. Ecotones: intermixing of two communities where
one transitions into another
-- causes an ‘edge effect’ of greater species
richness in the ecotone
-- edges can be inherent or induced
-- edges once thought to be good for wildlife
management, but can be detrimental
-- e.g., increased edge, more invasive species
such as cowbirds entering forests

13. Edge effects on forests
Changes in physical environment
e.g., temperature, humidity, light penetration
and wind
2. Direct biological changes
e.g., dead trees and tree fall, reduced leaf
fall, fewer forest birds
3. Higher order biological changes
e.g., increase in some insect populations
(butterflies and high light), increase in
insectivores, more disturbances to interior

14. Quiz
What is meant by fixed versus continuum communities and what are life zones?
What is palynology and how did the work by Margaret Davis help demonstrate the continuum concept?
What are trophic cascades and how did the work by Jane Lubchenco demonstrate this concept?
What is the Shannon diversity index and what patterns are present in most communities with a few rare and a few common species?
What is the Intermediate Disturbance Model? Graph its relationship to species diversity in communities.

15. Plant productivity and the number of bird species
in temperate zone habitats
Primary productivity No. of breeding
Habitat (g/m2/yr) bird species
Marsh
Grassland
Shrubland
Desert
Coniferous forest
Upland deciduous forest
Floodplain deciduous forest

19. Quiz
What is an ecotone and the ‘edge effect’? What are inherent vs. induced edges?
Graph and explain Foliage Height Diversity in relation to species diversity in a community.
Give the equation for species-area relationships. Why is this one of the few genuine rules in ecology?
Graph and explain the model for island biogeography on islands of different sizes and distances from the mainland.
How can the theory of island biogeography be applied to continental areas and conservation biology?