1. Population Distribution and Abundance (Chapter 9) Introduction
Ecologists usually define a population as a group of individuals of a single species inhabiting a specific area.
Characterized by the number of individuals and their density.
Additional characteristics of a population include age distributions, growth rates, distribution, and local abundance.

2. Distribution Limits
Physical environment limits geographic distribution of a species.

3. Two needle pinyon
Giant Sequoia

4. Temperature and Water Balance
Distribution of three Peromyscus species
Temperature and Water Balance
(Blackwell and Pivorun, 1979)

5. Kangaroo Distributions and Climate

6. Distributions of Plants along a Moisture-Temperature Gradient
Encelia species distributions correspond to variations in temperature and precipitation.

7. Microenvironmental forces

8. Distributions of Barnacles along an Intertidal Gradient

9. Distribution of Individuals on Small Scales
Random: Equal chance of being anywhere.
Regular: Uniformly spaced.
Clumped: Unequal chance of being anywhere.

10. Distribution of Individuals on Small Scales

11. Distribution of Tropical Bee Colonies
Hubbell and Johnson: aggressive behavior

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13. Distributions of Desert Shrubs
Traditional theory suggests desert shrubs are regularly spaced due to competition.
Phillips and MacMahon found distribution of desert shrubs changes from clumped to random to regular patterns as they grow.
Young shrubs clumped for (3) reasons:
Seeds germinate at safe sites
Seeds not dispersed from parent areas
Asexual reproduction

14. Distributions of Desert Shrubs
Phillips and MacMahon proposed as plants grow, some individuals in clumps die, reducing clumping.
Competition among remaining plants produces higher mortality.
Root zone competition
Eventually creates regular distributions.

15. Clumped Distributions of Individuals on Large Scales (resource hot spots)

16. Animal Size and Population Density
Relationship holds up within trophic levels (e.g., herbivores)

17. Plant Size and Population Density
Plant population density decreases with increasing plant size.
Underlying details are very different.
Tree seedlings can live at very high densities, but as the trees grow, density declines progressively until mature trees are at low densities.

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19. Commonness and Rarity
Rabinowitz devised commonness classification based on (3) factors:
Geographic Range of Species
Habitat Tolerance
Local Population Size
Populations that are least threatened by extinction, have extensive geographic ranges, broad habitat tolerances, and some large local populations.
All seven other combinations create some kind of rarity.

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21. Rarity
Rarity I
Extensive Range, Broad Habitat Tolerance, Small Local Populations
Peregrine Falcon
Rarity II
Extensive Rage, Large Populations, Narrow Habitat Tolerance
Passenger Pigeon

22. Rarity
Rarity III
Restricted Range, Narrow Habitat Tolerance, Small Populations
California Condor