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Population Distribution and Abundance (Chapter 9) Introduction

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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

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