Population Distribution and Abundance

1
Population Distribution and Abundance

• Chapter 9

2
Outline

• Distribution Limits
• Distribution Patterns
• Organism Size and Population Density
• Commonness and Rarity

3
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 abundance.

4
Distribution Limits

• Physical environment limits geographic
  distribution of a species.
• Organisms can only compensate so much for
  environmental variation.

5
Kangaroo Distributions and Climate
6
Tiger Beetle of Cold Climates
7
Distributions of Plants along a
Moisture-Temperature Gradient

• Encelia species distributions correspond to
  variations in temperature and precipitation.

8
Distributions of Barnacles along an Intertidal
Exposure Gradient

• Organisms living in an intertidal zone have
  evolved to different degrees of resistance to
  drying.
• Barnacles show distinctive patterns of zonation
  within intertidal zone.
• Connell found Chthamalus stellatus restricted to
  upper levels while Balanus balanoides is limited
  to middle and lower levels.

9
Distributions of Barnacles along an Intertidal
Gradient
10
Distribution of Individuals on Small Scales
11
Plant Abundance Along Moisture Gradients
12
Organism Size and Population Density