BIOL1111 - Chapter 26 Part 1 (W25) 2

Chapter 26: Population Ecology Overview

• Introduction to Population Ecology

  • Focuses on patterns of population growth and decline

  • Key factors:

    • r: intrinsic rate of increase

    • N: population size

    • K: carrying capacity

26.1 Introduction

• Population Growth Dynamics: Understand how populations grow and decline due to various environmental and biological factors.

26.2 Population Characteristics

• Key Questions:

  • What defines a population?

  • What is population density?

  • How is population dispersion characterized?

  • What is meant by the "age structure" of a population?

Geographic Range and Habitat

• Geographic Range: The spatial boundaries within which a population exists.

• Habitat: The specific environment characterized by biotic and abiotic features suitable for a population's life.

Population Size and Density

• Population Size: Total number of individuals in a population.

• Population Density: Number of individuals per unit area, indicating resource use and habitat availability.

Population Density and Body Size

• Generally, larger species exhibit lower population densities.

• Visual reference: Fig. 26.1, p. 690.

Counting Elephants

• Aerial counting can be misleading due to vegetation; careful methodology is required.

• Visual reference: Fig. 26.2, p. 691.

Population Dispersion

• Spatial Distribution: How individuals are spread across the environment.

  • Uniform Dispersion: Individuals repel each other, often due to resource scarcity.

  • Random Dispersion: Individuals are distributed without any specific pattern, common in stable environments.

Clumping

• Species can exhibit clumped dispersion due to social dynamics or resource availability.

• Examples:

  • Mushrooms with pitcher plants.

  • Social behavior in toque macaques.

  • Ducks clustering around available food and water sources.

  • Visual reference: Fig. 26.3, p. 691.

Further Population Characteristics

• Age Structure: Distribution of individuals across different age groups.

• Generation Time: Average interval from birth to the production of offspring.

Generation Time and Body Size

• Generation time typically increases with body size across various organisms.

• Visual representation indicates a logarithmic relationship compressing data into a line.

• Visual reference: Fig. 26.4, p. 692.

26.3 Demography

• Demography: Statistical analysis of population changes over time.

  • Growth Factors: Births and immigration.

  • Decline Factors: Deaths and emigration.

Life Tables

• Tool to summarize population demographics:

  • Track age-specific mortality, survivorship, and fecundity.

  • Defines a Cohort: A group of individuals of the same age.

• Example: Bluegrass Life Table shows mortality rates at various age intervals, survival projections, and fecundity rates.

• Refer to Table 26.1, p. 693.

Survivorship Curves

• Graphical representation of survival rates at different ages, showing three types:

  • Type I: High survivorship until late in life (e.g., Dall sheep).

  • Type II: Constant mortality across age classes (e.g., five-lined skink).

  • Type III: High juvenile mortality, lower as age increases (e.g., desert shrub).

  • Visual reference: Fig. 26.5, p. 694.

26.4 Evolution of Life Histories

• Life History Strategy Considerations:

  • Trade-offs in resource allocation for growth, reproduction, and survival.

  • Patterns observed across species for resource allocation and reproduction strategies.

Organismal Constraints

• Organisms have finite energy budgets shaping their growth and reproductive strategies.

• Energy can be stored if surplus is available, impacting life processes.

Energy Budget Uses

• Key Functions: Maintenance, growth, and reproduction.

• Investment in one function diminishes capacity in others, aiming to maximize survivorship and reproductive success.

Life History Evolution

• Energy allocation is subject to natural selection, refining strategies that maximize lifetime offspring. Variables analyzed include:

  • Age at maturity

  • Offspring size

  • Reproduction frequency and number of offspring

  • Size at maturity