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