Chapter 19

Chapter 19: Populations in Ecology

Learning Outcomes

  • Definitions to Know:
    • Ecology: The study of the interactions that living things have with each other and with their environment.
    • Population: All members of a single species that live together in a specified geographic region.
    • Community: All species living in a single geographic region.
    • Ecosystem: A community and all nonliving elements that interact with it.
    • Biome: Major terrestrial assemblages of communities that occur over wide geographic areas and have distinct physical characteristics.
    • Biosphere: The interactive collection of all the Earth’s ecosystems.
  • Understanding Environmental Factors: Understand how environmental factors shape populations.
  • Important Properties of Population Growth: Know the three important properties to consider while studying population growth:
    1. Population size
    2. Population density
    3. Population dispersion
  • Types of Population Growth: Know the different types of population growth and the determinants of growth rate.
  • Species Classification: Know the difference between r-selected and K-selected species.

Ecology

  • Definition of Ecology: The study of interactions between living things and their environment, encompassing both biotic and abiotic factors.

Populations

  • Ecosystem Considerations: The ecosystem must be considered when studying populations, as various environmental elements shape populations, including:
    • Temperature
    • Water
    • Sunlight
    • Soil
  • Range of Tolerance: Populations generally have a specific range of environmental conditions that they can tolerate, influencing their distribution and survival.

Population Distribution

  • Factors Influencing Distribution: Ranges of tolerance for multiple factors will determine where populations of a given species can be found. Examples include temperature changes impacting species habitat, as exemplified by changes in anchovy distribution due to temperature and dissolved oxygen levels.

Population Growth

  • Key Properties of Population Growth: Important properties to consider when studying population growth include:
    1. Population Size: The total number of individuals in a population.
    2. Population Density: The number of individuals per unit area, for instance, number per square kilometer.
    3. Population Dispersion: The distribution of individuals within the species' range, which can be categorized into three basic types:
    • Clumped Distribution: Results from uneven distribution of resources or social interactions.
    • Uniform Distribution: Results from competition for resources.
    • Random Distribution: Population distribution without significant influencing factors, which is uncommon in nature.

Models of Population Growth

  • Exponential Growth: Characterized by rapid growth where the population doubles with each generation.
  • Logistic Growth: Starts off like exponential growth but slows down as it approaches the carrying capacity of the environment.
  • Carrying Capacity (K): The maximum population density that a defined geographic area can sustain over time.
  • Visual Representation: Population density may be illustrated over time, showing exponential vs. logistic growth patterns.

Growth Rate

  • Definition of Growth Rate (r): Determined by both the birth rate (fecundity) and death rate (mortality) within a population.
    • If birth rate > death rate, the population experiences positive growth.
    • If birth rate = death rate, the population achieves zero growth.
    • If birth rate < death rate, the population encounters negative growth.
  • Intrinsic Rate of Increase (r): The growth rate can vary and be classified as:
    • High intrinsic rate of increase (e.g., r = 0.06)
    • Low intrinsic rate of increase (e.g., r = 0.02)
    • Zero population growth (r = 0)
    • Negative intrinsic rate of increase (e.g., r = -0.05)

Factors Influencing Growth Rate

  • Density Dependent Factors: Factors affecting population growth that are dependent on population size, such as disease and competition for resources.
  • Density Independent Factors: Factors influencing population growth that are independent of population size, generally related to environmental conditions that cause fluctuations in available resources.

Life History Adaptations

  • r-selected Populations: Governed mainly by growth rate, they display characteristics such as:

    • Smaller, short-lived organisms
    • High reproductive rates, producing many offspring
    • Little to no parental care is provided.

  • K-selected Populations: Governed mainly by carrying capacity, characterized by:

    • Larger, long-lived organisms
    • Few offspring produced
    • Greater parental care for offspring to ensure survival.

Survivorship Curves

  • Purpose: Show the percentage of a population that survives to a certain age and reflect different strategies in parental investment.
  • Types of Survivorship Curves:
    • Type I: Advocates protecting adults, demonstrating high survival rates among young.
    • Type III: Advocates protecting younger individuals, illustrating high mortality rates early on.

Graphs and Examples

  • California Least Tern: Population graphs showing breeding pairs and fledgling success illustrate both the dynamics of population growth and management strategies for conservation. Data from various years tracks changes in breeding success and survival rates, portraying the population's historical challenges and successes.