Limiting Factors and Population Dynamics in Ecology

Limiting Factors in Population Ecology

Definition of Limiting Factors

  • Limiting factors: Conditions that impact population size.
    • Determine or change the size of a population.

Types of Limiting Factors

Density Dependent Factors
  • Definition: Factors whose effects on the population vary with population density.
    • Examples include:
    • Competition: More competition in dense populations due to limited resources. Less competition in sparse populations.
    • Predation: Higher predation risk in sparse populations, as predators can easily locate and attack isolated prey.
    • Food Availability: Increased competition for food resources in high-density populations.
    • Disease: Spreads more easily in dense populations due to close contact between individuals.
Density Independent Factors
  • Definition: Factors that affect population size regardless of the population density. Largely abiotic factors.
    • Examples include:
    • Natural Disasters: Events such as fires, hurricanes, and tornados.
    • Human Activities: Deforestation and other environmental modifications.

Population Dynamics

Birth and Death Rates
  • Graph Interpretation:
    • X-axis: Population density.
    • Y-axis: Birth and death rates.
    • Density independent death rates remain constant regardless of population size.
    • Density Dependent Birth Rates: Tend to decline as population increases due to limited resources and competition.
Equilibrium Population Density
  • The stable number of individuals of a species that the environment can support.
  • Influenced by the balance of birth and death rates under given environmental conditions.
Feedback Loops
  • Negative Feedback Loops: Stabilize the population (e.g., increased predation leads to decreased prey populations).
  • Positive Feedback Loops: Can lead to population growth (e.g., increased population density providing more available mates for reproduction).

Boom and Bust Cycles

  • Example: Snowshoe hare and lynx populations in a decadal cycle.
    • Lynx populations tend to lag behind hare populations.
    • Population increases (boom) followed by steep declines (bust) create cyclical patterns.

Life History Strategies

r-Selected Species
  • Characteristics:
    • Operate far below carrying capacity.
    • Produce many offspring with low parental investment.
    • Traits associated: High mortality of offspring, Type III survivorship curve (many offspring die young).
K-Selected Species
  • Characteristics:
    • Operate near carrying capacity.
    • Produce fewer offspring with high parental investment.
    • Traits associated: High survival rate of offspring, Type I survivorship curve (few die young).

Ecological Niches

  • Fundamental Niche: The total range of environmental conditions under which a species can thrive.
  • Realized Niche: The actual conditions under which a species exists, determined by interspecific interactions and competition.

Competitive Exclusion and Resource Partitioning

  • Competitive Exclusion: When one species outcompetes another for resources.
  • Resource Partitioning: Different species use different parts of the habitat or different resources, reducing competition.
  • Character Displacement: Evolutionary changes in traits (e.g., size, color) due to competition, leading to divergent populations.

Coevolution

  • Definition: The process where two or more species evolve in response to each other.
  • Examples:
    • Predator-prey relationships lead to adaptations aimed at survival (e.g., toxins in prey and detoxification in predators).
    • Mimicry in prey species to avoid predation.

Conclusion

  • Understanding limiting factors and niche dynamics is essential for studying population ecology and community interactions. Feedback mechanisms play a crucial role in maintaining ecological balance and species diversity.