APES: unit 3

Specialist vs. Generalist Species

  • Specialist Species

Characterization:

  • Have a smaller range of tolerance or narrower ecological niche.

  • More prone to extinction due to specific requirements.

    • Example: Specific food requirements such as bamboo.

  • Less ability to adapt to new environmental conditions.

  • Generalist Species

Characterization:

  • Larger range of tolerance and broader ecological niche.

  • Less prone to extinction and often more likely to be invasive.

    • Example: Broad food requirements.

  • High adaptability and resilience in changing environments.

  • Concept of Niche Separation:

  • Specialist species utilize a narrow niche and specific resources.

  • Generalist species can occupy a broader niche, thus having varied resource use.

Learning Objectives and Essential Knowledge

  • Learning Objective ERT-3.A:

    • Identify differences between generalist and specialist species.

  • Essential Knowledge ERT-3.A.1:

    • Specialist species are advantaged in constant habitats, while generalist species do well in changing habitats.

  • Suggested Skill 1.B:

    • Concept explanation of environmental concepts and processes.

Characteristics of Specialist and Generalist Species

Specialist Species

  • Narrow ecological niche.

  • Less adaptable due to specialized needs.

  • More likely to become extinct.

  • Use a specific set of resources.

  • Highly affected by changing environmental conditions.

  • Have advantages in consistent environmental conditions.

Generalist Species

  • Broad ecological niche.

  • Adaptable to various environments.

  • Less likely to become extinct.

  • Utilize a variety of resources.

  • Exhibit high range of tolerance in various conditions.

  • Have advantages in changing environments.

K-selected vs. r-selected Species

K-selected and r-selected Species Overview

  • K-selected and r-selected species represent two reproductive strategies based on environmental stability.

Learning Objectives and Essential Knowledge

  • Learning Objective ERT-3.B:

    • Identify differences between K- and r-selected species.

  • Essential Knowledge ERT-3.B.1:

    • K-selected species characteristics:

    • Tend to be large with few offspring.

    • Live in stable environments, expending significant energy for offspring.

    • Mature slowly with high parental care.

    • Longer life expectancy and repeated reproduction.

    • Experience relatively high competition for resources.

  • Essential Knowledge ERT-3.B.2:

    • r-selected species characteristics:

    • Tend to be small with many offspring.

    • Expend minimal energy for each offspring.

    • Mature early with shorter life spans.

    • May only reproduce once or multiple times throughout their life.

    • Experience relatively low competition for resources.

Additional Concepts

  • Biotic Potential:

    • Refers to the maximum reproductive rate of a population in ideal conditions.

  • Reproductive strategies can transition or vary under different conditions.

  • K-selected species are more adversely affected by invasive r-selected species, which typically exhibit rapid population growth.

Characteristics of K-selected Species

  • High-quality focused reproduction with few offspring.

  • Heavy parental care to ensure offspring survival.

  • Generally fewer reproductive events compared to r-selected species.

    • Example: Most mammals and birds.

  • Long lifespan and time to reach sexual maturity, resulting in slow population growth.

  • More susceptible to disruption by environmental changes and invasive species.

Characteristics of r-selected Species

  • Focused on quantity of offspring with minimal to no parental care.

  • May reproduce only once (semelparity) but generally reproduce multiple times throughout their lifespan.

    • Example: Insects, fish, and certain plants.

  • Short lifespan and a quick approach to sexual maturity, allowing for a high biotic potential.

  • More likely to behave invasively and adapt better to rapidly changing environmental conditions.

Competition and Habitats

  • K-selected species usually inhabit areas with high competition for resources, maintaining population sizes near carrying capacity (K).

  • r-selected species often inhabit environments with lower competition, leading to population fluctuations and die-offs.

Traits Comparison Table

Trait

K-selected Species

r-selected Species

Life Span

Long

Short

Time to Reproductive Maturity

Long

Short

Number of Reproductive Events

Few

Many

Number of Offspring

Few

Many

Size of Offspring

Large

Small

Parental Care

Present

Absent

Population Growth Rate

Slow

Fast

Population Regulation

Density dependent

Density independent

Population Dynamics

Stable, near carrying capacity

Highly variable

Species Density and Population Dynamics

  • Discussion of density-dependent and density-independent factors affecting populations.

Density-Dependent Factors

  • Influence population growth based on size, including:

    • Food availability

    • Disease spread

    • Competition for resources

Density-Independent Factors

  • Affect population regardless of size, including:

    • Natural disasters (e.g., floods, fires).

Biotic Potential and Population Change

  • Biotic Potential: Defined as the intrinsic growth rate of a population under ideal conditions.

  • Population Dynamics:

    • Factors contributing to population size, including births, deaths, migration.

    • Example of population calculation:

    • Population Size = (Immigrations + Births) - (Emigrations + Deaths)

      • For an example scenario:

      • (19 + 5) - (6 + 0) = +18 elk; leading to a population of 70 elk.

Carrying Capacity (K)

  • Defined as the maximum number of individuals of a population that an ecosystem can support based on limiting resources such as food, water, and habitat.

  • Overshoot occurs when the population temporarily exceeds its carrying capacity, leading to resource depletion.

  • Die-off: A sharp decrease in population size when resource depletion leads to mass deaths.

Real-World Example of Overshoot and Die-off

  • Case Study: Reindeer of St. Paul Island

    • Introduction of 25 reindeer in 1910; gradual growth followed by exponential growth.

    • Resulted in overshooting carrying capacity and eventual population crash due to food resource depletion.

Surviving Density: Predator-Prey Dynamics

  • Predator-prey interactions demonstrate the cycles of population growth and decline through feedback mechanisms.

Age Structure and Population Growth

  • Understanding age structure diagrams and their predictive power regarding population growth rates.

  • High proportion of young individuals suggests rapid growth, while stable population shapes indicate equilibrium.

Total Fertility Rate (TFR) and Population Dynamics

  • TFR determines population trends based on reproductive behavior, influenced by various factors.

  • Replacement Level Fertility reflects the fertility needed to maintain population size, typically 2.1 in developed countries.

Factors Affecting TFR

  • Age of first childbirth, educational access, family planning availability, and government policy have significant impacts.

Demographic Transition Model

  • The demographic transition model outlines the shift from high birth and death rates to lower rates as nations develop economically.