Study Notes on Animal Population Dynamics and Survivorship Curves

Dynamics of Animal Groups

• Importance of Group Living
    - Animals depend on group living for resource access, particularly food.
    - Groups may increase chances of finding resources, but also have disadvantages.

• Disadvantages of Dense Populations
    - Increased competition for resources like food, water, and space.
    - Greater vulnerability to disease outbreaks, which can spread more rapidly in dense communities.
    - Example: COVID-19 impacted urban populations more than remote towns.

Factors Affecting Population Size

• Components Affecting Population Size
    - Abiotic Factors: Non-living environmental elements (e.g., temperature, water, nutrients).
    - Biotic Factors: Living factors that influence populations (e.g., predation, competition).

• Basic Factors Influencing Population Dynamics
    - Birth Rate (B): Number of births in a population over a time period.
    - Death Rate (D): Number of deaths in a population over a time period.
    - Immigration (I): Arrival of new individuals from outside the population.
    - Emigration (E): Departure of individuals from the population.
    - The simplified equation to measure population change:
  $\Delta N = B - D + I - E$

Survivorship Curves

• Definition of Survivorship Curves
    - A graphical representation of the number of individuals surviving at each age.

Types of Survivorship Curves

• Type I Survivorship Curve
    - Characteristics: High parental care, few offspring, low early mortality.
    - Examples: Elephants, lions, humans.
    - Explanation: Organisms tend to reproduce later in life, investing in fewer offspring with high parental investment.
    - Implication: Probability of death increases with age; strong parental care reduces mortality of young.

• Type II Survivorship Curve
    - Characteristics: Equal probability of dying at any age.
    - Example: Hydra.
    - Explanation: Organisms face consistent risks regardless of age (abiotic factors, shortages of nutrients).
    - Implication: Mortality is not age-dependent.

• Type III Survivorship Curve
    - Characteristics: Produce many offspring with little parental care, high early mortality.
    - Examples: Reptiles, plants, insects, fishes.
    - Explanation: Organisms like sea turtles lay many eggs; few survive to adulthood.
    - Implication: If young survive childhood, their chances of surviving to old age increase.

Reproductive Strategies

• K-selected Species
    - Description: Late reproduction, fewer offspring, high parental care.
    - Examples: Humans, elephants, certain birds.

• r-selected Species
    - Description: Early reproduction, many offspring, minimal parental care.
    - Characteristics: High mortality rates in young.
    - Implication: Focus on quantity of offspring over quality.

Factors Influencing Lifespan and Reproduction

• Key considerations affecting reproductive success:
    - Age of first reproduction.
    - Parental investment in offsprings.
    - Number of reproductive cycles per lifetime.

• Nexus Selection: A theory emphasizing maximizing lifetime reproductive success rather than focusing on the number of offspring produced within a single reproductive event.

Population Growth Models

• Population Change under Ideal Conditions
    - Ideal population growth occurs without limiting factors, leading to exponential growth.
    - Model Equation for Population Growth:
  $N(t) = N_0 + (r imes N_0 imes t)$
    where:
    - $N$ = number of individuals,
    - $r$ = growth rate,
    - $N_0$ = initial population size,
    - $t$ = time.

• Intrinsic Growth Rate (rI)
    - Definition: Maximum growth rate without limiting factors.
    - Explanation: Assumes unlimited resources leading to exponential population increase.

• Real-World Considerations
    - Limitations on growth due to factors such as resources, space, and predation.

Limiting Factors in Population Growth

• Density-Dependent Factors
    - Impact increases as population density increases,
    - Examples: Disease spread, competition for resources, nesting space.

• Density-Independent Factors
    - Affect populations regardless of density,
    - Examples: Natural disasters, extreme weather events, solar radiation.

Biodiversity and Non-native Species

• Native Species: Species that are endemic to a specific region and crucial for local ecosystems.
• Non-native Species: Introduced species that may disrupt existing ecosystems by competing with, preying on, or otherwise negatively impacting native species.

Environmental Disruptions and Succession

• Chapter 8.7 discusses disruptions to the environment,
    - Succession: The process by which ecosystems change and develop over time, usually after a disturbance.
    - Importance of understanding how ecosystems recover after disruptions and the role of biodiversity.