Population Ecology

POPULATION ECOLOGY

Global ecology: Focus on global interactions between ecosystems.
Landscape ecology: Examines spatial patterns and how they affect ecosystems.
Ecosystem ecology: Studies energy flow and nutrient cycling within ecosystems.
Community ecology: Analyzes interactions between different species in a community.
Population ecology: Investigates factors affecting population size and distribution of a species.
Organismal ecology: Looks into individual organisms and their adaptations to the environment.

What do I need to know?
- Major structural and dynamic characteristics of populations.
What do I need to think about?
- Populations have the potential for exponential growth but rarely realize it.
What do I need to understand?
- How life history traits provide tools to "Win the Game" or maximize growth in species like zebra mussels.
- Understanding of dependent and independent factors affecting populations.

Definition: Population ecology explores the biotic and abiotic factors that influence density, distribution, and size of populations.
Key Concepts:
- Population: A group of individuals of a single species living in the same general area.
- Described by boundaries and size.
- Characterized by density, dispersal, and demographics.

Definition: The number of individuals per unit area or volume.
Dynamic Factors:
- Births: Introduce new individuals into a population.
- Deaths: Remove individuals from a population.
- Immigration: Individuals moving into a population.
- Emigration: Individuals moving out of a population.

Dispersion: A pattern of spacing among individuals within the boundaries of the population.
- Types of Dispersion:
- (a) Clumped: Individuals are grouped in patches.
- (b) Uniform: Individuals are evenly distributed.
- (c) Random: Individuals are spaced in an unpredictable manner.

Definition: Study of the vital statistics of a population and how they change over time.
Vital Statistics:
- Survivorship: The proportion of individuals surviving at different ages.
- Reproductive rate: Includes:
- Fecundity: The number of offspring potentially produced per reproductive cycle.
- Fertility: The actual number of offspring produced.

Definition: A graphical representation of data in a life table.
Types of Survivorship Curves:
- Type 1: High survivorship until old age.
- Type 2: Constant mortality rate regardless of age.
- Type 3: High mortality in early life but survivorship increases for those who reach a certain age.

Reproductive table: An age-specific summary of reproductive rates of a population.
- Typically a snapshot of the population at a specific time, focusing on the total female reproductive output (fertility).

Function of four variables:
- Births, deaths, immigration, emigration.
Closed Population: A population with no immigration or emigration.
Growth Rate:
- Change in population size can be pronounced as:
  \text{Change in population size} = \text{Births} + \text{Immigrants} - \text{Deaths} - \text{Emigrants}

Basic Equation for Growth Rate (r): \Delta N / \Delta t = rN
- Where r = b - d (b = birth rate, d = death rate).

Definition: Growth under idealized conditions where the rate of increase is maximum (rmax).
Equations:
- \frac{dN}{dt} = r_{max}N
- Example: 1.0N, or 0.5N depending on conditions.

Location: Kruger National Park, South Africa post-hunting ban observed exponential growth in elephant population leading to:
- Elephant population increase from years 1900 – 1970 observed in the graphical representation.

Characteristics of Zebra Mussels:
- Highly invasive species with a max size of 50mm.
- Age of first reproduction: 2 years; Lifespan: 4-5 years.
- Fecundity/spawn: 40,000 eggs.
- Filtration capacity: 1 liter algae/day.
Invasion Routes: Hitchhiked from Europe via ship ballast to Great Lakes, particularly Lake St. Clair in the U.S.

Impact on Native Species:
- Loss of native mussels, alteration in energy flow, enhanced water clarity.
- Increased growth in aquatic plants, effects on fish communities (not fully studied).

Definition: The maximum population size that an environment can support.
Concept: Exponential growth cannot be sustained indefinitely due to limiting factors.

Definition: Describes growth rate declines as carrying capacity is approached.
Equation: \frac{dN}{dt} = rN\left(\frac{K - N}{K}\right)
- Produces a sigmoid (S-shaped) growth curve.

Hypothetical Population: $K = 1500$. Growth rate per capita varies as the population size approaches carrying capacity.
Calculation: Demonstrated through a table showing population size vs. growth rate.

Phenomenon Observations:
- Natural populations often overshoot carrying capacity and stabilize through high mortality (often termed as ‘compensation’).

Definition: Traits affecting reproduction and survival schedules of organisms.
Key Traits Include:
- Age of maturity, reproductive frequency, and number of offspring.

Maximization Strategy Characteristics:
- Fast growth rate, early maturation, high fecundity, larger offspring size.
Types of Strategists:
- R-Strategists: Live fast, reproduce often, no care for offspring.
- K-Strategists: Live slowly, care for fewer offspring, mature later.

Density-independent regulation: Not affected by population size (e.g., abiotic factors).
Density-dependent regulation: Affected by biotic factors such as competition, predation, and disease.

Focus: On complex interactions. Nature is influenced by multi-variable conditions, incorporating both density-dependent and independent factors.