Population Growth + Ecology

Ecology: The study of how organisms interact with the environment.
- The environment includes:
- Physical surroundings
- Other organisms
Important for understanding two main aspects:
- Distribution: Where organisms are found.
- Abundance: How many organisms are in a given area.

Earth’s climate significantly impacts the structure and distribution of terrestrial biomes.
Climate: Refers to the long-term prevailing weather conditions in an area.

Biotic Factors: Living components of the environment.
Abiotic Factors: Nonliving components, including:
- Temperature
- Precipitation
- Sunlight
- Wind
Climate is largely driven by solar energy and planetary movement.

Temperature differences drive air and water circulation:
- Most heat and light is concentrated between the Tropics of Cancer and Capricorn.
- Heat causes air to rise, leading to rain.
- Cooler regions cause air to fall, absorbing water.

Caused by the Earth's axial tilt:
- Seasonal variation increases towards the poles.
- Regions near the equator experience minimal seasonal differences.

Mountain Ranges: Influence climate patterns, leading to wet and dry sides due to air circulation dynamics.

Different climates create different terrestrial biomes.
Biomes are a major determining factor for the presence or absence of specific species in an area.

Factors that limit population distribution include:
- Dispersal: Movement of individuals or gametes.
Population ecology focuses on what restricts:
- Density: Number of individuals in a population.
- Distribution: Spatial arrangement of individuals within the population.

Ecologists utilize mathematical models to understand and predict population growth.

Intrinsic Rate of Increase (r): Describes how quickly a population grows based on the number of individuals already present.
- Defined by rates of births and deaths under ideal conditions.
- Example:
- r = 1: Each individual contributes 1 new individual per generation.
  - Starting with 100 individuals results in 200 (100 + 100) after one generation.
- r = 0.5: Each individual contributes 0.5 new individuals per generation.
  - Starting with 100 individuals increases to 150 after one generation.

Exponential Growth: Occurs when resources are unlimited, allowing populations to grow at their intrinsic rate.
- Typically observed in:
- New populations
- Recovering populations.
Example of exponential growth rates:
- Bacterial populations under optimal conditions
- Invasive species that establish quickly in new environments
- Some species of r-selected organisms, such as certain fish and insects.
Growth Representation (Example Data)

Logistic Growth Model: Takes into account the carrying capacity of the environment.
- Carrying Capacity (K): The maximum population size that an environment can sustain.
- Growth pattern:
- Starts exponential but slows as the population approaches carrying capacity.

Impact on population dynamics:
- K-selection: Traits that are sensitive to density (density-dependent).
- Advantages in high-density environments.
- R-selection: Traits that maximize reproduction (density-independent).
- Advantages when populations are at low densities.
The existence of trade-offs:
- Between number of offspring produced and the resources available for each offspring

dN/dt = rN

ΔN/Δt = B-D