Bio

🧬 Unit 1.1 β€” Population Ecology & Distribution of Organisms

1. Ecology

Ecology = the study of the interactions between living organisms and their environment.

Community

A group of different species living and interacting together.

  • Includes biotic factors

  • Does not include abiotic factors

Ecosystem

Includes:

  • Biotic factors = living

  • Abiotic factors = nonliving

Ecology focuses on energy flow and chemical cycling between organisms and their environment.

2. Biotic vs. Abiotic Factors

🟒 Biotic = living

Examples:

  • Herbivores

  • Carnivores

  • Parasites

  • Competitors

  • Other organisms that provide food

πŸ”΅ Abiotic = nonliving

Examples:

  • Temperature

  • Water

  • Oxygen

  • Salinity

  • Sunlight

  • Rocks

  • Soil

SARS-CoV-2

For this class, SARS-CoV-2 is considered abiotic because viruses are not made of cells and are not considered living organisms.

3. Biomes

Biome = a large geographic area classified by its climate and the plants and animals adapted to those conditions.

🌎 Terrestrial biomes = land

  • Tropical rainforest

  • Temperate forest

  • Desert

  • Tundra

  • Grassland

🌊 Aquatic biomes = water

  • Oceans

  • Coral reefs

  • Lakes

  • Rivers

  • Wetlands

  • Estuaries

⭐ The ocean is the largest biome on Earth.

Examples:

  • White Mountain National Forest β†’ temperate forest

  • Summit of Mount Washington β†’ alpine tundra

4. Climate & Terrestrial Biomes

Climate is the main factor influencing the distribution of terrestrial organisms and biomes.

4 major components of climate:

  1. Temperature

  2. Precipitation

  3. Sunlight

  4. Wind

β˜€ Which one drives the others?

Sunlight

Earth's curvature causes sunlight to hit different parts of Earth at different angles.

Different sunlight intensity β†’ uneven heating β†’ differences in temperature, wind, and precipitation

5. Latitude & Climate

Earth's temperature zones are based on latitude.

More direct sunlight

β†’ warmer

More indirect sunlight

β†’ cooler

Example:

Hamden, CT (41Β°N) is generally colder than Honolulu, HI (21Β°N) because Hamden receives more indirect sunlight.

Why is January winter in the Northern Hemisphere?

The Northern Hemisphere is tilted away from the Sun, causing less direct sunlight.

⚠ Earth's distance from the Sun is not the main cause of seasons.

6. Global Precipitation Patterns

Because sunlight is distributed unevenly across Earth, it creates global patterns of:

  • Temperature

  • Wind

  • Precipitation

🌴 Near the equator

Usually warm + high precipitation

β†’ Tropical rainforests

🏜 Around 30° N and 30° S

Often dry

β†’ Major deserts

7. Mountains & Climate

Mountains can affect local and regional climates.

Altitude effect

Higher elevation β†’ cooler temperature

Rain shadow effect

When moist air hits a mountain:

Windward side
β†’ air rises
β†’ cools
β†’ precipitation occurs
β†’ wetter

Leeward side
β†’ air descends
β†’ becomes warmer/drier
β†’ less precipitation
β†’ drier

This creates a rain shadow.

Example:

The Mojave Desert is influenced by the rain shadow of the Sierra Nevada.

⭐ A mountain range blocks air flow most effectively when it is positioned perpendicular to the prevailing winds.

8. Climographs

Climograph = a graph showing the average temperature and precipitation of a region.

You can use a climograph to predict a biome.

Look for:

Warm + very wet
β†’ Tropical rainforest 🌴

Very dry
β†’ Desert 🏜

Very cold
β†’ Tundra ❄

Moderate precipitation + seasonal temperatures
β†’ Temperate forest/grassland

⭐ Seasonal patterns are important, not just yearly averages.

9. Disturbances

Disturbance = a natural or human-caused event that removes organisms or reduces available resources.

Examples:

  • Fire

  • Hurricanes

  • Drought

  • Human development

Disturbances can change the distribution of biomes.

Some natural disturbances can actually be necessary.

πŸ”₯ Example: Fires can help maintain some grasslands.

10. Aquatic Biomes

Aquatic biomes are mainly characterized by their physical and chemical environments.

Important factors include:

  • Light

  • Water depth

  • Distance from shore

  • Temperature

  • Salinity

Aquatic Zones

β˜€ Photic zone

Water that receives enough sunlight for photosynthesis.

πŸŒ‘ Aphotic zone

Water with little or no sunlight.

πŸ– Littoral zone

Shallow water near the shore.

🌊 Limnetic zone

Open, well-lit water away from the shore.

Thermocline

A layer where temperature decreases rapidly as water depth increases.

⭐ The photic zone is especially important because photosynthesis by producers forms the foundation of the aquatic food web.

11. Distribution of Species

A species' geographic range is determined by dispersal barriers and ecological factors.

Dispersal barrier

Something that prevents a species from reaching an area.

Examples:

  • Oceans

  • Mountains

  • Highways

  • Lack of habitat space

Ecological factors

Conditions that determine whether a species can survive and reproduce.

Examples:

  • Temperature

  • Water

  • Food

  • Habitat

🦟 Malaria mosquitoes

The factor that most limits where malaria-carrying mosquitoes can live is abiotic factors, especially climate/temperature.

Why?

The mosquitoes need suitable temperatures to survive and reproduce. If the climate is unsuitable, they cannot maintain a population.

12. Population Size

A population's size is dynamic, meaning it changes over time.

Population size changes because of:

  • Births

  • Deaths

  • Immigration

  • Emigration

Formula:

Change in population = (births βˆ’ deaths) + (immigration βˆ’ emigration)

Population increases:

Births + Immigration

Population decreases:

Deaths + Emigration

13. Population Size vs. Population Density

Population size

= total number of individuals

Population density

= number of individuals per unit of area or volume

Terrestrial populations

Usually measured using area.

Example:

20 deer/kmΒ²

Aquatic populations

Can be measured using volume.

Example:

20 fish/mΒ³

14. Dispersion vs. Dispersal ⭐

These are easy to mix up!

Dispersion

= how individuals are spaced throughout an area.

Dispersal

= movement of individuals from one location to another.

Dispersion = spacing

Dispersal = movement

15. Exponential Growth πŸ“ˆ

Exponential growth = population increases at a constant rate when conditions allow rapid reproduction.

The population can grow very quickly.

Example:

10 β†’ 20 β†’ 40 β†’ 80 β†’ 160

Can populations grow exponentially forever?

❌ No.

Resources are limited.

Eventually:

  • Food becomes limited

  • Space becomes limited

  • Competition increases

  • Other environmental factors limit growth

16. Logistic Growth πŸ“Š

Logistic growth occurs when environmental limitations slow population growth.

The population eventually approaches the carrying capacity (K).

Carrying capacity (K)

The maximum population size that a particular ecosystem can support.

Think:

K = the environment's limit

Populations can sometimes overshoot carrying capacity and then decline.

Different species in the same ecosystem can have different carrying capacities.

17. Intraspecific vs. Interspecific

Intraspecific

Intra = within

Interaction or competition within the same species.

Example:

Two deer competing for food.

Interspecific

Inter = between

Interaction between different species.

Example:

Deer and rabbits competing for plants.

⭐ INTRA = within
⭐ INTER = between

18. Density-Dependent Factors

A density-dependent factor becomes more important as population density increases.

Think:

More crowded β†’ bigger effect

Examples:

  • Competition

  • Disease

  • Parasites

  • Predation

These provide negative feedback, which helps regulate population size.

Example:

If many animals live close together, a disease can spread more easily.

19. Density-Independent Factors

A density-independent factor affects a population regardless of its density.

Examples:

  • Extreme cold

  • Drought

  • Floods

  • Fires

  • Hurricanes

Think:

It doesn't matter how crowded the population is.

Moose example 🫎

Hunger from competition for food
β†’ Density-dependent

Transmissible parasites
β†’ Density-dependent

Exceptionally cold winter
β†’ Density-independent

20. Population Dynamics

Population dynamics = changes in population size over time.

Populations fluctuate because of complex interactions between:

Biotic factors + Abiotic factors

For example:

Food availability β†’ population changes
Disease β†’ population changes
Weather β†’ population changes
Competition β†’ population changes

⭐ Unit 1.1 Learning Objectives β€” QUICK REVIEW

Make sure you can explain each of these:

1. Contrast biotic and abiotic factors.

Biotic = living
Abiotic = nonliving

2. List 3 factors that influence climate.

Temperature, precipitation, sunlight, wind

3. Predict a biome from a climograph.

Use temperature + precipitation + seasonal patterns.

4. Distinguish aquatic zones.

Photic vs. aphotic = light
Littoral vs. limnetic = location relative to shore

5. Relate climate to terrestrial biomes.

Climate strongly determines which biome can exist in an area.

6. List factors that influence species distribution.

Dispersal barriers + ecological factors, especially climate and habitat.

7. Summarize how population changes are measured.

Births βˆ’ deaths + immigration βˆ’ emigration

8. Describe density-dependent regulation.

As population density increases, factors such as competition, disease, and parasites have stronger effects.

🧠 THE MOST IMPORTANT THINGS TO MEMORIZE

If you are short on time, focus on these:

Biotic β†’ living
Abiotic β†’ nonliving

Climate β†’ major factor controlling terrestrial biomes

Sunlight β†’ drives global climate patterns

Climograph β†’ temperature + precipitation

Photic β†’ light
Aphotic β†’ no/little light

Littoral β†’ near shore
Limnetic β†’ open water

Dispersion β†’ spacing
Dispersal β†’ movement

Exponential β†’ rapid/constant growth

Logistic β†’ limited growth

K β†’ carrying capacity

Intra β†’ same species

Inter β†’ different species

Density-dependent β†’ depends on crowding

Density-independent β†’ doesn't depend on crowding

Population change =
(births βˆ’ deaths) + (immigration βˆ’ emigration)