Organisms and Populations

Notes

1. Ecology

Ecology is the branch of biology that studies the interactions between organisms and their environment.

Levels of Ecological Organization

Organism

Population

Community

Ecosystem

Biome

Biosphere

2. Organism and Environment

Every organism survives by interacting with:

(A) Abiotic Factors

Temperature

Water

Light

Soil

(B) Biotic Factors

Plants

Animals

Microorganisms

3. Major Abiotic Factors

(A) Temperature

Most organisms live between 25°C–35°C

Extreme temperatures affect metabolism.

Based on temperature tolerance:

Eurythermal → tolerate wide temperature range

Stenothermal → tolerate narrow temperature range

Examples

Camel → Hot desert

Polar bear → Cold regions

(B) Water

Water is essential for:

Photosynthesis

Digestion

Respiration

Transport

Organisms are:

Aquatic

Terrestrial

(C) Light

Light affects:

Photosynthesis

Flowering

Migration

Reproduction

Plants are classified into:

Short-day plants

Long-day plants

Day-neutral plants

(D) Soil

Important properties:

Soil texture

pH

Minerals

Water-holding capacity

4. Responses to Abiotic Factors

(1) Regulate

Maintain constant internal temperature.

Examples:

Humans

Birds

Mammals

(2) Conform

Body temperature changes with surroundings.

Examples:

Frog

Lizard

Fish

(3) Migrate

Move temporarily to a suitable habitat.

Example:

Siberian crane

(4) Suspend

Become inactive during unfavorable conditions.

Examples:

Hibernation (bear)

Aestivation (snail)

Diapause (insects)

5. Adaptation

Adaptation = Structural or physiological change helping survival.

Desert Plants (Xerophytes)

Adaptations:

Thick cuticle

Sunken stomata

Spines instead of leaves

Deep roots

Example:

Opuntia

Desert Animals

Camel:

Fat stored in hump

Concentrated urine

Less sweating

Kangaroo Rat:

Hardly drinks water

Gets metabolic water from food

6. Population

Population = Group of individuals of the same species living in a particular area.

Example:

All mango trees in a garden.

7. Population Attributes

These are characteristics of a population, not an individual.

(A) Population Density

Number of individuals per unit area.

Example:

200 deer in a forest.

(B) Natality (Birth Rate)

Birth of new individuals.

Increases population.

(C) Mortality (Death Rate)

Death of individuals.

Decreases population.

(D) Immigration

Entry of individuals.

Population increases.

(E) Emigration

Leaving of individuals.

Population decreases.

(F) Sex Ratio

Male :…