UNIT 2 Population Ecology

ecology

study of interactions among organisms and between organisms and their environment

what is environment?

all living and non-living surroundings that affect an organism

2 biotic factors

plants; animals

2 abiotic factors

Water, sunlight

biotic

living or once-living

abiotic

non-living parts of the environment

organism

one single living things

population

same species living in the same area

community

different populations living together

ecosystem

all biotic + abiotic parts of an area

Biome

large group of ecosystems with similar climate, plants, animals

Biosphere

all places on Earth where life exists

Population size

Total number of individuals of a species in an area at a particular time.

Population density

Population density Number of individuals of a species per unit area.

High density

More competition/disease risk; easier to find mates or form groups.

Low density

More space/resources; harder to find mates/groups; may be more vulnerable to predators.

Uniform

Evenly spaced, often due to territories or competition. Example: desert shrubs competing for water

random

No clear spacing pattern; possible when resources are abundant. Example: trees in a forest.

Clumped

Individuals grouped together, often around resources; most common pattern. Example: elephants at a watering hole.

Age structure

Distribution of individuals across age groups: pre-reproductive, reproductive, post-reproductive.

Age-structure diagrams

Visual representations of population age structure; useful for predicting growth.

Wide base / many young

Population is likely to grow; wider base generally means faster growth.

More even age groups

The population tends to be more stable.

Narrow base / older population

The population may decline.

sex ratio

Proportion of males to females; a 50:50 ratio is often used as a reference for reproductive potential.

Individuals ENTER a population

birth + immigration

Individuals LEAVE a population

death + emigration

Population change formula

(Births + Immigration) − (Deaths + Emigration)

Survivorship curve

Graph showing how many individuals survive at each age.

Type I

Low mortality until old age; many survive to old age.

Type II

Mortality is relatively steady across life.

Type III

High mortality early in life; few survive to adulthood.

Exponential growth

Rapid growth under ideal conditions; J-shaped; rarely continues indefinitely.

Logistic growth

Growth starts rapidly, slows, then stabilizes; S-shaped.

Limiting factor

Environmental factors that limit population growth.

Density-dependent

Effect changes with population density. Examples: food availability, water supply, and disease.

Density-independent

The effect does NOT depend on density. Examples: forest fire, drought, deforestation.

Carrying capacity (K)

Largest population size in an environment can support at a certain time.