Population

Population sampling

Study of plants and animals in a habitat to determine species and population size

Purpose of population sampling

To determine what species are present and how many individuals exist

Main assumption of sampling

Samples taken are representative of the entire habitat

Importance of population sampling

Helps understand biodiversity, distribution, and abundance

Standard sampling units

Used to ensure samples represent the study area

Types of sampling methods

Random, systematic, stratified

Random sampling

Samples taken at random locations in a uniform habitat

When random sampling is used

Uniform area, large habitat, limited time, reduce observer bias

Random sampling method

Use grid and random number table to select sampling locations

Advantage of random sampling

Removes observer bias

Limitation of random sampling

May not cover all areas equally

Systematic sampling

Samples taken at fixed intervals across a habitat

Systematic sampling tool

Transects

Use of systematic sampling

Study environmental gradients and zonation

Transect definition

Sampling line across habitat to observe changes in species

Types of transects

Line transect and belt transect

Stratified sampling

Sampling different sections of a habitat separately

Use of stratified sampling

When habitat has different zones or strata

Reason for stratified sampling

Habitats are rarely uniform

Advantage of stratified sampling

Ensures all habitat areas are represented

Ecological sampling techniques

Used to study smaller representative samples

Factors affecting sampling method

Time available, organism mobility, habitat type

Moving organisms

Sampled using traps or mark and recapture

Non-moving organisms

Sampled using quadrats

Transect sampling

Used to study transition between communities

Zonation

Gradual change in species across environmental gradient

Line transect

Sampling along a straight line to record species presence

Line transect advantage

Shows species distribution

Line transect limitation

Does not show abundance clearly

Belt transect

Continuous strip or series of quadrats along transect

Belt transect advantage

Shows species abundance and distribution

Quadrat

A square frame of known size used for sampling

Quadrat size

Usually 1 m² or 0.5 m²

Use of quadrats

Estimate population of sedentary organisms

Sedentary organisms

Organisms that do not move

Quadrat estimates

Density, frequency, percentage cover

Density definition

Number of individuals per unit area

Density formula

Density = Total individuals ÷ Total area sampled

Density unit

Organisms per m²

Frequency definition

Number of quadrats in which species occurs

Frequency formula

Frequency = Quadrats with species ÷ Total quadrats

Percentage frequency formula

(Quadrats with species ÷ Total quadrats) × 100

Percentage cover definition

Percentage of area covered by species in quadrat

Percentage cover estimation

Visual estimate of area occupied by species

Advantage of percentage frequency

Quicker and uses exact numbers

Second advantage of percentage frequency

Less subjective than percentage cover

Disadvantage of percentage frequency

Does not consider size of organisms

Second disadvantage of percentage frequency

Does not show abundance within quadrat

Advantage of percentage cover

Shows abundance and size of species

Disadvantage of percentage cover

Subjective and slower to estimate

Representative sample

Sample that accurately reflects the habitat

Sampling accuracy

Increases with more quadrats

Sampling reliability

Improved by repeating sampling

Importance of sampling

Provides data for conservation and environmental management

Sampling of moving organisms

Difficult because animals move or may not be visible

Challenge in sampling animals

Movement and hiding make accurate counting difficult

Method for moving organisms

Mark-release-recapture (Lincoln Index)

Mark-release-recapture method

Animals are captured, marked, released, and recaptured to estimate population size

Step 1 mark-recapture

Capture and mark individuals harmlessly

Step 2 mark-recapture

Release individuals back into habitat

Step 3 mark-recapture

Allow time for mixing with population

Step 4 mark-recapture

Recapture a second sample and count marked individuals

Population estimate formula

N = (n1 × n2) ÷ m2

N in formula

Estimated total population size

n1 in formula

Number of individuals captured and marked in first sample

n2 in formula

Total number of individuals in second sample

m2 in formula

Number of marked individuals recaptured in second sample

Example mark-recapture calculation

n1 = 10, n2 = 20, m2 = 4

Solution to example

N = (10 × 20) ÷ 4 = 50

Deer population example

n1 = 120, n2 = 80, m2 = 30

Solution deer example

N = (120 × 80) ÷ 30 = 320

Purpose of mark-recapture

Estimate population size of mobile organisms

Assumption 1 mark-recapture

Marked proportion in sample equals that in population

Assumption 2 mark-recapture

Organisms are captured randomly (no bias)

Assumption 3 mark-recapture

Marks are not lost or removed

Assumption 4 mark-recapture

Marking does not harm organisms or affect survival

Assumption 5 mark-recapture

Marked individuals mix randomly with population

Assumption 6 mark-recapture

Chance of capture is the same for all individuals

Assumption 7 mark-recapture

Organisms are not trap-shy or trap-happy

Assumption 8 mark-recapture

Population is closed (no immigration, emigration, births, deaths)

Closed population definition

Population size remains constant during study period

Trap-shy organisms

Avoid traps after first capture

Trap-happy organisms

More likely to be recaptured after first capture

Limitation of mark-recapture

Inaccurate if assumptions are not met

Use of mark-recapture

Birds, fish, mammals, insects

Abiotic factors

Non-living environmental factors affecting organisms

Importance of abiotic factors

Influence distribution, abundance, and activity of organisms

Examples of abiotic factors

Temperature, pH, light, dissolved oxygen, nutrients

Terrestrial abiotic factors

Temperature, rainfall, light intensity

Aquatic abiotic factors

Water current, dissolved oxygen, nutrients, turbidity

Dissolved oxygen (DO)

Amount of oxygen dissolved in water

Importance of DO

Essential for survival of aquatic organisms

Total suspended solids (TSS)

Particles suspended in water affecting clarity

Effect of high TSS

Reduces light penetration and photosynthesis

pH

Measure of acidity or alkalinity

Importance of pH

Affects enzyme activity and organism survival

Conductivity

Measure of dissolved ions in water

Light intensity

Amount of sunlight reaching organisms

Importance of light

Controls photosynthesis rate

Turbidity

Cloudiness of water due to suspended particles