Biology UNIT 3

Genetic, species, ecosystem diversity

Genetic diversity = variety of alleles within a species; Species diversity = number of species + relative abundance; Ecosystem diversity = variety of habitats, communities and ecological processes

Biological species concept

Species = organisms that interbreed to produce fertile offspring; reproductive isolation prevents interbreeding

Limitations of BSC

Doesn’t apply to fossils, asexual organisms, hybrids, apomixis, ring species, infertile castes

Linnaean classification + taxa order

Hierarchical system: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species; groups organisms by shared characteristics

Binomial nomenclature

Two‑word scientific name: Genus capitalised + species lowercase; italicised

Dichotomous key

Identification tool using paired statements to narrow down organism identity

Lincoln index

Capture–recapture method to estimate population size; N = (M × n) ÷ m

Species richness, evenness, relative abundance

Richness = number of species; Evenness = how evenly individuals are distributed; Relative abundance = proportion of each species

Percentage cover + frequency

Cover = area occupied by species; Frequency = proportion of quadrats containing species

Simpson’s Diversity Index

SDI = 1 − Σ[n(n−1)] ÷ [N(N−1)]; High SDI = high biodiversity

Sampling methods

Random = equal chance; Systematic = set intervals; Stratified = sample different habitat strata

Sampling techniques

Quadrats, line transects, belt transects, capture–recapture

Minimising sampling bias

Large sample size, random numbers, consistent criteria, calibrated equipment

Biotic factors affecting distribution

Food availability, competition, predation, disease

Abiotic factors affecting distribution

Space, shelter, water, nutrients, temperature, pH, light, humidity, salinity

Habitat + microhabitat

Habitat = area with specific conditions; Microhabitat = small specialised area within a habitat

Distribution patterns

Uniform = evenly spaced; Random = unpredictable; Clumped = grouped around resources

Habitat variation + sampling reliability

Varied habitats cause uneven species distribution → affects accuracy of sampling methods

Specht classification

Classifies ecosystems by vegetation structure and growth form

Holdridge life zone

Classifies ecosystems using precipitation, temperature, humidity

Exponential growth (J‑curve)

Rapid growth with no limiting factors; population increases faster over time

Logistic growth (S‑curve)

Growth slows as carrying capacity is reached; stabilises around equilibrium

r‑strategists

Many offspring, low parental care, short life cycle, unstable environments

K‑strategists

Few offspring, high parental care, long life, stable environments

Population growth rate

r = (b + i) − (d + e); positive r = growth, negative r = decline

Energy flow in ecosystems

Light → chemical energy; biomass produced; energy lost as heat at each trophic level

Food chains + energy diagrams

Show energy transfer between trophic levels; only ~10% passed on

Ecological pyramids

Population, biomass, energy pyramids; energy pyramid always upright

Gross vs net productivity

GPP = total energy fixed; NPP = energy available to consumers after respiration

Water cycle

Evaporation → condensation → precipitation → runoff → infiltration → transpiration

Carbon cycle

Photosynthesis, respiration, decomposition, fossilisation, combustion

Nitrogen cycle

Fixation → nitrification → assimilation → ammonification → denitrification

Predation

Predator kills prey; regulates populations; density‑dependent

Competition

Rivalry for resources; interspecific + intraspecific

Mutualism

Both species benefit

Commensalism

One benefits; other unaffected

Parasitism

Parasite benefits; host harmed

Ecological niche

Role + resource use + interactions of a species

Competitive exclusion principle

Two species cannot occupy same niche; one outcompetes the other

Keystone species

Disproportionate impact; maintains biodiversity + community structure

Food web analysis

Identify keystone species, interactions, predict effects of species removal

Overexploitation

Excessive harvesting → population collapse → trophic cascades

Habitat destruction

Clearing vegetation → biodiversity loss → altered community structure

Monoculture

Single crop → low biodiversity → unstable ecosystem → soil depletion

Pollution

Air, water, soil contamination → ecosystem disruption → microplastics, eutrophication

Carrying capacity

Max population environment can support; changes with resources

Climatic events

Fires, floods, cyclones alter resources, habitats, carrying capacity

Ecological succession

Gradual change in species composition over time

Primary succession

Starts on bare rock; pioneer species first

Secondary succession

Occurs after disturbance; soil already present; faster than primary

Pioneer species

Tolerant, fast‑growing, r‑strategists, wind‑dispersed, nitrogen‑fixing

Successional changes

Biodiversity ↑ biomass ↑ competition ↑ shift from r‑strategists → K‑strategists

Spatial scale

Comparing ecosystems across different locations

Temporal scale

Comparing ecosystems across time (short‑term vs long‑term changes)