A revision summary of OCR A level Biology Populations & Sustainability 6.3.2
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Population growth curve Competition – the interaction between living organisms, when
Lag Slow growth – low rate of resources are in limited supply for whole population
phase reproduction, births>deaths, Intraspecific – competition between members of the same
organisms adjust to species
conditions - ↓food = ↓pop size = ↓competition = ↑pop size
Log Exponential growth – Interspecific – competition between different species
phase plentiful resources, high - 2 species cannot occupy same niche (the role of an
reproduction, organisms in a habitat)
Stationa Carrying capacity – max Predator-prey
ry pop size that can be 1. ↑prey = ↑food for predators = ↑predators
phase supported. births = deaths, 2. ↑predators = ↓prey
stable but fluctuating, 3. ↓prey = ↓food for predators = ↓predators
Limiting factors 4. ↓predators = ↑prey
Limiting Factors – restrict final size of population
Density- Impacts Abiotic – temp, light, pH, water,
dependant vary with oxygen, humidity Sustainability – exploitation of resources without compromising
pop size Biotic – predators, disease, biodiversity or ability to meet future needs.
competition, toxic by-products - Increasing human population means increase in need/ demand for
Density- Affect pop Natural events – earthquakes, fires, resources – uncontaminated water, shelter, clothes, food, medicine.
independe regardless volcanic eruptions, storms. - Sustainable resource = renewable resources that are exploited in a
nt of size way that means they will not run out.
Immigration – movement of individual organisms into an area Timbe Smal Coppicing – tree is not felled, timber removed regrows.
increases pop size. r l 1. tree trunks cut close to the ground leaving a stump
Emigration – movement of individuals away from area decreases prod- scale 2. new shoots form from the surface (stool)
Conservati Active management Reclamation – uction 3. shoot rapidly regrow & mature
on involving human interaction process of restoring Rotational coppicing – allows time for newly coppiced
to maintain biodiversity ecosystems that have trees to grow while other trees are coppiced.
(genetic, species, habitat) been damaged. - Maintains biodiversity as trees do not grow enough
- Sustainable Legal protection to block out light.
development - natural Removal of predators - Succession cannot occur & more species survive
resources can be used Provide resources Pollarding – cuts the trees higher up so animals cannot
without running out eat the new shoots that grow.
Preservati Maintenance of ecosystems Restricting/ banning Larg Felling – felled trees are destroyed & will not regrow
on in their current state by human interference e - habitats destroyed, ↓soil minerals, ↑soil erosion
protecting the area scale Selective cutting – removing only the largest trees
Reasons - A small area, exposes less soil, reducing soil
Ethical – humans have a moral responsibility to maintain biodiversity erosion, increasing ability for plants to grow again
as all organisms have a right to exist. Tree replanting – plant far apart to ↓competition,
Social – aesthetically attractive, educational, ecotourism, exercise, manage pests & pathogens = ↑yield
relaxation Fishin Fishing quotas – limit no of certain species of fish allowed to
Economic – provide resources for human use and income e.g., food, g be caught within an area.
drugs, timber. Large nets allow smaller fish to escape
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