1.3 Ecology

Ecosystem

The interaction of a community of organisms with the non-living (abiotic) parts of their environment

Community

All the different populations of organisms living in the same habitat

Population

All the individuals of the same species living in the same habitat

Habitat

The place where an organism lives

Interdependence

How organisms in a community depend on each other for food, shelter, pollination, seed dispersal etc.

Stable community

One where all biotic and abiotic factors are balanced and population sizes remain roughly constant

Examples of stable communities

Tropical rainforests, oak woodlands, coral reefs

What do plants compete for?

Light, space, water and mineral ions

What do animals compete for?

Space, food, water and mating partners

Intraspecific competition

Competition between individuals of the same species

Interspecific competition

Competition between individuals of different species

Abiotic factor

A non-living factor that can affect a community

Examples of abiotic factors

Light intensity, temperature, moisture levels, soil pH, wind intensity, CO2 levels, oxygen levels

Effect of light intensity on a community

Light needed for photosynthesis → affects plant growth → affects food and shelter for other organisms

Effect of temperature on a community

Affects rate of photosynthesis and distribution of species

Effect of soil pH on decomposition

Affects rate of decay → affects how fast mineral ions return to soil

Effect of wind on plants

Affects rate of transpiration → affects temperature and photosynthesis rate

Effect of CO2 levels

Affects rate of photosynthesis; some organisms thrive in high CO2 environments

Effect of oxygen levels in water

Fish need high oxygen concentration; levels in water vary greatly

Biotic factor

A living factor that can affect a community

Examples of biotic factors

Food availability, new predators, new pathogens, competition

Effect of new pathogen on a population

Population has no resistance → can be wiped out quickly

Effect of competition on a population

Better-adapted species outcompetes the other until it can no longer breed

Structural adaptation

Physical shape or feature of an organism (e.g. sharp teeth, camouflage, blubber)

Behavioural adaptation

The way an organism behaves (e.g. playing dead, basking, courtship)

Functional adaptation

Adaptations involving processes like metabolism or reproduction (e.g. concentrated urine, late implantation)

Extremophiles

Organisms adapted to survive in extreme conditions (e.g. high temperature, pressure or salt)

Cold climate adaptations

Small surface area to volume ratio; thick insulation (blubber, fur)

Dry climate adaptations

Adapted kidneys for concentrated urine; active in cooler parts of day; rest in shade; larger SA:V ratio

Plant adaptations to dry conditions

Curled leaves, extensive roots, waxy cuticle, water-storing stem tissue

Producer

Photosynthetic organism at the start of a food chain (e.g. plant, algae); makes glucose from sunlight

Primary consumer

Herbivore that eats producers; trophic level 2

Secondary consumer

Carnivore that eats primary consumers; trophic level 3

Tertiary consumer

Carnivore that eats secondary consumers; trophic level 4; apex predators have no predators

Prey

Animals eaten by predators

Predator

Animals that kill and eat other animals

Transects and quadrats

Tools used to measure the distribution and abundance of species in an ecosystem

Predator-prey cycle

As prey increases, predators increase → prey decreases → predators decrease → prey increases again

How CO2 is removed from air

Photosynthesis by green plants and algae

How CO2 is returned to air (respiration)

Plants, algae, animals and decomposers all respire, releasing CO2

How CO2 is returned to air (combustion)

Burning wood and fossil fuels releases carbon stored from photosynthesis

Role of decomposers in carbon cycle

Break down dead organisms and waste; respire and return mineral ions to soil

Water cycle step 1

Sun's energy evaporates water from seas and lakes, forming water vapour

Water cycle step 2

Transpiration in plants also produces water vapour

Water cycle step 3

Water vapour rises and condenses to form clouds

Water cycle step 4

Precipitation (rain, snow, hail) returns water to land; runs into lakes and seas

Three factors affecting decomposition

Temperature, water availability, oxygen availability

Effect of temperature on decomposition

Warmer = faster reactions; too hot = enzymes denature and decomposition stops

Effect of water on decomposition

Microorganisms grow faster with water; water needed for respiration; makes food easier to digest

Effect of oxygen on decomposition

Most decomposers are aerobic; more oxygen = faster decomposition

Compost

Decayed biological material used as a natural fertiliser; aerobic conditions produce heat, speeding decay

Methane gas production

Anaerobic decomposition of waste by microorganisms; burnt as fuel in biogas generators

Biogas generator conditions

Maintained at ~30°C; methane cannot be stored as liquid so must be used immediately

Investigating decomposition

Measure pH change of milk with lipase at different temperatures; phenolphthalein turns clear when fat breaks down

How environmental change affects species distribution

Changes in temperature, water availability, and atmospheric gas composition cause migration or extinction

Effect of climate change on species

Insects may migrate to hotter regions; lichen cannot survive where sulfur dioxide is present

Biodiversity definition

The variety of different species of organisms on Earth or within an ecosystem

Why is high biodiversity important?

Keeps ecosystems stable; species less dependent on each other; source of food and medicines

How humans reduce biodiversity

Building, farming, quarrying, pollution, deforestation, using raw materials faster than they are replaced

Water pollution sources

Sewage, fertilisers, toxic chemicals

Air pollution sources

Smoke, acidic gases (e.g. sulfur dioxide)

Peat

Material formed when plant matter doesn't fully decay due to lack of oxygen; found in acidic, waterlogged bogs

Why are peat bogs important?

Habitat for many species, especially migrating birds; stores carbon

Why are peat bogs being destroyed?

Drained for farming, used as compost, or burned as fuel; releases CO2; forms slowly

Deforestation definition

Cutting down large numbers of trees to use the land for something else

Reasons for tropical deforestation

Land for cattle/rice fields; crops for biofuels (sugarcane, maize)

Problem of deforestation 1

Burning trees releases CO2 → contributes to global warming

Problem of deforestation 2

Fewer trees means less CO2 absorbed through photosynthesis

Problem of deforestation 3

Loss of habitats → reduced biodiversity

Global warming definition

Rising global temperatures caused by increased greenhouse gases (CO2 and methane)

Consequences of global warming

Melting ice caps, rising sea levels, species migration, species extinction, reduced biodiversity

Trophic level 1

Producers (plants and algae) — make food by photosynthesis

Trophic level 2

Primary consumers — herbivores

Trophic level 3

Secondary consumers — carnivores that eat herbivores

Trophic level 4

Tertiary consumers — carnivores that eat other carnivores; apex predators

How decomposers break down matter

Secrete enzymes; matter broken into small soluble molecules that enter the microorganism by diffusion

Pyramid of biomass

Shows relative biomass at each trophic level; gets smaller going up

Why does biomass decrease up trophic levels?

Not all biomass can be eaten; biomass is lost in respiration, urea, faeces

% energy transferred by producers

About 1% of incident light energy used in photosynthesis

% biomass transferred between trophic levels

Approximately 10%

Why is biomass lost between levels?

Respiration (CO2 produced), urea in urine, faeces, inedible parts (bones, hooves)

Efficiency of biomass transfer formula

(Biomass transferred to next level ÷ Biomass at previous level) × 100

Why are there fewer organisms at higher trophic levels?

Less biomass available; energy lost at each transfer

Food security definition

Having sufficient food to feed the population

Factors threatening food security

Rising birth rate, changing diets, new pests/pathogens, climate change, conflict

Intensive farming techniques

Small cages to reduce movement; high temperatures to reduce energy lost to thermoregulation; high protein feed

Ethical issues with intensive farming

Animals kept in distress; increased infection risk; very low standard of living

Why are fish populations declining?

Humans fishing faster than populations can regenerate

Net size restrictions (fishing)

Larger nets allow small fish to escape → reach breeding age → sustain population

Fishing quotas

Limits on how many fish of a species can be caught in an area over a time period

Mycoprotein

Protein-rich food made from fungus Fusarium; grown on glucose syrup aerobically; suitable for vegetarians

Benefits of mycoprotein over meat

Reduces land use and methane production

GM bacteria and insulin

Bacteria genetically modified to produce insulin; purified and used to treat diabetes

GM crop benefits

Can be made pest-resistant or weather-resistant to increase yields; can be modified for better nutrition (e.g. Golden rice)

Biodiversity conservation method 1

Breeding programs to prevent endangered species becoming extinct

Biodiversity conservation method 2

Protection and regeneration of rare habitats

Biodiversity conservation method 3

Reintroduction of hedgerows and field margins to support more species

Biodiversity conservation method 4

Reducing deforestation and CO2 production to slow global warming

Biodiversity conservation method 5

Recycling waste instead of landfill to reduce habitat loss and slow resource depletion

Positive human interactions with ecosystems

Maintaining rainforests, reducing water pollution, preserving scientific areas, replanting hedgerows and woodlands