Ecology flashcards

Key points

• Habitat: the place where an organism lives.
• Population: all the organisms of one species living in a habitat.
• Community: the populations of all the different species living in a habitat.
• Ecosystem: a community of living organisms interacting with the non-living parts of its environment.

Key points

• Species in a community depend on each other for food, shelter, pollination and seed dispersal.
• Remove one species and the animals that ate it lose food, while the organisms it ate may increase.
• A stable community has its species and environmental factors in balance, so population sizes stay roughly constant.
• Old woodland and coral reefs are stable communities, and can take centuries to recover if destroyed.

Key points

• Abiotic (non-living): light intensity, temperature, moisture, soil pH and mineral content, wind, and carbon dioxide or oxygen levels.
• Biotic (living): how much food there is, new predators, new pathogens, and competition from other species.
• Plants compete for light, space, water and mineral ions; animals compete for food, mates and territory.
• Both kinds of factor decide where organisms can live and how many there are.

Key points

• Lay two tape measures at right angles and use random numbers as the coordinates for each quadrat.
• Count the organisms in each quadrat, then find the mean number per quadrat.
• Scale up: multiply the mean by the number of quadrats that would fit in the whole area.

Formula

Field 200 m², quadrat 0.25 m²

Key points

• Lay a tape measure in a line across the habitat, for example from a hedge out into a field.
• Place quadrats at regular points along the line, such as every 2 m.
• Count the species in each quadrat, or estimate the percentage of the quadrat it covers.
• Measure an abiotic factor, such as light intensity, at each point to look for a link.

Key points

• Producers, such as plants and algae, make glucose by photosynthesis. Every food chain starts with one.
• The Sun is the source of energy for almost every food chain.
• Primary consumers eat producers, secondary consumers eat primary consumers, and tertiary consumers eat secondary ones.
• The arrows show the direction biomass and energy move: read each one as "is eaten by".

A food chain

Key points

• Predators are consumers that kill and eat other animals, their prey.
• When prey numbers rise, predators have more food, so more survive and breed.
• More predators eat more prey, so prey numbers fall, and then predator numbers fall too.
• The numbers rise and fall in cycles, with each predator peak a little after the prey peak.

Key points

• A trophic level is a feeding stage. Level 1 is the producers; apex predators, with nothing eating them, are at the top.
• Level 2 is the primary consumers (herbivores); levels 3 and 4 are carnivores.
• A pyramid of biomass shows the mass of living material at each level, drawn to scale.
• The producers' bar is at the bottom and is normally the widest, because every level above depends on it.

Key points

• Only about 10% of the biomass at one level reaches the next.
• Some is never eaten, such as roots, bones and wood, and some is egested as faeces.
• Some is lost as waste: carbon dioxide and water from respiration, and urea in urine.
• Much of the glucose is used in respiration, and the energy goes to the surroundings as heat.
• So too little is left to support more than about four or five levels.

Formula

Example

Key points

• Photosynthesis takes carbon dioxide out of the air: plants and algae lock the carbon into glucose, then biomass.
• Feeding passes the carbon along food chains.
• Respiration by plants, animals and decomposers returns carbon dioxide to the air.
• Combustion of wood and fossil fuels releases carbon dioxide too.
• Decomposers break down dead organisms and waste, returning carbon dioxide to the air and mineral ions to the soil.

Key points

• Heat from the Sun evaporates water from the sea, lakes and land, and plants lose water vapour by transpiration.
• The water vapour rises, cools and condenses into clouds.
• It falls as precipitation (rain, snow or hail), bringing fresh water to plants and animals on land.
• It then drains through the soil and runs off into rivers, back to the sea.

Key points

• Biodiversity is the variety of all the different species in an ecosystem, or on Earth.
• High biodiversity makes an ecosystem more stable: species rely less on any one other species for food or shelter.
• So losing one species has less effect on the rest of the community.
• People depend on biodiversity too, for food, materials and medicines.

Key points

• Building, quarrying, farming and dumping waste destroy habitats; peat bogs are drained for garden compost.
• Pollution kills plants and animals: sewage and fertiliser in water, smoke and acidic gases in air, toxic chemicals on land.
• Forests are cleared for cattle, rice fields and biofuel crops, destroying habitats and adding carbon dioxide.
• Burning fossil fuels adds carbon dioxide, and cattle and rice fields add methane: both cause global warming.
• Global warming floods low-lying habitats and changes where species can live and when they migrate.

Key points

• Breeding programmes for endangered species.
• Protecting and regenerating rare habitats, such as peat bogs.
• Replanting hedgerows and leaving field margins wild, giving food and shelter to many species.
• Cutting deforestation and carbon dioxide emissions, and recycling instead of sending waste to landfill.