Operation of Ecosystems:
Population = all the members of a single species that live in a habitat
● Habitat = the place where an organism lives
● Community = all the populations of different organisms that live together in a habitat
● Ecosystem = interaction of a community of living organisms with the non-living parts of their environment
● Interdependence = network of relationships between different organisms within a community → the whole
community can be affected if one of the species is removed or becomes very numerous
○ Importance of interdependence in a community:
■ Plants produce food by photosynthesis
■ Animals eat plants
■ Animals pollinate plants
■ Animals eat other animals
■ Animals use plant and animal materials to build nests and shelters
■ Plants need the nutrients from animal droppings and decay
● Plants and animals can migrate from one place to another → bring change
● Ecosystems depend on a constant input of:
○ Light from the sun
○ Rain from the atmosphere
● Interrelationships link together biotic and abiotic factors
Biotic factors:
→ Biotic factor = a living factor
● Availability of food
○ Plenty of food = organisms breed successfully
○ If food is in short supply , animals struggle to survive and they don’t breed
● Pathogens/parasites
○ Organisms have no resistance to disease
○ Pathogens could potentially damage or completely wipe out populations in a community
● New predators
○ Organisms have no defence against new predators
○ A new predator could decrease prey populations
● Interspecific competition (competition between species/new competitors)
○ A new species may outcompete another until the population of that species becomes too low for
breeding
■ eg/ red and grey squirrels live in the same habitat and eat the same food – grey squirrels
outcompete the red squirrels which leads to a population decrease of red squirrels
Abiotic factors:
→ Abiotic factor = a non-living factor
● Light intensity
○ Plants need light for photosynthesis
○ Decrease in the rate of photosynthesis → affects plant growth and leads to population decrease
○ Affects the distribution of plants and animals
○ Some plants are adapted to live in low light levels (more chlorophyll, large SA)
○ Breeding cycles of many animal and plant species are linked to day length and light intensity
● Temperature
○ Limiting factor on photosynthesis and the growth of plants
○ In cold climates, temperature is limiting → all the plants are small
○ Small plants → less food for herbivores → less food for carnivores
● Moisture levels
○ No water = no life
○ Plants and animals are relatively rare in deserts due to the lack of water
○ After rain → many plants grow, flower and make seeds quickly , while water is available
● Soil pH and mineral content
○ The level of mineral ions has an impact on the distribution of plants
○ Carnivorous plants (eg/ sundews) thrive where nitrate levels are low → can trap and digest animal prey
○ pH of the soil → major effect on what can grow on it and the rate of decay
○ Decrease in mineral content causes nutrient deficiencies → affects plant growth and leads to
population decrease
● Wind intensity/direction
○ Plants have the ability to transpire fast
○ Shape of trees and the landscape is affected
● Availability of oxygen (animals)
○ Huge impact on water-living organisms → most fish need a high level of dissolved oxygen
■ Some invertebrates can survive in water, with very low oxygen levels
● Availability of carbon dioxide (plants)
○ Limiting factor for photosynthesis and plant growth
○ Affects the distribution of plants
Scales of ecosystems:
● Local (habitat) = pond
● Regional = Lake District moorland
● Global biomes = South America’s tropical rainforest
● Earth
Food chains:
● Biotic community of ecosystem consists o f different species of plants/animals in different feeding groups
○ Producers (primary producer) = an organism that is able to absorb energy from the sun through
photosynthesis
○ Herbivores (primary consumer) = plant-eating animals
○ Carnivores (secondary consumer) = animals that feed on herbivores
○ Top carnivores (tertiary consumer) = animals that eat other carnivores and herbivores
● The relationships between these feeding groups are shown in the food chain
○ Food chain = simple models of feeding relationships in a community
○ Food web = a complex hierarchy of plants and animals relying on each other for food
● Pyramid of biomass = constructed to represent the relative amount of biomass in each level of a food chain
○ Reasons for loss of biomass:
■ Many parts of plant are not eaten
● eg/ bones
■ A lot of what animals eat is excreted
■ Energy is lost at each level
● Used for respiration
● Used for keeping constant body temperature
● Used for chasing prey
○ An animal’s daily calorie intake is used to stay alive rather than building new
biomass
Nutrient cycles:
● Nutrient cycling = a set of processes whereby organisms extract minerals necessary for growth before passing
them onto the food chain
○ All plants and animals depend on nutrients in food for their health and energy
○ Nutrients occur naturally in the environment → constantly being recycled
○ Decomposers = organisms that break down dead organic matter which is recycled to the environment
■ Help return nutrients to the soil
■ In the form of organic substance called humus
● Animals/plants die → decay due to decomposers/detritivores → minerals/nutrients are released into soil →
used up by plants