Unit 4: Section 2- Ecology

Energy Transfer and Productivity

Ecosystem- All the organisms living in a particular area and all the non-living (abiotic) factors
Energy mainly enters an ecosystem through photosynthesis. Producers convert sunlight into a form which can be used by other organisms
Energy is tranferred through the living organisms of an ecosystem when organisms eat other organisms.The stages (eg. primary, secondart, tertiary) are called trophic levels
Food chains and webs show energy transfer. Food chains show simple lines, and webs show lots of food chains and how they overlap.
Energy locked up in things that can't be eaten get recycled back into the ecosystem by decomposers
Not all energy is transfered between trophic levels
Plants can't use all the light energy (wrong wavelength, reflected, passes through), sunlight hits parts of plants which cannot photosynthesise, parts of food aren't eaten, parts of food are indigestable and get excreted
Gross productivity- energy taken in (absorbed). Not all available to next trophic level- respiratory loss (energy from respiration for movement or heat).
Net productivity- energy as biomass available to next trophic level

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Population size of a species varies because of abiotic factors, eg. light, water, space and temperature. When they're ideal for a species, organisms grow fast and reproduce successfully
Interspecific competition- organisms of a different species compete with each other for the same resources. Means resources available to both populations are reduced, leading to less energy for growth and reproduction, so smaller populations
Intraspecific competition- organisms of the same species compete. Resources are plentiful, so populations increase, and eventually resources are limited, so the populations decline. A smaller population means less competition, so populations grow to the maximum stable population size (the carrying capacity)
Predation- predator and prey populations are interlinked. As prey populations increase, the predators increase. This decreases prey populations, causing predators to decrease
Distribution varies because of abiotic factors (eg. a plant grows in a south facing region where solar input is greatest) and because of biotic factors (interspecific competition can affect distribution- a less well adapted species will be out-competed)
Niche- the role a species has in a habitat (eg. biotic interactions-diet and abiotic interactions). A niche can only be occupied by one species

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Distribution- the number of individuals of one species in a particular area. Can be determined through counting, or through calculating % cover
Abundance- where a particular species is within the are you are investigating
Frame quadrats can be used to investigate plant populations. They are placed on the ground at random points and the number of individuals is recorded. % cover can be measured by counting how much of the quadrat is covered by a plant species. Good for small areas
Point quadrats are placed on the ground at random points. Pins are dropped through the frame, and if it touches a species it is recorded (% cover also can be measured). Good for dense vegetation
Transects- Line- tape measure placed along a transect, species which touch it are recorded
Belt- data collected along the transect using frame quadrats
Interrupted- measurements taken at intervals along the belt
Measuring abiotic factors-
Climate (temperature, rainfall, humidity-hygrometer)
Oxygen availability (oxygen in dissolved water- O2 sensor)
Solar input (light intensity)
Edaphic (soil) factors (pH, moisture content)
Topography (relief-height readings, slope angle-clinometer, aspect-compass)

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Succession- the process by which an ecosystem changes over time
Primary succession- on land which has been newly formed or exposed. There's no soil or organic material to start with
Secondary succession- on land which has been cleared of plants, but where soil remains
Starts when species colonise the new land surface- the first species is called the pioneer species and it is the first seral stage. The organisms change the abiotic factors, and form soil through decomposition of humus.
This makes conditions less hostile, allowing plants to grow
At each stage, species which are better adapted to the improved conditions move in, out-compete the others and become the dominant species
As succession goes on, the ecosystem becomes more complex. New species move in- increasing species diversity and abundance
The final seral stage is the climax community- the largest possible community of species
The climax community of an ecosystem is dependent on the climate
Human activities can prevent succession, stopping the normal community from developing. When succession is stopped artificially, the climax community is called plagioclimax

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