7.4 Populations in ecosystems Flashcards
What is ecology?
the study of the inter-relationships between organisms and their environment. The environment includes both non-living factors, such as temperature, and living factors such as competition and predation
What are ecosystems?
made up of a community and all the non-living factors of its environment. The 2 major processes are:
- the flow of energy through the system
- the cycling of elements within the system
Within an ecosystem, there are a number of species made up of a group of individuals making up a population
What is a population?
group of individuals of one species that occupy the same habitat at the same time and are potentially able to interbreed
What can the size of a population vary as a result of?
- the effect of abiotic factors
- interactions between organisms, for example intraspecific and interspecific competition and predation
What is a community?
all the populations of different species living and interacting in a particular place at the same time
What is a habitat?
where an organism normally lives and is characterised by physical conditions and other organisms present
What is a niche?
how an organism fits into the environment. Refers to where an organism lives and what it does there
What is an abiotic factor? give examples
- non-living things that influence populations
- temperature, pH, water, light
What is a biotic factor? give examples
- living things that influence populations
- predators, disease, prey, food
What is carrying capacity?
the maximum stable population size of a species that an ecosystem can support
Name 4 abiotic factors that affect population growth
- temperature
- light
- pH
- water/humidity
What is intraspecific competition?
competition between organisms of the same species
What is interspecific competition?
competition between organisms of different species
What resources might organisms compete for?
food, water, shelter, minerals, light, mates
Describe the pattern of a typical predator-prey relationship in terms of population change
- prey is eaten by predator, resulting in predator population increasing and prey population decreasing
- fewer prey means increased competition for food, so predator population decreases
- fewer predators means more prey survives and the cycle begins again
How are quadrats used for estimating population size?
can be placed on grid coordinates, or at intervals along a belt transect. Results reported as either percentage cover or frequency. For slow-moving or non-motile organisms
What is random sampling?
employed when trying to eliminate bias. Two numbered axis can be laid out over the sample area. Generation of random numbers provides coordinates for areas to study
What is systematic sampling?
a similar grid is laid over the entire area, but samples are taken at regular intervals
What are things to consider when sampling?
- the sizes of the quadrat - size of species, kind of groups or colonies the species live in
- number of samples being taken in the area - the more you take, the more reliable the results
- position of each quadrat - to produce unbiased results
How do you calculate the estimated mean density?
total number of individuals counted/number of quadrats x area of quadrat
What is the equation for mark-release-recapture?
estimated population size = total number of individuals in 1st sample x number in the second/number of marked individuals recaptured
What is species richness?
number of different species in a habitat
What is species abundance?
number of individuals per species
How is mark-release-recapture used for estimating population size?
- a sample of a species is captured, marked then released back into the same area they were caught
- after a certain period of time another sample of the species is captured, and the number of marked organisms are counted
What assumptions does the mark-release-recapture method make?
- no marked individuals distribute evenly
- no migration in or out of the population
- few births or deaths
- method of marking does not affect survival
- mark does not come off
Why are ecosystems described as being dynamic?
- populations constantly rise and fall
- any small change can have a large effect
- biotic and abiotic factors may alter the conditions of the ecosystem
What is primary succession?
where an area previously devoid of life is colonised by a community of organisms
What is the brief process of primary succession?
- Pioneer species can survive harsh conditions and colonise the area
- they change abiotic factors of their environment e.g. decomposition adds nutrients to ground
- overtime, this allows more complex organisms to survive
What is the climax community and how is it reached?
the final stage of succession, where the ecosystem is balanced and stable. It is reached when the soil is rich enough to support large tress or shrubs, and the environment is no longer changing
How might species alter the environment that develops during succession?
- a species may improve the environment to make it more suitable for other species.
- Alternatively, a species may worsen the environment by making it less suitable for other species
What is conservation?
the protection and management of species and habitats, in order to maintain biodiversity. Methods need to be adapted to the ecosystem in question
How might succession be managed in order to aid conservation?
sometimes succession needs to be prevented in order to preserve an ecosystem at a certain point, e.g. stopping moorland from progressing into spruce forest. This is called a plagioclimax
What is secondary succession?
occurs in an area where life once existed but has been destroyed
What is the first stage of primary succession?
- the pioneer community - lichen or moss
- lichen hold water, which freezes and cracks the rock, beginning to form a ‘soil’ of powdered rock and organic matter
- asexual reproduction so they can build up a population rapidly
- able to withstand desiccation, extremes of temperature and low levels of nutrients
- ability to fix nitrogen from the atmosphere as if there is any soil it has little nutrients
What is stage 2 of primary succession?
- moss builds up and thickens
- the lichen and moss live, reproduce and decay. The rock also erodes, forms a soil layer. is receptive to seeds
- mosses and ferns cast shade to stop further growth of lichens
- their roots are longer and so further break up the rock
- large plants grow once soil is established
- they succeed the moss and lichen
What is the 3rd stage of primary succession?
- the continual decay of dead organic matter allows nutrients to build up, soil to become trapped and roots to establish
- larger plants grow fast and outcompete the pioneer species
What is stage 4 of primary succession?
- once nutrients have built up and soil is stable, tree seedlings and hedges can root. Eventually shade and out compete the shrubs
- each organism modifies the environment, so creating ideal conditions for growth for the next organism
- different habitats have different climax communities
- a climax community is in its equilibrium. The dominant species is determined by environmental factors
What is the process of secondary succession?
- much the same as primary except it occurs when the final stage is removed abruptly
- may be due to a natural disaster or by human influence such as deforestation and strip mining
- happens rapidly as soil structure, spores and seeds are already present
Why do people not always agree with conservation methods?
there is often a conflict between human needs e.g. income of food/resources and conservation
How can reintroduction of hedgerows help conserve species?
increases biodiversity by increasing sources of food and habitat for animals. Allows animals to migrate
Why may you not want succession to take place?
sometimes succession needs to be prevented in order to preserve an ecosystem at a certain point e.g. stopping moorland from progressing into a forest
How can fire prevent succession?
it allows secondary succession to occur so that pioneer plant species are being conserved as they will grow back first, tree species won’t have time to grow back before the next burning
How can mowing of grazing of animals be used to prevent succession?
grazing or regular mowing prevents large shrubs or trees growing and keeps vegetation low
