Population and Ecology

• definition of ecology the study of living things and their interactions with each other and their environment
• definition of ecosystems a characteristic community of interdependent species interacting with the abiotic components of their habitat.
• definition of population all the members of one species in an area that can breed with each other
• definition of community all the members of all species in an area
• definition of habitat the place in a ecosystem where an organism lives
• definition of niche the role of an organism in an ecosystem, generally a feeding role
• definition of biotic all the living and organic components of an ecosystem
• definition of abiotic all the non-living parts of an ecosystem
• carrying capacity is the maximum number that can be sustained in a population
• what is environmental resistance? all the factors that may slow down population growth
• definition of limiting factors? aspects of the environment which restrict population size and cause environmental resistance
• how to find species density? mean number of species per quadrat m^2 X area of habitat
• benefits of random sampling good - ensures sample is representative of the whole population of each species - removes bias
• method using quadrats 1- area of land being used is divided into a grid pattern using 10 metre measuring tapes to create coordinates 2- coordinates are selected using a random number generator 3- a quadrat is placed at each coordinate on the grid e.g the top left corner of the quadrat touching the coordinate 4- number of each species in quadrat is recorded 5- repeat 6- calculate the mean number of each species in the area
• method using transects - line transect: - run a tape measure across the area being studied - at every 2 metres identify the species touching the transect - calculate the mean belt transect: - run a tape measure across area being studies - place a quadrat at every 2 metres along tape measure - estimate the density, percentage frequency or percentage area cover
• mark, release, recapture method 1- in sampling area, capture the organisms u can find of one species 2- mark the organisms and count how many u have marked and record it 3- release the marked organisms 4- return to the sampling area and capture all the organisms of the species u can find 5- record how many u caught and how many of those are marked 6- calculate population
• in population growth curves for animals and bacteria what is the 1st stage? Lag phase - bacteria are synthesising enzymes and replicating DNA Lag phase - time for animals to reach sexual maturity
• in population growth curves what are the 2nd stages in animals and bacteria? log phase/exponential phase - for bacteria as food availability is high, the growth becomes exponential, cells divide rapidly + reproduction rate exceeds death rate log phase/exponential phase - plenty of food, competition for food, territory and habitats. population increases exponentially.
• in the population growth curve in animals and plants what is the 3rd stage? stationary phase: in bacteria the nutrients start to run out, reproduction and deaths in population stabilise. Death + reproduction rate are equal in animals competition is very high and there is not enough food for all individuals and environmental factors that slow down population growth - fluctuation in numbers
• in population curves in animals and bacteria what is the last stage? death phase: in bacteria the toxins in broth build up so deaths exceed reproduction rate and population decreases. in animals there could have been an introduction to a new disease not enough food more predators
• what are density dependent factors? things that affect population size e.g. competition, predation and disease. effect of the factor on the population is bigger when the population is higher
• what are density independent factors? affects populations where they are large or small. Tends to be abiotic factors and tend to be sudden changes to the environment.
• examples of density dependent factors? disease competition predation food supply
• examples of density independent factors? freezing flood fires droughts
• what is primary succession? takes place on land where there has been no exisitng life e.g on bare rock or sand dunes
• what is a climax community? a stable end point where there are no further successional stages
• what are the seral stages? pioneer species (lichens) > mosses > grasses > herbceous plants > shrubs > climax community
• how do the stages of succession work? - pioneer species which are lichens first colonise bare rock - lichen erode the rock and as they decompose a little soil builds up - the next organisms are mosses, spores are blown it which further erode the rock and decompose. - soil formed will eventually be deep enough for grasses to take root from seeds blown in by animals. - grass eventually replaced by herbaceous plants. - then replaced by shrubs - then final stage is climax community
• what happens to the soil during succession? - soil gets deeper, more nutrient rich, water holding capacity increases so biodiversity increases. - this is because each stage of succession makes conditions more favourable for the next community.
• what is secondary succession? where there has been previous existing life on cleared land meaning that succession occurs faster
• process of the carbon cycle - carbon dioxide in the air is taken in by plants through photosynthesis which fixes it into organic molecules - carbon dioxide is passed down through the trophic levels because producers are eaten etc… - these organisms respire returning CO2 into the air - organisms also die which results in formation of fossil fuels so carbon dioxide returns to air by combustion - decomposers that decompose the dead material also respire
• what are the factors that slow the rate of decay? ice, acid, dry
• how does deforestation affect the carbon cycle? - less CO2 uptake/less photosynthesis - CO2 concentration in the air builds up creating an insulating layer around the planet - light gets through trapping heat - causing a greenhouse effect leading to global warming
• process of the nitrogen cycle - nitrogen gas in the air is fixated by nitrogen fixing bacteria - nitrification - ammonium ions are oxidised to nitrites by nitrosomonas and then from nitrites to nitrates by nitrobacter - nitrates are absorbed by plants but when these die ammonification happens - decomposition by saprotrophs breaking down the amino acids from dead animals and plants into ammonium ions - denitrifcation - in waterlogged soils with anaerobic conditions, anaerobic bacteria such as pseudomonas can reduce nitrate ions back into nitrogen gas
• what are the nitrogen fixing bacteria? Rhizobium - found in the root nodules of legumes Azotobacter - found in the soil
• How can farmers make more aerobic conditions for nitrification? ploughing increases aeration
• what is the impact of agricultural fertilisers? too much fertiliser used or used before rainfall means that nitrates can leach into lakes and rivers causing eutrophication
• what is eutrophication? - nitrates in water cause rapid growth of algae - algae blocks out sunlight to plants - when algae die they are broken down by saprophytes and aerobic bacteria use up the oxygen in water to do this - so less oxygen means lower biodiversity