ecology

• an ecosystem is made up of living (biotic) and non-living (abiotic) parts
• in an ecosystem, the first level of organisation is individuals
• in an ecosystem, the second level of organisation is populations
• in an ecosystem, the third level of organisation is communities
• organisms need resources from both abiotic and biotic parts of an ecosystem to survive and reproduce
• resources are not infinite so different species and different individuals compete for resources
• plants often compete for water and minerals from the soil, as well as light and space
• animals often compete for food, mates and territory
• there is interdependence between different species, meaning that one species may rely on another species for different things
• a species may depend on another for food, shelter, pollination, and seed dispersal
• a community is stable when all the species and environmental factors are balanced and population sizes stay more or less constant
• food chains show the feeding relationships within a community
• food chains nearly always begin with a producer that makes its own food, usually a green plant or algae that can photosynthesise
• producers are eaten by animals called primary consumers
• primary consumers are eaten by secondary consumers
• secondary consumers are eaten by tertiary consumers
• an apex predator is at the top of the food chain
• predator-prey graphs show the cyclical nature of predator and prey populations in stable communities, a classic example being the canada lynx and snowshoe hare
• an increase in the hare numbers means more food is available for the lynx, so lynx numbers also increase
• the increase in lynx numbers means that the hares have more predators, so the hare numbers decrease
• the lynx then have less food available so their numbers decrease
• the decreasing lynx numbers allows the hare numbers to increase again, and the cycle repeats
• population sizes are interesting to ecologists, and they use experimental tools to look at ecosystems and their populations
• quadrats are square frames that can be used to estimate population sizes
• transects can be used to investigate the effect of a factor on the distribution of a species
• a transect line is a piece of tape that is stretched across the habitat of interest
• quadrats are placed at regular intervals along the transect line
• when discussing organism abundance, the terms that can be used are mean, mode, and median
• the arithmetic mean is the average value of a series of numbers, which is calculated by adding up all the values and then dividing by the number of recordings that have been made
• the mode is the most common value in a series
• the median is the middle value in a numerically ordered series
• using quadrats to estimate a population size: divide the habitat up into a series of quadrat-sized cells. randomly select a given number of cells, then go out into the habitat and place the quadrat in these positions. to evaluate the quadrat contents, either count the number of individual organisms of interest or record the percentage of the quadrat taken up by an organism. the samples from the quadrat are used to estimate the total population in a given area
• the total population in a given area = number counted x (total survey area / area sampled)
• the recycling of materials is essential as they provide the building blocks for future organisms
• one cycle that is particularly important for living organisms is the carbon cycle: carbon is present in all living organisms, so when organisms die, the carbon is recycled so that it can be used by future generations
• one cycle that is particularly important for living organisms is the water cycle: water moves on, above or just below the surface of our planet between different locations, such as rivers, oceans and the atmosphere, and in order for this cycle to be completed, water has to change state
• in the carbon cycle, carbon is removed from the atmosphere by producers who use it in photosynthesis. by consuming plant matter, animals obtain carbon compounds. carbon is returned into the atmosphere because of the respiration that happens in plant and animal cells. when animal and plants die, decomposes return the carbon locked in their bodies back to the atmosphere via decay
• combustion of fossil fuels is another source of carbon entry into the atmosphere
• in the water cycle, water evaporates from the earth's surface, before rising up into the atmosphere. once in the atmosphere, the water vapour cools and condenses into either rain or snow, which eventually returns to the earth's surface. the rain or snow will either become surface runoff or will travel through the earth as ground water. plants take up water through their roots
• biodiversity is the variety of all the different species in a given space