| what is a biotic factor | living things that affect the distribution of organisms
eg competition for resources, grazing, predation, food availability and disease |
| what is an abiotic factor | non-living things which affect the distribution of organisms
eg temperature, humidity, and light intensity |
| describe this predator prey interaction graph | the population of predators always lags behind the prey population
at low prey populations the predators cannot find enough prey to eat so the predator population will stay low
at higher prey populations the predators find more prey, eat them and the prey population will decrease
because they have eaten more, the predator population can reproduce more and their numbers will increase
lower prey populations limit how many prey can be found and eaten by predators so predator numbers will decrease
this pattern will continue giving a distinct graph |
| what effect does predation have on biodiversity | predation can increase biodiversity
for instance, predation can kill one species, which is in competition with a different species. This can allow the different species to gain resources they may not be able to if their competitors weren't killed, therefore increasing biodiversity |
| describe what occurs at different levels (low, intermediate and high) levels of grazing | at low levels of grazing the slower growing plant species die because they are out competed for resources by a small number of vigorous grass species which will hen dominate the habitat
at intermediate grazing levels some of the vigorous growing plants are eaten allowing the slower growing species to gain more of the resources to survive. This therefore results in a mixture of slower and more vigorous growing plant species so increasing biodiversity.
at high grazing levels, overgrazing could damage all of the plant species present and very few grow |
| what does food availability refer to | the availability of edible vegetation, eaten by herbivores or the availability of prey eaten by predators |
| name 5 abiotic factors affecting an organisms distribution | light intensity
temperature
soil moisture
pH
humidity |
| what instrument is used to measure soil pH | pH meter |
| what instrument is used to measure light intensity | light meter |
| what instrument is used to measure temperature | thermometer |
| what instrument is sued to measure soil moisture | soil moisture meter |
| what instrument is sued to measure oxygen concentration | oxygen meter |
| name a possible source of error & its solution for when using a light meter | casting a shadow over the light meter
to overcome this error do not stand between the sun and the light meter |
| name a possible source of error and its solution for when using a pH or soil moisture meter | moisture from previous reading left on the probe
to overcome this error wipe the probe dry between measurements |
| name methods of sampling live organisms | pitfall traps: to sample organisms living on the soil surface
tullgren funnel: used to sample organisms living in the soil
branch/tree beating: used to sample small organisms living in bushes or trees
quadrat: used to sample low growing plants or slow moving animals, eg snails |
| what is meant by replication of sampling | the samples taken of an ecosystem must be representative or that ecosystem, therefore an appropriate number of samples should be taken.
this should provide more reliable results which are more representative or the ecosystem |
| what are sampling techniques used for? | find out which plants and animals live in an ecosystem
find out how common or rate plants and animals are in a given ecosystem
investigate the reasons why the plant or animal lives there |
| describe how to sample using quadrats | a quadrat is used to mark off an exact area of the ground so that the organisms in that area can be identified and counted
in order to improve the reliability of the results:
- quadrats should be placed randomly
- multiple samples should be taken and average results calculated |
| what is the purpose of placing quadrats along a transect line | to assess species distribution in relation with any abiotic factor that varies across a measurable distance |
| name possible sources of error and solutions with pitfall traps | organisms may not be able to climb into container: make sure container is in line with soil surface
trapped organisms may be eaten by birds: cover trap with a raised stone or leaf
trapped organisms may eat each other: use a preservative such as 50% ethanol in the traps and check the traps regularly |
| name possible sources of error and solutions with quadrats | quadrats are not placed randomly: ensure quadrats are thrown at random
some plants that are partly in the quadrat are included and others are not: establish a rule for plants that are partially included and apply consistently do all quadrats in the study |
| what is a paired statement key | a key made up of pairs of statements to help identify an organism |
| what is an indicator species | species that by their presence or absence indicate environmental quality/levels of pollution |
| name one example of indicator species | lichens are often used as indicators of air pollution
shrubby lichens are not capable of growing in areas of high air pollutions whereas crusty lichens are capable of growing in areas of moderate to high levels of air pollution |
