populations in ecosystems Flashcards
what is a population?
individuals of the same species occupying one area one time that can potentially interbreed
what is a community?
all the populations of all the species in one area at one time
what is an ecosystem?
consists of the community and the non-living components of its environment.
what is a niche?
the role an organism plays in the ecosystem and how it interacts with the biotic and abiotic factors.
what is the advantage of 2 species occupying different niches?
reduces interspecific competition between them for….(ALWAYS GIVE AN EXAMPLE)
what is carrying capacity?
maximum population size an ecosystem can support
what 2 factors are important when estimating size of a population?
- To ensure the data collected is not BIASED the samples must be selected at random.
- To ensure the data collected is reliable, representative and suitable for statistical analysis a LARGE sample must be taken.
describe random quadratting
1) Form the area of sampling (e.g. field) into a grid shape with, for example, 2 measuring tapes at length + width for axes. Assign coordinates.
2) Coordinates are generated at random using a random
number generator. A quadrat is placed at these coordinates.
3) The number of organisms in the quadrat is then counted or percentage cover is estimated (pick the method most appropriate to the species. E.g. % cover for grass as too many to count, and each individual plant is difficult to identify)
4) This is repeated LARGE NUMBER OF TIMES or a running mean is calculated until the running mean shows little variation.
5) The running mean value would then be used to estimate the total number of organisms in the whole area ALWAYS SAY HOW THIS SHOULD BE DONE e.g. mean number per quadrat x how many quadrats can fit into the area.
describe line transects
1) Several belt transects are placed parallel across the area and numbered.
2) A transect is chosen at random using a random number button on a calculator. A quadrat is placed along the transect at regular intervals e.g. every 5m.
3) The number of organisms or percentage cover in the quadrat is then counted.
4) This is repeated across MANY PARALLEL TRANSECTS and a mean calculated at each interval e.g. mean at 5m, 10m, 15m etc.
5) The mean value for each distance would then be used to determine if the abundance of species changed across the area.
describe mark release recapture
1) A sample of animals of a particular species are captured, counted, marked and released.
2) The mark should not affect the organism’s survival e.g. should not be toxic/ make the animal more vulnerable to predation.
3) The animals are left for a long enough time to redistribute randomly back into the population.
4) A second sample is captured and the total number caught are counted, as well as how many are marked.
5)The formula ‘(number caught first time x number caught second time) ÷ Number marked in second sample’ is used to estimate population size
assumptions of mark release recapture
1) birth rate equals death rate / no immigration or emigration which may change the proportions of marked to unmarked animals
2) Sufficient time must be allowed between the first and second sample for all marked individuals to be randomly distribute throughout the population. However, the time period must not be so long that there are lots of births or deaths.
3) Survival should not be affected by the marks. The marks should not increase predation or be toxic.
how do abiotic factors affect distribution
temp: If too cold, the enzymes will not have enough kinetic energy to catalyse reactions. The organism’s overall activity will drop and may not be sufficient for survival. If too high, enzymes may start to denature and the overall activity will fall, again reducing ability to survive. Temperature can be measured using thermometer or data logger with temperature probe.
light intensity: needed for photosynthesis, therefore the more light available, the greater the rate of photosynthesis
As plants photosynthesise more, the more glucose is produced to be used in respiration to make ATP to provide energy for seed / spore production and the more the population will grow + the more food is available for animal populations
water + humidity: Organisms tend to lose water to the environment by evaporation, however, evaporation can be useful e.g. in thermoregulation (due to sweating) or movement of mineral salts and water through the xylem. The lower the humidity of the environment, the more water loss occurs.
Humidity can be measured using a whirling hygrometer or data logger with humidity probe.
pH: The pH of the environment can affect extracellular enzymes and surface proteins. The further from the optimum pH the more the proteins/ enzymes denature, the lower the population size and range of species.
how do biotic factors affect distribution
If several individuals share aspects of their niches then they will compete for light, nitrates, food, shelter, etc. The more individuals present, the greater the competition for those resources will become.
Interspecific comp: between different species
Intraspecific comp: between same species
Also, predation (an organism killing + eating another)
describe the predation graph
- Initially there is an increase in the prey population, providing more food for predators, so shortly after there is an increase in predator population.
- Predators eat more prey so the prey population decreases.
- With less food to eat the predator population then decreases as they die.
- So then the prey population increases as less are being eaten and the cycle starts again
define succession + describe it
A series of changes within a community and abiotic factors over time, species within the community are gradually replaced by other species.
1. Pioneer species are the only organisms adapted to the hostile, abiotic conditions and colonise this environment.
2. Over time these organisms change the environment / abiotic conditions (ALWAYS GIVE AN EXAMPLE e.g. plants add humus and nitrates and phosphates to the soil when they die.
3. This makes the environment less hostile and more suitable for a new different / named species to colonise.
4. This new species outcompetes the pioneer species, whose population decreases.
5. This replacement of species continues and the species diversity increases.
6. Eventually a climax community is reached- populations are stable + usually high biodiversity.
As succession proceeds there is a change from a less diverse, hostile environment with simple food webs to
a more diverse, less hostile environment with complex food webs which are more stable.
