## Biology Revision Notes Ecology Essay

Measuring pop density: count no of individuals in Quadrate area, for no of samples and calculate density per m squared b) Frequency: count no of hits in Quadrate area and calculate average free per meter squared c) % cover: proportion of ground cover, of species in Quadrate area, and calculate average % per meter squared (only used to study stationary or slow moving pops with fairly uniformed distribution across area) The importance to random sampling when estimating abundance is that it is no time-consuming to measure the number of individuals of every species in the entire rear, as samples are used. A running mean is calculated as an indication to whether or not enough samples have been collected and to ensure reliability. This is done by calculating a new mean value after each sample is taken, when enough sample is taken the mean will show little change.Systematic sampling: Recording what species are touching the line at each sampling point Placing 2 parallel lines across, a meter apart and recording what species are found between the 2 lines ( belt transect) Interrupted belt transects can be done by using one line ND placing a quadrant down at the equally spaced sampling point and recording abundance of species within the Quadrate. The position of the transect across the area should be random and enough transect should be performed to ensure data collected is reliable. Systemic sampling would be used instead of random sampling as it allows for a bigger sample to be taken, it is important to know how the species abundance varies across an area rather than what species are present.

A transect is a line across the area and sampling is done at set pre-determined intervals along the line. This is important so the data collected is reliable. Sample intervals would be taken by accordance to the area of the field being measured and the length of the tape e. G. Very meters. The method used to select the number of transects required to ensure reliability of data collected is by using a random number generator. Mark release recapture: Animals of a particular species are collected by netting or trap technique and counted Animals are then marked in some way Animals are then released and left to redistribute into the population A second future is carried out and the total number caught are recorded, as well as Jowl many of those captured are marked.

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Pop size is then calculated by IN *NO/Nm 3 examples of different methods used to trap samples of different mobile species: Mark release recapture 2. Pitfall traps 3.Potters Pitfall traps- underestimation sample can be affected by predators small enough to fall into traps Potters -Overestimation sample as it can take too long to get large sample using potters some species may be missed if the sample isn’t large enough. Ethical issues: ) Species should be studied in situ and not removed from position b) If removal or disturbance is necessary, the individuals should be returned to the same slot it possible (even if dead) c) As few individuals as possible should be removed d) There should be minimal damage to organisms or the habitat e) Sites should not be over used and be given time to recover A number of biotic factors affect the distribution of organisms.In more extreme biotic conditions, only those species with appropriate adaptations will be able to survive One biotic factor is temperature, his can be measured using thermometer or data logger with temperature probe. Competition- inter specific (between members of different species)- competitive nice exclusion principle (1 species in one niche only) Intra specific (between members of the same species) as they have exactly the same resource requirements, the come tends to be fiercer than inter specific come.

But in most cases, competition regulates population sizes because it affects birth and/or death rate. A graph to show the relationship between the population size of prey and predator

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