2.5 Investigating Ecosystems Flashcards
what is a dichotomous key
a stepwise tool for identification where there are two options based on different characteristics at each step. the outcome of each choice leads to another pair of options. this continues until the organism is identified
limitations of a dichotomous key
- the organism might not be in the key
- terminology can be difficult
- there might not be a key available for the organisms under investigation
- some features cannot be easily established in the field (i.e. whether an animal is endothermic or ectothermic)
where is random sampling used
if the same habitat is found throughout the area
where is stratified sampling used
used in two areas different in habitat quality
where is systemic sampling used
along a transect where there is an environmental gradient
biotic: ways to measure abundance of organisms that can move (motile)
- nets
- pitfall traps
- light traps
- flight interception traps
biotic: ways to measure abundance of organisms that cannot move (non-motile)
- quadrats (square frames of difference sizes)
- point frames
lincoln index, what is it used for?
estimating the pop. size of motile animals
lincoln index, how does it work?
The Lincoln Index is a method used to estimate the total population size of a species in a specific area using a technique known as mark-recapture. It is especially useful when counting every individual in a population is not practical. The steps involved in using the Lincoln Index are as follows:
- A sample of individuals is captured from the population. These individuals are marked in a harmless and easily identifiable way (e.g., with a non-toxic dye or a tag). The marked individuals are then released back into their habitat, ensuring they mix evenly with the rest of the population.
- After allowing time for the marked individuals to mix thoroughly within the population, a second sample is captured. The total number of individuals in this second sample is counted.
- In the second sample, the number of marked individuals that are recaptured is recorded.- pop size is estimated by equation
lincoln index equation
N = n1 x n2 / m
n= total pop of animals at the study site, n1= number of animals captured (marked and released) on first day, n2= number of animals recaptured on the second day, m= number of marked animals recaptured on second day
limiations of lincoln index
- animals may move in and out of the sample area
-> makes capture-mark-release-recapture method less reliable, data invalid - density of population in different habitats might vary
- may be many in one area, few in the other
- may be seasonal variations in animals that affect pop size
percentage cover
the proportion of a quadrats covered by a species, measured as a percentages (worked out for each species present)
quadrat methods
- percentage freq.
- percentage cover
- pop. density
percentage freq.
the % of quadrats in an area in which at least one individual of the species is found.
calc: taking number of occurences and dividing by the number poss. occurences
pop. density
the number of individuals of each species per unit area. it is calc by dividing the number of organisms by the total area of the quadrats
total number of a species in all quadrats/area of one quadrat x total number of quadrats
transect
- shows how organisms are distributed along an ecological gradient (changes in abiotic factors)
- whole transect can be sampled (continuous transect) or samples can be taken at points of equal distance along a transect (an interrupted transect)
- a line transect = simplest → tape measure laid out in the direction of the gradient, all organisms touching tape are recorded
- a belt transect → allows more samples to be taken a band usually between 0.5m-1m is sampled along a gradient
