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
- 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 extothermic)
- keys tend to examine physical features and not behavioural ones (2 species that may look similar might have different behaviours)
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 (capture-mark-recapture), 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
(n1 x n2)/nm
n1 = number caught in first sample + marked
n2 = number caugh in second sample
nm= number caught in second sample + prev. marked
limiations of lincoln index
capture-mark-recapture method
- 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 method notes
🔹 What is a Quadrat?
A square frame used to sample plants or slow-moving animals in an ecosystem.
🔹 Uses:
- Estimate population density and distribution
- Measure biodiversity
- Track ecosystem changes
🔹 How to Use a Quadrat:
- Place the quadrat (randomly or systematically).
- Count species or estimate % cover.
- Repeat for accuracy.
- Calculate Density:
total number of species in all quadrats / (area of one quadrat x total number of quadrats)
🔹 Limitations:
- not for large/motile animals
- miscounting possible
- quadrat sizes affects accuracy
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
why is biomass calculated
to show the total energy within a trophic level
limitation of estimating biomass in trophic levels
- involves killing of living organisms
- problems exist with measuring biomass of very large plants such as trees, and with roots and underground biomass
how to calc dry weight biomass
- sample is weighed in a container of known weight
- put in a hot oven (80C)
- after a specific time, sample is reweighed
- sample is put back into the oven
- repeated until same mass is recorded from 2 successive readings
- no further loss in mass shows that water is no longer present
to estimate total biomass
extrapolation technique
- mass of 1 organism / the average mass of several organisms is taken
- mass is multiplied by the total number of organisms to estimate total biomass
how can we quantify species diversity
simpsons diversity index
simpsons diversity index formula (you dont need to know formula off by heart, but need to know what symbols mean)
D = N(N-1)/SUMn(n-1)
N= total number of organisms of all species found, n= the number of individuals of a particular species
what can we do w simpsons diversity index
- make comparisons between areas containing the same type of organism in the same ecosystem
- high D value = a stable and ancient site, where all species have a similar abundance / evenness
- low D value = disturbance through logging, pollution, recent colonisation or agricultural management, where one species may dominate
ecological gradient definition
changes in enviornmental factors through space or where an ecosystem suddenly ends
abiotic and biotic changes can be seen here
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 a width between 0.5m-1m is sampled along a gradient -> quadrats placed at regular sample points + abudance of organisms within each is recorded
