2.5 Investigating Ecosystems

Question 1

what is a dichotomous key

Answer 1

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

Question 2

limitations of a dichotomous key

Answer 2

• 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)

Question 3

where is random sampling used

Answer 3

if the same habitat is found throughout the area

Question 4

where is stratified sampling used

Answer 4

used in two areas different in habitat quality

Question 5

where is systemic sampling used

Answer 5

along a transect where there is an environmental gradient

Question 6

Strengths of random sampling

Answer 6

• unbiased
• suitable for large popluations

Question 7

limitations of random sampling

Answer 7

• many don have access to some sample points
• in a large study area, some points may miss some places

Question 8

strengths systematic sampling

Answer 8

coverage of a whole study area

Question 9

limitations of systematic sampling

Answer 9

• may be biased bc places have different chances of selection
• patterns may be missed or areas exaggerated

Question 10

strengths stratified sampling

Answer 10

• flexible (can be used in many situations)
• good for comparing subsets

Question 11

limitations of stratified sampling

Answer 11

• most know the size of the subsets to get an accurate picture

Question 12

biotic: ways to measure abundance of organisms that can move (motile)

Answer 12

• nets
• pitfall traps
• light traps
• flight interception traps

Question 13

biotic: ways to measure abundance of organisms that cannot move (non-motile)

Answer 13

• quadrats (square frames of difference sizes)
• point frames

Question 14

lincoln index, what is it used for?

Answer 14

estimating the pop. size of motile animals

Question 15

lincoln index, how does it work?

Answer 15

• organisms are captured, marked, released and then recaptured
• pop size is estimated by equation

Question 16

lincoln index equation

Answer 16

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

Question 17

limiations of lincoln index

Answer 17

• 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

Question 18

percentage cover

Answer 18

the proportion of a quadrats covered by a species, measured as a percentages (worked out for each species present)

Question 18

quadrat methods

Answer 18

• percentage freq.
• percentage cover
• pop. density

Question 18

percentage freq.

Answer 18

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

Question 18

pop. density

Answer 18

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

Question 19

why is biomass calculated

Answer 19

to show the total energy within a trophic level

Question 20

what is dry weight biomass

Answer 20

when water is removed before biomass is emeasured

Question 21

limitation of estimating biomass in trophic levels

Answer 21

• involves killing of living organisms
• problems exist with measuring biomass of very lagre plants such as trees, and with roots and underground biomass

Question 22

how to calc dry weight biomass

Answer 22

• 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

Question 23

to estimate total biomass

Answer 23

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

Question 24

how can we quantify species diversity

Answer 24

simpsons diversity index

Question 25

simpsons diversity index formula (you dont need to know formula off by heart, but need to know what symbols mean)

Answer 25

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

Question 26

what can we do w simpsons diversity index

Answer 26

• 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

Question 27

ecological gradient definition

Answer 27

found when 2 ecosystems meet or where an ecosystem ends
abiotic and biotic changes can be seen here

Question 28

transect

Answer 28

• way to measure changes along an ecological gradient
• 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

Question 29

quadrats used to measuring change along an environmental gradient

Answer 29

• frame quadrats, empty frames of known area
• gird quadrats, frames divided into 100 small squares
• point quadrats, made from a frame with 10 holes, inserted into the ground by a leg, pin dropped through each hole in turn + species touched are recorded, total number of pins touching each species is converted to % frequency data

Question 30

why measure changes made by human impact

Answer 30

human activities can change abiotic and biotic factors of an ecosystem

human impacts can include: toxins from mining activity, landfills, eutrophication, oil spills, oxerexploitation

Question 31

case study for measuring human impact

Answer 31

amazon rainforest
- logging + deforistation
- satellite images used to monitor amount taking place
-> reliable
-> can cover large area
-> monitors change over time
-> visual impact useful for motivating actions against logging + deforestation