6.5.6 studying ecosystems

Question 1

describe quadrats

Answer 1

• often 1m square
• can have strings across every 10m = separates into 11 smaller squares

Question 2

what 2 types of data can be collected using quadrats

Answer 2

1. presence or absence of each species (distribution)
   = usually at least 50% of plant needs to be inside quadrat to count
2. number of individuals (abundance) of each species
   - estimated or counted
   - for some species (eg. moss, grass) it is difficult to count individuals so ecologists often estimate percentage cover

Question 3

what can help with estimating percentage cover of a species

Answer 3

= using a point frame

• lower frame into quadrat & record plants touching needles
• if frame has 10 needles, lower it 10 times in each quadrat (= 100 readings)
• bare ground must be recorded

Question 4

decisions to be made before starting sampling (quadrat)

Answer 4

1. where to place quadrat
   - if take samples from only 1 corner of field, the soil may be especially rich in nitrogen & species growing there are different to those in rest of field
2. how many samples to take
   - in a pilot study looking at species distribution, take random samples from across fields & make cumulative frequency table
   - plot cumulative frequency against quadrat number & point where curve levels off tells you how many quadrats to use

Question 5

how can you avoid biasing the sample & provide sample which is representative of whole habitat (quadrat)

Answer 5

either:

1. randomly position quadrats across habitat, using random numbers to plot coordinates for each one (random sampling)
   - lay out 2 tape measures on 2 edges of study site (look like axes on graph)
   - use calculator or pair of dice/random number table to generate pairs of random numbers
   - use pairs as coordinates to place quadrats & lay bottom left hand corner of quadrat at coordinate
2. take samples at regular distances across habitat, so sample every part of habitat to same extent (systematic sampling)

Question 6

equation to estimate population size of each species in whole habitat (quadrat)

Answer 6

(mean number of individuals of species in each quadrat) divided by (fraction of total habitat area covered by single quadrat)

Question 7

ways of sampling ecosystems

Answer 7

• quadrats
• transects

Question 8

what do transects look for

Answer 8

changes in vegetation across a habitat

Question 9

2 approaches to using a transect

Answer 9

1. line transect
   = at regular intervals & make notes of which species touching the tape
2. belt transect
   = at regular intervals place quadrat next to line (interrupted belt transect) or place quadrat next to line & move it along the line after looking at each quadrat (continuous belt transect)

Question 10

what does the distance between samples on a transect depend on

Answer 10

• length of line being looked at
• density of plants in habitat

Question 11

how can the way living things vary along the transect line be understood

Answer 11

• could compare number of organisms of each species at each sampling point along transect line
• could also plot abiotic factors (eg. soil temperature) on same scale, with distance on x-axis & temperature on y-axis = by lining up graph with kite diagram, can start to see how temperature affects distribution/abundance