Transects and Quadrats Rock Platform 1-2 lessons PDF

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MEASURING DISTRIBUTION AND ABUNDANCE  The distribution is where the population of a species is spread within an ecosystem. The distribution of plants often depends on the amount of moisture available. The distribution of animals depends on the vegetation available as food.  The abundance (the number of individuals in a population) of an organism varies from one part of the distribution to another.  Both distribution and abundance can change year by year.  The abundance can change even if the distribution does not. In field studies it is usual to measure the distribution and abundance of different animal and plant populations. To count all the organisms in a given population is usually not practical so scientists have developed a variety of sampling methods to estimate the distribution and abundance of species. The method used depends on the type of species.

Quadrats A quadrat is a square, rectangular or circular frame of chosen size. It is used to mark out an area in which the vegetation is to be sampled. The shape and size of the quadrat depends on the type of vegetation. Quadrats may be located randomly over the area being sampled or at regular intervals along a transect or grid.

Transects A transect is a cross section through an area. It is used to record the type and number of species present. It is useful for recording the relationship between a species and the abiotic factors in the area.

Capture-recapture  It is more difficult to estimate the population of animals than plants. This is due to the movement of animals, many animals being nocturnal, hiding and being scared off by the researcher.  This method involves tagging or marking a sample of the population and then releasing it.  The proportion of marked animals in subsequent recaptured samples gives a reasonable estimate of the total population: Total population = number of animals tagged x number of animals recaptured average number of tagged

animals recaptured

ON-LINE PRACTICAL ACTIVITY: MEASURING DISTRIBUTION AND ABUNDANCE OF ORGANISMS ON A ROCK PLATFORM Transect Technique A transect is a line across a site. At regular intervals a quadrat is placed along the tape for detailed examination. This virtual field study at the link is of the rock platform at Barwon Heads in northern NSW. http://www.rockyshores.net.au/virtual_fs.htm Use the photographs at the link to develop skills in data collection. Each photograph represents one sample taken at each of the intervals on Transect B. Each photo contains a quadrat and the organisms found at that sample point on the rocky shore. Photos start at 0m and extend to the low tide mark at 60m with 5m intervals between each sample. Using the Photos  In the photos of the quadrats identify the different organisms present, using the identification chart on page 4. For example, in the quadrat at 0m the only organism present is the little blue periwinkle.  In your group, count the numbers of animals of each species for the intervals you are assigned and record these in the Table 1 on page 3 (these tables will be put in a Google Doc for sharing). In your group, determine the most efficient method of counting the organisms eg, each take one quarter of the quadrat and count the number of each organism present in that quarter.  Estimate the percentage of cover for the different types of algae found on the rocks.  Write a brief description of each quadrat eg, is it high and dry, shallow crevices, deep pool

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 Summarise the findings in terms of predominant animal(s) and algae at each interval on the transect on page 5 Table 1: Data on animal and algal distribution from transect study Types of animals and Types of algae and % Distance number of each coverage of each along transect (m) 0 Little blue periwinkle 150 No algae present 5

1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5 6 0

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Description of quadrat

Dry, shallow crevices

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Quadrat Technique The images on the following two pages are of 5 random quadrats taken across the rock platform. This technique will be used to estimate the total population size on the platform for two species: the conniwinks and pink coralline algae. Instructions: 1. In your group, count the number of conniwinks and the % coverage of pink coralline algae for the quadrat assigned. 2. Record the data in Table 2 3. Calculate the average for number of conniwinks and % coverage of pink coralline algae in the quadrats. 4. Use the data below to estimate the total population size for this section of the rock platform. Table 2: Data on number of conniwinks and % coverage of pink coralline algae using random quadrats Quadrat number 1 2 3 4 5 Average

Conniwinks (number)

Pink coralline algae (% coverage)

   

Use the example in the diagram above to work out relationship between quadrat size and total habitat. 

Area of the rock platform habitat being sampled is 500m2.

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Each quadrat is 0.5m x 0.5m = 0.25m2 in area.

How many quadrats will fit in the habitat? Show your working.

What is the total population size for conniwinks and pink coralline algae in the habitat? Show your working.

QUADRAT 1

QUADRAT 2

QUADRAT 3

QUADRAT 4

QUADRAT 5

Capture–mark– recapture method Online virtual lab to use this method to estimate the size of a grasshopper population in a meadow, http://www.classzone.com/books/hs/ca/sc/bio_07/virtual_labs/virtualLabs.html

Modelling Capture-Recapture with Materials at Home 1. Obtain a cup containing 30+ objects, eg: smarties, dried beans, pasta 2. From the cup, CAPTURE a handful of beans. Count the number of beans that you’ve captured. Mark each of them with a marker. How many beans did you mark? (This number will be important for Questions 8 and 9.)

3. Put the marked beans back in the cup and shake up the cup. 4. From the cup, RECAPTURE a new handful of beans. 5. Count the number of total number of beans in your recapture and the number of marked beans. Record in the table. Return to the cup. 6. Repeat steps 4-5 for a total of ten trials.

TRIAL NUMBER

NUMBER OF MARKED BEANS IN RECAPTURE

TOTAL NUMBER OF BEANS IN RECAPTURE

1 2 3 4 5 6 7 8 9 10 Average

Total population = number of animals tagged x average number of animals recaptured average number of tagged animals recaptured

= Conclusion: How close was your estimate to the actual number of objects in your population? If you weren’t close can you think of reasons why? Name an animal population you would count using this method?...