Measuring abundance
The abundance of a species relates to how many members of a species is present within an ecosystem. Abundance can be measured by counting all the individual organisms that occur within the organism, however there are a variety of difficulties in relation to this method. Commonly the organism being studied is scattered throughout an ecosystem and this consequently results in the process being very time consuming. Different techniques are available that can be used to measure the abundance of an organism based on the entity being studied. It is both quick and easy to study abundance using quadrats.
Quadrats:
Abundance is measured using a device called a quadrat, which is simply a grid that is typically one metre by one metre placed randomly at different locations within an ecosystem. The sample of plants or animals that are within each quadrat are measured and a population estimate is made using a quadratic equation. (The estimated population = Average count per quadrat x The study area or quadrat area.) At Home bush bay ten, one meter by one meter quadrat's were placed at five metre intervals gaining proximity to the creek. Within each quadrat, The abundance of seedlings and crab holes was measured.
Materials:
- 1m by 1m quadrat
Methodology:
1. Randomly throw a quadrat 50 meters from the creek at Home bush bay.
2. Measure and record the abundance of seedlings and crab holes within the quadrat.
3. Repeat steps one and two at 5 meter intervals gaining proximity to the creek.
4. Calculate the total number of seedlings and multiply that by the total area sampled.
5. Calculate the total number of crab holes and multiply that by the total area sampled.
6. Estimate using the quadratic equation the abundance of the seedlings and the crab holes.
Results:
Seedlings - The seedlings were more abundant further away from the river because they have a greater chance of survival due to the fact that they have a lower frequency of tidal inundation.
Crab holes - There were a greater number of crabs closer to the creek due to the fact that they have better access to food sources such as algae and dead leaves. Consequently the mangrove crabs are able to support a greater population.
Capture - Recapture
The method of capture-recapture allows researchers to obtain a population estimate on mobile organisms. This sampling technique involves the temporary capture of the desired organism, these creatures are tagged and released. Another sample of organisms are caught and tagged. The number of previously tagged animals are counted and substituted in to the equation;
Estimated population =
First capture x second capture
---------------------------------------------------------------
Number of tagged organisms in second capture
Quadrats:
Abundance is measured using a device called a quadrat, which is simply a grid that is typically one metre by one metre placed randomly at different locations within an ecosystem. The sample of plants or animals that are within each quadrat are measured and a population estimate is made using a quadratic equation. (The estimated population = Average count per quadrat x The study area or quadrat area.) At Home bush bay ten, one meter by one meter quadrat's were placed at five metre intervals gaining proximity to the creek. Within each quadrat, The abundance of seedlings and crab holes was measured.
Materials:
- 1m by 1m quadrat
Methodology:
1. Randomly throw a quadrat 50 meters from the creek at Home bush bay.
2. Measure and record the abundance of seedlings and crab holes within the quadrat.
3. Repeat steps one and two at 5 meter intervals gaining proximity to the creek.
4. Calculate the total number of seedlings and multiply that by the total area sampled.
5. Calculate the total number of crab holes and multiply that by the total area sampled.
6. Estimate using the quadratic equation the abundance of the seedlings and the crab holes.
Results:
Seedlings - The seedlings were more abundant further away from the river because they have a greater chance of survival due to the fact that they have a lower frequency of tidal inundation.
Crab holes - There were a greater number of crabs closer to the creek due to the fact that they have better access to food sources such as algae and dead leaves. Consequently the mangrove crabs are able to support a greater population.
Capture - Recapture
The method of capture-recapture allows researchers to obtain a population estimate on mobile organisms. This sampling technique involves the temporary capture of the desired organism, these creatures are tagged and released. Another sample of organisms are caught and tagged. The number of previously tagged animals are counted and substituted in to the equation;
Estimated population =
First capture x second capture
---------------------------------------------------------------
Number of tagged organisms in second capture