An ecosystem is a physical environment with a particular set of conditions, plus all the organisms that live in it. An ecosystem can be natural or artificial. Natural ecosystems have high biodiversity, i.e. many different species of plants and animals coexist in the same .
Artificial ecosystems, for example, greenhouses, are designed and maintained for a particular purpose so they have lower biodiversity. Weedkillers, fertilisers and pesticides may be used in artificial ecosystems to prevent other animals and plants growing besides the crop. This leads to low biodiversity.
Forestry plantations are very very carefully set up, controlled and monitored. They will have less biodiversity due to the fact that they haven't been established for as long as natural woodland, and result from the relationships and interactions of the organisms that live there and their surroundings. Fewer species are introduced at the setting up stage and not all species survive the starts.
Fish farms show less biodiversity due to the shorter time they have existed unlike lakes. In the absence of many predators some fish species will thrive. Also there are fewer diseases which may result in too many of certain species reducing others.
A habitat is the part of the physical environment where an animal or plant lives. An organism will have adapted to its habitat, so it may be restricted to living there. It may only eat food there.
A community is the total number of individuals if all different populations of plants and animals that live together in a habitat at any one time.
A population is the total number of individuals of the same species that live in that certain area.
Ecosystems are self supporting in all factors, e.g. providing mates, shelter, but the one thing thy all rely on is an energy source (the sun) and producers at the bottom of the food chain.
The size and distribution of a population can be measures by using the following techniques:
Pooters are containers used to collect insects easily without harming them.
Sweepnets are used to collect insects in long grass or moderately dense woodland where there are lots of shrubs.
Pitfall traps are containers set into the ground that are used to catch small insects, e.g. beetles.
Quadrats are square frames that have sides usually 0.5m long. They are used to count a smaller, or representation of a population. You should throw them randomly on the ground, then count and record the number of each species within the quadrat. You can then estimate the population of each species in a given area.
When sampling, you must make sure you: take a big enough sample to make the results a good estimate - the larger the sample the more accurate the results. If you sample randomly - the more random the sample the more likely it is to be representative the population.
Capture - Recapture
Capture - recapture (also known as the Lincoin Index) is a method used to estimate a population size. Populations can be difficult to sample because species move around all the time.
Capture - recapture works as follows:
1. A trap is used to catch a sample of individuals, e.g. mice.
2. The sample is counted ans recorded and each individual is marked with a number tag/band or a dot of paint.
3. The individuals are released unharmed back into the enforcement, and are given time to redistribute themselves among the unmarked population.
4. Another sample of individuals is captured. Some of them are already marked and some of the unmarked.
5. The unmarked animals are counted and recorded. They are then marked and released.
Capture - Recapture (Continued)
This formula can then be used to estimate the total population size in the habitat:
No.in 1st sample (all marked) x no. in 2nd sample (marked and unmarked) Population size = ______________________________________________ No. in 2nd sample which were previously marked
When you use this method you have to:
- Assume thatno norganisms have died, immigrated or emigrated between sampling.
- Make sure that identicle sampling mathods are used from one visit to the next.
- Make sure that marking the organisms doesn't effect their survival, e.g. be careful when using paint on invertabrates because if too much is used it can enter their respiratory system and kill them.
The larger sample size, the more accurate the population size estimate.
A transect line is used to map the distribution of organisms. It is used for studies of how species changes across a boundary between habitats, e.g. a rocky shoreline.
1. A line like a tape measure is laid out.
2. Quadrats are distributes in regular intervals on the line, and the quadrats are counted.
Counting the animals and plants in quadrats along the line of a transect gives a lot of numbers, making it difficult to see trends and compare different parts of the habitat. So the data is presented as a kite diagram.
You can create a kite diagram by doing the following:
1. Use graph paper and begin by drawing a sketch of the habitat profile across the bottom to scale. 2. Draw a horizontal line above this and locate the quadrats - mark a vertical bar at each quadrat location (use 5 squares above and 5 squares below for Abundant, 4 for Common, 3 for Some, 2 for Few, 1 for only one). 3. Join the tops and bottoms of these bars. 'Not present' will be a point on the horizontal line, so the diagram that results will have a shape something like a kite. That is the profile and one species one. 4. Do the same for the next species, and so on.
Remember the presence or absence plus abundance of an organism is affected by other organisms in the area, e.g. predators, as well as other physical factor like the tides or water temperatures.
Correctly identifying species in a sample can be hard. Using keys can help to identify organisms correctly.
Here is an example of a simple key: