topic 4a: organism in the environment

Ecology is the branch of biology that studies these relationships and tries to make sense of them.


Key terms

  • Ecosystem: It is all of the living (biotic) organisms in an area and all the non-living (abiotic) conditions

  • Habitat: The place an organism lives

  • Population: All the organisms of one species in a habitat

  • Community: All the different species in a habitat


Biotic and abiotic factors

Biotic and abiotic factors will affect population sizes and distribution of species within ecosystems


Biotic:

  • Food availability

  • Predators

  • Competition from other organisms

  • Infection from pathogens


Abiotic:

  • Sunlight

  • Temperature

  • pH

  • Water

  • Minerals

  • Soil type

  • Salinity (salt levels)

  • Wind


Investigating population sizes

  • Ecologists work to study and monitor ecosystems

  • Part of this is monitoring population sizes and how they are distributed in the ecosystem

  • This can sometimes be very challenging

  • Therefore scientists use sampling techniques to get an estimation which is much quicker


  • Ecologists use a piece of apparatus called a quadrat to take samples

  • Quadrat is a square metal frame, usually one meter length (we use half) but will vary depending on where and what you are sampling

Practical

TASK: Compare the population of daisies in two areas of the school playing fields.


  1. Mark out a 10 meter by 10 meter area using large tape measures in both locations A and B.

  2. Use the random number generator function on your calculator to choose coordinates along the tape measures.

  3. Place the bottom left corner of your quadrat and that point.

  4. Count the number of daisies in the quadrat and record it in the table.

  5. Repeat steps 2-4 for at least 9 further readings

  6. Calculate the mean number of daisies per quadrat for each area.

  7. Multiply mean number by the no. quadrats that could be placed in the field 


Use equation:

Field area / quadrat area x mean in each quadrat


  • By taking other data such as the physical environmental (abiotic) factors at each location you can hypothesise why the populations are different


What is biodiversity?

  • Biodiversity is a measure of the variety of different species in an ecosystem


  • In general a high biodiversity is a good thing

  • Ecosystems are more stable and able to survive changes in the environment

  • Human impacts on the planet have drastically reduced biodiversity/ These include deforestation, global warming and pollution

Investigating biodiversity and measuring distribution

TASK: Measure how the distribution of organisms changes across a woodland path.

  • This shows how distribution of a species changes across a habitat

  • You can also take abiotic factor readings and then investigate if there is a relationship between these and the distribution of the species

  • You will use a transect as well as a quadrat

  • Instead of placing the quadrat randomly, it’s placed along the transect systematically


Practical steps:

  • Lay your transect across the path

  • Place a quadrat every meter next to the transect

  • You could look at one species and see how it changes across the transect (or you could look at the number of different species in each quadrat to measure how biodiversiy changes)

  • If you are counting grass or something similar then it’s easier to look at the percentage of the quadrat covered by the grass rather than count individual organisms

  • For each quadrat you should also take some abiotic data e.g. light intensity, temperature, soil pH


Once you have your data you can then plot a graph against a particular abiotic factor (e.g. light intensity) for each quadrat to see if there is a correlation