Topic 10.1 The nature of ecosystems

Question 1

Define ecosystem

Answer 1

All of the organisms living in a particular area, and all the non-living conditions found there. Can vary from very large e.g. biome, to very small e.g. microhabitat.

Question 2

Define and name the trophic levels

Answer 2

Describes an organisms feeding relationship with other organisms i.e. its position in the food chain. Producer, primary consumer, secondary consumer, tertirary consumer, decomposer.

Question 3

Give three ways we can represent ecosytem structure

Answer 3

• Pyramids of numbers (counting)
• Pyramids of biomass
• Pyramids of energy

Question 4

Give pros and cons of the three pyramids

Answer 4

Number = easiest to measure, but can be distorted by large organisms.

Biomass = more accurate, but dry mass has to be used.

Energy = most accurate, but hardest to measure.

Question 5

Suggest methods of assessing abundence and distribution of organisms

Answer 5

• Quadrats; square frames placed at random in an area to be investigated
• Transects; line or belt that runs across the area being investigated

Question 6

Suggest different ways abundence can be quantified

Answer 6

• Percentage cover
• Frequency (individual counting)
• ACFOR scale (abundent, common, frequent, occasional, rare)

Question 7

Why might we calculate a spearman’s rank correlation coefficient?

Answer 7

To measure correlation between two variables, i.e. the extent to which changing one variable affects the other variable.

Question 8

Explain how Spearman’s rank results are interpreted

Answer 8

Closer to 1 = more positive correlation

Closer to -1 = more negative correlation

Around 0 = no correlation

Question 9

Why might we calculate a t-test?

Answer 9

To determine if the means of two sets of data are significantly different from each other.

Question 10

Explain how t-test results are interpreted

Answer 10

The t-value obtained is compared to a critical value (found in a table) for a particular p value chosen by the researcher. If the t-value is greater than the critical value, the difference is said to be statistically significant.

Question 11

What is a habitat?

Answer 11

The place where an organism lives e.g. a pond

Question 12

What is a community?

Answer 12

A group of different species interacting in the same habitat