4. Communities and Ecosystems

Question 1

Do populations live in isolation?

Answer 1

no - they live together with other populations in ecological communities

Question 2

Define ‘community’.

Answer 2

a group of populations of different species living together and interacting with each other in an area.

Question 3

There are many types of interaction between populations in a community. Name one important relationship.

Answer 3

trophic relationships - where one population of organisms feeds on another population

Question 4

What is the complex network of feeding relationships in a community called?

Answer 4

a food web

If asked to describe what a food web is: “it shows how food chains are linked together into more complex feeding relationships within a community”

Question 5

What do communities of living organisms interact with?

Answer 5

their environment (duh)
- soil, water and air around them

Question 6

What is a communities ‘abiotic environment’?

Answer 6

the non-living surroundings

Question 7

How does a community form an ‘ecosystem’?

Answer 7

by the communities interactions with the abiotic environment

Question 8

Name one important interaction between community and abiotic environment?

I could equally have said: ‘Name one important interaction in an ecosystem?’

Answer 8

important interaction: transfer of chemical elements because these are an essential part of nutrient recycling

Question 9

Do ecosystems have the potential to be sustainable over long periods of time?

Answer 9

yes

Question 10

“If …. , ecosystems only require …. to continue indefinitely”. Fill in the blanks.

Answer 10

1 - nutrients are recycled

2 - a supply of energy, usually light,

Question 11

What experiment could you set up to show that “ecosystems only require a supply of energy and nutrients being recycled to continue indefinitely”?

Answer 11

a mesocosm - a small experimental area set up in an ecological research programme

Question 12

Draw a diagram of a mesocosm. (p55)

Answer 12

• 5 litre clear glass jar
• seal to prevent entry or exit of all chemical substances
• air containing oxygen and carbon dioxide
• mud from bed of pond
• pond water containing autotrophs, consumers, detritivores and saprotrophs

Question 13

Explain why autotrophs are in the mesocosm experiment. (p55)*

*This question may assume some knowledge about the mesocosm on page 55.

Answer 13

they are essential:

• produce carbon compounds
• regenerate oxygen use in cell respiration by other organisms in the mesocosm

Question 14

Explain why saprotrophs are in the mesocosm experiment. (p55)*

*This question may assume some knowledge about the mesocosm on page 55.

Answer 14

they are essential:

• decompose dead organic matter
• recycle nutrients

Question 15

Explain why consumers and detritivores are in the mesocosm experiment. (p55)*

*This question may assume some knowledge about the mesocosm on page 55.

Answer 15

may not be essential:

• normal part of ecosystems so they are included
• unethical to include large animals in mesocosms that cannot obtain enough food or oxygen

Question 16

What is a quadrat?

Answer 16

a square sample area used in ecological research

Question 17

How do you carry out quadrat sampling?

Answer 17

• locate an area and mark out gridlines along two edges of the area
• use random number generator to get two random numbers to use as coordinates
• place quadrat on ground with its corner at these coordinates
• record presence/absence of each species of interest inside the quadrat, or record number of individuals
• repeat with as many quadrats as possible

Question 18

What signals that you should do a chi-squared test?

Answer 18

if the presence or absence of two species is recorded in a large number of quadrats

Question 19

What does the ‘chi-squared test’ test?

Answer 19

in ecology it tests the association between two species

Question 20

Know how to do a chi-squared test. Dunno if you might be asked to do it in the exam.

Answer 20

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