2.5c Investigating Ecosystems (Abiotic Factors)

Question 1

What are “dichotomous keys”?

Answer 1

Dichotomous keys are a series of paired questions based on the physical characteristics of an organism.
There are a number of basic rules that must be followed when designing these keys:
- Use only visual/ observable characteristics
- Specific measurements if referring to size or weight
- Specific language in general

Question 2

What are the important rules of “dichotomous keys”?

Answer 2

• Use only visual/ observable characteristics
• Specific measurements if referring to size or weight

Question 3

What are some disadvantages of using “dichotomous keys”?

Answer 3

• May require some prior knowledge of terminology such as antenna, dorsoventral etc.
• Some organisms look very different at different stages in their life cycle.
• Parts of the organism may be damaged – lost a tail, leg etc.

Question 4

How do you measure biomass in the trophic levels?

Answer 4

• Decide on appropriate sampling size
• Identify 5 quadrats and harvest all vegetations in these
• Remove soil, insects and other NON-plant material
• Let dry (remove water content)
• Weigh it
• -> Keep repeating the dry and weigh stages to ensure the plant is actually completely dry, this is noticeable when the mass stays the same

Question 5

What are some disadvantages of measuring biomass in the trophic levels?

Answer 5

• Highly destructive as the vegetation is harvested and dried.
• Does not take account of underground mass (roots).
• Not very accurate for large vegetation like trees.
• It is not possible to get accurate figures for animals in the ecosystem.

Question 6

How do you measure energy in the trophic levels?

Answer 6

NPP = GPP - R
GPP –> biomass produced before respiration

Method:
All the same vegetation, all the same size. Quadrat B is covered in black sheeting (so no light reaches the plant)

In this example,
NPP = Quadrat C - Quadrat A
NPP = 100
whereas:
NPP = GPP - R
100 = GPP - 50
GPP = 150

Question 7

What’s a disadvantage of measuring energy in the trophic levels?

Answer 7

Highly unlikely all 3 quadrats are identical in terms of vegetation

Question 8

How do you measure secondary productivity?

Answer 8

Secondary productivity is that of animals in an ecosystem.
Given it’s unethical to kill animals any measurements would be inaccurate due to the variations in water content of different species.

GSP = food eaten - fecal loss 
NSP = GSP - R

Question 9

What’s a disadvantage of measuring secondary productivity?

Answer 9

• Not very accurate as it is not dry weight.
• Can only be used easily for small non-aggressive animals.
• Captivity may stress the animals and change their levels of productivity.

Question 10

What’s the definition of “species diversity”?

Answer 10

“Species diversity is the number of different species in a given area taking into account the richness and evenness of the species.”

Question 11

What’s the difference between richness and evenness?

Answer 11

Richness = measure of the number of different species in an area
–> more species means a richer environment

Evenness –> looks at the relative abundance of the species

Question 12

What’s the Simpson Diversity Index?

Answer 12

Index that combines richness and evenness

• N = total number of organisms of all species found
• n = number of individuals of a particular species

Question 13

What are some ways to record motile organisms?

Answer 13

• Traps
• Nets
• Pitfall Traps
• Aerial Photography

Question 14

What’s a problem with traps?

Answer 14

“Trap Happy”
–> animals are happy with being trapped as it gives them a secure bed and food + habituates them to humans

Question 15

How are sweep nets used?

Answer 15

Sweep nets
–> used to capture flying insects (swept through vegetation)
HOWEVER: easy to miss a lot of insects in dense vegetation

Question 16

How is kick sampling used?

Answer 16

• One person stands downstream with a net
• One meter upstream another person kicks the sediment and moves towards the net
• -> This disturbs invertebrates and a few small fish
• -> get caught in the net
• Empty the contents of the net
• -> count number of each type of organism

Question 17

What is a disadvantages of nets?

Answer 17

Very stressful for birds and bats and can result in injury.

Question 18

What is a pitfall trap and what should be watched out for when setting one up?

Answer 18

Basic principal is that there is a container sunk into the ground into which an organism can fall

HOWEVER:

• never put liquid in the bottom as it can drown the organism
• add holes in the bottom to allow water to drain out
• add food and bedding
• some sort of cover to keep rain and sunlight out

Question 19

What is Aerial photography?

Answer 19

This method can be used to investigate larger animals that live in open grassland environments
–> A grid can then be drawn over the photographs and a sample of squares identified using an appropriate sampling strategy

Question 20

What is the Lincoln Index?

Answer 20

This is an indirect method by which the size of an animal population can be estimated

• -> also called the “capture/mark/release/recapture” method
• usage is becoming more restricted to invertebrates and small mammals

Question 21

How do you carry out the Lincoln Index calculations?

Answer 21

Method:

• Capture as many animals as possible
• Record the number of animals that were caught
• Mark the organisms
• Release the animals back into their environment
• Capture again and record the organisms that were caught
• N = total population.
• n1 = number of animals marked in the first capture and released.
• n2 = number of animals recaptured (second sample).
• m2 = number of animals marked in the recapture (second sample).

Question 22

What are some assumptions of the Lincoln Index?

Answer 22

• proportion of animals marked in the second catch is the same as the proportion of marked to unmarked animals in the entire population
• enough time has elapsed to allow full mixing of marked and unmarked animals
• all animals are just as easily caught
• population is closed (no immi- or emigration)

Question 23

What are some problems of the Lincoln Index?

Answer 23

• Capturing the animals may injure them or alter their behavior.
• The mark may be toxic to some animals but not others – you may not know until it is tested on the organism under study.
• Marks may rub off between release and recapture.
• Marks may make the animal more or less attractive to predators.