Chapter 19 - Populations in ecosystems

Question 1

What is ecology

Answer 1

Ecology – the study of the inter-relationships between organisms (living) and their environment (non-living).

Question 2

What is the definition of a population

Answer 2

Population = number of individuals of the same species in the same habitat at the same time. That can breed to create a fertile offspring
Populations are dynamic as they change in size and composition

Question 3

labelled image of population graph

Answer 3

Question 4

Why is there a lag phase in a population graph

Answer 4

Lag phase – small number of bacteria, getting used to conditions but not dividing

Question 5

Why is there a log phase in a population graph

Answer 5

Exponential or log phase - exponential growth with bacteria dividing by binary fission, doubling in number for every generation. No limiting factors

Question 6

Why is there a stationary phase in a population graph

Answer 6

Stationary phase - growth reaches a plateau as the number of dying cells equals the number of dividing cells. Resources (e.g. respiratory substrate, oxygen) become limiting.

Question 7

Why is there a death phase in a population graph

Answer 7

Death phase - exponential decrease in the number of living cells. Resources run out and waste products reach toxic levels.

Question 8

What are the two types of population growth that are shown on population graphs

Answer 8

logistic growth - will reach a carrying capacity
exponential growth - no limiting factors

Question 9

graph of logistic growth

Answer 9

Question 10

graph of exponential growth

Answer 10

Question 11

Answer 11

Question 12

What are some examples of abiotic factors

Answer 12

• Temperature
• Light
• pH
• Water availability
• Humidity
• Oxygen levels

Question 13

Answer 13

Question 14

What are some examples of biotic factors

Answer 14

• Competition
• Predation
• Disease

Question 15

What is intraspecific competition

Answer 15

• Competition between individuals of the same species
• The more resource present, the less competition so the population gets larger
• The less resource present, the more competition so the population gets smaller

Question 16

What is interspecific competition

Answer 16

• competition between individuals of the different species

Question 17

Examples of interspecific competition

Answer 17

• Food
• Light
• Water

Question 18

What is the competitive exclusion principle

Answer 18

• Where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other.
• No two species occupy the same niche indefinitely.

Question 19

What is the definition of a niche

Answer 19

• the role an organism plays in the ecosystem
• e.g. what resources do they use, what do they eat, what eats them, what do they provide shelter for.

Question 20

What is predation

Answer 20

• When one organism (the predator) consumes another (the prey)
• Demonstrated in predator – prey cycles in natural environments
• Example: snowshoe hare and Canadian lynx

Question 21

example of a predator prey cycle

Answer 21

Question 22

What happens at each stage of the predator prey cycle

Answer 22

Question 23

What can cause an ununiform predator prey cycle graph

Answer 23

• Predators normally have other sources of food (more than one type of prey)
• Disease and climatic factors

Question 24

What is the definition of abundance

Answer 24

the number of individuals of a species in a given area (measured as frequency (number of) or percentage cover)

Question 25

What is the definition of distribution

Answer 25

where a species occurs within a given area With both of these you can investigate both the species and the factors influencing abundance or distribution – abiotic and biotic factors Distribution and abundance will both give you quantitative data

Question 26

What is sampling

Answer 26

* Used to provide an estimate of quantitative data * Less time consuming * Large number of samples needed to be representative of whole population

Question 27

What are the two types of quadrats

Answer 27

* Frame quadrats * Point quadrat

Question 28

what are the features of frame quadrats

Answer 28

* Open or gridded * Give a 2D (top down) image of area * Used with low level vegetation * Vary in size depending on size of organism sampled, and area

Question 29

what are the features of point quadrats

Answer 29

* Used with taller, layered vegetation * Give a 3D (side on) image of area * Count the number of times plants touch the pins

Question 30

what are the features of random sampling

Answer 30

* Random – reduces bias * Used to compare abundance in different areas * Non-motile organisms * Example: lichen on north and south side of a wall

Question 31

What is the method for random sampling

Answer 31

1. Use a tape measure to divide area into squares/sections 2. Obtain random coordinates using a calculator 3. Place quadrat at random coordinates 4. Count number of X in a quadrat and record 5. Use a large sample and calculate mean number per quadrat 6. Calculate total number of X in area e.g. mean number of plants per quadrat multiplied by number of quadrats in area (If question asks about comparing two areas – include: 7. Repeat for other area and compare)

Question 32

What are the features of systematic sampling

Answer 32

* Systematic – at regular intervals along a transect * Non-motile organisms * Used to investigate distribution along an environmental gradient * Can form a continuous belt transect * Example – light intensity as you move out from under a tree

Question 33

What is the method for systematic sampling sampling

Answer 33

1. Lay a tape measure along the length of the environmental gradient 2. At regular intervals along the transect, place a quadrat 3. Count the number of X in a quadrat and record 4. Continue for the length of the transect 5. Repeat for several parallel transects and calculate mean number in quadrat at each distance If the question asks about an abiotic factor, take readings for this in each quadrat

Question 34

What is the method for mark release recapture

Answer 34

Capture/collect sample, mark and release (ensure marking is not harmful) Allow time for organism to randomly distribute before collecting a second sample population = (number in first sample x number in second sample) / number recaptured

Question 35

What are the assumptions required for mark release recapture

Answer 35

* The marked sample must have time to mix back in with population * Marking must not affect survival of the organism – not toxic or increase risk of predation * No changes in population during period of the investigation

Question 36

What is succession

Answer 36

succession is a change in species in an area over time. It is caused by a change in abiotic factors brought about by species living in an area

Question 37

What are the stages in succession

Answer 37

1. Colonisation by pioneer species e.g. lichen 2. Species change the environmental conditions e.g. soil forms and organic matter and nutrient levels increase 3. Environment becomes less hostile  4. Leads to new species able to colonise 5. Previous species out-competed. 6. Increase in biodiversity as more food sources and habitats arise 7. Stable climax community is reached

Question 38

What is secondary succession

Answer 38

* Occurs on land that has previously been colonised * Land is altered due to fire, disease, grazing or agriculture * Soil remains with seeds and spores * Succession starts again and reaches the climax community much faster

Question 39

diagram for primary succession

Answer 39

Question 40

overall diagram for succession

Answer 40

Question 41

What are the similarities between primary and secondary succession

Answer 41

* Species change the abiotic factors to make them less hostile so new species can colonise and outcompete current species * Both increase in biodiversity and stability with time * Both end in a climax community

Question 42

What are the differences between primary and secondary succession

Answer 42

* Primary succession begins with barren land and secondary succession starts with land altered by e.g. fire, grazing, agricultural land clearance * Secondary succession already has soil containing seeds and spores but primary succession is barren with no soil

Question 43

What is the conservation of habitats

Answer 43

* Conservation is the protection and management of ecosystems * It often involves preventing succession reaching the climax community * It involves human intervention either directly or indirectly