Pop. Size & Ecosystems

Question 1

Define ecology.

Answer 1

The study of the relationships among organisms and their environment.

Question 2

Define ecosystem.

Answer 2

• The community of organisms (biotic) and non-living (abiotic) components of an area and their interactions
  Vary from very large, e.g. biome, to very small, e.g. microhabitat.

Question 3

Describe biotic and abiotic factors, giving
examples.

Answer 3

• Biotic - living features of an ecosystem, e.g. predators, disease
• Abiotic - non-living features of an
  ecosystem, e.g. light, temperature

Question 4

Define community.

Answer 4

All of the populations of different species
living together in a habitat.

Question 5

What is a habitat?

Answer 5

The region where an organism normally lives.

Question 6

Define population.

Answer 6

All organisms of the same species living with one another in a habitat at the same time.

Question 7

Define niche.

Answer 7

Describes how an organism ‘fits’ into an
ecosystem and its role in that environment.

Question 8

What do population numbers depend
on?

Answer 8

Birth rate
Death rate
Immigration
Emigration

Question 9

Define birth rate and death rate.

Answer 9

• Birth rate - the number of offspring born per thousand of population per year
  Death rate - the number of deaths per thousand of population per year

Question 10

What is immigration?

Answer 10

The number of individuals entering a region per thousand of population per year.

Question 11

What is emigration?

Answer 11

The number of individuals leaving a region per thousand of population per year.

Question 12

When do population sizes increase?

Answer 12

When births and immigrants are greater than deaths and emigrants.

Question 13

When do population sizes decrease?

Answer 13

When deaths and emigrants are greater
than births and immigrants.

Question 14

Describe the phases of population growth.

Answer 14

• Lag phase - period of slow population growth
• Log phase - period of rapid exponential population growth in which birth rate exceeds death rate
• Stationary phase - period of stability in which population numbers generally remain constant

Question 15

What is carrying capacity?

Answer 15

• The average size of a population that can be supported by an ecosystem over extended periods of time
• Varies depending on biotic and abiotic factors

Question 16

What is competition?

Answer 16

• When different organisms compete for the same resources (e.g. light, water, mates, territory) in an ecosystem
• Limits population sizes

Question 17

Describe density-dependent and density-independent factors, giving examples.

Answer 17

• Density-dependent factors - factors whose effects on population size differ with population density, e.g. competition, predation, disease
• Density-independent factors - factors whose effects on population size remain the same regardless of population density, e.g. climate

Question 18

What is abundance?

Answer 18

The number of individuals per species in a specific area at any given time.

Question 19

What is distribution?

Answer 19

The spread of living organisms in an ecosystem.

Question 20

What is sampling?

Answer 20

Selecting a group of individuals that will represent the whole target population. Allows us to measure the distribution and abundance of organisms.

Question 21

Suggest methods of assessing abundance and distribution of organisms.

Answer 21

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

Question 22

Suggest different ways abundance can be quantified.

Answer 22

• Percentage area cover
• Percentage frequency
• Density

Question 23

What is random sampling?

Answer 23

A sampling technique used to avoid bias, e.g. creating a square grid and generating random coordinates.

Question 24

What is systematic sampling?

Answer 24

Sampling technique used to determine the abundance and distribution of organisms along an area at periodic intervals, e.g. along a belt transect
* Commonly used in ecosystems where some form of gradual change occurs

Question 25

What is the source of energy for an
ecosystem?

Answer 25

Light energy
(other than ecosystems that rely on chemosynthesis)

Question 26

What is a trophic level?

Answer 26

The position that an organism holds in a food chain, food web, pyramid of numbers or pyramid of biomass.

Question 27

What is biomass and how is it transferred? How can we measure this?

Answer 27

The total weight of living matter in a certain area, transferred up trophic levels through consumption
Measured in terms of mass of carbon, or dry mass of tissue

Question 28

State the formula for efficiency of biomass transfer.

Answer 28

Efficiency = biomass transferred/biomass intake
x100

Question 29

Why is some energy never taken in at
each trophic level?

Answer 29

Some parts of food aren’t consumed
* Some parts of food are indigestible
Plants can’t use all light energy as some is the wrong wavelength

Question 30

Why is some energy lost at each trophic
level?

Answer 30

Respiration, lost as heat.

Question 31

What is a pyramid of biomass?

Answer 31

A table of the dry mass of living material at each trophic level of a food chain. This forms the shape of a pyramid.

Question 32

What is meant by net and gross primary productivity?

Answer 32

Gross primary productivity (GPP) - the rate of chemical energy fixture during photosynthesis by all producers in an ecosystem, measured in kJ m2 year-1

Net primary productivity (NPP) - the amount of chemical energy that is available to heterotrophs in an ecosystem

Question 33

How is net primary productivity calculated?

Answer 33

Calculated by subtracting chemical energy generated in respiration (R) from gross primary production:

net primary production (NPP) = gross primary production (GPP) - respiratory losses (R)

Question 34

What is meant by primary succession?

Answer 34

Where an area previously devoid of life is colonised by pioneer species.

Question 35

What is a pioneer species?

Answer 35

• Pioneer species colonise the area. They die, decompose and add nutrients to the ground
• Over time, this allows more complex organisms to survive

Question 36

What are seres?

Answer 36

Various intermediate stages in succession in an ecosystem progressing towards a climax community.

Question 37

Define secondary succession.

Answer 37

A type of succession in which a habitat is re-colonised after a disturbance.

Question 38

What is the climax community and how is it reached?

Answer 38

• The final stage of succession, where the
  ecosystem is balanced and stable
• Reached when the soil is rich enough to support large trees or shrubs and the environment is no longer changing

Question 39

How does succession affect species diversity and the stability of a community?

Answer 39

Succession increases species diversity
and the stability of the community.

Question 40

Give some examples of organisms that play an important role in decay.

Answer 40

• Detritivores - feed on dead organic matter
• Saprotrophs - feed by extracellular digestion

Question 41

Describe extracellular digestion by saprotrophs.

Answer 41

They release enzymes which catalyse the breakdown of dead plant and animal material into simpler organic matter.

Question 42

What is the carbon cycle?

Answer 42

The cycle through which carbon (in the form of carbon dioxide) moves between living organisms and the environment, involving respiration, photosynthesis and combustion.

Question 43

Describe the stages of the carbon cycle.

Answer 43

1. Photosynthesising plants remove CO2 from the atmosphere
2. Eating passes carbon compounds along a food chain
3. Respiration in plants and animals returns CO2 to the atmosphere
4. Organisms die and decompose. Saprotrophs break down dead
   material and release CO, via respiration
5. Combustion of materials (e.g. wood, fossil fuels) releases CO2