Populations in ecosystems

Question 1

What is an ecosystem?

Answer 1

Made up of a community and all of the non-living components of the environment. They are very dynamic systems

Question 2

What are the three phases in the usual pattern of growth for a natural population?

Answer 2

• period of slow growth - as organisms adjust to their environment
• period of rapid growth - ever-increasing number of individuals continue to reproduce
• period where population growth declines until stable - always fluctuations because food supply changes, disease, resource exhaustion and migration in/outward

Question 3

What can cause the size of a population to vary?

Answer 3

• abiotic factors
• interactions between organisms (inter/intraspecific competition)

Question 4

What is ecological niche?

Answer 4

How an organism fits into its environment, involving its adaptation to both biotic and abiotic factors which allow it to survive, reproduce and maintain a viable population

Question 5

How should you plot a growth curve when growth occurs rapidly?

Answer 5

Using log number of individuals

Question 6

Why does bacteria population eventually level off?

Answer 6

Initially there are no limiting factors so growth is rapid

• mineral ions are consumed as population grows larger
• bacteria at surface prevent light from reaching those beneath
• other species may be introduced which use the bacteria for food, or compete for light and mineral ions
• winter brings lower temperatures and lower light intensity

Question 7

What are some abiotic factors?

Answer 7

• temperature
• pH
• light/shade
• water and humidity

Question 8

What are some biotic factors?

Answer 8

• food supply
• predation
• inter/intraspecific competition
• disease

Question 9

How does light affect the organism?

Answer 9

• photosynthesis rate increases as light intensity increases
• opening of stomata
• kinesis

Question 10

How does wind/water current affect the organism?

Answer 10

• transpiration rates
• evaporation of water from animals
• seed dispersal - effects competition

Question 11

How does water/humidity affect the organism?

Answer 11

• transpiration rates
• evaporation from animals

Question 12

How does pH affect the organism?

Answer 12

• tertiary structure of enzymes

Question 13

How does temperature affect the organism?

Answer 13

• enzymes
• kinetic energy
• lower temp = more dissolved O2

Question 14

What techniques can be used to investigate populations?

Answer 14

• transect sampling - tape is stretched along a habitat and measurements taken at regular intervals (where conditions and organisms change over distance)
• gridded frame quadrat sampling - gridded quadrat placed at random coordinates ( collects frequency data)
• open frame quadrant sampling - quadrat without subdivisions placed at random coordinates (estimates percentage cover)
• point quadrat sampling - horizontal bar with 10 holes at set intervals, a pin is dropped into the holes and each species touching the pin can be counted (estimates percentage occurrence of individuals)

Question 15

How can you measure abundance of species?

Answer 15

• frequency eg. if the species occurs in 15/30 quadrats, frequency is 50%
• percentage cover

Question 16

How can you estimate population size through mark-release-recapture?

Answer 16

(number of species in sample 1 x number of species in sample 2) / number of marked individuals recaptured

Question 17

What assumptions does mark-release-recapture rely on?

Answer 17

• proportion of marked and unmarked individuals remains the same
• animals will evenly redistribute themselves
• must have a definite boundary (no in/outward migration
• no/few births and deaths
• method of marking is non-toxic and does not make the individual more/less likely to survive
• mark cannot be rubbed off

Question 18

What is succession?

Answer 18

How ecosystems change as new species colonise. Can result in a less hostile environment which makes it more likely for species to survive

Question 19

What are the stages of succession?

Answer 19

• initially a pioneer species will colonise. These pioneer species will make up a pioneer community
• the pioneer community will eventually die and decompose, and biological weathering will occur on rocks, releasing sufficient nutrients to support a colony of small plants. This creates a layer of top soil called humus and more favourable conditions
• death and decomposition of plants creates a thicker layer of soil that holds organic material and water, making it easier for more plants to grow
• the environment becomes less hostile, more species develop that act as food sources, food chains develop into complex food webs and communities become stable
• climax community consisting of animals and plants

Question 20

What does succession lead to?

Answer 20

• abiotic environment becomes less hostile
• greater variety of habitats and niches
• increased biodiversity
• more complex food webs
• increased biomass

Question 21

What are the reasons for conservation?

Answer 21

• personal - to maintain our planet and therefore our life support system
• ethical - other species have occupied the earth longer than us and should be allowed to coexist, respect is preferable to disregard
• economic - gigantic gene pool which can make millions of substances which may prove valuable in the future
• cultural and aesthetic - habitats and organisms enrich our lives, variety adds interest to everyday life and can inspire others eg. writers/poets/artists who entertain and fulfil us

Question 22

How can succession be prevented?

Answer 22

• temporarily introduce grazing animals to stop plants establishing themselves
• controlled fires to burn away shrubs and trees

Question 23

What impact does farming have on species diversity?

Answer 23

reduces diversity due to pesticides and monoculture

Question 24

What impact does farming have on genetic diversity?

Answer 24

decreases genetic diversity because farmers select for certain characteristics eg. crops with greatest yield, cows with greatest milk production, so the number of alleles within the population is reduced

Question 25

What is sampling?

Answer 25

selecting a group of individuals to measure that will represent the whole population