Populations in ecosystems Flashcards
The graph shows how gross productivity and biomass in an area changed with time in the succession from bare soil to mature woodland.
( Graph shows two lines, biomass and gross productivity against time in years on the same graph, they both look like rate of reaction graphs however the biomass line doesn’t plateau and the gross productivity one curves into a slight dip towards the end of it )
Suggest appropriate units for gross productivity.
- Unit of energy
Explain the decrease in gross productivity as the woodland matures.
( they both look like rate of reaction graphs however the biomass line doesn’t plateau and the gross productivity one curves into a slight dip towards the end of it )
- More competition for light
- So reduced photosynthesis
Use your knowledge of succession to explain the increase in biomass during the
first 20 years.
( they both look like rate of reaction graphs however the biomass line doesn’t plateau and the gross productivity one curves into a slight dip towards the end of it )
- Pioneer species
- Change in abiotic conditions
- Increase in diversity of species
Use the information in the graph and your knowledge of net productivity to explain why biomass shows little increase after 100 years.
( they both look like rate of reaction graphs however the biomass line doesn’t plateau and the gross productivity one curves into a slight dip towards the end of it )
- Net productivity = Gross productivity minus respiratory loss
- Decrease in gross productivity
Suggest one reason for conserving woodlands.
- Conserving niches
On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis.
Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.
- Geographical isolation
- Separate gene pools
- Variation due to mutation
- Different selection pressures
- Selected organisms survive and reproduce
- Leads to increase in allele frequency
Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release recapture method to estimate the number of Anolis sagrei on one of these islands.
- Collect a sample, mark and release
- Method of marking mustn’t harm the organisms
- Leave sufficient time for lizards to distribute before collecting a second sample
- Population = no. of first sample x no. of second sample / no. of marked lizards in the second sample
Large areas of tropical forest are still found on some Caribbean islands.
The concentration of carbon dioxide in the air of these forests changes over a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the concentration of carbon dioxide in the air changes:
- over a period of 24 hours
- at different heights above ground.
- High concentration of CO2 is linked with respiration at night
- No photosynthesis at night
- In light, more CO2 is used than produced
- Decrease in CO2 concentration with height
- At ground level there’s less photosythesis
To reduce the damage caused by insect pests, some farmers spray their fields of crop plants with pesticide.
Many of these pesticides have been shown to cause environmental damage.
Bt plants have been genetically modified to produce a toxin that kills insect pests.
The use of Bt crop plants has led to a reduction in the use of pesticides.
Scientists have found that some species of insect pest have become resistant to the toxin produced by the Bt crop plants.
The figure below shows information about the use of Bt crops and the number of species of insect pest resistant to the Bt toxin in one country.
( Figure shows two graphs, a line and bar graph
( The line graph represents Bt crops and bar graph represents the amount of resistant species )
( Line graph is “ area used to grow Bt crops / 10^6 ha “ against “ time in years “ )
( Bar graph is “ number of species of insect pest resistant to Bt toxin “ against “ time in years “. )
( The area of Bt crops grow in years ( Line graph ), after 6 years of growth, resistant insects appear and are steady for 4 years and start to grow in numbers after ( Bar graph ) )
Can you conclude that the insect pest resistant to Bt toxin found in the years 2002 to 2005 was the same insect species?
Explain your answer.
- No, the graph only shows the number of species not the name of the species
One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect.
Was he correct?
Explain your answer.
- No
- Mutations are random
- Only rate of mutation is affected by environment
- Different species don’t interbreed
- So mutation cannot be passed from one species to another
There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin.
Explain why there was a time lag.
- Initially there’s few insects with favourable allele
- Individuals with favourable allele will have more offspring
- Takes many generations for favourable allele to become the most common allele
Ecologists used a method called proportional sampling to estimate the population size of an
animal species.
This method is based on assumptions.
Two of the assumptions are given below.
- They know the size of the area, A, where the animal population lives.
- The animals are uniformly distributed in this area.
To carry out the method, the ecologists:
- chose a region of known size, R, inside area A
- counted the number of animals in region R. They called this number S
- assumed that the number, S, would be in proportion to the size of the total population, P, in area A.
Proportional sampling can be used to estimate the population size of a species that is uniformly distributed.
What is a species?
- Organisms that can interbreed and produce fertile offspring
What is meant by uniformly distributed?
- Same number of organisms in each species
Use the letters A, R and S to write an equation showing how proportional sampling is used to estimate the total size of a population, P.
Show your working.
( - P = total population
- A = the area of which the animals live
- R = Region of known size
- S = the number of animals in region R )
- P = A x S / R
Population size can be estimated using proportional sampling or mark-release-recapture.
How do the assumptions made in proportional sampling differ from those made in mark-release-recapture?
In mark-release-recapture:
- There’s no assumption that the organisms are uniformly distributed
- Size of total area isn’t required
