Populations Booklet

Question 1

What is an ecosystem? (1)

Answer 1

A dynamic system made up of a community and all non-living factors of its environment. They range in size.

Question 2

New Zealand pygmy weed has been introduced into many garden ponds and has spread to some natural ponds. Here, it competes with naturally occurring plants. Suggest how the introduction of pygmy weed may lead to a reduction in the biodiversity of the community in a natural pond. (3)

Answer 2

Interspecific competition - there is competition for resources eg light. This means there will be a reduction in the species. As a result, the consumers die.

Question 3

Give one advantage of calculating the index of diversity rather than just recording the number of species present. (1)

Answer 3

It shows the population sizes of the organisms (as well as the number of species).

Question 4

Explain what is meant by the ecological term ‘community’.

Answer 4

ALL of the populations of different species living and interacting in the same place at the same time.

Question 5

Suggest and explain one advantage to the fish of occupying different depths in the lake. (2)

Answer 5

At different depths there may be a greater availability of food as there is less competition between fish for prey.

Question 6

The position of the tree line is determined by abiotic factors.
What is meant by an abiotic factor? (1)

Answer 6

Non living factors, eg temperature, in an environment that influences the size of a population.

Question 7

Suggest abiotic factors that are likely to affect the position of a tree line on a mountain.

Answer 7

• rainfall
• light
• CO2
• wind
• temperature
• pH of soil

Question 8

The population is trees in the forest evolved adaptations to the mountain environment. Use your knowledge of selection to explain how.

Answer 8

If a tree had an advantageous allele, it shows variation from original colonisers and confers an advantage. As a result, it is better adapted for survival and also more likely to reproduce successfully. This will pass the advantageous alleles on to the offspring. (3)

Question 9

Ecologists studied a community of fish in a lake.

Explain what is meant by a community. (1)

Answer 9

All of the populations of different species interacting in a particular place at the same time.

Question 10

Ecologists can use the mark-release-recapture method to estimate the number of one species of fish in the lake. Describe how.

Answer 10

First, capture a sample and mark them (eg with paint). They’re then released. Some time later, a second sample is caught in the same area. Then you would use the equation: population = no of sample 1 x no of sample 2 / no marked in sample 2.

Question 11

The species of fish breeds at a certain time of the year. During this fish breeding season, the mark-release-recapture technique might not give an relatable estimate. Suggest one reason why. (1).

Answer 11

Because there may be many births - more than usual, so giving an inaccurate estimate of population size.

Question 12

The ecologists found that each species of fish had adaptations to its niche. One of these adaptations was the shape of its mouth.

Suggest how the shape of its mouth is an adaptation to its niche. (2).

Answer 12

Different mouth shape for different food. As there is competition between species (interspecific)

Question 13

Explain the meaning of the ecological term: population.

Answer 13

A group of individuals of one species that occupy that same habitat at the same time. They could interbreed.

Question 14

Splaying the meaning of the ecological term: community.

Answer 14

ALL of the populations of different species living and interacting in the same place at the same time.

Question 15

Explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100 by 150m. (3).

Answer 15

Randomly place quadrats (eg by random number generator).
Work out the mean per quadrat.
Multiply to give estimate for total field area.

Question 16

These two different species are thought to have evolved as a result of sympatric speciation.
Suggest how this might have occurred. (4)

Answer 16

Original population varies in one area. 
Creates genetic variability. 
Reproductive isolation (temporal isolation - eg mating only in the day, or courtship relationships become more specific).
Gene pools become increasingly different over time. 
Until interbreeding does not produce fertile offspring.

Question 17

Describe a practical technique which you could use to dine the mean population density of daisies on a lawn.

Answer 17

Random sampling
Use of large numbers of quadrats
Counting daisies and dividing by area

Question 18

Describe how you would investigate the distribution of marram grass from one side of the dune to the other. (3)

Answer 18

A belt transect - stretch tape across the sand dunes. Lay a frame transect next to the tape. Count plants or % cover. Then move the quadrat its own length across the line. The process is repeated.

Question 19

Marram grass is a pioneer species that grows on sand dunes. It has long roots and a vertically growing stem that grows up through the sand.
Sand dunes are easily damaged by visitors and are blown by the wind. Planting marram grass is useful in helping sand dune ecosystems to recover from damage.

Use your knowledge of succession to explain how. (2)

Answer 19

The growing stem stops the sand from moving by being blown in the wind. In turn, these secondary colonisers make the conditions less hostile; increasing the species diversity.

Question 20

Farmland previously used for growing crops was left for 39 years and developed into woodland. During this period, ecologists recorded an increase in the diversity of birds in the area.

Name the process that resulted in the development of woodland from farmland.

Answer 20

Succession.

Question 21

Explain the increase in the diversity of birds as woodland develops. (3).

Answer 21

Greater diversity of plants.
So more food sources.
And more habitats.

Question 22

The species that are present in a pine forest change during succession. Explain why (2).

Answer 22

As conditions become less hostile species dir and decompose, leaving humus, meaning other species can move in. And these species outcompete the pioneer species.

Question 23

Pine trees in the forest have leaves all year. Explain how this results in a low species diversity of plants within the forest. (1)

Answer 23

Only plants which can photosynthesise with less light remain (as it’s darker in forests - pine needles shade the light).

Question 24

Give two conditions for results from the mark-release-recapture technique to be valid. (2).

Answer 24

• the mark is not lost or rubbed off

- few births and deaths between the first and second sample

Question 25

Suggest one reason for conserving woodlands.

Answer 25

Economic reasons. For example living organisms could provide genes for medications which may prove valuable in the future.