19. POPULATIONS IN ECOSYSTEMS

Question 1

Define what a population is

Answer 1

A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

Question 2

Define a habitat

Answer 2

A place where a community of organisms live

Question 3

Define an ecosystem

Answer 3

A biological community of interacting organisms and their physical environment

Question 4

Define a community

Answer 4

All the populations of different species living in a habitat

Question 5

Name the three stages of a population growth curve

Answer 5

Lag phase, exponential phase, carrying capacity

Question 6

Compare the birth rate and the death rate in lag phase

Answer 6

Birth rate > death rate

Question 7

Explain why population growth is slow in the lag phase, even though resources are plentiful

Answer 7

Because the number of individuals is low

Question 8

Compare the birth rate and the death rate in the exponential phase

Answer 8

Birth rate > death rate

Question 9

Explain why population growth is fast in the exponential phase

Answer 9

Resources are plentiful and there are no limiting factors

Question 10

Define carrying capacity

Answer 10

The maximum population size that an environment can support

Question 11

Compare birth and death rates in carrying capacity

Answer 11

Birth rate = death rate

Question 12

Explain why the population size is stable in carrying capacity

Answer 12

Because resources are limiting

Question 13

Recall the 7 limiting factors of population growth rate and carrying capacity

Answer 13

Food, space, water, mates, parasites/pathogens/disease, light intensity/availability, nesting sites

Question 14

Which extra phase do bacterial populations experience at the end of the their population growth curves?

Answer 14

Death phase

Question 15

Why do bacterial populations experience a death phase after their carrying capacity?

Answer 15

As O2 is used up they respire anaerobically, producing ethanol. This becomes toxic and kills the bacteria.

Question 16

Within a habitat, different species occupy different niches. What are niches governed by?

Answer 16

Adaptations to biotic and abiotic factors, e.g. food sources

Question 17

What is the benefit of species occupying different ecological niches?

Answer 17

There is less competition for resources

Question 18

What type of competition exists between individuals of the same species?

Answer 18

Intraspecific

Question 19

What type of competition exists between individuals of different species?

Answer 19

Interspecific

Question 20

What is the competition exclusion principle?

Answer 20

When two species are competing for limiting resources, the one that uses the resources more effectively will ultimately eliminate the other

Question 21

How will increasing competition affect population size / population growth rate / carrying capacity?

Answer 21

Increasing competition will decrease population size / population growth rate / carrying capacity

Question 22

How will decreasing competition affect population size / population growth rate / carrying capacity?

Answer 22

Decreasing competition will increase population size / population growth rate / carrying capacity

Question 23

Why do population size fluctuate seasonally?

Answer 23

Because resource availability fluctuates seasonally, therefore so does competition, and so does population size

Question 24

Which type of species show seasonal fluctuations in population size?

Answer 24

Prey, herbivores, primary consumers

Question 25

Why do predator population sizes show regular, cyclic population sizes?

Answer 25

Because the predator population size will fluctuate after the prey population size. As the pre population decreases, intraspecific competition increases and the predator population decreases

Question 26

Out of the predator and prey, which population fluctuates first, and which fluctuates after?

Answer 26

The prey population fluctuates first (because it fluctuates with the seasons), and the predator population fluctuates after (because it is dependent on the prey population)

Question 27

Define succession

Answer 27

Succession is a change in a community over time due to changing abiotic factors

Question 28

What is a pioneer species?

Answer 28

The first species to colonise a habitat (after a disturbance)

Question 29

How do pioneer species make the habitat more suitable / less hostile for other species?

Answer 29

They change the abiotic factors

Question 30

Give two examples of how pioneer species may change the abiotic factors within a habitat to make them more suitable for other species

Answer 30

They may contain nitrogen fixing bacteria, which will increase the nitrogen-containing compounds in the soil. They may be decomposed by saprobiotic bacteria, increasing the nutrient content of the soil.

Question 31

What happens to the population of the pioneer species as the population of the second species increases?

Answer 31

It decreases

Question 32

Why does the pioneer species eventually disappear?

Answer 32

Because the second species is better adapted, and so outcompetes the pioneer species

Question 33

What happens to the biodiversity of an ecosystem as succession proceeds?

Answer 33

It increases

Question 34

What is a climax community?

Answer 34

The final stable community in succession

Question 35

Give three features of a climax community

Answer 35

1. it is stable 2. the abiotic factors are constant 3. the populations are stable (at carrying capacity)

Question 36

Name some factors that may affect the size of the community in a climax community

Answer 36

Nutrient availability, any factor that affects the rate of photosynthesis, disease, predators, space for nests, and competition

Question 37

Name some natural resources that humans use for their own benefit

Answer 37

Timber, crude oil, salt, metal ores

Question 38

Because the human population is so large, we are using our natural resources unsustainably. What does unsustainable mean?

Answer 38

We are using resources at a faster rate than they can replenish naturally

Question 39

What two things do we need to manage the conflict between to maintain sustainability?

Answer 39

Human need and conservation

Question 40

Define conservation

Answer 40

Conservation is the maintenance of biodiversity by restoring ecosystems

Question 41

Conservation is an active process. What does this mean?

Answer 41

It requires human participation and intervention

Question 42

Name four reasons for conservation

Answer 42

Maintaining / increasing biodiversity, protecting endangered species, conserving sources of medicine, reducing erosion and eutrophication

Question 43

What is the main loss to humans in the process of conservation?

Answer 43

Financial, e.g. cost of outlay or loss of income

Question 44

Name the process of sustainable timber production

Answer 44

Coppicing

Question 45

Why is coppicing sustainable?

Answer 45

Trees are kept alive whilst wood is harvested from them

Question 46

Describe rotational coppicing

Answer 46

Sections of forest are coppiced one at a time, leaving other sections to regrow so they are ready to be harvested again later

Question 47

Why does managing / halting succession increase global biodiversity?

Answer 47

By managing / halting succession, you will maintain different habitats and different food sources, increasing biodiversity

Question 48

When would you use a quadrat to sample species?

Answer 48

When estimating the number of species in an area

Question 49

Which type of sampling is quadrats?

Answer 49

Random sampling

Question 50

To be representative, why must sample sizes be large?

Answer 50

To minimise the effect of anomalies

Question 51

To be representative, why must samples be chosen at random?

Answer 51

To avoid bias

Question 52

What two ways can an area to be quadratted by mapped?

Answer 52

Using coordinates and using numbered areas

Question 53

If an area to be quadratted is mapped using coordinates, how would you choose your random sample?

Answer 53

Using a random coordinate generator

Question 54

If an area to be quadratted is mapped using numbers, how would you choose your random sample?

Answer 54

Using a random number generator

Question 55

Describe how you would calculate the total estimated population in an area using quadrats

Answer 55

1. Count the individuals in each quadrat 2. Find the sum of the individuals in each quadrat and divide by the numner of quadrats (giving the average individuals per quadrat) 3. Multiply by the total area

Question 56

When would you use a belt transect to sample a species?

Answer 56

When calculating a change in a population/community over a distance in response to a changing environmental factor.

Question 57

Which type of sampling are belt transects?

Answer 57

Systematic sampling

Question 58

Describe a disadvantage of using belt transects

Answer 58

They may not go through all representative areas

Question 59

What piece of equipment could be used to lay a belt transect?

Answer 59

Tape measure

Question 60

How do the quadrats have to be laid along the belt transect?

Answer 60

At regular intervals

Question 61

As well as counting the individuals in each quadrat along the transect, what else must you do?

Answer 61

Measure the abiotic factor using appropriate equipment

Question 62

Which statistical test would you apply to your data from a belt transect, and why?

Answer 62

Spearman's Rank, to calculate the correlation coefficient, which will calculate the strength of the correlation between two variables

Question 63

What is a kite diagram?

Answer 63

A diagram used to represent the abundance of species along a transect

Question 64

When would you calculate percentage cover when sampling?

Answer 64

When there are too many individuals to count, e.g. grass

Question 65

Why is using sampling to estimate the number of animals in an ecosystem problematic?

Answer 65

They are motile. So you could count the same organism twice and some not at all.

Question 66

Name the technique used to estimate animal populations in ecosystems

Answer 66

Mark, release, recapture

Question 67

What do we have to ensure about the method we use to mark individuals?

Answer 67

It doesn't come off It doesn't harm the individuals It doesn't increase their chance of being predated It doesn't change their behaviour

Question 68

Why do we leave a period of time between releasing the marked individuals, and recapturing the second sample?

Answer 68

To allow them to randomly disperse back into the population

Question 69

Recall the equation used to calculate the estimated population of animals using the mark, release recapture method

Answer 69

Estimated total population = number of organisms initially caught x number of organisms in second sample / number of marked organisms recaptured

Question 70

Apart from an appropriate marking method and leaving sufficient time to disperse, what other conditions are must be assumed for mark, release recapture to be valid?

Answer 70

No migration The same sampling method is used each time No breeding / births or death The sample size is large enough