3.7.4 Populations in ecosystems

Question 1

What is a community in ecology

Answer 1

A community is all the populations of different species living and interacting in the same habitat at the same time

Question 2

What is an ecosystem

Answer 2

An ecosystem is a community and the non-living abiotic factors in an area interacting as a system

Question 3

What determines the niche of a species

Answer 3

A species’ niche is determined by its adaptations to abiotic and biotic factors

Question 4

What is carrying capacity

Answer 4

Carrying capacity is the maximum stable population size that an ecosystem can support over time

Question 5

What abiotic factors affect population size

Answer 5

Abiotic factors affecting population size include temperature light water availability oxygen levels and soil pH

Question 6

What is interspecific competition

Answer 6

Interspecific competition is competition between individuals of different species for the same resources which can affect population sizes

Question 7

What is intraspecific competition

Answer 7

Intraspecific competition is competition between individuals of the same species for resources affecting survival and reproduction

Question 8

What is predation

Answer 8

Predation is when one organism (the predator) kills and consumes another organism (the prey) affecting population sizes

Question 9

How can population size of slow-moving organisms be estimated

Answer 9

Population size of slow-moving organisms can be estimated using randomly placed quadrats or quadrats along a belt transect

Question 10

What method is used to estimate population size of motile organisms

Answer 10

The mark-release-recapture method is used to estimate population size of motile organisms

Question 11

What assumptions are made in mark-release-recapture

Answer 11

No births deaths immigration or emigration marked individuals mix randomly with population marking does not affect survival or predation all marks are still visible

Question 12

Why are ecosystems considered dynamic

Answer 12

Ecosystems are dynamic because abiotic and biotic factors constantly change influencing population sizes and community structure

Question 13

What is primary succession

Answer 13

Primary succession is the process by which a barren area is colonised by pioneer species leading to a climax community

Question 14

What role do pioneer species play in succession

Answer 14

Pioneer species modify the abiotic environment making it more suitable for other species by adding organic matter improving soil structure and increasing nutrient availability

Question 15

How can new species affect the environment in succession

Answer 15

New species may change the environment to be more suitable for other species with different adaptations but less suitable for previous species

Question 16

How can changes in abiotic factors affect biodiversity

Answer 16

Changes in abiotic factors can create a less hostile environment increasing biodiversity by allowing more species to survive

Question 17

Why does conservation often involve managing succession

Answer 17

Managing succession prevents climax communities from forming maintaining habitats for certain species and preserving biodiversity

Question 18

Why is there a conflict between human needs and conservation

Answer 18

Humans need land resources and economic development which can conflict with conservation efforts to maintain biodiversity and ecosystem stability

Question 19

How can sustainability be achieved in conservation

Answer 19

Sustainability is achieved by balancing resource use with conservation efforts ensuring ecosystems and biodiversity are maintained for future generations

Question 20

What calculation is used in mark-release-recapture

Answer 20

Estimated population size = (number of marked individuals in first sample × total number in second sample) / number of marked individuals recaptured

Question 21

Mark, Release, Recapture – Assumptions (5)

Answer 21

1. No emigration/immigration;
2. No losses to predation;
3. Marking does not affect survival;
4. Birth rate and death rate equal;
5. (In this case) all belong to one population;

Question 22

Mark, Release, Recapture – Outline the method (4)

Answer 22

1.      Capture/collect sample, mark and release;

2.      Ensure marking is not harmful (to fish)
OR
Ensure marking does not affect survival (of fish);

3.      Allow (time for) fish to (randomly) distribute before collecting a second sample;

4.      (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;

Question 23

Describe how you could estimate the size of a population using random sampling (4)

Answer 23

1.  Use a grid OR Divide area into squares/sections;
2.  Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator;
3.  Count number/frequency in a quadrat/section; .
4.  Large sample and calculate mean/average number (per quadrat/section);
5.  Valid method of calculating total number of plant,
   e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in area

Question 24

Why repeat/ large sample size

Answer 24

So /representative;

Question 25

The scientist used percentage cover rather than frequency to record the abundance of algae present. Suggest why. (1)

Answer 25

too many to accurately count / individual organisms not identifiable / too small to identify / overlap;

Question 26

Describe use of systematic sample to count plants (5)

Answer 26

1. Systemic sampling (placing quadrat) at regular intervals along transect line; 2. Transect line from/to ……..; 3. Count number/frequency in a quadrat/section; 4.  Large sample and calculate mean/average number (per quadrat/section);

Question 27

Effect of increased plant/animal diversity on ecosystem (3)

Answer 27

1. Increase in plant diversity leads to more different types of food for animals; 2. Increase in variety of animals leads to increase in predator species; 3. Increase in more different niche/habitat;

Question 28

Define niche (3)

Answer 28

1. Niche is the role that a species plays in within a community; 2. Includes food resources; 3. No two species can occupy identical niche;

Question 29

Predator-Prey Relationship (4)

Answer 29

1. As pest numbers increase more food or predators, so they increase; 2. Increased predation of pests reduces numbers; 3. Low number of pests results in less food for predators, so their numbers decrease; 4. Low predator numbers allow pest population to rise as fewer are eaten;

Question 30

Succession (5)

Answer 30

1.  (Colonisation by) pioneer species; 2.  Pioneers/species/organisms change the environment/habitat/conditions/factors; 3.  (Environment becomes) less hostile for other/new species Accept previous species out-competed. 4.   increase in diversity/biodiversity; 5.  (To) climax community;

Question 31

Succession – Competition (3)

Answer 31

1. Pioneer species increases then decreases; 2. Principle of a species changing the conditions / a species makes the conditions; 3. New/named species better competitor / pioneer species outcompeted;

Question 32

Give two features of a climax community.

Answer 32

1.      Same species present (over long time) / stable community (over long time); 2.      Abiotic factors (more or less) constant (over time) 3.      Populations stable (around carrying capacity)

Question 33

Suggest one reason for conserving woodlands. (1)

Answer 33

1.      Conserving / protecting habitats / niches; 2.      Conserving / protecting (endangered) species / maintains / increases (bio) diversity; 3.      Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide; 4.      Source of medicines / chemicals / wood; 5.      Reduces erosion / eutrophication.

Question 34

Lake Malawi in East Africa has more species of fish than any other lake in the world. Suggest and explain how this speciation may have occurred.

Answer 34

1. Variation/differences due to mutation/s; 2. (Reference to) allopatric (speciation); Ignore sympatric speciation. 3. Smaller/different lakes have different environmental conditions OR Smaller/different lakes have different selection pressures; Accept different populations for different lakes. 4. Reproductive separation/isolation

Question 35

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes

Answer 35

Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;