3.7.4 Populations in ecosystems

Question 1

Mark, Release, Recapture – Assumptions (5)

Answer 1

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 2

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

Answer 2

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 3

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

Answer 3

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);
   .  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 4

Why repeat/ large sample size in experiments

Answer 4

So /representative;

Question 5

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

Answer 5

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

Question 6

Describe use of systematic sample to count plants (5)

Answer 6

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 7

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

Answer 7

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 8

Define niche (3)

Answer 8

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 9

Predator-Prey Relationship (4)

Answer 9

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 10

describe Succession (5)

Answer 10

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 11

Succession – describe Competition (3)

Answer 11

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 12

Give two features of a climax community

Answer 12

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 13

Suggest one reason for conserving
woodlands. (1)

Answer 13

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