Option C: Ecology and conservation (AHL) :C.5 Population ecology HL Paper 3

Date	November 2017	Marks available	2	Reference code	17N.3.HL.TZ0.15
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Predict	Question number	15	Adapted from	N/A

Question

Wild turkeys (Meleagris gallopavo) once inhabited most forested areas of North America. As an important food source for early European settlers, the population of M. gallopavo seriously decreased. Due to recent conservation efforts, population numbers are increasing.

The curve shows a population of M. gallopavo from 2000 to 2015 in Ohio in the mid-western USA.

State the range of years when exponential growth of the M. gallopavo population occurred.

[1]

a.i.

Suggest factors that could account for the growth curve of the M. gallopavo population.

[2]

a.ii.

State how the population of M. gallopavo may have been determined.

[1]

Hunting of M. gallopavo is currently regulated. Predict what would happen if the hunting regulations were removed.

[2]

Markscheme

2000–2008

a.i.

a. natality AND mortality

b. immigration AND emigration

c. resources/abiotic conditions/carrying capacity

d. predation/hunting

[Max 2 Marks]

a.ii.

capture–mark–release–recapture/Lincoln/Peterson method

a. population would decrease/may become extinct

b. open realized niche for other organisms

OWTTE

c. food web may change

d. less intraspecific competition

[Max 2 Marks]

Date	May 2017	Marks available	2	Reference code	17M.3.HL.TZ2.15
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Explain	Question number	15	Adapted from	N/A

Question

Most reef-building corals contain photosynthetic algae, called Zooxanthellae, that live in their cells. Coral bleaching can occur as a result of human-induced changes leading to the Zooxanthellae being ejected from the coral.

State the type of interaction that occurs between Zooxanthellae and reef-building corals.

[1]

State the trophic level of Zooxanthellae.

[1]

When coral is bleached, certain organisms become more common in the ecosystem such as the cnidarian Gorgonia, the echinoderm Diadema, other algae and certain sponges. State the term that is used for organisms whose presence provides evidence of the existence of a particular environmental condition.

[1]

A coat of algae builds up on coral reefs as a consequence of eutrophication. Explain the relationship between eutrophication and algal growth.

[2]

Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors.

[2]

Markscheme

symbiosis/mutualism

producers

indicator species

a. eutrophication is nutrient enrichment of a body of water

b. example of nutrients eg: nitrates

c. «nutrients» serve as fertilizer for the algae «promoting growth»

a. top-down factors refer to predation/herbivory/trophic level above another one

b. which limit/control population growth

c. named example of a top-down predator eg: parrotfish. Do not accept general names, like “fish”.

Date	May 2017	Marks available	6	Reference code	17M.3.HL.TZ1.17
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Discuss	Question number	17	Adapted from	N/A

Question

Discuss the factors affecting population growth that can result in an exponential growth curve.

Markscheme

a. exponential growth occurs in ideal/unlimited environment

b. population growth determined by natality, mortality, immigration and emigration

c. natality / births / reproduction increases population
OR
number of reproducing individuals determine the rate of growth

d. as long as natality is higher than mortality

e. low mortality leads to exponential growth

f. absence of limiting factors will lead to exponential growth

g. «limiting factors» could be «competition for» resources/habitat / presence of predators/diseases

h. higher mortality and/or emigration compared to natality and/or immigration cause population to decrease/rate of growth to slow

i. graph with exponential curve/exponential part of sigmoid curve labelled

Allow annotations on a sigmoid population graph.

Date	November 2016	Marks available	3	Reference code	16N.3.HL.TZ0.17
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	17	Adapted from	N/A

Question

State two bottom-up factors affecting algal blooms.

[2]

Explain how top-down factors control algal blooms.

[3]

Markscheme

minerals
OR
nutrients
OR
phosphorus
OR
nitrogen

Award [1] to any two factors stated.

Accept abiotic factors such as temperature, light, pH, CO2 concentration.

a. the herbivores / «first» consumers regulate algal bloom

b. predators of the herbivores help regulate algal bloom/reduce herbivore abundance/OWTTE

c. overfishing/death of predators/decreased reproduction of predators decreases algal bloom as herbivore population increases/OWTTE

Accept vice versa for marking point c.

d. habitat degradation can decrease algal bloom

e. pathogens of algae will decrease algal bloom
OR
alien/invasive species may compete for habitat and affect algal bloom/OWTTE

Date	November 2016	Marks available	3	Reference code	16N.3.HL.TZ0.16
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Describe	Question number	16	Adapted from	N/A

Question

Forest fires are very common in the Amazon forest. A study was performed to see the relationship between forest fragmentation, fire and management

Describe one method that could have been used to estimate the population size of a given tree in a forest after fire damage had occurred.

[3]

Outline how the edge effect can affect diversity in forests.

[3]

The number of plants in two fields of approximately the same size was counted.

Compare and contrast the richness and the evenness of the two fields.

[2]

Markscheme

ALTERNATIVE 1

a. transect through a given area

b. trees counted on transect

c. calculation of total population considering area

ALTERNATIVE 2

d. random sampling using quadrats

e. trees counted in quadrat

f. population calculated using area

ALTERNATIVE 3

g. GPS/Google Earth used to map individuals of a tree species

h. data base of data obtained

i. population density calculated using area

a. edge effect are the changes in community structures that occur at the boundary of two habitats

b. areas with small habitat fragments exhibit especially pronounced edge effects

c. edge species will always have a habitat
OR
edge biodiversity increases

d. if patches of forest are too small the non-edge species cannot find a habitat

e. «then» overall non-edge biodiversity is lower

a. same richness as they have the same number of species/total of individuals

b. field 1 has more evenness as more even distribution of numbers among the species

Accept correct use 2 of Simpson diversity index.

Date	May 2016	Marks available	6	Reference code	16M.3.HL.TZ0.18
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Evaluate	Question number	18	Adapted from	N/A

Question

Evaluate the methods used to estimate populations of marine organisms.

Markscheme

Sampling does not count every organism so may not be a true estimate

Highly mobile marine animals unevenly distributed so difficult to estimate population size

Transects/quadrats used to estimate populations of stationary organisms

Useful on rocky shores/beaches/intertidal zones/reef

Estimation of mobile larval stages of stationary organisms/coral more difficult

Capture-mark-release-recapture useful for mobile animals in restricted environments (Vice versa)

Example of organism can estimate by this technique

Drawback of technique

Echolocation/sonar used to estimate the population size of fish that form shoals

Echolocation cannot distinguish between species (Accept other valid limitation)

The age structure of «commercially» caught fish can be used to estimate population size

Restricted-age fish «as bycatch» dumped before landing so biased estimates
OR
Depends on accuracy/honesty of those catching fish

Date	May 2015	Marks available	6	Reference code	15M.3.HL.TZ2.12
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Describe	Question number	12	Adapted from	N/A

Question

Describe a named method for determining the size of fish populations and the challenges in conserving world fish stocks.

Markscheme

challenges:
d. maintain fish as an important food source for humans/other animals;
e. a sustainable yield means not overfishing an area/not causing a decline in the population/ not catching faster than the fish can replace themselves / OWTTE;
f. pollution threatens world fish stocks/habitat;
g. disagreements as to what is a sustainable population;
h. disagreements in the collection of data of population sizes;
i. requires international cooperation to define conservation measures/regulations/quotas;
j. difficult to reinforce/control regulations / monitor practices / OWTTE;
Award [4 max] if only challenges addressed.

Named method could be any of the three examples given above but the description and limitation must be based on one named method only.

Date	November 2015	Marks available	1	Reference code	15N.3.HL.TZ0.10
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Identify	Question number	10	Adapted from	N/A

Question

In South Korea, flocks of birds of the tit family (Paridae) forage together on trees for food. Researchers observed four species of Paridae to determine whether they shared the same habitat in the trees and whether their position on the tree depended on their size. The leafy part of the tree (crown) was divided into nine sections, three according to height from the ground and three according to the distance from the tree trunk. Observations were also made of birds foraging in the bushes surrounding the trunk and on the ground below the tree.

The chart shows the relative use of each section of the habitat by the birds.

State the relative use of the habitat by the Great Tit in the upper crown of the tree close to the trunk.

[1]

Identify the section of habitat used least by the birds.

[1]

Compare how the Varied Tit and the Marsh Tit use the habitat in the upper crown of the tree.

[2]

State how the distribution of birds changes with their size in the middle crown of the tree.

[1]

Suggest one reason why few Varied Tits were found far from trunk.

[1]

Discuss whether the results for the Varied Tit and Coal Tit indicate competitive exclusion.

[2]

Markscheme

medium to low

lower crown, far from trunk

smaller birds make more use of the habitat further from the trunk / larger birds make more use of the habitat closer to the trunk

their food is close to the trunk / fewer predators close to trunk / too big for small outside branches

Accept any valid suggestion.

a. the competitive exclusion principle states that no two species can coexist if they occupy the same niche/compete for the same resources;

b. competitive exclusion is supported as there is little overlap between the two species in the habitat;

c. competitive exclusion is not supported as there is some overlap between the species;

d. we do not have enough information about the resources required by each species to say if competitive exclusion is occurring;

Date	May 2013	Marks available	1	Reference code	13M.3.HL.TZ2.10
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Estimate	Question number	10	Adapted from	N/A

Question

In 2009, the town council of Dumfries in Scotland tested a project to prevent lesser black-backed gulls (Larus fuscus) from nesting in the town where they were causing problems. They released trained falcons into the town centre for 10 hours each day during a 10-week period when the gulls normally lay their eggs. Although the falcons are predators of the gulls, they did not kill the gulls during the study. The behaviour of the gulls was observed and the percentage time spent on three activities was recorded. The results were compared to a control group not exposed to falcons in another part of town.

• Rest: sitting on their nests, standing or preening their feathers

• Alert: remaining on the ground but disturbed and visibly agitated

• Flight: flying regardless of the cause

The pie charts show the results of the project.

State which activity decreased in weeks 1 to 5 as a result of exposure to the falcons.

[1]

Estimate the total percentage of time the gulls exposed to falcons spent flying and at rest in weeks 6 to 10.

………………….%

[1]

Compare the behaviour of the gulls exposed to falcons with the control group over the period of study.

[3]

Predict, using the data in the pie charts for weeks 1 to 5 and weeks 6 to 10, if the use of falcons will succeed in causing a long-term reduction in the number of gull nests in problem areas.

[2]

Markscheme

rest

75 (%) (accept answers in the range of 72 to 78 %)

a. comparison for one of the behaviours (rest/alert/flight) between the control group and the falcon group for weeks 1 to 5;
b. comparison for one of the behaviours (rest/alert/flight) between the control group and the falcon group for weeks 6 to 10;
c. comparison for one of the behaviours (rest/alert/flight) between weeks 1 to 5 for the control group and weeks 6 to 10 for the falcon group / converse;
d. comparison between the proportions/differences of overall behaviours for the control group with those for the falcon group for weeks 1 to 5/weeks 6 to 10 / overall change in all groups over time;
Award [1 max] for a correct comparison for each marking point. Do not award marks for a comparison between the control group only or the falcon group only.

Please refer to the clarification document for further guidance.

a. falcon group has closer values (in all categories) to control in weeks 6 to 10;
b. falcon group has more rest in weeks 6 to 10 than in weeks 1 to 5 so indication for more nesting;
c. insignificant/no long-term effect as gulls seem to become accustomed to falcons / trend is likely to continue / OWTTE;

Date	May 2013	Marks available	2	Reference code	13M.3.HL.TZ2.4
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Compare	Question number	4	Adapted from	N/A

Question

Investigators studied the behaviour of two species of small fish, the sand goby (Pomatoschistus minutus) and the black goby (Gobius niger), while they foraged for mud shrimps. The amount of food foraged by the gobies was measured after they had been fed or after they had been starved. The measurements were repeated when a predator of the gobies was introduced to the tank where they were feeding.

Calculate the decrease in mass of food foraged by fed sand gobies when a predator was introduced, giving the units.

[1]

Compare the effect that starvation had on both species of goby when no predator was present.

[2]

Describe the effect the predator had on the foraging of the gobies.

[2]

c (i).

Suggest a reason for the effect of the predator.

[1]

c (ii).

Markscheme

2.6 mg (units required) (accept answers in the range of 2.5 mg to 2.7 mg)
No working required.

both foraged more after starvation;
black goby increased the amount of food foraged more than the sand goby;

a. predator present causes both to forage for less food;
b. fed black gobies showed little change in foraging (with predator present);
c. starved gobies foraged more than fed gobies (with predator present);
d. relative foraging remains similar between the two species / black goby always forages less than sand goby;

c (i).

a. gobies may feed on smaller mud shrimps when predator present;
b. gobies may hide rather than forage when predator present / gobies may feed less efficiently if they are watching out for predators;
c. predator may also eat shrimp so less for gobies;
d. if predator eats gobies the total mass of food foraged is less / OWTTE;

c (ii).

Date	May 2013	Marks available	2	Reference code	13M.3.HL.TZ2.11
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Describe	Question number	11	Adapted from	N/A

Question

Distinguish between in situ and ex situ conservation.

[1]

The Atlantic cod is considered in many countries to be endangered due to overfishing. Describe two methods that could be used to estimate the cod population.

[2]

Outline one reason for the extinction of a named animal species.

[1]

Markscheme

in situ within the organism’s natural environment whereas ex situ taken out of natural environment / OWTTE

a. record size of catches from fishing boats;
b. capture, tagging, releasing and recapturing fish / Lincoln index;
c. sample fishes with trawling nets;
d. estimate population with echo sounder/sonar/fish finder;
Award marks only for the first two methods if more than two written.

name of species and what caused it to become extinct (both needed)
The named species must be extinct and not endangered.
eg:
passenger pigeon (became extinct when) hunted as a source of food

Date	November 2011	Marks available	2	Reference code	11N.3.HL.TZ0.11
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Outline	Question number	11	Adapted from	N/A

Question

In 1988 a fire destroyed large portions of forest in Yellowstone National Park, USA. Photograph A was taken soon after the fire and photograph B one year later. The photographs are of the same area.

Identify, with a reason, the type of succession that has taken place.

[1]

Outline a method that could be used to sample the plant population shown in photograph B.

[2]

Yellowstone National Park was the first national park in the world and is a designated biosphere reserve site. Outline the biogeographical features of nature reserves that promote conservation of diversity.

[3]

Markscheme

secondary succession as some plants/organic components were present before fire

describe method for ensuring random placement of quadrats in a grid; (do not accept transect)
different species present in quadrat identified and counted;
used to estimate species density/frequency/abundance/cover;

size:
large nature reserves usually promote conservation better than small ones;
large areas needed for far-ranging animals (e.g. grizzly bear);
larger areas have proportionally smaller perimeters/less affected by edges;

edge effect:
ecology of edges of ecosystems is different from central areas due to edge effects;
fragmentation (of forests) leads to increase in edges which will favour some species over others;

habitat corridor:
habitat/movement/wildlife corridors allow organisms to move between different parts of fragmented habitat;

To award [3] responses must refer to size, edge effect and habitat corridor.

Date	November 2012	Marks available	2	Reference code	12N.3.HL.TZ0.10
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Compare	Question number	10	Adapted from	N/A

Question

Knowledge of deep-water fish is important for fisheries and marine reserve management. Scientists analysed data from scientific trawls made from 1977 to 1989 (early period) and from 1997 to 2002 (late period). These were at depths from 800 m to 4800 m in the Porcupine Seabight and Porcupine Abyssal Plain area southwest of Ireland. The graphs represent the abundance of fish and the number of species for each of these trawls.

State the depth at which the maximum number of species per trawl were caught.

[1]

a .

Compare the abundance of fish between the early period (1977 to 1989) and the late period (1997 to 2002).

[2]

b (i).

Suggest one reason for the difference in the abundance of fish at depths down to 2000 m between the early period and the late period.

[1]

b (ii).

Discuss the evidence in these data for a decline in the biodiversity of fish between the early period and the late period.

[2]

State two types of interactions that are most likely to occur among deep-water fish.

1. …………………………………………………………

2. …………………………………………………………

[1]

Outline the concept of maximum sustainable yield in the conservation of fish stocks.

[2]

Markscheme

1550 (m) (accept answers in the range of 1450 (m) to 1650 (m))

a .

both show decrease in abundance as depth increases;
both show similar/low abundance at depths greater than 3000 (m); (accept values in range 2500 (m) to 3000 (m))
for depths less than 2500 (m) the abundance is (much) greater in the early period than in the late period; (accept values in range 2000 (m) to 2500 (m))
the highest abundance occurs in the late period (although) this is isolated;

b (i).

overfishing / pollution / change in sea temperature / change in food sources

b (ii).

no evidence that there are fewer species;
difficult to compare as more trawls in the early period /early period of longer duration than late period;
diversity may have increased from (around) 2000 (m) to 4000 (m) / outliers for greater species diversity are all late period;
not enough details about time of year/duration of trawls; (accept any other valid argument)
Do not accept answers stating only “not enough data”.

competition and predatory/predation (both needed)

is the maximum number of fishes of a species that can be caught/harvested without causing a population decline / still allowing a population to regenerate;
corresponds to the turning point of a population growth curve;
below that point yield is lower and population grows / above that point yield and population will decline;
used to determine fishing quotas;
difficulty in estimating populations;