IB DP Biology Option C: Ecology and conservation (Core topics) :C.1 Species and communities SL Paper 3

Date	November 2017	Marks available	4	Reference code	17N.3.SL.TZ0.15
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	15	Adapted from	N/A

Question

Explain reasons for differences in the realized niche and fundamental niche of an organism.

Markscheme

a. an ecological niche is an organism’s role/functional place in the environment

b. the fundamental niche is the potential niche and the realized niche is the actual niche

c. includes habitat/feeding/how it survives

d. limiting factors play a part on the actual distribution of species

e. competition prevents species occupying their fundamental niche

f. species show competitive exclusion

two species cannot occupy the same niche in an ecosystem

g. «in competitive exclusion» one species will replace the other species

The answers given in the markscheme may be awarded if the candidate explains a suitable example

For marking point g, do not accept “one species becomes extinct” as a standalone answer unless it is clear they
are referring only to the ecosystem under discussion

[Max 4 Marks]

Date	May 2017	Marks available	2	Reference code	17M.3.SL.TZ2.17
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	Outline	Question number	17	Adapted from	N/A

Question

The fire ant (Solenopsis geminata) is an effective colonizer and has become invasive in a number of ecosystems. Sometimes, efforts to eliminate this species have had an unexpected impact on community structure. It is argued that S. geminata can play a beneficial role in corn production. The graph shows how the presence of S. geminata
can impact insect diversity in areas where crops of corn are grown.

State the impact of S. geminata on insect species diversity.

[1]

Discuss whether S. geminata might play a positive role in corn production.

[3]

Researchers have argued that S. geminata is a keystone species in the corn agricultural system. Outline what is meant by a keystone species.

[2]

Markscheme

reduction in number of species/richness/diversity

a. biological control of/reduction in corn pests

b. reduction in the use of pesticides

c. damage on beneficial species OWTTE

d. reduction in insect diversity can have broad ecosystem negative impact
OR
example of negative effect

e. long-term effects unknown

definition

a. keystone species is one in which presence has a disproportionate impact on the ecosystem

impact

b. removal often leads to significant changes
OR
valid example

Date	May 2017	Marks available	3	Reference code	17M.3.SL.TZ2.14
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	Explain	Question number	14	Adapted from	N/A

Question

Paramecium aurelia and Paramecium caudatum are single cell organisms. They were grown separately and together. The population growth curves are shown.

Explain the results shown in this experiment.

Markscheme

a. when they are alone they both show a greater population than when together

b. two species cannot survive indefinitely in the same habitat if their niches are identical
OR
competitive exclusion

c. Paramecia compete for food/space

d. P. caudatum starts to disappear/decrease after day 6–8 days «whereas P. aurelia reaches a plateau» Vice versa
OR
the population of P.caudatum decreases much more than the population of P.aurelia

e. P. aurelia is better suited/fitted than P. caudatum

Date	May 2017	Marks available	1	Reference code	17M.3.SL.TZ1.13
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	State	Question number	13	Adapted from	N/A

Question

Reef-building corals are an association between two organisms: coral polyps and Zooxanthellae.

State the relationship between Zooxanthellae and coral reef species.

[1]

Describe the exchange of materials between the coral’s polyps and Zooxanthellae.

[2]

State one limiting factor on Zooxanthellae which affects coral reef formation.

[1]

Markscheme

mutualism

a. polyp is a source of carbon dioxide for the Zooxanthellae
OR
polyp is a source of ammonia/nitrogen for the Zooxanthellae

b. Zooxanthellae provide oxygen to the polyp
OR
Zooxanthellae provide sugars/glucose/glycerol/lipids/amino acids to the polyp

light / temperature / salinity / carbon dioxide / pH

Date	November 2016	Marks available	1	Reference code	16N.3.SL.TZ0.14
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Outline	Question number	14	Adapted from	N/A

Question

In 1997 in South Africa, a decision was made to decrease the use of mosquito-killing pesticides due to their negative effect on the environment. Mosquitoes are known to be responsible for the spread of malaria. In 2001 the decision was reversed and the use of pesticides was increased. The graph shows the estimated numbers of people with malaria in each year.

Outline the trend in the number of people with malaria during the period when the use of pesticides was decreased in South Africa.

[1]

One pesticide used in killing mosquitoes was DDT. Considering its harmful effects, discuss whether the decision to reintroduce it was justified.

[4]

Markscheme

the number of people with malaria increased

a. choice has to be made between damage to environment or increase in malaria

b. DT may lead to biomagnification/bioaccumulation in food chains
OR
taken up by species in lower trophic levels becoming more concentrated at higher trophic levels

c. causes harm to consumers at end of food chain
OR
example «eg: thin egg shells of falcons»

d. DDT is shown to be effective in reducing malaria

e. possible partial solution to be selective in areas sprayed with DDT

f. may kill insects that are not pests

Date	November 2016	Marks available	3	Reference code	16N.3.SL.TZ0.11
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Describe	Question number	11	Adapted from	N/A

Question

Chthamalus and Balanus are two species of barnacles that live attached to rocks between the low and high tide level of the sea. The distribution of each species is influenced by the presence of their own species and different species.

Distinguish between a fundamental niche and realized niche.

[1]

Suggest reasons that Chthamalus cannot live higher up the shore.

[2]

Describe how the distribution of Chthamalus and Balanus is affected when both are present.

[3]

Markscheme

realized is actual niche, fundamental is potential niche

a. must spend some of their time under water / prevent dehydration

b. need water for food/nutrients

c. need water for reproduction

d. more accessible to their predators

e. there are no rocks for them to live on
OR
there is no suitable habitat for them

a. Chthamalus and Balanus / both have a reduced distribution

b. they are in competition for part of the habitat on the rock

c. Balanus occupies some of the habitat of the fundamental niche of Chthalamus
OR
where the fundamental niche overlaps Balanus prevails/survives

d. the distribution of Balanus is unchanged in areas colonized by Chthalamus

e. Balanus is in competition with other species closer to low water

Date	May 2015	Marks available	2	Reference code	15M.3.SL.TZ1.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Describe	Question number	20	Adapted from	N/A

Question

The diagram below shows changing vegetation along a slope in a terrestrial ecosystem.

Describe how a transect can be used to investigate the distribution of plant species in this ecosystem.

[2]

The vegetation shown here has developed as a result of primary succession. Outline the changes that take place in the abiotic environment during primary succession.

[2]

Outline the abiotic factors that affect the distribution of plant species in an ecosystem.

[2]

Markscheme

a. random positioning of the transect;
b. transect is a line stretched over an area of study;
c. samples taken/species present recorded at regular intervals along the transect;
d. used to investigate effect of an abiotic variable/named example;

a. rocks begin to break down;
b. minerals begin to accumulate;
c. soil begins to develop;
d. water retention increases;
e. erosion of soil is reduced (by rhizoids and roots);

The question asks for an outline but most candidates have given a list of factors without a reason. Therefore award [1] for every two factors listed or [1] for each qualified factor.

water (distribution) for turgor/biochemical reactions/photosynthesis;
mineral / inorganic content / salinity of soil/water;
temperature (max, min, range, seasonal changes) / altitude;
light (intensity, duration, wavelength) for photosynthesis;
pH (range, average, changes) of soil/water;
wind (direction, strength);

Date	May 2015	Marks available	2	Reference code	15M.3.SL.TZ1.21
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Explain	Question number	21	Adapted from	N/A

Question

Explain the causes and consequences of biomagnification of a named chemical.

[3]

Explain the concept of niche.

[2]

Markscheme

a. named example of chemical (for example: mercury, DDT, PCBs, TBT, PAHs,heavy metals, selenium);
b. long lived / do not biodegrade / stored in body tissues / fat soluble;
c. present in small concentration in the environment;
d. chemical becomes more concentrated in the bodies of organisms at each successive trophic level;
e. reach toxic levels in top consumer/organisms near the end of the food chain / example of top consumer affected;
Award [2 max] if no named example of chemical.

a. includes all aspects of way of life of a species/role of the species in the ecosystem;
b. includes relationships within the community;
c. feeding relationships;
d. interaction with environment/spatial habitat;

Date	November 2015	Marks available	3	Reference code	15N.3.SL.TZ0.21
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	21	Adapted from	N/A

Question

State the process where pesticides such as DDT become more concentrated at each trophic level.

[1]

Explain what is meant by the niche concept.

[3]

Markscheme

biomagnification/bioaccumulation

a. every organism in an ecosystem has their own role;

b. (includes) spatial habitat/space inhabited by organism;

c. (includes) feeding activities of organism;

d. (includes) interactions with other species;

e. valid description of an organism’s niche including habitat, feeding activities and interaction with other species;

Date	May 2013	Marks available	3	Reference code	13M.3.SL.TZ2.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	Explain	Question number	20	Adapted from	N/A

Question

Explain the niche concept.

[3]

Outline one reason for the extinction of a named animal species

[1]

Markscheme

a. niche is an organism’s ecological role/mode of existence;
b. niche is how organism uses abiotic and biotic resources;
c. depends on where organism lives/habitat;
d. depends on organism’s nutrition/feeding activities;
e. depends on interactions (competition/herbivory/predation/mutualism) with other organisms;

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
Note: dinosaur is not a named species.

Date	May 2011	Marks available	2	Reference code	11M.3.SL.TZ1.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Define	Question number	20	Adapted from	N/A

Question

Define the terms fundamental niche and realized niche.

Fundamental niche: …………………………………………….. ……………………………………….

Realized niche: …………………………………………….. ……………………………………………..

[2]

Explain why the carnivores in an ecosystem tend to be fewer in number and have a smaller biomass than the herbivores in the same ecosystem.

[2]

Explain why carnivores tend to be more affected by biomagnification than organisms lower down the food chain.

[3]

Markscheme

Fundamental niche:
the potential niche / the niche the organism could occupy under ideal conditions / the full mode of existence given the adaptations of the species / OWTTE;

Realized niche:
the actual niche / the niche restricted by competition and environmental variables / the niche resulting from the limits placed on the species / OWTTE;
Responses must distinguish between the two types to gain credit.

energy transfer along the food chain is less than 100 % efficient;
10 % energy transfer between trophic levels;
nutrient transfer is less than 100 % efficient;
each carnivore needs to consume many prey organisms;
tendency for size of organisms to increase as trophic level increases;

mercury / DDT / other named example;
biomagnification is the accumulation of chemicals through the food chain;
chemicals that undergo biomagnification are stored/not broken down (in the bodies of the organisms that consume them);
chemicals are passed (unaltered) from one trophic level to the next;
chemicals become more concentrated in the bodies of each (subsequent) trophic level;
organisms higher up the food chain consume larger amounts of the chemical;

Date	May 2011	Marks available	2	Reference code	11M.3.SL.TZ2.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	Distinguish	Question number	20	Adapted from	N/A

Question

Explain the concept of an ecological niche.

[2]

Distinguish between fundamental niches and realized niches.

[2]

Markscheme

(ecological niche is) mode of existence/role of an organism within its ecosystem;
(ecological niche includes) its habitat/abiotic factors of the environment;
(ecological niche includes) what the species eats / how the species obtains food;
(ecological niche includes) interactions with other species;
(ecological niche includes) the set of all ranges of limiting factors an organism
tolerates / OWTTE;

fundamental niche is the niche for which a species has adaptations for success/potential mode of existence whereas a realized niche of a species is its actual mode of existence;
the realized niche is often smaller than the fundamental niche (of a species);
competition/predation is reason for the differences (between fundamental and realized niches);

Date	May 2012	Marks available	4	Reference code	12M.3.SL.TZ1.21
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Explain	Question number	21	Adapted from	N/A

Question

Explain how temperature and territory affect the distribution of animal species.

Temperature:

Territory:

Markscheme

temperature: [2 max]
body size/surface area to volume ratio affects the rate of animal metabolism/ability to conserve heat;
animals that regulate body temperature (homeotherms) can colonize a wider range of environments/habitats;
when animals have less control over their rate of metabolism (poikilotherms) choice of environment/habitat more determined by external temperatures;
fewer species can survive in extreme temperature and special adaptations are needed;

territory: [2 max]
some establish and defend an area within a suitable habitat to attract mates/maintain food supply/rear young/avoid predation/competition;
can lead to intra and inter specific competition for space;
a territory may be established by an individual/breeding pairs/groups / may be limited places suitable as territories which affects distribution;
territory may be permanent or temporary / for breeding period / nomadic/migratory animals;

Date	May 2012	Marks available	2	Reference code	12M.3.SL.TZ2.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	List	Question number	20	Adapted from	N/A

Question

Biotic factors involve the other organisms in the environment of an animal species. List two biotic factors that could affect the distribution of an animal species.

1. …………………………………………………………

2. …………………………………………………………

[2]

Research into a river ecosystem produced these approximate values: 25, 300, 6000 and 36 000 kJ m–2 yr–1. Using this data, construct a pyramid of energy showing four named trophic levels, each with their corresponding energy value.

[2]

Markscheme

predation;
competition;
disease;
food supply;

bars of decreasing size going upwards at least a third of the bar below;
the trophic level on each bar labelled correctly;

Date	May 2010	Marks available	3	Reference code	10M.3.SL.TZ1.27
Level	Standard level	Paper	Paper 3	Time zone	Time zone 1
Command term	Outline	Question number	27	Adapted from	N/A

Question

Outline three factors that affect plant distribution.

[3]

Outline a method used to correlate the distribution of plant species with an abiotic factor.

[2]

Markscheme

plant distribution closely linked to levels of abiotic factors in the environment;
given organism can survive only within a certain temperature range to which it is adapted;
water is a limiting factor in most terrestrial ecosystems and plants are classified according to ability to tolerate water shortage;
most plants can only tolerate narrow pH range;
light intensity/quality/wavelength and duration/photoperiod are important for photosynthesis;
most plants cannot tolerate large fluctuations in salinity/high salinity;
mineral nutrients affect plant fertility/soil structure/water retention;
Accept ONE correct reference to herbivore activity

transect used when there is a transition in habitats and populations;
description of use of a line or belt transect;
height variation/light intensity/salinity/various abiotic factors can be recorded;
along the transect, along with sampling of plant and/or animal species present;

Date	May 2010	Marks available	1	Reference code	10M.3.SL.TZ2.20
Level	Standard level	Paper	Paper 3	Time zone	Time zone 2
Command term	Describe	Question number	20	Adapted from	N/A

Question

List four factors that affect the distribution of plant species.

[4]

Describe one effect of plants on an abiotic factor in a pioneer community.

[1]

Markscheme

pH of soil;
water /humidity;
light;
temperature;
salinity;
mineral nutrients;
competition;
altitude;
pollinating agents;
predators / parasites;
slope;

adds humus to soil;
breaks down rock (through roots, chemicals, rhizoids);
holds soil/prevents erosion;
aerates soil;
provides shade;
reduces water content;

Date	November 2011	Marks available	1	Reference code	11N.3.SL.TZ0.19
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	List	Question number	19	Adapted from	N/A

Question

List two abiotic factors that affect the distribution of plant species.

1. …………………………………………………………
2. …………………………………………………………

[1]

State one example of secondary succession.

[1]

Distinguish between fundamental and realized niches.

[2]

Discuss the difficulties of classifying organisms into trophic levels.

[2]

Markscheme

temperature / water / light / soil pH / salinity / mineral nutrients
Award [1] for any two abiotic factors.

regrowth following forest fire/fallow land/earthquake / other example of secondary succession

fundamental niche is the potential mode of existence and realized niche is the actual mode of existence;
fundamental niche depends on the adaptation of a species;
competition/predation prevents a species from occupying its entire fundamental niche;
realized niche is usually smaller than fundamental niche;

organisms may fit into more than one trophic level;
omnivores consume organisms from all levels of the food chain;
there may be seasonal changes in trophic levels depending on food supply;
some organisms alter diet with their life cycle (e.g. some amphibians);

Date	November 2012	Marks available	3	Reference code	12N.3.SL.TZ0.21
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Outline	Question number	21	Adapted from	N/A

Question

Water is one factor that affects the distribution of plant species. Outline three other factors that can also affect plant distribution.

Markscheme

temperature affects metabolism/enzyme activity/transpiration rate/germination / each plant species has an optimum temperature range;
light affects rate of photosynthesis/(time of) flowering;
soil pH affects absorption of minerals/enzyme activity / each plant has an optimum pH range / some plants require acid soil / some plants require alkaline;
salinity affects the osmotic potential / most plants function in narrow range of salinity / salts affect the water uptake by the plants;
mineral nutrients required for synthesis of organic molecules;
presence of (suitable) pollinator/dispersal organisms to aid reproduction;
distribution (number and type) of predators/herbivores/diseases/pathogenic organisms which harm plants;
competition from other plants (for resources);
other valid factor with brief outline;
Accept examples for each factor eg nitrates are necessary for protein synthesis.
Award [0] for a list of factors.

Date	November 2010	Marks available	1	Reference code	10N.3.SL.TZ0.20
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Calculate	Question number	20	Adapted from	N/A

Question

Many factors affect the distribution of animal species including weather patterns. The mosquito Anopheles is a carrier of malaria, a disease that kills one to two million people annually. The eggs of the mosquito are laid in water and they hatch out as larvae before turning into adult mosquitoes. A study was undertaken to look at the influence of weather patterns on the incidence of bites on children. Being bitten increases the risk of catching malaria.

The graphs show human biting rates (HBR) by Anopheles gambiae and Anopheles funestus and precipitation over the study period.

Calculate the difference in peak HBR for A. gambiae and A. funestus for week 6.

[1]

Suggest how predictions of global climate changes, such as predictions of precipitation patterns, could be used to help control malaria.

[1]

Suggest another factor which might affect the ecological distribution of mosquitoes.

[1]

Markscheme

35 (accept answers in the range of 34 to 37)

a. spraying insecticides just before rainy seasons;

b. draining swamps before (and after) rain;

c. providing (endangered) population with repellents/mosquito nets before rainy season;

temperature / breeding site / food supply / predators / other reasonable answer

Do not accept global warming.

Date	November 2010	Marks available	2	Reference code	10N.3.SL.TZ0.21
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Distinguish	Question number	21	Adapted from	N/A

Question

Distinguish between fundamental niches and realized niches.

Markscheme

fundamental niche is the potential mode of existence whereas realized niche is the actual mode of existence;

adaption/competition/predation/powers of distribution are important in determining the realized niche;

Date	November 2010	Marks available	3	Reference code	10N.3.SL.TZ0.6
Level	Standard level	Paper	Paper 3	Time zone	TZ0
Command term	Evaluate	Question number	6	Adapted from	N/A

Question

The graphs show human biting rates (HBR) by Anopheles gambiae and Anopheles funestus and precipitation over the study period.

Evaluate the effect of increased precipitation on HBR for both species.

Markscheme

a. both species show relationship between elevated precipitation and higher HBR (e.g. between week 0 and week 8 / week 100 and week 108);

b. there is a lag between the period of precipitation and the increase in HBR;

c. sometimes elevated precipitation does not lead to peaks of HBR (e.g. week 27);

d. precipitation has a greater effect on Anopheles gambiae/A. gambiae;