Describe the body length frequency of the B. italica worms collected in this study.

The relationship between A. pallipes and B. italica is mutualistic.

A. pallipes feeds on algae and another worm, B. exodonta, lives inside A. pallipes as a parasite. State the trophic level of B. exodonta in this food chain.

Distinguish between mutualism and parasitism, providing another example of mutualism and another example of parasitism.

a. higher frequency of medium length worms 
b. shows normal distribution 
c. lower frequency at extremes

Allow correct numerical description of these points.

secondary consumer / third trophic level

a. in parasitism only one organism benefits whereas in mutualism both benefit 
b. example for both parasitism AND mutualism

Do not allow B. italica or B. exodonta as examples.

eg parasitic: human tapeworms AND mutualism: bacteria in human digestive tract

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.

Outline how the edge effect can affect diversity in forests.

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.

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.

Each of the mesocosms is an open ecosystem. State the property that makes the mesocosms open ecosystems.

Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.

Outline top-down effects on the bacteria in the four mesocosms. 

Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.

there is exchange of matter/energy
OR
there is an exchange between the surface of the water and the atmosphere ✔

 eg: matter could be nutrients/gas/water/minerals/etc; energy could be heat or light

soil and no fish «mesocosm» AND soil and fish «mesocosm» ✔

Both mesocosms required

Accept answers such as “the two with soil”.

a. zooplankton feed on bacteria reducing their numbers ✔

b. fish feed on zooplankton «therefore» increasing bacterial population ✔

a. conditions closer to levels experienced naturally by the organism ✔
OWTTE

b. natural variation of abiotic variables ✔
Accept examples, eg: temperature, dissolved oxygen

c. more natural behaviour/interactions ✔

d. not harm organisms by removing them from natural habitat ✔

Cryptococcus neoformans and the closely related species Cryptococcus gattii are human fungal pathogens. The reproduction of these yeast species on increasing concentrations of pigeon droppings (PD) was examined to determine whether they occupy the same or different ecological niches. The results for reproduction are expressed as a percentage relative to the control.

Suggest how this experiment shows that pigeon droppings represent a realized ecological niche for C. neoformans and a fundamental (but not a realized) niche for C. gattii.

a. the realized niche is the actual while the fundamental niche is «all of» the potential

b. «shared» fundamental niche shown by equal reproduction on control

c. C. neoformans reproduces on PD indicating a realized ecological niche

d. competitive exclusion decreases realized niche of C. gattii

e. C. gattii reproduces poorly on PD representing a fundamental niche
OR
C. gattii reproduces poorly on PD so not a realized niche

State two bottom-up factors affecting algal blooms.

Explain how top-down factors control algal blooms.

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

Predict one example of macroplastic pollution that is likely to be found in this lake.

State two possible effects on organisms of microplastic pollution.

Outline the effect of wind on the distribution of plastic pollution in this lake.

Suggest changes in the management of the national park that could reduce the amount of macroplastic pollution.

plastic bottles
OR
fishing gear
OR
plastic bags
OR
plastic wrappers

Award [1] for any source.
Allow any other valid named source.

a. ingestion can reduce feeding
OR
false feeling of satiation

b. microplastics absorb toxins from water

c. filter feeders ingest the microplastics with the toxins

d. biomagnifications/bioaccumulation

a. microplastic density higher along the «north» western shore than the eastern shore
OR
wind blows plastics to opposite coast
OR
wind blows plastics away from their source/city/camping grounds
OR
wind increases degradation of macroplastics into microplastics

b. wind causes currents which moves the plastics

c. macroplastic pollution less affected by wind than microplastic pollution

a. improve city waste disposal

b. recycling programs
OR
develop community service teams to collect plastics «around the lake»/OWTTE

c. place litter containers/garbage cans close to camping sites

d. fines for those causing pollution
OR
pass littering laws

Zoos devote much effort to preserving and breeding elephants in captivity. Data for births resulting from artificial insemination in zoos in the United States from 1960 to 2012 are shown below.

54% of successful artificial inseminations have resulted in miscarriages, stillborn births or premature deaths.

Evaluate the success rate of breeding elephants by artificial insemination using these data.

Discuss two advantages of ex situ conservation measures. 

State the two components needed to calculate the biodiversity of an area.

a. «not very successful as» less than half of the artificial inseminations have resulted in live births 

b. there are no data for artificial insemination that did not result in pregnancy / no data for normal breeding success «in zoos»

Accept answers in the converse: «not very successful as» more than half do not result in live births

a. raise awareness / gain widespread public/political support for conservation actions 

b. breed endangered species in captivity «for reintroduction» 

c. education/research opportunities 

d. lower maintenance/cost than in situ conservation 

e. protect endangered species

a. number of organisms of each species «present» 

b. «total» number of species
OR
«total» number of organisms of all species found

Some scientists estimate that available phosphorus reserves in the Earth will be completely depleted within approximately 100 years. Discuss the implications of these estimates.

The percentage of phosphorus in an ecosystem that is recycled per year is in most cases very small, and far smaller than the percentage of nitrogen that is recycled. Suggest reasons for this difference.

a. production of fertilizers will decrease/price of fertilizers will rise 

b. less food production / increase in cost of foods 

c. development of alternative methods of agriculture 

d. Phosphate needed by living organisms for nucleic acids/ATP so lack will affect growth negatively

a. largest store of phosphorus «in ecosystems» is in marine sediments and minerals/phosphate rock while nitrogen is in the atmosphere 

b. main source of release of phosphorous is by weathering of rocks «very slow process»/ nitrogen is by bacterial action 

c. high concentrations of nitrogen/low concentration of phosphorous «compounds» in living organism 

d. phosphorus is not a very soluble mineral

Define indicator species.

Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant.

Determine whether islands are open or closed ecosystems.

organism that is present/absent when specific environmental conditions exist
OR
organism used to assess a specific environmental condition

a. example  eg: DDT / mercury / cadmium

b. substance accumulates in «fat» tissue/not excreted «when consumed» 

c. contaminated organisms consumed «in large quantities» by higher level consumers 

d. pollutant becomes more concentrated at each higher trophic level / through the food chain 

e. some pollutants are more likely to be biomagnified «accumulate in fat tissue»
OR
some organisms are more likely to be affected by biomagnification than others
OR
biomagnification not the same at each trophic level 

Only [2] if verified example not given.

closed because islands do not exchange matter/nutrients with surroundings
OR
open because islands do exchange matter/nutrients with surroundings

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

State the trophic level of Zooxanthellae.

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.

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

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

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”.

Outline a method that could have been used in this study to measure the numbers of sea urchins per 0.25 m².

Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.

Sea urchins are destroying the giant kelp alga (Macrocystis pyrifera) marine forests of South East Australia. Suggest a reason that sea urchins might be an invasive species in this environment.

a. with quadrats (of 0.5 m side / 0.25m²);

b. (quadrats) position determined at fixed distance by transects
OR
(quadrats) position determined at random;

c. random sampling / capture-recapture;

d. average number calculated;

a. sea otters (feeding on sea urchins) limit sea urchin population;

b. the largest sea urchins are eaten;

c. shown by low biomass/small size (of sea urchins);

d. fewer/smaller sea urchins allow for increase in algae population;

e. sea otters have a top down effect;

Allow converse reasoning.

the sea urchins’ limiting factors in their original habitat are missing
OR
lack of (natural) predators for sea urchins

Most candidates did well on this question, especially strong ones, although there was evidence that many candidates are not familiar with population evaluation skills. Candidates should be aware that writing "quadrants" (with a "n") is questionable, and that although it may not be assumed that they knew what echinoderms or sea urchins were, the capture-mark-release-recapture method was not really appropriate to evaluate their numbers, given the very limited areas of 0.25 m².

The majority of candidates could suggest that the sea algae population could be affected by sea otters feeding on sea urchins; most nevertheless did not use the graphs or mention that a top down effect was present.

Many suggested that sea urchins' predators were not present, but too many irrelevant or blank answers were seen.

Define fundamental niche.

Outline a reason for organisms seldom occupying their entire fundamental niche.

Describe the relationship between Zooxanthellae and reef-building coral species.

the potential/full range of conditions under which an organism can live

competition for resources/named resource

OR

competitive exclusion «limits the niche»

a. «endo»symbiotic/mutualistic relationship

b. zooxanthellae/photosynthetic algae/dinoflagellates live in coral tissues

c. coral provides protection for algae/dinoflagellates

d. algae/dinoflagellates provide minerals/products of photosynthesis/oxygen/sugars to coral

[Max 2 Marks]

Outline the changes in elk population between the years 1930 and 2004.

List two biotic factors, other than wolf predation or culling, that could affect the elk population.

1.

2.

a. between 1930 and 1968 the numbers were reduced;

b. after 1968/in the 1970s the numbers increased;

c. in 1990s1995 the numbers decreased again;

d. lowest in 1968 and highest in 1990;

a. relative rates of natality;

b. disease/lack of food;

c. competition for the same resources;

d. immigration/emigration/migration;

The majority of candidates had no difficulty outlining the changes in elk population.

Many candidates could list two biotic factors, others did not pay attention to "biotic" and included abiotic factors.

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

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

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

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

2000–2008

a. natality AND mortality

b. immigration AND emigration

c. resources/abiotic conditions/carrying capacity

d. predation/hunting

[Max 2 Marks]

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]

Suggest how nitrogen and phosphate cycles can be disrupted by humans or extreme weather events.

a. excess rains/floods/irrigation can wash away nutrients/N/P by leaching;

b. excess rains/floods/irrigation can lead to waterlogged soils;

c. waterlogging leads to denitrification due to anaerobic conditions;

d. nutrients are added to the cycles by application of fertilizer;

e. nutrients are removed by the harvesting of agricultural crops;

Nitrogen:
f. lightning increases N in soil;

g. planting legumes increases N in soil;

Phosphate:
h. mining of P speeds up the P cycle/depletes P reserves;

i. phosphorus is added to waters in detergents;

j. phosphorus is mined/taken from rocks for making detergents/fertilizers;

Only the strongest candidates could focus on human impact and extreme weather events for this question, as most provided unorganized answers relating to knowledge addressed in previous papers about nutrient cycles in general, limited phosphate availability, pollution, global warming or eutrophication; some even mentioned earthquakes and volcanoes, which may be catastrophic, but are not weather events.

Identify the group that is most intolerant to pollution.

Deduce the meaning of n_i in this formula.

Deduce the meaning of a_i in this formula.

Outline how organisms in Group V could be used to measure pollution in an environment.

«group» I ✔

number of individuals of a species ✔

tolerance rating of that species ✔

a. group V organisms «could» contain indicator species ✔

b. group V organisms can survive in polluted environments «while others cannot» ✔

c. they have a high tolerance/BI index
OR
«relative number of» indicator species can be used to calculate the value of a biotic index ✔

d. the more group V present could indicate more pollution ✔
OWTTE

e. absence of group V could indicate a cleaner environment ✔

Identify how the pattern in mammals is different from reptiles and birds.

Describe how invasive species such as F. silvestris can have a significant impact on native species.

Suggest a method to limit the impact of F. silvestris on native species.

State the role of an indicator species.

Identify possible approaches to maintain the population of P. sandwichensis.

a. more extinct than endangered «in mammals as opposed to reptiles and birds»

b. total percentage extinct plus endangered mammals lower than reptiles and birds

[Max 1 Mark]

a. cats/invasive species compete with native species for food/habitat/resources

    OWTTE

b. invasive species/cats may reduce/endanger native populations

c. invasive species/cats may change the structure/balance of the food web/chain

[Max 2 Marks]

a. control population/sterilization «of cats»/culling/hunting

b. keep household cats indoors

[Max 1 Mark]

a. early warning system

b. provide information on environmental conditions/ecosystem

OWTTE

[Max 1 Mark]

a. ex-situ/zoos/captive breeding

b. control predators

c. in-situ/management of natural reserves/breeding habitats/parks/resources/clean-up pollution

d. education

    OR

    government legislation

Accept any other valid answer

[Max 2 Marks]

Outline three issues arising from the release of pollutants into the environment.

a. reduction in biodiversity

b. biomagnification occurs

c. change in abiotic conditions

    eg: loss of soil quality/loss of ozone layer

d. global warming

    eg: methane, acid rain, climate change

e. community changes

    eg: increase in pest species

f. health hazards/mutations

    eg: animals choking on plastic, cancer, etc

g. other valid issue

    eg: poisoning from toxins/pollutants

[Max 3 Marks]

Describe reasons that the availability of phosphates may become limiting to agriculture in the future.

Explain how eutrophication can occur from the excessive use of phosphates.

a. phosphate-rich rocks/resource is limited ✔ 

b. demand exceeds availability of phosphorus 
OR
there is greater consumption than P available ✔

c. cycling of phosphorus is slow ✔

d. as crops are removed, the phosphate levels within the soil is continually depleted ✔

e. there is no biological/industrial way to replenish the mineral «fast enough» OWTTE
OR
«phosphate» fertilizers need to be added «to replenish it in the soil»
OR
«lost phosphate» does not go back in the cycle ✔

a. phosphates are leached to lakes/rivers ✔

b. induces incremental growth of plants/bloom/algae ✔

c. algae do not let light go through water so less photosynthesis ✔

d. plants/algae die/decay ✔

e. bacterial decomposition consumes the oxygen ✔

f. creating state of hypoxia
OR
greater biochemical oxygen demand ✔

g. causing death of «aerobic» organisms ✔
eg: fish

Explain how an ecological community structure could be affected by the removal of a keystone species.

a. «keystone species» have a main/disproportionate role in the maintenance of the structure of a community ✔

b. not necessarily top predator/most abundant species
OR
affect other organisms even if they have a small biomass/productivity ✔

c. may impact a top-down/bottom-up control ✔

d. «if removed» cause increase in populations of secondary consumers and decrease of primary consumers ✔
OWTTE

e. «if removed» may cause loss of balance in food chain/community ✔

f. «if removed» may cause «drastic» loss of biodiversity
OR
extinction of species ✔

g. example of named keystone species ✔
eg: honey bees

h. example of role in the environment where they are found ✔
eg: pollinate flowers

i. example of change if removed ✔
eg: plant reproduction is reduced

This question can be answered by referring to one specific species

A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.

State one abiotic factor that will determine the type of ecosystem in a succession.

A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.

Predict the process of succession that takes place on exposed bare ground as the glacier retreats.

Compare and contrast food chains and food webs.

temperature/precipitation/rainfall/minerals /pH of soils/light/humidity/wind/slope (in this specific example)

a. (bare ground) colonized by microorganisms/pioneer species

b. thin soil forms from rock fragments / decomposing organisms

c. soil retains water from melting permafrost/ice

d. grasses/small plants/herbaceous plants/moss grow

e. (larger plants) create habitat for animals

f. weather/climate may limit plant size/biodiversity

OR

climax community forms

Similarities:

a. in both food webs and chains organisms are arranged by trophic levels/feeding positions 

b. both represent the transfer of food/energy in an ecosystem 

c. both include producers and consumers 

Differences:

d. one species could occupy different trophic levels in a food web but not in a food chain / converse 

e. food chain represents one possible feeding option for each organism but food web represents more possible feeding relationships/trophic levels

OWTTE
(max 1 for similarities)
(max 1 for differences)

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

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.

Distinguish between tropical rainforest and taiga in terms of nutrient stores, nutrient flows and climate. Gersmehl diagrams can be used to support your answer.

A type of ecosystem in Brazil is tropical rainforest. Construct a Gersmehl diagram on the outline provided, to show flows of nutrients between stores in tropical rainforests.

Gersmehl diagram showing the following:

a. thick arrow from soil to biomass:

b. thick arrow from litter to soil;

c. thin arrow from biomass to litter;

Most candidates did poorly on this question; some had difficulty drawing arrows in correct directions, and most could not indicate differences in flows using arrow thickness; blank answers were seen.

Discuss how crop plants obtain the phosphorus that they need to grow and whether the supply of phosphorus to crops is sustainable.

Natural cycle

a. plants absorb phosphorus from the soil by the roots

b. soil phosphorus comes from weathered «phosphate» rocks

c. «soil/organic» phosphorus «also» comes from humus/plant/animal residues/guano/microorganisms

d. phosphorus is a limiting «macronutrient» factor in plant growth
OR
phosphorus is necessary for vital functions/ATP/DNA
OR
deficiency of phosphorus «in soil» limits plant growth/production 

Sustainability

e. «natural» phosphorus cycle is slow/not sustainable with increased crop production

f. phosphorus is replenished «in the soil» by use of mineral/organic fertilizers

g. phosphorus/phosphate is «mainly» mined from «phosphate» rocks

h. rocks are becoming used up/inaccessible so non-sustainable/non-renewable
OR
the use of fertilizers is non-sustainable «with increased crop production»

i. increased demand for food/meat/dairy/grain increases demand for fertilizers

j. runoff/erosion/leaching of fertilizers decreases potential supply for crops/OWTTE

Discuss the causes and consequences of eutrophication.

causes:

a. excess nutrients/nitrates/phosphates in an aquatic system

b. natural runoff from soil/erosion/weathering of rocks

c. runoff of fertilizers «from agricultural land/golf courses»

d. partially treated sewage/animal waste discharged into waterways

consequences: [4 max]

e. algal blooms

f. blocks light for photosynthetic organisms

g. dead organisms sink to bottom of water and decompose

h. decomposers/microorganisms increase BOD/use oxygen

i. oxygen/DO availability for other organisms decreases

j. decrease in biodiversity/disappearance of organisms

OWTTE

[Max 6 Marks]

Distinguish between fundamental niche and realized niche.

State the month where the population reaches its maximum.

Outline how factor Y affects the species from January to April.

Suggest, with a reason, what factor Y could be.

fundamental niche is all potential conditions a species could live in whereas realized niche is actual conditions under which the species live

April

a. limited effect on low/stable population size from January to March
OWTTE.

b. large effect increases population size from March to April 
OWTTE.

c. niche conditions decrease from January to March 

d. niche conditions improve from March to April

a. factor 
eg temperature.

b. explanation
eg as temperature increases in spring «March to April» so the conditions for the species are more favourable.