Outline the similarities and differences between predation and competition.

Explain how predation may lead to stability in a population of the prey species.

Explain how predation may lead to long-term population decrease or extinction of the prey species.

With reference to named countries, discuss the effectiveness and impacts of two different strategies for stabilizing their human population.

Similarities:
both can be population/species interactions (interspecific);
in both two individuals are involved (includes both inter- and intra-specific);
both can lead to a stable equilibrium in populations;
both can lead to extinction of a species;
both limit population size;
at least one species is negatively affected in both;
both are density dependent;

Differences:
predation negatively affects one species / competition (usually) negatively affects both competitors;
predation involves animal species / competition may involve animal or plant species;
in predation, one species (predators) depends on the other / competition neither are dependent on the other;
(only) predation involves direct killing/eating of species;
(only) competition reduces available resources for both species;
competition can involve competing for habitat not just food;
the species involved in predation represent two different trophic levels, whereas competition may represent the same trophic level;

Award [3 max] if only similarities or only differences are stated.

[4 max]

as population of prey increases, more food is available for predators;
this leads to increase of predator population;
…so there is more predation / so prey population decreases;
…leading to cyclical changes around a stable equilibrium;
this is negative feedback / density dependent mechanism;

These marks can be awarded for appropriately annotated diagram, clearly demonstrating the marking points.
Answers that incorporate good/strong examples can help the student gain marks for EoI.
Do not award marks for just giving examples in this question.

[3 max]

there may be excessive/unusually high growth/predation by predator population so the prey species declines;
…eg if predator is a non-native/invasive/introduced species;
…or if predator’s limiting factors (eg disease/predation/climate) become more favourable;
predator populations may continue to grow unregulated by a given prey species if they feed on other prey species as well leading to the long-term decline of the given prey species;
If an environmental change causes decline of other prey species, predators with a choice of prey may focus predation more heavily on remaining species leading to their long-term decline;
if prey populations fall for some other reason (human hunting), the population may become too small to recover from predation;
If the prey species does not have time to reproduce then prey numbers will decline / if predation exceeds the natural rate of replenishment of the prey;

These marks can be awarded for appropriately annotated diagram, clearly demonstrating the marking points.
Answers that incorporate good/strong examples can help the student gain marks for EoI.
Do not award marks for just giving examples in this question.

[3 max]

Please note: although "quality of expression" marking is no longer used in exams, this question from a past syllabus may still be useful for student practice.

For each of two strategies (do not credit more than two strategies) award [4 max], but only [3 max] for an imbalanced discussion.

If more than two strategies are mentioned please credit the two highest scoring strategies.

If no named countries [6 max] but award no specific marks for the countries.

The sub-headings below are for guidance only. Credit should be given for the Marking points whether the student identifies them under these titles or not. E.g. One Child Policy may be identified as a strategy or an example etc

anti-natal policies:
Strategy: tax/welfare disincentives;
Effect:
too expensive to have many kids thus causing a reduction in birth rate;
limits costs to the state of providing facilities for kids;
the population is law abiding and so will have fewer children so abide by the law;
Impact:
gender preference leads to increased selective abortions/abandonment of babies;
For example, one child policy of China and the "little emperors";
the country has an aging population that requires healthcare;

Strategy: Education/promotion/provision of free/cheap contraception;
Effect:
population growth is slowed;
Impact:
individuals control their fertility;
conflicts with cultural/religious beliefs/norms;
For example, Philippines is a strongly Catholic country where the Church supports the ban on contraception;

Strategy: Emancipation/higher status/education of women;
Effect:
reduces the fertility rate of women in the country;
fewer children as women have more decision making/career opportunities available;
Impact:
this can enable families to increase economic productivity;
but this can upset male dominated societies/cultures/religions;
For example, in Uganda the more male children gives greater social status to men;

Pro-Natal policies
Strategy: Tax incentives;
Effect:
may prevent population decline;
…may have political benefits in maintaining economic productivity;
Impact:
population may already be unsustainable/beyond carrying capacity;
Is costly to the government;
increase proportion of young people to stabilise population distribution;
For example, France pays a bonus for each extra child born in a family;
free public transport etc to support the overall strategy of increasing family size;

Strategy: Welfare incentives/Extended maternity/paternity leave/subsidized childcare;
Effect:
increase number of children a family is willing to have, as little cost/allows the parents to be economically independent;
Impact:
high cost to businesses/industry as workers unavailable;
can lead to a rapidly growing population of young people;
For example, Singapore in the 1980s covered the cost of maternity leave for the first 4 babies;

Strategy: Laws against birth control/family planning;
Effect:
population will rise to the required number for the country;
Impact:
can be too authoritative with bans on contraception/no control over fertility;
cultural and religious requirements are met;
For example, Romania did ban abortions and strongly discouraged the use of contraception;

Strategy: Immigration laws;
Effect:
partly effective but illegal immigration still happens;
Impacts:
political divisions about what to do to stop illegal entry;
human rights might be breached with deportation of migrants;

Allow other reasonable answers like healthcare that specify how the population will be stabilised.

Award [7 max] for marking points above, and [1 max] for a clear conclusion that is justified by points raised.

Note to examiners: An isolated statement/opinion e.g. “tax incentives are the most effective strategy” should not be considered as a valid conclusion. A valid conclusion may, however, be stated within the body of the response rather than at the end, and may involve some balanced decision:

e.g. Emancipation/higher status/education of women is the most effective strategy because it simultaneously addresses many other social issues/human rights;  [1 max]

[8 max]

Expression of ideas [2 max]

The differences between predation and competition provided no problem for most candidates. The similarities were much more difficult for them to articulate. Weak answers showed glimpses of understanding and too vague was the annotation often used. Some candidates mentioned predation being a subset of competition this usually ended up with the candidate writing a confused answer.

Many candidates gave very clear, precise answers here showing a good understanding of predator/prey relationships. Some candidates were confused by the term “stability” and so wandered off the topic of the question.

The majority of candidates struggled with this question and many ended up repeating their answer to 2bi. In doing this they often managed to gain one mark from mentioning the prey reproduction rate. Stronger candidates mentioned invasive species or environmental changes for the prey. When candidates mentioned humans and hunting they usually assumed the humans were the predator by the fact they were hunting. This was not accepted as a correct answer. Hunting by humans could be used as a factor making the prey numbers very low, and so natural predation could make the species decrease or become extinct.

The candidates found naming two countries and 2 strategies for stabilizing human population straightforward. The tendency was to use one country per strategy, this was fine. The stronger candidates did use more countries for each strategy they used. Very few candidates mentioned more than two strategies or only one. The weakest part of the question was giving the effectiveness of the strategy. The candidates found the positive and negative impacts easier to write about.