Define the term species.

Avocets, seen in Figure 2, often gather in large populations of up to a few thousand birds before migrating.

Figure 2

[Source: https://en.wikipedia.org/wiki/Pied_avocet#/media/File:Avocet_from_the_Crossley_ID_
Guide_Britain_and_Ireland.jpg, by Richard Crossley — The Crossley ID Guide Britain and Ireland]

Describe a method to estimate the size of an avocet population.

Oystercatchers and avocets both feed on small animals in the mud of the wetlands. State the most likely relationship between these two species.

State its trophic level in the ecosystem.

Describe its role in the carbon cycle of the system.

a group of organisms that interbreed and produce fertile offspring

[1 max]

EITHER
capture-mark-release-recapture/capture-mark-release/capture-mark-recapture/Lincoln Index;
trap birds (in mist nets) and mark/tag them before releasing (m₁);
recapture a sample of birds after a sufficient period of time for individuals to mix;
calculate total population (P) from proportion of marked/tagged birds (m₂) in recaptured sample (R) / use Lincoln Index formula to calculate total population(P) = (number of animals first marked and released (m₁) x number of animals captured in second sample (R))/ number of marked animals in recapture (m₂);
suitable for closed population (not suitable for migrating birds).

OR

take aerial photograph of whole population/known fraction of population;
divide photograph into quadrats of known area;
count birds in a number of random quadrats;
calculate total population by multiplying for the whole area;
suitable for closed population (not suitable for migrating birds).

OR

set survey boundary/geographical range of species;
divide area into quadrats;
count birds within random quadrats/representative area (in real time rather than from photographs) / count all birds in area;
extrapolate bird numbers found to the whole area / calculate total population by multiplying for the whole area.

[3 max]

competition/niche-sharing

[1 max]

primary consumer/herbivore/second trophic level/trophic level 2

[1 max]

it is a carbon store;
it absorbs (organic) carbon from producers;
it provides (organic) carbon to consumers/carnivores;
it releases (inorganic) CO₂ through respiration;
it provides (organic) carbon to decomposers;
it provides carbon /carbon dioxide (CO₂) to atmosphere as it decomposes.

Do not accept ‘feeds off plants without reference to carbon/carbon compounds’.

[2 max]

Many students were able to clearly define the term species. A common error was to give a generalised definition e.g. species that have common characteristics.

This question was generally answered well. Most candidates achieved some marks for this question with many attaining full marks.

Most candidates correctly identified ‘competition’ as the relationship between oystercatchers and avocets.

The majority of candidates answered this question correctly.

Response to this question was variable. Common error was not to directly answer the question or ensure the response referred to flows or stores within the carbon cycle.