Question 1: Discuss Excellence

Kauri snails, or pūpū-rangi (Paryphanta spp.), are northern giant land snails that evolved in New Zealand before two nocturnal predators, possums and hedgehogs, were introduced. They live in fertile soil full of earthworms and can live 20 years or more. They are most active at night and spend the day under leaf litter or plants. Their droppings show they eat mainly earthworms and some small snails, whose shells supply calcium. They mate mostly from April to July, apparently set off by weather such as rain, and lay about six eggs three times a year, in a hole they dig or under leaf litter at the foot of a tree. Hedgehogs (Erinaceus europaeus) are also out at night and eat kauri snails; where it is cold they may hibernate for some months of the year, once the ground falls below 11 °C. Brushtail possums (Trichosurus vulpecula), also nocturnal, eat kauri snails too, spotting the slow snails from up in the trees.

Evaluate reasons for the coexistence and survival of these species in Northland.

The 2024 paper, page 2 ↗ Marking schedule, page 2 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

1 Start with predation. How does it support the possum’s survival?
Kauri snails are a large, slow, easily found food for the possum. More food means a better chance of surviving and more energy to breed, which increases the possum’s reproductive success.
2 The possum and the hedgehog compete for snails. When does that competition ease?
While the hedgehog hibernates. For those months the possum has the snails to itself, gets more food, and its reproductive success increases.
3 What does hibernation do for the hedgehog itself?
It saves energy when food is scarce and the cold is harsh, so the hedgehog survives to breed when conditions improve: its reproductive success increases.
4 What does the possum gain from being nocturnal?
Its activity matches its prey’s, and at night it competes with fewer species for food (mainly the hedgehog), so it eats more and its reproductive success increases.
5 How does the snail survive alongside two predators?
At night it has plenty of food and does not dry out, which raises its survival. Laying three times a year, when conditions suit, gives more young that survive, which replaces losses to predation and raises its reproductive success.
6 So why can all three coexist, and how secure is that?
Each behaviour raises that species’ survival and reproductive success, so all three persist in Northland. But the snail’s numbers have fallen since nocturnal predators arrived; it coexists because its breeding keeps up with its losses.

Answer Predation gives the possum a large, slow, easily found food, raising its survival and reproductive success. Its competition with the hedgehog eases while the hedgehog hibernates, when the possum has the snails to itself. Hibernation lets the hedgehog save energy while food is scarce and the cold is harsh, so it survives to breed. Being nocturnal keeps the possum in step with its prey and leaves it fewer competitors at night, mainly the hedgehog, so it eats more. The snail survives alongside both predators because night brings plenty of food and no drying out, and because laying three times a year, when conditions suit, produces more surviving young to replace those eaten. Each behaviour increases that species’ survival and reproductive success, which is why all three persist in Northland; the coexistence is uneasy, though, because the snail’s numbers have fallen since nocturnal predators arrived, and it persists only while its breeding keeps up with its losses.

What the marker wanted

Achieved The describe points: both relationships, night activity for the snail, hibernation, laying more than once, and the possum’s night activity.
Merit Those explained, each linked to survival or reproductive success.
Excellence Discusses how the relationships and behaviours of all three species support survival and reproductive success, through six possible points: predation feeding the possum; competition easing while the hedgehog hibernates; the snail’s night activity bringing more food AND less drying out; laying three times a year, when conditions suit, giving more viable young; hibernation saving energy through scarcity and cold; and the possum’s night activity reducing competition and matching its prey. Each must end on survival or reproductive success. Two give E7; three or more, E8.

One answer, N0 to E8. In 2024 the Excellence points are counted higher than usual: two give E7, three or more E8.

In our words, from NZQA’s 2024 marking schedule.

Common mistake

Explaining each animal’s advantages one by one, without linking them together or to overall reproductive success. NZQA’s 2024 report says that is where Merit answers to Question One stopped.

How did it go?

Got it moves it further out. Review brings it back tomorrow.