| Date | November 2019 | Marks available | 3 | Reference code | 19N.1.SL.TZ0.3 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Figure 9(a): Fact file on the round goby (Neogobius melanostomus)
- An invasive species from Asia.
- First discovered in the St Lawrence River in 1990.
- Females lay eggs three times a year; up to 5000 eggs at a time.
- Young fish mature quickly.
- Can eat up to 4000 eggs of other fish in 15 minutes.
- Aggressively defend the best egg-laying sites, out-competing the native mottled sculpin (Cottus bairdii).
- Eat invasive zebra mussels.
- Eaten by native fish, such as lake trout and yellow perch.
Figure 9(b): Pictures of the round goby and mottled sculpin
Using Figures 9(a) and 9(b), identify one feature of the round goby that shows it is an r-selected species.
With reference to Figure 9(a), outline how the round goby both positively and negatively affects the St Lawrence River ecosystem.
With reference to Figure 9(a), explain why the realized niche of the mottled sculpin has changed in recent years.
Markscheme
frequent egg laying (3 times per year);
many eggs laid at one time (5000);
young fish grow quickly / early maturity.
Positive [2 max]:
provide additional food source for native fish (e.g. yellow perch);
eat other invasive species, such as the zebra mussel.
Negative [2 max]:
increased competition for food, outcompeting native fish;
outcompetes the native mottle sculpin for the best egg-laying sites;
outcompetes native species which may become extinct;
eat other fish eggs, reducing populations/biodiversity;
introduce disease, reducing populations/biodiversity.
Accept any other reasonable response.
Do not accept only ‘outcompetes native species’, for credit must be linked to competition for food, egg laying sites or species extinction.
Do not accept ‘aggressively takes the habitat of native species’.
resources declined due to competition with round goby;
competition for/loss of nesting sites;
loss of food resources due to additional competition;
realized niche has changed because of impacts of climate change affecting temperature.
