How relationships between species keep an ecosystem stable

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Growth of two model species alone and together (model data)

   species	growth alone (model units)	growth together (model units)
   M	20	26
   N	20	20

2. 1.

   Bo reads the model data on growth. Which relationship fits the table?

   • Competition: both species grow less when together
   • Parasitism: species M gains and species N is harmed
   • Mutualism: both species gain, because species N did not lose
   • Commensalism: species M gains and species N is unchanged

3. Two Paramecium species grown alone and together (model data)

   species	count alone	count together
   Paramecium aurelia	160	140
   Paramecium caudatum	150	0

4. 2.

   Esme reads the model data on two Paramecium species in a test tube. Which relationship fits the table?

   • Mutualism: both species do better together than they do alone
   • Parasitism: Paramecium aurelia gains from Paramecium caudatum
   • Competition: both use one limited resource, and one drops to 0
   • Commensalism: both species gain from sharing the same test tube

5. Shoots on a host plant with different numbers of model parasites on it (model data)

   parasites on the host plant	shoots on the host plant
   0	20
   2	17
   4	14
   6	11

6. 3.

   Kira reads the model data on host plants. Which statement fits the table?

   • Each 2 extra parasites go with 3 fewer shoots, and the host keeps shoots
   • Each 2 extra parasites go with 3 more shoots, so the parasites help the host
   • Each 2 extra parasites go with 6 fewer shoots on the host
   • One parasite removes the host, so shoots would be 0 at 2 parasites

7. Two model parasites and their hosts (model data)

   parasite	days its host stays in the habitat	days it needs to reach a new host	new hosts reached
   X	10	30	0
   Y	60	30	3

8. 4.

   Luz reads the model data on two parasites. Which parasite reaches new hosts, and why?

   • Parasite Y: its host stays 60 days, so Y needs 60 days to move
   • Parasite X: its host stays 10 days, and a quick loss helps a parasite
   • Parasite X: it needs 30 days, the same as Y, so it reaches the most
   • Parasite Y: its host stays 60 days, longer than the 30 days it needs
9. 5.

   Milo reads the graph. The cycle repeats every 10 years. In which year will the lynx count peak the second time?

   • Year 10: 2 years before the second hare peak at year 12
   • Year 16: 4 years after the second hare peak at year 12
   • Year 14: the cycle is 10 years after the lynx peak at year 4
   • Year 12: the year of the second hare peak, read as the lynx peak
10. 6.

    Noah reads the graph. Which statement about when the two counts start to fall fits the graph?

    • The lynx count falls after its year 2 peak, one year before the hare count falls after its year 3 peak
    • Both counts fall after the same peak, in year 3, so neither one comes first
    • The hare count falls after its year 3 peak, one year before the lynx count falls after its year 4 peak
    • The hare count falls after its year 2 peak, one year before the lynx count falls after its year 3 peak
11. 7.

    Pia reads the graph. In the year the lynx count peaks, what is the hare count doing?

    • At its lowest: the hare count is down at 10 by the lynx peak
    • Falling: the hare peak came 2 years earlier, and hares are at 40
    • Rising: the hare count peaks 2 years after the lynx peak
    • At its peak: both counts peak in the same year

12. Removing one species from a model stream community of 12 species (model data)

    species removed	individuals before removal	species left
    banded tetra	30	6
    stream snail	400	11
    stream moss	900	10

13. 8.

    Ren reads the model data. Which species is the keystone species of the stream?

    • Stream snail: removing it leaves the most species, 11, so it matters most to the stream
    • No species is key: after one removal the stream keeps most of its species
    • The banded tetra: the fewest species are left, though it has the fewest individuals
    • Stream moss: it has the most individuals, 900, so removing it must matter most

14. Phosphorus in two model streams (model data)

    stream	banded tetras	phosphorus level (model units)
    with tetras	30	60
    without tetras	0	15

15. 9.

    Tala reads the model data. By what percent is the phosphorus level lower without the banded tetras?

    • 75 percent: the level falls by 45 out of 60
    • 45 percent: the fall of 45 units written as a percent
    • 25 percent: 15 out of 60 is the share that is left
    • 0 percent: one absent species leaves the phosphorus the same
16. 10.

    Zee reads the graph. Which statement fits it?

    • The tetras are not key, because 30 individuals is a small count
    • Stream R falls from 12 to 7 species after year 4, while stream S stays at 12
    • After year 4, stream S falls from 12 to 7 species while stream R stays at 12
    • Stream S returns to 12 species, so removing one species does not matter