How relationships between species keep an ecosystem stable

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Ari reads the graph. The pattern keeps repeating. In which year will the lynx count reach its third peak?

   • Year 26: lynx peaks are 10 years apart, starting at year 6
   • Year 22: 2 years before the third hare peak, with lynx first
   • Year 24: the year of the third hare peak
   • Year 36: three cycles of 10 years after the lynx peak at year 6
2. 2.

   Bo reads the graph. The hare count falls from its peak of 80 to 20 by year 6. Which statement fits the graph?

   • The hare count fell 75 percent, and the lynx peak came 2 years after it
   • The hare count fell 60 percent, and the lynx peak came 2 years after it
   • The hare count fell 25 percent, and the lynx peak came 2 years after it
   • The hare count fell 75 percent, and the lynx peak came 2 years before it

3. Read this first

   A model stream after the banded tetras are absent (model data)

   year	banded tetras	phosphorus level (model units)	stream plants (percent cover)
   1	30	60	80
   2	0	15	78
   3	0	15	60
   4	0	15	40

4. 3.

   Jun reads the model data. The banded tetras are absent from year 2. Which sequence fits the table?

   • Plant cover falls first, and the phosphorus level falls after it
   • Phosphorus falls first, and plant cover falls in the years after
   • Plant cover changes little, because 30 tetras are a small count
   • Plant cover stays near 80, because plants do not interact with the tetras
5. 4.

   Kira reads the graph. Which explanation fits why the two lines differ?

   • Paramecium caudatum needs a partner species to grow, so its count levels off alone
   • The test tube itself holds Paramecium caudatum back, so its count falls
   • Both species share one niche, so both counts should fall to 0 in the shared tube
   • Paramecium aurelia uses the same limited resource and outcompetes it in the tube
6. 5.

   Luz reads the graph. Which explanation fits why the host count with the parasite stays above 0?

   • A parasite removes its host quickly, so the graph must show another relationship
   • The parasite takes nothing from its hosts, so the count fell by chance
   • The parasite needs time to spread, so its hosts are weakened, not removed
   • The parasite helps its hosts, so the count with it should rise

7. Notebook

   Notes on a hare and lynx record (classmate's notebook), 4 lines. Columns: line, entry. Line 1: Hare peaks came in years 3 and 13, so one cycle lasted 10 years. Line 2: Lynx peaks came in years 5 and 15, so each lynx peak came 2 years after a hare peak. Line 3: Because the lynx peaks come 2 years later, the lynx count leads the hare count. Line 4: If the pattern holds, the next hare peak will be in year 23.

8. 6.

   Pia reads a classmate's notebook about a hare and lynx record. Which line has the mistake?

   • Line 4: the next hare peak is in year 20, not year 23
   • Line 2: peaks in years 5 and 15 come 4 years after the hare peaks, not 2
   • Line 1: peaks in years 3 and 13 are 8 years apart, so one cycle is not 10 years
   • Line 3: a peak 2 years later means the lynx count follows the hare count

9. Notebook

   Notes on a model stream (classmate's notebook), 4 lines. Columns: line, entry. Line 1: The 20 banded tetras supply 90 percent of the stream's phosphorus. Line 2: The 800 stream snails supply the other 10 percent. Line 3: So the stream snail is the keystone species, because it has the most individuals. Line 4: Without the tetras, the phosphorus supply would change greatly.

10. 7.

    Ren reads a classmate's notebook about a model stream. Which line has the mistake?

    • Line 4: removing one species cannot change a whole community
    • Line 2: 800 individuals must supply more than 20 individuals
    • Line 3: a keystone species is picked by its effect, not by its count
    • Line 1: 90 percent and 10 percent do not add up to a whole of 100 percent

11. A bird and a tree, measured over a year (model data)

    partner	measure	without the other	with the other
    bird	safe nest sites	0	3
    tree	leaves on a branch	400	400

12. 8.

    Tala reads the model data. Which claim goes with the right reason?

    • Claim: commensalism. Reason: the bird and the tree both gain something from the nest
    • Claim: mutualism. Reason: the tree is not harmed by the nest, so the tree gains too
    • Claim: commensalism. Reason: the bird gains 3 sites and the tree's 400 leaves stay the same
    • Claim: parasitism. Reason: the bird gains a nest site and the tree has a nest on its branch

13. Three species in a model stream of 12 species (model data)

    species	individuals	share of the phosphorus supplied (percent)	species left if it is removed
    banded tetra	20	90	5
    stream moss	700	6	11
    stream snail	300	4	11

14. 9.

    Zee reads the model data. Which claim goes with the right reason?

    • Claim: the banded tetra is not keystone. Reason: 20 individuals is too small a count to matter much
    • Claim: no species is keystone. Reason: removing moss or removing snail still leaves 11 of the 12 species
    • Claim: the banded tetra is keystone. Reason: removing it leaves 5 species, though it has the fewest individuals
    • Claim: stream moss is keystone. Reason: it has the most individuals, 700, so it matters most to the stream

15. Host plants and parasites in one model plot (model data)

    year	host plants	parasites
    1	50	10
    2	48	14
    3	46	18

16. 10.

    Noah reads the model data on host plants with a parasite living on them. Which claim goes with the right reason?

    • Claim: the hosts are not harmed. Reason: the host count is above 0 in year 3
    • Claim: this is not a parasite. Reason: a parasite removes its host, and 46 plants are left
    • Claim: the hosts will be gone by year 4. Reason: a parasite removes its host quickly
    • Claim: the hosts are harmed but not removed. Reason: they fall from 50 to 46, not to 0