How relationships between species keep an ecosystem stable
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Ari reads the graph. The pattern keeps repeating. In which year will the lynx count reach its third peak?
- Year 36: three cycles of 10 years after the lynx peak at year 6
- Year 24: the year of the third hare 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
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 before it
- The hare count fell 60 percent, and the lynx peak came 2 years after it
- The hare count fell 75 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
Kira reads the graph. Which explanation fits why the two lines differ?
- Paramecium aurelia uses the same limited resource and outcompetes it in the tube
- The test tube itself holds Paramecium caudatum back, so its count falls
- Paramecium caudatum needs a partner species to grow, so its count levels off alone
- Both species share one niche, so both counts should fall to 0 in the shared tube
Luz reads the graph. Which explanation fits why the host count with the parasite stays above 0?
- The parasite takes nothing from its hosts, so the count fell by chance
- The parasite helps its hosts, so the count with it should rise
- The parasite needs time to spread, so its hosts are weakened, not removed
- A parasite removes its host quickly, so the graph must show another relationship
Read this first
Counts of two model species that use the same resource (model data)
year species X species Y 1 60 60 2 50 45 3 40 30 4 44 36 5 48 42 6 52 48 Milo reads the model data. Species Y uses a different area of the habitat from year 4. Which explanation fits the counts?
- The two species began to help each other as partners, so both counts began to rise
- A different area lessens the overlap in resources, so both counts began to rise
- The two species now use the very same area, so both counts began to rise again
- The move changed nothing for species X, so its rise was by chance
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.
Pia reads a classmate's notebook about a hare and lynx record. Which line has the mistake?
- Line 1: peaks in years 3 and 13 are 8 years apart, so one cycle is not 10 years
- Line 4: the next hare peak is in year 20, not year 23
- Line 3: a peak 2 years later means the lynx count follows the hare count
- Line 2: peaks in years 5 and 15 come 4 years after the hare peaks, not 2
Notebook
Notes on four pairs of living things (classmate's notebook), 4 lines. Columns: line, entry. Line 1: A fungus and an alga in a lichen both gain, so it is mutualism. Line 2: A bird and the tree that holds its nest both gain, so it is commensalism. Line 3: A model parasite gains and its host plant is harmed, so it is parasitism. Line 4: Two plant species that share a limited supply of water both lose some growth, so it is competition.
Esme reads a classmate's notebook about four pairs of living things. Which line has the mistake?
- Line 3: a host that is harmed means the pair is in competition, not parasitism
- Line 2: in commensalism the tree is unchanged, so the bird alone gains
- Line 1: a lichen is commensalism, because both partners gain
- Line 4: plants that share a supply of water help each other to grow
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.
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 1: 90 percent and 10 percent do not add up to a whole of 100 percent
- Line 3: a keystone species is picked by its effect, not by its count
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 Zee reads the model data. Which claim goes with the right reason?
- Claim: stream moss is keystone. Reason: it has the most individuals, 700, so it matters most to the stream
- 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
Host plants and parasites in one model plot (model data)
year host plants parasites 1 50 10 2 48 14 3 46 18 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 harmed but not removed. Reason: they fall from 50 to 46, not to 0
- Claim: the hosts are not harmed. Reason: the host count is above 0 in year 3
- Claim: the hosts will be gone by year 4. Reason: a parasite removes its host quickly
- Claim: this is not a parasite. Reason: a parasite removes its host, and 46 plants are left