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 22: 2 years before the third hare peak, with lynx first
- Year 26: lynx peaks are 10 years apart, starting at year 6
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 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
- 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
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
- 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
Luz reads the graph. Which explanation fits why the host count with the parasite stays above 0?
- 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
- 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
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 2: peaks in years 5 and 15 come 4 years after the hare peaks, not 2
- Line 3: a peak 2 years later means the lynx count follows the hare count
- 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
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 1: a lichen is commensalism, because both partners gain
- Line 2: in commensalism the tree is unchanged, so the bird alone gains
- 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 2: 800 individuals must supply more than 20 individuals
- Line 4: removing one species cannot change a whole community
- 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
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 Tala reads the model data. Which claim goes with the right reason?
- Claim: mutualism. Reason: the tree is not harmed by the nest, so the tree gains too
- Claim: commensalism. Reason: the bird and the tree both gain something from the nest
- Claim: parasitism. Reason: the bird gains a nest site and the tree has a nest on its branch
- Claim: commensalism. Reason: the bird gains 3 sites and the tree's 400 leaves stay the same
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: 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
- 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