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 24: the year of the third hare peak
- Year 26: lynx peaks are 10 years apart, starting at year 6
- Year 36: three cycles of 10 years after the lynx peak 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 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
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 Jun reads the model data. The banded tetras are absent from year 2. Which sequence fits the table?
- 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
- Plant cover falls first, and the phosphorus level falls after it
Kira reads the graph. Which explanation fits why the two lines differ?
- 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 caudatum needs a partner species to grow, so its count levels off alone
- Paramecium aurelia uses the same limited resource and outcompetes it in the tube
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 move changed nothing for species X, so its rise was by chance
- 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
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 1: a lichen is commensalism, because both partners gain
- Line 3: a host that is harmed means the pair is in competition, not parasitism
- Line 4: plants that share a supply of water help each other to grow
- Line 2: in commensalism the tree is unchanged, so the bird alone gains
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 3: a keystone species is picked by its effect, not by its count
- 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 4: removing one species cannot change a whole community
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: 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
- 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
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: 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: stream moss is keystone. Reason: it has the most individuals, 700, so it matters most to the stream
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: this is not a parasite. Reason: a parasite removes its host, and 46 plants are left
- Claim: the hosts are not harmed. Reason: the host count is above 0 in year 3
- Claim: the hosts are harmed but not removed. Reason: they fall from 50 to 46, not to 0
- Claim: the hosts will be gone by year 4. Reason: a parasite removes its host quickly