3A) Assessment of Variation & Natural Selection In Populations

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Dandelion Height by Path

Dandelion Height by River

Sample

Height Cm

Sample

Height Cm

1

17

1

30

2

15

2

34

3

12

3

40

4

10

4

25

5

5

5

20

6

12

6

23

7

11

7

22

8

7

8

30

9

8

9

33

10

14

10

18

Avg.

11.1

Avg.

27.5

Black Mustard in Shade

Black Mustard in Sun

Sample

Height Cm

Sample

Height Cm

1

35

1

70

2

30

2

60

3

40

3

58

4

33

4

67

5

28

5

73

Avg.

33.2

Avg.

65.6

Canadian Thistle Under Mat

Canadian Thistle Not Under Mat

Sample

Height Cm

Sample

Height Cm

1

10

1

40

2

17

2

30

3

20

3

52

4

24

4

38

5

31

5

34

6

28

6

33

7

16

7

32

8

12

8

37

Avg.

19.75

Avg.

37

At our ecosystem we discovered and analyzed three main trends regarding variation in certain populations. We found the trend that the plants by the river were taller than the plants closer to the path because since there was less wind, they needed to be taller to gain access to wind and light. This trend was shown in the dandelion (Taraxacum officinale) population. Another trend we found was that the plants in the shade were shorter than the ones in the sun because their growth was made more difficult by the lack of sunlight. This selective pressure was shown in the black mustard (Brassica nigra) population. A third trend we found was that the plants under the mat at the site were shorter than the ones not under the mat. This selective pressure was found in the Canadian thistle (Cirsium arvense) population.