AGEC 2370 Intra & Interspecific Plant Competition
Adam Borton
Student #7695780, Group 7
Introduction:
Plant growth and development depends on a variety of environmental factors. This
includes nutrient availability, available sunlight and competition between plants. Competition
between plants of the same species and plants of different species can affect the plant structure of
a community. Competition between differing plant species is known as interspecific competition.
Interspecific competition usually causes an increase in biomass of one species, while decreasing
population biomass or density in another (Tilman, 1997). In this lab, we observed how seed
density and plant competition effect parameters of plant growth and survivorship of plants.
Materials and Methods:
We began this experiment on October 7th, 2014 in the Animal Sciences Building. On this
day we planted 9 pots of barley and canola using varying seed densities. The seed densities for
the pots were 10 seeds/pot, 30 seeds/pot and 90 seeds/pot. The amounts of each type of plant
were altered in each pot with some pots having just one type of plant and others having both.
This was done to simulate interspecific competition and intraspecific competition in order to gain
understanding of how each type of competition may effect plant growth. Interspecific
competition between the barley and canola always involved equal amounts of both (for example,
in the 90 seed density pot, 45 barley plants and 45 canola plants were planted). After the seeds
were planted, the pots sat for 5 weeks and underwent 16 hours of light and 8 hours of darkness
daily. On November 18th, 2014 we recorded the proportion of plants which survived in each pot.
1
The plants were given a numerical value and then 10 were selected using a random digits table.
Once the 10 plants were chosen, plant height, number of leaves and leaf area were measured and
recorded. When measuring plant height, the length was recorded based on the distance from the
bottom of the stem, to the bottom of the uppermost, dominant leaf. When recording number of
leaves, dry, brown leaves were excluded and small cotyledons were included. After the data was
obtained, the entire class pooled the results and means for proportion of survivors and each
parameter of growth were calculated. Standard error of the mean was also calculated for each.
Results:
For barley planted with interspecific competition, it appears the mean proportion of
survivors decreases as seed density goes up (Table 1). The same was true for canola under
interspecific competition, which also decreased as seed density went up (Table 1). For
intraspecific competition, the proportion of survivors for barley changed very little as seed
density went up. Proportion of survivors fluctuated a little for canola intraspecific, as it decreased
at 30 seeds but then increased again in the 90 seed pot (Table 2). Mean plant height decreased as
seed density went up for interspecific barley and interspecific canola (Table 1). Mean plant
heights of intraspecific barley and canola appeared to fluctuate a little but did not decrease as
much (Table 2). When observing the mean number of leaves and mean area of leaves for both
canola and barley, interspecific competition resulted in a decrease in leaves and a strong decrease
in leaf area as seed density increased (Table 1). The same was true in the intraspecific pots for
canola and barley, with number of leaves and mean leaf area strongly decreasing as seed density
increased (Table 2).
When comparing the graphs of plant height for barley under interspecific and
intraspecific competition conditions, there appears to be relatively little interaction. This is
2
because the mean plant height calculated at each of the three seed densities show approximately
the same amount of decrease in both interspecific and intraspecific tests which suggests little
interaction (Figures 1 and 2). This differed from the canola plants which were subjected to
interspecific and intraspecific competition. Plant height increased from a seed density of 10 to a
seed density of 30 in intraspecific competition, but decreased in interspecific competition. The
means moving in opposite direction suggests there is some interaction between the two test
subjects (Figures 3 and 4).
Discussion:
I think both intraspecific competition and interspecific competition were observed in this
laboratory based on the fact that for most growth parameters, as seed density went up, many of
the values decreased. Whether the competition be between the plant of the same species or that
of another species, many of the growth parameters decreased as plant biomass increased possibly
due to the lack of availability of water and nutrients or access to adequate light. On average,
based on the data calculated in this laboratory, both intraspecific competition and interspecific
competition had similar effects on how well the plants did. When comparing both barley and
canola, often times interspecific competition would result in higher values for most plant
parameters. However, the inverse was true where intraspecific values would be higher than
interspecific values for both plants. This idea makes sense in the fact that interspecific
differences between plants may cause different plant species to behave differently (Tilman et al.
1997). This idea may explain why such differences in values are observed between canola and
barley for intraspecific and interspecific competition.
As plant biomass increases, competition for availability of light becomes the key factor as
light powers many of the plants essential functions. (Aerts, 1999). The plants were exposed to 16
3
hours of light a day, meaning they were getting plenty of sunlight. As the seed densities rise,
many of the mean growth parameters begin to decrease. This could be a direct result of some
plants becoming outcompeted for sunlight leading to less growth. This hypothesis could be tested
by altering the amount of sunlight the plants received daily and then comparing the results to this
experiment. If you decreased the light available from 16 hours to possibly just 8 hours and then
observed less growth for all parameters, you could potentially conclude that sunlight is a critical
factor in how well the plants do. You could test the opposite as well, perhaps increasing the
sunlight and then observing what effect it has on the plants as well.
A source of error when calculating leaf area could have occurred when determining the
length and width of the leaves. Getting the precise spot where the leaf begins to determine the
length was often times left to our judgment. Similarly, when determining the width, you would
need to measure the point which maximizes the width, by measuring the leaf at is widest point.
Variability in these locations may cause slight variability in answers. Another source of error
could be the formulas used to calculate the area of the leaves. Leaves vary in shape considerably.
Because of this, I would conclude that it is highly unlikely that the formulas used for both barley
and canola can calculate perfect area of the leaves because of the variation of shape amongst the
leaves. This would lead to overestimation and underestimation of total areas leading to more of
an estimate on leaf area then a reliable precise calculation.
4
References:
Aerts, Rien. "Interspecific competition in natural plant communities: mechanisms, trade-offs and
plant-soil feedbacks." Journal of Experimental Botany 50.330 (1999): 29-37.
Tilman, David, Clarence L. Lehman, and Kendall T. Thomson. "Plant diversity and ecosystem
productivity: theoretical considerations." Proceedings of the National Academy of
Sciences 94.5 (1997): 1857-1861.
Tilman, David. "8: Mechanisms of Plant Competition", Plant Ecology, 2nd Ed.; Blackwell
Science, Oxford, England (1997). Pp 239-261.
5
Tables and Figures:
Table 1
Seed
Density
Barley
Interspecific
Canola
Interspecific
Barley
Interspecific
Canola
Interspecific
Barley
Interspecific
Canola
Interspecific
Mean plant
height
Mean # of
leaves / plant
Mean leaf
area
10
Mean
proportion
surviving
0.91
18.38
4.38
97.92
10
0.89
14.29
4.06
40.28
30
0.87
18.72
4.16
72.97
30
0.83
9.99
3.83
16.14
90
0.84
17.28
3.63
41.06
90
0.65
9.15
3.60
10.44
Seed
Density
Mean plant
height
Mean # of
leaves / plant
Mean leaf
area
10
Mean
proportion
surviving
0.93
18.96
4.68
87.75
10
0.86
12.82
4.81
56.83
30
0.90
15.52
3.76
51.44
30
0.75
13.26
4.46
29.91
90
0.91
15.17
3.43
31.64
90
0.83
11.50
3.54
16.16
Table 2
Barley
Intraspecific
Canola
Intraspecific
Barley
Intraspecific
Canola
Intraspecific
Barley
Intraspecific
Canola
Intraspecific
6
Table 3
Seed
Density
Barley
Interspecific
Canola
Interspecific
Barley
Interspecific
Canola
Interspecific
Barley
Interspecific
Canola
Interspecific
SEM for
plant height
SEM for # of
leaves / plant
SEM for
leaf area
10
SEM for
proportion
surviving
0.022
1.324
0.089
2.825
10
0.032
0.871
0.195
2.758
30
0.025
0.590
0.073
2.889
30
0.013
0.440
0.083
0.923
90
0.007
0.851
0.076
1.727
90
0.028
0.247
0.104
1.059
Seed
Density
SEM for
plant height
SEM for # of
leaves / plant
SEM for
leaf area
10
SEM for
proportion
surviving
0.007
0.594
0.098
3.398
10
0.046
1.124
0.101
3.732
30
0.008
0.460
0.058
1.716
30
0.027
0.625
0.039
1.578
90
0.010
1.039
0.055
1.025
90
0.019
0.449
0.086
0.83003
Table 4
Barley
Intraspecific
Canola
Intraspecific
Barley
Intraspecific
Canola
Intraspecific
Barley
Intraspecific
Canola
Intraspecific
7
Barley Interspecific Competition
40.00
Plant Growth (cm)
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0
10
20
30
40
50
60
70
80
90
100
Seed Density
Figure 1: Barley Interspecific Competition effect on Plant Height
Barley Intraspecific Competition
35.00
Plant Height (cm)
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0
20
40
60
80
100
Seed Density
Figure 2: Barley Intraspecific Competition effect on Plant Height
8
Canola Interspecific Competition
Plant Height (cm)
25.00
20.00
15.00
10.00
5.00
0.00
0
20
40
60
80
100
Seed Density
Figure 3: Canola Interspecific Competition effect on Plant Height
Canola Intraspecific Competition
30.00
Plant Height (cm)
25.00
20.00
15.00
10.00
5.00
0.00
0
20
40
60
80
100
Seed Density
Figure 4: Canola Intraspecific Competition effect on Plant Height
9
Appendix:
Sample Calculation for calculating mean:
Calculation uses data from Barley Interspecific: mean proportion surviving (10 seeds)
Mean proportion surviving =
Mean proportion surviving =
𝑠𝑢𝑚 𝑜𝑓 𝑎𝑙𝑙 𝑝𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛𝑠 𝑜𝑓 𝑠𝑢𝑟𝑣𝑖𝑣𝑜𝑟𝑠
# 𝑜𝑓 𝑡𝑟𝑖𝑎𝑙𝑠
0.60+1+0.80+1+1+1+1
7 𝑡𝑟𝑖𝑎𝑙𝑠
Mean proportion surviving = 0.91
Sample Calculation for calculating SEM:
Calculation uses data from Barley Interspecific: mean proportion surviving (10 seeds)
SEM = √s2 / n
Variance = ∑ (Ni – Mean N)2 / n – 1
Variance = (0.61 – 0.91)2 / 7 – 1
Variance = (-0.3)2 / 6
Variance = 0.015
Calculations remain the same for each group’s data
Variance = ∑ 0.015 + 0.00135 + 0.002017 + 0.00135 + 0.00135 + 0.00135 + 0.00135
Variance = 0.023767
SEM = √0.023767 / 7
SEM = 0.022
10
Sample Calculation for calculating leaf area for Canola:
Area calculated below is for one leaf:
π
Area = ( 4 ) (
𝑤𝑖𝑑𝑡ℎ+𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑙𝑒𝑎𝑓 2
)
2
π
Area = ( 4 ) (3.8 + 3.9)2 / 2
Area = 11.6
Continue to calculate area for each leaf for all 10 plants
Sum areas together and divide by number of plants
Area = ∑ of all leaf area for 10 plants / 10 plants
Sample Calculation for calculating area for barley plants:
A = length x width
A = 16.2 x 3.4
A = 55.08
Continue to calculate area for each leaf for all 10 plants
Sum areas together and divide by number of plants
Area = ∑ of all leaf area for 10 plants / 10 plants
11
Initial of all
members group
(copy in all rows)
Group
#
(copy
in all
rows)
Seed
density
treatment
mean
proportion
surviving
mean
plant
height
mean
number of
leaves /
plant
total leaf
area /
plant
MT, KA, AB, JP
7
90
Barley Intraspecific
0.9
9.7
3.2
27.74
MT, KA, AB, JP
7
90
Canola Intraspecific
0.76
12.8
3.5
13.9
MT, KA, AB, JP
7
90
Barley Interspecific
0.96
13.81
2.9
29.32
MT, KA, AB, JP
7
90
Canola Interspecific
0.71
10.64
3.7
5.03
MT, KA, AB, JP
7
30
Barley Intraspecific
0.93
13.81
3.7
57.2
MT, KA, AB, JP
7
30
Canola Intraspecific
0.83
12.68
4.7
31
MT, KA, AB, JP
7
30
Barley Interspecific
0.67
12.3
3.9
64.55
MT, KA, AB, JP
7
30
Canola Interspecific
0.73
10.8
3.6
13.6
MT, KA, AB, JP
7
10
Barley Intraspecific
0.9
14.97
3.7
67.64
MT, KA, AB, JP
7
10
Canola Intraspecific
0.7
16.7
4.5
47.9
MT, KA, AB, JP
7
10
Barley Interspecific
1
17.68
3.4
90.5
MT, KA, AB, JP
7
10
Canola Interspecific
0.8
14.95
5.5
26.78
12
Group #
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
Seed density
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
30
30
30
30
30
30
30
30
30
30
treatment
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
mean proportion
surviving
0.60
1.00
0.80
1.00
1.00
1.00
1.00
0.90
0.90
0.90
0.90
1.00
1.00
0.90
1.00
0.40
1.00
1.00
1.00
1.00
0.80
0.90
1.00
1.00
1.00
0.60
0.80
0.70
1.00
1.00
0.60
1.00
0.80
1.00
0.67
0.93
0.87
0.83
mean
plant
height
(cm)
17.88
8.70
14.00
18.08
14.30
38.00
17.68
19.28
19.80
18.22
19.17
14.30
27.00
14.97
13.87
21.52
5.40
13.56
8.70
22.00
14.95
9.67
8.84
7.65
18.29
26.60
22.00
16.70
20.82
17.19
17.50
18.61
18.63
26.00
12.30
16.40
10.00
17.81
mean
number
of
leaves /
plant
4.20
4.50
3.75
4.80
5.00
5.00
3.40
4.33
4.56
4.67
4.78
6.00
4.71
3.70
4.00
4.20
3.60
4.80
1.33
5.00
5.50
5.56
4.40
3.80
5.80
4.50
5.10
4.50
4.10
3.90
4.40
3.70
3.90
5.20
3.90
3.40
3.20
4.40
13
total leaf
area /
plant
(cm2)
97.84
136.65
96.25
70.36
93.20
100.62
90.50
76.80
126.88
106.46
85.48
57.00
94.00
67.64
41.46
37.26
40.37
20.87
34.52
80.70
26.78
31.95
45.67
52.62
35.66
79.12
104.89
47.90
67.34
59.49
67.34
55.26
114.68
82.12
64.55
37.32
57.63
66.37
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Interspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Barley Intraspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Interspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
0.80
0.93
1.00
0.93
0.80
0.87
1.00
0.80
0.73
0.86
0.73
0.97
0.47
0.57
0.97
0.73
0.73
0.83
0.84
0.78
0.64
0.91
0.96
0.77
0.96
0.94
0.92
0.76
0.92
0.93
0.98
0.90
0.44
0.38
0.91
0.80
0.76
0.57
0.71
0.98
0.61
0.73
14.60
15.85
20.20
13.81
7.77
10.53
6.70
10.17
7.96
16.00
10.80
11.00
10.92
7.50
16.53
13.19
21.00
12.68
14.21
13.95
16.60
19.02
13.39
30.00
13.81
10.72
11.92
14.55
12.70
15.62
31.00
9.70
7.68
8.77
8.75
9.32
6.90
12.00
10.64
11.02
9.50
9.40
4.00
3.60
4.00
3.70
4.50
3.70
3.40
3.30
3.50
4.80
3.60
4.90
4.50
4.40
4.20
4.10
4.42
4.70
3.40
3.50
4.10
3.20
3.90
4.42
2.90
2.90
3.40
4.00
3.30
3.30
3.89
3.20
4.50
4.30
3.30
2.80
2.60
4.00
3.70
3.60
3.10
2.70
14
60.37
35.26
45.93
57.20
15.46
5.78
18.70
22.31
24.87
12.26
13.60
31.45
25.15
37.42
28.20
45.98
10.20
31.00
45.51
41.91
41.45
27.62
37.65
63.99
29.32
35.25
42.71
37.33
30.95
24.53
23.00
27.74
7.45
5.78
5.32
16.82
24.51
8.19
5.03
10.92
16.29
11.73
4
5
6
7
90
90
90
90
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
Canola Intraspecific
0.96
0.79
0.95
0.76
15.66
7.10
15.00
12.80
4.10
3.30
4.50
3.50
15
17.37
28.26
14.67
13.90