Population Growth and Competition in Lemna sp. And Spirodela sp.1
Ovric P. Estioko Group Smiley Sec. F-2L
June 24, 2013
1
A technical paper submitted in partial fulfillment of the requirements in Bio 150 (Principles of Ecology) laboratory under Ms. Romella Beringuela, 1st sem., 2013-2014.
ABSTRACT
Population growth and competition on two aquatic species, Lemna and Spirodela were observed in respect with population size and carrying capacity. Fronds of both plants were placed in jars labelled as pure and mixed culture, with two treatments for each culture. The cultures were observed every other day for three weeks with the number of fronds being counted on each observation. After observations, both aquatic species generally increased population in both pure and mixed cultures. Therefore, population size can exceed the carrying capacity.
INTRODUCTION
In a certain population, the number of individuals increases or decreases with time. This change in the number of individuals in a population is termed as population growth. Processes such as birth and immigration controls the growth rate at which there are new individuals that will be added to a certain population In contrast, death and emigration controls the growth rate at which individuals leave a certain population (Smith & Smith, 2009). A population may grow in either two ways. The first is exponential population growth, which is a geometric increase of a population. Second, the logistic growth, indicates a growth levelling off as population size approaches the carrying capacity of a specific environment (Cuevas et al., 2012). According to Begon, Townsend & Harper (2006), a competition is the interaction between individuals brought about by a requirement in common resources that may lead to deprivation of another individual who is also competing with. There are two types of competition: intraspecific and interspecific. The former is a competition among
similar species while the latter is a competition between different species (Cuevas et al., 2012). This exercise, conducted on June 24, 2013 at the Institute of Biological Sciences in the University of the Philippines Los Baños, aimed to observe and analyze the population growth and competition in Lemna sp. And Spirodela sp. The specific objectives were: 1. to demonstrate changes in the populations of pure and mixed cultures of Lemna sp. and Spirodela sp.; 2. to compare the growth of Lemna sp. and Spirodela sp. in different types of media; and 3. to determine the effects of intraspecific and interspecific competition on both species.
MATERIALS AND METHODS
Three replicate jars were prepared for treatments A and B. Treatment A has 50 mL tap water and treatment B has 5 g soil plus 50 mL tap water. 8 fronds of Lemna were introduced to one set of treatments A and B. The same number of fronds of Spirodela was also introduced to another set of the same treatments. The separating of fronds was avoided during the preparation of the experiment. These represented pure cultures of Lemna and Spirodela where the initial population (No) was 8. Four fronds of Lemna sp. and four fronds of Spirodela sp. were introduced to the remaining set of treatments.
These represented the mixed culture of Lemna and Spirodela where the initial population was also 8. After preparing the cultures, the jars were then covered with transparent plastic and was punched few small holes for aeration. The cultures were kept in the designated areas, making sure that all fronds were floating on the media. For each treatment, the total number of fronds of Lemna and Spirodela were counted every other day until the frond count levels off. Visible new buds which were almost half the size of the old buds were also counted as separate individuals. It was noted that fronds that have turned yellow or those that have dried up will not be counted. After each observation, it was made sure that no fronds were left adhering to the sides of the bottle and that all fronds should be floating on the media. Graphs of pure and mixed cultures of Lemna and Spirodela grown in the different treatments were constructed and was separated for each treatments. Frond count vs. time was plotted on the first graph for Lemna grown as pure and mixed cultures while the pure and mixed cultures of Spirodela were plotted on the second graph. The instantaneous rate of growth (r) at each observation interval in all cultures was computed using the formula: r = ln λ
λ = N(t+1) / Nt
where λ = annual finite rate of increase Nt = population in time t N(t+1) = population at the next observation
day
RESULTS AND DISCUSSION
As seen in Table 2D.1, results showed that both species of aquatic plants generally increased in populations in both the pure and mixed cultures on both treatments. In the pure culture section, Lemna has a higher population in the tap water treatment compared to its population in the tap water + soil treatment. Based on the carrying capacity on tap water treatment, Lemna has a higher carrying capacity than Spirodela’s. The tap water used in treatment A maybe rich in nutrients because Lemna grows best in eutrophic waters with an element of organic enrichment from leaf litter (Centre for Ecology & Hydrology, 2004). This may explain why it has less population in the tap water + soil treatment, since the soil may contain some nutrients not needed by Lemna that lessened the nutrients of the tap water that is needed by Lemna. In the other hand, Spirodela has a higher population in the tap water + soil environment compared to its population in the tap water environment. Based on carrying capacity on tap water + soil treatment, Spirodela has higher carrying capacity than Lemna’s. A possible reason for this is that Spirodela eats up pollutants in water. It also sokes up excessive amounts of nitrogen, phosphates and potassium out of detergents, ammonia and waste water and also survives off the nitrates produced by waste products of fish and other animal residents (LIFE 1020 Student Group 9, 2013).
In the mixed culture section, the two aquatic plants has the highest population in the tap water + soil environment
compared
to
their
population
in
the tap
water
Table 2D.1. Population growth of pure culture and mixed culture of Lemna and Spirodela sp. Population Size Observation Number
Date of Observation
Age of Culture (days)
Lemna Pure Cultures
Spirodela Pure Cultures
A
B
A
B
Mixed Cultures A
B
L
S
L
S
1
June 24
1
8
8
8
8
4
4
4
4
2
June 26
3
22
14
12
12
5
5
8
9
3
June 28
5
26
18
19
16
6
8
12
10
4
July 01
8
36
21
25
27
7
10
14
22
5
July 03
10
37
29
31
33
8
11
24
24
6
July 05
12
40
35
34
37
10
14
27
29
7
Jul 08
15
42
42
37
44
13
18
31
33
8
July 10
17
49
47
39
49
20
24
47
35
9
July 12
19
54
49
47
53
27
29
54
39
environment, with Lemna having a higher population compared to Spirodela. In the tap water environment, Spirodela has a higher population compared to Lemna. Since Lemna grows best in eutrophic waters (Centre for Ecology & Hydrology, 2004), theoretically, Lemna should have a higher population compared to the Spirodela population in the tap water treatment. A possible source of error maybe due to lack of time in observation of the cultures. Another source of error maybe that the tap water may be polluted or that it may contained some nutrients such as nitrogen, ammonia, etc. that made the Spirodela boosted in population more than the Lemna population. On the tap water + soil treatment, it is shown that Lemna has a higher population compared to the Spirodela population. A possible reason for this is that the Spirodela may be taking in nutrients from the treatment that does not need by Lemna, which to the advantage of Lemna, takes in the rest of the nutrients that it really needs. On the interspecific competition of the mixed cultures on the two treatments, the Competitive Exclusion Principle was the dominant concept. It states that no competing species cannot coexist. However, coexistence was permitted on the two competing aquatic species because of their difference in ecological niche (Silvertown and Doust, 1993). All of the population growth curves on Figures 2D.1 to 2D.4 exhibited an S-curve, except for the population growth curve of Lemna mixed culture on Figure 2D.1. As
observed, the Lemna cultures has a well-established S-curves compared to that of Spirodela. Results shown in Table 2D.2 that Lemna and Spirodela cultures, pure and mixed, on both treatments, showed an instantaneous rate of growth greater than one, which meant
60
54 49
Population Size (N)
50 40 40
36
30
42
37
27
26
Lemna Pure Culture
22
20
Lemna Mixed Culture
20 13 8 4
10
5
6
7
8
10
0 0
5
10
15
20
Age of Cultures (Days) Figure 2D.1. Population growth curve of pure and mixed culture of Lemna sp. grown in tap water.
47
50 45 37
Population Size (N)
40
39
34
35
31
30
29
25
24
25 19
20
8
10
4
5
Spirodela Mixed Culture
14
12
15
Spirodela Pure Culture
18
8
10
11
5
0 0
5
10
15
20
Age of Cultures (Days) Figure 2D.2. Population growth curve of pure and mixed culture of Spirodela sp. grown in tap water.
60
54 47
Population Size (N)
50
49
42 40
35 29
30
31 27
24
Lemna Pure Culture
21
Lemna Mixed Culture
18
20
14 8 4
10
12
14
8
0 0
5
10
15
20
Age of Cultures (Days) Figure 2D.3. Population growth curve of pure and mixed culture of Lemna sp. grown in soil + tap water.
60 53 49
Population Size (N)
50
44 39
37
40 33
29
27
30
22 20
33
35
24
Spirodela Pure Culture Spirodela Mixed Culture
16 8 4
10
12 9
10
0 0
5
10
15
20
Age of Cultures (Days) Figure 2D.4. Population growth curve of pure and mixed culture of Spirodela sp. grown in soil + tap water.
that the population on all the treatments, whether pure or culture, was exponentially increasing. The population size can be greater than the carrying capacity. This is possible because of an abundance in resources in a specific environment. However, the growth of the population will be negative, indicating a population decrease until the population size and the carrying capacity will become equal and stable (Cuevas et al., 2012).
SUMMARY AND CONCLUSION
Population growth and competition were observed in two aquatic species, Lemna and Spirodela. Fronds of each were placed in jars labelled as Pure and Mixed culture, with two treatments for each culture. Treatment A has tap water only while treatment B has tap water + soil. The cultures were observed every other day for three weeks with the number of fronds being counted on each observation. In the pure culture section, Lemna has a higher population on the tap water treatment compared to its population in the tapwater + soil treatment with Spirodela showing opposite results.
In the mixed culture section, Lemna has a higher populations on both treatments than the Spirodela population. On computation of the instantaneous growth, a general trend occur in both aquatic plants in which their population is exponentially increasing with an r value greater than one. Therefore, population size can exceed its carrying capacity. But when this happen, growth will be negative, indicating a population decrease until the population size will equal the carrying capacity and become stable. However, this speculation needs to be validated by further studies on population growth and competition on other relative species. It is also recommended that the time of observation on the cultures should take about a month so as to get significant results.
LITERATURE CITED
Begon M., Townsend, C.R. & Harper, J.L. (2006). Ecology: From individuals to ecosystems (4th ed). Oxford, UK: Blackwell Publishing Ltd.
Centre for Ecology & Hydrology. (2004). Information sheet: Lemna species (Duckweeds). Retrieved from http://www.ceh.ac.uk/sci_programmes/documents/duckweeds. pdf. Accessed July 22, 2013.
Cuevas, V.C., Cervancia, C.R., Zafaralla, M.T., Lit, I.L., Jr., Barrion-Dupo, A.L.A. & Lambio, I.A.F. (2012). Exploring Ecology (no ed.). University of the Philippines Los Baños: Environmental Biology Division, IBS.
Life 1020 Student Group 9. (2013). Growth of Spirodela polyrhiza in creek water, distilled water, and tap water. Retrieved from https://sites.google.com/site/experiments spring2013/duckweed-populations/group-9. Accessed July 23, 2013.
Smith, T.M. & Smith, R.L. (2009). Elements of Ecology (7th ed). San Francisco, CA: Pearson Benjamin Cummings.
