Transcript Population Dynamics of Daphina magna in relation to

Population Dynamics of Daphina magna in relation to Carrying Capacity in Closed Ecological Systems
Reported by Yuichi “Eugene” Saito and David Barbee
Faculty Mentor: Frieda Taub
School of Aquatic and Fisheries Sciences, the University of Washington, Seattle WA 98105
number of Daphnia
The image processing
increased the contrast of Daphnia
magna with the surrounding
medium, and allowed living
individuals to be counted by eye.
Goal: Does container size affect Daphnia
populations in Open and Closed
Ecological Systems?
Nutrients recycle through organisms and constitute food
chains and food webs. On Earth, the process of nutrient cycling
takes place on a scale that is difficult to study. Closed Ecological
Systems (CES) are miniature models of our planet; they function
with little substance exchange. Solar energy is the only substantial
input. CES are a way to study how resources are recycled on earth
without the difficulty of a large scale.
*Daphnia can be reproductively mature six days after birth.
Methods
A total of 36 ecological systems (ES) were setup in 6
closed bottles of 3 sizes with matching open bottles for
comparison, so 18 Closed Ecological Systems (CES) and 18
Open Ecological Systems (OES).
Data were gathered
biweekly by counting the population of Daphnia magna.
Volume of air remaining
Nutrient fluid volume (percent
of total volume)
Kent water (70% of fluid)
T82 w/ C&P (25% of fluid)
Ankistrodesmus (2% of fluid)
Scenedesmus (2% of fluid)
Daphnia magna
Number of replicates for closed
cap (treatment)
Number of replicates for loose
cap (control)
Hours of Light:Dark
Temperature
2%
272-ml
73-ml
3%
12%
98%
525ml
187.5ml
15ml
15ml
20
97%
185.5ml
66.75ml
5.3ml
5.3ml
10
88%
44.8ml
16ml
1.3ml
1.3ml
2
6
6
6
6
6
6
18 to 6
20 Celsius
Other Equipment
PowerMac G4 w/ MacOS 9.2.2
Adobe Photoshop 6.0
Nikon Coolpix 995 digital camera with tripod
electro luminescent backlight
Percival Scientific model I-36LL incubator
open
80
60
40
20
0
73 ml
272 ml
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
755 ml
closed
73 ml
size
Figure1. The peak mean populations
increased as container size increased
in both closed and open systems.
Replicate 1
Replicate 4
0.3
Replicate 2
Replicate 5
272 ml
open
755 ml
size
Figure 2.
Open system: The peak mean
densities increased as container
size decreased
Closed system: Low mean peak
density
in
largest (755ml)
containers, but high densities in
smaller (73ml, 272ml) containers
Diagram of experimental setup,
using a Nikon Coolpix 995
digital camera
Replicate 3
Replicate 6
73 ml CES
73 ml OES
0.2
0.1
0
Daphnia density (/ml)
Data analysis: We compared mean peak density of Daphnia
among three different sizes of open and closed systems by using
the two-way ANOVA statistical test to determine significance.
1. Bottle size effect if there is any difference between small,
medium, and large bottles.
2. Open vs. closed treatment effect if there is any difference
between open and closed systems.
3. Interaction effect between “open effect at small, medium, and
large sizes” and “closed effect at small, medium, and large sizes.”
265 ml OES
0.3
265 ml CES
0.2
0.1
0
0.3
755 ml CES
755 ml OES
0.2
0.1
0
0
10
20
30
40
0
10
Day
Results
Experimental Setup Summary
755-ml
closed
100
Before and after the image analysis
process: Daphnia contrast with the
surrounding medium is enhanced.
We explored the concept how size and
volume effect the self-sustaining closed
ecological systems. We set up three sizes of
CES in closed bottles consisting of inorganic
medium, two species of algae, and the grazer
Daphnia magna. We also set up the same sized
systems in open bottles for comparison.
Total bottle volume (ml)
120
Daphnia density(/ml)
Introduction
A photographic process
was developed to count large
populations of Daphnia
Of the 36 ES, 29 had Daphnia populations persisted to day
36. In these 29 ES, the population peak occurred between days
11 and 21. 6 OES and 2 CES lost the Daphnia populations by
day 36.
A comparison of mean peak Daphnia populations resulted in
greater the number of Daphnia as bottle size increases (Fig.1);
however, the mean peak density (animals/ml) was reversed;
greater density in smaller bottles (Fig.2).
Tests of mean peak density (animals/ml) differences:
1. Bottle size effect: The larger the bottle, the more Daphnia per
system, but the lower the density (Daphnia /ml), p = 0.013 at 
= 0.05.
2. Open vs. closed treatment effect: Closed systems had lower
densities (Daphnia/ml) than open systems, p = 0.001 at  =
0.05.
3. Interaction effect: Significant as well, p = 0.092 at  = 0.10.
20
Figure 3. A comparison of the mean Daphnia densities over 36
closed and open systems: Daphnia populations reached the
densities (highest birthrates), but then crashed (highest death
smallest open systems. Systems with lower Daphnia peaks
persistence of Daphnia populations.
30
40
days between
highest peak
rates) in the
had greatest
Conclusion
The peak number of Daphnia increased as the container
size increased, but the peak density of Daphnia magna (/ml)
might be inversely related to size of bottles: the smaller the
container is, the greater the density is. The carrying capacity of
Daphnia magna to date seemed to be correlated to not only
bottle sizes but also availability of gas exchanges. Rapid
increase of algae results in rapid increases of Daphnia
population, which was remarkably observed in the open
system. Closure restricts gas exchange, especially of CO2
which is required for photosynthesis and of O2, a waste product
of photosynthesis, but a requirement of Daphnia. Greater
Daphnia populations in the open systems suggests that CO2
may have been limiting. The “Kent water” is the source of
bicarbonate, the only significant CO2 source, other than
Daphnia respiration.