Biology Lab Essay: An Examination of Tribolium Confusum Population in regards to Food and Space – Brandon Skenandore
Total word count: 1754
Time spent researching and writing: ~10 hrs + lab time
Certain studies have shown that population growth can be monitored with the beetle Tribolium confusum in relation to both food and space. Certain cannibalistic tendencies have been found with these beetles. Studying these beetles for over a month in varying habitats showed there was a drastic increase in population with larger amounts of food, and slower population growth with more space and the same amount of food. This experiment provides a direct test of the role of food, space, and cannibalism in a long-term study of population dynamics.
In 1798, Thomas Malthus found that varying populations of both plants and animals are geometrically progressive. Population increases exponentially, while food supply increases at the same rate. Because of the geometrical progression, any animal or plant could spread over every place possible; however, populations of species remain fairly constant because of the death factor and therefore do not grow indefinitely. Also, there is something in place that restricts population growth (Malthus 1798).
The Tribolium confusum, or confused flour beetle, can be used to test Malthus’s statement with certain hypotheses and predictions that test specific limiting factors, such as food and space. Studies have found that this beetle species shows certain cannibalistic tendencies in which the adults predate the pupae/eggs and the larvae predate the eggs. When the adult beetles predate the pupae, this is a more effective regulation of adult numbers than the larvae predating the eggs (Young 1970). Without these mechanisms in place, the Tribolium confusum population can grow exponentially (Benoit et al. 1998) (…)
The survival of Tribolium confusum is independent of density during the initial population growth. Once the adult density rises, the survival of the beetles in the younger stages (egg, larvae, pupae) is reduced (Brereton 1962). By reducing the beetles in their younger stages, the adult population is also reduced.
The Tribolium confusum are proper candidates for a study of limiting factors because of the growth time and costs. The growth period for these beetles is relatively fast. After 5-12 days of fertilization, the egg hatches into larvae. The larvae last 22-100 days, and the pupae last around 8 days. These beetles are cheap and easy to examine, due to the fact that they can live off of flour with relative moisture, and vermiculite can be used to create artificial space. The life span of the Tribolium confusum tends to last 200 days; our study will take place within that time.
Our two hypotheses are: The amount of food is a limiting resource for the population of Tribolium confusum, and the amount of space is a limiting resource for the population of Tribolium confusum. Our first prediction is that the more food available this species has, the more the population will grow. Our second prediction is that the more space they have the more the population will grow.
Materials and Methods:
In order to test whether food and/or space are limiting factors on population growth, we created different artificial environments for Tribolium Confusum to live and reproduce. For this experiment, 5 treatments were created. This experiment involved 5 different wide-mouth, half-pint mason jars. These jars were all the same size, and contained different amounts of living space (flour + vermiculite) and food (flour) for the beetles. A measured amount of flour mixture and/or vermiculite were added to each jar. Treatment A received 3g of the flour mixture. Treatment B received 10g of the flour mixture. Treatment C received 50g of the flour mixture. Treatment D received 10g of the flour mixture, mixed with vermiculite to the volume of the 50g flour mixture (treatment C). Treatment E received 3g of the flour mixture, mixed with vermiculite to the volume of the 50g flour mixture.
Table 1. Amount of Flour and Vermiculite added to 5 different Treatments. Note that the mass of flour in treatment A is the same as treatment E, and the mass of flour in treatment B is the same as treatment D.
|Treatment:||Mass of Flour||Vermiculite|
|D||10g||Fill to the volume of C/E|
|E||3g||Fill to the volume of C/D|
After the flour and/or vermiculite were added to their respective jars, 10 adult Tribolium confusum were added to each jar. Each jar was covered with a paper towel, two mesh layers, and a ring to secure the treatment. These jars were then placed in a lab with the same environmental conditions to allow for accurate results.
After 63 days, the treatments were reopened and the Tribolium Confusum were counted in their respective stages (larvae, pupae, and adults). More precise equipment would have been necessary in order to count the eggs, du to their extremely small size.
Treatments C, D, and E will be used to see how the amount of food affects population growth. Treatments B and D, as well as A and E will be used to see how the amount of available space affects population growth.
Our class averages were taken for each treatment. Treatment C had the largest amount of Tribolium Confusum, followed by treatments B, D, A, and E. See table 2 for the results.
Table 2. Class averages of population numbers for each treatment. Note the extremely large numbers of Treatment C in comparison to the other treatments.
|Larvae||Pupae||Alive Adults||Dead Adults|
Figure 1. Different amounts of beetle population growth for treatments C-D-E. Note the large disparity between treatments.
According to Figure 1, it is apparent that there is a very drastic change in population with the treatments that were given different amounts of food with the same space. Treatment C was given the most food with the same amount of space as treatments D and C, and the population growth was over 4 times that of treatment D and nearly 12 times that of Treatment E.
Figure 2. Variation in population growth between treatments B-D. Note the relatively small, but apparent disparity between treatments. Treatment B had less space, but more population growth than treatment D.
Figure 3. Variation in population growth between treatments A-E. Note again the small disparity. Treatment A had less space, but marginally more population growth than treatment E.
According to figures 2 and 3, the difference in space given to the Tribolium confusum appears only to marginally affect the population growth. These respective treatments had the same amount of food, but different amounts of space. Both studies indicated only a 32% difference in population growth. In this case between treatments B and D, treatment D (which actually had more space) appeared to make the population smaller than treatment B. This is contrary to our first prediction in that more space does not necessarily mean more population growth. The test between treatments A-E is similar, and since these two treatments had the same amount of food but treatment E had more space, treatment E had about 32% less population growth than treatment A.
Our first hypothesis stated that the amount of food is a limiting resource for the population of Tribolium confusum. Our prediction was that the more food each treatment has, the larger and faster that population would grow. Treatments C-D-E show a very direct relationship between food and population growth. These three treatments had the same amount of space with different amounts of food, so our prediction that the more food the Tribolium confusum have, the larger their population will grow, stands correct.
When it comes to the limit that space has on population growth, our prediction was proven to be false. We predicted that the more space the Tribolium confusum have, the more the population will grow. In this case there ended up being less population when more space is added. This could be proven by a number of factors that we were unable to test. One possible factor could have been that the Tribolium confusum beetles did not meet as often because of the greater space, and therefore were unable to mate and lay eggs quite as often. Also, bringing back Young’s study, which found cannibalistic tendencies with this beetle population, there may have been more rampant cannibalism on the eggs and pupae than the other treatment (Young 1970). The food was more spread out with more space, and the adult and larvae may have predated the eggs and/or pupae more than before, because of the lower food/space ratio. While over a longer period of time, more space may have been better for the beetles had there been more food, this short study showed an initial slower population growth for the beetles.
Furthermore, Benoit found that these cannibalistic tendencies have a stabilizing effect on the population. His study found that if each stage of the beetle (egg, pupae, larvae, beetle) were allowed to grow on its own without the cannibalistic aspect, the adult population would grow exponentially (Benoit 1998). In this case, it appears that the cannibalism helps to stabilize the beetle’s population. To see the effect of cannibalism we can compare figure 3 to figure 1. In figure 1, there were 149 pupae and 23 adults, creating a ratio of about 6:1. In figure 3, when there was less food, there were 6 pupae and 9 adults, creating a ratio of 2:3. By looking at these results, we can assume that there must have been some cannibalism by the adults because of the lack of food, in that there were 3 adults to every 2 pupae with less food, and only 1 adult to every 6 pupae with unlimited food.
This study will ultimately help us to understand more about the Tribolium confusum beetle population’s tendencies for cannibalism and population regulation.
While this study did help us to find the relationship between food/space and population growth, this was only for a short period of time. If we were to study these Tribolium confusum for a longer period of time, we would be able to understand how this population ultimately grows and regulates itself when, and if, the population reaches its greatest size. Also, it may help to further study the effects of cannibalism on this population, by studying further what might happen if we were to seclude the beetle population at each stage in life (similar to Young’s study) to ultimately know how this beetle population regulates itself.
Malthus, T.R. 1798. An Essay on the Principle of Population.
Benoit, H.P., Edward McCauley, and John R. Post. 1998. Testing the Demographic Consequences of Cannibalism in Tribolium Confusum. Ecology 79.8: 2839-2851.
Young, A.M. 1970. Predation and Abundance in Populations of Flour Beetles. Ecology 51.4: 602-619.
Brereton, J L. G. 1962. A Laboratory Study of Population Regulation in Tribolium Confusum. Ecology 43.1: 63-69.