Predation, Body Size, and Composition of Plankton




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Literature Analysis of J.L. Brooks and S. I. Dodson’s Classic Ecology Paper,

Predation, Body Size, and Composition of Plankton”

David Golowo, Jr.

BIOL 112 Literature Paper

Brooke Wheeler, TA

December 17, 2005




Literature Analysis of J.L. Brooks and S.I. Dodson’s Classic Ecology Paper

Predation, Body Size, and Composition of Plankton”


The classic paper that was selected was J. L. Brooks and S.I. Dodson’s 1965 paper titled “Predation, Body Size, and Composition of Plankton”. This paper studies the effects of marine planktivores on lake plankton. In it, Brooks and Dodson elaborate on the size and composition of planktons and how the planktivores’ competition and predation affect plankton populations and plankton body size.

Before writing a brief synopsis of the classic paper, it is expedient to give a brief summary of the subject of the paper. Planktons are tiny open-water plants, animals, or bacteria. The name, like the word planet, is derived from a Greek root that means “wanderer.” These organisms range in size from microscopic bacteria and plants to larger animals, such as jellyfish. Plankton generally have limited or no swimming ability and are transported through the water by currents and tides. The plankton communities serve as a base for the food chain. Planktons can be divided into three major size classes: the phytoplanktons, which are microscopic plants and bacteria, the zooplanktons, which are microscopic animals, and the macrozooplanktons, which are larger fish eggs and larvae and pelagic invertebrates. Planktons are often used as indicators of environmental and aquatic health because of their high sensitivity to environmental change and short life span (Pennak 1946).

A brief synopsis of the classic paper: Brooks and Dodson examined the distribution several zooplanktons of diverse sizes including Daphnia, a large zooplankton which is dominant in most of the lakes of southern New England but is scarce in many lakes near the eastern half of the Connecticut coast. Daphnia are also known to feed on smaller zooplankton species and some phytoplanktons. Their studies showed that there was great diversity among planktons in New England lakes than planktons in Connecticut lakes. Their studies also showed that those lakes in New England that lacked the planktivore Alosa pseudoharengus (a herring-like fish) had higher plankton diversity than those lakes in Connecticut that had an abundance of the planktivore. Their main objective was to find out what factors increased or decreased the size of planktons bodies, their populations, and what were the roles of predation and competition in plankton communities. To find results, they introduced Alosa pseudoharengus into the diversified New England lakes in 1942. After ten years, the Alosa pseudoharengus became dominant and greatly reduced the population sizes of the zooplankton Daphnia and other large planktons while smaller-sized planktons like Cyclops bicuspdatus, which are normally ignored by the Alosa psuedoharengus, became prevalent in the lakes. Upon the completion of their experiment, Brooks and Dodson theorized that predation and competition were key factors that affected the size and diversity of zooplanktons as well as phytoplanktons in New England lakes (Brooks and Dodson, 1965).

Predation by Alosa pseudoharengus reduced the population distribution of Daphnia and other larger zooplankton types in New England lakes. Alosa normally avoids the shores and preys heavily upon zooplanktons that tend to avoid this shore too. Interestingly, Daphnia normally swims five meters deep and avoids the shore. This made them easy targets for the Alosa. So when the Alosa was introduced in the New England lakes, they eliminated Daphnia in many lakes and severely reduced Daphnia populations in other lakes. Only those species in the lake that were extremely small (including some smaller and under-developed Daphnia) were overlooked by the predator and survived. The higher the competition among the predators for Daphnia and other large zooplankton species grew, the more quickly the plankton populations were eliminated (Brooks and Dodson, 1965).



Predation also affected the size of the plankton bodies. Most animals that prey on others choose their food on the basis of its size, the abundance, edibility, and the ease with which it is caught. This is consistent with the concept of size-dependent predation by Alosa. These predators mostly fed on the larger sized Daphnia, which is four times larger than the most of the smaller species. However, if the larger zooplanktons were quickly eliminated, the Alosa tended to feed on zooplanktons of reasonable size and phytoplanktons. The majority of smaller zooplanktons had a modal size of 0.285 mm in the presence of Alosa but had a modal size of 0.785 mm in the absence of Alosa. So in zooplankton and phytoplankton communities where Alosa was predominant, food resources for the plankton decreased, plankton size tended to be lower, and productivity and biomass in plankton communities were also lower. Hence, predation not only affected the body size and population size of the plankton, it also affected the composition of the various plankton communities (Brooks and Dodson, 1965).

Brooks and Dodson’s classic paper has inspired other ecologists to do more research on plankton communities. Three ecologists among the many ecologists whose work were influenced by Brooks and Dodson’s earlier work will be discussed. For instance, Michael Lynch, in his July 1977 paper “Zooplankton Competition and Plankton Community Structures”, frequently quoted Brooks and Dodson and reaffirmed that predation definitely played a role in plankton community structure. In addition to Brooks and Dodson’s work on plankton predation, he inferred that predation of larger zooplankton by planktivores helps maintain the plankton community. He reasoned that since larger zooplanktons consume smaller zooplanktons as well as phytoplanktons, their predation by plantktivores will serve to maintain the phytoplanktons, which are considered to be primary producers (Lynch, 1977). In another paper, “Predation by Gelatinous Zooplankton and Resource Limitation as Potential Controls of Arcartia tonsa Copepod Populations in Chesapeake Bay” , Jennifer E. Purcell et al theorized that predation on a plankton population reduces population size. This time, the predator was a zooplankton, the gelantinous zooplankton Chrysaora quinquecirrha, and it fed on phytoplanktons. Remaining true to the size sufficient theory stressed by Brooks and Dodson, Purcell at al found through experimentation that the zooplankton heavily preyed upon dominant and larger phytoplanktons like the Mnemiopsis leidyitia Consequently, the phytoplankton population and biomass decreased drastically (Purcell et al, 1994). Additionally, Milbrink and Bengtsson, in their 1991 paper, “The Impact of Size-Selective Predation on Competition between two Daphnia Species: A Laboratory Study”, reaffirmed Brooks and Dodsons’ earlier paper that the size of the zooplankton was a factor for predation. Their study examined the influence of size-selective predation on competition between two rockpool Daphnia species D. magna and D. longispina. Two different predator profiles were used, one simulating a gape-limited predator (a vertebrate), and the other simulating a size-dependent (invertebrate) predator. Predation was done by manually removing fixed percentages of populations in susceptible size-classes in accordance with the profiles. Their results showed that vertebrate predation was mainly size-dependent (like Brooks and Dodson had shown in their earlier work), while invertebrate predation had very little effect on the zooplankton in the rockpool. Hence, the vertebrate predator reduced the population size of the zooplankton and affected its distribution and species composition in the zooplankton community (Milbrink and Bengtsson, 1991). The works of these three ecologists described above all emphasize the size sufficient hypothesis and resource-based competition, phenomenon that was studied earlier by Brooks and Dodson. As a result of their work and others that followed, we have gained a greater understanding of the dynamics that surround plankton size and populations and how they are affected by predation and competition by other higher organisms. These studies also help us to apply these phenomena to other higher organisms because the size hypothesis and the resource-based competition hold true for higher organisms at higher trophic levels.

Brooks and Dodson’s work has also inspired current research on planktons. Roger Harris writes in the Journal of Plankton Research that extensive research has been done on zooplankton predator-prey interactions. In his paper “The role of zooplankton predator-prey interactions in structuring plankton communities”, he wrote that ecologist Gus Paffenhoefer’s 2002 work on planktons provided valuable information on the structuring of plankton communities. Paffenhoefer’s studies go into depth on zooplankton feeding mechanisms and community-building. It gave further insight on how the zooplankton population is affected by the predation of predators like marine fish (Harris, 2005). Another current research on planktons was conducted by Susanne Fietz et al. In their paper “Regional, Vertical and Seasonal Distribution of Phytoplankton and Photosynthetic Pigments of Lake Baikal”, they studied plankton in Lake Baikal, Siberia. Through their experiment, they revealed that in addition to predation, other factors helped to determine the size of plankton communities. They theorized that temperature, stratification, and the availability of natural resources ( chlorophyll, in this case) were essential in determining the composition and subsequent sizes of various plankton communities especially phytoplanktons. They used a combined methods approach, including microscopy and HPLC-based pigment analysis (Fietz et al, 2005). In an additional research, S. Fonda Umani et al, in 1991 studied the predation of microzooplankton and mesozooplankton. Their studies showed that predation of these zooplanktons by higher vertebrates fueled the upper trophic levels of these higher organisms (as Brooks and Dodson had stated in their earlier work). Their work also dwelled on the predation of these planktons by higher vertebrates and proved that increase in the biomass and primary production of these planktons depended on the intensity of predation (Umani et al, 2005).

There are many interests that have developed over the years concerning planktons. Some of these interest span from how planktons can be used for food for humans to how they will influence global biogeochemical cycles in years to come. In the recent paper, “The first 25 years of Journal of Plankton Research: looking into the future”, Harris et al emphasized that plankton studies will continue in the future to help us understand more about the earth’s biosphere. They stated that these communities of microscopic organisms play a key role in global biogeochemical cycles as well as in providing the basis of the food web, supporting the aquatic living resources exploited by humans (Harris et al, 2004). Future studies will also give us vital information that may help us efficiently tackle issues like global warming (since planktons play a key role in global biogeochemical cycles) and help us understand trophic levels of microorganisms. Another area of interest will involve how radiation (like ultraviolet or gamma radiation) affects the composition and populations of planktons. Additionally, it would be fruitful to know if plankton could be used for human consumption. These last two topics are topics that literature was not found on.

In concluding, plankton community structures are affected by predation of higher organisms. The intensity of predation affects the size of the plankton and the various plankton populations. Brooks and Dodson’s work in 1965 proved that predation of plankton by planktivore depended on their size and abundance. Other later work by ecologists coincided with the earlier work of Brooks and Dodson. Current research on plankton is mainly projected at studying the predation of planktons and the affect of such predation on plankton body size and populations. Future work on plankton will include the role of plankton in global biogeochemical cycles.



References

Brooks, J.L., and Dodson, S.I. (1965) Predation, Body Size, and Composition of Plankton. Science,150, 28 – 35.


Fietz, Susanne et al. (2005) Regional, vertical and seasonal distribution of phytoplankton and photosynthetic pigments in Lake Baikal. Journal of Plankton Research,27, 793 – 810.
Harris, Roger. (2005) The role of zooplankton predator-prey interactions in structuring plankton communities. Journal of Plankton Research, 27, 957
Harris, Roger et al. (2004) The first 25 years of Journal of Plankton Research: looking into the future. Journal of Plankton Ressearch, 26, 1 – 3.
Lynch, Michael. (1977) Zooplankton Competition and Plankton Community Structure. Limnology and Oceanography, 22, 775 – 777
Milbrink, G. and Bengtsson, J. (1991) The Impact of Size-Selective Predation on Competition between two Daphnia Species: A Laboratory Study. The Journal of Animal Ecology, 60, 1009 – 1028.
Pennak, R. W. (1946) the Dynamics of Fresh-water Plankton Populations. Ecology Monographs, 16, 339 – 335.
Purcell, J.E., White, J.R., and Roman, M. R. (1994) Predation by Gelatinous Zooplankton and Resource Limitation as Potential Controls of Acartia tonsa Copepod Populations in Chesapeake Bay. Llimnology and Oceanograph, 39, 263 – 278.
Umani, S. F. , Tirelli, V., Beran, A., Guardiani, B. (2005) Relationships between microzooplankton and mesozooplankton: competition versus predation on natural assemblages of the Gulf Trieste (northern Adriatic Sea). Journal of Plankton Research, 27, 973 – 986.


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