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Qi Peng November 16, 2005 Biology 112 Literature Analysis Paper In the past decades, the study of aquatic food cycle relationships had tremendous impact on the overall field of ecology, contributed many important data that redefined various ecological concepts, and provided us with many important principles. Among these studies, an early paper published by Raymond Lindeman is especially important because of its introduction of trophic-dynamic viewpoint on the community concept. Years after the publication, the concepts explained in Lindeman’s paper are still widely used by researchers to clarify their points and support their findings. “The trophic dynamic aspect of Ecology” was published by Lindeman in 1942, and the whole paper could be divided into two parts. In the first part, Lindeman defined certain concepts regarding trophic dynamics, and made some generalizations of productivity and biological efficiencies regarding aquatic systems. In the second part, Lindeman attempted to explain the succession in lake system and the trophic-dynamics of this succession process through the concepts and generalizations he introduced in the first part. Major viewpoints guiding synecological thoughts at the time were: 1) the static species-distributional viewpoint; 2) the dynamic species-distributional viewpoint; 3) the tropic dynamic viewpoint. (Lindeman) while either species-distributional viewpoint draw clears lines between different plant and animal groups within a community, the tropic dynamic viewpoint adopted in Lindeman’s paper emphasizes the relationship of tropic or “energy availing” relationships within the community unit to the process of succession. (Lindeman) through analysis of these relationships, Lindeman concluded that a biotic community can not be clearly differentiated from its abiotic environment, so he defines the ecosystem as “composed of physical-chemical-biological processes active within a space time unit of any magnitude” (Lindeman) , in other words, the biotic communities plus their abiotic environment. Within this system, Lindeman further groups organisms into several trophic levels such as producer and primary consumer, with each successively dependent upon the preceding level as a source of energy. (lindeman) Generally, the more remote an organism is from the initial source of energy, the more efficient it is in using its food supply, but the percentage loss of energy due to respiration is also greater. (Lindeman) With above generalizations, Lindeman then analyzed the trophic dynamics in Hydrarch Succession. He noted that this dynamic process involves the change in specie composition, and productivities. (Lindeman) Specifically, in the case of Lake Entrophication, the total productivity increase exponentially before the lake reaches Eutrophic level. But once reaching eutrophic state, both the productivity level and organism biomass of the lake decreases. Lindeman explained this paradox by emphasizing on the oxygen supply of the lake. As many highly productive organisms rapidly consume dissolved oxygen of the lake in eutrophic state, oxygen supply diminishes and causes those highly productive organisms to die out. In their place, many organisms that are tolerant to anaerobic conditions take over the lake. Because these organisms take advantage of reduction instead of oxidation, their productivity are considerably lower than their aerobic counterparts. (Lindeman) Therefore, oxygen supply becomes the determinant factor in productivity and specie composition of a lake. As mentioned by Lindeman, the validity of this interpretation in a more universal scale was still uncertain at that time. (1942) Researchers such as Huchinson challenged this interpretation by stating that only lakes already well-supplied with nutrients can have a true eutrophication process. Therefore, other factors such as the nutrient supply and the morphometric character of the lake all play an important part in hydrarch succession. (Huchinson 1961) Among the needed nutrients, Tilman noted in his experiment that phosphorus and nitrogen are especially important factors. ( Tilman, 1976) Recent study of lake systems hint that Hydrarch Succession are influenced by many different factors, not only by oxygen supply and nutrient supply, but also by the temperature, weather, age of the lake, types of organisms living in the lake and the depth of the lake etc. Even similar lakes with only a few points of difference could have totally different productivity curve and future specie composition in the long run. (Meckler, 2004) It certainly would be helpful for future trophic study to generalize a principle composed with all above factors, so researchers could use computer generated model to predict the specie composition and productivity of each trophic level in the future. Another important concept of Lindeman’s paper that was used by researchers frequently is the relationship of number among producers and all levels of consumers. According to Lindeman, the animals at the base of a food chain are more abundant while those towards the end become progressively fewer in number. (Lindeman) This is caused by increasing energy loss towards the end of food chain and the progressively increasing size of the predator on top of the food chain. (Lindeman) This interpretation implies an important aspect of trophic-dynamics in both lacustrine and terrestrial cycles: the ratio of predators are very dependent on prey. Prey can limit predator population because excess predators with limited prey population increase competition thus eliminate excess predators. Therefore, in the case of simply one predator vs. one prey situation, there is always a set ratio between the two populations, and the ratio is determined mostly by factors such as the available resources of the prey. (Elton, 1927) This relationship is termed “bottom up”, or Eltonian pyramid of numbers. (Arditi, 1989) this relationship suggests that the biomass of organisms at any trophic level is a function of the productivity of their resource base. (Mathew et al 1997) Two predictions emerge from this approach : that more productive ecosystems will have more trophic levels, and that the biomass of organisms at all trophic levels will increase with the basal productivity of the ecosystem. (Mcqueen et al, 1986) These arguments provide an intuitive intepretation, but they are at odds with the predictions of the simplest mathematical formulations of predator-prey interactions that include any dynamic feedback from consumers to their resources. (Mathew et al 1997) Alternatively, other researchers such as Hairston argued for another approach that focuses on how the number of trophic levels in a system influences partitioning of biomass among all the trophic levels, which is termed “top down” ( Hairston 1960) Based on a dualistic assumption that a given trophic level is regulated either by resource competition or by predation, “top down” approach suggests that the number of trophic levels functioning in an ecosystem determines its trophic structure. (Hairston 1960) For example, plants are expected to dominate in ecosystems with odd numbers of trophic levels, whereas herbivores will dominate in ecosystems with an even number of levels. Recently, through data taken from experiments on Lake Eutrophication, researchers used the same fundamental approach as “top down” to argue that the abundance of secondary carnivores accounts for much of the variation in plant and herbivore biomass in lakes that is not explained by nutrient levels. (Carpenter et al 1984) Although these two contrasting views (bottom-up vs. top-down) are very different from each other in terms of their methods and their predictions on the patterns of variation in biomass at adjacent trophic levels, recent experiment data seem to lend support for both perspectives. A bottom-up approach argues that all trophic levels should increase with productivity. Numerous studies in aquatic systems and some evidence in terrestrial systems show patterns of positive covariation between plant and herbivore biomass, supporting the "bottom-up" perspective. In contrast, much experimental evidence for trophic cascades in enclosure and biomanipulation studies in aquatic systems, and an increasing number of similar studies in terrestrial systems, argues for the "top-down" perspective. (Mathew et al, 1997) Therefore, it seems these two approaches might not be mutually exclusive of each other. In certain areas, bottom-up approach works more strongly, in other areas, top-down approach works more strongly. Instead of two theories going to the opposite direction, most researchers today view bottom-up approach and top down approach as two ways of trophic structuring emphasizing in different aspects of trophic-dynamics. Bottom-up approach emphasized on the horizontal factors of a trophic structure, specifically in which multiple species at the same trophic level compete for resources and share predators. (Mathew et al 1997) Top- down approach emphasized on the vertical factors of a trophic structure, that the number of trophic levels present under different conditions influence the pattern of biomass partitioning among trophic levels. More specifically, top down approach viewed resource limitation and predator limitation as having relatively exclusive roles, predicting that biomass partitioning into trophic levels would depend on whether there were an even or odd number of trophic levels. (Mathew et al 1997) Therefore, in order to accurately and precisely examine how productivity and predation jointly affect trophic structure, a theory that synthesizes these two views into one is desired in the ecological field. Researchers today such as Power (1992) and Oksanen (1981) have attempted to synthesize the above two theories into one. However, as of today, a relatively simple, yet precise model is yet to be discovered by ecologists tomorrow. Discovery of such model could clarify many unsolved mysteries in ecology such as the historical distribution of species in specific systems. Furthermore, such a model will be very useful in predicting species distributions and bio-manipulation experiment, thus help us better understand and protect the environment. Therefore, working on such a model would certainly become an exciting new area of ecology. Literature Cited Arditi R, Ginzburg LR. 1989. Coupling in predator-prey dynamics: ratio-dependence. J. Theor. Biol. 139:311–26 Carpenter SR, Kitchell JF. 1984. Plankton community structure and limnetic primary production. Am. Nat. 124:159–72 Elton C. 1927. Animal Ecology. London: Sidgwick & Jackson Hairston NG, Smith FE, Slobodkin LB. 1960. Community structure, population control, and competition. Am. Nat. 44:421–25 Hutchinson GE (1961) The paradox of the plankton. Am Nat 95:137–145 The American Naturalist Lindeman, R.L. 1942. The trophic-dynamic aspect of ecology. Ecology 23:399 – 418. Mathew A. Leibold, Jonathan M. Chase, Jonathan B. Shurin, and and Amy L. Downing, (1997) “SPECIES TURNOVER AND THE REGULATION OF TROPHIC STRUCTURE” Annual Review of Ecology and Systematics, Vol. 28: 467-494 (Volume publication date November 1997) Meckler A N (2004) New organic matter degradation proxies: valid in lake systems? Limnology and oceanography 49: 2023—2033. November McQueen DJ, Post JR, Mills E. 1986. Trophic relationships in freshwater pelagic ecosystems. Can. J. Fish. Aquat. Sci. 43:1571–1581 Oksanen L, Fretwell SD, Arrüda J, Miemela P. 1981. Exploitation ecosystems along gradients of primary productivity. Am. Nat. 118:240–61 Power ME. 1992. Top-down and bottom-up forces in food webs: Do plants have primacy? Ecology 73:733–746 Schindler DW, Armstrong FA, Holmgren SK, Brunkill GJ. 1971. Eutrophication of lake 227, Experimental Lakes Area, Northwest Ontario, by addition of phosphorus and nitrates. J. Fish. Res. Board Can. 28:1763–82 Tilman D (1976) Ecological competition between algae: experimental confirmation of resource-based competition theory. Science 192:463–465