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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
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Hutchinson GE (1961) The paradox of the plankton. Am Nat 95:137–145 The American
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