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K. Leach
Paine’s article “Food Web Complexity and Species Diversity” explored a number
of topics, including resource partitioning, species diversity, predator-prey relationships,
and population dynamics. His main statement of the paper held that, “Local species
diversity is directly related to the efficiency with which predators prevent the
monopolization of the major environmental requisites by one species” (Paine 1966, pg.
65). His hypothesis extended to include that “the proportion of predatory species is
known to be relatively greater in certain diverse situations” (Paine 1966, pg. 65). In
testing his hypothesis, measures of local diversity were approximated rather than
measured quantitatively. In three different geographical locations, Baja California,
Mukkaw Bay, and Costa Rica, “subwebs”, or smaller divisions of the food web in a
community, consisting of small intertidal herbivores were studied in relation to species
diversity (Paine 1966). He concluded that local species diversity appears to be directly
correlated to predation intensity, there was no direct correlation between predator density
and latitude, and that if predation has the ability to prevent monopolies, the positive
feedback mechanism should increase species diversity until some limitation is reached.
Limitations could include space, as they often do in marine communities, such as for
barnacles, or it may simply be the removal of prey by other predators that causes
exclusion of a particular consumer. Paine’s study illustrated a key element in the
maintenance of species diversity, the function of predators (Paine 1966).
A paper published in 1979 written by Anthony J. Krzysik and entitled, “Resource
allocation, Coexistence, and the Niche Structure of a Streambank Salamander
Community,” extended Paine’s work by elaborating on the types of resources that
influence species diversity (Krzysik 1979). Paine’s study dealt mostly with the
partitioning of food between predators in order to sustain species diversity, but Krzysik
used more advanced quantitative methods to investigate resource partitioning and the
development of community organization. His methods included investigating four
aspects of microhabitat, which were “substrate, substrate moisture, proximity to surface
water, and size/type of cover utilized” (Krzysik 1979, pg. 173). The streambank
community was chosen because of the small number of necessary resource dimensions,
which are able to be studied quantitatively and the relationships between the dimensions
are apparent. Salamanders were chosen because of the wide range of species, body sizes,
and habitat preferences amongst them. Over 4000 of six species of salamanders were
selected and studied over a 2 yr period to determine in which ways they utilized the
microhabitats. The collected data was the analyzed and computed using SPSS (Statistical
Package for the Social Services) programs (Krzysik 1979). Of the many qualitative and
quantitative results found throughout this study, an important implication was that the
salamander community appeared to be well-adapted due to the following findings: “total
niche overlap is low, therefore minimizing competitive interactions, Interspecific
predation could not be documented and must be minimal, and demographic strategies are
consistent in all macrohabitats regardless of congeneric composition” (Krzysik 1979, pg.
173). It is clear that in Krzysik’s study, several elements, rather than just predator-prey
allocation, are influencing species diversity.
Another important factor influencing species diversity is the presence or absence
of other species, as explained in Tore Slagsvold’s paper “Habitat Selection in Birds: On
the Presence of Other Bird Species with Special regard to Turdus pilaris” (Slagsvold
1980). In this study, data from repeated surveys, “a total of 498,” taken at four different
forest locations in Norway was collected to determine the correlation between habitat
preferences of some birds and the presence of Turdus pilaris (Slagsvold 1980). Sought
after questions included whether or not the nesting positions of other bird species changes
with changes in the nesting positioning of the protector species, Turdus pilaris in this
case, and also whether or not the population size of the protector species was correlated
with the population size of other bird species (Slagsvold 1980, pg. 523). The results of
the study found that some bird species, especially Fringilla montifringilla held close
association with the protector species and the annual distribution changes were positively
correlated due to reliance on the protector species. Other species, such as Acanthis
flammea were positively correlated with the protector species due to their being social
species. Some species that were expected to fit the trend did not and this could be
accounted for by the decreased population of crows, which increased interspecific
competition. Species that were dependent upon the protector species also seemed to use
the protection as an advantage, increasing breeding and nesting frequencies. The final
conclusion of the paper held that the “Presence of Corvus corone seemed to increase bird
species diversity of the community whereas the reverse was found if Turdus pilaris was
present” (Slagsvold 1980, pg. 523). Therefore, this study underscores the relationship
between the types of species in a community and its species diversity.
An article entitled “Activity and Prey Election in the Sea Otter: Influence of
Population Status on Community Structure,” describes the influence of population
density on species diversity. The authors describe how when studying the population
dynamics of a system there are two main perspectives, depending on whether you are
viewing a system from the “top down,” or the way in which the consumers influence the
prey populations, or viewing a system from the “bottom up,” which studies the influence
of prey quality on the consumers (Estes et al. 1982). The papers discussed thus far have
mostly held the top down perspective, focusing on the consumers. The Estes et al. paper
attempts to combine the two perspectives in the study of sea otters in three different
locations, including Armchitka Island, where the sea otter population has been
approximately at equilibrium for the past 30 years, Attu Island, and Blanco Reef Oregon,
for which the otter population of the latter two locations is well below equilibrium due to
recent reestablishment of colonies (Estes et al. 1982). The oceans surface was scanned
via binoculars and telescopes to determine sea otter activity, which was classified as
either “foraging, resting, grooming, traveling, or interacting” (Estes et al. 1982). Careful
measures were taken to reduce bias by observing at several locations, to ensure that the
observed area included locations where all activities were performed, and ensuring that
the locations were completely visible (Estes et al. 1982).
The results of the study were that the sea otters in Armchitka spent “55% of
daylight hours foraging…and fish made up over 60% of their overall diet,” and “At both
Attu and in Oregon, sea otters spent 17% of daylight hours foraging…and herbivorous
macroinvertebrates made up their entire diet” (Estes et al. 1982). In Armchitka, where
sea otter population was at equilibrium, the sea urchin population was low and the
macroalgae was abundant and ungrazed. In addition, the abundance of nearshore fishes
was relatively higher, so the sea otters utilized this food source for their own diet.
However, due to increased population density and thus increased competition, as well as
the increased difficulty in catching fish rather than herbivores such as sea urchins, the sea
otters had to spend more time foraging in order to survive. However, at the other two
locations, the herbivores were abundant, macroalgae was overgrazed or absent, nearshore
fishes were scarce, and the competition was decreased due to a decreased sea otter
population, which allowed the otters to devote less time to foraging (Estes et al. 1982).
This study directly underscores the influence of population density upon species diversity
in a community.
An article entitled “Associational Plant Defenses and the Maintenance of Species
Diversity: Turning Competitors into Accomplices,” not only differs from the four
previous articles in that it focuses on plant diversity, but it studies the way in which
mutualistic behaviors between species affects species diversity. The author, Mark E.
Hay, wanted to determine the extent to which different plant species cooperated rather
than competed and when it was in their best interest (Hay 1986, pg. 618). He conducted
field work in a lake via underwater quadrats and microcosms, measuring a variety of
situations and combinations of palatable and unpalatable plants and in all seasons. Some
palatable plants included Ulva, Enteromorpha, Hypnea, and Chondria, and some
unpalatable species included Sargassum and Padina. His results were that in the absence
of herbivorous fishes and urchins, there is considerable competition between palatable
and unpalatable species and that unpalatable species could greatly reduce the number of
palatable species, but the palatable species did not have considerable effects on the
unpalatable species. However, the palatable plants gained significant protection from
insects, fish, and other predators by “associating with abundant competitors that were less
susceptible to herbivory” (Hay 1986, pg. 638). Therefore, species diversity, distribution,
and abundance in these plant communities was dependent upon their mutualistic
competition and cooperation.
Due to the wide range of topics focused on in Paine’s papers, it is possible to find
a number of studies that can be traced back to his findings. One paper published in 2002,
entitled “Food Web Complexity and Chaotic Population Dynamics,” is a complete
reiteration and extension of Paine’s findings, as the experimenters use supercomputer
simulations to create food web modes and quantitatively describe things that were not
technologically possible in 1966, when Paine’s paper was published (Fussman & Heber
2002). One current area of research involves “Diversity, Scale, and Climate-Richness
Relationships,” and attempts to analyze the many factors, such as space and time, that
affect diversity (The Biodiversity Research Group 2005). Another current researcher is
Russell Schmitt, who attempts to “understand general processes and mechanisms that
influence abundance and dynamics of populations and…species composition and
diversity of communities,” via subtidal field experiments and observations (Schmitt
2005). “The Buell-Small Succession Study” examines the various trends in “community
and species relationships in oldfield succession,” (BSS 2005). These ongoing research
projects do not even begin to encompass all that is currently happening in the field with
these topics.
While much progress has been made in extending and analyzing the work done by
Paine in 1966, there are still some holes in the research that exist. Some of the holes, he
was even aware of. He stated in his paper that it must be known if “resource monopoles
are actually less frequent in the diverse area than in comparable systems elsewhere, and,
if so, why this is so” (Paine 1966). He went on to say that “we must learn something
about the multiplicity of energy pathways in diverse systems, since predation-induced
diversity could arise either from the presence of variety of subwebs of equivalent rank, or
from domination by one major one” (Paine 1966, pg. 73). These holes in the research
still persist as it is difficult to determine what exactly constitutes a diverse area and how
to find one that is not diverse to determine the effect of predator-prey relationships on the
population dynamics. It is also difficult to keep track of the energy pathways in a system
in the wild, as the system is always susceptible to immigration, emigration, as well as
disturbance and other factors. Perhaps in the future, if laboratory controlled habitats can
be adequately designed to replicate those in the wild, energy flow can be measured more
directly and more of the holes dealing with species diversity research will be filled.
References
Biodiversity Research Group. 2005. School of Geography
http://www.geog.ox.ac.uk/research/biodiversity/diversity/.
BSS. 2005. The Buell-Small Succession Study
http://www.ecostudies.org/bss/research/projects.html.
Estes, J. A., R. J. Jameson, and E. B. Rhode. 1982. Activity and Prey Election in the Sea
Otter: Influence of Population Status on Community Structure. The American
Naturalist 120 (2): 242-258.
Fussmann, G. F. and G. Heber. 2002. Food Web Complexity and Chaotic Population
Dynamics. Ecology Letters 5: 394-401.
Hay, M. E. 1986. Associational Plant Defenses and the Maintenance of Species
Diversity: Turning Competitors Into Accomplices. The American Naturalist 128
(5): 617-641.
Krzysik, A. J. 1979. Resource Allocation, Coexistence, and the Niche Structure of a
Streambank Salamander Community. Ecological Monographs 49 (2): 173-194.
Paine, R. F. 1966. Food Web Complexity and Species Diversity. The American
Naturalist 100 (910): 65-75.
Schmitt, R. 2005. UCSB
http://www.lifesci.ucsb.edu/eemb/faculty/schmitt/research/research.html.
Slagsvold, T. 1980. Habitat Selection in Birds: On the Presence of Other Bird Species
with Special Regard to Turdus pilaris. The Journal of Animal Ecology 49 (2):
523-536.
The paper relies heavily on direct quotation. Try to incorporate ideas and discuss
concepts in your own words. Further research/more studies would be helpful in actually
tracing the research based on Paine’s paper. The development of concepts from your
classic paper would be clearer if you discussed the ideas from Paine’s paper and how
later research built on them. As it is, there are several summaries of studies put back to
back.
This paper has been cited in excess of 1880 times since 1980. This is an enormous
impact factor. I did not finish your paper with a clear feeling of where all those citations
have been taking the field. You spend a bunch of space on Krzysik, yet that paper has
been cited only 47 times and is likely only one small offshoot of Paine’s classic. You
select and describe well a set of other minor-player papers like Krzysik, but at the end of
the day, the reader is left without a clear feeling of the profound impact Pain’s paper had
and why it had that impact.
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