Jesse McWilliams
Eric Hammerly
Kim Bruce
Josh Greenberg
SLOSS in Bachelor Reserve
Our primary goal was to test the SLOSS theory in a regional ecosystem. Our initial hypothesis was simply that the larger islands would harbor a more diversified set of species than smaller islands (the smaller islands combined totaling the same amount of square meters as the one large island) on an insect level.
We based our decision to study SLOSS on the issue of reserves, reserve size and, consequently, how the reserve size is related to the diversity (and abundance) of species. Abundance became a point of contention within the group, so it was not included within our hypothesis but within the discussion of relevance in the progress report. It will, however, occupy a significant portion of this report. Much of this project has been based on The Song of the Dodo, particularly the discussion's on reserve size and construction, diversity and the basic SLOSS argument (including MacArthur and Wilson). We also used the work and articles contained in Biosphere 2000, plus other articles such as Walter V. Reid's article "Biodiversity Hotspots", John Terborgh's "Preservation of Natural Diversity: The Problem of Extinction Prone Species", Simberloff and Apolle's "Island Biogeography Theory and Conservation Practice" and Wiens' "Habitat Fragmentation: Island vs. Landscape Perspectives in Bird Conservation". These articles served to not only elaborate on our findings, but also make them applicable and relevant to more macroscopic views of island Biogeography and reserve size. We used Wiens' article to increase the scope of this project more, by introducing the idea of habitat fragmentation and preserve size, hoping to draw a well-rounded conclusion concerning the necessity of conserving large islands of habitats. This collaborated well with many principles of Island Biogeographic theory that this project addressed: specifically biological diversity and island (or reserve) size. Aside from the rare exceptions (which will be addressed in this report) "it must be realized that several small areas, adding up to the same total area as the single large area, are not biogeographically equivalent to it: they will tend to support a smaller species total" (Apolle and Simberloffe, 285). Only with an accurate understanding of reserve size can we, as humans living in a "developed" world, make effective decisions in maintaining the biological diversity that is the symbol and sustainer of our complex, intricate and interrelated ecosystems of earth.
We selected two sites for study, both in the west/southwest quadrant of Bachelor Reserve (from the Oxford-Milford access). One site (Site A) was an abandoned field setting, with scattered juniper and honeysuckle and plenty of vegetative ground cover in the form of grass, ragweed and other such ground-hugging cover. There were few leaves in Site A. The other site (Site B) was in a mixed osage/honeysuckle transitional forest, the only ground cover being in the form of leaves. There were many osage oranges, or "monkey balls, hedgeapples" etc., scattered throughout the sight.
Much of the basis for our experimental design was based on Diamond's theoretical conclusions that:
"-A large reserve can hold more species at equilibrium than a small reserve.
-A group of reserves that are tenuously connected to-or at least clustered near each other will support more species than a group of reserves that are distinct or arrayed in a line.
-A round reserve will hold more species than an elongated one" (Quammen, 445).
We cut a total of 14 plywood squares (a square being as close to a round reserve as we could get). Two of the squares were ½ meter squared. Four of the squares were ¼ meter squared. Eight of the squares were 1/8 meter squared. This was split down the middle and divided into Sites A and B. Both A and B received one large board, two medium boards and four small boards. The goal was to have equal areas for the most accurate measurement possible: four small squares equaled one large square, two medium squares equaled one large square, etc. Each plywood square was hammered into the ground, and checked to insure that the wood was no more than a millimeter from the soil if that was possible. All grass, shrubs and leaves beneath the projected site for each piece of plywood were removed for ease in counting.
All squares in both sites were clustered around each other to increase species diversity for all the squares. The goal was to make sure to establish, if necessary, some sort of minimum viable population, at least on a microscopic scale, would survive and hold underneath their respective squares. Another reason for the proximity of each square to the other was the need to test one ecosystem with each site. If all eight small squares were placed in an area with naturally greater diversity, then the results would be biased and non-productive. To further increase accuracy, two sites were used in two different environments - allowing us much greater freedom in making the few generalizations that our particular project allowed us. The trends we noticed could now be free of being totally ignorant of other environments, and organisms, of the area.
We also collaborated not only with the class, but also with the teacher in organizing our project. We went through much debate in determining the size and number of the squares that we should use. What we strove to do was create the most representative experiment feasible, and fourteen squares divided over two sites in two different environments gave us this. We also took into account Terborgh's warning before drawing too many similarities between main land islands and islands: "I must warn against the application of island data to isolated patches of habitat on the mainland. The two situations are analogous but not equivalent. An island receives comparatively few immigrants of any kind, but the populations in an anomalous pocket of habitat are constantly exposed to the pressure of invasion from species in adjacent habitats" (Terborgh, 718). What this means is that each board, while analogous, or comparable to a real island, must be treated more as an isolated habitat that shares common characteristics with an island. We used this to our advantage. One fear of this project was the fall season and the prospect of cold fingers and no organisms beneath the boards. Terborgh himself drew a graph of simple islands vs. land bridge islands. As the reproduced graph below shows, the capability of those islands with land bridges to accept new species was extraordinary. If the low numbers of bugs that we found represented a trend, the choice for the close proximity Terborgh hinted at seems to be well-accounted for.
We found a number of samples that were preserved in a 60% alcohol, 40% water solution, which will be given to the class for observation. We also have set up a web site to aid in description and effective communication between the class and ourselves. Our goal is to describe abundance and diversity, and reserve size and design. Also the importance of the limiting factors of island Biogeographic theory will be addressed. One such factor are stochastic factors, especially weather - specifically temperature. Temperature and insect abundance will be examined through the comparison of two graphs and other; verbal explanations - and how weather played a limiting factor in the experiment. Also, the lack of dispersal ability will be examined. Dispersal ability appears to be especially important in the case of non-flying insects, and it can be a significant limiting and result-skewing factor. The importance of this SLOSS project and habitat fragmentation will also be examined in class. The research that has been done on inter and intra reserve relationships - and why we based our design on this research - and what our findings tell us about the reserve design and SLOSS. We have taken pictures of both sites, including photographs of the surrounding environments. We will also strive to convey, through photographs, possible mainland populations. Numerous graphs will be used to convey, support and elaborate upon the material presented. The goal here is to make the numbers easy and not overloading. Simple graphs will be used, the numbers written down. The goal is to show trends and how they tie to the varying factors of board size, temperature and environment (the differences between Site A and Site B).
We started this project by putting boards out on the week of October 10th. We checked beneath the boards the next week on the 15th, and found that no insects had moved beneath the board. We had five successful weeks, from October 22nd through November 19th, of discovery and observations. It's these five weeks that are the basis for our data. The most abundant organism we found was the prolific pill bug. In total we found 20 different species of organisms between the two different sites. In terms of overall abundance,Site A, the field setting, had nearly three times more than Site B, the osage/honeysuckle canopy forest.
The large boards had, as predicted, the most different species and the highest overall abundance. The medium boards had the least in terms of both overall abundance, but had a higher number of different species than the small boards, with thirteen. The small boards had a higher overall abundance than the medium boards, but fewer species, with 11. This is due to the high numbers of pillbugs, which will be discussed later. The large boards, in accordance with the SLOSS theory, had 16 individual species, more than both the small boards and the medium boards. Coupled with the higher abundance of these sixteen different species, the large boards were much more effective as reserves.
We kept simple field journals to record our data. Besides listing numbers, we recorded other signs of life, from grass shoots to signs of earthworms with the intent of recording signs of colonization and movement.
Every graph included was derived from our data set and put into a graph. We derived our P-value to aid our statistical confidence of the graphed data. The mean was used to make the gathering of the data accurate and reflective of all the numerical information, and in order to set trends.
Our simple hypothesis was proven true, in accordance with Island Biogeographic Theory. The larger preserve had the greatest number of individual species in both Site A and Site B throughout the course of the sampling period. The severe fluctuations, however, in both abundance and species numbers, shows that equilibrium was not reached in the testing period. What becomes of "issue is the definition of sufficient time: one can reasonably claim for some taxon and location that turnover is so slow that equilibrium will never be reached" (Apolle and Simberloff, 285). In this situation, one could assume that the temperature fluctuations of the study time, October and November, played a significant role in these fluctuations. Trends must be kept generalized, as only daily comparisons between number of species and high and low temperatures could show distinct and definite trends. The two graphs do, roughly mirror each other, but drawing specific conclusions would be erroneous. These graphs merely highlight the comparison between temperatures and numbers of different species.
October 22 was only two weeks after the boards had been put into the ground. While cold temperatures had preceded this date, Apolle and Simberloff's fore-mentioned observations come into play. The only way to draw significant parallels would be daily monitoring. However, in-between the dates of October 29th and November 11th, a sort of plateau was reached. Could this be the same plateau that MacArthur and Wilson reached of equilibrium? It could, but the evidence isn't sufficient, and the data sheet explains why. Underneath the small boards there was an impressive number of pill bugs, starting in-between the October 29 and November 5 testing dates, indicating rapid domination by the pill bugs in excessive numbers. On the date of November 5, there were 83 pill bugs beneath the small boards of Site A, collectively. Equilibrium, it seems, is unprovable within the short time of this study. Without equilibrium the relationship between temperature and the number of species becomes more of a representation, a description of trends in temperature and species - and should be treated as such.
One of the basic stochastic factors for this project was weather and seasonal changes. Certainly the number of pill bugs were related, in some way, to the fluctuations in weather and change in seasons. Also of importance were the basic habits of each individual species throughout the year, an important climatic distinction, given the varying seasons of the area.
The basic implications remain the same, and unchanged. The larger boards, beyond any doubt, harbored a more diversified and abundant group of species. While the highest abundance of insects during any one sampling period came from beneath the small boards, it appears, thanks to the use of the mean in representing data, these outrageous abundances (of pillbugs) are just anomalies.
It seems our findings were the result of the applied SLOSS theory. Though individually our results didn't match the species-area curve of MacArthur and Wilson, collectively there was a basic relationship. What's the deal with pillbugs? Why were they found in such high numbers under the small boards of Site A? It seems that these abundance's are the result of a combination of dispersal ability and establishment. "If dispersal is difficult, establishment is difficulty squared" (Quammen, 144). This leads to a possible observation: the large boards were too difficult for the pillbugs to colonize in the same numbers the small boards allowed. If there are more pillbugs than available habitat, then perhaps they had to move beneath the small boards. Diamond found something similar: "Despite their ability to disperse, such species are often found to be confined to islands or patches . . ." (Diamond, 1028). A little more speculation: perhaps the pillbugs have really bad dispersal ability, but the small boards were placed over their nests or colonies. Reid describes something known as hotspots: "This is because hotspots of species richness do not often incled relatively rare species - hotspots that are ranked highest for richness often contain overlapping sets of common species, while failing to capture rarer species" (Reid, WRI institute). Wiens points out yet another possibility: "the facet of interspecific competition and assures that the survival expectancy of remaining populations increases as their competitors drop out" (Weins, 716). The pillbugs colonized and dominated to such an extent that they out-competed all other organisms and grew to the enormous populations they did. Perhaps it is seasonal. Perhaps pillbugs preferred the small boards. But speculation serves only to hint at further study. SLOSS theory, however, does not appear to relate abundance, and therefore the pill bugs do not disrupt out data.
The large reserve held a significant advantage in playing host to more insects, in both abundance and species diversity. They were less susceptible to the "winking out" described by Quammen, and are, in general, much more stable - a definite concern of any reserve. The smaller the island, the less overall species. Our project, by basic design, mirrored both metapopulation and equilibrium theories on a microscopic scale. "Metapopulation, defined loosely, is a population of populations"(Quammen, 598). It consists of a series of small populations that are susceptible to winking out. There is no mainland species. Habitat fragmentation, which has been called "the single greatest threat to biological diversity" (Wiens, 597), is quite similar in form to the eight total small pieces of plywood. Throughout the experiment these small pieces of plywood were susceptible to winking out (as metapopulation accounts for). However, continuing with the idea of equilibrium theory, what if the large boards acted as a sort of mainland for species, on a microscopic scale. While the small boards winked out, they were soon recolonized. While colonization patterns of insects wasn't the goal of this paper, it is still an important realization: that the experiment design could have worked to mirror both metapopulation and equilibrium theories. What makes this important, on a much, much larger scale, is that the larger reserve, the greater diversity and abundance. The greater the diversity and abundance, the more stable the population.
Scattered throughout the Oxford area are many rows of cornfields. In-between these rows are often islands of woods, fragments of habitat - similar to the small boards. Wiens details several negative consequences to such fragmentation: "In addition to an overall loss of habitat, the size of the habitat remnants is reduced, blocks of habitat become widely separated and the proportion of habitat that is close to patch boundaries increases and the edges become more abrupt. As a result of the area effects, population sizes are reduced, leading to the disappearance of some species from small fragments and an increased sensitivity of the remaining populations to chance events" (Wiens, 597). Further supporting our data is Diamond: "for conservation strategy have concluded that some large refuges are essential to minimize extinction rates and to ensure certain species any chance of survival at all" (Diamond, 1027). On November 12, the only species of insect besides pillbugs under the eight small boards were two lone earthworms. The conservative implications are real and profound; the increased destruction we do to large tracts of habitat is more long-term and decisive than we think. "Currently, the single greatest threat to wildlife is loss of habitat, either through outright loss of areas used by wild species, degradation, or fragmentation" (Kaufman and Cecilia, 357). One 10,000 mile square of continuous habitat is not equal to ten 1,000 mile square fragments. Such manipulations, based solely on area, can lead to wide-scale extinction's, as populations are split and divided and become metapopulations, subject to winking out and therefore extinction.
BIBLIOGRAPHY
1) Apolle, L.G. and Simberloff, D.S. Island Biogeography Theory and Conservation Practice. Nature
2) Kaufman, Donald and Cecilia, Franz. Biosphere 2000: Protecting our Global Environment. Duburque, IA. Kendall 1999, 3rd edition
3) Quammen, David. Song of the Dodo. Simon and Schuster Inc. 1996
4) Reid, Walter V. Biodiversity Hotspots. World Resources Institute
5) Terborgh, John. Preservation of Natural Diversity: The Problem of Extinction Prone Species. American Society of Zoologists symposium, 1974
6) Wiens, John A. Habitat fragmentation: island v landscape perspectives on bird conservation. Grant by U.S. National Science Foundation
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