Lambir subterranean ant project

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Subterranean Ant Distribution in Differing Soils at Lambir Hills National Park

Marlee Morris and Samira Rudig-Sotomayor

Abstract

The forest in Lambir Hills National Park grows on many different types of soil which give rise to different niches. Two factors that seem most important in determining the subterranean ant diversity are plant diversity and soil type. We hypothesized that the subterranean ant species may occupy different niches in different soil types. We sampled the ant diversity by setting up underground bait traps using water bottles, soapy water and Milo. Unfortunately, our sample size was not large enough to find a significant different in subterranean ant biodiversity between clay, fine loam and sandy loam in the Lambir Hills CTFS plot.

Introduction

Tropical rainforest biodiversity is a subject that has captured the interest of biologists worldwide. Research in this field started out, not surprisingly, with the largest organism in this habitat: trees. The extreme tree diversity seen in tropical rainforests has since been attributed to the availability of different niches, for example, different soil type (Leigh 2004). Understanding the basis for tree diversity is imperative for analyzing the biodiversity of insects. In fact, substantial evidence has been provided to suggest that insect diversity is a direct function of plant diversity (Novotny 2006). This finding is particularly interesting because it opens up the possibility of investigating to see if the same pattern applies to individual kinds of insects. If soil type affects the diversity of trees, and types of trees determine the diversity of herbivorous insects, does soil type itself affect the diversity of insects?

Figure 1: Ants in collection bottle


Question

  • Does soil type affects the diversity of subterranean ants? This is an important question, because if true, it would suggest that diversity of insects depends on occupying different niches not necessarily related to their food source (trees).

Methods

Field methods

The ant samples were be collected by a unique collecting method. We collected empty water bottles and cut circular holes in four sides. These bottles were then filled with approximately one inch of water. To attract the ants we placed a Milo and sugar coated tube of tape in the center of the bottle. Three samples were taken from each of three soil types, clay, sandy loam and fine loam, for a total of 9 water bottle traps. The traps were left in their respective soils for 24hrs. The ant samples were then collected, and the ants for each trap were washed into petri dishes. In the first two sets of traps (clay and fine loam) ant numbers were low enough for us to count each individual. However, the last three traps (sandy loam) contained thousands of ants. To count these individuals, we spread the content of each bottle into a tray, counted a subset of that tray, and applied that count to the rest of the tray .

Analysis

Our statistical hypothesis for this experiment is that soil type is a statistically significant factor in affecting subterranean ant diversity. The null hypothesis is that soil type is not a statistically significant factor in affecting ant diversity. To test these hypotheses we performed an ecological diversity index based on a linear model using the “Shannon” index using 'R'. We grouped all our data into Table 1 where C stands for clay, SL stands for sandy loam, and FL stands for fine loam. The four ant species observed were grouped into four morphologies labeled M1-4.

Results

Table 1: Summary of our collection data

The overall counts from our traps are shown in Table 1, and it is readily apparent that the results are skewed with a huge abundance of individuals from the sandy loam plot. There were 24 individuals and 4 species in clay soil, 2 individuals and 1 species in fine loam soil, and roughly 8400 individuals and 1 species in sandy loam soil. Our results from performing the ecological diversity index analysis showed that soil type does not in fact impact ant diversity. Table 2 illustrates that although diversity decreases from clay to fine loam and from clay to sandy loam, the sample sizes were too small to provide statistical significance.

Table 2: The relationship between soil type and diversity

Discussion

This result is not surprising after observing the recorded counts. Very few ants were recorded in the clay and fine loam traps. The sandy loam traps, in fact, contained thousands of ants more than the traps from either of the other two sites. While we would like to believe this is simply a result of the effectiveness of our traps, it is more likely that we unknowingly placed our sandy loam traps in the middle of an ant colony. If this is the case, then the insignificance of our analysis should be expected. Additionally, one of our fine loam traps was contaminated by non-subterranean ants, and data from that trap had to be disregarded. This lowered our analysis of fine loam to two traps, decreasing again the power of the test and the possibility of significance. However, this result should not be discouraging. A definite, though maybe not statistically significant, decrease was seen in the number of species of ants between clay and the other soil types. Perhaps with an increase in sample size and decrease in placing traps in ant colonies, significance would be achieved. A future experiment should be performed, perhaps after the sampling and randomization methods have been refined.

References

  • Leigh, E. G. (2004), 'Why do some Tropical Forests Have So Many Species of Trees?', Biotropica, 36(4), 447-473.
  • Novotny, V., Drozd, P., Miller, S. E., Kulfan, M., Janda, M., Basset, Y., Weiblen, G. D. (2006), 'Why Are There So Many Species of Herbivorous Insects in the Tropical Rainforest?', Science, 313, 1115-1118.
  • Ryder Wilkie, K.T., Mertl, A.L. & Traniello, J. F. A. (2007), 'Biodiversity below ground: probing the subterranean ant fauna of Amazonia', Naturwissenschaften, 94, 725-731.