A bullet ant on the forest floor. In the tropics, insects grow to sizes that are huge in comparison to temperate zone insects. Photo by Hays Cummins
Discussion: The quantitative data sets do not tell a very complete story. The actual data was surprising in some ways, but generally does not seem to exhibit any sort of trend. Simply put, there is not enough data from the collected samples to warrant a statistical analysis for the data sets. It was expected that the highest insect diversity would occur in lowland forest or mountain forest and the collected data does support that supposition. Almonds and corals sampling found 8 species of insect to be present, which was the highest diversity found in the quantitative samples. The high organism count from San Pedrillo may most likely be attributed to the fact that a termite tunnel was disturbed. This accounts for the fact that 31 of the 36 total collected insects were termites.
One of the termites collected in the San Pedrillo sample. Termites accounted for 31 of the 36 insects collected.
Disturbance did not appear to have a major impact on diversity. The Drake Bay sample was intentionally taken from a site of disturbance, but the data from this site is not obviously deviant from the other data sets. Repeated sampling would be needed to determine if this finding is valid. Even though the site was disturbed, there were several species of plant present in the area, and the absence of monoculture in this disturbance may help explain why the diversity was not compromised in a disturbed site.
The final conclusion from the data obtained is that not enough data was collected to make any conclusions. The 3 sets of data are not random in that all were taken from plots of ground not more than a few meters away from frequently traveled paths. All the samples were obtained by ground collection, which is biased due to the fact that few species of neotropical insect are exclusively ground dwellers. The 3 sets of data do not meet the criteria of n (n-1) =30, which was chosen as the standard minimum number of samples (n) needed to have a statistically diverse and valid series of data sets. Samples were taken during a time of torrential rainfall, and since samples were from the ground, water runoff certainly must have played a major role in determining the outcome of sampling and collection data. This may best be exemplified by the San Pedrillo sample where the day before sampling the forest was nearly knee deep in rapidly running water. No time was allotted for the populations to recover before sampling was done, and therefore, the data is not going to be an accurate depiction of the true diversity present in the area. To reiterate, the data obtained from sampling does not represent a discernable trend and neither supports nor discredits the hypothesis; more samples must be taken for any valid conclusions to be drawn.
The qualitative observations were not as vague as the numerical data. While the observations do not have any weight in the scientific community as proof of a hypothesis, they were significant enough that the researchers in this group believe that a trend is observable. The observations in Monteverde were cause to believe that insects do thrive in benign environments. There were so few insects observed in the high altitude regions, such as the bog, Arenal and the mountain brush land, that it can be concluded: high altitude and low temperature are not conducive to high insect diversity. It also must be considered that these microclimates contained many species of highly specialized plants and often were inhospitable in other ways such as soil acidity. The data from La Selva is not very useful because the weather conditions made observations very difficult to make, and as such the observations are extremely biased.
Volcanic rocks are home to some black moss and lichen species. Plants were sparse and small with waxy cuticle. The lack of plant life coupled with the rough texture of the leaves makes herbivory difficult and, possibly, as a concequence insects were not observed.
While it must be considered that the observations appear to support the hypothesis of benign environmental support of insect diversity, it is not in any way to be accepted as truth. The data sets combined with the observations make a fair case in support of the hypothesis. The lack of supportive, quantitative evidence discredits the case that is made by observations, however. The real truth of this experiment is that more data is needed to make a valid conclusion; however, the trend appears to support the hypothesis.
Problems with this experiment were numerous. There was not enough time to adequately take samples from the research areas. The sample quality suffered as a consequence in several ways: the samples were not taken from remote areas far from human disturbance, and the samples were not taken over a broad range of times (most were taken near noon). The heavy rains caused some bias to be manifested in the results and also prevented the researchers from taking more samples. The rains may have also washed some insects away, or caused the insects to burrow in order to avoid the rain. The samples did not typically include flying insects, thus, insect traps would be useful as a tool in measuring insect diversity.
The trend in insect diversity observed in this experiment, most likely, may be attributed to high levels of plant biomass and high temperatures supporting many insect species. Long term experimentation of insect migration may provide some insight to the speciation speciation patterns of certain groups of insects. Noting the insight of the intermediate disturbance hypothesis and the recruitment limitation hypothesis, it may be possible to gain insight as to the role of canopy disturbance and population isolation as a possible mechanism for speciation in insects. This may help to explain the origin of tropical insect diversity; are new species generated all the time, or does the benign environment simply act like a museum for ancient species?
Insects like this horned Goliath Beetle are massive in size and look primordial.
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