Category: Independent Project

Participants: Patricia Argetsinger, Shannon Bunch, Ingrid Chlup, Rick Dutra, Dorene Medlin, and Sarah Poe

Site: La Selva Biological Station, OTS

Key Words: Biodiversity, Heliconia, Primary Forest and Secondary Forest

Summary: After collecting Heliconia and studying the number and types of insects found in the bracts of the plant, we found no significant difference in biodiversity from primary to secondary forest plants.
 

Introduction

"Nearly 40% of the potential net primary productivity of earth is used or dominated by humanity or foregone as a result of land use change (Vitousek, 1994)." In Costa Rica alone, 83% of forest has been cleared primarily for beef production (Kricher, 1997). If land that has been cleared is allowed to grow back without outside intervention a secondary forest results. It is believed that even after centuries a secondary forest has not completely re-established the biodiversity found in the primary forest (Terborgh, 1992).

Biodiversity refers to species richness or how many different species are present and the abundance of each. The highest biodiversity has an equal distribution of a large number of species. Diversity is reduced when extinction exceeds speciation (Kricher, 1997). Therefore, such things as habitat loss, wildlife trade, introduced species, pollution, and fragmentation can affect it. Fragmentation, for example, impacts biodiversity by creating an island effect. Small islands have fewer species than larger islands and fragments further from an immigration source have fewer species than those that are closer (NAAEE, 1997).

Research shows the lack of biodiversity in secondary forests can be caused by the removal of seed dispersers when deforestation occurs. This is true even when mature forest is present within 500 meters of the succesional forest (Terborgh, 1992). Additionally, the treatment of the deforested area while it is used as pasture land can impact the species that can be maintained during succession (McDade, 1994).

Biodiversity is vital to the health of the biosphere. The loss of a keystone species can eradicate an entire food web. In addition, some species that are lost may have the potential for medical uses.

The goal of this project was to compare the biodiversity between primary and secondary forest. We expect higher species diversity at the primary forest sites. To test this hypothesis we looked at insect diversity found in the Heliconia sp. found in primary and secondary forests. Heliconia is a plant that flourishes in light gaps and supports multiple species of insects.
 
 

Methods

The general procedures we used to conduct the research included the following: identification of variables and controls, materials and supplies, collection protocols, sites and number of samples. Our methods were divided into two sections: field protocol and lab protocol. Our Field Protocol was to locate specimens in collection sites (refer to map), measure distance off the trail, place ziplock bag over specimen, cut and seal the bag. The bag was labeled with date, coordinates, and forest type. After we collected the specimens, we returned to the laboratory. Our Lab Protocol was to observe and record physical data, place each specimen in ethanol for 10 minutes, dissect it and rinse the parts in ethanol. We then filtered the solution and dried the collection paper. Finally, we observed, counted and recorded the number of macroscopic organisms in each flower. Finally, we analyzed and interpreted the collected data.
 
 

Results

The average insect species diversity found was compared using the Shannon-Wiener Diversity Index. Heliconia found in primary forests was found to have a 0.405 index, while those found in the secondary forest was found to have a 0.460 index. When the mean values were compared with a t-test, they were found to have no statistical difference (t = 1.33, d.f. 22, p = 20%). We also found a correlation between the number of bracts on a stem and species diversity. (R² = .5487)
 
 

Discussion

According to results from prior research, species diversity is generally greater in primary forests than in secondary forests. Our data does not support this finding.
One possible explanation for this contradiction is the proximity of primary and secondary forests. There was no gap between the two forests where samples were taken, making it possible that no hindrance existed in seed dispersal. In further research of biodiversity, it may be necessary to use fragments of forests instead of plots that are adjacent.

In addition to proximity, it is possible that using the one species of flower to represent insect species contributed to the lack of correlation between prior research and our results. The same types of species are likely to be found on Heliconia plants. Thus, this does not provide a representative sample of insects present in both areas.

Another factor that may impact our findings exists in our data collection methods. After analyzing the design of the project, we can recommend refinements to the project design. Background research and clear definition of terms prior to fieldwork is essential. We need to identify and control as many variables as possible. This needs to be strongly controlled. Our field data sheets should include measurement of temperature, humidity, light, height of plant specimen, description of surrounding vegetation, number of bracts, soil type and exact location of specimen. We should use a field guide to identify the species we are collecting. Our lab dissection, collection and identification procedures should be clearly defined.
 
 

Acknowledgments

We would like to thank the WWNFF and OTS for the field-oriented learning opportunities and instructional research experiences that help make this study possible.
 

Literature Cited

Berry, Fred, and W. John Kress. 1991. Heliconia: An Identification Guide, pp. 188. Smithsonian Institution Press, Washington.

Kricker, John. 1997. A Neotropical Companion, pp. 339-350. Princeton University Press, Princeton, N.J.

Janzen, Daniel H. 1983. Costa Rican Natural History, pp. 710-711. University of Chicago Press, London.

McDade, Lucinda A., Kamaljit S. Bawa, Henry A. Hespendeide, and Gary S. Hartshorn. 1994. La Selva Ecology and Natural History of a Neotropical Rain Forest., pp 77-78. University of Chicago Press, Chicago.

Terborgh, John. 1992. Diversity and the Tropical Rain Forest, pp. 215. Scientific American, N.Y.

Vitousek, Peter M. 1993. Beyond Global Warming: Ecology and Global Change. Ecology 75:1861-1876.

Woelflein, Luise (ed.). 1997. The Biodiversity Debate: Exploring the Issue, pp. 1-7. NAAEE’s Publication, Troy, OH.