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A Comparison Of Insect Species Richness On Native Guazuma Ulmifolia (Guacimo) Trees Growing In Proximity To Non-Native Mangifera Indica (Mango) Versus Guazuma Ulmifolia (Guacimo) Isolated From The Mangifera Indica (Mango) Tree

The purpose of this investigation was to determine whether the proximity of the non-native mango (Mangifera indica) to the local guacimo (Guazuma ulmifolia) affects the insect species richness of the guacimo trees. Branches of Guazuma ulmifolia within close proximity to Mangifera indica were sampled as well as Guazuma ulmifolia located in areas free of Mangifera indica. A morphospecies count was performed on samples collected from ten guacimo trees, five located in close proximity to mango and five trees isolated from mango areas. Results suggest that there may be no significant difference in the number of morpho species richness.

Human alterations of the environment influence ecosystems and the interactions among the fauna and flora within them. A common occurrence in tropical regions is the presence of introduced species. Even when these species are non-invasive there are possible affects on native species. Our project is an investigation into the possible effects of an introduced species on a native species. At Parque Nacional Palo Verde, there exist remnant Mango (Mangifera indica) groves planted by local settlers before the park was established. We are interested in assessing the impact these Mango (Mangifera indica) trees have had on the species diversity on adjacent native trees. We chose to measure the impact on the Guazuma ulmifolia tree – a species occurring adjacent to Mangifera and common to the area. By comparing the relative species richness of insects on Guazuma ulmifolia trees that are adjacent to Mangifera indica trees to Guacimo trees further away from the Mangifera indica trees, we hoped to assess the impact the Mango trees have on species richness.

Two mango groves were scouted to determine a species of tree occurring adjacent to Mango trees. Two initial candidates were identified – the Stemmademia obovata tree and the Guazuma ulmifolia tree. The Guazuma ulmifolia tree was chosen because of relative abundance and availability adjacent to Mango trees. The Guazuma ulmifolia is also widely distributed throughout Palo Verde National Park.

Five trees of Guazuma ulmifolia that were adjacent (within 25 meters) to the Mangnifera indica were chosen for sampling. As a control, five Guazuma ulmifolia trees in the area but not closer than 25 meters to the Mangifera indica trees were chosen to sample as comparison trees. Six branches approximately 30 centimeters long were selected from each tree. Three samples from each tree were taken on consecutive days with the exception of trees 9 and 10 (see note). On day one, the samples were taken during a slight drizzle between 1:00 and 3:00PM. On day two, samples were taken between 8:00 and 9:30AM under cloudy skies. A gallon zip-lock bag was used to quickly bag the branches. After bagging, the branches were quickly pruned from the tree and the bag was sealed. Care was taken to minimize disturbance of the branches prior to bagging. The branches chosen were between 120cm and 360cm above the ground. The non-adjacent trees were an average distance of 8.4m from the road with the furthest tree being 16.6m from the road. The adjacent trees were an average distance of 11.7m from the road with the furthest tree being 14.0m from the road. The branches were then shaken and examined over a white sheet and insects were collected with an aspirator, vial or plastic bag. Insects were classified by order through visual inspections and tallied for each tree sampled. Spiders collected could not be identified to order by visual inspections and were therefore eliminated as part of the species tally. Species richness was then tallied for each tree category..

Note: All six samples for trees 9 and 10 (Non-Adjacent Trees) were taken on day 2 because tree sample 8 initially was treated as a non-adjacent tree but turned out to be adjacent after all. The adjacent mango was non-representative of mango but still changed the station of sample number eight from non-mango to mango. Since tree 8 was then treated as an adjacent tree, the need for more non-adjacent trees became apparent. On day two, two additional non-adjacent trees were tagged and sampled and added to the non-adjacent pool of data.

The results suggest that there may be no significant impact of mango on insect diversity on guacimo trees. The sample sizes proved too small to reach an asymptote for an accurate estimate of total species richness, and therefore, there was no way to distinguish differences between the two groups. However there may be some relative differences in that the adjacent guacimo trees do seem to show a trend towards greater species richness. Further investigations could improve sampling methods and increase the number of samples. Additional sampling through beating samples would complement the data collected through bagging. Interspersion of samples may also eliminate any collection bias that may occur during the collections. Lastly, additional numbers of trees would enlarge the total samples collected allowing for a more complete evaluation. In addition, although non-insect arthropods were included in our sampling their identification proved problematic. There were many different spiders, millipedes and pseudoscorpions but it was difficult to identify them as morphospecies because of their small size and the lack of dissecting microscopes

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Chart 1:Comparison of Species Richness	Table 1: Species data and t-test




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