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SMALL GROUP FIELD PROJECT
SPECIES RICHNESS COMPARISON
BOB BURTCH, JACK GREEN, MATT HAYS, JENNIFER SNYDER
BACKGROUND AND PURPOSE:
Species diversity is a characteristic unique to the community level of biological organization. Species richness is a component measure of species diversity and a function of the number of species found in any defined geographic area. Our field project has sought to investigate the species richness in three different habitat types. These habitats are found within the area surrounding the Wilson Botanical Garden, Costa Rica.
The southern portion of Costa Rica, like all of Costa Rica, was once a continuous sea of tropical rainforest. Beginning in the1950’s, people began to migrate to this area and utilize the land. Much of the pre-existing rain forest has since been cut down to accommodate the influx of people, now numbering in the tens of thousands. Land has been cleared for agriculture, much of which is involved in the production of coffee. The commiserate loss of native habitat for indigenous wildlife species is well documented in scientific literature. Many species of mammal, bird, reptile, amphibian, and insect, has had to adapt to these rapid changes or perish. Unfortunately, it is believed that some species have indeed met with extinction and many others have suffered drastic reductions in population size. Fragmentation of continuous tracts of rainforest has resulted in island like effects, separating populations of many organisms from one another. Organisms that lack the ability to disperse or transfer themselves from one tract to another have found it difficult to maintain genetic continuity and potentially are prone to a higher incidence of catastrophic elimination.
Species utilization of these “newly” created habitats is potentially critical to the continued survival of any life form. It was the intent of our field project to investigate the number of species found in some of these disturbed habitats and compare this data to an intact primary rainforest ecosystem. Species richness, the number of different species found in each habitat type, was utilized to assess the comparative impact of deforestation in a coffee farm and a cleared meadow against that of a small (200 hectare) primary forest environment.
We believe that the primary forest will show the greatest amount of species richness for birds and the meadow will show the greatest species richness for lepidopterans and the coffee farm will show the least numbers of species.
MATERIALS AND METHODS:
To accomplish our task we chose to perform walking surveys of each habitat type. These walking surveys were not done in any form of a straight line or in any plot method. We chose not to utilize these techniques because of the difficulty of accomplishing these types of tasks in the primary forest environment. The forest environment was extremely steep and very densely vegetated making it impossible to safely run any form of a transect or plot count. As a result, we chose to simply enter each area, all four of us, and walk to a randomly chosen area at least 20 meters from the edge of the area. We then simply remained there for a total one hour and counted each species of bird that we saw. We then did the same for butterflies. A variation occurred at the primary forest site as there was very little activity at the chosen site so after an hour we walked further up the trail and added several more species to our list. We performed this task at the same time of day for each different habitat type. We did not tally the number of organisms of each species for fear of counting each organism more than once. This is why our counts represent species richness and not species diversity. Species diversity is a function of both the number of species in an area and also the number of individuals sighted within each species.
DATA :
|
Animal |
Species
richness (number of species) |
|
bird |
0 |
|
lepidopteran |
0 |
Data
table 1: Coffee plantation, Monday morning
Animal
|
Species
richness (number of species) |
|
bird |
5 |
|
lepidopteran |
17 |
Data
table 2: Pasture, Tuesday morning
|
Animal |
Species
richness (number of species) |
|
bird |
15 |
|
lepidopteran |
19 |
Data
Table 3: Primary forest, Wednesday morning
For photos, see related adobe photoshop file named
“photos for species richness at Las Cruces.”
DISCUSSION:
We have partially confirmed our hypothesis. The primary forest does have the highest species richness for birds. The coffee farm had no birds. The number of lepidopterans was surprising to us. We thought the meadow would have the highest species richness for lepidopterans, but in fact the primary forest at Las Cruces had a higher species richness for lepidopterans as compared to meadow and coffee farm. We speculate that the monoculture of a coffee farm is poor habitat for birds and lepidopterans even during pollination season. Coffee is not pollinated by birds or lepidopterans, but primarily self pollinated (94%) and the remaining by wind and hymenopterans, and coffee fruit is not a preferred food for either taxa. The meadow seems to have some good habitat for lepidopterans with grasses, forbs, sedges, and a few small scattered trees, but there is little tree habitat for birds. A few grassland birds were found. Historically, Costa Rican birds did not evolve in a grassy habitat so only some can utilize grasslands. Rainforests are good habitat for birds because of the availability of food and shelter. The microclimate in the rainforest is more humid and dark than the meadow or coffee plantation. Because of the conditions rainforests are good for moths and butterflies. Limitations to our study include variations in sight distances. In the meadow, we had long sight lines and in the primary forest we had limited vision. To compensate for this, we used bird calls in the primary forest. Whether those bird calls were effective to offset the lack of visibility is unknown.
Another limitation is the stratification in the primary forest. Many lepidopterans live in the upper canopy, undetected by us. Further research should accomodate the counting of butterflies in the upper canopy and census at various times of the day. Also, traps or butterfly nets would help in identification and counting. A high blind would be good for bird observation.
It should be noted that we spent time in the rainforest habitat, adding to our species richness. We spent over the one hour time limit observing there, possibly skewing our results. Had we limited our time to one hour our results would have been 9 bird species and 7 butterfly species.