This lab was performed to take a community analysis. This lab was to cover plant communities. The purpose of this lab is to show that habitats are not made up of randomly placed plants or animals. Instead, each factor of a habitat affects the other factors. Abiotic factors affect which types of plants and animals can survive in that habitat, but the actual organisms in that environment affect each other as well. We have covered abiotic factors in other labs and seen how they can change from one area to another. This lab was made to focus on just the biotic factors and how they relate to one another.
The first part of the lab was to identify plant communities. For this two sections of forest were sampled and a count of the different species of trees and their numbers was collected. The first site was at the Volga River Recreation Area. As a group we lined up single-file and walked straight through a section of trees. We kept the distance between each person at no more than a few feet and every tree that was in the path of our line was counted and identified. We only counted trees more than an inch in diameter. Saplings were not counted. Once we had covered enough ground we turned our line 90 degrees and walked for another set distance and once again counted and identified every tree. Once these counts were done we all reported our numbers to the instructor who totaled them and produced a final count of each species and the total number of each. The second plant community sample came from the Arkansas Ozarks upland forest. The data on plant species and numbers was provided to up by the instructor. Using the data we collected we had to determine the species, their numbers, relative abundance and species dominance for the communities at the Volga River Recreation area and the Arkansas Ozarks forest. Then we had to compare the two sites and determine the total number of plants, the species richness, diversity and dominance.
These calculations were fairly easy and required only some basic math. The total numbers and species types were obtained from our counts in the field and the numbers provided by the instructor. Relative abundance was figured by pi = ni / N where pi is the relative abundance and ni is the number if individuals of species i collected. N refers to the total number of organisms collected.
Species dominance was determined by C = pi2. C is the species dominance and pi2 is the sum of the relative abundance squared.
When we compared the two communities we had to know the total number of organisms (N) and the species richness (R). Species richness refers to the number of different species present. Diversity was calculated as D=1/(Nmax/N). D is the diversity and Nmax is the number of individuals in the most abundant species. The overall species dominance was figured by taking the species richness divided by the total number of trees counted and then squaring that number. The results of these calculations are shown in the following tables.
|Volga River Recreation Area|
|Arkansas Ozarks Upland Forest|
|Southern Red Oak||1||.000501||.00000026|
|Parameter||Volga River Rec. Area||Arkansas Ozarks Forest|
|Total Number (N)||366||1996|
When we look at the charts and compare them we can see some very obvious differences immediately. The most obvious difference is that the Ozark Forest had a lot more total trees. The Ozark site had 1,996 trees while the Volga site only had 366. The Arkansas Ozarks also had a much greater diversity than the Volga Recreation Area site. In fact when we look at the comparison chart we see that the species richness of the Volga site was only 4 while the richness of the Ozarks site was at 25. That means there was just over six times the number of species in the Ozarks site than there was at the Volga site. The species diversity also proved to be greater because of this. The Volga site had a species diversity of 1.656 while the Ozarks site was at 2.654. So what does this information mean? The species richness simply shows that there were more separate species of trees found in the Ozarks. The species diversity is a much more interesting number. If twenty-four of the twenty-five species of trees found in the Ozarks site only had one of itís kind and the one species was accountable for the other 1,972 trees, then the Ozarks Forest site would prove to be a very non-diverse place, dominated by one single species. However, this is not what we find. The most dominant tree (the Winged Elm) only had 752 out of the nearly 2,000 trees counted. This number is over double the 366 trees we find in the Volga Recreation areaís most abundant tree, the White Pine. What we see, despite this difference in numbers is that the Ozarks Forest has a diversity of 2.654 and the Volga only has a diversity of 1.656. What this means is that even though the Arkansas site had more trees and a higher number in itís most populous species, the diversity of the other trees is more evenly spread in the Ozarks. Taking a closer look at this aspect we can look at the charts and see that in the Volga Recreation area the forest was dominated by two trees, the White Pine and the Shagbark Hickory. In contrast the Arkansas Ozarks Forest had ten different species numbering over forty individuals and five of those were over a hundred. This means that the diversity in plant species was much more distributed in the Ozarks.
Despite the differences between the two there were a few similarities. The two sites did share one species of tree, the Red Cedar. Because the total number of trees counted at the two sites differs greatly a comparison of the actual trees counted wouldnít accurately portray the differences in these numbers. Instead we use relative abundance and species dominance to highlight the differences and similarities.
When we look at the Red Cedar numbers from each site we see some interesting numbers. The actual number of trees varies greatly between the two sites (four at the Volga site and thirty-nine at the Ozarks site). However, as mentioned before these numbers are useful. Instead when we look at the relative abundance we see that the Ozarks site was at .019 while the Volga site was at .0109. That is a difference of only a few thousandths. We also see that the species dominance for the Ozarks site was at .00038 and the Volga site was at .0001. That is a difference of not even four millionths. What these numbers show us is that even though the actual numbers of individuals may vary the relative abundance and dominance can show us the differences more accurately.
The final chart shows how the two sites compared against each other. The species richness and the diversity of the Arkansas Ozarks was much higher then that of the Volga River Recreation Area. This shows how much more diverse the Ozark site was from the Volga site. The final number in the cart is the species dominance number. These two numbers were actually fairly close together. The Volga Rec. site had a species dominance of .000119. The Arkansas site had a species dominance of .000156. What this number tells us is that even though the Arkansas site had a greater number of total trees, a higher number of diversity, and greater species richness than the Volga Rec. site, the two sites were still dominated by only a few species.
Now that all the data has been collected itís time to understand what it all means. Without ever going to the Arkansas Ozarks we can get the feeling of the diversity just by looking at the charts. We can see that only a few species dominate the Volga Recreation Area site while many species share the Arkansas Ozarks site. While we didnít measure the abiotic factors of either location it stands to reason that the difference lies in those factors. Arkansas is much further south and therefore has a warmer climate. The soil types between the two are also different. These different abiotic factors, and the resulting differences in tree species, show the way in which the organisms within an ecosystem can be affected by different conditions.