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Many factors contribute to the diversity of life in an environment. The

availability of nutrients and sunlight, along with other factors that play a

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pivotal role in determining what and how much life an area can sustain.

While studying the Second Law of Thermodynamics, it came to my attention

that the classical pyramid shape of the producer, C1, C2, C3, biomass pyramid

did little to take into account the amount of detrital input. I hypothesized

that the amount detrital input greatly effected the number of C1, C2, and C3

consumers and thus the overall biodiversity of an ecosystem.

Further, if you

could find a test-bed where detrital input was the only real difference between

two similar ecosystems you would find that organisms of each ecosystem

would be adapted to the peculiar conditions. This adaptation would lead you

to find vast differences in the taxonomic groups associated with each

With this in mind, I first set out to find two similar ecosystems were I

could test this hypothesis.

Second, to sample, categorize and compare the

diversity of these ecosystems along taxonomic lines. Next, I planned to use

several of the widely accepted diversity indexes (Simpson’s Index, Shannon’s

Index the Chi-Square Test) to compare statistically, the diversity of my

Scientific Law states that in order to test the effects of one factor in an

equation you must eliminate all other factors . In order to test the detrital base

as the limiting factor, all other limiting agents must be eliminated. In a field

experiment this is technically impossible; though it is possible to come close by

choosing two ecosystems that are very similar.

In order to keep this experiment as simple as possible the ecosystem

chosen had to be nearly self contained and small. The smaller and more

contained the ecosystem the less chance for outside input that could destroy

our results. Alazan and Bernaldo creek provided just the type of test-bed

needed for this experiment. Both are third order creeks in the same

geographic area that are subject to same weather and climate conditions, but

differ considerably in the amount of detritus available. (Fleet)

Alazan creek is a third order stream that feeds into the Angelina River.

It is bordered by several species of indigenous trees that form a small gallery

of overhanging branches. This gallery consisted of (pine, oak, sweetgum trees)

and was limited to a range of about twenty five feet from the edge of the

stream. These gallery trees are surrounded by open cattle grazing fields

covered by short grasses and an occasional scrub brush. Alazan creek ranged

from ten to fifteen feet wide with a water depth of six inches to two feet. The

water was generally clear, and flowed at a brisk ten to twelve mile per hour

pace. The creek bottom was primarily sand with little or no mud. Turbitity was

low to moderately low and the creek had a high oxygen content. Detrital input

was low and limited to leaves from the gallery trees.

Bernaldo creek is a third order creek that similarly empties into the

Angelina River. Bernaldo creek differs substantially in that it is entirely

surrounded by typical east Texas piney woods. (The particular area that

samples were taken from appeared to be relatively low lying in comparison to

the surrounding woods.) It is likewise ten to fifteen feet wide but, is

considerably deeper at four to eight feet than Alazan creek. Bernaldo creek

flows at a much slower pace, approximately six to eight miles per hour. The

bottom of Bernaldo creek consists largely of mud, which gives the water a

darker color. Overall turbitity is high and overall oxygen content is low.

Human disturbance at both creeks was minimal. Although at Alazan

creek the surrounding area was used for grazing animals and at Bernaldo

creek the sight that specimen were actually taken from was a concrete

washout bridge. Both sights appeared to be in a flood plain, one that probably

becomes inundated on a monthly basis during the rainy season.

Weather conditions at the time of the sampling were typical of east

Texas in spring, therefore unusual conditions caused by atypical weather can

be eliminated. What it boils down to is, the only difference between the two

creeks was the amount of detrital material available and the conditions

Starting the week of February 8, 1999 daily 1p.m. trips were made by

four lab groups to both Alazan and Bernaldo creeks. During these trips

observations were made on terrain, topography, climate, vegetation and

specimens were taken from several spots along each creek. The specimen

were taken by netting at various depths and locations. The nets used had a

pore size of approximately 2 millimeters on four sides and a canvas bottom

(see diagram 1) and were attached to poles 8 feet long. In order to take a

sample, a student placed the scoop nets open end up stream and allowed the

water and it’s contents to be strained. The nets were then quickly pulled from

the water and the samples collected were immediately taken to opened

garbage bags and sorted through. (see diagram 2) When any living creature

was found, it was placed in a collection jar (labeled for the particular creek it

was taken from) to be examined later. The collection jars contained an

organic die known as FAA. FAA is a combination of formalin, ethyl alcohol,

and Rose Bengal and tints most of the small “bugs” a red/pink color.

The following week each lab examined the specimen jars one by one

and separated the contents by taxonomic groups. Once each creek’s

specimens had been counted and categorized by class period, a list was

compiled for the weeks totals. This list was then used to test by comparison

the validity of our hypothesis. (for the complete list and breakdown see chart 1)

The hypothesis I was attempting to prove had three parts. The first and

most general was the creek with the greater detrital base would have greater

biodiversity. This can be proven in several ways. The first is to simply count

the number of species present in each of the two creeks and compare the

results. This is called richness, which is the number of species/taxonomic

groups. In that case Alazan creek contained 13 species/ taxomic groups and

Bernaldo creek had 17. Therefore, Bernaldo creek which had the greater

detrital base had 4 more species than Alazan creek. A second part of counting

species is to determine the evenness of the the creeks. Evenness is the

measure of how evenly divided the individuals are among the taxonomic

Next I used several of the accepted diversity indexes to statically prove

which creek had the greater diversity. Simpson’s Index is the number of times

it would take to pick two individuals of the same species/taxonomic group.

Simpson’s index is calculated by the equation:

Where: N=Total number of species/taxonomic

n=Number of individuals of a species. (Cox)

In this case Bernaldo creek had a Simpson’s Index of .017712946 and

Alazan creek had a Simpson’s Index of .0092367032. That’s a difference of

.0084762429, or a 91 % greater chance of getting two of the same organisms.

This shows a significantly greater level of diversity for Bernaldo creek than for

Shannon’s Index in determined by the equation:

H’=3.3219[log N – 1/N E(Ni log Ni)]

With “N” being the total number of individuals in

the sample, “Ni” being the number of individuals in

each species/taxonomic group, and “E” being the

Bernaldo creek had a Shannons Index of 2349.0908. Alazan creek had

a Shannon’s Index of 1876.1630. That’s a difference of 473.9278, or

approximately 40%. The proves that the diversity in Bernaldo creek is higher

than the diversity of Alazan creek.

“The null hypothesis that the two Shannon diversity indices come from

communities equal in diversity can be tested by a test a “t” test.” This test is

used to calculate chance of a type one error. The equation for this is:

The “t” value for the above was 3.290 significantly within our accepted margin

Next, the Chi-Square test was performed, it’s information is given by the

X^2=E{(observed-expected)} / expected

Where: expected value is given by {(row total x

column total) / grand total} and “E” is the

The evidence collected in our study significantly proves the hypothesis.

All of the confidence intervals were met and exceeded in each test with out

exception. This was also the case with each of my peers that performed this

experiment. Although this increases the general knowledge on the impact of

detrital input into a system there is more to be learned.

There were three main sources of potential errors in this experiment.

First, there needed to be more samples taken from more places and at

different times of the year. Four samplings from one spot on the creek are not

enough to draw conclusions about the entire system. What if the area tested

was near some source of point pollution? This could have an effect on the

immediate area but cause no down stream effects due to rapid break down, or

simple dilution. What if the area picked was more diverse during summer?

Next, an unforeseen problem occurred when the crayfish began eating many

of the “bugs” in the collection jars. This caused many of our

species/taxonomic groups to be under represented because they got eaten

before they could be counted! What about animals that were so small they

slipped through the holes in the nets? What about burrowing worms? None

of these animals are represented in the sampling. Had these species/groups

been represented some of the statistics might have been a little different.

In the future this test should be modified in a manner to correct some of

the afore-mentioned problems. With those modifications a person could build

an even stronger case to support the hypothesis.

Cite this Biomass

Biomass. (2018, Jun 09). Retrieved from https://graduateway.com/biomass-essay/

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