Stream Diversity 1
Stream Diversity
Stream Diversity
Taylor Brown
Department of Biological Sciences, Illinois State University, Normal Il 61761-4160
Stream Diversity 2
Abstract
The richness of various streams was compared against each other across two portions of each
stream. The slow, deeper section of the stream known as the pool and the fast, shallow part called the
riffle were the two portions of streams. Data was collected by using nets to gather samples and a flow
reader to measure the current speed. The comparison led to results which proved that each pool and
riffle from each stream was significantly different than any other tested in this experiment. Many
factors influence a stream’s species richness, however not all will affect it with enough change to alter
the overall relative species richness. Species richness was found to be higher in stream pools than in
stream riffles.
Keywords include: pool, riffle, species diversity, biological diversity, species richness, and Shannon Index.
Introduction
Species diversity, or biological diversity, is defined as how rich an environment is with different
species. The more species that are present in an environment, the more diverse it is. Species Richness
can be described as the total number of unique species in a sample (Anderson et al. 2011). Stream
sampling is important in understanding the quality and survivorship of the stream. By sampling what
species live in the stream, you can tell the pH of the stream along with the richness of life that can be
supported. A more acidic, lower pH, stream will most likely have less richness than a stream with a
more neutral pH level.
In the past, countless experiments have been done on analyzing stream diversity. Many of
these experiments have focused on invertebrates as a source of information considering that
invertebrates make up most of the macrofaunal diversity in streams (Finn et al. 2011). Not all sampling
Stream Diversity 3
is as easy as collecting invertebrates for sampling. Many experiments suffer the tradeoff of sampling
intensity per site and total number of sites due to limited resources (Huang et al. 2011).
Comparing stream diversities can be very important. By following a stretch of water from one
stream to the next, you can observe samples from each part and see how the local environment at each
point influences the stream. A harsher environment
In this experiment, the purpose was to compare the species richness of three different streams
by sampling pools and riffles within each stream. Our hypothesis was that there would be a greater
amount of species richness in the pools than in the riffles.
Methods
The experiment took place on March 19, 2012 at various streams in central Illinois. Little
Kickapoo Creek, Turkey Creek, Bray Creek, and Frog Creek were the locations for stream sampling.
Samples were collected by wearing waders and walking in the stream. D-nets were used to stir up the
ground and catch invertebrates flowing downstream. Once collected, the invertebrates were held in
containers and brought back to lab. The stream velocity was recorded by a Flo-Mate Model 2000
Portable Flowmeter. Microsoft Excel 2010 was used to perform calculations. The calculations
performed were as follows: how diverse the area was with species (species richness, S), average species
richness, species richness standard error, and the Shannon Index (H’).
Results
The Shannon Index is a diversity tool that favors communities in which highly distinct species are
more abundant (Allen et al. 2009). The higher the Shannon Index value is, the higher the species
richness is. For the three pool samples, Frog had a Shannon Index value of 1.348111, Little Kickapoo 1
Stream Diversity 4
had 1.946331, and Turkey Creek 1 had 1.200115. For the riffles, the Shannon Index for Bray was 1.5483,
1.6941 for Little Kickapoo 2, and 1.3191 for Turkey Creek 2.
Species richness for both pool and riffle were averaged. Pool samples resulted in a mean of
14.33 for species richness with a standard error of 0.666667. Riffle samples had an average of 11.33 for
species richness and a standard of 1.20185 In comparing the species richness values, a t-test was able to
be performed which generated a p-value. Any p-value less than 0.05 is considered significant. The pvalue for this experiment was 0.0472. Since it is less than 0.05, this means that there was a significant
difference in species richness between the six sampling sites.
Figure 1 shows the difference in species richness between the average species richness in pools
and the average species richness in riffles. The pool samples yielded higher species richness than did the
riffle samples. Figure 2 shows the relationship between species richness and stream velocity. As
velocity increases, species richness, in both pools and riffles, decreases. Figure 3 shows how species
richness compares to the number of species present. The further right a line goes, the more species
there are. The more flat a line is the more even the number of individuals for all specie are. The area
with the greatest diversity will have the flattest line that goes the furthest right on the graph.
Discussion
The hypothesis for this experiment was that there would be a greater amount of species
richness in the pools than in the riffles. Once the experiment concluded, the hypothesis was proven
true. Species diversity was higher in the pools than in the riffles. I believe that species diversity is higher
in pools due to the species being able to withstand the slow moving currents better. In a riffle, the
water level is much lower and moves over a rocky bottom. Keeping in mind what a riffle is, it seems
Stream Diversity 5
likely that fewer species can survive in the considerably harsher conditions of a riffle compared to a
pool.
Lucky for us, this experiment was conducted at a time when nature was fairly stable. Changes in
weather can have a rather large impact on the survivorship of the invertebrates in streams. A drought
can also have negative effects on the stream. With a drought, the water level will fall and killing many
invertebrates which happen to make their home closer to the surface of the water when water levels
are high. Riffles tend to not be affected so badly with droughts since their water level is as low as it is.
Had a drought occurred recently, our results would have been very different. Since pool life would have
suffered, species richness would most likely be higher in the riffles. Other than a serious drought, there
are not many factors that would alter the species richness values of invertebrates in pools and riffles.
Invertebrates are very good at adapting to whatever nature throws their way. There are relatively few
environmental variables that change the variance in species richness (Hassall et al. 2011).
Another factor which may affect how pools and riffles differ is the availability of food.
Depending on how the landscape is along the stream, either the pool or riffle may be supplied with
more food. Provided all the factors are the same except the availability of food, a pool in one stream
may have more species richness than the next riffle downstream than and a riffle in another stream may
have more species richness than its pool located right downstream.
Literature Cited
Allen, B., Kon, M., & Bar-Yam, Y. (2009). A new phylogenetic diversity measure generalizing the shannon
index and its application to phyllostomid bats. The American Naturalist, 174(2), 236-243.
Anderson, R.C., V.A. Borowicz, S.A. Juliano, S.S. Loew, and C.F. Thompson. (2011). Ecology laboratory
manual BSC 201 fall 2011. Beta Lambda Chapter of the Phi Sigma Society, Normal
Stream Diversity 6
Finn, D. S., Bonada, N., Múrria, C., & Hughes, J. M. (2011). Small but mighty: headwaters are vital to
stream network biodiversity at two levels of organization. Journal of the North American
Benthological Society, 30(4), 963-980.
Hassall, C., Hollinshead, J., & Hull, A. Her Majesty the Queen in Right of Canada, Biodivers Conserv.
(2011). Environmental correlates of plant and invertebrate species richness in ponds. Canada:
Her Majesty the Queen in Right of Canada.
Huang, J., Cao, Y., & Cummings, K. S. (2011). Assessing sampling adequacy of mussel diversity surveys in
wadeable illinois streams. . Journal of the North American Benthological Society, 30(4), 923-934.
Figure 1: Pool vs. Riffle Species Richness
Species Richness in Pool vs. Riffle
16
14
Species Richness
12
10
8
6
4
2
0
Pool
Riffle
Stream Diversity 7
Figure 2: Relationship Between Species Richness and Stream Velocity
Species Richness vs. Stream Velocity
16
y = -6.651x + 15.076
Species Richness
(number of species)
14
12
10
8
6
4
2
0
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
Velocity (m/s)
Figure 3: Dominance-Diversity Plot
2.5
Dominance-Diversity Plot
2
Frog Pool
Little Kickapoo Pool
Log10(abundance)
1.5
Turkey Creek Pool
Bray Riffle
1
Little Kickapoo Riffle
Turkey Creek Riffle
0.5
0
0
-0.5
1
2
3
4
5
Rank
6
7
8
9
10