Download Species Diversity of Aquatic Invertebrates in St. Olaf

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Species Diversity of Aquatic Invertebrates in St. Olaf Ponds
Heather Bouma-Johnston, Cassie Davis, Ambele Mwamelo
Abstract
We conducted this experiment to study the aquatic invertebrate diversity in three St. Olaf
College ponds: Regents Pond, Big Pond, and Baseball Pond. Aquatic biodiversity is important to
ecology because it is essential to both the health of our environment and to human life. We
collected invertebrate samples at each of the ponds, documented the the number and abundance
of the species found, and used this data to calculate the species diversity of the ponds with
Shannon’s and Simpson’s Diversity Indices. Our results indicated that larger ponds (Baseball
and Big Ponds) had more diversity than smaller ponds (Regents Pond) and that ponds with more
shoreline development (Regents Pond) had less biodiversity than ponds with more natural
surroundings (Baseball and Big Pond). We also found a negative correlation between
temperature and species diversity, with Regents Pond (the warmest pond) having the least
species diversity. Overall, we found that there are three main factors that influence diversity in
St. Olaf ponds-- temperature, pond size, and development around the pond.
Introduction
Aquatic biodiversity affects both human life and the health of the environment, making it
a valuable area of study. We depend on many aquatic plants and animals, and their ecological
functions, for our survival. For example, plants such as wild rice, wasabi, watercress, taro, and
lotus, all only grow in freshwater lakes and streams and are important for some human diets
(Edible Water Plants: Aquatic Vegetables, 2008). Furthermore, many organisms (such as wood
frogs and salamanders) have important life stages in ponds, but also interact with other
ecosystems; thus, the loss of pond species diversity could have negative impacts on many other
habitats, as well (Yeager and Brittingham 2014). Understanding what factors influence pond
biodiversity can help with conservation measures and protecting aquatic ecosystems for the
future.
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Warmer aquatic temperatures are often associated with a decrease in species diversity.
In streams in Malaysia, studies show that water temperature is negatively correlated with two
species of shredders (Salmah et al. 2014). Similarly, studies in Oman attributed low faunal
diversity in streams to high water temperature (Boulaaba et al. 2014). Possible explanations for a
decrease in diversity with higher water temperatures include a corresponding decrease of oxygen
in the water (Suski et al. 2006, Horne 1971), a decrease in egg hatching and breeding activity due
to lost temperature cues (Boulaaba et al. 2014, Horne 1971), and inhibition of some organisms’
metabolic functions (Suski et al. 2006). Thus, we predicted that the St. Olaf pond with warmest
water temperature will have lowest species diversity.
Larger areas provide a more extensive habitat, with more resources, and thus are often
associated with increased species diversity. While there is not complete consensus that this is
true for all aquatic ecosystems (Oertli et al. 2002), there are studies showing a positive
correlation between pond size and species diversity for many populations in ponds, including
dragonflies (Kadoya et al. 2004), snails (Brönmark 1985), and diving beetles (Lundkvist et al.
2001). Thus we predicted that the larger St. Olaf ponds (Baseball Pond and Big Pond) would
have higher species diversity than Regents pond, which is very small.
Shoreline development has been shown to have a negative impact on many aquatic
communities. In comparisons between forested and agricultural ponds (surrounded by natural
vegetation) and urban ponds, studies show that urban ponds have significantly lower
biodiversity. In this study, the most ideal landscape, with the highest biodiversity, was a mosaic
of forest and open habitats surrounding wetlands (Gagne and Fahrig 2007). Vegetation
surrounding ponds actually plays an important buffering role, impeding direct runoff of nutrients
into the water. This is increasingly important in areas where nutrient flow includes toxic
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substances, such as pollutants dioxin, polychlorinated biphenyls, and road de-icing salts
(Trombulak and Frissell 2000). Influx of these nutrients and toxins can suppress growth and
cause mortality. In one study, tadpoles exposed to road de-icing salts experienced significantly
lower survivorship, decreased time to metamorphosis, reduced weight and activity, and increased
physical abnormalities with increasing salt concentration (Sanzo and Hecnar 2006). Since
Regents Pond is urbanized, with shoreline development of roads and parking lots, we predicted
that it would have the lowest species diversity. Baseball Pond and Big Pond, however, are
located in a more natural setting. Big Pond in particular was in the ‘ideal’ setting of forest
surrounded by wetlands (described above), and should have a correspondingly higher species
diversity.
In our experiment, we determined which St. Olaf ponds had the highest aquatic
invertebrate species diversity: Regents Pond, Big Pond, or Baseball Pond. We hypothesized that
temperature, pond area, and shoreline development would have the largest effects on pond
biodiversity, and that ponds with a colder temperature, a bigger area, and less shoreline
development would contain the highest species diversity.
Methods
In order to determine the environmental characteristics of Regents Pond, Baseball Pond,
and Big Pond, we measured the turbidity of the water (with a Secchi Tube), the water
temperature, and the depth of the shore. Furthermore, we observed the surroundings of the ponds
and the vegetation that grew in and around them. Using a Dnet, we collected 18 samples from
each pond, with the goal of studying different types of invertebrates and their populations in
varied habitats. We placed the collected samples into buckets that were 1/5 filled with the
respective ponds’ water and brought them to the lab for analysis. In order to view the samples
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more clearly, it was important to separate the water samples into smaller containers. Then we
collected organisms of interest and identified them under a microscope. Once identified, we
estimated the population of each invertebrate by counting different invertebrates in small
containers and extrapolating the total population in the whole sample from that small sample.
We used Anova One-way statistical tests to analyze the difference in the species richness
between the three ponds. We then used a pairwise comparison of means to find which specific
ponds had significant differences in species richness. We also used Anova One-way statistical
tests to analyze differences in the species diversity (as determined by both Simpson’s and
Shannon’s Diversity Index) between the three ponds. We then used a pairwise comparison of
means to find which specific ponds had significant differences in species diversity. Finally, we
calculated linear regression to analyze potential correlation between depth and temperature and
species diversity (Shannon’s and Simpson’s diversity index) for the three ponds. We used R
commander to run all statistical analyses.
Results
There is a significant difference in the species richness between Regents Pond, Big Pond,
and Baseball Pond (Oneway- ANOVA, p=.0268). There is a significant difference in species
richness between Big Pond and Regents Pond (Pairwise comparison of means, p=0.0237). There
is not a significant difference in species richness between Big Pond and Baseball Pond (Pairwise
comparison of means, p=0.6726) or Regents Pond and Baseball Pond (Pairwise comparison of
means, p=0.1077). Big Pond had the highest species richness, followed by Baseball Pond and
then Regents Pond with the lowest species diversity (Fig. 1).
There is a significant difference in species diversity between the three ponds, measured
by both Shannon’s diversity index (Oneway­ANOVA, p= 0.00252; fig. 2) and Simpson’s
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diversity index (Oneway­ANOVA, p=0.00192; fig. 3). With indexes, Baseball pond and Big
pond had high species diversity, while Regents pond had much lower species diversity.
In both Shannon’s and Simpson’s species diversity index, there was a significant
difference between Big Pond and Regents Pond (Pairwise comparison of means, Shannon
p=.00539, Simpson p=0.00254) and Regents Pond and Baseball Pond (Pairwise comparison of
means, Shannon p=0.00442, Simpson p=0.00654). There was not a significant difference in
species richness between Big Pond and Baseball Pond for either index (Pairwise comparison of
means, Shannon p=0.99345, Simpson p=0.86554).
There is no correlation between the depths of all the ponds and species diversity
according to their Shannon diversity index values (Linear Regression, p=0.22473). There is also
no correlation between the depths of all the ponds and species diversity according to the Simpson
diversity index values, either (Linear Regression, p=0.2763).
There is a correlation between the temperature of all the ponds and species diversity
according to both the Shannon diversity index (Linear Regression, p=0.0312; Fig. 4) and the
Simpson diversity index (Linear regression, p=0.0312; Fig. 5). In both cases, an increase in
temperature is correlated with a decrease in species diversity. This is illustrated by a negative
correlation between temperature and diversity index in Shannon’s index (Fig. 4) and a positive
correlation between temperature and diversity index in Simpson’s index (Fig. 5)
Figures
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Fig. 1: Plot of Average
Species Richness vs. Pond
Site. There is a significant
difference in species richness
between the three ponds
(Oneway-ANOVA, p=.0268).
Big Pond had the highest
species richness, followed by
Baseball Pond and then
Regents Pond with the lowest
species diversity. Error bars
represent standard error of the
means.
Fig. 2: Plot of Species
Diversity (Shannon’s Index)
vs. Pond Site. There is a
significant difference in species
diversity between the three
ponds in relation to the
Shannon’s diversity index
(Oneway-ANOVA, p=0.00252).
The Baseball Pond had the most
species diversity very closely
followed by the Big Pond and
then Regents Pond which dips
down to have the least amount
of species diversity. Error bars
represent standard error of the
means.
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Fig. 3: Plot of Species Diversity (Simpson’s Index) vs. Pond Site. There is a significant
difference in species diversity between the three ponds according to the Simpson’s diversity
index (Oneway-ANOVA, p=0.00192). According to this index, Regent’s Pond has the least
amount of diversity, while Baseball Pond and Big Pond have the most species diversity. Error
bars represent standard error of the means.
Fig. 4. Linear Regression of
Shannon Diversity Index vs.
Temperature. There is a
significant relationship
between the ponds’
temperatures and their
Shannon diversity indexes
(Linear Regression,
p=0.0312). The green line
indicates the line of best fit for
the correlation. There is a
negative correlation, showing
that with an increase of
temperature, there is a
decrease in diversity in all
three ponds.
Fig. 5 Linear Regression of
Simpson’s Diversity Index vs.
Temperature. There is a
significant relationship between
the species diversity (as measured
by the Simpson diversity index)
and temperature (Linear
Regression, p=0.0312). The green
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line indicates the line of best fit for the correlation. There is a negative correlation, indicating that
with an increase in temperature, there is less diversity.
Fig. 6. St. Olaf College Natural Lands Map. The three ponds used in our study include
Regents Pond, Baseball Pond, and Big Pond. This map indicates their location, surrounding
environment, and size.
Discussion
We found that three main factors affect the aquatic invertebrate diversity in St. Olaf College
ponds: temperature, size of the pond, and the amount of development around the pond. Our
results supported our hypothesis on all accounts: increased pond area, decreased development,
and colder temperatures lead to an increase in aquatic invertebrate diversity.
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In terms of shoreline development, we expected the diversity to be the highest in Baseball Pond
and Big Pond because of their locations in the Natural Lands surrounded by plant life. Regents
Pond, because of its location in a parking lot and its composition of mainly runoff, we expected
to have the lowest species diversity. This hypothesis was supported, because our results indicate
significantly higher species diversity in Baseball Pond and Big Pond than Regents Pond. These
results are consistent with prior research indicating that urbanized ponds with shoreline
development have significantly lower species diversity (Gagne and Fahrig 2007). It is possible
that Regents Pond’s loss of an essential ‘vegetation buffer,’ which controls the amount of
nutrient influx in runoff, contributes to an increase in nutrients, including harmful chemical
pollutants such as dioxin, polychlorinated biphenyls, and road de-icing salts (Trombulak and
Frissell 2000). Studies show that an increase in such pollutants can lead to a decreased
survivorship of some species (Sanzo and Hecnar 2006), and thus a decrease in species diversity.
We expected to find a greater species diversity in Baseball Pond and Big Pond, the larger ponds,
than Regents Pond, the smaller pond. A larger pond is a bigger habitat for plant and animal life,
and has a greater availability of resources, which increases habitat diversity. This is consistent
with our results and with most of the previous research on this topic. Some of the pond
populations which show similar results to our own –more species diversity in a larger pond
area—are dragonflies (Kadoya et al. 2004), diving beetles (Lundkvist et al. 2001), and snails
(Brönmark 1985).
As for temperature, we expected the pond with the highest temperature to have the lowest
species diversity. Our results confirm that there is indeed a negative correlation between higher
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water temperature and species diversity, with Regents Pond having the highest temperature and
lowest species diversity. This is consistent with other studies, as well, where higher stream
temperatures in Malaysia (Salmah et al. 2014) and Oman (Boulaaba et al. 2014) resulted in lower
aquatic species diversity. There are a range of reasons for why higher aquatic temperature
results in lower species diversity. Warm water holds less oxygen and can lead to hypoxic
conditions that make it difficult for species to survive. In a study completed on fairy shrimp and
phyllopods, Horne (1971) attributed seasonal variation in shrimp diversity to changes in
temperature and corresponding hypoxic conditions which limit survival. Another explanation is
a decrease in breeding activity of adults (Boulaaba et al. 2014) as well as a decrease in egg
hatching (Horne 1971) due to changes in temperature cues, both of which contribute to decreased
population growth rates. Finally, higher temperatures can inhibit metabolic functions such as the
replenishment of white muscle energy stores in largemouth bass as well as impede physiological
functions by elevating plasma cortisol concentrations (Suski et al. 2006), all of which decrease
survival.
Aquatic biodiversity is essential not only to our environment but also to humans’ everyday lives.
Pond organisms can influence species in other ecosystems, and many humans depend on aquatic
plants and animal for food. Understanding the key factors behind aquatic invertebrate diversity
is important to the conservation and protection of these important aquatic environments.
According to our research the best way to conserve the species biodiversity in aquatic
environments is to have large ponds, rather than small ponds, in natural environments rather than
urban surroundings.
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