Change in Taxonomic Composition due to Supra-seasonal Drought Conditions between 2010 and 2013
By Briana Albini
Sevilleta National Wildlife Refuge
University of Hawaii at Hilo
Abstract
Droughts are a disturbance that affects both water systems and the ecology within and surrounding
these water systems. In particular, supra-seasonal droughts can have a devastating effect on the ecology
of streams due to their random occurrences and extended disturbance time period. Aquatic
invertebrates have better adapted to seasonal droughts because they occur periodically, but have not
adapted to supra-seasonal droughts due to their random nature. At the Sevilleta National Wildlife
Refuge, in New Mexico, I performed a study to test if there was any connection between a supraseasonal drought and the diversity of invertebrates between the years 2010 and 2013. I collected
invertebrates from 11 wet sites using two techniques combined. The first technique was to insert a
sponge into the water source and leave it there for 10 days; the second technique was to take sediment
from within a 15x15cm quadrate. I also took dry sediment samples from three other dried water sources
to see if there were any dormant invertebrates in the sediment. In addition, vegetation and scat surveys
were taken from the area surrounding the drinkers. These surveys were used to see if there is any
correlation between vegetation, animal usage of water sources, and taxonomic richness. It was found
that the vegetation did have a correlation with richness (R2 = 0.3536). Animal usage had no correlation
with richness (R2 value = 0.0353). The drinker at San Lorenzo East had the greatest taxonomic richness
with 11 taxa. No taxa were found from dry sediment sources. After performing a paired t-test, there
was found to be no significant difference between the taxonomic richness between 2010 and 2013. My
findings suggest that there is no difference between 2010 and 2013 taxonomic richness in the drinkers
and springs of the Sevilleta National Wildlife Refuge, but there was a lot of turnover.
Introduction
The ecology of drought is little studied, with knowledge being fragmented and scattered over a wide
range of topics (Lake 2003). Droughts in streams can be seen as a disturbance to the ecology of the
water system (Lake 2003). Some droughts are periodic and happen seasonally, while other droughts are
supra-seasonal and last longer than normal weather and seasonal conditions would have allotted (Lake
2003). Supra-seasonal droughts are considered ramp disturbances because they increase in strength (of
disturbance) over the course of time (Lake 2003). They are also characterized as being unpredictable
and marked by declines in precipitation and water availability. This disturbance can have a central role
as to how the stream community is structured (Lake 2000). In response to supra-seasonal droughts,
biota will either be resistant (withstand the drought) or have resilience (the ability to recover from the
drought) (Lake 2003).
Due to the unpredictable nature of supra-seasonal drought conditions, invertebrates with evolved
adaptations for seasonal drought conditions may not be able to maintain the high levels of resistance
and resiliency that they maintain with seasonal droughts (Lake 2003). One strategy used by aquatic
invertebrates is to burrow into the sediment in the dried water source and remain dormant until water
returns to the system; another strategy is to move to refugia to survive (De Jong and Canton 2013).
These invertebrates create a ‘seedbank’, a form of resistance, to survive drought disturbance
(Stubbington and Datry 2013). Drought conditions reduce the number of lotic habitats and increase the
number of lentic habitats where water and stream areas remain (Lake 2003). Surface water sources such
as spring sources or standing pockets of water along a dried creek bed become refugia for invertebrate
communities. But as these pockets of water reduce in volume, conditions in these water sources can
fluctuate. Generally, nutrient concentrations can increase while dissolved oxygen can decrease. Over
extended periods of time, some invertebrates may not be able to handle these extremes and this can
lead to drastic population loss for different species which will decrease the overall diversity in an aquatic
system.
Due to New Mexico’s supra-seasonal drought over the past few years, environmental conditions in
springs and drinkers on the Sevilleta National Wildlife Refuge may have changed, leading to changes in
invertebrate community diversity. Drinkers may be considered refugia since they have water year round,
but may be difficult for aquatic invertebrates to find because of the small surface area of water in a very
dry system. The amount and size of refugia can potentially increase the strength of the resilience of
invertebrates by creating habitats for potential colonizers (Burk and Kennedy 2013). At the Sevilleta,
some springs and drinkers have dried up since 2010 and others have decreased water levels. Due to the
drought conditions, invertebrate diversity may have decreased in springs and drinkers since 2010.
Methods
This experiment was conducted on the Sevilleta National Wildlife Refuge in New Mexico. Sites consisted
of drinker wells and natural springs. Flowing drinkers and natural springs as well as dry drinkers and
springs, were used in this experiment. A total of 3 springs and 10 drinkers were used in this experiment
(See Figure 1 & 2).
Drinkers
Springs
Nunn
Cibola*
McKenzie*
Rio Salado
San Lorenzo East*
San Lorenzo West
Gibbs*
Goat Draw*
Bronco*
Esquivel
Canyon*
West Mesa S. & E.*
222 (Tule)*
Figure 1. Listing of the Sevilleta drinkers and springs sampled in 2013; those with asterisks were also
sampled in 2010. The Bronco drinker and the springs, Cibola and Rio Salado, were all dry.
Survey of Aquatic Invertebrates from wet drinkers and springs
To collect samples of invertebrate communities in both drinkers and springs I combined two sampling
methods. The first method was using a 15x15 cm quadrate on the bottom of a drinker or spring. During
this method, I used a razor blade to scrape the bottom of the drinker to loosen invertebrates attached
to the bottom. I then used a turkey baster to collect invertebrates in the uplifted sediment. This mixture
was then placed into sealable plastic bags and placed on ice until I was able to place formalin in each
sample to kill invertebrates. Samples were then placed into refrigerator until processed at a later time.
The second method used to collect invertebrate communities was to use a sponge and leave it at the
bottom of the water source for a total of 10 days. The sponge was tied to a washer that would anchor
the sponge to the bottom of the water source. The sponge was then tied to a long string that was tied to
the exterior of the water source; the string and washer would help stabilize the sponge and allow for
easier removal of the sponge when removed. When sponges were removed, they were placed into
sealable plastic bags with water from the source added to it, then placed on ice until return to a
laboratory to add formalin and kill all invertebrates within sample. Samples were then placed into
refrigerator until processed at a later time.
Separation and Identification Procedures
For each quadrate sample, I separated invertebrates from sand, silt and mud using a sieve (53
micrometers). Organisms were found using a microscope and separated from mud using a fine tipped
brush and forceps. Invertebrates were then placed into a vial with a 70% ethanol mixture to preserve for
identification. Once invertebrate samples were cleaned, they were removed from vials and placed into
Petri dishes to separate and identify orders of invertebrates and micro crustaceans found. The amount
of each order found in each sample was recorded. Identification of organisms was based upon taxa keys
with the help of Dr. Ayesha Burdett.
Sponge samples were processed differently than quadrate samples. Sponges were rinsed to remove any
invertebrates. After a layer of sponge was cleaned, it would be cut and removed to clean inner layers of
the sponge until the entire sponge was cut and removed of any invertebrates. This was done above a
sieve to catch any invertebrates from being lost. After cleaning out the sponge, all material on the sieve
transferred onto a Petri dish to remove invertebrates. Again, invertebrates would be found using a
microscope and separated from mud and plastic clippings using a fine tipped brush and forceps. Once
invertebrate samples were clean they were removed from their vial and identified in the same manner
as were the quadrate samples.
Survey of vegetation and scat samples
I performed vegetation and scat surveys to determine the state of the vegetation surrounding the water
source and give a better understanding of the differences between the water sources. This may also
show how much wildlife uses the water sources which could affect invertebrate diversity. A visual
assessment was recorded at each spring or drinker based on what the vegetation cover and structure
surrounding the water body consists of. Four 50m transects, going in the cardinal directions, beginning
at the wet edge of each water source were measured for vegetation and scat. At each 5 m interval a 1m
quadrate was surveyed to determine percent vegetation cover. There was a total of 10 survey quadrates
per transect and a total of 40 quadrate surveys per water source.
Survey of aquatic invertebrates from dry drinkers and springs
I performed a dry sediment survey to determine if there were aquatic invertebrates that used a lifehistory strategy of burrowing underground in the dried stream beds until water returned to the system.
If invertebrates used this strategy they may be the base community when water returns to the system.
Using a trowel, I collected sediment samples at the surface level (0-3cm). According to One sample was
taken from the center of each dry drinker/spring or visually last place where water was stagnant.
Samples were labeled accordingly and taken to the lab. In the lab, samples were placed in jars with
mesh netting to keep any possible invertebrates from escaping. Reverse osmosis water was placed with
each sediment sample. Each sample was observed to see if any invertebrates emerge over the course of
ten days, checking to see how many emerged on the 1st and 10th day. Ten days was chosen as the
amount of time to let the water set because the minimum amount of time used in methods by
Stubbington and Datry (2013) was a period of 1 to 7 days, and the next group was 8 to 30. I decided to
choose a time within the second grouping but also within the constraints of my limited time.
Results
Looking at the total abundance for the wet sites in 2013, there was a greater amount of invertebrates
found in the West Mesa South sample than any other sample site (See Figure 3). For taxa richness of the
wet sites in 2013, the most taxa found in one site was 11 (San Lorenzo East). The taxa found at San
Lorenzo East were from the orders Diptera, Ostracoda, Ephemeroptera, and Gastropoda. The least
amount of taxa found in one site was zero (Esquival) (See Figure 4). No statistical tests to compare
abundance and richness between the drinkers and springs were conducted on the wet site samples due
to lack of wet springs samples that could be collected.
Taxonomic richness was then compared to both vegetation and scat mean percentages to see if there
was any correlation between them. In the scatter plot between taxonomic richness (S) and animal use,
the trend showed that there was no correlation as indicated by the low R2 value (See Figure 5). The
trend between S and vegetation had a weak positive correlation (See Figure 6). Therefore as
surrounding drinker or spring vegetation increased, S increased within the water source. For dry sites in
2013, there were no invertebrate taxa found in any of the samples.
There was a trend for taxonomic richness (S) in 2010 to be similar to that in 2013: sites in 2010 with high
S also tended to have high S in 2013, whereas water sources with low S in 2010 would have low S in
2013 (See Figure 7). A scatter plot of the data sets was created but the correlation was not significant
due to the high variability of the low amount of sampled sites. There is no difference between the
taxonomic richness of invertebrates in drinkers and springs between the years 2010 and 2013 (twotailed t-test, p = 0.818).
Since there was no significant difference between the taxonomic richness of aquatic invertebrates
between 2010 and 2013, I decided to see if there was a difference in the taxa present at each site
between 2010 and 2013, or simply I decided to look at the turnover for each site. In each of the turnover
charts I created, only one taxon at most was transferred between 2010 and 2013 (See figure 8). So there
is little or none of the taxon from 2010 in the 2013 invertebrate communities. The majority of the taxa
found in 2010 were from the order Coleoptera, while the majority found in 2013 was Diptera. The order
Ostracoda and the family Hydrachnidae were only found in 2013.
Discussion
The results of my study suggest that there is no difference in the taxonomic richness of the springs and
drinkers between 2010 and 2013. This was opposite of what I had predicted and it is also very surprising
because there was such a great change in the drought conditions of the area and several springs and
drinkers had dried since the 2010 data was collected. The drought disturbance should make it so that
the few drinkers with water become refuges, and then later recolonization should occur after the supraseasonal drought finishes (Chester and Robson 2011). Due to the lack of abundance data in 2010, I could
not look at the difference in diversity, because diversity includes abundance and taxonomic richness.
One of my secondary questions, of whether or not there would be invertebrates in the dried sediment
beds was also proven to have no invertebrates within any of the samples. I found this result to be both
expected and surprising for two reasons. I somewhat expected this because Stubbington and Datry
(2013) found that there is a negative correlation between harshness of the environment and seedbank
survival. So as there is an increase in environmental harshness, such as a supra-seasonal drought, there
is an decrease in survivorship of a seedbank. The reason I was surprised by these results is because
Stubbington and Datry (2013) also state that recolonized wet areas are usually done by invertebrates
from other sources, not by those emerging from the previously dried sediments. But those that do have
life stages that can survive in dried sediment conditions were found in many of the wet samples I
gathered (Stubbington and Datry 2013). Some of these taxa include gastropod mollusks, Coleoptera and
Diptera. Since these were distributed across many of the wet drinkers and springs, I expected to see
them in the dried sediments.
To improve my study, I would like to change my methods to help reduce variables. For wet sites, I would
take quadrate samples on the day I removed the sponge from the drinker instead of taking a quadrate
sample the day I insert the sponge. Some invertebrates may leave or enter the water system within the
duration that the sponge is left in the drinker, so by taking the quadrate the same time that the sponge
is removed I can reduce the possibility of sampling different communities. Another way my study could
have improved is if abundance numbers from past studies were available. It would help me gain a better
understanding of difference of diversity of invertebrate communities. Finally, more wet springs from
2013 to compare to 2013 drinkers would have been beneficial to be able to answer my question about
drinkers being refugia. Unfortunately the supra-seasonal drought of this year dried up all but one spring,
therefore delaying further analysis and comparisons.
For future study, I would recommend sampling wet drinkers and springs again. With these new points, it
would be easier to see how turnover changes with drought conditions over multiple years. It also can
look at abundance levels and find new trends within how many invertebrates can occupy a drinker.
Abundance and taxonomic richness together can give a better picture as to how diversity in the drinkers
and springs have changed over time better than just one variable or the other. Additional long term
survey data is valuable to watch ‘lag effect’ of diversity change over time (Boulton 2003).
Acknowledgements
Thank you to NSF, Sevilleta LTER Program, and US Fish & Wildlife for making this opportunity possible. I
would also like to thank my mentor Dr. Ayesha Burdett for supporting and guiding me through this
project as well as Becky Bixby for supplemental support. To Amanda Martinez for collecting the 2010
data and Scott Collins, her mentor, for sharing the data with me, I am grateful. A big thanks to Amaris
Swann, for coordinating this program and making sure everything runs smoothly. Also I would like to
thank Brennan Davis for being my field partner and helping me out with surveys and sampling. Finally,
thank you to everyone else who has supported and helped me this summer.
Additional Figures
Figure2. Map of the Sevilleta Wildlife Refuge and the drinkers and springs that were sampled; those in
pink were sampled in both 2010 and 2013, and those in blue were additionally sampled in 2013.
Total Abundance for Wet Sites
# of Invertebrates
1500
1000
500
0
Figure 3. need caption here
Springs and Drinkers
Canyon
Esquival
San Lorenzo W.
W. Mesa E.
Goat Draw
San Lorenzo E.
W. Mesa S.
McKenzie
Tule (222)
Nunn
Gibbs
# of Taxa
Taxonomic Richness for Wet Sites
12
10
8
6
4
2
0
Canyon
Esquival
San Lorenzo W.
W. Mesa E.
Goat Draw
San Lorenzo E.
W. Mesa S.
McKenzie
Tule (222)
Nunn
Gibbs
Springs and Drinkers
Figure 4. need caption here
Animal Use vs Richness
5
Mean % Scat
4
y = -0.0676x + 1.8015
R² = 0.0353
3
2
1
0
0
2
4
6
8
Taxonomic Richness (S)
10
12
Figure 5. correlation between Animal Use and Taxonomic Richness in Sevilleta wet drinkers and springs
2013.
Mean % Vegetation
Vegetation vs Richness
60
50
40
30
20
10
0
y = 1.3961x + 22.139
R² = 0.3536
0
2
4
6
8
10
12
Taxonomic Richness (S)
Figure 6. correlation between Vegetation and Taxonomic Richness in Sevilleta wet drinkers and springs
2013.
Change in Diversity between 2010 & 2013
12
# of Taxon
10
8
6
4
2
0
Drinkers and Springs
Dytiscidae (Col)
Hydrochus (Col, Hydr)
Curculionidae (Col)
Chironominae (Dipt, Chird)
Tanypodinae (Dipt, Chird)
Euparyphus (Dipt, Strat)
Coricidae (Hem)
Trichorixa (Hem, Corix)
Uvarus (Col, Dyt)
Hydrophilidae (Col)
Carabidae (Col)
Ceratopogonidae (Dipt)
Sciomyzidae (Dipt)
Hemiptera
Corixidae (Hem)
Veliidae (Hem)
Tenebrionidae (Col)
Hydrocolus (Col, Dys-Hydro)
Diptera
Ephydridae (Dipt)
Stratiomyidae (Dipt)
Notonectidae (Hem)
Corixinae (Hem, Corixidae)
Baetisca (Eph, Baet)
Laccophilius (Col, Dyt)
Derallus (Col, Hydr)
Culicidae (Dipt)
Simuliidae(Dipt)
Caloparyphus (Dipt, Strat)
Notonecta Linnaeus (Hem, Not)
Corisella (Hem, Corix)
Physa (Gast, Phys)
Figure 7. change in taxonomic richness between 2010 and 2013 Sevilleta drinkers and spring.
Figure 8. The turnover of the Sevilleta wet drinkers and spring between 2010 and 2013. The species pool
and the top arrow represents what inverts enter into the system in 2010. The arrow pointing directly
down represents what species transfer into the 2013 system from 2010 and the curved arrow
represents the what species exit the system between 2010 and 2013. The bottom arrow represents the
new species that enter into the system. All the diagrams are drinkers except for Cibola.
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