Trophic, Habitat, Disturbance and Conservation Linkages Between Aquatic Communities in Two ...

239 Pages·2013·4.56 MB·English

by  Kate E. Miller

Wesleyan ♦ University

TROPHIC, HABITAT, DISTURBANCE AND CONSERVATION LINKAGES BETWEEN
BAT AND AQUATIC COMMUNITIES IN TWO CONNECTICUT RIVERS

By
Kathleen Elisabeth Miller
Faculty Advisor: Dr. Barry Chernoff

A Dissertation submitted to the Faculty of Wesleyan University in partial fulfillment of the
requirements for the degree of Doctor of Philosophy
Middletown, Connecticut May 2013
Acknowledgements
This dissertation and the many years of work it represents would not have been possible
without the participation, help and support of many individuals. Michelle Tipton and Ross
Heinemann have been great friends and wonderful colleagues, and I can’t imagine my time at
Wesleyan without them. This document owes them both - Ross contributed the organic
matter, substrate, and GIS data I used, as well as field and bug work. Michelle was my
partner in the early days of invertebrate identification and database management, and was
always up for fishing. Thanks to Heather Olin, the first student in the lab to take up with
stream ecology, for getting me started down this path. Benthic macroinvertebrate data was
collected, processed and identified and field work conducted by numerous patient and
talented (and fun!) undergraduates in the lab, too many to name here – thank you all. A
special thank you goes to Gabrielle Jehle, Megan Hughes, Renee Fortin, Sarah Gignoux-
Wolfsohn, Sarah Donelan, and Nick Fields. We were often joined by undergraduate and
graduate students, along with friends from the community, who gamely volunteered for a day
of fishing or scrubbing rocks. Having such a supportive group of Bio grad students who
understood the strange life of a graduate student was great (thanks Sarah!). I am very thankful
to Dr. Scott Reynolds for the bat recording equipment lent and advice freely given. Thanks to
Joel Labella for the life support he provided to the older units and for teaching me (patiently)
something of electrical connections. Jen Rose, of Wesleyan’s Quantitative Analysis Center
helped me survive, and succeed, at modeling. Gary Miner from StatSoft took time to help me
with the nuts and bolts of data mining. Mike Beauchene from the CT DEEP provided prompt,
accurate information about their benthic macroinvertebrate and Fish monitoring programs.
I’m so happy to have met many bat researchers over the last couple of years, and appreciate
their insights and work on behalf of these amazing creatures; their feedback helped me to
further scrutinize, and hopefully, improve my analysis and conclusions. My work was funded
in part by Wesleyan University. In addition, the study utilized data from the Zemko dam
monitoring project, which was funded by the Connecticut Chapter of the Nature
Conservancy. My thesis committee members, Dr. Mike Singer, Dr. Fred Cohan and Dr. Phil
Resor have given me helpful advice, encouraging words and much appreciated patience.
Thank you to the staff of the Biology Department and its Chair in my final year, Dr. Sonia
Sultan, and to the E&ES Department and Graduate Studies for all your help. I am very lucky
to have had a wonderful support system including many good-natured friends who assisted
me in various field tasks (and put up with my mysterious, time-consuming work and
complaining). This endeavor would not have been possible without the countless small and
large acts of encouragement and support from my family, especially my many parents. Most
of all I am grateful to my husband Bob for being the type of life partner that supported this
quest, and to my children, Ryan and Gwyn, for their love and sometimes, understanding.
Finally, much appreciation goes to my advisor, Dr. Barry Chernoff, for bringing me into
Wesleyan and for his support, and the willingness to let me to pursue bats.

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TROPHIC, HABITAT, DISTURBANCE AND CONSERVATION LINKAGES BETWEEN
BAT AND AQUATIC COMMUNITIES IN TWO CONNECTICUT RIVERS
By
Kathleen Elisabeth Miller

Abstract

The goal of this work was to explore connections between foraging bats and stream
ecosystems. While many studies have considered the influence of (mostly adult) prey
and habitat, few have sought to integrate their direct, indirect and interacting effects.
The first chapter seeks to identify influential prey and habitat variables and to
produce models that explain the abundance of certain bat groups and associated
benthic macroinvertebrates (BMI). The second chapter documents bat, BMI and fish
communities before and after white-nose syndrome (WNS) became established in our
state, and looks for evidence of a “release” response in the prey community of BMI,
and the competitor community of fish. Numerous environmental variables were
considered to help rule out potentially confounding effects of ecological variability. It
has been suggested that because of the connection between bats and BMI, known to
be sensitive to water quality and commonly used as indicators of stream health, that
bats may also be bioindicators for rivers. The third chapter is a case-study testing this
potential by comparing sites’ bat richness and abundance with BMI and fish water
quality metrics. Over four years (2008-2012) at eight study sites along two
Connecticut rivers, the Coginchaug and the East branch of the Eightmile, data was
collected on bats, BMI and fish communities; adjacent terrestrial habitat; near and far
landcover; and in-stream conditions of organic matter, substrate and water. Myotis, P.
subflavus and E. fuscus were strongly associated with the abundance and/or habitat of
two dominant groups of BMI, Diptera and Trichoptera (especially Hydropsychidae).
Declines in WNS-vulnerable groups were consistent with others’ accounts, and data
indicate an increase to groups with lower mortality, particularly E. fuscus. Evidence
for predator and competitive release effects, i.e. increases to abundance of BMI and
fish, was inconclusive, though arguably sufficient to warrant further investigation.
There were little direct associations between measures of bat activity, such as
richness and abundance, and BMI and fish metrics. Results indicate that low bat
activity may be useful as an indication of poor stream conditions, while high bat
activity may indicate greater nutrient inputs, productivity and biodiversity of the
aquatic community.

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Table of Contents
Introduction………………………………………………………………………… 1

Chapter 1: Associations between bats, benthic macroinvertebrates and habitat in
riverine landscapes

Abstract……………………………………………………………………………..7
Text……………………………………………….…………………………………8
Figures……………………………………………………………………………. .43
Appendices…………………………………………………………………………58
References………………………………………………………………………….77
Chapter 2: Changes to bat and aquatic communities due to white-nose syndrome

Abstract……………………………………………………………………..............93
Text……………………………………………….………………………………...94
Figures……………………………………………………………………………...131
Appendices…………………………………………………………………………150
References………………………………………………………………………….166
Chapter 3: A Case-Study of Bats as Bioindicators of Water Quality
Abstract…………………………………………………………………….............178
Text……………………………………………….………………………………..179
Figures……………………………………………………………………………...205
Appendices………………………………………………………………………....217
References……………………………………………………………………….…224

Conclusion…………………………………………………………………….……232
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Introduction

In Connecticut, most of our smaller rivers, for much of the time, flow unseen. They
are obscured by wetlands or the vegetated buffers encouraged by the state’s Inland/Wetland
Act. They are far from road and development, or hide in plain sight under bridge crossings
and behind parking lots. While we may consider the river itself to be aquatic, it exists only in
interaction with the land, a product of the landscape’s use, topography and geology, present
and past, near and far, upland and upstream. This “riverine landscape” is diverse and
complex, encompassing water, riverbed, banks, wetland, floodplain, field and forest, farm
and housing development. It is dynamic, overflowing its banks with heavy rainfall and
shrinking to half its size in drought. Rain carries all manner of small items from the land –
leaves, sand, silt, fertilizer, sewage, pesticides, litter, wood, insects – that collectively
influence its physical and biological composition. The interface of land and water offers a
complex and rich “ecotone”, and one can typically find compressed within its borders a
diverse community of aquatic, amphibious and terrestrial creatures. These winding
ecosystems offer much to wildlife: open corridors for flight and movement, refugia from
human activity and a variety of changing habitat types and food.
It was the interactions of some of these organisms, within the context of this riverine
landscape, that I chose to study for my doctoral project. Specifically, the changing
communities of benthic macroinvertebrates, bats, and fish. The connection between these
groups is not immediate or intuitive for most people. Benthic macroinvertebrates (“BMI”) are
the diverse organisms that occupy a river’s every substrate – pebbly bottom, sandy shoal,
soggy leaf pile, fallen tree – and include insect larvae along with other arthropods, worms,
and mollusks. Fishers know about the insect larvae, like mayflies and caddisflies, which can
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live from weeks to years in the water then emerge, synchronously, with others of their species
to mate and lay eggs. Various fish will consume them at any life stage including the winged
adults as they lay their eggs or fall back into the water by accident, wind, or at the end of their
feverish adult lives. And this is where the bats come in. Rivers are favorite haunts for many
insectivorous bat species, a reliable source of aerial food, a linear corridor with relatively
clear airspace and water for drinking.
I was motivated to study these interactions by a desire to explore biological
connections between the aquatic communities that were the lab’s concern to the river’s
terrestrial landscape. In reviewing the literature a number of gaps in knowledge were evident.
While bats’ use of stream corridors and consumption of aquatic insects were well
documented, there was relatively little research connecting bats to their prey at the larval life
stage. Those studies that did look at BMI were usually in disturbed systems – such as in
forests that had been burned or downstream of sewage treatment plants – and very few
simultaneously considered the impact of habitat. From a conservation perspective, connecting
bats to BMI could be a valuable thing to do. As widely recognized bioindicators of stream
health and water quality, BMI are regularly sampled by environmental agencies and much of
the data is public. Connecting bats to BMI is to connect them to information that could be
used to identify, protect or even enhance important foraging habitat, without the cost or years
of work this research might otherwise entail. I also realized that our lab’s perspective, which
also included fish, water conditions, habitat and landscape, was unusually broad, and had the
potential to provide some more comprehensive insight into the interactions of this system.
In 2008, the first year of the study, I was most concerned with two related questions:
whether or not benthic macroinvertebrates, the larval stage of bats’ adult prey, could predict
relative use of the river by different bat groups and how habitat might influence both BMI
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and bats. I designed my project to encompass the rivers – the Coginchaug and the East
Branch of the Eightmile – and study sites that had been the long-term focus of the lab, and
added sites that would contribute further diversity of habitat. Based on the natural history of
the most common bats in our region, the little brown, the big brown and the tri-colored bat, I
gambled that I would find bats at some of the sites, and further, that differences in activity
levels would be linked to variability in the BMI community and the habitat. I also gambled
that there would be any bats at all. White-nose syndrome (WNS), a fungal infection just
emerging in the region, had been detected in Connecticut, and there was growing evidence
that the disease had the potential to cause substantial mortality in New England. Another
research question arose from this nascent ecological disaster – what would happen if, or
sadly, when, the bats disappeared? Would their absence result in changes to the communities
in which they had been enmeshed?
Manipulative studies – those that control all or at least some conditions while
manipulating only the variables of interest – can isolate the influence of the variable of
interest. The results provide persuasive proof of cause and effect, at least under certain
circumstances. In contrast, observational studies such as mine have a central dilemma – how
to isolate the effects of the key variables of interest within the context of complex and
variable environmental and biological conditions?
One approach is to sample a large number of sites so that significant patterns may be
apparent beyond the “noise” of variability. This was not possible in my case due to practical
constraints, not the least of which was the time required to process and quantify BMI
samples. Alternatively (with luck, additionally) one can measure as many variables as
possible to test for confounding effects and identify the separate influence of the variables of
interest. This is the approach I chose. The Chernoff Lab had been exploring BMI and fish
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communities at a number of rivers since 2005 and had begun to assess the influence of water
chemistry (such as dissolved oxygen and conductivity) and conditions (such as temperature
and depth) and habitat both within and beyond the river proper (e.g. the composition of the
river bottom, vegetation on the banks, and tree canopy). Ross Heinemann, a Master’s student
in the Environmental and Earth Sciences Department embarked on a complementary project
to assess organic matter and the effects of landcover at various spatial scales, adding more
environmental variables to the list of influences I could consider.
The study included eight sites, four at each river, over the course of four years (2008-
2011). The two rivers and their basins are divided by the Connecticut River, and differ in
many respects. The Coginchaug River is approximately 15 miles long, of relatively low
gradient and has numerous large and small dams. It flows northward through seven towns,
and the amount of developed landcover increases as the river converges with the Mattabessett
River near its mouth with the Connecticut. Testing by regulatory and non-profit agencies
indicates impairment of water quality due to agricultural inputs and non-point source
pollution and the river has recently become the focus of regional planning efforts to improve
water quality. In contrast, the Eightmile River is in a largely rural and forested portion of the
state, with little historic or current development, and low road density. It flows south through
a steep topography. Water quality here is considered good, and the Eightmile was designated
a Wild and Scenic River by Congress in 2008. Downstream from study sites the river joins
the Connecticut eight miles above its mouth at Long Island Sound, hence its name.
At the heart of each study site was an area of riffle, defined as a portion of the river
with a coarser bed breaking the water’s surface, where benthic macroinvertebrates were
sampled. This was nested within a larger river segment considered for fish and environmental
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conditions, itself contained within near- and far-stream habitat that was considered for
landcover composition, particularly proportion forested or developed.
My dissertation is organized into three chapters, which, while distinct, are also
cumulative and sequential. The first is entitled “Associations between the abundance and
habitat of benthic macroinvertebrates and foraging bats in river corridors”. Here I investigate
my original questions about the influence of BMI and habitat on foraging bats. These
questions are complicated by the number and interactions of variables considered and the
desire to tease out and quantify different types of effects. For example, the proportion of the
landscape that is developed may influence the conductivity and therefore dissolved oxygen of
the water, which in turns affects certain BMI. To an aquatic invertebrate a tree canopy may
matter because it regulates light and organic matter, while to a bat it may – depending on the
bat’s size – represent clutter to navigate around or protection from predators. I used Structural
Equation Modeling, a technique that tests a model built from independent associations and
information from the literature, to determine the most important direct and indirect effects
and to identify models that best describe the interactions between bats, BMI and habitat.
The second Chapter, “Changes to bat and aquatic communities due to white-nose
syndrome” is the study that came out of the consequences of white-nose syndrome in our
region. The Northeastern United States is unfortunate to be at the nexus of this devastating
disease, estimated to have killed at least 5 million bats. Early information showed that effects
might be species-specific, with the smaller Myotis and Perimyotis especially vulnerable and
other, larger, genera potentially less so. There is another way that observational studies may
provide insight into a system, and that is by documenting the effects of dramatic disturbance.
I began monitoring bats at study sites in 2008, when the disease had been detected in
Connecticut hibernacula but no significant mortality had yet been documented. By the winter
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of 2009 its effects were evident, and thousands of bats were found dead. This study
documents the impact of a biological disturbance, WNS, on the inter-species communities of
foraging bats. Based on the results from the first study, I also sought to determine whether or
not the profound and rapid changes to the bat community constituted a “release” from
predation or competition that could be detected in the prey community of BMI and their
aquatic predators, fish. To isolate these effects a long list of environmental conditions also
had to be considered.
Finally, the third chapter, “A Case-Study of Bats as Bioindicators of Water Quality”,
considers more directly the meaning of a connection between bats and their BMI prey. BMI
communities are often used, along with other data, as “indicators” of aquatic ecosystem
health. Given the connection between foraging bats and BMI, could bats be used, as well, to
indicate relative stream health? Considering bats as bioindicators of a variety of conditions
has been posited by a number of researchers. However, few studies have explored specific
links between different measures of bat activity and components of water quality indices, and
few if any consider information provided by a fish IBI (Index of Biotic Integrity). The
purpose of this study was to contribute to this discussion by evaluating the overlap and
differences between metrics of more established water quality bioindicators (BMI and fish)
and bat activity at the study sites. Within the variables measured, I also considered what other
conditions relative bat activity levels might indicate – for example the abundance of BMI
considered bat prey, or the proportions of forest and development.

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