An Experimental Study of Vertical Habitat Use and Habitat Shifts in ...

An Experimental Study of Vertical Habitat Use and Habitat Shifts in Single-species
and Mixed-species Shoals of Native and Nonnative Congeneric Cyprinids
Brandon J. Keplinger
Thesis Submitted to the
Davis College of Agriculture, Forestry, and Consumer Sciences
at West Virginia University
in partial fulfillment of the requirements
for the degree of
Master of Science
in
Wildlife and Fisheries Resources
Stuart A. Welsh, Ph. D., Chair
Kyle J. Hartman, Ph. D.
Daniel A. Cincotta, M. S.
Division of Forestry
Morgantown, WV
2007
Key Words: nonnative fish, aquaria study, congeneric species, Greenbrier River,
mixed-species shoal, vertical habitat use and segregation, interspecific interactions

Abstract
An Experimental Study of Vertical Habitat Use and Habitat Shifts in Single-species
and Mixed-species Shoals of Native and Nonnative Congeneric Cyprinids
Brandon J. Keplinger
This thesis includes two chapters. The first (Chapter 1) is a literature review
focusing on the ecological consequences of introduced fishes on host communities, and
specifically on native fishes of similar morphology and phylogenetic origins. The second
(Chapter 2) is a manuscript synthesizing the aquaria based study of the interspecific
relationships, with respect to habitat utilization, between two syntopically occurring
congeneric species pairs in the Greenbrier River. Each pair consists of an introduced and
a native cyprinid species. Several species native (often endemic) to the New River
watershed are experiencing reductions in abundance and distribution. Meanwhile, a
concurrent increase has occurred in the abundance and distribution of similar nonnative
species. Chapter 2 focuses on the interspecific interactions that occur with respect to
vertical water column position between a pair of native species, Notropis scabriceps
(New River shiner) and Cyprinella spiloptera (spotfin shiner), and a pair of nonnative
species, Notropis telescopus (telescope shiner) and Cyprinella galactura (whitetail
shiner). These four species occur in the Greenbrier River (a tributary to the New).
Observations were made using aquaria and vertical position categories. All four species
were observed under allotopic and syntopic trials. Allotopic trials provided evidence for
segregation in vertical water column preferences but syntopic trials revealed integration
and mixed-species shoals. Laboratory-observed patterns of native/nonnative species
integration likely occur in wild populations (in the New River drainage). If laboratoryobserved
patterns of species integration also occur in wild populations, then competitive
interactions will likely occur owing to the close association between native and nonnative
species in the use of vertical habitat space. Additional studies, however, are
needed to verify experimental findings in the natural environment of the Greenbrier River
system.

Acknowledgements
I would like to thank Dr. Stuart Welsh, the WVU Department of Forestry and
Natural Resources, and the WVU Cooperative Wildlife and Fisheries Research Unit for
allowing me the opportunity to attend graduate school and be a part of this very
interesting study. Thanks also go to Dr. Kyle Hartman and Dan Cincotta for serving on
my committee and their useful suggestions for improving my thesis. Additionally, I
would like to thank the WVU Department of Biology for providing employment and
teaching assistantships, and the US Forest Service for project funding.
I would like to extend special thanks to those individuals that helped with the
project: Dustin Smith, Dustin Wichterman, Jason Stolarsky, Holly Henderson, Roy
Martin, and last but not least, Samantha Warner, who provided hours of physical
assistance without pay. Thanks also go to Dr. Seidel for statistical guidance.
Finally, I would like to thank my family for their support and encouragement and
my fiancée Samantha Warner for her love and devotion.
iii

TABLE OF CONTENTS
ABSTRACT........................................................................................................................ ii
ACKNOWLEDGEMENTS............................................................................................... iii
LIST OF FIGURES .............................................................................................................v
LIST OF TABLES...............................................................................................................v
CHAPTER 1: LITERATURE REVIEW.............................................................................1
Literature Review...........................................................................................................1
Review of Study Area/Related Studies .........................................................................16
LITERATURE CITED ................................................................................................22
CHAPTER 2: LABORATORY OBSERVED INTERSPECIFIC INTERACTIONS
BETWEEN NATIVE AND NONNATIVE GREENBRIER RIVER CONGENERICS ..30
ABSTRACT.................................................................................................................30
INTRODUCTION .......................................................................................................32
METHODS ..................................................................................................................34
Specimen Collection and Transport.......................................................................34
Aquaria Setup.........................................................................................................35
Allotopic and Syntopic Experiments ......................................................................35
RESULTS ....................................................................................................................37
Notropis Congeners ...............................................................................................37
Cyprinella Congeners ............................................................................................38
DISCUSSION..............................................................................................................39
LITERATURE CITED ................................................................................................43
APPENDIX........................................................................................................................46
iv

LIST OF TABLES
Table 1. Results of Chi square Tests for Independence for Notropis congeners..............46
Table 2. Results of Chi square Tests for Independence for Cyprinella congeners...........47
LIST OF FIGURES
Figure 1. Relationship between allotpic vertical positions of Notropis and Cyprinella
congeners .....................................................................................................................48
Figure 2. Relationship between vertical placements of Notropis and Cyprinella
congeners during all syntopic trials and tank replications...........................................49
Figure 3. Relationship between allotpic and syntopic vertical positions
of all Notropis and Cyprinella congeners ....................................................................50
v

Chapter 1: Literature Review
Literature Review
Extensive literature searches were performed on such topics as niche theory,
speciation, competitive exclusion (and other outcomes of nonnative species
introductions), characteristics of host watersheds susceptible to invasion, common
characteristics of invasive fish species, the risks of hybridization with native species, and
behavioral habitat segregation. To understand the competitive relationships between
closely related species and the harmful possibilities of mixing similar vicariant species,
one must first begin to understand the tenets of niche theory and competitive exclusion.
Uninterrupted biological succession among similar species over time is necessary
for increasingly close-knit associations and reciprocal adaptations (Odum 1969). Long
periods of uninterrupted interactions between biotic communities allow the possibility of
coexistence and an increase in the degree of species specialization (MacArthur and
Levins 1967, Odum 1969). This is especially true when considering areas possessing
migration barriers (Pianka 1966). Migratory pathways would be eliminated, disallowing
the onslaught of congeners or similar species that could compete with species typifying
the current assemblage. Thus, symbiotically coevolved species assemblages are often
formed within areas in which natural isolating barriers occur (Pianka 1966). This
assumes that factors allowing divergence and co-evolution, such as time and ecological
stability, are present and substantial enough to create ecologically stable communities
(Pianka 1966, Odum 1969, Schoener et al. 1979). The net result of uninterrupted
succession over time is stability; however, perturbations of the community’s interspecific
framework and anthropogenic stresses can deteriorate this stability (Odom 1969).
1

In order for similar species to avoid competitive exclusion they must be capable
of partitioning some aspect of the trophic, spatial, or temporal variables of habitat usage
(MacArthur and Levins 1964, Pianka 1974). Effects of competition, such as decreased
survivorship and fecundity, are reduced through natural selection in lieu of more
favorable traits (Murray 1986). Differentiation of breeding strategies, behavior,
susceptibility to biochemical hazards, or resistance to the effects of environmental
stochasticity is needed for interspecific traits to remain distinct (Harper et al. 1961). Such
evolutionary specializations are more pronounced in complex, heterogeneous
environments (Murray 1986). Increased niche dimensionality allows greater ecological
packing, thus allowing an environment to accommodate a greater number of species
(MacArthur and Levins 1967). Similarly, it is believed that the number of related species
coexisting in a given ecosystem is strongly dependent on the width and overlap of those
species’ niches (Pielou 1972). Complete, non-interbreeding competitors cannot coexist
without evolutionary divergence, readjusted niche widths, or competitive elimination of
one of the species (Hardin 1960, Pianka 1966, Pianka 1974). Problems occur when
ecological processes set into place through disturbances disrupt stable evolutionary
processes (Pianka 1966). The introduction of a non-indigenous species that acquires
already utilized niche space in a new region would be an example of such a disturbance.
The chance exists for competitive exclusion to occur if two similar, geographically
separated species are mixed (Hardin 1960). To make matters worse, established
introduced species often utilize a realized niche that more closely resembles its
fundamental niche in the host community (Li and Moyle 1981). Thus, species
2

transported from habitats that are more compartmentalized between species will likely
exploit a broader niche in a more depauperate host community.
Authors have long since commented on the deleterious effects that introduced and
invasive species have on host ecosystems (Elton 1958, Lachner et al. 1970, Magnuson
1976, Ross 1991). Any new biological addition to an aquatic ecosystem will result in a
modification of that ecosystem (Courtenay and Hensley 1980). Introductions into
undisturbed habitats require the competition of space and food (Herbold and Moyle
1986). Thus, native individuals cannot reach maximum probabilities of survival and
reproduction in the presence of introduced competitors (Murray 1986). This implies that
direct or indirect competition will occur with resident species in the host ecosystem
(Courtenay and Hensley 1980). Reviews of most exotic fishes indicate some undesirable
effect on native fish assemblages (Ross 1991).
Several outcomes can result from the introduction of non-indigenous species.
Introduced species may fail to become established, become established with varying
influences on sympatric species, and full establishment causing the displacement of the
native species (Courtenay and Hensley 1980, Ross 1986, Walser et al. 2000). Ecological
interactions among the native and nonnative species will dictate the outcome of an
introduction.
The degree of success obtained by a nonnative in displacing native species will
play a large roll in how greatly the host system is affected. Nonnative species success
can be directly or indirectly affected by a variety of biotic and abiotic interactions in the
new environment (Angermeier and Winston 1998, Mooney and Cleland 2001). As
environmental stability and food availability increase, niche breadths should decrease and
3

species diversity should increase (MacArthur and Levins 1967). Therefore, biotic
factors, abiotic factors, or both could control a system’s species assemblage (Ross 1991).
This depends mainly on the population stability of those species as controlled by
environmental stochasticity and competition amongst species within that assemblage
(Ross 1991). More stable aquatic environments (communities at equilibrium) would
more likely be controlled primarily by competitive factors between species. However,
those that experience harsh environmental fluctuations (communities not at equilibrium)
would likely be primarily influenced by abiotic factors such as high flows in aquatic
systems (Ross 1986, Freeman et al. 1988, Ross 1991). It is reasonable to assume that
highly invadable aquatic systems will share many of these biotic/abiotic factors thought
to increase the chances of successful invasions. Due to the fact that this thesis is solely
directed towards interactions between small, non-piscivorous fishes, we should be most
concerned with factors regulating the ecological interactions between those species.
Many of these factors will be discussed in greater detail at this time.
Abiotic factors include environmental conditions (water quality, climate, geology,
gradient, flow, etc.), suitable habitat availability, watershed connectivity, and
geographical isolation. However, the biology of a given species will determine whether
or not these abiotic factors will be beneficial or deleterious. In order for aquatic
invasions to occur the introduced environment must be suitable for that species’ survival.
The more suitable the introduced environment is for nonnative introductions, the more
susceptible the native assemblage is to change after that species has become established.
Fluctuating environmental conditions can alter the state of environments to
benefit or inhibit the colonization of introduced species. It has been stated that climate
4

stability is an indicator of the number of potential “coarse-grained” - specialist - species
in a given area (MacArthur and Levins 1964). Both temperature (Courtenay and Hensley
1980) and flow (Cross et al. 1983) have been speculated to be inhibitors of introduced
species in colonizing a new area. Temperature has been postulated as a major factor
governing the distribution of a sensitive shiner species, Notropis scabriceps, in the
Greenbrier River (Shingleton et al. 1981) and in many high gradient, high altitude
streams (Burton and Odum 1945). Changing environmental conditions have been cited
as factors that could potentially reduce the effects of interspecific competition by
alternating the level of favorability between two species (Murray 1986). A study of a
cyprinid species in an environmentally unstable southwestern river suggested that habitat
partitioning was of lesser importance to the perpetuity of community structure. Instead,
adaptability to various temporal fluctuations in flow, pH, temperature, and dissolved
oxygen were attributed to the species’ success (Matthews and Hill 1980). Alternatively,
altered environmental conditions may also disrupt native assemblages by reducing the
range of native populations and allowing the establishment of less sensitive species. A
study of shiners in the Arkansas River basin suggests that flow is the main factor limiting
the invasive congener Notropis bairdi from expanding its range upstream where the
native Notropis girardi has already been displaced (Cross et al. 1983). Similarly, Percina
roanoka, introduced to the Greenbrier River, has been shown to hold position in higher
velocities than the native Etheostoma flaballare without actively swimming (Matthews et
al. 1982, Matthews 1985). This suggests that the introduced species in this case can
occupy fast water areas that the native confamilial species cannot. Another study
suggests that a species assemblage in a southern Appalachian stream is very dynamic,
5

noting that the abundance of some species is more susceptible to, and thus regulated by,
environmental factors (Freeman et al. 1988). This is mainly due to morphological
features and the ability of benthic fish to hold position more efficiently than water
column species during increased flow. There is no doubt an abundance of instances
where environmental conditions have disallowed introduced species to colonize new
environments. However, it is very difficult to document an attempt at colonization by a
species if that species fails to become established before its presence can be recorded
(Williamson and Fitter 1996).
Suitable habitat availability can determine whether or not a species becomes
established and persists in a new environment (Courtenay and Hensley 1980).
Competitors will eventually exclude one another from habitats that are homogeneous
with respect to a limiting resource (Dueser and Porter 1986, Murray 1986). The number
of fish species an aquatic system can hold at equilibrium depends greatly on habitat size
and complexity (Harper et al. 1961, Magnuson 1976). For example, increased
environmental variability has been correlated with a decrease in niche overlap in
sympatric desert lizard species (Pianka 1974). Habitat complexity is often lower in small
aquatic environments than in large ones. Increased susceptibility to local extinctions is a
common result of this phenomenon (Magnuson 1976). With respect to introduced
species, mandatory habitat characteristics may already be utilized or completely absent in
the host environment. Thus, if an introduced species requires a particular habitat
characteristic colonization may not be feasible in the new area.
Low watershed connectivity or the degree of geographical isolation can limit the
ease of which an invasive species can reach a particular stream segment through natural
6

arriers (Harper et al. 1961, Jenkins et al. 1972, Magnuson 1976, Sheldon 1988). Natural
barriers to migration include cataracts, intense gradients, and interior areas of remote
tracts of land. Isolated watersheds can be very susceptible to invasion by non-indigenous
species which can somehow migrate or are transported into undisturbed areas (Magnuson
1976, Herbold and Moyle 1986, Mack et al. 2000). Insularity is also positively linked
with geographical specialization, which is suggested to be a characteristic of extinction
prone species (Angermeier 1995). The construction of impassable artificial barriers, such
as dams and reservoirs, fits into this category. Species richness above was reduced
shortly after an artificial impoundment was erected in the Red River drainage in
southwest Oklahoma. The presumably extirpated cyprinid species above the dam,
Notropis bairdi and Hybognathus placitus, were likely replaced by two similar minnow
species, Notropis atherinoides and Notropis stramineus (Winston et al. 1991).
Furthermore, the ability to transport species across geographic regions is increasing due
to technological advances (Elton 1958, Courtenay and Hensley 1980, Moyle 1986,
Mooney and Cleland 2001). Therefore, the importance of watershed connectivity
becomes less prominent in areas with a high degree of anthropogenic activity.
Biotic factors are primarily dependent on the degree of biological interactions
within a community. Thus, these factors become very important in the restructuring of
biotic communities following the introduction of nonnative species. Biotic factors are
either associated with the introduced or the invading species, their native assemblages, or
biological characters that can be affected in either. These include the following: the
degree of species depauperacy and niche availability in the respected assemblages;
degree of habitat specialization, competitive interactions, and genetic variability
7

exhibited by species involved; the presence of congeneric or taxonomic relatives in the
host assemblage; hybridization and introgression; number of invading individuals in the
source population and the frequency of those invasions; predator and parasite interactions
in the host environment; and anthropogenic disturbances.
The effects of introduced species on an ecosystem can be intensified if the
environment is under-saturated (Moyle 1986, Angermeier 1995, Angermeier and
Winston 1998, Case 1991). In theory, the greater the number of species in an
environment, the smaller the amount of existing niche space available to immigrants. As
the number of fish species decreases in an aquatic environment, the ability of immigrants
to become established increases (Magnuson 1976, Perry et al. 2002). The New River is
historically depauperate in native fish species (Jenkins et al. 1972, Hocutt et al. 1978,
Cincotta 1999, Wellman 2004). Isolated aquatic systems with natural barriers to
migration often have low levels of species diversity (Jenkins et al. 1972, Magnuson 1976,
and Sheldon 1988, Angermeier 1995). If niche partitioning is important in structuring
species assemblages then partitioning should increase as species number increases
(Schoener 1974). Therefore, resistance to invasion should also increases as species
richness increases (Elton 1958, Magnuson 1976, Angermeier and Winston 1998, Walser
et al. 2000). Similarly, disparity of freshwater habitat may limit resources and increase
the importance of resource partitioning, making competitive interactions much more
important (Ross 1986).
Released niche space and decreased diversity provides an opportunity for the
colonization of invasive species (Hocutt and Hambrick 1973). Simberloff (1981) stated
that areas possessing vacant niches due to impoverished species numbers are susceptible
8

to nonindigenous species invasions. However, it has been argued that invading
organisms rearrange communities and existing niches instead of filling an empty niche
(Herbold and Moyle 1986). For this reason, terms such as underutilized and available
niche space will be used in the context of this paper (Mack 2000, Herbold and Moyle
1986). This can only occur if there is exploitable niche space that can be utilized by the
invading species (Courtenay and Hensley 1980, Mack et al. 2000, Mooney and Cleland
2001). Alterations of fish communities can be very destructive to natural systems as
introduced species can interrupt the partitioning of niches evolved over time (Mooney
and Cleland 2001). The importance of niche partitioning in natural fish assemblages
possessing small, non-game congeneric species has been discussed extensively in past
literature (Gilbert 1969a, Hocutt and Hambrick 1973, Adamson and Wissing 1977, Page
and Schemske 1978, Baker and Ross 1981, Finger 1982, Matthews et al. 1982, Paine et
al. 1982, Surat et al. 1982, Hlohowskyj and White 1983, Vadas 1992, Chipps et al. 1993,
Eisenhour 1995, Strange 1998). In assemblages that are regulated by density dependent
interactions, competition plays a large role in partitioning those species’ niches (Freeman
et al. 1988, Ross 1991).
The degree of ecological specialization is strongly linked to habitat availability,
an abiotic factor mentioned above. A variety of different habitat and microhabitat types
can be used by fish species. This depends greatly on the complexity of life history
characteristics. It has been suggested that species with narrow niche-breadths are “ideal
candidates” for introduction due to the low likelihood of substantial competition with
native species (Li and Moyle 1981). The range of microhabitats used is positively
correlated with species abundance and the likelihood of successful introduction into a
9

new environment (Dueser and Porter 1986, Angermeier 1995). The majority of
introduced species that have become established are opportunists, some are generalists,
but none are truly specialists (Courtenay and Hensley 1980, Walser et al. 2000). In fact,
geographic and habitat specialists have been found to be more prone to extinction as
natural habitats continue to change (Angermeier 1995). Large geometrical and ecological
distances between habitat patches increases mortality of specialist fish species. This is
largely due to increased energy demands, predation, and exposure to unfavorable
conditions associated with excessive migratory efforts (Kolasa 1989). Anthropogenic
alterations exacerbate this effect by reducing the availability and proximity of suitable
habitat patches (Kolasa 1989).
Competitive interactions are very important, especially when considering
saturated watersheds with little underutilized niche space (Angermeier and Winston
1998). Competition can also occur over a variety of different habitat axes. Ross (1991)
included three primary axes: spatial (horizontal or vertical), temporal (seasonal and
diurnal periodicity of feeding and reproduction), and trophic (size and type of food and
substrate). Competition is the dominant force involved in the segregation of
microhabitats (Dueser and Porter 1986). A study assessing the microhabitats of
congeneric rodents showed that the distribution of only one species was determined more
by competition than by habitat structure (Dueser and Porter 1986). However, that species
was a recent entrant into the island’s fauna, having a relatively short period of time to
experience “competitive co-evolution” with the other species. A study of a cyprinid fish
community in an environmentally unstable southwestern stream suggested that
competition played a huge role in those species’ seasonal abundance. Dwindling food
10

esources and physico-chemical stressors increased niche overlap by concentrating
individuals in more profitable, stable habitats (Matthews and Hill 1980). There is
evidence of reproductive niche partitioning in many fish species. For example, darters
have evolved several different types of reproductive strategies utilized over a variety of
substrates, which reduces congeneric and confamilial spawning site competition (Page
and Swofford 1984). Prolonged spawning seasons, a temporal issue, results in a greater
reproductive potential. If an invasive species could reproduce more often over a longer
period of time, it may allow the competitive exclusion of native species (Courtenay and
Hensley 1980). Interference and exploitation competition for spatial position was
demonstrated when three Cottus species were found sympatrically in an Oregon stream
(Finger 1982). A study observing the variation in habitat use of eight southeastern
cyprinids demonstrated an overlap in the spatial and seasonal dimensions of two
confamilial species (Baker and Ross 1981). The authors attributed the coexistence of the
two similar species to diel feeding patterns. Notropis longirostris fed diurnally while
Ericymba buccata fed nocturnally (Baker and Ross 1981). Competition over food and
habitat has been suspected as the mechanism responsible for the establishment of an
introduced shiner species into the resident fish community (Walser et al. 2000).
However, introduced and native species can thrive sympatrically if resources such as
food in the host ecosystem are non-limiting (Moyle 1986, Walser et al. 2000).
Interspecific competition is highly connected to the acquisition and maintenance of niche
space. The structure of existing fish assemblages are the result of a legacy of competition
between similar species and the subsequent partitioning of niche hypervolume. It has
been suggested that co-evolved species are “ideal candidates” for introductions into a
11

host environment, proposing that a lesser chance of substantial niche overlap exists under
these circumstances (Li and Moyle 1981). Infringement of non-indigenous species upon
niche space already allocated to native members of a native assemblage can disrupt the
structured evolution of that community. The effects of introduced shiner species on
native congenerics have been well documented: Mathur (1977), Cross et al. (1983), and
Walser et al. (2000).
The genetic capability of a species to adapt to a new area may determine whether
an introduced species will become established. Differences between coexisting species
today are primarily due to past competitive interactions (Harper et al. 1961, Surat et al.
1982). The genetic makeup of a newly introduced species population depends on the
genetic variability of those founding individuals. In a study of sympatric shiner species,
the genetic differences between populations in different drainages were hypothesized to
be due to founder populations from different genetic refugia (Dowling et al. 1989).
Genetic change, occurring within the founder populations introduced to new ecosystems,
is one mechanism involved in the common “lag phase” observed after an introduction
(Mooney and Cleland 2001). If the species is genetically capable of evolving
characteristics beneficial to the new environment, a subsequent population boom may
occur. This may lead to the competitive exclusion of a similar native species. Species in
the native assemblage may also evolve in response to an established introduced species
(Mooney and Cleland 2001). If this doesn’t occur, the native species may experience
dramatic population declines or extirpations due to the inability to withstand competitive
forces (Elton 1958, Mack et al. 2000). Geographically isolated species will be exposed to
different forces of selection, which often leads to differential adaptations (Harper et al.
12

1961). Similar species from watersheds devoid of major migration barriers may exploit a
greater degree of stream connectivity and increased gene flow between species members.
Thus, species located below major migration barriers are known to have a higher
frequency of genetic heterogeneity than the same species located above the barrier
(Echelle et al. 1976). This suggests that the displacement of native species by congeneric
endemics could occur due to greater genetic diversity-or plasticity- (Hocutt and
Hambrick 1973) when transported across migratory barriers.
The introduction of species into areas where congeneric natives are present can be
especially deteriorative to the native species (Hocutt and Hambrick 1973, Hlohowskyj
and White 1983, Ross 1986, Winston et al. 1991, Mack et al. 2000, Walser et al. 2000,
Perry et al. 2002). Niche partitioning and competitive interactions have been shown to be
rather complex within assemblages possessing multiple congeneric species (Paine et al.
1982). It is safe to assume that introductions to such environments would further
complicate, and possibly interrupt, ecological processes already in place. The
replacement of two cyprinid species above a Red River impoundment depicts a common
pattern. The superseding species were morphologically, chromatically, and ecologically
similar (Winston et al. 1991). Strong evidence links decreased ecological separation
between species with increased taxonomic distance (Ross 1986). Competition between
closely related species is probable due to the lack of evolutionary divergence and similar
habitat specialization (Hlohowskyj and White 1983). Congeneric species tend to be very
cross compatible, which raises concerns relating to the effects of heterospecific
reproductive interactions (Mooney and Cleland 2001).
13

Hybridization with introduced species is often given little attention but can be
very detrimental to cross compatible species in the host watershed (Harper et al. 1961,
Courtenay and Hensley 1980, Perry et al. 2002). Native species can experience reduced
fitness and a high chance of extinction due to the effects of hybridization with nonnative
species (Dowling et al. 1989). Genetic introgression can lead to functional extinctions,
reducing population numbers and genetic integrity to the point where a species plays no
practical role in ecosystem processes (Harper et al. 1961, Mooney and Cleland 2001,
Perry et al. 2002). Similar species with similar habitat preferences and spawning habitats
will have a high probability of hybridization (Mayden and Burr 1980). Nest associated
broadcast spawning is a reproductive characteristic of many shiner species (Schwartz
1972). Close proximity reproduction and temporal overlap in reproductive trials suggest
a high likelihood of hybridization (Mayhew 1983, Menzel 1978). Studies have revealed
that the effects of introgression may be greater in one species than the other (Dowling et
al. 1989, Eisenhour 1995). This seems to be especially true with rare species. The
potential for hybridization and introgression may be increased due to the difficulty a
species encounters in finding mates of their own species (Mayhew 1983, Dowling et al.
1989). Literature citing evidence of hybridization in shiner species include: Menzel
(1978), Burkhead (1983), Mayhew (1983), Dowling and Moore (1985), and Dowling et
al. (1989). In fact, the hybridizing capacity of shiner species has been documented as
being truly extensive (Schwartz 1972).
Invasive species populations can begin with a small number of individuals
(Simberloff 1986). However, a larger founder population will increase the probability of
establishment (Williamson and Fitter 1996). If small, introduced populations are to
14

persist, severity of environmental forces become very important (Mack et al. 2000). This
suggests that the probability of a species establishing in a new environment would
increase as the number of attempts increases (Williamson and Fitter 1996). This becomes
especially important when dealing with bait bucket introductions, as the numbers of
species escaping is often quite small.
Predators and pathogens can limit the ability of a susceptible invasive species to
inhabit an area (Kotler and Holt 1989, Mathur and Stein 1993, Humphries et al. 1999).
Selective predation was cited as one of the factors altering the abundance of two native
Notropis species in a lentic environment (Hartman et al. 1992). Pathogens can be cointroduced
with the non-indigenous species (Elton 1958, Li and Moyle 1981).
Documentation also exists linking introduced fish with the transfer of pathogens to
resident amphibians (Kiesecker et al. 2001). Environmental stressors derived from
ecological alterations can even impact the effects of parasites within the host community
(Lafferty and Kuris 1999).
The potential for an introduced species to colonize an area increases with the
amount of anthropogenic disturbance (Moyle 1986, Karr 1991, Winston et al. 1991,
Angermeier 1995, Mack et al. 2000, Perry et al. 2002). Artificial barriers, such as dams
and reservoirs, can alter biotic communities by providing a source of nonindigenous
species through stocking and bait-bucket introductions (Winston et al. 1991).
Alternatively, the deterioration of natural migratory barriers and the sophistication of
transportation will allow increased mixing of species over time (Elton 1958).
Consequently, the rate of introductions has increased sharply since the 1960’s (Courtenay
and Hensley 1980, Ross 1991, Mooney and Cleland 2001). The effects of ecosystem
15

alteration may reduce the habitat suitability essential for native species (Moyle 1986),
especially those sensitive to factors such as turbidity (Gilbert 1969a, Eisenhour 1995).
Rapid eutrophication was cited as a factor reducing the abundance of two native Notropis
species in a lotic environment (Hartman et al. 1992). Introduced species could capitalize
on released niche availability if they can survive in the host environment. Stream
turbidity has even been hypothesized to pose problems in mate recognition that may lead
to hybridization with congeneric species (Eisenhour 1995).
Review of Study Area/Related Studies
Available information is summarized concerning the species, watersheds, and
similar studies for that which this review was conducted. Although the study discussed
in Chapter 2 was designed to observe potential interactions which can occur between
native and nonnative species, the focal species were selected from the New River
drainage (specifically from the upper Greenbrier Watershed).
The New River system contains a relatively large number of endemic and
introduced species (Hocutt and Hambrick 1973, Cincotta et al. 1999, Wellman 2004,
Hocutt et al. 1978). Draining approximately 17,918 km 2 the New River flows through
the states of Virginia, North Carolina, and West Virginia (Stauffer et al. 1995). Parts of
the Blue Ridge, Ridge and Valley, and Appalachian Plateau geographical provinces are
transected. Several species are endemic to the upper New River system (Hubbs and
Trautman 1932, Hocutt et al. 1978, Jenkins and Burkhead 1994). These include the New
River shiner (Notropis scabriceps), the Kanawha darter (Etheostoma kanawhae), the
Kanawha minnow (Phenacobius teretulus), the Appalachia darter (Percina
16

gymnocephala), the bigmouth chub (Nocomis platyrhynchus) Bluestone sculpin Cottus
sp., albino cave sculpin Cottus sp., and the candy darter (Etheostoma osburni). Kanawha
Falls separates the upper Kanawha (New River) and lower Kanawha drainages. This
major fish migration barrier is a likely contributor to the large number of endemic species
in the New (McKeown et al. 1984). Fish species isolated above and below migratory
barriers at the time of formation could undergo speciation and genetically divergence
from ancestral species. Other authors documenting fish distributions throughout the New
River (and associated tributaries) within the borders of West Virginia include
Goldsborough and Clarke (1908), Hubbs and Trautman (1932),Jenkins et al. (1972),
Hocutt and Hambrick 1973, Hocutt et al. (1978 and 1979), Beckham (1980), Hess (1983),
Neves (1983), Lobb (1986), Easton et al. (1993), Jenkins and Burkhead (1993), Addair
(1994), Easton and Orth (1994), Stauffer et al. (1995), Cincotta et al. 1999, Messinger
and Hughes (2000), Paybins et al. (2000), Messinger and Chambers (2001), and Wellman
(2002).
The Greenbrier River, draining approximately 4000 km 2 , flows through the
Monongahela National Forest in the counties of Pocahontas and Greenbrier in West
Virginia (Hocutt et al. 1978). It ends its course as a tributary to the New River upstream
of Kanawha Falls after flowing southward along the eastern border of the state. The
Greenbrier River flows within the New River watershed and shares with it several
endemic species: Notropis scabriceps, Etheostoma osburni, Percina gymnocephala,
Phenacobius teretulus, and Nocomis platyrhynchus. However, it is also associated with
problems concerning that system. Approximately 50% of the New River fish species are
not native to the watershed (Wellman 2004). Many of these fishes are now established
17

in the upper Greenbrier River and occur sympatrically with native species of the same
family (Hocutt et al. 1978, Cincotta et al. 1999). Included in this group are non-game
species such as the telescope shiner (Notropis telescopus), silverjaw minnow (Ericymba
buccata), Roanoke darter (Percina roanoka), variegate darter (Etheostoma variatum),
whitetail shiner (Cyprinella galactura), fathead minnow (Pimephales promelas), and
spottail shiner (Notropis hudsonius).
The most prevalent theories concerning the mode of congeneric nonnative species
introductions into the Greenbrier River involve human facilitation. The arrivals of many
fishes were most likely due to bait-bucket introductions (Hocutt and Hambrick 1973,
Cincotta et al. 1999, Wellman 2004). Bait-buckets containing baitfish originating in
other watersheds could be inadvertently or purposefully dumped into the New River
drainage. Other authors have discussed the effects of bait-bucket introductions (Gilbert
1969b, Magnuson 1676, Moyle 1986, Sheldon 1988, Winston et al. 1991, Walser 2000).
A sequence of reintroductions and extirpations of two cyprinid species in the Red River
drainage in Oklahoma is likely the result of such events. Bait-bucket introductions,
providing a source for new individuals, are the likely causes of the sporadic appearances
of Notropis bairdi and Hybognathus placitus above the artificial Red River impoundment
(Winston et al. 1991). Adding to these inadvertent introductions, early management
strategies often included the stocking of game fish and baitfish into depauperate
watersheds (Magnuson 1976, Li and Moyle 1981, Sheldon 1988, Cincotta et al. 1999).
Congeneric species pairs are two species from the same genus and are therefore
similar with regards to both genetics and physical appearance. The following studies
discussed in this thesis will involve two congeneric pairs. The current status of the native
18

species and the fact that the nonnative species have been collected within the upper
Greenbrier River exemplifies the importance of these studies. Each of the following
nonnative congeners are, or are hypothesized to be, expanding their range in the upper
New River system.
The spotfin shiner, Cyprinella spiloptera, is native to the Greenbrier River
system, is a slow water generalist, and varies little in spatial and temporal habitat use
(Vadas 1992). Cyprinella spiloptera is often found in small to moderately large streams
over a variety of different substrates and tends to gather in pools along the banks of
streams (Gibbs 1957). The whitetail shiner, Cyprinella galactura, is native to the
Tennessee River drainage. This species is often found in rocky runs of small streams and
less frequently found in pools or riffles (Gibbs 1961). Cyprinella galactura has, at some
point, been introduced to the upper Greenbrier watershed, becoming increasingly
abundant after exhibiting minor initial populations (Wellman 2004). There is also
evidence of intergeneric hybridization of Cyprinella galactura with a threatened
confamiliar species (Burkhead 1983) and with Cyprinella spiloptera (Gibbs 1961).
The New River shiner, Notropis scabriceps, is endemic to the New River (Hocutt
et al. 1978). It is often found in sandy/rocky runs and flowing pools of small streams
(Jenkins and Burkhead 1994). The telescope shiner, Notropis telescopus, is native to the
Cumberland and Tennessee Rivers on the east side and the White, St. Francis, and Little
River drainages on the west side of the Mississippi River drainage (Gilbert 1969a). It
prefers clear, flowing waters of medium sized upland creeks and has been introduced and
established in the New River (Gilbert 1969a). Since being introduced to the New River
the telescope shiner has experienced widespread population increases and has become
19

ubiquitous, appearing in all channel units (personal observation). Similar preferred
temperatures of Notropis sabriceps and Notropis telescopus have been measured to be
19.3°C and 20°C respectively (Cherry et al. 1977, Shingleton et al. 1981).
Effort must be applied to gain understanding of the interactions that are occurring
between native and introduced species currently found in the upper Greenbrier watershed.
Field sampling and population analyses are not enough to quantify competitive
interactions and indicators of competitive exclusion among congenerics (Herbold and
Moyle 1986). Several studies have demonstrated the importance of interspecific
interactions on fish distributions through both horizontal and vertical spatial scales.
Natural and artificial environments were used to show that exploitation and interference
competition were important factors involved in regulating the distribution of three Cottus
species (Finger 1982). Space was determined to be the competitive dimension allowing
the coexistence of the three species. Field observations have been used to document the
spatial variation of eight cyprinid fishes and to make inferences on the role of habitat
segregation in structuring the community (Baker and Ross 1981). However, it has been
suggested that aquarium studies should be utilized to detect interspecific interactions
between potentially competing species (Simberloff 1981, Ross 1991). Observations of
six Ozark minnow populations indicated vertical stratification when individuals were
placed among congeneric or confamilial sympatric species (Gorman 1988). Overlaps of
water column positions suggest an overlap in the spatial aspect of pelagic minnow
species’ ecological niches (Baker and Ross 1981, Gorman 1988). Similarly, aquarium
studies can be used to detect shifted habitat usage as a consequence of introducing similar
nonnative species (Marchetti 1999). However, shifts in vertical distribution behavior of
20

cyprinid fishes due to introductions of nonnative congeners have been largely
overlooked.
The following laboratory study was designed to focus on the specific behavioral
interactions between the aforementioned species pairs to supplement current field studies.
Significant water column segregation suggests that congeners are partitioning niche
space, an effective behavior adapted to reduce competition and adverse interspecific
interactions in natural cyprinid guilds. Four 246 L aquaria and vertical water column
categories were used to quantify the vertical placement of these congener species under
two different trial conditions. Allotopic trials were conducted to quantify the “preferred”
water column position of each species before syntopic trials were conducted. Thus, the
allotopic positions were used for comparison against syntopic trials, where the congener
species were introduced into the same aquaria. The main objectives for this study were to
quantify differences in vertical habitat use of these species pairs under allotopic and
syntopic conditions and to quantify shifts in vertical habitat use that occur from syntopic
to allotopic conditions.
21

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29

Chapter 2: An Experimental Study of Vertical Habitat Use and Habitat Shifts in
Single-species and Mixed-species Shoals of Native and Nonnative Congeneric
Cyprinids
Abstract
Non-native fishes have multiple impacts on native fish communities, including
impacts associated with competition for space. Watersheds that are historically
depauperate of fish fauna, such as the New River in North Carolina, Virginia, and West
Virginia, are especially susceptible to invasions of non-native fishes. Over 50% of the
fish species currently found in the New River drainage are introduced, including Notropis
telescopus (telescope shiner) and Cyprinella galactura (whitetail shiner). Several studies
have documented vertical water column positioning as the primary mode of habitat
segregation of syntopic cyprinid species. Few studies, however, have examined the
effects of non-natives on vertical habitat use of native cyprinids. The primary objective
of this study was to quantify habitat shifts of two native species of the New River
drainage (Notropis scabriceps and Cyprinella spiloptera) in the presence of non-native
congeners (N. telescopus and C. galactura). Four 246 L aquaria and six vertical position
categories were utilized to experimentally examine shifts in water column positions.
Allotopic trials were conducted to quantify “preferred” positions of individual congener
species and used as controls for comparison with syntopic trials. Tests identified
differences in vertical distributions between allotopic combinations of congeneric pairs,
syntopic combinations of congeneric pairs, and single species allotopic versus syntopic
combinations. Congeneric species of each pair differed significantly in vertical habitat
use. Significant differences also occurred between allotopic and syntopic positions of all
species. Additionally, species of both pairs concomitantly shifted toward mid-water
30

categories. This finding suggests that when found syntopically, the two species
demonstrate some degree of integration similar to that of multi-species shoals. If
laboratory-observed patterns of species integration also occur in wild populations, then
competitive interactions will likely occur owing to the close association between native
and non-native species in the use of vertical habitat space. Additional studies are needed
to verify experimental findings in the natural environment of the Greenbrier River
system.
31

Introduction
Non-native fishes negatively impact native populations through multiple
pathways (Meffe 1985, Ross 1991, Mooney and Cleland 2001), including competition for
food or space (Hocutt and Hambrick 1973, Mathur 1975, Walser et al. 2000). Following
ecological theories of competitive exclusion (Hardin 1960), limiting similarity
(MacArthur and Levins 1967) and niche (Pielou 1972, Pianka 1974), competitive
interactions are expected between non-native species and closely-related native species.
Aquarium-based studies of vertical segregation in minnows have emphasized expected
similarities within behaviors and habitat use of closely-related species (i.e., an historical
ecology emphasis on phylogenetic constraints on habitat use, Gorman 1988, 1992). Also,
researchers have emphasized morphological correlates on use and segregation of habitats
among closely-related species, such as mouth position and its deterministic influence on
benthic, pelagic, or surface foraging (Mendelson 1975, Surat et al. 1982, Page and
Swofford 1984). Alternatively, some closely-related species integrate as mixed-species
shoals, such as minnows (Cyprinidae), and this strategy may improve foraging success or
predator avoidance (Mendelson 1975, Magurran and Pitcher 1983, 1987). Multispecific
aggregations suggest a historic legacy of strong behavioral relationships amongst
cyprinid guilds. Both mutual responsiveness and selective forces, required to reduce
competition and maintain species identity, are required for mixed-species shoals to
function (Mendelson 1975). However, little is known of the occurrence and
consequences of mixed-species shoals of native and non-native minnows. Given recent
conservation concerns of fish introductions and impacts of non-natives (Rahel 2000),
additional research needs focused on native/non-native species interactions.
32

Introductions of non-native fishes have increased dramatically within the past
century (Courtenay and Hensley 1980). Drainages with naturally low species diversity,
such as the New River drainage of North Carolina, Virginia, and West Virginia, have
typically incurred the largest numbers of introduced species (Jenkins and Burkhead
1994). The New River drainage not only has a high proportion of non-native fishes (over
50% nonnative, Wellman 2004), but also includes a diverse endemic fish fauna
(bigmouth chub Nocomis platyrhynchus, New River shiner Notropis scabriceps,
Kanawha minnow Phenacobius teretulus, Kanawha sculpin Cottus kanawhae, Bluestone
sculpin Cottus sp., albino cave sculpin Cottus sp., Appalachia darter Percina
gymnocephala, Kanawha darter Etheostoma kanawhae, and candy darter Etheostoma
osburni). Within the last half century, range distributions have decreased for many of
these New River endemics (Chipps 1993b, Cincotta et al. 1999, Burns 2007), but few
research efforts have focused on the relationship or non-relationship between a
concurrent increase in nonnative diversity (number of species and population sizes) and a
decrease in population sizes and range distributions of native species.
Many non-native fishes have recently expanded their distributional ranges within
the lower New River drainage and tributaries, such as the 4000 km 2 Greenbrier River
watershed of West Virginia, including whitetail shiner Cyprinella galactura, telescope
shiner Notropis telescopus, Roanoke darter Percina roanoka, rainbow darter Etheostoma
caeruleum, and variegate darter Etheostoma variatum (Wellman 2004). The fish fauna of
the Greenbrier River drainage includes seven of the nine New River endemics (excluding
Kanawha darter and Bluestone sculpin) and has relative high population sizes of two nonnative
minnows, telescope and whitetail shiner. The ecological influences of these non-
33

native cyprinids on their native congeners, New River shiner and spotfin shiner
Cyprinella spiloptera, are undocumented, but Burns (2007) estimated population sizes of
both introduced species to be greater than the native congeners in most Greenbrier River
sampling sites.
The objective of this aquaria-based experimental study was to quantify
interactions between two congeneric pairs of native (N. scabriceps and C. spiloptera) and
non-native (N. telescopus and C. galactura) cyprinids of the New River drainage. The
study was designed and conducted following discovery of population declines of N.
scabriceps and C. spiloptera in the presence of range expansions and population size
increases of the introduced N. telescopus and C. galactura.
Methods
Specimen collection and transport
I collected two species of native minnows (N. scabriceps and C. spiloptera) and
two species of their non-native congeners (N. telescopus and C. galactura) with a 1.5m x
3m x 0.3cm mesh seine from the East Fork Greenbrier River, North Fork Deer Creek,
Deer Creek, and Meadow Creek. Approximately 100 –130 adults of each species were
collected for transport to the laboratory with the following size ranges: N. scabriceps (55
– 82mm SL), N. telescopus (57 – 82mm SL), C. spiloptera (68 – 84mm SL), and C.
galactura (68 – 86mm SL). Fishes were transported from stream to laboratory in 189.3L
(50 gal) insulated coolers. Water during transport was aerated, salted (

Aquaria setup
In the laboratory, fishes were separated by species and transferred to aquaria and
holding tanks (with bottom substrates of < 6.4 mm diameter from the East Fork
Greenbrier River). Four 246 L (65 gal) glass aquaria (91.5 mm x 45.8 mm x 53 cm) and
two 379 L (100 gal) reservoirs were used as observation and holding tanks, and were all
connected in a recirculation system with a 379 L sump. The sump was connected to a
sequence pump that recirculated water to all aquaria and holding tanks at a rate of
approximately 2.6 L/min. Carbon filters, bio balls, substrate vacuum, fresh water
substitutions, and frequent monitoring were employed to maintain appropriate water
quality. Salinity levels were kept at 2-3 ppt and water temperature varied between 18.4 -
24°C throughout all trials. Fishes were fed daily with frozen bloodworms (genus
Glycera) and frozen brine shrimp (genus Artemia). Photoperiod was maintained with
florescent lights (plant bulbs) and an electric timer (14 hr light, 10 hr dark). Fishes were
given a minimum of one week acclimation time before data collection (but all individuals
were actively feeding within aquaria on the same day as transport).
Allotopic and syntopic experiments
Aquaria-based experiments were designed to examine vertical distribution shifts
of two native minnows (C. spiloptera and N. scabriceps) in response to the presence of
non-native congeners (C. galactura and N. telescopus). Water column positions of each
species within aquaria were observed separately (allotopic trials) and concomitantly for
each congeneric native/non-native species pair (syntopic trials). Six vertical categories
described positions of individual fishes within the water column of aquaria (similar to
that of Gorman 1988). Vertical position categories (each 8.5 cm high) were defined as
35

enthic, near-benthic, lower-pelagic, mid-pelagic, upper-pelagic, and surface pelagic
(Gorman 1988). Position locations of individual fishes were determined by horizontal
lines (8.5 cm intervals on white poster board) located on the backside of each aquaria.
For both Cyprinella and Notropis pairs, species were segregated into three groups
(20 individuals of each species in three separate tanks). Then, I conducted a total of nine
trials with a crossover-based design where each native species group of 20 individuals
was rotated with each congener group of 20 individuals and with each aquarium
(syntopic trials). As a control, the positions of 40 individuals were observed for each
species without the presence of its congener (allotropic trials). For allotopic trials, I used
one group (40 individuals total) of each Notropis species (total of two tanks) and two
groups (80 individuals total) of each Cyprinella species (total of four tanks). Fewer
Notropis groups in allotopic trials resulted from a lower number of available individuals
of N. scabriceps. The use of equal numbers of individuals of each species (n=20) within
tanks and equal numbers of individuals among tanks (n=40) controlled for effects of
disproportionate abundances.
Video cameras recorded individual positions during allotopic trials. Before data
collection, 45 minutes of tape elapsed to allow individuals to adjust to the video camera
and tripod. It was later realized, however, that camera recordings would not allow
adequate resolution of two species during syntopic trials. Therefore, a tarpaulin was
draped from the lab ceiling in front of aquaria to reduce observer effects, and individual
fish positions were viewed through rectangular slits in the tarpaulin. For camera
recordings and direct observations, individual fish positions were collected at least 30
seconds apart until 160 (allotopic) or 100 (syntopic) positions were recorded per trial.
36

Data were collected during periods of stationary positions of all individuals, and excluded
when individuals behaved abnormally or transitioned between vertical categories.
Separate chi-square tests examined difference in vertical distributions between the
syntopic pairs, allotopic trials, and syntopic-allotopic trials (alpha = 0.05). Modal peaks
(those categories in which species most frequently occurred) and modal counts (the
number of modal peaks of a category for a single species during 9 syntopic trials) were
determined by histograms for all trials.
Results
Notropis Congeners
Allotopic and syntopic trials supported a difference in vertical distributions
between N. scabriceps and N. telescopus. For allotopic trials, vertical distributions of
Notropis scabriceps were found in significantly lower (P < 0.05) categories than those of
Notropis telescopus (Table 1, Figure 1). The highest numbers of N. scabriceps occurred
in the 0 to 8.5 cm benthic zone (n=136) with the remaining individuals in the 8.5 to 17
cm near-benthic zone (n=24, Figure 1). For N. telescopus, the number of individuals was
distributed normally within the first 5 categories with the modal peak in the 17 to 25.5 cm
lower pelagic area (n=43, Figure 1). In 7 of the 9 syntopic trials, vertical distributions of
Notropis scabriceps were significantly lower (P < 0.05) than those of Notropis telescopus
(Table 1, Figure 2). Out of the nine trials, six modal counts of N. scabriceps in the
benthic zone occurred concomitantly with 6 modal counts of N. telescopus in the nearbenthic
zone. Notropis scabriceps had two modal counts in the near-benthic zone when
37

N. telescopus had modes in the lower-pelagic zone, and both species shared modal
numbers in the lower pelagic zone during a single trial.
For both Notropis species, vertical distributions differed significantly (P < 0.05)
between allotopic and syntopic trials (Table 1, Figure 3). The magnitude of difference
between allotopic and syntopic trials was largest for N. scabriceps. Specifically, N.
scabriceps was primarily benthically-positioned during allotopic trials (within benthic
and near benthic zones), but expanded its vertical position in the presence of N.
telescopus to include 17 and 5 percent of its occupancy within the lower pelagic and
pelagic zones, respectively. Vertical distribution expanded for N. scabriceps and
contracted in groups of N. telescopus. Hence, the two species shifted habitat and
integrated during syntopic trials. Despite integration during syntopy, the high power of
Chi-square tests supported significant separation of the two Notropis species.
Cyprinella Congeners
Cyprinella spiloptera and C. galactura differed in vertical distributions during
allotopic trials and segregated in 7 of 9 syntopic trials. For allotopic trials, vertical
distributions of C. spiloptera were found in significantly lower (P < 0.05) categories than
those of C. galactura (Table 2, Figure 1). During allotopic trials, C. spiloptera polarized
vertical distributions with the mode in the benthic zone (53% of individuals) and the
remaining majority (27%) in the surface-pelagic area (Figure 1). Cyprinella galactura
also had a modal peak in the benthic zone (60% of individuals) during the allotopic trials,
but had the next highest percent occurrences in the near benthic (21%) and pelagic (12%)
zones. In 7 of the 9 syntopic trials, vertical positions of C. spiloptera were significantly
38

higher (P < 0.05) than those of C. galactura (Table 2, Figure 2). Out of the nine trials, C.
spiloptera had modal counts in the benthic zone (n=3), the near-benthic zone (n=5) and
the middle pelagic zone (n=1), whereas counts of C. galactura peaked modally in the
benthic zone (n=6) and the near-benthic zone (n=2). Both species shared modal counts in
the benthic zone during 3 trials and in the near-benthic zone during one trial.
For both Cyprinella species, vertical distributions differed significantly (P < 0.05)
between allotopic and syntopic trials (Table 2). For C. spiloptera, the syntopic trials
revealed a shift toward mid-water column categories relative to the polarized use of
benthic and surface-pelagic zones during allotopic trials (Figure 3). Specifically, C.
spiloptera expanded its vertical distribution in the presence of C. galactura to include 27,
15, 10, and 5 percent of individuals within the near-benthic, lower-pelagic, pelagic, and
upper-pelagic zones, where the remainder occurred within benthic and surface pelagic
areas (32%). The allotopic and syntopic distributions of C. galactura differed
significantly (p < 0.05), and C. galactura shifted slightly toward pelagic positions in the
presence of C. spiloptera during syntopic trials. Hence, the two species shifted habitat
and integrated during syntopic trials.
Discussion
In this aquaria study, both congeneric pairs of Notropis species and Cyprinella
species significantly differed in vertical distributions within the water column, but the
magnitude of this difference was greatest between allotopic trials relative to that of
syntopic trials. Although allotopic trials supported interspecific segregation, syntopic
trials supported increased integration of vertical distributions. Although native and non-
39

native species pairs were partially segregated, species in syntopy interacted as a mixedgroup
without interspecific antagonistic behavior. Based on the concept of competitive
displacement and depending on a species’ generality of habitat use, one would expect a
reduced range of water-column distribution of a native species following the introduction
of a closely-related species (Pielou 1972). However, competitive displacement is not a
general rule in the ecology of fishes, and many studies have demonstrated coexistence of
closely-related species, as well as benefits of mixed-species shoals (Magurran and Pitcher
1983, 1987).
Water depths during normal flows within the upper Greenbrier River system are
greater than those available within the study aquaria, and therefore allow additional space
for segregation between the study species. Species integration, however, likely results
during periods of reduced water column depths during dry summers (Gorman 1988).
Thus, vertical position patterns may change during the low flows of summer, during a
time of competitive crunch (Wiens 1977). Our results suggest that within a water column
space of 51cm, N. scabriceps and N. telescopus rarely used space within 17 cm of the
surface. Therefore, these two species may be in close association during low and high
flows, although direct observational studies (such as snorkeling) are needed to quantify
interactions between the study species within the Greenbrier River drainage. Both C.
spiloptera and C. galactura used the upper water column position in the study aquaria,
and separation between these two species may increase within deeper habitats of the
Greenbrier River.
Vertical segregation between species in this experiment, consistent with a large
body of literature (Baker and Ross 1981, Gorman 1988, Chipps et al. 1993a), supports a
40

elationship between mouth position and habitat use in fishes. Benthic-oriented fishes
typically have inferior of subterminal mouths and pelagic fishes have terminal or
supraterminal mouth positions (Mendelson 1975). Notropis telescopus and C. spiloptera
were more pelagically-oriented, each having mouths that are more terminally-positioned
than their congeneric counterparts. Mouth position is generally viewed as a phylogenetic
or historical constraint, with a strong proximate influence on habitat use. Increased
integration during syntopy as reported in this study provides evidence of a strong species
interaction influence over morphologically-correlated use of habitat in cyprinids.
In contrast to segregation by competitive displacement, studies have documented
integration through mixed-species shoals (Magurran and Pitcher 1983, 1987, similar to
mixed-species flocks of birds, Morse 1970). Previous interspecific contact may not be
required for two species, such as a native/non-native species pair, to closely-associate and
benefit symbiotically from interactions, such as by improved foraging success (Magurran
and Pitcher 1983) or by predator avoidance (i.e., safety in numbers, Allan and Pitcher
1986, Mathis and Chivers 2003). Based on general observations during my experiments,
the more pelagically-oriented species of each pair fed more aggressively during syntopic
trials, hence, there was no qualitative evidence for a mixed-shoal advantage of foraging
for both species. The number of individuals per tank in allotopic trials (n = 40) was equal
to that of syntopic trials, so the data do not support evidence for an influence of density
on syntopic integration, as one would expect from a “safety in numbers” explanation of
predator avoidance.
In conclusion, the laboratory-based experimental study demonstrates a difference
in vertical use of habitat between two native/non-native congeneric pairs. The
41

interspecific separation of vertical habitat use (as found in allotopic trials) decreased
during syntopic trials owing to an increase in interspecific integration. Based on concepts
of competition, I expected segregation during syntopy as a mechanism to reduce
competitive interactions. Integration of species during syntopic trials, however, may be
interpreted as a predator avoidance behavior associated with mixed-species shoals. It is
unknown if the native/non-native species of this study integrate and co-occur in mixedspecies
shoals within the Greenbrier River system. Recent population assessments
indicate disproportionate population sizes of these native and non-native minnows
(Chipps et al. 1993b, Burns 2007), and additional research is needed to compare
experimental results with native/non-native interactions occurring within the Greenbrier
River drainage.
42

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45

Table 1. Results of Chi square Tests for Independence for Notropis congeners, N. scabriceps (Ns) and N.
telescopus (Nt). P values < 0.05 indicated significant vertical differences between species.
Group with
Tank Ns Group Nt Group P value higher vertical N
tank position
Allotopic trials
1 & 2 A A P < .0001 Nt 320
Syntopic trials
1 A A P < .0001 Nt 200
2 B B P < .0005 Nt 200
3 C C P < .0001 Nt 200
1 C B P < .0001 Nt 200
2 A C P < .0166 Nt 200
3 B A P < .6997 — 200
1 B C P < .0001 Nt 200
2 C A P < .0031 Nt 200
3 A B P < .3900 — 200
Allotopic and syntopic trials combined
1–3
Allotopic A vs.
Syntopic A - C
— P < .0001 Syntopic 320
1–3 —
Allotopic A vs.
Syntopic A - C
P < .0001 Allotopic 320
46

Table 2. Results of Chi square Tests for Independence for Cyprinella congeners, C. spiloptera (Cs) and C.
galactura (Cg). P values < 0.05 indicate significant vertical differences between species.
Group with
Tank Cs Group Cg Group P value higher vertical N
tank position
Allotopic trials
1, 2, 3 &
4 A & B A & B P < .0001 Cs 320
Syntopic trials
1 A A P < .3400 — 200
2 B B P < .0028 Cs 200
3 C C P < .6301 — 200
1 C B P < .0001 Cs 200
2 A C P < .0024 Cs 200
3 B A P < .0111 Cs 200
1 B C P < .0003 Cs 200
2 C A P < .0059 Cs 200
3 A B P < .0107 Cs 200
Allotopic and syntopic trials combined
1–4
Allotopic A &
B vs. Syntopic
A - C
— P < .0001 Syntopic 320
1–4 —
Allotopic A &
B vs. Syntopic
A - C
P < .0355 Syntopic 320
47

Total Number of Occurrences
160
140
120
100
80
60
40
20
0
Allotopic Notropis 120
100
80
60
40
20
0
1 2 3 4 5 6
Allotopic Cyprinella
1 2 3 4 5 6
Vertical Position Categories
Figure 1. Relationship between allotopic vertical positions of Notropis and Cyprinella
congeners. Gray bars represent native species while hollow bars represent non-native species. P
values of all allotopic trials are displayed in Tables 1 and 2.
48

Notropis
Cyprinella
60
Tank 1 (Rep 1)
60
Tank 1 (Rep 1)
40
40
20
20
0
0
60
40
20
Tank 2 (Rep 1)
80
60
40
20
Tank 2 (Rep 1)
0
0
60
Tank 3 (Rep 1)
40
Tank 3 (Rep 1)
40
20
20
0
0
Total Number of Occurrences
80
60
40
20
0
60
40
20
0
60
40
20
0
Tank 1 (Rep 2)
Tank 2 (Rep 2)
Tank 3 (Rep 2)
60
40
20
0
40
20
0
40
20
0
Tank 1 (Rep 2)
Tank 2 (Rep 2)
Tank 3 (Rep 2)
60
Tank 1 (Rep 3)
40
Tank 1 (Rep 3)
40
20
20
0
0
60
40
20
0
60
40
20
Tank 2 (Rep 3)
Tank 3 (Rep 3)
60 Tank 2 (Rep 3)
40
20
0
40 Tank 3 (Rep 3)
20
0
1 2 3 4 5 6 1 2 3 4 5 6
0
Vertical Position Categories
Figure 2. Relationship between vertical placements of Notropis and Cyprinella congeners
during all syntopic trials and tank replications. Gray bars represent native species while
hollow bars represent non-native species. P values of all trials are displayed in Tables 1 and 2.
49

Total Number of Occurrences
160
140
120
100
80
60
40
20
0
80
60
40
N. scabriceps
N. telescopus
100
80
60
40
20
0
120
100
80
60
C. spiloptera
C. galactura
20
40
20
0
0
1 2 3 4 5 6 1 2 3 4 5 6
Vertical Position Categories
Figure 3. Relationship between allotopic and syntopic vertical positions of all Notropis and
Cyprinella congeners. Syntopic data were scaled down to fit the number of observations
accumulated in allotopic trials. Gray bars represent allotopic trends while hollow bars represent
syntopic trends. P values of all allotopic and syntopic trials are displayed in Tables 1 and 2.
50