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\begin{document}

\title{Changes to the trophic structure of a desert fish community following
river regulation and species turnover: implications for an endangered
top predator}



\author[1]{Eliza I. Gilbert}%
\author[1]{Nathan Franssen}%
\affil[1]{US Fish and Wildlife Service Southwest Region}%


\vspace{-1em}



  
  \date{May 27, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
A poor understanding of factors leading to species decline can result in
inefficient or ineffective species restoration. Endangered Colorado
Pikeminnow ( \emph{Ptychocheilus lucius)} was nearly extirpated from the
San Juan River, NM, USA and recent efforts to reestablish the species
via hatchery augmentation of juveniles has yet to reach the targeted
number of adults in the system. To assess how changes to the river's
food web could be limiting reestablishment of this top predator, we used
stable isotope (\selectlanguage{greek}δ \selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ \selectlanguage{english}\textsuperscript{15}N)
signatures of the fish community pre- (museum specimens) and post river
regulation with coincident extirpations and invasions. Following river
regulation, four of five community-wide trophic structure metrics used
to quantify resource use diversity were reduced and species turnover
likely had little effect per se. For species sampled in both time
periods, shared trophic resources generally increased (mean niche
overlap = +35.7\%). However, Colorado Pikeminnow experienced a large
decrease in niche breadth (-72\%) and diet mixing models suggested a
shift from piscivory towards insectivory in contemporary collections.
Our results suggested an overall reduction in basal resource
availability after river regulation. We suggest increased reliance on
similar resources may be limiting fish prey for Colorado Pikeminnow,
ultimately contributing to the slow and limited reestablishment in the
San Juan River. This study adds to the growing body of knowledge
provided by museum specimens and stable isotope analyses to identify
food-web dynamics that are a departure from historical conditions which
can provide novel information critical to imperiled species management
in modified systems.%
\end{abstract}%



\sloppy


\textbf{Changes to the trophic structure of a desert fish community
following river regulation and species turnover: implications for an
endangered top predator}

Running title: Fish community trophic changes following historic habitat
alteration

Eliza I. Gilbert\textsuperscript{1} and Nathan R.
Franssen\textsuperscript{2}

\textsuperscript{1} U.S. Fish and Wildlife Service, New Mexico
Ecological Services Field Office, San Juan River Basin Recovery
Implementation Program, Albuquerque, NM 87113.

\textsuperscript{2} U.S. Fish and Wildlife Service, New Mexico
Ecological Services Field Office, Albuquerque, NM 87113.

Correspondence to: E.I. Gilbert, U.S. Fish and Wildlife Service, New
Mexico Ecological Services Field Office, San Juan River Basin Recovery
Implementation Program, Albuquerque, NM, USA. Email:
egilbert24@gmail.com

\emph{Acknowledgements}

We thank the New Mexico Department of Game and Fish for funding
contemporary tissue collection and stable isotope analysis. The U.S.
Fish and Wildlife Service funded historical tissue collection and stable
isotope analyses. This work would not have been possible without
specimen curation by the Division of Fishes at the Museum of
Southwestern Biology at the University of New Mexico. We would like to
specifically acknowledge the Curator of Fishes, Dr. Thomas Turner and
the Collections Manager Emily DeArmon for permission and assistance in
collecting tissue samples. We would also like to thank Scott Durst for
helpful comments on a previous version of the manuscript.

\textbf{Abstract}

A poor understanding of factors leading to species decline can result in
inefficient or ineffective species restoration. Endangered Colorado
Pikeminnow (\emph{Ptychocheilus lucius)} was nearly extirpated from the
San Juan River, NM, USA and recent efforts to reestablish the species
via hatchery augmentation of juveniles has yet to reach the targeted
number of adults in the system. To assess how changes to the river's
food web could be limiting reestablishment of this top predator, we used
stable isotope (\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N)
signatures of the fish community pre- (museum specimens) and post river
regulation with coincident extirpations and invasions. Following river
regulation, four of five community-wide trophic structure metrics used
to quantify resource use diversity were reduced and species turnover
likely had little effect per se. For species sampled in both time
periods, shared trophic resources generally increased (mean niche
overlap = +35.7\%). However, Colorado Pikeminnow experienced a large
decrease in niche breadth (-72\%) and diet mixing models suggested a
shift from piscivory towards insectivory in contemporary collections.
Our results suggested an overall reduction in basal resource
availability after river regulation. We suggest increased reliance on
similar resources may be limiting fish prey for Colorado Pikeminnow,
ultimately contributing to the slow and limited reestablishment in the
San Juan River. This study adds to the growing body of knowledge
provided by museum specimens and stable isotope analyses to identify
food-web dynamics that are a departure from historical conditions which
can provide novel information critical to imperiled species management
in modified systems.

\textbf{Keywords}

Retrospective, river regulation, stable isotope, resource use

\textbf{1 \textbar{} INTRODUCTION}

No ecosystem has escaped human alteration and a poor understanding of
factors leading to species decline can result in inefficient or
ineffective species restoration (Craig \emph{et al} ., 2017; Roni
\emph{et al} ., 2018). For riverine ecosystems, major anthropogenic
alterations occurred in the 20th century through dam construction,
concomitant flow regulation, and establishment of nonnative fishes; all
which contributed to the imperilment of many native fishes (Burkhead,
2012; Kominoski \emph{et al} ., 2017; Lamothe and Drake, 2018). In
certain cases, the primary cause of imperilment can be directly linked
to nonnative fish predation (Vander Zanden \emph{et al} . 1999; Pelicice
and Agostinho, 2009; David, 2017). In other cases when there has a poor
understanding of ecosystem dynamics prior to severe habitat and species
alteration, researchers may find it difficult to identify initial causes
of native species declines, determine the extent to which they can be
reversed, and assess trade-offs in recovery efforts (Cochran-Biederman
\emph{et al} ., 2015; Thurstan, 2022). Such knowledge gaps can also lead
to extensive management efforts such as habitat manipulation (e.g.,
increasing structural complexity, mimicking variable flows, and
reestablishment of floodplain connection) and nonnative species control
that may not necessarily restore ecosystem processes needed to
reestablish imperiled species if efforts are not sufficient to address
proximate causes of population declines (Booth, 2016; Albertson, 2018).

Limited trophic resource availability is a potential proximate cause of
some species' declines but changes to food-web dynamics can be difficult
to isolate and quantify (Naiman \emph{et al} ., 2012; Albertson \emph{et
al} ., 2018; Booth, 2016; Thoms and DeLong, 2018). The difficulty arises
because changes in food-web dynamics can be mediated by synergistic
indirect abiotic (habitat homogenization and fragmentation) and biotic
(reduced prey diversity and abundance or competition with nonnative
species) effects from river regulation and fish community compositional
changes (Naiman \emph{et al} ., 2012; Booth, 2016; Haubrock, 2018).
Nevertheless, trophic resource use studies have the capacity to increase
our understanding of changes in riverine food-web dynamics although
there is a scarcity of unaltered systems for comparison (Turner \emph{et
al} ., 2015; McManamay \emph{et al} ., 2018; Vander Zanden, 2003). In
certain instances, species or habitat compositional gradients can be
used to make comparisons but these studies are not able to detect a
departure from conditions prior to severe alterations, which might
identify trophic resources that supported a more stable ecological
system (Haubrock \emph{et al} ., 2018; Rogosch and Olden, 2020;
Pennock\emph{et al} ., 2021). However, with the availability of museum
specimens, use of stable isotopes, and advances in Bayesian statistical
analyses, methods exist to use a hypothesis-driven framework to detect
departures from a historical condition and changes to food-web dynamics
that may underly the continued imperilment of native fishes
(Turner\emph{et al.} , 2015; Alp and Cucherousset, 2022).

The Colorado River Basin is a well-known example of a riverine ecosystem
whose 20\textsuperscript{th} century alteration resulted in the
imperilment of many native fishes, including the system's historical top
predator Colorado Pikeminnow (\emph{Ptychocheilus lucius} )
(Tyus\emph{et al} ., 1982; Minckley et al. 2003). In the San Juan River
subbasin, Colorado Pikeminnow was nearly extirpated by the 1990s (Ryden
and Ahlm, 1996; Ryden, 2003). However, 20 years of conservation
management that included mimicking a more-natural hydrograph from the
most upstream reservoir, intensive removal of large-bodied nonnative
fishes, and a hatchery augmentation program that stocked over 5 million
juvenile fish, reestablished Colorado Pikeminnow (Franssen \emph{et al}
., 2016). Yet, the current Colorado Pikeminnow adult population is
relatively small because age-specific survival rates of stocked fish are
low (Clark \emph{et al} ., 2018). A significant contribution to these
low survival rates seems unlikely to be driven by nonnative fish
predation as neither Colorado Pikeminnow nor more common fishes,
responded positively to intensive nonnative fish removal (Franssen
\emph{et al} ., 2014); possibly because the most abundant large-bodied
nonnative fish, Channel Catfish (\emph{Ictalurus punctatus} ), is not
highly piscivorous (Hedden \emph{et al} ., 2021; Pennock \emph{et al} .,
2021; Hedden\emph{et al} ., 2022). Additionally, attempts to mimic a
more-natural hydrograph have been hampered by increased aridity in the
San Juan River basin (Pennock \emph{et al} ., 2022).

Given piscivorous Colorado Pikeminnow likely benefit from a robust fish
prey base (Vanicek and Kramer, 1969), some of the slow and limited
reestablishment of the species to the San Juan River could be due to
trophic deficiencies caused by river regulation and species turnover
(Franssen \emph{et al} ., 2007). To assess this hypothesis, we used
Bayesian methods to conduct stable isotope analyses of the river's fish
community prior to and after river regulation that was coincident with
species compositional changes. To isolate the effects of species
turnover, we quantified changes to community-wide trophic structure
metrics (diversity of assimilated basal resources, food chain length, as
well as overall resource use diversity, similarity, and distribution)
with and without the inclusion of extirpated and new invasives. We then
calculated changes in trophic niche overlap for fish species present
before and after river regulation to explore potential changes in
resource competition. To better understand any changes in both
community-wide trophic structure metrics and niche overlap, we
quantified changes in trophic dispersion (niche breadth). Finally, we
inferred specific changes in trophic resource use of Colorado Pikeminnow
between time periods using an isotopic diet mixing model.

\textbf{2 \textbar{} METHODS}

\textbf{2.1 \textbar{}} \textbf{Study system - river regulation and fish
community changes}

The San Juan River is the second largest tributary in the Colorado River
Basin (Thompson, 1982) and has undergone severe hydrological alteration
and fragmentation (Figure 1). Construction of Glen Canyon Dam in 1957 on
the Colorado River created Lake Powell inundating lower reaches of the
San Juan River. The upper reaches were further fragmented by Navajo Dam,
completed in 1962; and altered the river's natural flow regime by
limiting spring peak flows and elevating summer base flows (Propst and
Gido, 2004). Currently, the San Juan River consists of approximately 360
km of riverine habitat. In the 1990s, river ecologists began
highlighting the importance of a river's annual peak discharge in
creating fish habitat as high flows can create and maintain fish habitat
through increased channel heterogeneity (Poff, 1997; Van Steeter and
Pitlick, 1998). This research supported the establishment of Navajo Dam
flow recommendations developed to mimic the timing, frequency, and
duration of the San Juan River's natural hydrology albeit at reduced
magnitudes (Holden, 1999; Pennock \emph{et al} ., 2022). Although Navajo
Dam operators attempted to meet these flow recommendations, continued
significant deviations from the natural hydrograph and the establishment
of nonnative vegetation likely continued to simplify and narrow the
river's channel which precluded inundation of the floodplain
(Gido\emph{et al} ., 2013; Bassett, 2015; Franssen \emph{et al} .,
2015).

The naturally depauperate San Juan River fish community experienced
compositional changes prior to and after river regulation. Nonnative
Channel Catfish (\emph{Ictalurus punctatus} ) was stocked into the
Colorado River Basin for food and recreation in the late 1800s and is
the second most abundant large-bodied fish in the San Juan River
(Franssen \emph{et al} ., 2016, Fuller and Neilson, 2022). Common
small-bodied nonnative fishes like Fathead Minnow (\emph{Pimephales
promelas} ) occupied the system prior to the closure of Navajo Dam but
Red Shiner (\emph{Cyprinella lutrensis} ), which is often the most
abundant small-bodied fish, likely established a population in the 1980s
(Franssen \emph{et al} ., 2015; Nico \emph{et al} ., 2022; accession
records University of New Mexico Museum of Southwestern Biology
{[}MSB{]}). The native fish community consists of five large-bodied
endemic Colorado River Basin species: Bluehead Sucker (\emph{Catostomus
discobolus} ), Flannelmouth Sucker (\emph{Catostomus latipinnis} ),
endangered Razorback Sucker (\emph{Xyrauchen texanus} ), Roundtail Chub
(\emph{Gila robusta} ), and endangered Colorado Pikeminnow
(\emph{Ptychocheilus lucius} ). The remaining two native species are
small-bodied Speckled Dace (\emph{Rhinichthys osculus} ) and Mottled
Sculpin (\emph{Cottus bairdii} ). Although there are no data on fish
abundances prior to construction of Navajo Dam, monitoring of an
application of a lethal chemical treatment downstream of Navajo Dam in
the 1960s indicated the most common species collected in this location
were Flannelmouth Sucker and Roundtail Chub (Olson, 1962). Due to a lack
of natural recruitment, populations of Colorado Pikeminnow and Razorback
Sucker only persist in the San Juan River through ongoing hatchery
augmentation and Roundtail Chub is functionally extirpated
(Franssen\emph{et al} ., 2016).

\textbf{2.2 \textbar{} Fish tissue collection}

To assess changes to the trophic structure of the San Juan River's fish
community, we obtained fish tissue for isotopic analysis from a
historical period that was just prior to closure of Navajo Dam (1959 to
1961) and a contemporary period, which comprised the years 2003 -- 2014.
We attained historical samples (\textasciitilde{}0.5 g of white muscle)
from fish accessioned to MSB (supplemental material) and used
raft-mounted electrofishing and seines to collect contemporary samples
(see Franssen \emph{et al} ., 2015 for details). Contemporary tissue
samples consisted of white muscle, except for Colorado Pikeminnow and
Channel Catfish. For these species, we sampled approximately 5
mm\textsuperscript{2} of tissue from the caudal fin. In addition to
contemporary fishes, we sampled riffles and backwaters for invertebrates
from the Order Ephemeroptera (\textasciitilde{}2.5 mg dry mass;
Franssen\emph{et al} ., 2019). All contemporary tissue samples were
preserved in table salt in the field and rinsed before processing
(Arrington and Winemiller, 2002). Apart from historical Colorado
Pikeminnow, we only included species with a sample size of 10 or more.
To help control for ontogenetic trophic changes within species and
between periods, we restricted the minimum size of fishes analyzed to 50
mm total length (TL) and the maximum to that available from MSB (Table
1). All samples were dried at 60\selectlanguage{ngerman}ºC for at least 24 hours before being
homogenized into powder via a mortar and pestle.

\textbf{2.2 \textbar{} Stable isotope analysis}

We analyzed fish and invertebrate samples at the Stable Isotope Mass
Spectrometry Laboratory at Kansas State University, Manhattan, KS, USA,
and the Center for Stable Isotopes at the University of New Mexico,
Albuquerque, NM, USA. Isotopic values were standardized between
laboratories using tetramin® fish food for isotopic calibration and we
reported results using the common delta notation (\selectlanguage{greek}δ \selectlanguage{english}%0\selectlanguage{english}) calculated by:

\selectlanguage{greek}δ \selectlanguage{english}%0 \selectlanguage{english}= {[}(R\textsubscript{sample}/R\textsubscript{standard}) -- 1){]} \selectlanguage{ngerman}×
10\textsuperscript{3}.

We pre-processed data prior to analyses by removing obvious outliers
(i.e., \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C or \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N values more than
two standard deviations from taxon-specific means). Due to differences
in Colorado Pikeminnow and Channel Catfish tissue types sampled between
time periods (i.e., muscle tissue from historical samples and fin tissue
from contemporary samples), we used mean fin-to-muscle conversions. For
Colorado Pikeminnow (\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C = -1.29 and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N = +0.56), we used the conversion from
Franssen\emph{et al} . (2016) and for Channel Catfish
(\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C = -1.08 and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N = +0.58), we
used Maitland (2020). Additionally, we corrected museum specimens for
the effects of formalin preservation which depletes
\textsuperscript{13}C by 1.0 %0 and enriches\textsuperscript{15}N by 0.53
%0 (Edwards \emph{et al} ., 2002). Finally, variable lipid concentration
can introduce bias into isotopic analyses because they are more depleted
in \textsuperscript{13}C than proteins and carbohydrates (Post \emph{et
al} ., 2007). Therefore, we corrected \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values by
the ratio of C:N in samples following Post \emph{et al} . (2007) using
the formula:

\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C\textsubscript{corrected} =
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C\textsubscript{raw} - 3.32 + 0.99 \selectlanguage{ngerman}× C:N

\textbf{3 \textbar{} DATA ANALYSIS}

\textbf{3.1 \textbar{} Community-wide trophic structure metrics}

We assessed trophic structure change between the historical and
contemporary San Juan River fish community using five community-wide
metrics derived to quantify and test ecologically relevant hypotheses
related to food webs (Layman \emph{et al} ., 2007; Table 2). These
metrics included: \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C range (CR),
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N range (NR), centroid distance (CD), nearest
neighbor distance (NND), and standard deviation of the nearest neighbor
distance (SDNND). Ranges of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N are simple metrics that measure the diversity of
assimilated basal resources and food chain length, respectively.
Centroid distance quantifies a food web's overall resource use diversity
and is calculated as the Euclidian distance from each species' mean
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N to the global centroid
(i.e., the mean \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N value
for all species). Nearest neighbor distance (NND) is a measure of the
trophic similarity among species and is the mean of the shortest
Euclidian distance between each species' \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N mean. A food web with a smaller NND suggests
trophic ecologies are similar and redundant among species while a larger
NND indicates more divergent trophic niches. We also calculated the
standard deviation of the NND (SDNND) because it is less influenced by
sample size than NND. A comparably lower SDNND suggests differences in
species' trophic niches in a food web are more evenly distributed.

To assess differences in the five community-wide trophic structure
metrics between the two periods, we used the R package
\emph{SIBER}(Jackson \emph{et al} ., 2011) which employs a
Bayesian-based Markov Chain Monte Carlo (MCMC) algorithm to produce
posterior probability distributions for each metric of interest using
observed \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N values. To
produce these distributions, we used two chains of 4,000 iterations,
discarded the first 1,000 iterations, included vague priors (a normal
distribution for the mean and an inverse Wishart distribution for
sigma), and tested for model convergence using the Gelman-Rubin ratio
(R-hat) using the R package \emph{coda} (Gelman and Ruben, 1992; Jackson
\emph{et al} ., 2011). All R-hat were \textless{}1.01. For each metric,
we then calculated the probability the difference between historical and
contemporary period trophic metric was greater than zero by subtracting
posterior probability distributions and quantified the percent of the
resultant distribution that was greater than zero. To isolate effects of
species turnover on changes to the trophic structure of the community,
we analyzed the community with (all species sampled) and without species
turnover (only the core species present in both time periods).

\textbf{3.2 \textbar{} Core species niche overlap and dispersion}

For species present before and after river regulation (core species), we
calculated species pairwise trophic overlap (i.e., niche overlap) to
quantify potential changes in resource competition. We used the R
statistical package \emph{nicheROVER} which employs a Bayesian framework
to estimate the directional probability that a randomly drawn individual
of one species overlaps into the niche of another in
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N space (Swanson\emph{et
al} ., 2015; Lysy \emph{et al} ., 2021). We used a resampling routine of
10,000 draws to randomly sample from each species pair, maintained
\emph{nicheROVER} 's default priors (flat
Normal-Independent-Inverse-Wishart distribution), and assessed model
convergence (all R-hat \textless{}1.01). From each species' directional
niche overlap posterior probability distribution, we then calculated the
probability the difference between time periods was greater than zero.

To identify potential changes in the diversity of trophic resources used
by individual core species (i.e., collected in both time periods), we
employed the \emph{SIBER} package which uses a Bayesian method to
calculate standard ellipses areas corrected for small sample sizes
(SEA\textsubscript{B}) from observed \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N (Jackson \emph{et al} ., 2011). We calculated
SEA\textsubscript{B} because it can be interpreted as a species' core
isotopic niche breadth and because ellipses contain 40\% of the sample,
the metric can be used when samples sizes differ between populations
(Jackson \emph{et al} ., 2011; Layman \emph{et al} ., 2012). Although
SEA\textsubscript{B} corrects for small samples, samples size
\textless{} 10 are prone to underestimates (Jackson \emph{et al} .,
2011). Therefore, we included historical Colorado Pikeminnow (n = 6) in
our analysis with the understanding that the
SEA\textsubscript{B}estimates could be artificially low. We incorporated
the same MCMC algorithm parameters used to calculate fish community-wide
trophic structure metrics and assessed model convergence (all R-hat
\textless{}1.01). To assess whether niche dispersion differed for each
core species, we calculated the probability the difference between
historical and contemporary SEA\textsubscript{B} posterior probability
distributions were greater than zero using the same procedure described
above.

\textbf{3.3 \textbar{} Colorado Pikeminnow diet composition}

To estimate Colorado Pikeminnow contemporary and historical diet
composition, we used a Bayesian stable isotope mixing model in the R
package \emph{MixSIAR} (Stock \emph{et al} ., 2018). We used this model
to estimate the posterior probability distributions of the proportion
each fish and invertebrate prey contributed to Colorado Pikeminnow's
isotopic signatures. The model accounts for uncertainty resulting from
multiple prey items, variation in signatures among prey and the
predator, and isotopic fractionation (trophic discrimination factors)
between predator and prey. However, for the mixing model to be
informative, isotope signatures among prey items need to be
statistically dissimilar (Stock \emph{et al} ., 2018). Therefore, we
first estimated isotopic differences in prey items using two Bayesian
ANOVAs (one for \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and one for
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N) with vague priors and assessed significant
differences using posterior credible intervals with the R
package\emph{brms} (B\selectlanguage{ngerman}ürkner, 2017). All prey items except Flannelmouth
Sucker and Speckled Dace were dissimilar by at least one isotope for
both time periods but we kept all species separate with the
understanding that Flannelmouth Sucker and Speckled Dace posterior
probability distributions would be similar and less uniquely
informative. We excluded Channel Catfish as potential prey because a
laboratory feeding study suggested it is unlikely to greatly contribute
to Colorado Pikeminnow's diet (Gilbert \emph{et al} ., 2018).

Because we lacked historical invertebrate samples, we used contemporary
invertebrate samples to estimate historical invertebrate isotopic
values. To do so, we assumed a mean isotopic shift in invertebrates from
the contemporary to historical period but retained the variability
observed in contemporary samples. Following this assumption, we
estimated historical invertebrate \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N values by calculating the mean difference of
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N between periods for
known invertivorous fishes (Flannelmouth Sucker, Speckled Dace, and
Fathead Minnow) and then subtracted this from each contemporary
invertebrate isotope value (mean value shift of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C =
+0.32 and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N = +3.14).

We used one mixing model for each time period to assess changes to the
resource use of Colorado Pikeminnow. To complete input data for each
mixing model, we used separate trophic discrimination factors (mean and
standard deviation) for potential fish prey ([?]\textsuperscript{13}C =
0.82 \selectlanguage{ngerman}± 0.10 and \selectlanguage{english}[?]\textsuperscript{15}N = 2.76 +- 0.35) and invertebrates
(\selectlanguage{english}[?]\textsuperscript{13}C = 0.83 +- 0.29 and \selectlanguage{english}[?]\textsuperscript{15}N = 2.93
+- 0.23) as estimated by Franssen \emph{et al} . (2017). Priors for the
proportion of prey in the diet for each model included 0.05 for
invertebrates with the remaining proportion distributed evenly among
fish prey species. We chose these prior probabilities because the most
comprehensive Colorado Pikeminnow diet study suggested the species
converts entirely to piscivory by 150 mm TL (Vanicek and Kramer, 1969),
although a more recent stable isotope analysis suggested invertebrates
contributed to the diet of fish as large as 300 mm TL (Franssen \emph{et
al} ., 2019). We computed each mixing model with three chains of
3,000,000 iterations, discarded the first 200,000, and thinned chains by
retaining every 100\textsuperscript{th} draw (Stock \emph{et al} .,
2018). We again determined model convergence (all R-hat \textless{}1.01)
and report predicted posterior distributions of proportional
contributions of each prey item to the diet of Colorado Pikeminnow
between time periods. As with all prior analysis, we assessed changes
between periods by subtracting posterior probability distributions of
interests to determine the probability the difference was greater than
zero.

\textbf{4 \textbar{} RESULTS}

From each period we were able to obtain tissue for
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N analysis from six San
Juan River fishes. Sample sizes for each species were smaller for the
historical (n range = 6 -- 13) compared to the contemporary period (n
range = 23 -- 385) but the size range of each species sampled was
similar (Table 1). Overall, the global mean \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N of
fishes increased from 9.36%0 (SD = 1.35) to 12.76%0 (SD = 1.43) between
periods (Figure 2). Mean \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C of fishes demonstrated
less change with the historical mean of -22.67%0 (SD = 1.33) compared to
the contemporary mean of -22.74%0 (SD = 0.96).

\textbf{4.1 \textbar{} Community-wide trophic structure metrics}

Analysis of the fish community's trophic structure suggested an overall
reduction of trophic resource use following river regulation with a
limited amount due to species turnover (Table 2). With probabilities
\textgreater{} 0.90, core fish species experienced reductions in both
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C (27.2\% decrease in \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C range)
and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N (28.7\% decrease in \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N
range), assimilated less diverse trophic resources (26.2\% decrease in
CD), and niches became more similar (27.9\% decrease in NND). When
including all species, the reduction in basal resource assimilation
(\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C range) decreased by 32.9\%. The establishment of
Red Shiner likely contributed to retaining the food chain length
(probability of change in \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N range = 0.55) as it
assimilated the lowest \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N values (mean
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N = 11.0, SD = 1.5%0; Table1 and Figure 2). However,
most of the reduction (probability [?] 0.92) in degree of trophic
diversity (CD) and niche similarity (NND) between time periods was due
to factors other than species turnover as the average difference in the
percent change between all and core species for these trophic metrics
was 4.15\%. The only community-wide trophic structure metric that did
not change for either core (probability = 0.65) or all species
(probability = 0.67) was the standard deviation in nearest neighbor
distances (SDNND).

\textbf{4.2 \textbar{} Core species niche overlap and breadth}

Most species demonstrated an increase in the overlap of their niche into
another between time periods. Of the 20 species pairs, 16 had a
probability [?] 0.89 of an increase in their niche overlap (Table 3).
Between periods and among all species, mean niche overlap increased by
35.7\%. For a given species, increases in niche overlap was highest for
Channel Catfish (mean = 51.3\%), followed closely by Colorado Pikeminnow
(49.5\%) and Speckled Dace (46.3\%); whereas Fathead Minnow (25.4\%) and
Flannelmouth Sucker (6.1\%) showed limited increases in niche overlap.
For Colorado Pikeminnow, the largest niche overlap increase was into the
niche of Fathead Minnow (67.3\%) and the least was into Channel Catfish
(37.3\%). For these nonnative fishes, niche overlap into Colorado
Pikeminnow did not likely change between time periods (Fathead Minnow =
0.25 and Channel Catfish = 0.63 probability).

With a probability [?] 0.90, the niche breadth of four of the five core
species changed between the historical and contemporary period (Table
4). Species with the largest niche breadth declines were Colorado
Pikeminnow (72\%) and Speckled Dace (33\%). Whereas Flannelmouth Sucker
niche breadth likely increased by 165\% and Fathead Minnow by 126\%. A
change in niche breadth was least likely (probability = 0.81) for
Channel Catfish. Between periods and among species, the largest core
niche breadth was historical Colorado Pikeminnow
(SEA\textsubscript{B}mean = 7.59 and 95\% CI = 3.29 -- 17.04). Colorado
Pikeminnow's niche breadth may have been greater than all other
historical species analyzed as only the size of Speckled Dace's niche
breath slightly overlapped (3.00, 1.72 -- 5.31). The smallest historical
niche breadth observed was Channel Catfish (1.25, 0.73 -- 2.15) followed
closely by Roundtail Chub (1.29, 0.71 -- 2.33). In the contemporary
period, the largest niche breadth occurred in Flannelmouth Sucker (5.31,
3.49 -- 8.08), followed by two species that had similar sized niche
breadth, Red Shiner (4.32, 3.64 -- 5.14) and Fathead Minnow (4.31, 3.07
-- 5.97). Contemporary Channel Catfish continued to have the smallest
niche breadth (1.58, 1.35 -- 1.85).

\textbf{4.2 \textbar{} Colorado Pikeminnow diet composition}

Isotopic biplots between Colorado Pikeminnow and potential prey items
corrected for trophic discrimination suggested our analysis incorporated
most potential prey items (Figure 3). The mixing models resulted in
substantial predicted overlap in the proportion each diet item was
consumed within periods (Figure 4). However, Colorado Pikeminnow
demonstrated a predicted increase in invertebrate consumption
(probability = 0.94) from a historical median of 2.4\% (95\% CI = 0.0 --
30.5\%) to a contemporary median of 24.9\% (18.1 -- 33.2\%). The diet
mixing models predicted Red Shiner (median = 28.4\%, 95\% CI = 10.6 --
41.6\%) took the place of Fathead Minnow (29.0\%, 2.7 -- 68.6\%) as the
mostly highly consumed fish prey. Consumption of Flannelmouth Sucker and
Speckled Dace, which was difficult to distinguish due to similar isotope
values, averaged \textasciitilde{} 18\% for each species and consumption
by Colorado Pikeminnow may not have changed between periods
(probabilities of 0.68 and 0.73, respectively). Prior to its extirpation
and similar to other native potential prey, Roundtail Chub was predicted
to have contributed \textasciitilde{}18\% (median = 17.9\%, 1.5 --
53.7\%) to Colorado Pikeminnow's diet.

\textbf{5 \textbar{} DISCUSSION}

By comparing historical and contemporary food webs in the San Juan
River, we gained insight into trophic relationships among species, which
supports a prior hypothesis that resources could be limiting the
reestablishment of Colorado Pikeminnow in this modified system
(Franssen\emph{et al} ., 2007; Franssen \emph{et al} ., 2019). Our
results indicate the fish community reduced its overall trophic resource
use, potentially increasing competition for resources, and Colorado
Pikeminnow experienced a reduction in resource use likely due to a shift
to feeding lower in the contemporary food web. Together, these results
suggest trophic resource availability may be reducing prey fish
populations, and in conjunction with the absolute loss of Roundtail
Chub, could be hindering Colorado Pikeminnow's ability to completely
transition to piscivory and limit their ability to persist in the San
Juan River.

Our results are consistent with other studies that demonstrated
decreased resource use by fishes following river regulation
(DeLong\emph{et al} ., 2011; Turner \emph{et al} ., 2015; Thoms and
DeLong, 2018). Here we were also able to identify species turnover per
se (loss of Roundtail Chub and addition of Red Shiner) as having a
limited effect on this trophic contraction. The reductions in trophic
resource diversity could stem from the loss of upstream inputs, limited
floodplain exchange, and overall habitat simplification which can reduce
primary basal and secondary consumer diversity and abundance
(Vannote\emph{et al} ., 1980; Junk \emph{et al} ., 1989; Turner \emph{et
al} ., 2015; Ward \emph{et al} ., 2002; Winemiller \emph{et al} ., 2010;
Zeni and Casatti, 2014). Additionally, deviations of the natural flow
regime can shift macroinvertebrate communities (Bunn and Arthington,
2002), potentially altering sources of carbon incorporated into the food
web (e.g., relative abundance of allochthonous shredders vs.
autochthonous scrapers). The changes we observed in the San Juan River
fish community's trophic structure indicated resource sharing increased
which has the potential to affect population dynamics of native fishes.

Results assessing changes to trophic niche overlap indicated competitive
interactions among all species potentially intensified between time
periods. Invertebrate size, abundance, and diversity can substantially
decrease after dam construction and all fishes included in our analysis
likely forage on invertebrates at some period of their lifetime (Bunn
and Arthington, 2002; Zeni and Casatti, 2014; Caldwell \emph{et al} .,
2018). While changes to the San Juan River invertebrate community are
unknown, if invertebrate numbers are insufficient, competition for this
prey could reduce overall fish abundances (Van Poorten \emph{et al} .,
2018). Indeed, the densities of invertivorous Flannelmouth Sucker,
Bluehead Sucker, Speckled Dace, and Red Shiner have declined in the San
Juan River over the last two decades following ongoing deviations from
the natural flow regime (Pennock \emph{et al} ., 2022). Given the
surprising and significant increase in niche overlap by Colorado
Pikeminnow into all other species, this may also be indicative of a
paucity of fish prey given their presumed piscivorous nature (Vanicek
and Kramer, 1969; Franssen \emph{et al} ., 2007; Franssen \emph{et al}
., 2019). Bioenergetics modeling assessing production and current fish
prey abundances could be a useful path forward in quantifying the
ability of the system to support Colorado Pikeminnow, however, to be
information such modeling may need to include ontological prey
preferences and Colorado Pikeminnow predation rates.

Competition for resources can cause intraspecific individual
specialization (Ara\selectlanguage{ngerman}újo et al. 2011; Bolnick et al. 2010), which may
explain some trophic dispersion changes of fishes between time periods.
Two trophic generalists, Flannelmouth Sucker and Fathead Minnow, able to
consume algae and detritus in addition to invertebrates increased their
relative niche breadth (i.e., standard ellipse area) between time
periods. Although this diet flexibility could be advantageous in
situations where resources are limited, if specialization is towards
resources that are less energetically efficient, population abundances
could decline (Floeter \emph{et al} ., 2004). Colorado Pikeminnow and
Speckled Dace deceased their diversity of resource use, which could be
in response to environmental change because they are habitat (Speckled
Dace; Gido \emph{et al} ., 1997) or trophic (Colorado Pikeminnow;
Vanicek and Kramer, 1969) specialists. Thus, these species may be unable
to adapt when trophic resources when they become limited (Bolnick
\emph{et al} ., 2010; Araújo \emph{et al} ., 2011; Sanchez-Hernandez
\emph{et al} ., 2021).

Results from the stable isotope mixing models suggested Colorado
Pikeminnow shifted towards increased insectivory in the current food
web. Although we introduced uncertainty into our finding by estimating
isotopic variation of historical invertebrates, we think our results are
plausible because complete piscivory has been documented for
wild-spawned Colorado Pikeminnow \textgreater{}150 mm TL elsewhere in
the Colorado River Basin (Vanicek and Kramer, 1969) and the
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N signature of the two largest historical Colorado
Pikeminnow sampled here also indicated high piscivory rates.
Additionally, contemporary consumption of invertebrates was described in
a previous investigation where the diet of Colorado Pikeminnow 100 --
350 mm TL in the San Juan River was estimated to be
\textasciitilde{}25\% invertebrates (Franssen \emph{et al} ., 2019).
However, due to similar isotopic signatures among prey fishes, modeled
results had relatively high levels of uncertainty. Further insights into
prey consumption through stomach analysis may be required to identify
potential prey preferences of Colorado Pikeminnow and confirm the
relatively high predicted consumption of invertebrates in the current
food web.

Combined, cur results suggest Colorado Pikeminnow fed on relatively few
fish prey contemporarily compared to historic conditions possibly due to
reduced prey fish abundances. Although historical fish prey abundances
that supported Colorado Pikeminnow in the San Juan River are unknown, a
shift to greater insectivory could have implications for growth and
survival of stocked individuals that infrequently recruit to the adult
life stage (Clark \emph{et al} ., 2018; Franssen \emph{et al} ., 2019).
For piscivorous fishes like Colorado Pikeminnow, the ability to move
through ontogeny from an invertebrate diet to more energetically
efficient fish prey is necessary for rapid growth (Mittelbach and
Persson, 1998) and subsequent survival (Nilsson and Br\selectlanguage{ngerman}önmark, 2000;
Persson \emph{et al} ., 1996).

For piscivores like Colorado Pikeminnow, the establishment of some
nonnative species could be useful in subsidizing a reduced prey base
(Boltovskoy \emph{et al} ., 2018; Maerz \emph{et al} ., 2005). For
example, our mixing models suggested Colorado Pikeminnow consumed a
significant quantity of nonnative Fathead Minnow in both periods and
nonnative Red Shiner in the contemporary period. Increased densities of
these small-bodied nonnative fishes have been correlated with higher
body condition in Colorado Pikeminnow suggesting they could be an
important food source (Osmundson \emph{in review} ). Thus, managers may
need to consider how reductions in these prey species could impact the
availability of trophic resources for Colorado Pikeminnow.

\textbf{6 \textbar{} CONCLUSIONS}

Given the lackluster success of reintroducing extirpated fish
populations from hatchery broodstock (Cochran\selectlanguage{english}-Biederman \emph{et al} .,
2015; Lamothe and Drake, 2019), managers will undoubtedly need to
identify ways to improve factors that contributed to initial (and
current) population declines to make long-term conservation progress.
Here, we address this challenge by identifying and quantifying the
relative influence of continued and new stressors on the conservation of
an imperiled species. Our study suggests that further assessing whether
contemporary prey abundances are limiting the establishment of Colorado
Pikeminnow in the San Juan River is an important next step in
identifying requisite management actions under continued river
regulation and native species loss. This study further contributes to
the growing understanding of trophic structure changes that may occur
following river regulation (e.g., DeBoer \emph{et al} . 2022;
DeLong\emph{et al} . 2011; DeLong \emph{et al.} 2021; Thoms and DeLong,
2018; Turner \emph{et al} ., 2015).

\textbf{DATA AVAILABILITY STATEMENT}

The data that support the findings are available from the corresponding
author upon request.

\textbf{ORCID}

Eliza I. Gilbert http://orcid.org/0000-0003-0426-4065

Nathan Franssen https://orcid.org/0000-0002-4401-7838

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\textbf{Tables}

Table 1. The number (n), size range (total length), and bulk
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N isotope mean and
standard deviation values of fishes and invertebrates sampled from the
San Juan River, USA during a historical (H: 1959-1961) and contemporary
(C: 2003-2014) period. Size data for contemporary \emph{Pimephales
promelas} were not collected but were likely \textless{}100 mm TL.\selectlanguage{english}
\begin{longtable}[]{@{}llllllllll@{}}
\toprule
\begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
Species\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
Species code\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
H (n)\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
Size (mm)\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
C (n)\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
Size (mm)\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C\strut
\end{minipage} & \begin{minipage}[b]{0.10\columnwidth}\raggedright\strut
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Catostomus latipinnis}\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
CATLAT\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
52-128\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-24.7 (0.7)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10.0 (0.9)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
23\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
48-100\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-22.6 (1.8)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
12.3 (1.5)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Cyprinella lutrensis}+\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
CYPLUT\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
134\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
20-65\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-22.9 (1.5)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
11.0 (1.5)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Gila robusta}\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
GILROB\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
11\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
89-119\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-22.6 (1.4)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
9.5 (1.7)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Ictalurus punctatus}+\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
ICTPUN\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
13\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
62-295\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-23.4 (0.5)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10.8 (0.8)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
282\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
45-300\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-21.9 (0.9)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
11.7 (0.9)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Pimephales promelas}+\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
PIMPRO\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
53-68\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-25.6 (1.2)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
8.7 (0.5)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
37\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-24.3 (1.8)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
11.9 (1.5)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Ptychocheilus lucius}\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
PTYLUC\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
6\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
170-590\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-22.5 (1.8)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10.9 (1.7)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
385\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
170-560\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-21.7 (0.8)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
13.2 (0.9)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\emph{Rhinichthys osculus}\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
RHIOSC\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
13\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
51-81\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-24.0 (2.2)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
10.3 (1.9)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
70\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
50-80\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-24.3 (1.7)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
11.9 (1.3)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
Ephemeroptera\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
INVERT\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
40\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
-26.4 (2.3)\strut
\end{minipage} & \begin{minipage}[t]{0.07\columnwidth}\raggedright\strut
8.1 (2.3)\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

+ Nonnative species

Table 2. Community-wide trophic metrics derived by Layman \emph{et al} .
(2007) for the historical (1959 -- 1961) and contemporary (2003-2014)
San Juan River fish community: \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C range (CR),
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N range (NR), centroid distance (CD), nearest
neighbor distance (NND), and standard deviation nearest neighbor
distance (SDNND). Values are posterior probability distribution means,
percent change of those means, and probability the difference between
the posterior probability distributions was greater than zero.\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
\begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Metric and description\strut
\end{minipage} & \begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Community composition\strut
\end{minipage} & \begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Historical\strut
\end{minipage} & \begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Contemporary\strut
\end{minipage} & \begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Percent change\strut
\end{minipage} & \begin{minipage}[b]{0.16\columnwidth}\raggedright\strut
Difference Probability\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CR - diversity of basal resources\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
All species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.52\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.69\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-32.9\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.97\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Core species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.32\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.69\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-27.2\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.91\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
NR - food chain length\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
All species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.72\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.83\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
4.0\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.55\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Core species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2.72\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.94\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-28.7\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.98\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
CD - degree of trophic diversity\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
All species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.17\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.89\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-23.9\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.99\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Core species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.07\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.79\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-26.2\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.98\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
NND - niche similarity\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
All species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.14\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.89\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-21.9\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.92\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Core species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
1.11\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.80\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-27.9\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.93\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
SDNND - distribution of similarity\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
All species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.35\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.38\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
8.6\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.67\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Core species\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.38\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.34\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
-10.5\%\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
0.65\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

Table 3. Historical (1959-1961) and contemporary (2003-2014) mean 95\%
niche overlap calculated from posterior probability distributions
derived from \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N obtained
from fish present in the San Juan River, USA during both periods. Mean
distribution difference is the mean of the difference between posterior
probability distributions and probability of difference is the
likelihood the difference in the distributions was greater than zero.
Species codes are presented in Table 1.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Core species pairs and niche overlap direction\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Historical mean 95\% niche overlap\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Contemporary Mean 95\% niche overlap\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Mean distribution difference\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
Probability of difference\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PTYLUC into CATLAT\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
40.6\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
89.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
51.3\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.99\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PTYLUC into RHIOSC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
20.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
61.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
42.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PTYLUC into ICTPUN\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
23.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
60.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
37.3\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PTYLUC into PIMPRO\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
12.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
79.1\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
67.3\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
CATLAT into PTYLUC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
83.1\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
47.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
-34.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.03\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
CATLAT into RHIOSC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
42.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
50.9\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.1\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.73\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
CATLAT into ICTPUN\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
25.1\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
50.8\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
25.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.94\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
CATLAT into PIMPRO\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
37.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
71.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
33.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.96\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
RHIOSC into PTYLUC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
48.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
71.3\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
23.6\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.92\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
RHIOSC into ICTPUN\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
40.8\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
81.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
40.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.99\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
RHIOSC into CATLAT\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
50.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
92.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
42.6\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.99\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
RHIOSC into PIMPRO\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
16.9\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
94.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
78.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
ICTPUN into PTYLUC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
67.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
77.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
10.2\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.63\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
ICTPUN into CATLAT\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
49.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
98.9\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
48.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.94\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
ICTPUN into RHIOSC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
34.8\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
93.9\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
59.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
ICTPUN into PIMPRO\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
11.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
97.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
87.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PIMPRO into PTYLUC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
60.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
39.9\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
-19.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.25\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PIMPRO into CATLAT\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
45.8\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
73.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
27.5\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
0.89\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PIMPRO into ICTPUN\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
5.4\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
46.0\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
41.1\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
PIMPRO into RHIOSC\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
6.8\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
58.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
52.7\strut
\end{minipage} & \begin{minipage}[t]{0.17\columnwidth}\raggedright\strut
1.00\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

Table 4. Historical (1959 -- 1961) and contemporary (2003-2014) mean
Bayesian standard ellipse area corrected for small samples sizes
(SEA\textsubscript{B}) calculated from San Juan River fish tissue
analyzed for stable isotopes \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N. For species present during both periods,
SEA\textsubscript{B} percent change and probabilities the difference in
posterior distributions was greater than zero are presented.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
Species & Historical & Contemporary & Percent change & Probability of
difference\tabularnewline
\midrule
\endhead
\emph{Catostomus latipinnis} & 2.02 & 5.31 & 165\% & 0.99\tabularnewline
\emph{Pimephales promelas}\textsuperscript{+} & 1.88 & 4.31 & 126\% &
0.99\tabularnewline
\emph{Ictalurus punctatus}\textsuperscript{+} & 1.25 & 1.58 & 23\% &
0.81\tabularnewline
\emph{Rhinichthys osculus} & 3.00 & 1.98 & -33\% & 0.90\tabularnewline
\emph{Ptychocheilus lucius} & 7.59 & 2.12 & -72\% & 0.99\tabularnewline
\emph{Gila robusta} & 1.29 & & &\tabularnewline
\emph{Cyprinella lutrensis}\textsuperscript{+} & & 4.32 &
&\tabularnewline
\bottomrule
\end{longtable}

\textsuperscript{+} Nonnative species

\textbf{Figures}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Figure 1. The San Juan River between Navajo Reservoir and Lake Powell
located within the San Juan River Subbasin (inset dark grey), part of
the Colorado River Basin (inset light grey).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

Figure 2. Stable isotope specimen values (individual dots) and standard
ellipse areas calculated using 95\% confidence intervals derived from
fish tissue collected in the San Juan River, USA. Species codes are
presented in Table 1.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

Figure 3. Bi-plots of the mean and standard error (\selectlanguage{ngerman}±1) of stable isotope
values derived from Colorado Pikeminnow (grey dots) and prey tissue
sampled from the San Juan River, USA. Prey values are corrected for
trophic discrimination and species codes are presented in Table 1.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

Figure 4. Scaled posterior density estimates of prey contributions to
the historical (1959-1961) and contemporary (2003-2014) diet of San Juan
River Colorado Pikeminnow constructed using the stable isotopes
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C and \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{15}N. Species codes are
presented in Table 1.

\selectlanguage{english}
\FloatBarrier
\end{document}

