Southeastern Naturalist
473
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
22001155 SOUTHEASTERN NATURALIST 1V4o(3l.) :1447,3 N–4o8. 33
Muskrat Predation of Native Freshwater Mussels in Shoal
Creek, Alabama
Andrew J. Edelman1,*, John Moran2, Timothy J. Garrabrant1,
and Kaley C. Vorreiter1
Abstract - Widespread decline of native freshwater mussels has increased their susceptibility
to extinction from environmental factors such as competition, disease, and predation.
Mammals, in particular Ondatra zibethicus (Common Muskrat), are well documented as
major predators of freshwater mussels. We assessed the impact of Common Muskrats on the
native freshwater-mussel community in Shoal Creek, AL. We surveyed 12.7 km of Shoal
Creek for signs of mussel predation by Common Muskrats. Based on the species composition
of observed shell middens, Common Muskrats foraged on all 6 native mussel species
in Shoal Creek, including federally listed threatened and endangered species (Hamiota altilis
[Finelined Pocketbook] and Pleurobema georgianum [Southern Pigtoe], respectively).
Common Muskrats appeared to feed on native mussels based on their natural availability
rather than exhibiting strong size-selective predation.
Introduction
Freshwater mussels are some of the most diverse and endangered fauna in the
continental US (Williams et al. 1993). This group has experienced a drastic decline
in abundance and diversity over the last century (Bogan 1993, Downing et
al. 2010). As a result, of the known freshwater-mussel species in the US, 6% are
extinct, ~25% are federally listed as endangered or threatened, and 50% are considered
species of special conservation concern (Williams et al. 1993, 2008). The
southeastern US is considered a region of high diversity for freshwater mussels
within North America and hosts 94% of US species and 95% of federally protected
species (Lydeard and Mayden 1995, Williams et al. 2008).
Decline of freshwater mussels is due to a variety of influences including habitat
modification, invasive species, loss of host fish, pollution, and overharvesting (Bogan
1993, Downing et al. 2010, Williams et al. 1993). These factors have caused
some freshwater-mussel populations to be composed mainly of older individuals
with reduced reproductive output that are restricted to short stream reaches (Williams
et al. 2008). The combination of these pressures has lowered the long-term
viability of many freshwater-mussel populations, exposing them to increased likelihood
of extinction caused by environmental factors such as competition, disease,
and predation that typically are not a grave threat to the persistence of healthy
populations (Downing et al. 2010, Williams et al. 1993). Localized predation may
contribute to the decline of isolated freshwater-mussel populations (Kopij 2011,
1Department of Biology, University of West Georgia, Carrollton, GA 30118. 2National
Forests in Alabama, US Forest Service, Montgomery, AL 36107. *Corresponding author -
aedelman@westga.edu.
Manuscript Editor: Roger D. Applegate
Southeastern Naturalist
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
474
Neves and Odom 1989). Freshwater mussels are predated by a variety of mammalian
species including Neovison vison (Schreber) (American Mink), Procyon lotor
L. (Northern Raccoon), Lontra canadensis (Schreber) (Northern River Otter), and
Ondatra zibethicus L. (Common Muskrat) (Williams et al. 2008). In particular,
Common Muskrats (hereafter referred to as Muskrats) are well-documented as major
predators of freshwater mussels, the effects of which are easily studied because
they leave extensive midden piles of empty shells (Bovbjerg 1956, Diggins and
Stewart 2000, Erickson 2001, Evermann and Clark 1920, Haag 2012, Hersey et
al. 2013, Hoggarth et al. 1995, Lacki et al. 1990, Neves and Odom 1989, Owen
et al. 2011, Tyrrell and Hornbach 1998, Watters 1995, Zahner-Meike and Hanson
2001). Muskrats are usually considered herbivores, but can feed heavily on freshwater
bivalves in certain ecosystems or when fresh vegetation is seasonally scarce
(Evermann and Clark 1920, Hersey et al. 2013, Lacki et al. 1990, Zahner-Meike and
Hanson 2001). While healthy populations of mussels can often sustain high levels
of predation, the effect of predation on endangered mussels can lead to further decline
(Haag 2012, Hoggarth et al. 1995, Kopij 2011, Neves and Odom 1989).
Our objective was to assess the scope of Muskrat predation on an isolated
community of native freshwater mussels in Shoal Creek, AL, by examining shell
remains in Muskrat middens. The freshwater-mussel community in Shoal Creek,
similar to many other southeastern US rivers, is fragmented by lake impoundments
and has been invaded by Corbicula fluminea (Müller) (Asiatic Clam). Six native
freshwater mussel species inhabit Shoal Creek, and most of them are considered
species of conservation concern (Dolloff et al. 2012, Mirarchi et al. 2004): federally
endangered Pleurobema georgianum (Lea) (Southern Pigtoe), federally threatened
Hamiota altilis (Conrad) (Finelined Pocketbook), and 3 Alabama state species
of conservation concern including Strophitus connasaugaensis (Lea) (Alabama
Creekmussel), Villosa nebulosa (Conrad) (Alabama Rainbow), and V. umbrans
(Lea) (Coosa Creekshell). Villosa vibex (Conrad) (Southern Rainbow) also inhabits
Shoal Creek, but is not of conservation concern (Dolloff et al. 2012). Significant
predation of freshwater mussels by Muskrats in Shoal Creek has been anecdotally
documented during stream surveys (Warren et al. 2004). In addition, native mussel
species at this locality are impacted by the fragmented nature of the river system,
which may decrease genetic diversity and recruitment within each segment. Both
of the federally protected species in Shoal Creek are highly localized in their distribution
and require intact river systems for long-term survival (Dolloff et al. 2012,
Williams et al. 2008). We expected that Muskrats in Shoal Creek would selectively
feed on the larger species and individuals as reported in other studies (reviewed in
Owen et al. 2011).
Field-Site Description
Our study system, Shoal Creek, is ~32 km long and drains an area of 122 km2
in Cleburne and Calhoun counties, AL. The Shoal Creek watershed is primarily
forested, and except for a 4-km segment at its mouth, is almost completely contained
within the Shoal Creek Ranger District of the Talladega National Forest.
Southeastern Naturalist
475
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
Four public roads cross Shoal Creek, and the Pinhoti Trail and Pine Glen Recreation
Area occur along its banks. Within the Talladega National Forest, there are
3 free-flowing, but fragmented segments of Shoal Creek created by man-made
impoundments (Fig. 1): (1) above Sweetwater Lake (10 km in length), (2) between
Sweetwater Lake and Highrock Lake (9.6 km in length), and (3) between Highrock
Lake and Whiteside’s Mill Lake (5.5 km in length). Villosa nebulosa, V. umbrans,
and V. vibex have been documented in all 3 segments of Shoal Creek. Strophitus
connasaugaensis and H. altilis are only known to occur in the 2 upper segments
Figure 1. Location of sampled Muskrat middens along Shoal Creek, AL. The winter/spring
stream survey extent is marked by the thick, black line.
Southeastern Naturalist
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
476
of Shoal Creek from Highrock Lake to above Sweetwater Lake, whereas P. georgianum
only occurs between Sweetwater and Highrock lakes (Dolloff et al. 2012,
Warren et al. 2004).
Methods
We visually searched for signs of mussel predation by Muskrats at Shoal Creek
during 2 survey periods (summer and winter/spring). One day each month during
the summer period, we surveyed a stretch of Shoal Creek beginning at the Forest
Road 500 crossing near the Pine Glen Recreation Area and traveling upstream (n =
3 surveys, conducted on 20 June, 16 July, and 24 August 2012). The survey on 20
June 2012 extended 1.2 km upstream, and the 16 July and 24 August 2012 surveys
extended 650 m upstream (Fig. 1). The summer survey period occurred as part
of a larger monitoring effort of the mussel population in association with bridge
construction at the road crossing near the Pine Glen Recreation Area. The summer
survey period was relatively informal (we did not map locations) and consisted of
1 person (J. Moran) walking along the streambed and collecting any observable
predated native mussels (paired valves only). We collected only native species and
recorded neither the number of middens nor the number of shells in middens during
the summer survey period.
The winter/spring survey period occurred periodically from 14 December 2012
to April 6 2013, during which we inspected a 12.7-km stretch of Shoal Creek from
3.2 km upstream of Highrock Lake to just below Coleman Lake (Fig. 1). At these
survey locations, Shoal Creek is considered a second-order stream with widths of
~5–8 m (Dolloff et al. 2012). Unlike the summer survey, we inspected each stream
stretch only once during the winter/spring survey. For the winter/spring survey period,
we developed a more formalized survey methodology and included multiple
simultaneous observers. We surveyed by walking line transects with observers
spaced ~2–3 m apart along the stream channel. We proceeded slowly upstream as
a group while visually searching for mussel-shell middens along the immediate
stream banks, partially submerged and emerged logs and rocks, and streambed
(Erb and Perry 2003, Zahner-Meike and Hanson 2001). We bypassed deep pools
due to our inability to see the streambed. All observers wore polarized sunglasses
to reduce glare and used view buckets to look at promising locations under the water
surface. When a shell midden was identified, we centered one to four 0.25-m2
quadrats on the site (number of quadrats depended on size of area covered by the
midden) and collected all visible, empty shells within each quadrat (both native and
invasive species). We mapped all shell-midden locations using a global positioning
system (GPS) receiver.
We identified to species all shells collected during the summer and winter/spring
survey periods and measured the length on the longest shell-axis. In addition, for
shells collected during the winter/spring surveys, we classified shells as either recent
or older predation events (e.g., intact periostracum and shiny nacre indicated
recent event), and examined them for signs of predation (e.g., broken shells and
incisor and claw marks). Muskrats typically feed on mussels by inserting their
Southeastern Naturalist
477
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
incisors between the valves and prying upward leaving characteristic teeth and
claw marks. This action can break the shell of thinner-shelled mussel species, but
leaves thicker-shelled species intact (Dillon 2000, Erb and Perry 2003, Haag 2012,
Zahner-Meike and Hanson 2001). Given that older predated shells were difficult to
identify to species, we only used recently predated shells (as described above) in
all analyses of the winter/spring survey period. To avoid counting individuals more
than once in the winter/spring survey period, we assigned unpaired valves a value
of 0.5 in all counts. We quantified prey selection of Muskrats during the winter/
spring survey period by examining Manly’s selection and standardized selection ratios
(Manly et al. 2002) for native mussel species. We calculated the selection ratio
(wi) as the proportion of the species eaten divided by the proportion of the species
available. If wi > 1, then the species was eaten more than expected by availability,
and less than expected if wi < 1. The standardized selection ratio (β, ranges from
0 to 1) usually provides a less-biased estimate, and we calculated it as wi divided
by the sum of wi for all species. For each species, we compared β to the baseline
value (1 divided by the number of species) to determine if a species was over-
(β > baseline) or under-utilized (β < baseline). We determined the availability and
distribution of shell lengths of native species in Shoal Creek based on a previous
survey for live mussels conducted on the same stream segments in 2011 (Dolloff et
al. 2012). We pooled data from the Dolloff et al. (2012) survey for both the quantitative
and qualitative surveys at all sites. We tested for evidence of prey selection
overall with a log-likelihood chi-squared test and for each species by examining
Bonferroni-corrected 95% confidence intervals for selection ratios (Manly et al.
2002). We employed R package adehabitatHS software (Calenge 2006) to conduct
the selection analysis. We compared the frequency distributions of shell lengths
(paired valves only) between the winter/spring survey period and the Dolloff et al.
(2012) survey data with a 2-sample Kolmogorov-Smirnov test to determine if sizeselective
predation occurred. Previous surveys of Shoal Creek have demonstrated
that mussel abundance is highly variable in this study system even in spatially
adjacent sites (Dolloff et al. 2012). Thus, given the less-rigorous survey methodology
and more spatially restricted nature of the summer-survey period which likely
contributed to a less-representative sample, we did not compare these data directly
with the winter/spring survey period data or the Dolloff et al. (2012) survey data.
Results
Summer survey period
During the summer survey period, we found 54 shells in June, 23 shells in July,
and 67 shells in August. In general, we frequently found larger-sized predated
mussels in piles on top of submerged and emerged large rocks and logs. We often
found smaller-sized mussel shells in scattered piles located in shallows (less than 20 cm
water depth) with a mix of small gravel and sand substrates that appeared to have
been recently disturbed. We collected predated shells from 6 native mussel species
(Table 1) with the federally endangered and threatened species (H. altilis and
P. georgianum) accounting for about 15% and the state species of conservation
Southeastern Naturalist
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
478
concern (S. connasaugaensis, V. nebulosa, and V. umbrans) accounting for about
62% (Table 1).
Winter/spring survey period
We found 10 middens during the winter/spring survey period, 3 between Highrock
Lake and Sweetwater Lake and 7 between Sweetwater Lake and Coleman
Lake (Fig. 1). Middens tended to be located in shallows, and we frequently found
them on or next to submerged and emerged rocks and logs. Middens contained a total
of 552 whole shells and 827 half shells. The number of shells in middens ranged
from 2 to 434.5 (mean ± SE = 96.6 ± 174.1 shells). We observed predation signs on
about 27% (259.5 of 965.5 shells) of all collected shells. We collected shells from
7 different species; the invasive C. fluminea accounted for ~88% of total shells
(851.5 of 965.5 shells). Paired valves of C. fluminea found in middens were shorter
in length (21.8 ± 0.4 mm, n = 130) than paired valves of all native mussel species
combined (58.6 ± 1.3 mm, n = 89; 2-tailed t-test: t = -27.0, P < 0.001). Of the native
species shells collected (n = 114), the federally endangered and threatened species
accounted for less than 6% and the state species of conservation concern accounted
for about 69% (Table 2).
There was no indication of size-selective predation of native mussels by Muskrats.
The pooled paired-valve lengths from all native species did not exhibit any
difference in frequency distributions between midden- and stream-survey samples
(2-sample Kolmogorov-Smirnov test, D = 0.10, P = 0.60; Fig. 2). There was no
Table 2. Mean shell length (± SE), number, percentage, and prey-selection ratios of freshwater mussels
found in all Muskrat middens during the winter/spring survey period at Shoal Creek, AL. Shell
length calculated from paired valves only. Stream availability (SA) based on 2011 survey of live mussels
(n = 203) in Shoal Creek (Dolloff et al. 2012). wi 95% CI = 95% Bonferroni confidence interval;
intervals that span 1 indicate random prey selection.
Shell length Midden SA
Species (mm) n % % wi ± SE wi 95% CI β
Hamiota altilis 55.7 ± 7.0 4.5 3.9 5.2 0.76 ± 0.42 -0.25–1.77 0.12
Pleurobema georgianum 36.1 ± 7 2.0 1.8 1.0 1.68 ± 1.67 -2.32–5.69 0.27
Strophitus connasaugaensis 62.4 ± 1.3 46.0 40.4 34.9 1.16 ± 0.17 0.74–1.57 0.18
Villosa nebulosa 51.5 ± 3.0 20.5 18.0 25.0 0.72 ± 0.17 0.31–1.13 0.11
Villosa umbrans 51.9 ± 2.9 12.5 11.0 13.0 0.84 ± 0.27 0.19–1.50 0.13
Villosa vibex 64.8 ± 2.5 28.5 25.0 20.8 1.2 ± 0.26 0.58–1.82 0.19
Table 1. Mean shell length (± SE), number, and percentage of freshwater mussels found in all Muskrat
middens during the summer-survey period at Shoal Creek, AL.
Species Shell length (mm) n Midden %
Hamiota altilis 49.3 ± 3.8 9 6.3
Pleurobema georgianum 39.2 ± 1.7 13 9.0
Strophitus connasaugaensis 58.9 ± 1.9 29 20.1
Villosa nebulosa 37.9 ± 1.2 26 18.1
Villosa umbrans 41.6 ± 1.0 34 23.6
Villosa vibex 55.0 ± 1.0 33 22.9
Southeastern Naturalist
479
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
evidence of prey selection by Muskrats based on relative abundances of native
mussel species in middens (χ2 = 3.5, df = 5, P = 0.63). Examination of selection
ratios for each native species indicated that prey selection was random (95% CI for
all wi included 1; Table 2). The standardized selection ratios also revealed a similar
pattern of random predation for each species (all β values close to baseline value of
0.167; Table 2).
Discussion
Based on shells collected at middens, Muskrats appeared to prey on native
mussels according to their relative abundances in Shoal Creek. The prey-selection
ratios for each native mussel species were near values predicted if Muskrats captured
species based on natural availability (Table 2). Our results did not indicate
that larger species or individuals were preyed upon at higher rates than expected by
availability (Table 2, Fig. 2). These findings are in contrast to several other studies
that reported size-selective or species-selective predation on freshwater mussels
by Muskrats based on similar midden-sampling techniques (Diggins and Stewart
2000, Erickson 2001, Jokela and Mutikainen 1995, Neves and Odom 1989, Owen
et al. 2011, Tyrrell and Hornbach 1998, Watters 1995, Zahner-Meike and Hanson
2001). This discrepancy between our results and those of other studies may be due
to differences in habitat and mussel communities of sampled sites. The previous
studies occurred in larger aquatic habitats (rivers and lakes) that often had greater
Figure 2. Shell-length frequency (grouped into 10-mm size classes) for all native freshwater
mussels (paired valves only) found in Muskrat middens during the winter/spring survey
period (dark gray bars, n = 89) and stream-survey samples from Dolloff et al. 2012 (light
gray bars, n = 173) at Shoal Creek, AL.
Southeastern Naturalist
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
480
mussel-species diversity and size ranges (reviewed in Owen et al. 2011) compared
to Shoal Creek. Muskrats preferentially prey on mussels that range from 20 to 90
mm in length (Diggins and Stewart 2000, Erickson 2001, Jokela and Mutikainen
1995, Neves and Odom 1989, Owen et al. 2011, Zahner-Meike and Hanson 2001).
Muskrats may avoid mussels >90 mm in length because they are too energetically
costly to extract, whereas mussels less than 20 mm are likely difficult to find (Owen et al.
2011). All 6 native mussel species and sampled individuals in Shoal Creek were
within the preferred size range of Muskrats, which may account for the lack of a
strong difference between shell sizes observed in the middens and available in the
stream (Fig. 2).
Predation by Muskrats can influence the local community structure of native
mussels, most obviously by reducing the abundance of preferred-size individuals
or species (Diggins and Stewart 2000, Erickson 2001, Jokela and Mutikainen
1995, Zahner-Meike and Hanson 2001). Muskrats are primarily herbivores, but the
percentage of their diet derived from carnivory varies depending on habitat (Willner
et al. 1980). In marsh habitats with abundant wetland vegetation, very little of
their diet consists of animal matter (Lacki et al. 1990). However, in stream habitats
with little vegetation or when vegetation is seasonally scarce, animal matter may
constitute the majority of the Muskrat’s diet (Evermann and Clark 1920, Hersey et
al. 2013, Zahner-Meike and Hanson 2001). Shoal Creek is a small, second-order
stream with little aquatic vegetation. Thus, Muskrats at this location likely derive
a significant proportion of their diet from animal matter including freshwater mussels.
Our results, confirmed that Muskrats preyed on all native mussel species in
Shoal Creek. Predation by Muskrats of the rare and federally listed H. altilis and
P. georgianum is of greatest conservation concern given these species’ highly
restricted distributions and low population sizes (Dolloff et al. 2012, Warren et
al. 2004). The extent to which predation is contributing to the overall decline of
freshwater mussels is uncertain, but other processes such as pollution and habitat
destruction are considered greater threats (Downing et al. 2010). Although healthy
populations of freshwater mussels may be able to sustain high levels of predation,
further loss of individuals in declining or low-abundance populations via localized
predation may pose a serious threat (Neves and Odom 1989). Mussel communities
at Shoal Creek exhibit relatively low abundances most likely because of the low
productivity of the headwater stream system (Warren et al. 2004), a characteristic
that may place this community at greater risk of decline from predation. Low abundance
coupled with isolation of stream segments by human-made impoundments
on Shoal Creek may reduce probability of recolonization of sites by mussels after
intense predation by Muskrats and other predators.
Invasive C. fluminea were very common in middens at Shoal Creek even
though their shell size averaged near the lower range preferred by Muskrats. Density
of C. fluminea has not been measured at Shoal Creek, but this species is more
abundant than all other native mussel species combined and is highly visible on
the streambed (A.J. Edelman, pers. observ.) likely making them easy for Muskrats
and other predators to find. Given the high fecundity of C. fluminea (Sousa et al.
Southeastern Naturalist
481
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
2008), populations of this species can presumably sustain intense levels of predation.
However, the impact of this additional and highly abundant food source may
indirectly alter the predator–prey dynamics between Muskrats and native mussels
and should be the subject of future study. It has been demonstrated in other
ecological systems, that introduced-prey species can have negative and positive
indirect effects on native prey species via the mechanisms of apparent competition
and indirect facilitation (Jaworski et al. 2013, Roemer et al. 2002, White et
al. 2006).
Temporary control of Muskrat populations at Shoal Creek through removals
could be considered as a potential option to aid in the recovery of native mussel
populations (Neves and Odom 1989). Limited removal of Muskrats may be most effective
at locations of high mussel-diversity or during reintroduction efforts. Future
studies could examine how Muskrat removal affects freshwater-mussel communities
to determine whether this is an effective management strategy.
Acknowledgments
We thank Jonathan Stober for technical assistance with this project and 2 anonymous
reviewers for their helpful comments. The Department of Biology at the University of
West Georgia and the Shoal Creek Ranger District, Heflin, AL, provided equipment for
this project.
Literature Cited
Bogan, A.E. 1993. Freshwater bivalve extinctions (Mollusca: Unionoida): A search for
causes. American Zoologist 33:599–609.
Bovbjerg, R. 1956. Mammalian predation on mussels. Proceedings of the Iowa Academy
of Science 63:737–740.
Calenge, C. 2006. The package “adehabitat” for the R software: A tool for the analysis of
space and habitat use by animals. Ecological Modelling 197:516–519.
Diggins, T., and K. Stewart. 2000. Evidence of large change in unionid mussel abundance
from selective Muskrat predation, as inferred by shell remains left on shore. International
Review of Hydrobiology 85:505–520.
Dillon, R.T. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press,
Cambridge, UK. 509 pp.
Dolloff, C.A., C. Krause, C. Roghair, and J. Moran. 2012. Freshwater-mussel inventory in
Cheaha Creek and Shoal Creek, Talladega National Forest, Alabama, 2011. USDA Forest
Service Southern Research Station, Blacksburg, VA. 26 pp.
Downing, J.A., P. Van Meter, and D.A. Woolnough. 2010. Suspects and evidence: A review
of the causes of extirpation and decline in freshwater mussels. Animal Biodiversity and
Conservation 33:151–185.
Erb, J., and H. Perry Jr. 2003. Muskrats (Ondatra zibethicus and Neofiber alleni). Pp.
311–348, In G.A. Feldhamer, B.C. Thompson, and J.A. Chapman (Eds.). Wild Mammals
of North America: Biology, Management, and Conservation. Johns Hopkins University
Press, Baltimore, MD. 1232 pp.
Erickson, J.M. 2001. Influences of Muskrat predation on population structure of Margaritifera
margaritifera (Molluska: Unionoidea) at stream sites in St. Lawrence County,
New York. Proceedings of the North Dakota Academy of Science 55:59.
Southeastern Naturalist
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
482
Evermann, B.W., and H.W. Clark. 1920. Lake Maxinkuckee: A physical and biological
survey. Indiana Department of Conservation Publiction 7:1–660.
Haag, W.R. 2012. North American Freshwater Mussels: Natural History, Ecology, and Conservation.
Cambridge University Press, Cambridge, UK. 538 pp.
Hersey, K.A., J.D. Clark, and J.B. Layzer. 2013. Consumption of freshwater bivalves by
Muskrats in the Green River, Kentucky. American Midland Naturalist 170:248–259.
Hoggarth, M.A., D.L. Rice, and D.M. Lee. 1995. Brief note: Discovery of the federally
endangered freshwater mussel Epioblasma obliquata obliquata (Rafinesque, 1820)
(Unionidae), in Ohio. Ohio Journal of Science 95:298–299.
Jaworski, C.C., A. Bompard, L. Genies, E. Amiens-Desneux, and N. Desneux. 2013. Preference
and prey switching in a generalist predator attacking local and invasive alien pests.
PLoS ONE 8:e82231.
Jokela, J., and P. Mutikainen. 1995. Effect of size-dependent Muskrat (Ondatra zibethica)
predation on the spatial distribution of a freshwater clam, Anodonta piscinalis Nilsson
(Unionidae, Bivalvia). Canadian Journal of Zoology 73:1085–1094.
Kopij, G. 2011. The endangered Swan Mussel, Anodonta cygnea (L., 1758), is threatened
by the Common Otter, Lutra lutra. Folia Malacologica 19:191–192.
Lacki, M.J., W.T. Peneston, K.B. Adams, F.D. Vogt, and J.C. Houppert. 1990. Summerforaging
patterns and diet selection of Muskrats inhabiting a fen wetland. Canadian
Journal of Zoology 68:1163–1167.
Lydeard, C., and R.L. Mayden. 1995. A diverse and endangered aquatic ecosystem of the
Southeast United States. Conservation Biology 9:800–805.
Manly, B., L. McDonald, D. Thomas, T. McDonald, and W. Erickson. 2002. Resource Selection
by Animals: Statistical Analysis and Design for Field Studies. Kluwer Academic
Press Publishers, Dordrecht, The Netherlands. 222 pp.
Mirarchi, R., J. Garner, T. Haggerty, M. Mettee, and P. O’Neil (Eds.). 2004. Alabama Wildlife.
Volume 2: Imperiled Aquatic Mollusks and Fishes. University of Alabama Press,
Tuscaloosa, AL. 255 pp.
Neves, R.J., and M.C. Odom. 1989. Muskrat predation on endangered freshwater mussels
in Virginia. Journal of Wildlife Management 53:934–941.
Owen, C.T., M.A. McGregor, G.A. Cobbs, and J.E. Alexander Jr. 2011. Muskrat predation
on a diverse unionid mussel community: Impacts of prey-species composition, size, and
shape. Freshwater Biology 56:554–564.
Roemer, G.W., C.J. Donlan, and F. Courchamp. 2002. Golden Eagles, Feral Pigs, and insular
carnivores: How exotic species turn native predators into prey. Proceedings of the
National Academy of Sciences 99:791–796.
Sousa, R., C. Antunes, and L. Guilhermino. 2008. Ecology of the invasive Asian Clam,
Corbicula fluminea (Müller, 1774), in aquatic ecosystems: An overview. Annales de
Limnologie-International Journal of Limnology 44:85–94.
Tyrrell, M., and D.J. Hornbach. 1998. Selective predation by Muskrats on freshwater
mussels in 2 Minnesota rivers. Journal of the North American Benthological Society
17:301–310.
Warren, M.L., W.R. Haag, S.B. Adams, and A.L. Sheldon. 2004. Population-size estimates
and distribution of freshwater mussels in Shoal Creek, Talladega National Forest, Alabama.
USDA Forest Service Southern Research Station, Oxford, MS. 42 pp.
Watters, G.T. 1995. Sampling freshwater mussel populations: The bias of Muskrat middens.
Walkerana 7:63–69.
Southeastern Naturalist
483
A.J. Edelman, J. Moran, T.J. Garrabrant, and K.C. Vorreiter
2015 Vol. 14, No. 3
White, E.M., J.C. Wilson, and A.R. Clarke. 2006. Biotic indirect effects: A neglected concept
in invasion biology. Diversity and Distributions 12:443–455.
Williams, J.D., M.L. Warren Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation
status of freshwater mussels of the United States and Canada. Fisheries 18:6–22.
Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama and
the Mobile Basin in Georgia, Mississippi, and Tennessee. University of Alabama Press,
Tuscaloosa, AL. 908 pp.
Willner, G.R., G.A. Feldhamer, E.E. Zucker, and J.A. Chapman. 1980. Ondatra zibethicus.
Mammalian Species 141:1–8.
Zahner-Meike, E., and J.M. Hanson. 2001. Effect of Muskrat predation on Naiads. Pp.
163–184, In G. Bauer and K. Wächtler (Eds.). Ecology and Evolution of the Freshwater
Mussels Unionoida. Springer, New York, NY. 396 pp.