Comparative Ecology of Notropis albeolus, N. ardens
and N. cerasinus (Cyprinidae)
in the Upper Roanoke River Drainage, Virginia
ERIC M. SURAT, WILLIAM J. MATTHEWS' and JEFFREY R. BEK
Biological Station and Department of Zoology, University of Oklahoma, Kingston 73439 (WIM);
and Biology Department, Roanoke College, Salem, Virginia 24153 (EMS, JRB)
ABSTRACT: Foods, feeding periodicity and microhabitat use are reported for coexisting Notropis albeolus, N. ardens and N. cerasinus in the upper Roanoke River
drainage, Virginia. All three species primarily occupied pool habitats, ate aquatic insect larvae or terrestrial adult insects, and were diurnal feeders. Notropis ardens
(subgenus Lythrunis) was ecologically segregated from N. albeolus and N. cerasinus (both
subgenus Luxilus) in vertical spacing in the water column and in taxa of foods used. The
two Luxilus species were ecologically more similar, segregated only by vertical differences in microhabitat. Overlaps in resource use among the three species pairs suggested congruence of phylogenetic and ecological similarities.
INTRODUCTION
The phenomenon of resource partitioning is well-documented in reptile, bird and
mammal communities (cf., Pianka, 1973; Schoener, 1974), and in numerous
freshwater fish communities closely related, coexisting species differ ecologically, e.g.,
in microhabitat, food or feeding chronology (Hartley, 1948; Keast, 1965, 1966, 1978;
Zaret and Rand, 1971; Werner and Hall, 1976, 1979; Werner et al., 1977). It has often
been assumed that some segregation in resource use is a requisite for coexistence of
species, and that observed ecological differences among coexisting taxa result from past
or present competitive interactions. However, uncritical acceptance of a competition
model to account for ecological differences among coexisting fish species may be unwarranted (Sale, 1979), and the plausibility of alternative hypotheses should be considered. Mendelson (1975), for example, suggested that coexisting minnows used
resources in patterns set by morphological preadaptation.
In eastern North America, minnows of the genus Notropis (Cyprinidae) often occur
in multispecies aggregations, using habitats and foods that superficially appear similar.
However, Starrett (1950), Whitaker (1977), Gillen and Hart (1980) and Hoover (1981)
showed trophic segregation among coexisting Notropis species, and Moyle (1973) and
Baker and Ross (1981) demonstrated that coexisting Notropis species segregated vertically into different microhabits. Mendelson (1975) showed that four coexisting
Notropis were ecologically segregated more by use of space than by diet. While these
studies suggest the importance of dietary and microhabitat segregation among coexisting Notropis, there has been too little comparative research within this diverse genus
(at least 119 species) to permit generalization about mechanisms that facilitate species
coexistence. In this study we evaluate ecological segregation among three syntopic
Notropis species, with emphasis on microhabitat, food and feeding chronology in a complex upland stream system. We also provide information on cold vs. warm weather
ecology of the species.
Our study focuses on Notropis albeolus (white shiner, subgenus Luxilus), N. ardens
(rosefin shiner, subgenus Lythrurus) and N. cerasinus (crescent shiner, subgenus Luxilus),
which are the three most common Notropis in the upper Roanoke River drainage above
Salem, Virginia (Jordan, 1889; Cairns et al. 1971; Jenkins, 1979). All three coexist in
the river mainstream and in larger tributaries, but N. cerasinus occurs somewhat further
'Address reprint requests to Matthews.
13
14
107(1)
THE AMERICAN MIDLAND NATURALIST
upstream than the others (Jenkins and Freeman, 1972). In the mainstream, all three
species are often collected in a single seine haul. Schwartz and Dutcher (1962) described foods of N. cerasinus, and Meredith and Schwartz (1959) described summer
foods of N. ardens, but little comparative ecological information has been published on
these species (Snelson, 1980; Gilbert, 1980a, 1980b).
DESCRIPTION OF THE STUDY AREA
The Roanoke River drainage has 83 native fish species, comprising probably the
"most diverse and distinctive fish fauna of all drainages on the Atlantic slope of the
United States" (Jenkins and Freeman, 1972). This study was conducted in the
Roanoke River, South Fork Roanoke River and their tributaries, in Roanoke and
Montgomery counties, Virginia (Fig. 1). A physical and biotic description of this part
of the drainage is provided by Dickson (1979). The South Fork Roanoke River
originates from spring-fed tributaries on the steep slopes of the Blue Ridge Mountains,
then flows N and E through the Ridge and Valley Physiographic Province to join the
North Fork near the Montgomery-Roanoke county line (Fig. 1). Most tributaries are
high-gradient streams, with distinct riffles and pools and bottoms of bedrock, rubble,
gravel or sand. The main river valley is less steep than the surrounding slopes; thus
mainstream gradients are less (Table 1). The South Fork and the Roanoke River proper consist of large riffle areas, occasional deep pools and long stretches of relatively
uniform channel. Bottoms are gravel, rubble and boulders in riffles; sand, silt and
detritus in pools, and a mixture of substrate types in the channels. Most of the streams
are well-shaded by the surrounding mountains or by a canopy of deciduous trees.
Valleys are devoted to livestock, and surrounding mountain slopes are heavily
forested. No serious point sources of pollution are known.
METHODS AND MATERIALS
We made seven collections at each of 10 stations (Fig. 1) from April 1978 through
March 1979, including all seasons in the sampling. Additionally, we include in this
ROANOKE CO.
e
MONTGOMERY CO.
'SALEM
2
09
3 a-
ROANOKE
•
to" '
i Ck(3.
,SHAWSVILLE
s
ot'
co
5
G
1
%
•
8
5
10
Km
Fig. 1. —Regular collecting localities in the upper Roanoke River drainage, Virginia, April
1978-March 1979
SURAT ET AL.: NOTROPIS ECOLOGY
1982
15
analysis some data from collections made in October and December 1977, and
February and March 1978. At Station 5 we made collections every 3 hr on 17-18
August and 14-15 October 1978, to provide information on feeding chronology of the
species.
At each station we collected fish for approximately 1 hr by seining discrete
microhabitats such as riffles, pools and channels, using a 1.2 x 1.8 m, 4.7 mm bar mesh
seine. In each microhabitat, current speed was measured 15 cm below the surface with
a General Oceanics propellor-type meter. All fish were preserved in 10% formalin and
later transferred to 40% isopropanol. We used a hand-held underwater viewer to
determine vertical distributions of the three Notropis in the water column, making
observations in pool habitats at Station 5 during daylight hours on 17 September 1978,
9 January 1979 and 14 April 1979 for a total of 30 min viewing time on each date.
Fish for food habitat study were sexed and assigned a relative index of "stomach"
( = alimentary canal anterior to first distinct bend) fullness on a scale from 0 = empty
to 5 = full. The stomachs (only) were then opened and contents identified to the lowest
practical taxa. Because Notropis macerate food, making counts of individual items difficult, we used the occurrence method of food analysis based on the percentage of fish
in which a given food item occurred (Hynes, 1950). A total of 264 stomachs of adult
Notropis were analyzed from spring, summer and autumn collections at Stations 1 and 5
where all three species were common. An additional 90 stomachs from adult fish collected in deep pools at Stations 3 and 4 during winter (when relatively few fish were
taken at other stations) were included in the analysis.
Food and habitat niche breadths (B) for each species were determined following
Pianka (1973):
1
B —
P?
i
in which P i represents the proportion of the ith microhabitat or food type actually used
by the species. Niche overlaps (gm ) were determined by:
E
Pij
P ik
0J k
E Pi
in which P d , Pa are proportions of the resource i used by species j and k. Prior to
calculation of food breadth or overlap values, use of food taxa was converted to relative
percentages so that total use of all food categories equalled 100% for each species. The
overlap formula thus yields values from 0 ( = no overlap) to 1.0 ( = complete overlap).
No statistical procedure has been developed to test significance levels of overlap values;
we thus follow Pianka and Pianka (1976) in considering values greater than 0.75 to indicate high overlap among species.
RESULTS
Habitat use. —We took 10,231 Notropis of the three species in our collections. All
three species were common or abundant at most stations (Table 1); however, at Stations 9 and 10, located on small spring branches, few or no Notropis occurred. Although
N. cerasinus and N. albeolus occurred slightly further upstream and were more abundant
at most stations than N. ardens, 2 x 2 contingency table analysis of presence-absence in-
16
THE AMERICAN MIDLAND NATURALIST
107(1)
dicated a strong positive similarity in the occurence of all species (X' tests; p < 0.01 for
all species pairs). Largest numbers of all three species occurred at fifth-order
mainstream locations with relatively low stream gradients and widths in excess of 10 m
(Table 1).
Within collecting localities the three species primarily occupied pools during both
cold and warm seasons (Table 2), and thus exhibited high horizontal microhabitat
overlap values (Table 3). Notropis ardens occupied channel habitats more than either N.
cerasinus or N. albeolus and had wider microhabitat breadth (Table 2), but like the other
species, most N. ardens were captured in pool areas. All three species showed peak occurrence at current speeds of 1-25 cm/sec, although more N. ardens than the other
Notropis were collected at velocities > 25 cm/sec (Table 4). Overlap values among all
species pairs were, however, high with respect to the current speeds of habitats they
used (Table 3). During cold weather collections in February-March 1979 the Notropis
species, like most other Roanoke River fishes, showed marked changes in habitat use,
as they were absent from several localities where they had been common during warm
months. In winter collections we found large numbers of the three species only in deep
pools at Stations 3, 4 and 5 and all three species exhibited low habitat breadth (Table
2).
In contrast to the small horizontal differences in their microhabitats, the species
showed moderate to pronounced vertical separation in the water column (Fig. 2).
Notropis cerasinus was most abundant near the substrate, N. albeolus was common in both
midwater and benthic habitats, and N. ardens primarily used midwater space. Of 277
N. cerasinus observed in September and 493 in April, 80% and 66%, respectively, were
within 8 cm of the substrate. In September, 54% of 118 N. albeolus were seen in midwater and 46% were near the bottom. In April, 53% of 322 N. albeolus were in midwater and 43% were near the bottom. Too few N. ardens were seen for analysis in
September, but of 152 individuals observed in April, 82% were in midwater
microhabitat and only 15% were within 8 cm of the bottom. Separation in the water
column thus comprised a spatial axis over which N. ardens and N. cerasinus showed a
reduction in niche overlap (Table 3).
Food use. —A total of 22 kinds of items were found in the stomachs of the Notropis
taken in spring, summer and autumn at Stations 1 and 5. The three species were
omnivorous, and no single food item dominated their diet. Diet breadth values were
high and similar for all species (Table 5). There was no recognizable seasonal trend in
diet overlaps among species. Overlap values were high overall for all species pairs but
TABLE 1. -Characteristics of collecting localities and numbers of Notropis collected in the upper Roanoke River, Virginia—April 1978 —March 1979
Station
Width
(m)
Gradient
(m/km)
Stream
Order
N.
ardens
N.
albeolus
N.
cerasinus
Mainstreams
1
2
3
4
5
25
30
25
15
25
8.8
6.2
2.8
2.5
3.4
5
5
5
5
5
190
98
50
207
219
668
159
805
769
831
304
188
729
1133
688
Tributaries
6
7
8
9
10
10
10
10
5
1
22.2
15.4
12.3
20.5
20.5
4
4
4
2
2
Totals =
125
20
0
0
0
909
109
115
16
2
0
3474
98
215
172
6
0
3533
1982
SURAT ET AL.: NOTROPIS ECOLOGY
17
greatest between the two Luxilus. During all seasons N. ardens exhibited moderate diet
segregation from the other two species (Table 3). Notropis albeolus and N. cerasinus,
which share both horizontal and vertical habitat space, also overlapped markedly in
food use at all seasons and overall (Table 3).
Items appearing most frequently in stomachs of the Notropis were aquatic insect larvae (particularly Chironomidae, Ephemeroptera, Odonata and Hydropsyche), terrestrial
insects and algae. Vertical differences in habitats used by the species were reflected in
their diets as more N. ardens, the midwater species, contained terrestrial insects
(presumably taken from the water surface) than did the other species (Table 5). A
higher percentage of the more benthic N. albeolus and N. cerasinus contained sand and
the benthic invertebrate taxa Chironomidae, Ephemeroptera and Hydropsyche. While
these invertebrates also occur in the water column as components of the drift, they do
so primarily at night (Hynes, 1970) while these minnow species feed mostly during
daylight hours (see below). The relative scarcity of certain benthic invertebrates in the
diet of N. ardens thus further suggests that this species feeds in the middle and upper
parts of the water column more than do N. albeolus and N. cerasinus.
In winter, when most minnows we collected were crowded together in a few deep
pools, all three species showed a marked reduction in mean stomach fullness (Table 5).
The decrease in volume of food in their stomachs may relate to decreased availability of
foods (e.g., terrestrial insects), restriction of foraging space or a decreased requirement
for food as a result of lowered metabolism at cold temperatures. Despite decreased
feeding in winter, the specimens collected in early March seemed in good physical condition, i.e., were not emaciated.
Feeding periodicity.- All three species were diurnal feeders, with onset of feeding approximately at dawn and an increase in stomach fullness throughout the day. Feeding
activity of the three species ceased after sunset, as stomach fullness declined markedly
in 2400 hr and 0300 hr samples (Figs. 3 and 4). Overlap in feeding times was very high
among all species pairs (Table 3). Laboratory feeding tests we conducted indicated that
at 20 C food items required approximately 4 hr to pass through the stomachs of
Notropis; thus actual time of ingestion of food found in stomachs was considered to be as
much as 4 hr prior to capture.
TABLE 2. -Percent occurrence of Notropis of the upper Roanoke River in riffle, pool and
channel habitats, during warm vs. cold seasons
Riffle
Channel
Pool
Habitat
breadth
8.0
1.6
5.7
35.9
15.4
12.5
56.0
83.0
81.8
2.23
1.40
1.45
April-Nov. 1978
N. ardens
N. albeolus
N. cerasinus
3.9
11.8
10.1
37.1
17.1
11.5
59.0
71.1
78.4
2.05
1.82
1.57
Feb.-March 1979
N. ardens
N. albeolus
N. cerasinus
16.4
4.2
9.7
1.6
3.7
4.2
82.0
92.1
86.1
1.43
1.17
1.33
Total-All seasons
N. ardens
N. albeolus
N. cerasinus
6.7
7.9
9.5
31.4
14.1
10.4
61.9
77.9
80.1
2.06
1.58
1.51
Dec. 1977-March 1978
N. ardens
N. albeolus
N. cerasinus
Species
Pair
Habitat use
Diet
Vertical
Current
speed
Spring
Summer
Autumn
Winter
Overall
Feeding
schedule
(August)
0.959
0.877
0.968
0.536
0.784
0.685
0.633
0.823
0.984
N. ardensN. cerasinus
0.943
0.540
0.964
0.734
0.768
0.559
0.738
0.811
0.946
N. albeolusN. cerasinus
0.999
0.877
0.996
0.899
0.904
0.918
0.907
0.926
0.977
Riffle-PoolChannel
N. ardensN. albeolus
THE AMERICAN MIDLAND NATURALIST
TABLE 3. —Ecological overlaps among minnows of the upper Roanoke River drainage
1982
SURAT ET AL.: NOTROPIS ECOLOGY
19
DISCUSSION
The three species pairs differed considerably in their levels of ecological segregation, and no single factor, e.g., microhabitat, food use or feeding schedule, consistently
separated all pairs. Notropis ardens differed from N. cerasinus by vertical segregation in
the water column, and the two species differed moderately in prey at all seasons. Of the
three pairs, they exhibited the greatest overall ecological difference. Notropis ardens and
N. albeolus showed some spatial segregation, as the latter occurred lower than N. ardens
in the water column. Moderate differences in food use were evident between N. ardens
and N. albeolus throughout the year. Ecological differences between N. ardens-N. albeolus
and N. ardens-N. cerasinus are similar in magnitude to those reported among other coexisting cyprinid species (Moyle, 1973; Mendelson, 1975; Baker and Ross, 1981). Our
finding that N. ardens is a midwater or surface feeder agrees with Meredith and
Schwartz (1959), and our interpretation of N. cerasinus as a bottom feeder agrees with
Schwartz and Dutcher (1962).
Notropis albeohts and N. cerasinus overlapped strongly in horizontal microhabitat use,
food use and time of feeding. The only difference we found between the two species
that might be of biological significance was that of partial vertical separation, N.
cerasinus being the more substrate-oriented. While this species pair may be ecologically
segregated in some other subtle way we did not detect, previous studies of cyprinid
assemblages at approximately the same resolution as ours have typically shown more
differences between species than we found between N. albeolus and N. cerasinus.
Mendelson (1975) indicated that four coexisting Notropis species in a small stream
seemed morphologically preadapted for their ecological roles in the community rather
than having been "molded by mutual interaction into a functional unit." Our results
are consistent in part with Mendelson's hypothesis, as general ecological relationships
among N ardens, N albeolus and N. cerasinus reflect similarities and differences in their
morphology which are congruent with their taxonomic relationships at the subgeneric
level. Notrapis ardens, which has a streamlined body and posteriorly positioned dorsal fin
characteristic of members of the subgenus Lythrurus, occupies midwater and swift-water
T
.IiARDENS
13
T
N. ALBEOLU§ M
CERASINUS M
20 40 60 80 100
% Fish
Fig. 2. —Percent occurrence of three Notropis species in upper ( = top 8 cm), middle, or lower
( = on or within 8 cm of bottom) portion of the water column. N = N. albeolus, 440; N. ardens,
153; N. cerasinus, 770; data pooled for Sept. 1978 and April 1979
20
107(1)
THE AMERICAN MIDLAND NATURALIST
microhabitats more than the two Luxilus species. Baker and Ross (1981) similarly
reported a species of the subgenus Lythrurus (Notropis rose:* pinnis) to be more surfaceoriented than six of seven other coexisting cyprinid species in a Gulf coastal stream.
The similarity of N. cerasinus and N. albeolus along the niche axes we evaluated is conTABLE 4. —Percent occurrence of Notropis at different measured current speeds in the upper
Roanoke River drainage, April-November 1978
Species
Current speed (cm/sec)
0
N. albeolus
N. ardens
N. cerasinus
1994
453
2561
11.2
14.5
9.9
1-25
60.3
51.2
66.1
26-50
51-75
76-100
13.9
26.3
14.7
5.1
3.3
5.9
7.8
4.4
2.4
101-125 126-150
0.1
0
0
1.7
0.2
1.0
MEAN FULLNESS
OCTOBER
X
X= N. ARDENS
26
0= N. ALBEOLUS 104
e. N. CERASINUS 110
0
00 0
0 0
0
o ,0
Di
TIME
Fig. 3. —Mean fullness of stomachs of the three Notropis species at 3-hr intervals 17-18 August
1978. Sample size for N. ardens at 1200 was so small ( = 1) that the point is not connected to the
curve
TABLE 5. -Percent of individual fish stomachs containing each item, by season. ALB = Notropis albeolus; ARD = Notropis ardens; CER =
Notropis cerasinus. Larvae = 1; pupae = p; adults = a
Item
Mean fullness
Diet breadth
6.7
0
3.3
3.37
7.21
25.0
54.2
12.5
2.19
5.51
16.7
10.0
13.3
2.27
8.20
July-Aug. 1978
Sept.-Nov. 1978
ALB ARD CER
30
30
30
March 1979
ALB
30
50.0
0
10.0
6.7
46.7
16.7
16.7
20.0
0
10.0
10.0
6.7
0
0
16.7
0
3.3
0
3.3
ARD
30
16.7
0
6.7
0
36.7
3.3
36.7
6.7
13.3
20.0
0
6.7
3.3
0
3.3
0
0
0
0
CER
30
40.0
0
0
3.3
30.0
3.3
16.7
10.0
3.3
3.3
0
0
0
0
0
0
0
0
0
23.3
3.3
3.3
0
10.0
0
6.7
0
13.3
3.3
0
0
0
0
16.7
0
0
0
0
16.7
0
3.3
0
13.3
13.3
33.3
0
13.3
13.3
0
0
0
0
43.3
0
0
0
0
20.0
0
0
0
26.7
3.3
10.0
3.3
10.0
6.7
0
0
0
0
10.0
0
0
0
0
ALB
30
26.7
0
13.3
0
16.7
0
6.7
20.0
3.3
0
0
0
0
0
0
0
3.3
0
0
3.3
26.7
3.3
3.3
16.7
0
13.3
33.3
10.0
20.0
36.7
10.0
6.7
16.7
3.3
36.7
50.0
30.0
6.7
0
3.3
0
0
0
1.46
5.91
0.53
4.17
2.90
8.83
2.57
7.50
2.17
7.22
2.30
7.12
2.50
7.24
2.30
7.06
ARD
30
0
0
6.7
6.7
13.3
0
0
6.7
0
0
0
0
0
0
0
3.3
0
0
0
CER
30
16.7
0
10.0
10.0
26.7
3.3
3.3
26.7
0
0
3.3
0
0
0
0
0
0
0
0
ALB
120
34.2
0.8
6.7
1.7
27.5
5.8
15.0
11.7
5.0
5.8
4.2
5.0
0
0
6.5
0
1.7
0
0.8
Total
ARD
114
CER
120
12.3
0
4.4
0
20.2
5.3
25.4
3.5
8.8
8.8
0
1.8
0.9
0
14.9
0.9
0
0
0
25.8
0
7.5
0.8
28.3
2.5
13.3
10.0
3.3
4.2
0.8
0
0.8
0.8
5.0
0
0
0.8
0
13.3
0
6.7
9.2
15.8
5.0
7.9
20.2
3.5
20.0
23.3
15.0
1.30
5.86
9.42
8.39
SURAT ET AL.: NOTROPIS ECOLOGY
N=
Chironomidae (1)
Chironomidae (p)
Other Diptera (1)
Other Diptera (p)
Ephemeroptera
Plecoptera
Odonata
Hydropsyche
Other Trichoptera
Coleoptera (a)
Coleoptera (p)
Coleoptera (1)
FIerniptera
Cogdalus
Terrestrial insects
Hydracarina
Oligochaeta
Gastropoda
Fish eggs
Leafy & woody
material
Algae
Sand
April-May 1978
ALB ARD CER
24
30
30
26.7
36.7
16.7
0
0
0
0
6.7
0
3.3
0
0
36.7
16.7
30.0
6.7
4.2
0
23.3
30.0
33.3
3.3
6.7
0
0
3.3
0
10.0
0
6.7
3.3
0
0
13.3
0
0
3.3
3.3
0
0
3.3
0
10.0
12.5
10.0
0
0
0
0
0
0
0
0
0
0
0
0
8.70
o-•
107(1)
THE AMERICAN MIDLAND NATURALIST
22
gruent with their common ancestry as members of the subgenus Luxilus (Menzel, 1976,
1977; Buth, 1979). Luxilus species are typically deep-bodied, slab-sided cyprinids, and
not as streamlined as Lythrurus species.
Although Notropis albeolus and N. cerasinus are ecologically similar, the slight differences between them in resource use relate to morphological differences which
Menzel (1976) suggested are due to past interactions between the species. In the
Roanoke drainage, where N. albeolus and N cerasinus have a long history of coexistence,
N. albeolus is more slim-bodied and streamlined than N. cerasinus (Gilbert, 1964;
Menzel, 1976), which coincides with our finding that N. albeolus occurs in midwater
more than does N. cerasinus. Notropis albeolus is the only member of the subgenus Luxilus
in the Neuse, Tar and Cape Fear drainages of North Carolina (Gilbert, 1964). In these
drainages, N. albeolus are deeper-bodied and less streamlined than northern N. albeolus
5
AUGUST
X= N. ARDENS
68
MEAN FULLNESS
0= N. ALBEOLUS 120
• = N. CERASINUS 120
4
3
2
<19°
\4:300
00
\:)
ez>
0
el0.,0
e
0
0 0300
co0
0
0 0
430
TIME
Fig. 4. —Mean fullness of stomachs of the three Notropis species at 3-hr intervals 14-15 October 1978. Too few N. ardens were collected to permit construction of a curve, but the trend for
this species follows August results
1982
SURAT ET AL.: NOTROPIS ECOLOGY
23
which are sympatric with N. cerasinus. Differences in morphology (including the jaw
angle and size of mouth and jaw in addition to streamlining) between northern and
southern N. albeolus are so pronounced that Gilbert (1964) recognized them as separate
races. Menzel (1976) suggested that the body form of northern N. albeolus resulted from
character displacement due to interaction with N. cerasinus. Our finding that the two
species are ecologically similar, yet not completely so, supports his hypothesis.
Acknowledgments. - For field assistance we wish to thank D. S. Cherry, P. Clinevell, M.
Fleshman, J. Giattina, D. Hadden, M. Hall, P. Johnson, B. Lambert, S. Larrick, J. Robinson
and J. Stockett. We thank R. E. Jenkins for a most helpful critical review of the manuscript. We
gratefully acknowledge the many courtesies of the Alan Sisson family, who freely gave access to
collecting sites, and of J. C. Thompson, Jr., Department of Biology, Roanoke College. This
study was funded by the Department of Biology, Roanoke College, and by a grant to WJM from
the Virginia Academy of Science.
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MENZEL,
SUBMITTED 1 DECEMBER
1980
ACCEPTED
27 MAY 1981