Behavioral Ecology Vol. 15 No. 4: 679–686
DOI: 10.1093/beheco/arh064
Behavioral interactions between salamanders
and centipedes: competition in divergent taxa
Cari-Ann M. Hickerson, Carl D. Anthony, and Jill A. Wicknick
Department of Biology, John Carroll University, University Heights, OH 44118, USA
Red-backed salamanders, Plethodon cinereus, use territorial advertisement in the form of agonistic displays and pheromonal scent
marking as a mechanism for intraspecific interference competition. Although ecological and behavioral interactions among
species of salamanders have been well studied, little is known about the interactions between territorial P. cinereus and other
ecologically similar species, such as large predatory invertebrates. Our field data indicate that P. cinereus and a large syntopic
centipede, Scolopocryptops sexspinosus, exhibit negative spatial associations in natural habitats, possibly indicating interspecific
territoriality. Only seven instances of salamander/centipede co-occurrence were recorded from a field sample of 247 occupied
cover objects. Cover object size was positively correlated with salamander SVL (tip of the snout to the anterior end of the cloaca),
but there was no correlation of cover object size to centipede length. Data on the ability of P. cinereus to differentiate among
chemicals on the substrate suggest that visual cues are not necessary to elicit a territorial response from intruding salamanders.
Although in laboratory trials salamanders behaved similarly toward intruders of both species, biting was directed only toward
centipedes. Salamanders spent significantly more time approaching centipedes than they did approaching other salamanders.
Approach behavior was often associated with nose tapping and may be an investigative, rather than aggressive, behavior. We
suggest that territorial P. cinereus respond similarly to intruding salamanders and centipedes, but that they escalate more readily
to biting centipedes because S. sexspinosus is sightless and thus unable to respond to visual signals. Key words: aggression,
centipede, Plethodon cinereus, salamander, Scolopocryptops sexspinosus, spatial distribution. [Behav Ecol 15:679–686 (2004)]
nterspecific competition is an important ecological factor
that defines community and guild structure. In addition,
selection for reduced interspecific competition results in
character displacement when ecologically similar species coexist. Thus, studies of competitive interactions among species
are crucial to our understanding of ecological and evolutionary processes. Most studies of interspecific competition consider sympatric congeners because it is assumed that closely
related species tend to compete more strongly (Darwin,
1859; Jaksic, 1981). Guilds have been described within birds
(Holmes et al., 1979; Root, 1967), insects ( Joern and Lawlor,
1981), salamanders (Hairston, 1980), desert lizards (Pianka,
1980), and mammals (MacMahon, 1976). Although most of
the focus in the investigation of guild structures remains within closely related groups, a few researchers have examined
interactions between unrelated taxa. Introduction and removal experiments have shown that insects and frogs compete
for pond periphyton (Morin et al., 1988) and that lizards
compete with spiders for insect prey (Schoener and Spiller,
1987). Studies examining guilds encompassing different phyla
could help to assess the importance of competition in community structure.
Interactions among species that comprise guilds may range
from exploitative competition, in which one individual is
more efficient at acquiring resources than another, to interference competition, in which one individual physically excludes another from access to resources. Territoriality, a type
of interference competition, is one way in which species compete for resources such as food or space. It is an important
mechanism mediating competition within and between
I
Address correspondence to C. D. Anthony. E-mail: canthony@jcu.
edu. C. M. Hickerson is now at Department of Biological, Geological,
and Environmental Science, Cleveland State University, Cleveland,
Ohio 44115, USA. J. A. Wicknick is now at University of
Montevallo, Department of Biology, Montevallo, Alabama 35115, USA.
Received 30 March 2003; revised 8 September 2003; accepted 11
October 2003.
salamander species (Anthony et al., 1997; Gergits, 1982;
Nishikawa, 1985; Wrobel et al., 1980). Terrestrial salamanders
remain on the surface and forage in leaf litter as long as the
surface remains wet but will move under rocks and logs as
conditions become too dry for them to freely roam on the
forest floor. For salamanders, territoriality is adaptive because
moisture and prey can become concentrated under cover
objects. Therefore, territories beneath rocks and logs on the
forest floor allow salamanders access to the surface for longer
periods, and they become refugia for isolated prey populations as the forest dries. Extensive laboratory and field evidence shows that the red-backed salamander, Plethodon cinereus
(Caudata: Plethodontidae), is territorial (Gergits and Jaeger,
1990; Horne and Jaeger, 1988; Jaeger, 1981; Jaeger et al.,
1982). Individuals of P. cinereus exhibit site tenacity, advertise
their presence in and are able to defend an area, and expel
intra- and interspecific intruders from that area.
P. cinereus and some members of the class Chilopoda occupy
the same microhabitat, consume similar types of prey, and
are similar in body size. Both P. cinereus and the centipede
Scolopocryptops sexspinosus (Scolopendromorpha: Scolopocryptopidae) are widely distributed in eastern North America
(Petranka, 1998; Shelley, 2002) and can be found living in soil
and humus and under rocks, bark, and rotting logs on the
forest floor (Lewis, 1981; Petranka, 1998). Blower (1955) described S. sexspinosus as a ‘‘surface roamer’’ that moves about
in the litter when moisture is abundant and later retreats to
cover objects. This use of microhabitat is similar to that of
P. cinereus (Fraser, 1976). Roberts (1956) examined the gut
contents of five species of Lithobius centipedes from an English
woodland and found that during March and April approximately 70% contained Collembola remains, a common prey
item for P. cinereus (Jaeger, 1990). In addition to consuming
similar types of prey, the foraging tactics adopted by both
salamanders and centipedes are quite similar. Similar to
P. cinereus, centipedes emerge to hunt mostly at night and in
periods of high moisture and cooler temperatures (Summers
and Uetz, 1979). Laboratory studies of salamanders and centi-
Behavioral Ecology vol. 15 no. 4 International Society for Behavioral Ecology 2004; all rights reserved.
Behavioral Ecology Vol. 15 No. 4
680
pedes have demonstrated a comparable switch in behavioral
search tactics. At high prey densities, salamanders ( Jaeger and
Barnard, 1981; Jaeger et al., 1982) and centipedes (Formanowicz and Bradley, 1987) adopt a sit and wait tactic, whereas
at low prey densities, search activity increases. It is not known
if centipedes are territorial, but they bite (Lewis, 1981; Shelley,
2002; Williams and Hefner, 1928), and could potentially
injure or kill a similarly sized salamander. Thus, there is
potential for exploitative or interference competition between
P. cinereus, and temperate forest centipedes.
The purpose of the present study was to examine ecological
and behavioral interactions between the red-backed salamander, P. cinereus, and an ecologically similar centipede species,
S. sexspinosus. Although P. cinereus and S. sexspinosus occupy
the same microhabitat, it is unknown whether they negatively
associate within that microhabitat. The first part of the present
study included the collection of field data on the microdistribution of these two species. We questioned whether the
two species co-occur under the same cover objects on the
forest floor or whether they exhibit negative associations.
Classic studies of species removal in zones of overlap give
strong support for competitive interactions between species
and show the importance of spatial distribution in determining species interactions (Connell, 1961; Hairston, 1980).
The second part of the present study was designed to
resolve the following question: Can members of P. cinereus
differentiate between a substrate formerly occupied by a centipede and one formerly occupied by a common prey species?
The ability of P. cinereus to recognize differences in chemicals
(pheromones) deposited on a substrate is thought to give
intruding salamanders information necessary to make decisions about whether or not to increase agonistic behavior in
a given encounter with a territorial resident (Simons et al.,
1997). Littlewood and Blower (1987) found that in laboratory
trials the common brown centipede, Lithobius forficatus, deposits a chemical mark on damp filter paper that affects the
behavior of conspecifics. The pheromone is apparently sexspecific and may function in intraspecific chemical communication. The final aspect of the present study was to examine
aggressive behavior of P. cinereus toward centipedes. Individuals of P. cinereus have been shown to exhibit aggressive
behavior toward conspecifics (see Jaeger, 1984), congenerics
(see Jaeger et al., 1998), ambystomatid salamanders (Ducey et
al., 1993), and carabid beetles (Gall et al., 2003). Aggressive
behavior between species that are thought to compete may
indicate a behavioral mechanism of interference competition.
Microhabitat separation, the ability to use chemoreception to
identify threatening intruders, and aggressive territorial behavior are all suggestive of competitive interactions between
species. We therefore proposed the following hypotheses: (1)
P. cinereus and S. sexspinosus will exhibit negative spatial associations on the forest floor, and (2) individuals of P. cinereus
will behave similarly to conspecifics and to centipedes.
Specifically, we predicted that residents of P. cinereus would
exhibit similar levels of aggressive behavior toward conspecific
and centipede intruders and that resident salamanders would
exhibit similar levels of aggressive behavior in response to the
odors of both species.
METHODS
Distribution in the natural habitat
To determine distribution patterns of P. cinereus and S. sexspinosus, field data were collected from 10 forested sites in
northeastern Ohio (Cuyahoga County) during September
and October 2001. We overturned 100 cover objects (logs,
rocks, and bark greater than 25 cm2) at each of the 10 sites.
For each cover object, we noted whether adult P. cinereus and
adult S. sexspinosus co-occurred, occurred alone, or were
absent. The ‘‘absence’’ category consisted of cover objects that
had juveniles of either study species, or other species of
salamanders or centipedes beneath them. Cover objects that
did not meet these criteria were excluded from the analysis;
thus, we only included cover objects that were suitable for use
by salamanders and centipedes. Frequency of P. cinereus/
S. sexspinosus co-occurrence was compared to an expected
frequency by using a two-tailed chi-square test with a ¼ 0.05
(Zar, 1999).
Territory quality
Individuals should compete for high-quality territories when
resources are limited. Larger cover objects are thought to be
superior because they hold moisture and associated prey for
longer time periods, and larger salamanders are thought to be
better territory holders owing to the advantages that large size
confer during territorial conflicts (Mathis, 1990a). Therefore,
the largest salamanders should be found in the best territories
(i.e., under the largest cover objects).
On 7, 11, and 16 June 2001 we recorded the sizes of cover
objects and associated salamanders and centipedes in a
forested area in Independence, Cuyahoga County, Ohio
(41 23944.090 N; 81 39921.770 W). We worked systematically
through the site to avoid measuring cover objects more than
once. Each cover object occupied by individuals of P. cinereus
or S. sexspinosus was measured (greatest length times greatest
width). Salamanders were measured from the tip of the snout
to the anterior end of the cloaca (SVL). Centipedes were
measured from the tip of the upper mandible to the posterior
end of the last body segment. Relationships between cover
object size and salamander SVL or centipede body length
were analyzed by using two-tailed Spearman rank correlation
a ¼ 0.05 (Mathis, 1990a; Zar, 1999). To ensure independence
of samples, cover objects that contained more than one
individual were not used in either analysis.
Recognition of chemicals on the substrate
Twelve adult males of P. cinereus (more than 32 mm SVL;
Pfingsten and Downs, 1989) and 12 presumed adults
(unsexed) of S. sexspinosus (more than 32 mm) were collected
from Independence, Cuyahoga County, Ohio (41 23944.090
N; 81 39921.770 W) in June 2001. We assumed that centipedes
were adults because they were similar in size to brooding
females that we observed in the field. Individuals of both
species were housed separately in 15-cm-diameter Petri dishes
(1.6 cm deep) lined with damp filter paper. Chambers were
maintained in a controlled environment at 17 6 1 C and 12-h
light/12-h dark photoperiod. Each individual was fed 20–30
fruit flies (Drosophila virilis) and allowed to mark territories
with pheromones for 5 days. Flies not eaten from experimental containers were removed 2 days before testing. Flies were
placed on control substrates at the same time that experimental animals were fed and were removed the day of testing,
just before the trial in which they were used. Flies were
removed from the experimental containers earlier than from
the control containers to ensure that the scent of the flies had
time to dissipate from experimental containers. This was to
avoid confusing the salamanders with the scent of prey in
addition to the scent of conspecifics or centipedes. On day 6,
individuals of P. cinereus were randomly tested in one of three
trial types. There were two experimental conditions, P. cinereus
on a conspecific’s substrate or P. cinereus on a centipede’s
substrate, and a control condition (substrate occupied by
D. virilis alone). Twelve trials were conducted for each of the
Hickerson et al.
•
Behavioral interactions between salamanders and centipedes
three conditions from 1000–1500 h in February 2002.
Salamanders were observed under indirect lighting (two 15W GE fluorescent Cool White bulbs, 3.0 lux). Treatments and
controls were evenly dispersed across test dates (Hurlbert,
1984). Comparisons among treatments were made using twotailed paired Wilcoxon signed-rank test. We reduced a to
0.025 because each data set was used twice in each analysis.
Each salamander was placed on one of the three types of
substrates under an opaque, circular habituation dish (5 cm
diameter by 1.6 cm deep) for 5 min. The dish was then lifted,
and the salamander was permitted to react freely to the scent
on the rest of the substrate. Individuals whose substrates were
being used in a trial were held in a clean holding chamber
lined with damp filter paper. Salamanders whose territory was
used in a trial and who were to be tested the same day
remained in the holding chamber until they were tested. This
avoided cross-contamination of another salamander’s scent
onto the home territory. Each salamander was tested in the
control condition and each of the two experimental conditions. Frequency and duration of the following behaviors
were recorded for P. cinereus: (1) All trunk raised (ATR) was
considered an aggressive posture; the legs are extended such
that the head, trunk, and sometimes tail are lifted off of the
substrate ( Jaeger, 1984). (2) Flattened (FLAT) was considered
a submissive posture; the entire ventral surface of the body is
in contact with the substrate ( Jaeger, 1984). (3) Nose tapping
the substrate (NTS) was considered an investigative behavior,
contact of the nasolabial cirri to the substrate. Often the
salamanders would hold their snout to the substrate for
several seconds at one time, and sometimes to fecal pellets.
(4) Escape (E) behavior was defined as circling the periphery
of the chamber while pressing the snout or body upward
against the Petri dish lid at the edge of the testing arena. This
is considered a submissive behavior (Wise and Jaeger, 1998).
Aggressive behavior
Adult male salamanders (P. cinereus, n ¼ 30) and adult
centipedes (S. sexspinosus, n ¼ 30) were collected from the
same forested area described above and tested for agonistic
interactions in June 2001. Individuals of each species were
collected and housed separately in 15-cm-diameter (1.6 cm
deep) clear plastic Petri dishes lined with damp filter paper.
Both species were fed Drosophila virilis ad libitum. Chambers
were maintained in a controlled environment at 17 6 1 C and
12-h light/12-h dark photoperiod. Salamanders and centipedes were weighed and measured prior to testing (mean SVL
and mass of salamanders ¼ 38.60 mm, SE ¼ 0.51 and 1.09 g,
SE ¼ 0.03, mean body length and mass of centipedes ¼ 40.77
mm, SE ¼ 0.78, and 0.204 g, SE ¼ 0.01).
Before experimental interactions, individuals were kept in
separate containers for 5 days, enough time to allow marking
of the substrate with pheromones ( Jaeger, 1981). Thirty
resident salamanders were randomly paired once with an
intruding conspecific and once with an intruding centipede,
for a total of 60 trials. Trials were run from 1000–1700 h in
June and July 2001. On day 6 an intruding centipede or
conspecific was placed in a resident salamander’s chamber,
under an opaque circular habituation dish (5 cm diameter by
1.6 cm deep). The resident salamander was also lifted and
replaced in its own chamber under an opaque habituation
dish, to control for handling. After a 5-min habituation period,
both habituation dishes were lifted, allowing interaction
between resident and intruder. Behavioral interactions were
observed and recorded for both resident and intruder for 15
min under the lighting conditions described above. The first
interactive behavior (either look toward or move toward)
signaled the start of the 15-min trial period. Each salamander
681
Figure 1
Relationship between cover object size (cm2) and (a) SVL (mm) of
Plethodon cinereus (R 2 ¼ .321, p ¼ .004) and (b) total body length
(mm) of Scolopocryptops sexspinosus (R 2 ¼ .118, p ¼ .275).
was used as a resident and an intruder in intraspecific trials
but only as a resident in interspecific trials. One week was
allowed to pass between use as a resident or an intruder, and
no salamander was paired with the same individual more than
once. Size asymmetries were minimized to reduce the fighting
advantage by the larger animal (Mathis, 1990a). This was
accomplished by randomly pairing individuals within three
size classes. Paired individuals differed by a mean of 2.44 mm
(6 1.8 mm).
The frequency and duration of the following behavior patterns (as defined in Jaeger, 1984) were recorded for P. cinereus
residents. The following were aggressive behaviors: all trunk
raised (ATR), as defined in previous section; look toward
(LT), salamander turns its head in the direction of the other
animal; move toward (MT), salamander approaches the other
animal in a direct path that would result in contact if the
movement were to continue; and biting (BITE), closing of the
jaws around any part of the other animal’s body and immediately releasing the grip. The following were considered
submissive behaviors: flattened (FLAT), as defined in previous
section. Look away (LA) salamander turns its head away from
the other animal; and move away (MA), salamander increases
the distance between itself and the other animal. Other behaviors were as follows: nose tapping substrate (NTS), as
defined in previous section; nose tapping animal (NTA),
contact of nasiolabial cirri to other animal’s body; front trunk
raised (FTR), considered a resting posture, the head and
anterior half of the trunk are raised off the substrate; walk
on (WO), salamander makes contact with and moves over
the other animal; and walk under (WU), salamander makes
bodily contact with the other animal, moving or nudging
under it.
Behavioral Ecology Vol. 15 No. 4
682
Figure 2
Behavior of P. cinereus when
placed on substrates previously
occupied by a conspecific (Pc
indicates Plethodon cinereus),
a centipede (Ss indicates Scolopocryptops sexspinosus) or on
a control substrate (fly: Drosophila virilis). (a) Mean time
(s) spent in aggressive ATR
posture. (b) Mean frequency
of aggressive ATR posture. (c)
Mean time (s) spent nose
tapping the substrate (NTS).
(d) Mean frequency of nose
taps to substrate (NTS). (e)
Mean frequency of escapes.
Lowercase letters above the
bars indicate statistical differences at p ¼ .025.
Statistical comparisons were made between the behavior of
resident salamanders in intraspecific trails and resident
salamanders in interspecific trials by using paired Wilcoxon
signed-rank tests (two-tailed). Paired tests were used because
each salamander was tested once with a conspecific and once
with a centipede intruder. We compared the behavior of resident salamanders in intraspecific trials to their behavior when
they were tested as intruders by using paired Wilcoxon signedrank tests. One-tailed tests were used for this comparison
because previous studies support the prediction that resident
salamanders are more aggressive and less submissive toward
conspecific intruders (Anthony et al., 1997; Jaeger, 1984;
Mathis, 1990b;). a was set at 0.05 for all comparisons (Zar,
1999). An aggression index using the aggressive behaviors MT
and LT and the submissive behaviors MA and LA was
calculated as [(MT þ LT) (MA þ LA)] (Mathis et al., 2000)
and used in all of the above comparisons.
RESULTS
Distribution in the natural habitat and territory quality
Weather conditions varied among sampling trips (temperature range ¼ 9 C21 C), but both species were active on the
surface during each sampling day (mean number of salamanders ¼ 18, SE ¼ 3.5; mean number of centipedes ¼ 15.5,
Hickerson et al.
•
Behavioral interactions between salamanders and centipedes
SE ¼ 5.1). Of 247 occupied cover objects sampled, we found
that there were only seven instances in which adults of P.
cinereus and S. sexspinosus co-occurred under the same cover
object. This is significantly less than would be expected by
chance (v2 ¼ 65.4, p , .001). Salamanders were found alone
under 85 cover objects, centipedes were found alone under 79
cover objects, and 76 cover objects housed neither adult P.
cinereus or adult S. sexspinosus. Salamanders co-occurred under
three cover objects, and centipedes co-occurred under five
cover objects. These data were not included in the analysis.
Cover object size ranged from 124–2580 cm2 (mean ¼ 780.4
cm2, n ¼ 55) and was positively correlated with SVL of P.
cinereus (p ¼ .004) (Figure 1a). However, body length of
S. sexspinosus showed no correlation with cover object size
(p ¼ .275) (Figure 1b).
Recognition of chemicals on the substrate
Salamanders spent significantly more time in ATR when
placed on substrates previously occupied by either conspecifics (z ¼ 2.71, p ¼ .007) or centipedes (p ¼ .006) (Figure 2a
and Table 1). Frequency of ATR did not significantly differ
across treatments (Figure 2b). P. cinereus spent significantly
less time nose tapping the substrate of flies than that of other
salamanders (z ¼ 2.51, p ¼ .01) (Figure 2c). Time spent nose
tapping the substrate of centipedes was not significantly different from time spent nose tapping salamander (z ¼ 0.36, p ¼
.72) or fly (z ¼ 1.41, p ¼ .16) substrates (Figure 2c). Differences in frequency of nose taps were not significant (z ¼ 1.81,
p ¼ .07) between salamander and fly substrates (Figure 2d);
there was no significant difference in the frequency of nose
taps between salamander and centipede (z ¼ 0.47, p ¼ .64) or
centipede and fly (z ¼ 1.49, p ¼ .14) substrates. There was
a tendency for P. cinereus to exhibit higher levels of escape
behavior when exposed to a centipede’s substrate compared
with a conspecific’s substrate (z ¼ 1.95, p ¼ .05) (Figure 2e),
and frequency of escape by salamanders was significantly
higher on centipede substrates compared with the control
(z ¼ 2.39, p ¼ .02) (Figure 2e). The mean number of escapes
was nearly double on centipede substrate compared with
salamander trials and control trials (Table 1).
Aggressive behavior
Comparisons of the aggression indices revealed that P. cinereus
was more aggressive as a resident than as an intruder (T ¼
2.70, p ¼ .012), but there were no differences in time spent in
ATR (T ¼ 0.56, p ¼ .58) or FLAT (T ¼ 0.30, p ¼ .77) between
residents and intruders. The response of residents of P. cinereus
toward intruding conspecifics was comparable to intruding
centipedes, with no differences in the aggression index (T ¼
0.43, p ¼ .67) (Figure 3a) or time spent in ATR (z ¼ 0.25, p ¼
.80) (Figure 3b). Residents of P. cinereus spent significantly
more time approaching (MT) centipede intruders than conspecific intruders (z ¼ 2.10, p ¼ .037) (Figure 3c). Interestingly, the only biting that occurred in any trials was P. cinereus
residents biting centipede intruders (mean ¼ 0.23, z ¼ 2.33,
p ¼ .02) (Figure 3d). Biting occurred in 8% of interspecific
trials. Salamander residents spent on average half the amount
of time in submissive (FLAT) position during interspecific
trials compared with intraspecific pairings (z ¼ 1.54, p ¼ .07)
(Table 2). Residents of P. cinereus spent more time WO (z ¼
2.77, p ¼ .006) and WU (z ¼ 2.37, p ¼ .018) salamander
intruders than centipede intruders (Figure 3e,f).
Qualitative summary of centipede behavior
The centipedes were typically unresponsive to salamander
movement and usually remained still unless contact was made
683
Table 1
Behaviors of P. cinereus when placed on substrates previously
occupied by conspecifics, centipedes, or on the control substrates
that were previously occupied by fruit flies (Drosophila virilis)
Behavior:
Time (s) spent in
ATR
NTS
ESCAPE
FLAT
Frequency of
ATR
NTS
ESCAPE
FLAT
P. cinereus
(n ¼ 12)
S. sexspinosus
(n ¼ 12)
flies
(n ¼ 12)
226.1 (60.8)
0–653
21.4 (3.68)
2–41
26.8 (11.4)
0–111
73.4 (47.5)
0–465
225.1 (51.4)
0–555
21.2 (5.40)
0–70
35.9 (12.3)
0–141
26.7 (12.9)
0–139
96.0 (36.1)
0–393
10.8 (2.83)
0–34
20.4 (8.07)
0–84
14.8 (9.00)
0–108
7.08
0–15
15.4
2–27
2.58
0–9
0.50
0–3
9.25
0–22
17.3
0–30
4.58
0–11
0.75
0–3
6.42 (2.17)
0–23
11.3 (9.32)
0–34
2.25 (2.90)
0–7
0.42 (0.15)
0–1
(1.69)
(2.25)
(0.97)
(0.26)
(1.94)
(2.80)
(1.25)
(0.28)
Means, standard errors (parentheses), and ranges are presented.
See text and Fig. 2 for significant differences.
by the salamander. During all trials, centipedes frequently
groomed their antennae, especially following contact with the
salamander or its fecal pellets. When moving, centipedes
circled the edge continuously and infrequently (10% of trials)
crossed through the middle of the test chamber. There were
several instances when centipedes appeared to sample the
shed skin or fecal pellets of a salamander with their antennae.
When centipedes walked into salamanders, making contact
with their antennae, they often immediately reversed direction, stopping along the edge at the opposite side of the
chamber. There were 15 instances (25% of trials) in which the
centipedes walked on the salamanders. This action most often
resulted in a flip by the salamander in which it spun its entire
body approximately 180 degrees, but sometimes resulted in
bites by the salamander. Both P. cinereus and S. sexspinosus
displayed escape behavior after bites.
DISCUSSION
Salamanders and centipedes were negatively associated in our
field sites. Only seven instances of salamander/centipede cooccurrence were recorded from a field sample of 247 occupied
cover objects. Negative spatial association is suggestive of competition for cover objects on the forest floor ( Jaeger, 1979).
Marvin (1998) found that, in sympatry, individuals of P.
glutinosis and P. kentucki were usually found alone under cover
objects, and he concluded that these species compete for
space. Alternatively, negative spatial associations may result
from differences in microhabitat use. Although we observed
no obvious differences in microhabitat between species,
variables such as soil temperature, moisture, and pH were
not quantified in the present study.
It is unclear what factors determine territory (cover object)
quality for these species. Several researchers have examined
the possibility that large cover object size defines a superior
quality territory because large objects hold moisture longer,
providing refuge for invertebrate prey. Our findings were
similar to those of Mathis (1990a) for P. cinereus. She found
684
Behavioral Ecology Vol. 15 No. 4
Figure 3
Behavior of residents of P.
cinereus during pairings with
intruding
centipedes.
(a)
Mean aggression index (see
text). (b) Mean time (s) spent
in aggressive all trunk raised
(ATR) posture. (c) Mean time
(s) spent approaching (MT)
centipede intruders. (d) Mean
frequency of biting (BITE) intruding centipedes. (e) Mean
time (s) spent walking on
(WO) intruding centipedes.
(f) Mean time (s) spent walking under (WU) intruding
centipedes. Lowercase letters
above bars indicate statistical
differences at p ¼ .05.
that SVL was positively correlated with cover object area and
larger salamanders were better competitors. Other researchers have found no such correlations between SVL and cover
object size in salamanders (Anthony et al., 2002; Faragher and
Jaeger, 1997; Gabor, 1995; Quinn and Graves, 1999). For
centipedes, we found no relationship between cover object
area and resident size. It is possible that cover object size may
not be as important for centipedes as it is for salamanders
because centipedes have the ability to burrow through soil
underground and can perhaps locate enough prey and keep
from desiccating without the use of large cover objects.
However, Fraser (1976) suggested that when salamanders are
forced to retreat underground, their foraging opportunities
are limited. If centipedes prey on similar invertebrates as
salamanders and if those prey are limited underground, cover
object quality should be important for both species.
Males of P. cinereus responded similarly to centipede
substrates and to substrates of other male conspecifics, but
had a tendency to attempt escapes more frequently on substrates with centipede odors. The scent of the centipedes or of
male conspecifics was sufficient to cause salamanders placed
on these marked substrates to display a threat posture. Horne
and Jaeger (1988) established that females of P. cinereus only
needed olfactory cues left on fecal pellets to display threat
postures. Jaeger et al. (1986) found that males of P. cinereus
did not differ in the amount of time spent in threat postures
in the presence of their own fecal pellets compared with the
fecal pellets of conspecifics. Therefore, they concluded that
for males a visual display is necessary to release a threat
posture. Our conclusions differ from those of Jaeger et al.
(1986). Not only did male P. cinereus spend more time in ATR
(a threat posture) when on substrates of conspecifics, they
behaved similarly when placed on a centipede substrate. Thus,
males of P. cinereus in this study detected and responded to
both salamander and centipede odors in a way consistent with
territorial response to a conspecific intruder.
Hickerson et al.
•
Behavioral interactions between salamanders and centipedes
Individuals of P. cinereus tended to exhibit escape behavior
in Petri dishes that had been occupied by S. sexspinosus more
often than during other trials. Lopez and Martin (2001)
reported that amphisbaenians were also able to discriminate
between snake and scolopendrid centipede odors, and Littlewood and Blower (1987) provided evidence for intraspecific
chemical communication in the centipede, Lithobius forficatus.
Thus, some species of centipedes produce recognizable odors.
In the present study, salamanders tended to move away from
centipede odors but not away from odors of conspecifics.
From pheromonal markers of conspecifics, both resident and
intruding salamanders are able to assess the size and sex of
one another and determine if the contest should escalate
(Mathis, 1990b). Perhaps individuals of P. cinereus are able to
determine if intruding centipedes pose a threat by having the
ability to recognize the chemicals deposited by those individual centipedes.
In behavioral trials, individuals of P. cinereus behaved in
a similar manner toward intruding conspecifics and intruding
centipedes, exhibiting similar levels of aggressive behavior.
However, resident salamanders spent more time MT centipede intruders than conspecific intruders and biting by salamanders was only observed in interspecific trials. We believe
that the approach (MT) of individuals of P. cinereus toward
centipedes was investigative in nature rather than aggressive.
Wrobel et al. (1980) stated that for P. cinereus, an encounter
begins when one individual approaches another, initiating a
sequence of aggressive behavior patterns. In the present study,
residents did not follow an approach with aggressive behavior
when paired with centipedes, but rather the salamander approached with hesitation by slowly rocking the entire body
forward without movement of the limbs until the forward
motion forced the salamander to very slowly pick up a limb
and take a step in the forward direction. The approach was
usually followed by NTA and NTS. Once nose tapped by the
salamander, the centipede would usually flee in the opposite
direction. It is possible that the aggression index of
salamanders paired with centipedes was elevated because of
the increased duration of the MT component of the index.
However levels of ATR were consistent with the aggression
index in conspecific and heterospecific trials.
We observed very few instances of biting during the present
study. All biting that occurred was directed toward centipedes
by salamanders in interspecific trials. Centipedes have been
recorded in the guts of some plethodontid salamanders
(Fraser, 1976) and Hoffman (1954) reported a juvenile
S. sexspinosus in the gut of an adult P. richmondi. However, we
believe the relationship between adults of P. cinereus and
adults of S. sexspinosus is most likely not a predator/prey
relationship because the size asymmetry between the two
species is too small for a salamander to consume an adult S.
sexspinosus. Perhaps most interesting is that all members of the
centipede family Scolopocryptopidae lack ocelli and are
considered sightless. S. sexspinosus does not have good visual
acuity and can only respond minimally to changes in light and
dark (Lewis, 1981). P. cinereus usually resolves territorial
contests by using visual displays and bites only as a last resort
( Jaeger et al., 1982). In a recent study in which individuals of
P. cinereus were paired with carabid beetles, there was no biting
by P. cinereus of conspecific intruders or intruding beetles;
both have fairly good vision (Gall et al., 2003). We hypothesize
that P. cinereus is forced to escalate to biting in contests with S.
sexspinosus because these centipedes are unresponsive to visual
threat displays.
The data from all three components of this study are
supportive of competitive interactions between the centipede
S. sexspinosus and the territorial salamander P. cinereus. Salamanders and centipedes exhibited negative spatial distribu-
685
Table 2
Behaviors of residents of P. cinereus when paired with conspecific
and centipede intruders.
Resident
Behavior
ATR
LT
MT
WO
BITE
FLAT
LA
MA
WU
NTS
NTA
FTR
Intruder
Intraspecific
(n ¼ 30)
Intraspecific
(n ¼ 30)
Interspecific
(n ¼ 30)
344.2 (49.3)
0–753
4.40 (0.39)
0–8
95.2 (12.8)
0–260
39.1 (11.3)
0–232
0
—
36.2 (17.6)
0–370
1.10 (0.23)
0–5
34.3 (11.2)
0–291
7.27 (2.81)
0–52
9.23 (1.66)
0–30
2.70 (0.57)
0–11
519.6 (43.8)
147–900
357.3 (53.4)
0–841
4.20 (0.43)
0–8
144.4 (21.7)
0–402
3.30 (2.60)
0–79
0.23 (0.09)
0–2
15.4 (13.5)
0–406
1.0 (0.23)
0–4
32.5 (11.1)
0–233
0
—
8.23 (1.40)
0–33
2.67 (0.62)
0–16
527.3 (51.7)
59–900
373.8 (47.1)
0–797
2.9 (0.38)
0–7
77.4 (15.5)
0–398
35.4 (11.2)
0–221
0
—
30.8 (11.6)
0–260
0.73 (0.23)
0–5
41.5 (8.73)
0–180
4.30 (2.27)
0–59
10.4 (1.73)
0–32
1.77 (0.42)
0–9
472.1 (42.4)
103–900
The left two columns show mean resident data when paired with
intraspecific intruders, or interspecific intruders. The right column
gives means for P. cinereus as intruders paired with intraspecific
residents. Means, standard errors (parentheses), and ranges are
presented. LT, LA, NTS, NTA, and BITE were recorded as frequency
of occurrence. All other data were recorded in seconds.
tions, salamanders exhibited escape behavior when presented
with centipede odors, and resident salamanders responded
similarly to centipede and salamander intruders. Gall et al.
(2003) argued that through combinations of territorial and
predatory behavior, carabid beetles may have negative effects
on salamander populations. We concur that such interactions
between small vertebrates and large predatory invertebrates
may be important determinants of community composition of
forest floor predators.
We thank the Cengic family for allowing us to collect on their property
and Case Western Reserve University for providing access to Squire
Valleevue Experimental Farm. The Ohio Department of Natural
Resources granted collecting permits. Paul Cengic, Jennifer Fields,
Jessica Hickey, and Moria Nagy provided assistance in the field. This
research was conducted with prior approval of the Institutional
Animal Care and Use Committee at John Carroll University (IACUC
No. 2001-110). The manuscript benefited from the comments of two
anonymous reviewers.
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