Behavioral Ecology
doi:10.1093/beheco/ari070
Advance Access publication 22 June 2005
Behavioral ecology of disturbed landscapes: the
response of territorial animals to relocation
Catherine E. Burns
Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street,
New Haven, CT 06511, USA
Intraspecific territorial interactions are common for a large variety of wildlife species. This often results in high-quality habitat
being occupied by dominant individuals, with subordinates relegated to lower quality habitat. The role that these territorial
interactions play in influencing the redistribution of animals that have been evicted from their native home ranges remains
unclear. My goals were to determine (1) how the density of conspecifics in the new habitats impacts resettlement patterns and
(2) to what extent prior dominance status is maintained when an animal is forced to relocate. I relocated white-footed mice
(Peromyscus leucopus) from high-quality, oak-dominated hardwood and lower quality, white pine forests to novel sites and released
them along the ecotone of these two habitat types. I relocated mice first in the presence and then in the absence of a natural
density of resident mice. Habitat selection and resource acquisition of relocated mice were assessed via mark-recapture livetrapping and passive integrated transponder tagging. Relocated mice selected high-quality habitat significantly more often when
resident mice were absent, illustrating the importance of territorial interactions for determining resettlement patterns of relocated individuals. Data on resource acquisition also reflected the competitive influence of resident mice—relocated mice were
significantly more successful accessing food resources in the treatment without residents. The habitat of origin did not significantly impact habitat selection or resource acquisition, indicating that all relocated individuals were at a disadvantage compared
to residents. Key words: habitat quality, habitat selection, Peromyscus, territory, white-footed mouse. [Behav Ecol 16:898–905 (2005)]
ource-sink and ideal-despotic distribution theories predict
that for territorial animals, socially dominant individuals
will occupy high-quality habitat due to their competitive superiority (Fretwell and Lucas, 1970; Halama and Dueser, 1994;
Holt, 1987, 1996; Jaenike and Holt, 1991; Kawecki, 1995;
Pulliam, 1988; Pulliam and Danielson, 1991). Low-quality
habitat should contain subordinate, younger, or weaker conspecifics that have not acquired the size, strategy, or status
needed to occupy high-quality sites. Empirical evidence supports these theories for a variety of species (Bowers and Smith,
1979; Holmes et al., 1996; Korytko and Vessey, 1991; Linzey,
1989; Madison, 1977; Martell, 1983; Metzgar, 1971; Moller,
1991; Sullivan, 1979). This behavioral framework of habitat
selection also can be used to formulate hypotheses about redistribution patterns of territorial animals responding to disturbances, such as anthropogenic landscape alteration, which
result in the eviction of resident individuals from their native
home ranges. As human population expansion leads to increased conversion of land cover, it is increasingly important to
understand the individual- and population-level consequences
of these changes.
I apply these concepts from behavioral ecology to address
the following pressing issues related to wildlife conservation:
What effect will habitat loss have on wildlife residing in and
around the impacted area? How will animals respond to eviction from their native habitat, and what affects their ability to
successfully establish new home ranges? Does habitat loss impact some individuals (e.g., subordinates) more than others?
For species whose distributions are largely governed by intraspecific territorial interactions, behavioral insights are likely
S
Address correspondence to C.E. Burns. E-mail: catherine.burns@
yale.edu.
Received 18 October 2004; revised 16 May 2005; accepted 23 May
2005.
The Author 2005. Published by Oxford University Press on behalf of
the International Society for Behavioral Ecology. All rights reserved.
For permissions, please e-mail: [email protected]
to prove extremely useful for answering these questions
(Caro, 1998; Lima and Zollner, 1996).
Predicting redistribution patterns for territorial species in
heterogeneous landscapes requires understanding how an
individual’s dominance status is affected on eviction from its
natural home range. This requires distinguishing (1) whether
relocated animals are at a competitive disadvantage, regardless of prior dominance status, as compared with residents of
intact neighboring habitats or (2) whether animals maintain
their dominance status when forced to relocate to new areas.
The first outcome would impact only those individuals that
were immediately affected by the landscape disturbance. This
scenario could result in very low reestablishment success leading ultimately to the relocated individuals’ decreased fitness
or death. The second outcome could result in domino effects,
where an influx of dominant individuals from a disturbed
habitat causes residents of the newly selected habitat to be
evicted and so on. Such effects could impact individuals across
much larger spatial scales than the first scenario. Potentially,
domino effects could force a large number of animals into
low-quality habitat (including ‘‘sinks,’’ where population growth
is negative). This could result in population declines across
the mosaic landscape, while individual-level impacts on the
animals in the directly disturbed area were negligible.
To address these issues, I experimentally investigated the
importance of territorial interactions for the redistribution
and resource acquisition of white-footed mice (Peromyscus leucopus) after relocation to novel heterogeneous environments.
White-footed mice exhibit density-dependent territorial interactions (Halama and Dueser, 1994; Linzey, 1989; Wolff, 1985),
lending this species to investigations of the effects of territoriality on relocation success. I focused on the response of mice
in the first month after relocation. This period should sufficiently characterize the response to relocation due to the rapid
rate at which territorial interactions are likely to ensue after
introduction of ‘‘strangers’’ to a landscape occupied by conspecifics (Dewsbury, 1988; Korytko and Vessey, 1991; Randall
Burns • Behavior and relocation success
899
Table 1
Hypotheses, predictions, and evidence in support of or against each alternate hypothesis
Evidence for or against
(1/)
Prediction
Hypothesis
A
B
Dominance status is negatively
impacted for all evicted
individuals
Animals retain the dominance
status they held prior to relocation
C
Dominance status does not shape
redistribution patterns
D
Redistribution is based on habitat
affinity only
Residents
present
Residents
absent
Residents
present
Residents
absent
Few relocated individuals select
high-quality habitat, regardless of
habitat of origin
Animals originally from highquality habitat select high-quality
habitat but those from poor
quality-habitat do not
Many relocated individuals select
high-quality habitat, regardless of
origin
Relocated individuals
preferentially select the habitat
type that they were originally from
Many relocated individuals select
high-quality habitat, regardless of
origin
Many relocated individuals select
high-quality habitat, regardless of
origin
1
1
1
Many relocated individuals select
high-quality habitat, regardless of
origin
Relocated individuals
preferentially select the habitat
type that they were originally from
1
A plus (1) sign indicates experimental evidence in agreement with the predictions for each hypothesis, and a minus () sign indicates
disagreement. Only one hypothesis (A) that dominance status is negatively impacted for all evicted individuals was supported by evidence
from both components of the relocation experiment.
et al., 2002; Rowley and Christian, 1976; Schradin, 2004).
Further, the consequences associated with foraging in an occupied unfamiliar setting, such as decreased food consumption, should be most strongly manifested immediately after
relocation. These results in turn provide insight into the likely
longer term fitness consequences for relocated individuals
and into the probability of population-level consequences.
The response of mice to relocation, with respect to habitat
selection, was assessed in light of four alternate hypotheses
and corresponding predictions (detailed in Table 1). The
dominance status of all individuals may be compromised by
relocation, regardless of their initial status (Hypothesis A); all
relocated animals may maintain the dominance status they
held prior to relocation (Hypothesis B); habitat selection after
relocation may be unrelated to dominance status, with all
individuals capable of accessing high-quality habitat (Hypothesis C); or redistribution patterns may simply reflect preference for a specific habitat type (‘‘habitat affinity,’’ Hypothesis
D). Because these hypotheses generate predictions that partially overlap in some cases (see Table 1), distinguishing
between these competing hypotheses requires assessing the
response of relocated animals both in the presence and in
the absence of resident conspecifics. Resource acquisition
ability, as measured by access to seed trays and changes in
body mass, was predicted to reflect the same patterns described in Table 1 for Hypotheses A–D.
Hypotheses A and B assume that an animal’s habitat of origin is a reflection of its dominance status, based on a history of
habitat selection decisions influenced by territorial interactions. Therefore, individuals initially found in high-quality
habitat are assumed to be competitively dominant and those
in lower quality habitat competitively inferior. Although this
so-called ideal-despotic distribution is supported by empirical
evidence in other systems (e.g., birds, Petit JL and Petit DR,
1996; lizards, Carlsbeek and Sinervo, 2002; and squirrels,
Wauters et al., 2001) and for Peromyscus (Halama and Dueser,
1994; Korytko and Vessey, 1991; Linzey, 1989; Morris, 1991),
I will also assess the validity of this assumption for the animals in
this study. To my knowledge, this is the first field experiment to
directly test the effect of intraspecific interactions on the relocation success of animals evicted from their native home ranges.
METHODS
Study sites
The relocation experiment was performed during June–
August 2002 at three replicate sites—Lost Pond 1 (LP1), Lost
Pond 2 (LP2), and Morse Pond (MP)—named for nearby
ponds within the Yale-Myers Research Forest in Northeastern
Connecticut, USA. All sites were ,2 km apart, with LP1 and
LP2 separated by 200 m. Each site consisted of mixed hardwood forest, dominated by oak (Quercus sp.), sugar maple
(Acer saccharum), and hickory (Carya sp.), immediately adjacent to single-species white pine forest (Pinus strobus). There
was a sharp transition between the two habitat types due to
a land-use history dominated by agriculture and plantation
monocultures. Prior to initiation of the experiment, a livetrapping grid was set up across each site to tag resident mice. The
grid covered 1 ha (100 3 100 m) of each habitat type extending from the transition zone (Figure 1). Resident P. leucopus at
the three sites naturally occurred at densities of 28.0, 18.5,
and 9.5 mice/ha for LP1, LP2, and MP sites, respectively,
immediately prior to the first relocation event (for details on
Figure 1
Diagram of one of the three replicate sites, depicting 1 ha each of
adjacent oak-dominated hardwood (high quality) and white pine
(lower quality) forests, with a sharp transition zone. Relocated mice
were released along the transition zone in the presence and absence
of residents. Circles indicate seed tray placement.
900
estimates of resident densities, see Small Mammal Sampling).
For simplicity of presentation, these densities are referred to
as ‘‘approximately 30, 20, and 10 mice/ha’’ when discussed in
the subsequent text. Resident densities reflect the minimum
number known alive based on trapping records and were
statistically significantly different between all three sites
(ANOVA, F2,9 ¼ 23.02, p , .001).
To confirm differences in habitat quality between hardwood
and pine forests at the relocation sites, I conducted an assessment of survival and reproduction for P. leucopus residents of
LP1 during the summer of 2001 and prerelocation in 2002
using livetrapping and nest-box surveys (Burns, unpublished
data). LP1 was comparable to the other two sites in the composition and structure of both the overstorey vegetation and
small mammal communities. Persistence times of adult residents (those with .1 capture) were 50% higher in hardwood
forest ð
x ¼ 61 daysÞ compared to pine forest ð
x ¼ 39 daysÞ: Reproductive output per unit time, as measured by number of
offspring produced per female, was comparable for both
habitat types, leading to an estimated fitness advantage for
mice in hardwood forest. Four years of data on survival and
reproduction of mice residing in these two habitat types in
the Yale-Myers Research Forest also support this habitat
ranking (Burns, unpublished data). Across the continent, oakdominated hardwood forest serves as an extremely high-quality
habitat for white-footed mice (Adler et al., 1984; Morris, 1989;
Schnurr et al., 2002). The natural density of mice prior to the
relocation experiment was higher in the hardwood habitat at
all three sites (LP1: 53% hardwood, 39% pine, 8% transition;
LP2: 48% hardwood, 40% pine, 12% transition; MP: 64%
hardwood, 36% pine). ‘‘Transition’’ residents were mice that
were captured only at trapping stations directly on the sharp
transition between the two habitats or in both hardwood and
pine habitats but always within 15 m of the transition zone.
Small mammal sampling
I conducted livetrapping using a grid of Sherman traps at
stations separated by 15 m across the entire site (105 traps
per site). Bait consisted of crimped oats and black oil sunflower seeds. Cotton batting was supplied during cold nights
(low temperature: ,13C, 55F). I set traps immediately
before dusk and checked them shortly after sunrise the
following morning. I fitted all captured mice with a uniquely
numbered ear tag and passive integrated transponder (PIT)
tag (see below) and recorded their capture location, body
mass, sex, molt status (pelage), and reproductive condition.
PIT tags are miniature computer chips injected subcutaneously between the shoulder blades whose signal allows batterypowered readers to record an individual’s presence within a
target area, for example, seed trays.
I compared two treatments: first, relocating mice in the
presence of the natural density of resident mice and, second,
relocating new individuals to the same sites in the absence of
residents. In this way, I was able to compare habitat selection
and resource acquisition when the choice was ‘‘free’’ versus
when confounded by interactions with resident conspecifics.
During the first treatment, resident mice remained on each
site throughout the study period. I trapped at each of the
three study sites for at least three nights during the week preceding each relocation to ear and PIT tag all resident mice.
Very few untagged residents were caught after each relocation
event—across the three sites, only 8.1% of residents captured
postrelocation were untagged adults. Resident mouse densities reported (see Study Sites) are based on animals captured
during this period of preliminary trapping.
For the second treatment (conducted on the same sites the
week after completion of Treatment 1), I removed resident
Behavioral Ecology
mice from the site via intensive removal trapping conducted
over at least four nights within the week leading to the relocation of new mice. Captured resident mice were moved .2 km
from the study site to minimize the chance of their return to
the site. Any resident mice captured during subsequent followup livetrapping to monitor the movement of relocated mice in
Treatment 2 were removed from the site. At each site, four or
fewer resident adult mice were found farther than 15 m inside
each site’s periphery during the month-long duration of
Treatment 2. Removal trapping on the periphery was ongoing
and more intensive, as anticipated, because the surrounding
contiguous habitat was inhabited by P. leucopus. (During the
month of monitoring after the relocation for Treatment 2,
a total of four mice were captured at and removed from peripheral traps at MP, 14 at LP2, and 22 at LP1.) All other
species captured during livetrapping, primarily southern redbacked voles (Clethrionomys gapperi), northern short-tailed shrews
(Blarina brevicauda), eastern chipmunks (Tamias striatus), and
red squirrels (Tamiasciurus hudsonicus) were immediately
released at the point of capture.
Mice targeted for relocation were captured in oak-dominated hardwood and white pine forests 5–10 km from the
release sites. Half of the relocated mice were captured in
hardwood and half in pine forests. At sunrise, after overnight
trapping to collect mice for relocation, I transported the mice
to the study sites by car, allowed approximately 30 min for
resettling after transport, and released them by opening one
end of the trap by hand. Care was taken to aim the open end
of the trap along the transition zone and not toward either
habitat. (Note: on release, mice typically moved below ground
within a few meters, and a pilot study using fluorescent
powder to track movement of relocated mice indicated that
movement within the first 12 h was limited, suggesting that
postrelocation movement is not systematically driven by the
response of mice to the method of release [Burns, unpublished data]). Ear and PIT tagging and baseline data collection were performed as described earlier. Mice were relocated
to the transition zone between the two habitat types (Figure 1),
at intervals of 7.5 m (Nreleased/site/treatment ¼ 11–12, for a total
of 67 relocated mice). I randomly assigned mice to release
points. The sex ratio released at each site was 1:1, or if N ¼
11, 5:6. At the time of relocation, there was no significant
difference in body mass between mice obtained from hardwood versus pine forests or for those relocated to each of the
three sites (two-way ANOVA, origin: F1,63 ¼ 0.080, p ¼ .778;
site: F2,63 ¼ 2.084, p ¼ .133). No juvenile mice (defined as
those with gray pelage) were relocated.
Trapping was resumed for three consecutive nights each
week during the month after each relocation. The first relocation was initiated at LP2 on 13 June 2002, at LP1 on 22 June
2002, and at MP on 30 June 2002. The subsequent relocation
(Treatment 2) was initiated at LP2 on 16 July 2002, at LP1 on
25 July 2002, and at MP on 1 August 2002. On each capture,
all resident and relocated mice were identified by tag number
and baseline data were collected.
I monitored access of relocated and resident mice to seed
trays for six consecutive nights immediately after each release.
There were eight seed tray stations at each site, with four
in each habitat type (Figure 1). PIT readers (Mini-Portable
Reader or FS2001F, Biomark, Inc., Boise, ID) were set up at
two stations in each habitat type (four locations per site) for
the first three nights after relocation and then moved to the
two remaining stations within each habitat type for three
nights to ensure full coverage of the study site. Seed tray stations included a PIT reader attached to a seed tray (petri dish
filled with ’60 g [dry weight] crimped oats) and to a deep
cycle gel-cell battery. The resources supplied at the seed trays
constituted a negligible percentage of the locally available
Burns • Behavior and relocation success
901
food resources. All PIT readers automatically recorded which
mouse accessed the seed tray and how many foraging bouts
each individual engaged in during the course of the night.
On completion of the experiment, each relocated mouse
was determined to have selected hardwood, pine, or transition
habitat. A mouse was assigned to either the hardwood or pine
forest if all its captures were located within that habitat type. If
an individual was recaptured in both habitats, the mouse was
assigned to the habitat ultimately selected. Mice assigned to
the transition zone included those that were recorded only
along the transition line or those that were recorded in both
hardwood and pine forests but always within 15 m of the
transition line. Mice that were never captured after the initial
release were recorded as having selected no habitat.
Statistical analyses
I tested for treatment effects on the number of relocated
mice selecting high-quality habitat using contingency tables
(Pearson’s v2 test). First, I tested for site-level variation in the
response, and when this was not found to be significant, I tested
for treatment effects without site as a factor in the analysis.
I assessed resource acquisition by comparing (1) the number
of individuals accessing seed trays at any point postrelocation
(using contingency tables, as above, including Fisher’s Exact test
when needed due to small sample size), (2) the log-transformed
average number of foraging bouts exhibited per individual per
night, and (3) the change in body mass over the course of the
study period. Data analyzed for change in body mass (3) was
limited to mice captured during the last week of trapping to
estimate likely long-term impacts of relocation, as opposed to
more transient short-term responses immediately after relocation. The log transformation of the number of foraging bouts
was necessary to normalize the distribution. Change in body
mass was used as a more general indicator of foraging success
to account for resources acquired at and away from the seed
trays. I used two-way ANOVAs, including site as a factor, to compare resource acquisition (2 and 3 above) for relocated mice in
treatments with and without resident conspecifics and to compare resource acquisition for relocated versus resident mice.
I also compared resource acquisition of relocated individuals
originally obtained from high- versus low-quality habitats (regardless of habitat selected postrelocation) and for mice selecting high- versus low-quality habitats (irrespective of habitat of
origin). Because variation due to site was nonsignificant for
almost all analyses, these statistics are presented only when significant. SPSS and S-Plus statistical packages were used for
the analyses (Crawley, 2002; S-Plus, 1998; SPSS, 2002). Post hoc
power analyses were conducted using SPSS and G*Power
(Buchner et al., 1997).
Resource acquisition data could be analyzed using either
a two-way ANOVA or a split-plot ANOVA. I opted for the
two-way ANOVA, given the scale of the experiment. Logistical
limitations prevented me from obtaining sufficient numbers
of replicates to examine statistical interactions between say
habitat selection and background densities of mice in different habitats, the prime value of carrying out a split-plot analysis. Background differences between habitats were assumed,
based on prior sampling in these habitat types in Northeastern Connecticut, USA (Burns, unpublished data), and on
other research on P. leucopus in heterogeneous landscapes
(e.g., Adler et al., 1984; Morris, 1989, 1991).
selected the higher quality hardwood habitat significantly
more often when residents were absent (Pearson’s v2 ¼
3.71, df ¼ 1, p ¼ .05; Figure 2). Mice relocated in the presence
of residents had marginally lower success persisting on-site
after relocation than did mice relocated in the absence of
residents (23/33 ¼ 70% remained on-site with residents,
30/34 ¼ 88% without; Pearson’s v2 ¼ 3.482, df ¼ 1, p ¼
.062). In addition, I observed a 61% reduction in the average
persistence time (number of days on-site after relocation) of
mice relocated in the presence versus in the absence of residents (t ¼ 2.550, df ¼ 54, p ¼ .014).
When residents were present, mice originally obtained from
high-quality and low-quality habitats did not differ significantly in their ability to access high-quality habitat after
relocation (Fisher’s Exact test, p ¼ .242; Table 2). Post hoc
power analysis indicated that the sample size was sufficient to
detect a significant difference, if one existed (power ¼ 0.9,
a ¼ .05, effect size ¼ 0.545). Likewise, when residents were absent, habitat of origin did not significantly impact the ability of
relocated mice to gain access to high-quality habitat (Fisher’s
Exact test, p ¼ .494; Table 2). The observed patterns of habitat
selection support Hypothesis A, that dominance status is
RESULTS
Habitat selection
Relocated mice were more successful colonists when residents
were absent than when they were present. On the whole, they
Figure 2
Habitat selected by relocated mice in the presence and absence of
resident mice. ‘‘Transition’’ indicates mice that were recorded along
or always within 15 m of the transition zone. ‘‘None’’ represents mice
that were never captured after the initial release. Data shown are combined across the three sites. Nresidents present ¼ 33; Nresidents absent ¼ 34.
Mice selected hardwood (compared with all other options) more
often when residents were absent (Pearson’s v2 ¼ 3.71, df ¼ 1,
p ¼ .05). Site-level variation was not significant (p ¼ .196).
Table 2
Number of mice originally relocated from hardwood versus pine
forests successfully relocating to high-quality hardwood habitat in
the presence and absence of resident conspecifics
Resident mice present
Resident mice absent
Origin
Did not select
hardwood
Selected
hardwood
Did not select
hardwood
Selected
hardwood
Hardwood
Pine
12
13
6
2
7
10
10
7
‘‘Did not select hardwood’’ includes individuals that selected pine
or transition habitat and those that did not persist within either
habitat after relocation.
Behavioral Ecology
902
Table 3
Resource acquisition of resident and relocated mice, with data combined across all three sites
Percentage of mice
accessing seed trays
Mouse categorya
All relocated mice (irrespective
of origin or habitat selection)
Relocated mice (by origin)
Hardwood
Pine
All resident mice (irrespective
of habitat of residency)
Resident mice (by habitat)
Hardwood
Pine
a
Change in body mass (g) 6 SE
Residents
present
Residents
absent
Residents
present
Residents
absent
Residents
present
Residents
absent
48% (N ¼ 33) a
74% (N ¼ 34) b
1.15 6 0.23
(N ¼ 16) a#
0.82 6 0.13
(N ¼ 25) b#
0.46 6 0.41
(N ¼ 13) a$
0.65 6 0.26
(N ¼ 13) b$
56% (N ¼ 18) c
71% (N ¼ 17) d
40% (N ¼ 15) e
76% (N ¼ 17) f
1.13 6 0.25
(N ¼ 10) c#
1.18 6 0.48
(N ¼ 6) e#
1.06 6 0.22
(N ¼ 12) d#
0.61 6 0.13
(N ¼ 13) f #
0.79 6 0.65
(N ¼ 7) c$
0.08 6 0.47
(N ¼ 6) e$
0.90 6 0.29
(N ¼ 5) d$
0.50 6 0.38
(N ¼ 8) f $
0.94 6 0.40
(N ¼ 5) g#
1.44 6 0.31
(N ¼ 9) i#
1.13 6 0.16
(N ¼ 14) h#
0.28 6 0.09
(N ¼ 7) j#
0.50 6 0.58
(N ¼ 4) g$
0.14 6 0.67
(N ¼ 7) i$
0.69 6 0.28
(N ¼ 8) h$
0.25 6 0.52
(N ¼ 4) j$
Relocated mice (by habitat selected)
Hardwood
63% (N ¼ 8) g
Pine
Average number of foraging
bouts (log transformed) per
mouse per night 6 SE
82% (N ¼ 17) h
75% (N ¼ 12) i
100% (N ¼ 7) j
44% (N ¼ 78) k
—
1.49 6 0.18
(N ¼ 35) k#
—
0.58 6 0.22
(N ¼ 73) k$
—
38% (N ¼ 40) l
—
—
—
0.56 6 0.28
(N ¼ 40) l$
0.65 6 0.40
(N ¼ 29) m$
—
50% (N ¼ 38) m
1.29 6 0.25
(N ¼ 15) l#
1.65 6 0.26
(N ¼ 19) m#
—
—
Lowercase letters (e.g., a, b, c . . .) are listed for each category to facilitate comparison with statistical tests reported in the text.
Mice are categorized as relocated or resident, and relocated mice are further subdivided by habitat of origin (e.g., hardwood native) and by the
habitat selected after relocation.
negatively impacted for all relocated individuals, but do not
support Hypotheses B–D (Table 1).
Resource acquisition
The number of all relocated individuals (regardless of their
initial origin) successfully accessing seed trays was significantly
higher in the absence of local residents than in their presence
(Fisher’s Exact test, p ¼ .047; Table 3: a versus b). In the
presence and in the absence of resident mice, relocated mice
exhibited little difference in their ability to access seed trays,
regardless of habitat of origin (Fisher’s Exact test, p $ .5;
Table 3: c versus e, d versus f ). Similarly, relocated mice that
selected high- versus low-quality habitats did not differ in their
ability to access seed trays, either in the presence or in the
absence of residents (Fisher’s Exact test, p $ .5; Table 3:
g versus i, h versus j). These results indicate that relocated
mice experience a reduction in dominance status in the presence of residents and that this is not dependent on previous
dominance status, which supports Hypothesis A (Table 1).
A greater percentage of residents of low-quality pine forests
accessed seed trays than did residents of high-quality hardwood forest (Table 3: l versus m). Overall, approximately the
same percentage of resident mice utilized seed trays (44%) as
did relocated mice (48%). Both resident and relocated mice
were more successful gaining access to seed trays at sites with
a lower density of resident mice (Figure 3A).
Post hoc power analyses revealed sufficient power to detect
an effect when mice were relocated in the absence of residents
(power ¼ 0.8 to distinguish between effects due to habitat of
origin and .0.9 for effects due to habitat selected). Power was
lower for tests of treatment differences when residents were
present (power ¼ 0.2 to distinguish between effects due to
habitat of origin and 0.6 for effects due to habitat selected).
Therefore, although power was sufficient to detect an effect, if
one existed, of habitat of origin or habitat selected on seed
tray access when residents were absent, there may have been
insufficient power to detect an effect when residents were
present.
The average number of foraging bouts exhibited by relocated mice did not differ in the presence versus in the absence
of residents (two-way ANOVA, F1,37 ¼ 1.816, p ¼ .186; Table 3:
a# versus b#). Relocated mice originally obtained from hardwood and pine forests exhibited a comparable number of
foraging bouts per night when residents were present (twoway ANOVA, F1,12 ¼ 0.015, p ¼ .904; Table 3: c# versus e#). In
the absence of residents, mice originally from high-quality
hardwood forest exhibited a marginally significantly higher
number of foraging bouts compared with those from lowquality pine forest (two-way ANOVA, F1,21 ¼ 4.088, p ¼ .056;
Table 3: d# versus f #). Relocated mice selecting hardwood forest in the absence of residents exhibited significantly more
foraging bouts than did those selecting pine forest (two-way
ANOVA, F1,17 ¼ 10.886, p ¼ .004; Table 3: h# versus j#). There
was no difference when residents were present (two-way
ANOVA, F1,10 ¼ 0.280, p ¼ .608; Table 3: g# versus i#). Resident
and relocated mice exhibited comparable numbers of foraging bouts (two-way ANOVA, F1,47 ¼ 2.368, p ¼ .131; Table 3:
a# versus k#). All mice exhibited significantly more foraging
bouts at low-density sites (two-way ANOVA, F2,47 ¼ 3.346, p ¼
.044; Figure 3B). Patterns of foraging bouts for mice relocated
in the presence of resident mice provide additional support
for Hypothesis A, in that mice originally from either highor low-quality habitats exhibited comparable numbers of
Burns • Behavior and relocation success
903
Figure 4
Change in body mass of relocated mice in the presence and absence
of resident mice (two-way ANOVA, F1,22 ¼ 5.926, p ¼ .023). Bars
show standard errors. Nresidents present ¼ 13; Nresidents absent ¼ 13.
Figure 3
Decreased seed tray access for relocated and resident mice at higher
density sites. Resource acquisition is assessed by comparing (A) the
proportion of individuals accessing seed trays (Nrelocated mice ¼ 33;
Nresident mice ¼ 82) and (B) the average number of foraging bouts
exhibited per individual per night (Nrelocated mice ¼ 16; Nresident mice ¼
35). Bars show standard errors.
foraging bouts. Patterns for mice relocated in the absence of
resident mice provide evidence that habitat of origin does indeed reflect differences in dominance rank (see Discussion).
Relocated mice lost weight when in the presence of resident mice (
x ¼ 0:46 6 0:41 g) and gained weight (
x¼
0:65 6 0:26 g) when relocated in the absence of resident mice
(two-way ANOVA, F1,22 ¼ 5.926, p ¼ .023; Table 3: a$ versus b$;
Figure 4). I detected no significant difference in weight
change between relocated mice originally from high- versus
low-quality habitats or for mice selecting high- versus low-quality habitats in either treatment (Table 3: c$ versus e$, d$ versus
f $, g$ versus i$, h$ versus j$). Post hoc power analyses revealed extremely low probabilities of detecting a significant
effect, with an observed power of 0.06 for the latter two comparisons. Therefore, body mass data alone do not allow me to
distinguish between Hypotheses A and B. In contrast to relocated mice, resident mice from both high- and low-quality
habitats gained weight during the experiment. There was not
a significant difference in weight gain between residents of
hardwood versus pine forests (two-way ANOVA, F1,65 ¼ 0.023,
p ¼ .880; Table 3: l$ versus m$).
DISCUSSION
In the absence of residents, mice originally from high-quality
habitat exhibited more foraging bouts than mice originally
from low-quality habitat. This provides empirical support for
my assumption that habitat of origin is a reliable indicator of
an individual’s dominance status (the ideal-despotic distribution, as predicted by Fretwell and Lucas, 1970). This finding
agrees with previous studies that showed Peromyscus populations to adhere to predictions of the ideal-despotic distribution (Halama and Dueser, 1994; Linzey, 1989; Morris, 1989;
Wolff, 1985).
Within this context of density-dependent habitat selection,
behavioral flexibility enabled the animals in this study to
actively respond to eviction from their native home ranges.
The patterns of redistribution show that relocated mice can
accurately assess differences in habitat quality in unfamiliar
settings. They also indicate that mice can incorporate information on the density of conspecific residents into their
habitat selection decisions. Consequently, my results do not
support the two hypotheses (C and D) that posited that territorial interactions were unimportant for the redistribution of
relocated individuals. Not all relocated mice were able to reestablish home ranges in high-quality habitat when resident
mice were present. Redistribution also was not primarily driven
by habitat-affiliation patterns. A high proportion of relocated
mice selected high-quality hardwood habitat in the absence of
resident mice, regardless of their habitat of origin.
The observed patterns of habitat selection strongly support
Hypothesis A, which states that dominance status is negatively
impacted for all relocated mice. Again, this assumes that habitat of origin was an accurate reflection of the individual’s
dominance status prior to relocation. Many mice could not
access high-quality habitat in the presence of residents regardless of their habitat of origin; yet, they did so frequently in the
absence of residents. Resource acquisition patterns provide
additional support for Hypothesis A, albeit weaker support
due to limited statistical power in some cases. The ability of
relocated mice to acquire food resources (as indicated by
change in body mass and percentage of mice accessing seed
trays) was enhanced when conspecifics were absent. The
weight loss experienced by relocated mice when residents
were present is a likely indicator of longer term repercussions
as weight loss has potential negative consequences for both
survival and fecundity.
When residents were present (Treatment 1), I was unable to
reject the null hypothesis that an individual’s origin (and
hence dominance status) did not impact their resource acquisition ability (providing support for Hypothesis A). It remains
possible that low statistical power resulting from small sample
Behavioral Ecology
904
sizes obscured differences between resource acquisition abilities of mice from high- and low-quality habitats. However,
sufficient power did exist to assess any effect of origin on
habitat selection after relocation, and none was detected, indicating that substantial differences in resource acquisition
ability are unlikely.
Empirical studies from other systems provide a plausible
explanation for the observed loss of status of all mice relocated in the presence of resident conspecifics. Increased aggression toward unfamiliar, or ‘‘intruder,’’ individuals when
compared to familiar neighbor conspecifics has been observed in a variety of species—coined the ‘‘dear enemy’’ phenomenon. Lizards (Husak and Fox, 2003; Massot et al., 1994;
Trigosso-Venario et al., 2002), fish (Hojesjo et al., 1998; Leiser
and Itzkowitz, 1999; Utne-Palm and Hart, 2000), and small
mammal populations (Randall et al., 2002) have been shown
to exhibit this preferential treatment of neighbors and intense
aggression toward intruders. The prevalence of this type of
social dynamic lends support to the data provided in this study
that have shown dominance of all relocated (intruder) individuals to be compromised. In addition to experiencing generally elevated levels of aggression due to the unfamiliar social
environment, all relocated animals, regardless of prior dominance status, are also less familiar with their physical environment than are residents. This disorientation may disrupt the
ability of relocated animals to find refuge from competitors
and may increase the time and energy needed for foraging,
likely exacerbating their competitive disadvantage. These negative effects of relocation should be independent of dominance status.
In this study, I presented relocated mice with two habits
from which to choose. In a mosaic landscape with several
habitat types representing a wider range of habitat quality
than that in this study (and hence a greater range along the
dominance hierarchy), it remains possible that mice evicted
from very high-quality habitat could resettle in intermediateto low-quality habitat. Hypothetically, they could use their
competitive edge to push the residents of that habitat into
the next lowest quality habitat. This domino effect from one
habitat to another is possible only if relocating animals are
from higher quality habitat than the neighboring habitats
and maintain their competitive edge in unfamiliar territory.
My data indicate that such domino effects are unlikely, even
when a wider range of habitats is available because all relocated animals appear to experience loss of dominance status.
Individuals emigrating from low-quality habitat are particularly unlikely to have success reestablishing home ranges in
new habitat unless densities are low. For cases in which habitat
alteration is anticipated and the survival and successful relocation of local wildlife is a goal, performing habitat modifications during low-density periods is one strategy to enhance the
probability of successful reestablishment.
Site-level differences in resident density also played a role in
resource acquisition of both resident and relocated mice,
most notably in the percentage of mice accessing seed trays
and in the number of foraging bouts exhibited. As site-level
density increased, the proportion of resident and relocated
mice accessing seed trays (Figure 3A) and the number of foraging bouts exhibited (Figure 3B) decreased. Thus, as the
density of white-footed mice increases in a habitat, both residents and relocated individuals become excluded from highquality food resources with increasing frequency (see Mitchell
et al., 1990, for comparable effects in Gerbillus allenbyi and
Gerbillus pyramidum). Moreover, when residents were present,
all mice had greater success at seed trays in the lower density,
low-quality habitat than they did in higher density, highquality habitat. These patterns suggest that there is reduced
pressure from competition in these lower quality habitats.
In this study, manipulating the presence of conspecific residents was sufficient to cause significant changes in patterns of
resettlement and resource acquisition. I did not consider the
importance of interspecific competitors on the response of
relocated mice as the other species of small mammals sharing
these sites have been shown not to compete strongly with
white-footed mice (Adler, 1985; Nupp and Swihart, 2000,
2001; Wolff and Dueser, 1986). The results of this study
should be generalizeable to other wildlife species for which
the strength of intraspecific competition outweighs that of
interspecific competition (e.g., many species of herbivores,
Gurevitch et al., 1992; a variety of small mammals, Huitu et al.,
2004, and Ostfeld et al., 1993; and fish, Osenberg et al., 2002).
For relocated white-footed mice, traditional source-sink and
ideal-despotic distribution theories do not predict the response of animals to relocation. If dominance status is not
context dependent, then in novel settings, relocated mice
should maintain their dominance status completely. To the
contrary, I have shown that all relocated individuals, regardless
of habitat of origin, suffer from relocation to novel areas when
residents are present. Thus, the prognosis for territorial animals that are evicted from their native home ranges is not an
encouraging one. However, the likelihood of domino effects is
low, suggesting that the immediate impact of individual dispersal due to habitat loss will minimally impact individuals in
surrounding unperturbed areas. Assessing relocation patterns
in light of territorial interactions between resident and relocated individuals illustrates the value of incorporating information on animal behavior into wildlife management.
I thank E. Crew, L. DeMarchis, and E. Jones for helping me carry out
the field experiment. O. Ovadia, E. Palkovacs, J. Reuning-Scherer,
O. Schmitz, M. Smith, M. Urban, and two anonymous reviewers
offered appreciated advice on the data analysis and manuscript preparation. The research was supported in part by grants from the
National Science Foundation (NSF predoctoral research fellowship),
Sigma Xi Grants-in-Aid-of-Research, the American Museum of Natural
History (T. Roosevelt Memorial Fund), and the Carpenter/Sperry
Fund and Department of Ecology and Evolutionary Biology Chair’s
Discretionary Fund at Yale University.
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