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Use of Probability of Detection When Conducting Analyses of Surveys of Mesopredators: a Case Study from the Ozark Highlands of Missouri

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Abstract

We surveyed 14 communities of mesopredators in the Ozark Highlands of southern Missouri to examine the effect of landscape and surveying efforts on probability of detection of raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana). Virginia opossums had a higher probability of detection than raccoons. Mean size of forested patches had a negative effect on probability of detection, suggesting that the hypothesis that abundance of mesopredators increases in small patches of forest is an artifact of sampling. We suggest that it is important for researchers to include probability of detection when analyzing data from surveys of mesopredators. Muestreamos 14 comunidades de depredadores medianos en las Ozark Highlands del sur de Missouri para examinar el efecto de factores de paisaje y esfuerzos de muestreo en la probabilidad de detección de mapaches (Procyon lotor) y tlacuaches (Didelphis virginiana). Los tlacuaches tuvieron una probabilidad de detección mayor que los mapaches. El tamaño medio de parches de bosque tuvo un efecto negativo en la probabilidad de detección, sugiriendo que la hipótesis de que la abundancia de los depredadores medianos suba en parches pequeños del bosque es artefacto de muestreo. Sugerimos que es importante que los investigadores incluyan la probabilidad de detección cuando analicen datos de muestreos de depredadores medianos.
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Use of Probability of Detection When Conducting Analyses of Surveys of
Mesopredators: a Case Study from the Ozark Highlands of Missouri
Author(s): Michael V. Cove, Liisa M. Niva, and Victoria L. Jackson
Source: The Southwestern Naturalist, 57(3):257-261. 2012.
Published By: Southwestern Association of Naturalists
DOI: http://dx.doi.org/10.1894/0038-4909-57.3.257
URL: http://www.bioone.org/doi/full/10.1894/0038-4909-57.3.257
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THE SOUTHWESTERN NATURALIST 57(3): 257–261 SEPTEMBER 2012
USE OF PROBABILITY OF DETECTION WHEN CONDUCTING
ANALYSES OF SURVEYS OF MESOPREDATORS: A CASE STUDY FROM
THE OZARK HIGHLANDS OF MISSOURI
MICHAEL V. COVE,LIISA M. NIVA,AND VICTORIA L. JACKSON*
Department of Biology and Earth Science, University of Central Missouri, Warrensburg, MO 64093
*Correspondent: vjackson@ucmo.edu
ABSTRACT—We surveyed 14 communities of mesopredators in the Ozark Highlands of southern Missouri to
examine the effect of landscape and surveying efforts on probability of detection of raccoons (Procyon lotor)
and Virginia opossums (Didelphis virginiana). Virginia opossums had a higher probability of detection than
raccoons. Mean size of forested patches had a negative effect on probability of detection, suggesting that the
hypothesis that abundance of mesopredators increases in small patches of forest is an artifact of sampling. We
suggest that it is important for researchers to include probability of detection when analyzing data from
surveys of mesopredators.
RESUMEN—Muestreamos 14 comunidades de depredadores medianos en las Ozark Highlands del sur de
Missouri para examinar el efecto de factores de paisaje y esfuerzos de muestreo en la probabilidad de
detecci´on de mapaches (Procyon lotor) y tlacuaches (Didelphis virginiana). Los tlacuaches tuvieron una
probabilidad de detecci ´on mayor que los mapaches. El tama˜
no medio de parches de bosque tuvo un efecto
negativo en la probabilidad de detecci ´on, sugiriendo que la hip´otesis de que la abundancia de los
depredadores medianos suba en parches peque ˜
nos del bosque es artefacto de muestreo. Sugerimos que es
importante que los investigadores incluyan la probabilidad de detecci ´on cuando analicen datos de muestreos
de depredadores medianos.
Management of mesopredators has become important
because, in the absence of large carnivores, these smaller
predators can become abundant and threaten migratory
birds and small mammals (Crooks and Soul´e, 1999;
Sinclair et al., 2005). Three common mesopredators,
Virginia opossums (Didelphis virginiana), raccoons (Procy-
on lotor), and striped skunks (Mephitis mephitis), occur
sympatrically throughout most of North America. Similar
requirements for resources by these generalists have
allowed them to become ubiquitous members of most
natural and human-altered forested communities
(Schwartz and Schwartz, 2001).
While studies of larger predators often aim to estimate
true abundance (Kays et al., 2008), studies that examine
ecology of mesopredators often use indices of abundance
for analysis: rate of capture (unique captures/100 trap-
nights; Disney et al., 2008) and rates of visitation to scent
stations or relative abundance (Crooks and Soul´e, 1999;
Dijack and Thompson, 2000; Sinclair et al., 2005). In
several recent studies, researchers attempted to model
relative abundance of raccoons, Virginia opossums, and
striped skunks as functions of landscape and local
habitats (Crooks and Soul´e, 1999; Dijack and Thompson,
2000; Sinclair et al., 2005; Disney et al., 2008) to predict
risk of predation for forest-nesting birds. In their study in
Missouri, Dijack and Thompson (2000) suggested that
abundance of raccoons was related positively to latitude,
density of streams, and mean size of patches on
agricultural lands, whereas abundance of Virginia opos-
sums was related positively to mean distance between
patches of forest, latitude, density of streams, and related
negatively to contagion. They determined that abun-
dance of striped skunks did not relate to any character-
istic of landscape examined. Other studies (Crooks and
Soul´e, 1999; Sinclair et al., 2005; Disney et al., 2008) have
suggested that abundance of mesopredators increases as
size of forested patches decreases.
Although variable detection may be accounted for to
some degree in indices of abundance, the assumption is
that probability of detection is constant and unaffected by
habitat, surveying effort, or surveying method. Disney et
al. (2008) attempted to compare indices of abundance
between rates of visitation at scent stations and rates of
capture for raccoons and Virginia opossums in a
fragmented-forested landscape, but detected no associa-
tion between the two methods. This suggests that indices
of abundance, in general, are not appropriate for
predicting true relationships of abundance or habitat.
As an alternative to abundance or indices of abundance,
MacKenzie et al. (2005, 2006) suggested using the state-
variable occupancy (W) when trying to elucidate relation-
ships of habitat or distribution of species. This approach
uses maximum-likelihood models to estimate occupancy
by incorporating the additional parameter of probability
of detection (ˆp), which also can vary as a result of
covariates of the model.
We suspect that surveying effort and covariates of
habitat (i.e., heterogeneity of habitat and size of forested
patch) will have effects on probability of detection and
will bias indices of abundance if these are not accounted
for prior to analysis. Our study aimed to examine how
these variables affect probability of detection for three
mesopredators in the Ozark Highlands of southern
Missouri. In particular we attempted to model covariates
that were revealed to be significant predictors of
abundance from two studies in the central United States
(Dijack and Thompson, 2000; Disney et al., 2008), as well
as other predictors that we believed to be biologically
significant.
MATERIALS AND METHODS—Our study area included 10 counties
in the Ozark Highlands of southern Missouri from Randolph
County as the northern limit and the Arkansas border as the
southern limit. Surveys were conducted on public lands
managed by the Missouri Department of Conservation,
Missouri Department of Natural Resources, the United States
Forest Service, and one private farm. Although trapping
furbearers was legal and could be conducted on the lands in
our study area, no reported trapping occurred at our sites prior
to or during our surveys. We selected 14 sites with 5 sites at the
northern edge of the Ozark Highlands and 9 sites in the
southern portion of the region. The northern and southern sites
were separated by >100 km and all sites were >4 km apart to
ensure independence and allow analysis of landscape similar to
Dijack and Thompson (2000). The use of 14 sites was similar to a
study by O’Connell et al. (2006) in which they used 13 sites to
estimate parameters of occupancy and detection for medium
and large mammals.
Second-growth Quercus-Carya (oak-hickory) and mixed-hard-
wood forests dominate the Ozark Highlands, which are
interspersed with woodlands, savannas, prairies, and agricultural
lands (Nigh and Schroeder, 2002). Our trapping sites primarily
consisted of oak and mixed-hardwood forests; however, grass-
lands, croplands, and wildlife food plots also were common.
Little was noted regarding composition of the understory, but
most sites were characterized by nonnative shrubs, cool-season
grasses, and forbs. Average temperature during our surveys was
8.48C (range, 3.1–18.78C).
During October 2008–April 2009, we set medium (106) and
large (108) Tomahawk live traps (Tomahawk Live Trap Co.,
Tomahawk, Wisconsin) >100 m apart along established animal
trails and natural funnels. Number of traps deployed at each site
was 8–22 and was dependent on size of the area and availability
of traps. This led to differences in trapping effort: 75 8SE
trapnights/site (range, 28–137), but our analysis accounted for
this variation. Because we believed that inclement weather and
low temperatures would affect detection negatively, we did not
trap during precipitation events or when temperature was <08C.
We baited traps with mackerel or sardines and marshmallows
and checked traps during 0700–1200 h. Initially, traps were set
and run for 2–4 consecutive nights. After the last evening, traps
were locked open, revisited after a 3–5-day rest period, and run
again for an additional 2–4 evenings. Missing data from
incomplete surveys at some sites (<8 full days) was accommo-
dated by the occupancy-modeling approach (MacKenzie et al.,
2006).
Once animals were captured, they were anesthetized with an
intramuscular injection of Ketamine hydrochloride-Aceproma-
zine (10 mg/kg and 1mg/kg, respectively). Standard measure-
ments and gender were recorded for all animals that were
handled. In some instances, animals were released without
being handled or escaped before being handled. Each animal
also received an individually numbered Monel ear tag (National
Band and Tag Co., Newport, Kentucky). Following recovery,
animals were released at the site of capture. All procedures were
in accordance with guidelines of the American Society of
Mammalogists (Gannon et al., 2007) and the University of
Central Missouri Institutional Animal Care and Use Committee
(permit 10-3209).
Using ArcGIS 9.3.1 (Environmental Systems Research
Institute, Redland, California), we overlaid all trapping
locations onto a digitized land-use-land-cover map. Following
the analysis of landscape by Dijack and Thompson (2000), we
created a 2-km-radius buffer at each site using a central point
among the traps to measure covariates of landscape. We
measured cumulative lengths of all roads and streams and
used the Patch Analyst extension in ArcGIS 9.3.1 (R. Rempel,
http://flash.lakeheadu.ca/~rrempel/patch/index.html) to
measure total forested edge, mean size of forested patch, and
total number of patches within each buffer. To test the
hypothesis that latitude affects detection of mesopredators,
we classified sites as northern and southern groups. We also
included surveying effort per site (trapnights) as a covariate to
be used in modeling. We standardized all continuous covariates
to z-scores for analysis, but no other transformation was
performed (Long et al., 2011). We did not include seasonal
variation or covariates of temperature because our surveys were
conducted over the course of one season. Additionally, because
we did not trap in poor weather or low temperatures, we
believe that any seasonal or temperature variation had little to
no effect on our estimates.
Lack of recaptures of individual mesopredators precluded
estimation of true abundance for our study sites. Prior to
analysis, we decided to group Virginia opossums and raccoons
into one model due to their similar, generalist, ecological
requirements, but maintained an additional covariate of species
to model species-specific effects. We kept models of stripped
skunks separate because we anticipated different effects of
covariates based on previous studies (Dijack and Thompson,
2000; Disney et al., 2008). We then compiled all trapping
records to create a binary history of detection (detected =1,
not detected =0) for all three mesopredators. We developed
13 a priori models (Table 1) based on biologically plausible
explanations of occurrence and detection and results of
previous research (Dijack and Thompson, 2000; Disney et al.,
2008). We included a null model with no effect of covariates
and a global model that contained all eight possible covariates
to ensure that there was no covariate interaction that lead to
nonconvergence in the saturated model. For analysis, we used a
single-season analysis in program PRESENCE 2.4 (J. E. Hines,
http://www.mbr-pwrc.usgs.gov/software/presence.html). Be-
258 vol. 57, no. 3The Southwestern Naturalist
cause our na¨
ıve estimates of occupancy were high, we believed
raccoons and Virginia opossums occurred at all sites and we
fixed the parameter for occupancy to 1.0 and only evaluated
probabilities of detection as affected by covariates of surveying
and habitat. This is similar to the first step of the two-step
process employed by Yates and Muzika (2006) and Long et al.
(2011) to first determine how variables affect probability of
detection and then use those covariates as a constant set when
deriving estimates of occupancy.
The best approximating models were selected based on the
Akaike Information Criterion corrected for small samples
(AIC
c
) and Akaike weights (w
i
). We selected the 95% confidence
set (summed w
i
=0.95) of the supported models and removed
the remaining models that were not contained in the
confidence set to redistribute the Akaike weight among the
top models. We then conducted model averaging (Burnham
and Anderson, 2002) using spreadsheet software designed by B.
Mitchell (www.uvm.edu/%7Ebmitchel/software.html) to esti-
mate species-specific probabilities of detection and effects of
covariates across multiple models.
RESULTS—We detected six species of mammals during
the 1,052 trapnights from 73 sampling occasions. The
most commonly detected mesopredator was the Virginia
opossum (n=83), followed by the raccoon (n=47).
Striped skunks were captured only on four occasions and
were excluded from analyses. Other incidental captures
included the eastern woodrat (Neotoma floridana,n=3),
eastern fox squirrel (Sciurus niger,n=2), and eastern
cottontail (Sylvilagus floridanus,n=1)
Of the 13 a priori models, only seven were contained
in the 95% confidence set. A difference in probability of
detection between species was supported by five of the
seven models comprising the 95% confidence set (Table
1). Raccoons had a lower probability of detection than
Virginia opossums, 0.46 0.04 SE and 0.64 0.05 SE,
respectively. Mean size of forested patch appeared as a
negative covariate in three of the top models (Tables 1
and 2), which agreed with the direction of our a priori
hypothesis. Latitude, trapping effort, and total number
of patches were all contained in the 95% confidence set
of the model, but had little effect on parameters of
detection with confidence intervals that strongly over-
lapped zero (Tables 1 and 2). Directions of effect of
covariates, however, all agreed with our a priori
hypotheses. Streams, roads, and total forested edge were
TABLE 1—Descriptions and expected direction of a priori models (except the global model with all covariates) for detection of
mesopredators from surveys conducted in the Ozark Highlands of southern Missouri, October 2008–April 2009.
Hypothesis Model Structure of model Expected result
No effects of habitat or survey on
detection
p(.) b
0
Increasing mean size of forested patch
will affect detection negatively
p(mean size of forested patch) b
0
+b
1
(mean size of forested
patch)
b
1
<0
Increasing trapping effort at sites will
affect detection positively
p(trapping effort) b
0
+b
1
(trapping effort) b
1
>0
Increasing total number of patches will
affect detection positively
p(total number of patches) b
0
+b
1
(total number of
patches)
b
1
>0
Species-specific detection and positive
influence from latitude
p(species +latitude) b
0
+b
1
(species) +
b
2
(latitude)
b
1
<0, b
2
>0
Species-specific detection and negative
influence from roads
p(species +road) b
0
+b
1
(species) +b
2
(road) b
1
<0, b
2
<0
Species-specific detection and positive
influence from streams
p(species +stream) b
0
+b
1
(species) +
b
2
(stream)
b
1
<0, b
2
>0
Species-specific detection and positive
influence from increasing total edge of
forest
p(species +total edge of forest) b
0
+b
1
(species) +b
2
(total
edge of forest)
b
1
<0, b
2
>0
Species-specific detection and positive
influence from increasing total number
of patches
p(species +total number of
patches)
b
0
+b
1
(species) +b
2
(total
number of patches)
b
1
<0, b
2
>0
Species-specific detection and positive
influence from increasing trapping
effort
p(species +trapping effort) b
0
+b
1
(species) +
b
2
(trapping effort)
b
1
<0, b
2
>0
Species-specific detection and negative
influence from increasing size of
forested patch
p(species +mean size of forested
patch)
b
0
+b
1
(species) +b
2
(mean
size of forested patch)
b
1
<0, b
2
<0
Species-specific detection, negative
influence from mean size of forested
patch, positive influence from latitude,
and positive influence from increasing
trapping effort
p(species +mean size of forested
patch +latitude +trapping
effort)
b
0
+b
1
(species) +b
2
(mean
size of forested patch)
+b
3
(latitude) +
b
4
(trapping effort)
b
1
<0, b
2
<0,
b
3
>0, b
4
>0
September 2012 Cove et al.—Analysis of mesopredator surveys 259
not contained in the 95% confidence set and appeared
to have no effect on probability of detection.
DISCUSSION—We determined that several covariates
influenced ability to detect mesopredators in our
surveys. All of these covariates have been suggested as
drivers of abundance of mesopredators from other
studies (Crooks and Soul´e, 1999; Dijack and
Thompson, 2000; Sinclair et al., 2005; Disney et al.,
2008), but these studies did not consider probability of
detection in their analyses and we caution use of indices
of abundance for drawing inferences about landscape.
We suggest that modeling occupancy and the state
variable of occupancy is a more appropriate approach
to modeling relationships of habitat of mesopredators.
This approach also is advantageous because multi-season
and co-occurrence models of species have been
developed and can be used to make strong inferences
about factors that affect extinction and colonization of
sites and dynamics of community interactions
(MacKenzie et al., 2006).
Our surveys used varying numbers of traps per site due
to availability of traps (raccoons often damaged the
medium-sized traps and rendered them unusable) and
constraints of forested patches. Disney et al. (2008) also
used varying numbers of traps (2–14) at different forested
sites, leading to 80–560 trapnights/site. The occupancy-
modeling approach allowed us to test how trapping effort
affected our ability to detect presence of mesopredators.
Although we believe that future surveying efforts should
be standardized as much as possible, our results suggest
that surveying effort (i.e., varying number of traps per
site) explained only limited variation in our ability to
detect mesopredators. We acknowledge that larger
differences in trapnights per site may have more
pronounced effects on probability of detection, but this
can be modeled as a covariate of site to improve
inferences in future surveys.
We were unable to estimate occurrence or probability
of detection of striped skunks due to few detections.
Neither the study by Dijack and Thompson (2000) nor
that of Disney et al. (2008) was able to collect sufficient
data for striped skunks to make inferences about their
abundance. Our trapping results also demonstrated that
striped skunks are detected infrequently and future
studies should aim to improve surveying techniques for
this species.
Dijack and Thompson (2000) suggested that abun-
dance of raccoons and Virginia opossums in Missouri was
influenced by latitude. They noted that agricultural lands
in the northern portion of the state were dominated by
croplands, whereas agricultural lands in the southern
portion of the state were used more often for hay and
pasture. Agricultural crops do provide an additional
source of food for mesopredators, but there is a
correlation between increasing agricultural lands and
decreasing size of forested patches (Dijack and Thomp-
son, 2000). Because we were unable to estimate true
abundance from our surveys, we were unable to examine
a numerical response for mesopredators to these
alterations of landscape. However, interspecific and
intraspecific interference competition often drive dy-
namics of communities and populations of carnivores
(Palomares and Caro, 1999) and, in this instance,
dynamics of mesopredators. Smaller patches of forest
surrounded by agricultural land should not exhibit a
true increase in abundance of mesopredators due to
increased interference competition and limited resourc-
es associated with the isolated patch.
TABLE 3—Model-averaged estimates of coefficients for covar-
iates, unconditional standard errors, and 95% CIs in models of
detection comprising the 95% confidence set from surveys of
mesopredators conducted in the Ozark Highlands of southern
Missouri.
Covariate bestimate SE Lower CI Upper CI
Intercept 0.194 0.206 –0.210 0.598
Species –0.575 0.198 –0.963 –0.187
Mean size of
forested patch –0.548 0.164 –0.869 –0.227
Latitude 0.431 0.266 –0.090 0.952
Trapping effort 0.001 0.001 –0.001 0.003
Total number of
patches 0 0 0 0
TABLE 2—Statistics for models of probability of detection derived from surveys of mesopredators conducted in the Ozark Highlands
of southern Missouri. Included are models from the 95 % confidence set.
Model AIC
c
DAIC
c
Akaike weight
Number of
parameters -2 log-likelihood
W(.),p(species +mean size of forested patch) 120.48 0.00 0.351 4 110.74
W(.),p(mean size of forested patch) 120.98 0.49 0.274 3 113.98
W(.),p(species +latitude) 121.18 0.70 0.247 4 111.44
W(.),p(species +mean size of forested patch +
latitude +trapping effort)
123.88 3.40 0.064 6 107.88
W(.),p(species +trapping effort) 125.96 5.48 0.023 4 116.22
W(.),p(species +total number of patches) 126.12 5.64 0.021 4 116.38
W(.),p(trapping effort) 126.27 5.79 0.019 3 119.27
260 vol. 57, no. 3The Southwestern Naturalist
Our results that probabilities of detection are higher at
northern sites and that probability of detection is related
negatively to size of forested patch corresponds with
suggestions of Dijack and Thompson (2000) and Disney
et al. (2008) because higher abundance might influence
probability of detection. However, the exact relationship
between abundance and probability of detection has not
been examined. Furthermore, the use of scent stations in
these studies (Dijack and Thompson, 2000; Disney et al.,
2008) cannot distinguish between individual animals and
the high rates of detection for this method are also a poor
indicator of true abundance because a single individual
can visit all stations at a single site in one evening (Disney
et al., 2008). Our results suggest that activities of
mesopredators are more restricted in small patches of
forest within fragmented landscapes causing an increase
in the probability of detection, which creates an artifact
that abundance also is high.
We do not believe that any study has produced
significant evidence that true abundance of mesopreda-
tors increases in smaller patches of forest. Disney et al.
(2008) suggested that rates of visitation at scent stations
were measures of activity by animals and that activity of
raccoons and Virginia opossums were concentrated in
smaller patches of forest, leading to increased risk of
predation on forest-nesting birds. We believe that this
hypothesis more accurately reflects the increased risk of
predation on nests than does the suggestion that
abundance of mesopredators is higher in smaller patches
of forest.
Although our study was modest, we believe that the
relationship between probability of detection and pa-
rameters in our analysis is evident and, with larger
samples in future studies, the exact relationship and
driving forces can be explored more robustly. Relative
abundance and rates of capture are inaccurate indices of
abundance, unless modeled as functions of sampling and
covariates of habitat. We suggest that occupancy model-
ing is a more appropriate approach, but abundance of
mesopredators also can be estimated directly by marking
individuals and using capture-recapture analyses, or by
using the repeated-count models of Royle and Nichols
(2003). This is evidence that future surveys will benefit
from inclusion of a parameter for probability of
detection when objectives include estimating occupancy
of sites (patches) or relationships of habitats for
common mesopredators and exploring risk of predation
on nests.
This research was funded by the Missouri Department of
Conservation. We thank personnel of the Missouri Department
of Conservation, Department of Natural Resources, and the
United States Forest Service, as well as the Corson family, for
allowing us access to their land for our surveys. We thank D.
Fantz and anonymous reviewers for their help.
LITERATURE CITED
BURNHAM,K.P.,AND D. R. ANDERSON. 2002. Model selection and
multimodel inference: a practical information-theoretic
approach. Second edition. Springer-Verlag, New York.
CROOKS, K. R., AND M. E. SOUL´
E. 1999. Mesopredator release and
avifaunal extinctions in a fragmented system. Nature
400:563–566.
DIJACK,W.D.,AND F. R. THOMPSON, III. 2000. Landscape and edge
effects on the distribution of mammalian predators in
Missouri. Journal of Wildlife Management 64:20–216.
DISNEY, M. R., E. C. HELLGREN,C.A.DAVIS,D.M.LESLIE,JR., AND D.
M. ENGLE. 2008. Relative abundance of mesopredators and
size of oak patches in the cross-timbers ecoregion. South-
western Naturalist 53:214–223.
GANNON, W. L., R. S. SIKES,AND THE ANIMAL CARE AND USE
COMMITTEE OF THE AMERICAN SOCIETY OF MAMMALOGISTS. 2007.
Guidelines of the American Society of Mammalogists for the
use of wild animals in research. Journal of Mammalogy
88:809–823.
KAYS, R. W., M. E. GOMPPER,AND J. C. RAY. 2008. The landscape
ecology of coyotes based on large scale estimates of
abundance. Ecological Applications 18:1014–1027.
LONG, R. A., T. M. DONOVAN,P.MACKAY,W.J.ZIELINSKI,AND J. S.
BUZAS. 2011. Predicting carnivore occurrence with noninva-
sive surveys and occupancy modeling. Landscape Ecology
26:327–340.
MACKENZIE, D. I., J. D. NICHOLS,N.SUTTON,K.KAWANISHI,AND L. L.
BAILEY. 2005. Improving inferences in population studies of
rare species that are detected imperfectly. Ecology 86:1101–
1113.
MACKENZIE, D. I., J. D. NICHOLS,J.A.ROYLE,K.H.POLLOCK,L.L.
BAILEY,AND J. E. HINES. 2006. Occupancy estimation and
modeling. Academic Press, Burlington, Massachusetts.
NIGH, T. A., AND W. A. SCHROEDER. 2002. Atlas of Missouri
ecoregions. Missouri Department of Conservation, Jefferson
City.
O’CONNELL, A. F., JR., N. W. TALANCY,L.L.BAILEY,J.R.SAUER,R.
COOK,AND A. T. GILBERT. 2006. Estimating site occupancy and
detection probability parameters for meso- and large
mammals in a coastal ecosystem. Journal of Wildlife
Management 70:1625–1633.
PALOMARES,F.,AND T. M. CARO. 1999. Interspecific killing among
mammalian carnivores. American Naturalist 153:492–508.
ROYLE, J. A., AND J. D. NICHOLS. 2003. Estimating abundance from
repeated presence/absence data or point counts. Ecology
84:777–790.
SCHWARTZ,C.W.,AND E. R. SCHWARTZ. 2001. The wild mammals of
Missouri. Second revised edition. University of Missouri
Press, Columbia.
SINCLAIR, K. E., G. R. HESS,C.E.MOORMAN,AND J. H. MASON. 2005.
Mammalian nest predators respond to greenway width,
landscape context and habitat structure. Landscape and
Urban Planning 71:277–293.
YATES, M. D., AND R. M. MUZIKA. 2006. Effect of forest structure
and fragmentation on site occupancy of bat species in
Missouri Ozark forests. Journal of Wildlife Management
70:1238–1248.
Submitted 5 April 2011. Accepted 10 May 2012.
Associate Editor was Jennifer K. Frey.
September 2012 Cove et al.—Analysis of mesopredator surveys 261
... The prevalence (and intensity) of the MRH has also been linked to the maintenance of species diversity and system productivity (Brashares et al., 2010). Small carnivores can benefit indirectly from agriculture and habitat modification by using the edge habitats created by land clearing to penetrate forests and capitalize on birds, insects, and small mammals that depredate crops and inhabit edge habitats (Dijak & Thomson, 2000;Cove et al., 2012bCove et al., , 2014. We suspect that regardless of circumstances, as abundances and distributional changes occur, the ecological release of small carnivores can play a large role in their effects on threatened species. ...
... The highly adaptable raccoon is now considered an important exotic species across portions of Europe, Russia, and Japan, where it is considered a threat to biodiversity (Lotze & Anderson, 1979;Ikeda et al., 2004;García et al., 2012). Many studies have focused on understanding the environmental drivers of raccoon occurrence and abundance because of their potential threat to migratory songbirds and other susceptible taxa, but few studies have quantified their direct effects on threatened species (Donovan et al., 1997;Dijak & Thomson, 2000;Cove et al., 2012b). Eagan et al. (2011) quantified the effects of reducing raccoon abundance, with results revealing that whitefooted mice, Peromyscus leucopus, increased in density as a direct response to the removal. ...
Chapter
The absences of large carnivores from many ecosystems, human‐induced landscape changes, and resource supplementation have been theorized to increase the abundance of small carnivore species around the world. Overabundant and/or unconstrained small carnivores can have significant effects on specific prey species that, in some cases, can cascade through entire ecosystems. Here, we review the effects of small carnivores on threatened species. We focus on four well‐studied families (Procyonidae, Mephitidae, Mustelidae, and Herpestidae) and emphasize that this is a global conservation issue with consequences for biodiversity. We review and compare the impacts that small carnivores can have on a variety of prey taxa including small mammals, nesting avian and reptilian species, and rare invertebrates. We differentiate between native and exotic small carnivores because this is often an important distinction in terms of the impact severity and range of effects. In addition to direct lethal effects (i.e. predation), small carnivores can also impact threatened species as disease vectors and through competition or overexploitation, which can disrupt communities via ecological release or extinction. Furthermore, we explore other case studies in which small carnivores have had positive effects on threatened species and discuss studies that reveal other taxa responsible for exerting stronger negative effects on threatened prey. We offer some concluding remarks about global small carnivore conservation and emphasize the need for decision‐analytic approaches and robust analyses that can improve our assessment of how populations of threatened species can be affected. To date, indirect effects are especially difficult to measure in the field and many studies have provided only anecdotal or correlative results, signalling a need for improving our scientific methodologies and management approaches.
... With the apparent rarity of large carnivores in our surveys and in the different land-use matrices, mesopredators were the most commonly detected guild at all sites. Although this may provide evidence for the MRH, this is likely a consequence of concentrated populations of the smaller carnivores and the effect of scent lures at cameras [40]. Additionally, mesopredators may be tolerant of habitat disturbance and utilize agricultural food resources. ...
... Additionally, mesopredators may be tolerant of habitat disturbance and utilize agricultural food resources. This highlights the difficulties in comparing indices such as capture frequencies for landscape associations of mesopredators, because landscape influences and concentration of individuals in forest fragments have been observed to affect detection probability and inference [40]. ...
Article
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Noninvasive camera-traps are commonly used to survey mammal communities in the Neotropics. This study used camera-traps to survey medium and large mammal diversity in the San Juan – La Selva Biological Corridor, Costa Rica. The connectivity of the corridor is affected by the spread of large-scale agriculture, cattle ranching, and a growing human presence. An occupancy modeling approach was used to estimate corridor species richness and species-specific detection probabilities in 16 forested sites within four different matrix-use categories: eco-lodge reserves, tree plantations/general reforestation, cattle ranches, and pineapple/agricultural plantations. Rarity had a highly negative effect (β = -1.96 ± 0.65 SE) on the ability to detect species presence. Corridor richness was estimated at 20.4 ± 0.66 species and was lower than that observed in protected areas in the Neotropics. Forest cover was significantly less at pineapple plantations than other land-use matrices. Richness estimates for different land-use matrices were highly variable with no significant differences; however, pineapple plantations exhibited the highest observed richness. Given the limited forest cover at those sites, we believe that this reflects the concentrated occurrence of medium and large mammals in small forest patches, particularly because the majority of pineapple plantation communities were generalist mesopredators. Fragmentation and connectivity will need to be addressed with reforestation and limitations on pineapple production for the region to function as an effective corridor. Occupancy modeling has only recently been applied to camera-trap data and our results suggest that this approach provides robust richness and detection probability estimates and should be further explored.
... • (1) a true state of increased mesopredator and herbivore abundance due to increased human-derived resources in the suburbs, and • (2) concentrated activity of mammals in small fragmented forest patches versus the expansive forest tracts in other studies (e.g. Cove et al., 2012b). ...
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Camera traps are commonly used for mammal surveys and many recent studies have published variable trap success rates. All published reports have focused survey efforts in protected areas or large contiguous forests, but we used camera traps in a highly altered suburban landscape. We selected 22 camera trap sites in Warrensburg and Lee’s Summit, Missouri and surveyed for a total of 308 trapnights (TN) of effort. Procyon lotor (raccoon) had the highest trap success (38.96/100 TN), followed by: Didelphis virginiana (Virginia opossum, 37.34/100 TN); Odocoileus virginianus (white tailed deer, 27.92/100 TN); Sciurus niger and S. carolinensis (fox and gray squirrel, 19.48/100 TN); Vulpes vulpes (red fox, 8.77/100 TN); Canis latrans (coyote, 7.79/100 TN); Sylvilagus floridanus (cottontail rabbit, 3.90/100 TN); Urocyon cinereoargenteus (gray fox, 2.92/100 TN); Lynx rufus (bobcat, 1.95/100 TN); and Mephitis mephitis (striped skunk, 1.62/100 TN). These results are higher than any other published findings. We used 1-3 kg of deer meat as bait at each camera station and we believe this increased our trap success of mesopredators (Cove et al., 2012) versus studies that used no bait. However, our trap success for deer, squirrels, and rabbits were also higher than those published and these species were not attracted to bait. We hypothesize that the increased trap success in our study reflects (1) a true state of increased mesopredator abundance due to increased human-derived resources in the suburbs, and (2) concentrated activity of mammals in small fragmented forest patches versus the expansive forest tracts in other studies.
... Many of those species are common and highly associated with humans; e.g., northern raccoons and eastern gray squirrels. These synanthropes are likely responding to more fine-scale covariates, as exemplified by raccoons, most positively associated with housing densities and the associated human refuse, outdoor pet food, bird feeders, and other resource subsidies in anthropogenic and heterogeneous landscapes [47][48][49]. These unmodeled species will likely interact with other taxa, and therefore, warrant further examination with higher resolution habitat and anthropogenic covariates. ...
Article
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Finding balance between the needs of people and wildlife is an essential component of planning sustainable landscapes. Because mammals make up a diverse and ecologically important taxon with varying responses to human disturbance, we used representative mammal species to examine how alternative land-use policies might affect their habitats and distributions in the near future. We used wildlife detections from camera traps at 1591 locations along a large-scale urban to wild gradient in northern Virginia, to create occupancy models which determined land cover relationships and the drivers of contemporary mammal distributions. From the 15 species detected, we classified five representative species into two groups based on their responses to human development; sensitive species (American black bears and bobcats) and synanthropic species (red foxes, domestic cats, and white-tailed deer). We then used the habitat models for the representative species to predict their distributions under four future planning scenarios based on strategic versus reactive planning and high or low human population growth. The distributions of sensitive species did not shrink drastically under any scenario, whereas the distributions of synanthropic species increased in response to anthropogenic development, but the magnitude of the response varied based on the projected rate of human population growth. This is likely because most sensitive species are dependent on large, protected public lands in the region, and the majority of projected habitat losses should occur in non-protected private lands. These findings illustrate the importance of public protected lands in mitigating range loss due to land use changes, and the potential positive impact of strategic planning in further mitigating mammalian diversity loss in private lands.
... Fire occurred in mature, native-dominated forest in the Ensenada sector of Guánica Forest, PR. Transect point 0 is at the intersection of the trail and PR 325 occurrence, ѱ(Aho et al. 2014;Cove et al. 2012;MacKenzie et al. 2006;Pan 2001), represented in this case by the predicted probabilities (i.e., of species occurrence at a given distance along the trail) from each GLM model, as an indicator of the expected pattern of post-disturbance colonization. Each dependent variable was tested against a particular independent variable or set of interacting variables that were considered to have a possible impact on species distribution. ...
Article
Full-text available
Introduction: A fundamental challenge to the integrity of tropical dry forest ecosystems is the invasion of non-native grass species. These grasses compete for resources and fuel anthropogenic wildfires. In 2012, a bulldozer from the Puerto Rico Electric Power Authority cleared a 570-m trail from a state road into a mature dry forest section of Guánica Forest to control a wildfire. We monitored colonization by a non-native invasive grass (Megathyrsus maximus), a highly invasive tree (Leucaena leucocephala), and a native grass (Uniola virgata), as well as natural regeneration, along the bulldozer trail. We determined whether bulldozing facilitated colonization by these species into the forest and the extent of spread. Results: Distance from propagule source and temporal variations strongly influenced colonization by our three focal species. Megathyrsus maximus invaded along the trail from source populations by the state road. The establishment of new colonies of M. maximus seedlings went as far as 570 m inside the forest (i.e., at the end of the bulldozer trail), but we found most new colonies within 270 m of the road. Leucaena leucocephala exhibited a similar spreading pattern. Before disturbance, Uniola virgata was distributed widely across the forest, but the highest densities were found in areas near the latter portion (> 401 m) of the bulldozer trail. Subsequently, the species formed new clumps along more than half of the trail (250 to 570 m), apparently colonizing from undisturbed patches nearby. Conclusions: Bulldozing facilitated the invasion of non-native vegetation. The projected community assemblage will be more fire-prone than before since M. maximus carries fire across the landscape better than U. virgata, emphasizing the capacity of invasive plant colonization to alter local ecological processes after only a single wildfire and bulldoze event. Our results provide a valuable baseline for short-term vegetation response to anthropogenic disturbances in tropical semi-deciduous dry forests.
... This relationship was similar for the detection of tayras and raccoons in the study area. The consequence of such concentrated foraging activities in small forest patches and forest edges has also been shown to be responsible for exposing nesting song birds to increased predation risk (Cove, Niva & Jackson, 2012;Dijack & Thompson, 2000;Donovan et al., 1997). However, none of the habitat covariates examined in this analysis were significant predictors of mesopredator occurrence. ...
Article
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Loss of large mammalian carnivores may allow smaller mesopredators to become abundant and threaten other community members. There is considerable debate about mesopredator release and the role that other potential factors such as land-scape variables and human alterations to land cover lead to increased mesopredator abundance. We used camera traps to detect four mesopredators (tayra, Eira barbara; white-nosed coati, Nasua narica; northern raccoon, Procyon lotor; and common opossum, Didelphis opossum) in a biological corridor in Costa Rica to estimate habi-tat covariates that influenced the species' detection and occurrence. We selected these mesopredators because as semi-arboreal species they might be common nest predators, posing a serious threat to resident and migratory songbirds. Pineapple production had a pronounced positive effect on the detectability of tayras, while forest cover had a negative effect on the detection of coatis. This suggests that abun-dance might be elevated due to the availability of agricultural food resources and foraging activities are concentrated in forest fragments and pineapple edge habitats. Raccoon and opossum models exhibited little influence on detection from habitat covariates. Occurrence models did not suggest any significant factors influencing site use by nest predators, revealing that all four species are habitat generalists adapted to co-existing in human altered landscapes. Furthermore, fragmentation and land cover changes may predispose nesting birds, herpetofauna, and small mammals to heightened predation risk by mesopredators in the Neotropics.
Data
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The mesopredator release hypothesis (MRH) has been suggested as a reason why many mammalian generalist mesopredators flourish and become abundant. However, the MRH has only been examined in a limited number of field studies. Some studies have argued that coyotes (Canis latrans) act as top predators in fragmented forest systems and coyote presence has a positive effect on song bird diversity and abundance by controlling mesopredator abundance. We integrated camera trap data and occupancy modeling to determine the factors that affect coyote detection probability and habitat use in a fragmented suburban landscape in central Missouri. We then examined the influence of coyote presence and other habitat variables on mesopredator detection probability and habitat use in the same system. Coyote detection was negatively related to increasing forest cover, whereas red fox (Vulpes vulpes) detection was positively related to increasing urbanization. Coyote occurrence models suggested little habitat selection, while the mesopredator occurrence models suggested an affinity for urbanization. Although there was a slight negative effect of coyote presence on site use by other mesopredators, we suggest that the smaller species are better adapted to coexisting with humans and thus have increased in abundance.
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Resumen Los lineamientos para el uso de especies de mamíferos de vida silvestre en la investigación con base en Sikes et al. (2011) se actualizaron. Dichos lineamientos cubren técnicas y regulaciones profesionales actuales que involucran el uso de mamíferos en la investigación y enseñanza; también incorporan recursos nuevos, resúmenes de procedimientos y requisitos para reportes. Se incluyen detalles acerca de captura, marcaje, manutención en cautiverio y eutanasia de mamíferos de vida silvestre. Se recomienda que los comités institucionales de uso y cuidado animal (cifras en inglés: IACUCs), las agencias reguladoras y los investigadores se adhieran a dichos lineamientos como fuente base de protocolos que involucren mamíferos de vida silvestre, ya sea investigaciones de campo o en cautiverio. Dichos lineamientos fueron preparados y aprobados por la ASM, en consulta con profesionales veterinarios experimentados en investigaciones de vida silvestre y IACUCS, de quienes cuya experiencia colectiva provee un entendimiento amplio y exhaustivo de la biología de mamíferos no-domesticados. La presente versión de los lineamientos y modificaciones posteriores están disponibles en línea en la página web de la ASM, bajo Cuidado Animal y Comité de Uso: (http://mammalogy.org/uploads/committee_files/CurrentGuidelines.pdf). Recursos adicionales relacionados con el uso de animales de vida silvestre para la investigación se encuentran disponibles en (http://www.mammalsociety.org/committees/animal-care-and-use#tab3).
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Guidelines for use of wild mammal species are updated from the American Society of Mammalogists (ASM) 2007 publication. These revised guidelines cover current professional techniques and regulations involving mammals used in research and teaching. They incorporate additional resources, summaries of procedures, and reporting requirements not contained in earlier publications. Included are details on marking, housing, trapping, and collecting mammals. It is recommended that institutional animal care and use committees (IACUCs), regulatory agencies, and investigators use these guidelines as a resource for protocols involving wild mammals. These guidelines were prepared and approved by the ASM, working with experienced professional veterinarians and IACUCs, whose collective expertise provides a broad and comprehensive understanding of the biology of nondomesticated mammals in their natural environments. The most current version of these guidelines and any subsequent modifications are available at the ASM Animal Care and Use Committee page of the ASM Web site (http://mammalsociety.org/committees/index.asp).
Article
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Interspecific killing among mammalian carnivores is common in nature and accounts for up to 68% of known mortalities in some species. Interactions may be symmetrical (both species kill each other) or asymmetrical (one species kills the other), and in some interactions adults of one species kill young but not adults of the other. There is a positive significant relationship between the body masses of solitary killer species and body masses of their victim species, and grouping species kill larger victims than solitary species. Interactions and consumption of the victim appear more common when food is scarce or disputed. In response to killers, victim species may alter their use of space, activity patterns, and form groups. Consequences of interspecific killing include population reduction or even extinction, and reduction and enhancement of prey populations, and may therefore have important implications for conservation and management of carnivores and their prey.
Article
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Changes in structure and arrangement of forests may influence the distribution of bat communities by affecting roosting and foraging habitat. Using Anabat bat detectors, we determined presence of bat species at 316 sample plots in southeastern Missouri, USA, through qualitative identification of echolocation calls collected. We used maximum-likelihood estimation techniques incorporating detection probabilities into estimation of site occupancy by species of bats. We compared a priori models at 2 geographic scales using information theoretic methods. At the local-site scale, eastern pipistrelle (Pipistrellus subflavus) and red bat (Lasiurus borealis) occupancy was most influenced by structural characteristics of forested areas, whereas Indiana bats (Myotis sodalis) were influenced most by density of large-diameter snags that could provide roosting habitat. At the landscape scale, occupancy of Indiana bats was directly related to amount of nonforested land cover. Northern long-eared bat (M. septentrionalis) occupancy was inversely related to edge. These data describe implications of forest fragmentation and provide information that can be used when integrating forest-management practices into bat conservation.
Article
Los mesodepredadores (por ejemplo, el mapache Procyon lotor, el tlacuache Didelphis virginiana y el zorrillo rayado Mephitis mephitis) han recibido considerable atención debido a su vinculación con la disminución de poblaciones de aves a través de un incremento en la depredación de nidos, especialmente en paisajes fragmentados por fuerzas antropogénicas. Las relaciones de la abundancia de mesodepredadores con los tamaños del parche de hábitat han recibido menos atención que las relaciones con otras mediciones de fragmentación, en particular con las características de borde. Probamos la hipótesis de que la abundancia relativa de mesodepredadores (por ejemplo, mapaches y tlacuaches) estuvo negativamente relacionada con el tamaño de parche de bosque. Delineamos 15 parches de bosque de encino (Quercus) de 0.2 a 55.3 hectáreas dentro de un mosaico de pastizales y bosques en la ecoregión de “cross-timbers” de Oklahoma. Se usaron estaciones odoríferas y trampas de captura viva dentro de estos parches para establecer índices de abundancia relativa en los veranos de 2003 y 2004. Ambos índices de abundancia relativa se relacionaron débil y negativamente con el área de parche de bosque. Sin embargo, la tasa de captura y de visitas a las estaciones odoríferas no fueron correlacionadas consistentemente durante el estudio. Nuestros resultados sugirieron que los dos métodos para establecer un índice de abundancia proporcionaron información diferente sobre respuestas funcionales y numéricas al tamaño de parche. Nuestra evidencia de que era más probable encontrar a los mesodepredadores dentro de la ecoregion de “cross timbers” en parches más pequeños de bosque de encino, podría tener implicaciones para el éxito de anidación de las aves en estos parches.