DEPARTMENT OF BIOLOGY, ANGELO
STATE UNIVERSITY, SAN ANGELO, TX
A B S T R A C T : The purpose of this study conducted at the Devils River State Natural Area – Big Satan Unit (DRSNA - BSU), in Val Verde County, Texas, has been to delineate the seasonal vegetative
resource selection of the White-ankled mouse (Peromyscus pectoralis), comparing trap-line indices of abundance, to geospatial plant community data. Trapping data were collected from traplines over a 21 month period (Feb 2013 - October 2014), resulting in 10,607 trap-nights and 185 P. pectoralis captures. Using ArcGIS software, trap-lines were buffered by the known approximate
convex-polygon home range of P. pectoralis (A = 3,340m2), and spatially overlaid with the known active vegetation series of DRSNA – BSU. The percentage of each habitat within the buffered trapline area was tested against the abundance indices of P. pectoralis using multiple linear regression modeling. Positive correlations were observed in winter and fall among the Lechuguilla-Sotol
(P<0.001), Blackbrush (P<0.007), Guajillo (P<0.05), and Ashe Juniper-Oak vegetation series (P<0.03). Data suggests that vegetative habitat selection by P. pectoralis varies seasonally, and is likely
dependent on the degree of seasonal resource availability within each vegetation type.
• A strong correspondence between small mammal assemblages and vegetation composition is well documented in research within various
environments, and it is well known that small mammals typically will occur within, and move among, habitat patches distinguished on the
basis of floristic composition (Monjeau et al. 2011). Habitat data collected by Mullican & Baccus (1990) suggests that the pattern of use of
microhabitats by P. pectoralis is related to inherent selection rather than to interspecific competition. Furthermore, working under the
assumption that P. pectoralis’ spatial distribution is associated with its habitat requirements, identifying those habitat requirements is an
effective means to understanding and accurately predicting the distribution of this species within a mosaic landscape.
VEGETATION
SERIES
1
2
Guajillo
Ashe JuniperOak
3
Blackbrush
4
• A substantial amount of ecological information exists in the literature for Mexican populations of this species; however there have been
limited habitat/resource selection studies of P. pectoralis in Texas populations. These Texas habitat studies have additionally been limited
locally to areas of central, west-central, northern, and far west Texas (Figure 2). There has to-date been a lack of ecological studies
conducted on this species in southwestern Texas, including a deficit in habitat suitability studies conducted in a highly mosaic region.
Because of the paucity of habitat studies in this region, an in-depth habitat suitability study was conducted, comparing vegetation series to
trapping data.
Ceniza
STUDY SITE CHOICE
OTHER INDICATOR SPECIES
% OCCUPIED
Guajillo
Vasey Oak
Slimleaf Heliotrope
Texas Sotol
Gregg’s Ash/Slim Tridens
33%
Ashe Juniper
Vasey Oak
Blackbrush
Texas Persimmon
Ceniza
Texas Persimmon
5
LechuguillaSotol
Lechuguilla
Sotol
6
Curly
MesquiteSideoats Grama
Curly Mesquite
Sideoats Grama
7
• To conduct a study of this nature, three study site criteria must be met: (1) a large sample size of P. pectoralis will be needed, (2) a mosaic of
habitat types must be present, and (3) a study area must be chosen that is rocky throughout, to control for the known affinity for rocky
areas. These three criteria are met at the Devils River State Natural Area – Big Satan Unit (DRSNA – BSU), which is located at the confluence
of three different level III ecoregions which has created a mixing of floral communities (Figure 2.). Peromyscus pectoralis has been captured
within the following habitats: Curly Mesquite-Sideoats Grama, Lechuguilla-Sotol, Blackbrush, Ceniza, Ashe Juniper-Oak, and Guajillo Series.
These vegetation series were identified by Keith (2011) and named by their dominant plant species (Figure 3.). The dominant and indicator
species within the vegetation series used for analysis are described in more detail in Table 1.
DOMINANT SPECIES
Other
NA
Texas Mountain Laurel
Ceniza
Guajillo
Blackbrush
Agarito
R E S U LT S & C O N C L U S I O N S
A
B
SEASONAL CAPTURE TOTALS
60
26%
Mesquite
Silver Bluestem
Ceniza
Guajillo
13%
Evergreen Sumac
Texas Sotol
Curly Mesquite
Tobosa
13%
Guajillo
Agarito
Rio Grande Stickpea
Wright’s Threeawn
Ocotillo
9%
Prickly Pear
Ceniza
Blackbrush
Texas Persimmon
3%
INDIVIDUALS CAPTURED
#
• The distribution of Peromyscus pectoralis is broadly within central-northern Mexico continuing into the state of Texas (Figure 1.), where the
species can be found in the Edwards Plateau regions, central Great Plains, the northern extent of the south Texas plains, and the Chihuahua
desert regions of west Texas (Griffith et al. 2004). Based on capture location data, the most documented abiotic habitat affinity of P.
pectoralis is an association with rocky areas including cliffs, limestone outcrops, or talus slopes with some form of woody vegetation
SPECIES DISTRIBUTION (Schmidly 1972; Schmidly 1974; Kilpatrick and Caire 1973; Baccus and Horton 1984; Etheredge et al. 1989).
LACK OF RESEARCH
ON HABITAT
SUITABILITY
R E S U M E N : El objetivo de este estudio realizado en el Parque de Área Natural Estatal Devils River – Big Satan Unit (DRSNA - BSU), ha sido para determinar la selección de recursos
vegetativos a través de las estaciones por el Ratón tobillo blanco, (Peromyscus pectoralis), vía la comparación de índices de abundancia (usando trampas de línea) con datos de vegetación
geoespaciales del área. Se realizaron muestreos durante un periodo de 21 meses (febrero de 2013 a octubre de 2014), lo cual equivalió a 10,607 noches de trampa y resulto en 185
capturas de P. pectoralis. Una área equivalente al ámbito de hogar de P. pectoralis (A = 3,340m2), basado en la distancia alrededor de la trampa de línea, fue espacialmente montada sobre
las series de vegetación de DRSNA-BSU usando ARC-GIS. Utilizando un modelo de regresión lineal múltiple, el porcentaje de cada hábitat dentro el ámbito de hogarse estimó contra los
índices de abundancia de P. pectoralis. Se observó una correlación positiva entre el invierno e otoño y varias series de vegetación: Lechuguilla-Sotol (P<0.001), Blackbrush (P<0.007),
Guajillo (P<0.05), and Ashe Juniper-Oak (P<0.03). Los datos sugieren que la selección de hábitat vegetativo de P. pectoralis varía estación almente y es probable que dependen del grado de
disponibilidad de recursos temporales dentro de cada tipo de vegetación.
TABLE 1. Table below displays the dominant and indicator species commonly found
within each of the vegetation series used in our analysis, identified by Keith (2011).
INTRODUCTION
UNDERSTANDING
HABITAT
REQUIREMENTS
C LINT N . M ORGAN AND
R OBERT C . D OWLER
5000
TOTAL TRAP NUMBER
4000
0.03
TOTAL TRAP NIGHT
3500
40
0.025
3000
30
0.02
2500
20
2000
0.015
1500
0.01
1000
10
0
SPRING
SUMMER
FALL
SEASONAL MEAN ABUNDANCE INDICES
0.035
4500
50
WINTER
NA
C
SEASONAL TRAPPING EFFORT
500
0.005
0
0
WINTER
SPRING
SUMMER
FALL
WINTER
SPRING
SUMMER
FALL
FIGURE 4. Trap capture and effort data displaying A) the seasonal capture totals of Peromyscus pectoralis at DRSNA – BSU, B) the seasonal trap-number and trap-night data totals, and C) the
seasonal abundance index averages.
3%
SEASONAL VEGETATION
CORRELATIONS
• Winter: Lechuguilla-Sotol Series, Blackbrush Series, and Ashe Juniper-Oak Series (Table 2.)
• Spring: Lechuguilla-Sotol Series
• Summer: No vegetation series correlations were observed during the summer months, which may be a result of low trap success. Alternatively this species has been documented to
switch to 40% animal matter consumption in the summer months which may decrease it’s dependence on vegetation based resources (Baccus et al. 2009).
• Fall: Blackbrush Series, Guajillo Series
TABLE 2. Table below displays the results of the best habitat model for the regression
analysis, performed with vegetation series as independent predictor variables.
TERM
Winter Model
ß
SE
P
BLACKBRUSH SERIES
0.713
Lechuguilla-Sotol Series
0.024
0.004
0.0001*
Blackbrush Series
0.019
0.008
0.0466*
Ashe Juniper-Oak Series
0.013
0.004
0.0168*
Lechuguilla-Sotol Series
0.021
0.006
0.0019*
Guajillo Series
0.010
0.007
0.1624
Ashe Juniper-Oak Series
0.006
0.004
0.1784
Spring Model
Summer Model
0.448
-0.003
0.002
0.2681
Ashe Juniper-Oak Series
0.001
0.002
0.5390
Guajillo Series
0.022
0.009
0.0369*
Blackbrush Series
0.042
0.013
0.0036*
0.025
0.013
0.0625
-0.011
0.008
0.1497
Whole Study Model
Lechuguilla-Sotol Series
Curly Mesquite-Sideoats Grama
Series
*Significant Correlation
D ATA
C OLLECTION
0.047
• Beginning in Feb 2013 monthly sampling was conducted at DRSNA – BSU with a primary objective to provide TPWD with a baseline assessment of the mammalian fauna of the state natural
area. For the purpose of this habitat selection study, capture data were collected from a total 105 trap-lines, over a 21 month period with trapping ending in October 2014, resulting in 10,607
trap-nights. In efforts to fulfill the baseline assessment objective of this project, trapping efforts were not uniform. Additionally, activity patterns of mice within the genus Peromyscus has been
observed to fluctuate seasonally, thereby influencing trap success (Figure 4.). To account for sampling variability, trap-line capture data were compiled as a function of meteorological season, and
abundance indices were calculated per trap-line within each seasonal grouping from captures/trap-night. This in effect, equalizes all sampling effort and accounts for the seasonal influence on
trap success.
FIGURE 2. Map above displays the Level III ecoregions of Texas (Omnerik 1987) as
well as the locations of other P. pectoralis habitat studies conducted in TX.
T RAP- LINES
G EOREFERENCED
HOME RANGE
B UFFERS
G E N E R AT E D
VEGETATION DATA
OVERLAID ON
BUFFERS
ASHE JUNIPER-OAK
SERIES
• The association of P. pectoralis with the Lechuguilla-Sotol Series is a novel vegetation affinity, with none of the dominant or indicator species within this series explicitly
known to be foraged upon by Peromyscus mice. Possible resources provided by this vegetation series include (Table 1.) Wright’s threeawn (Aristida purpurea), foliage of
Guajillo (Senegalia berlandieri), Rio Grande Stickpea (Calliandra conferta), or even the offshoots, seeds or seedlings of the Lechuguilla (Agave lechuguilla) may be a food
source as they are known to be eaten by deer and javelina (Pecari tajacu).
• An association between P. pectoralis and Ashe juniper is well supported in the literature. Baccus et al. (2009) observed in winter only Ashe Juniper (Juniperus ashei)
berries and green sumac berries were the important food staples of the study population. Our data suggest that when this food resource is available (Ashe juniper
berries), the abundance indices of P. pectoralis should increase in areas with higher percentages of Ashe juniper.
0.381
M AT E R I A L S & M E T H O D S
FIGURE 1. Map above displays the known distribution of P. pectoralis within the
state of Texas.
LECHUGUILLA-SOTOL
SERIES
0.011
Ceniza Series
Fall Model
FIGURE 5. Map of the Devils River State Natural Area – Big Satan Unit displaying the trap-line vegetation buffers generated
to obtain vegetation series percentages within the buffered area. Outlines of trap-lines are color-coded seasonally: Winter
= yellow, Spring = red, Summer = purple, Fall = light blue.
R2
• The Blackbrush vegetation series consists of two dominant species, Blackbrush (Acacia rigidula) and Texas persimmon (Diospyros texanus), with both exhibiting the most
direct impact on that habitat (Table 1.). The Texas persimmon bears fruits that are a common food item for a variety of Texas wildlife. The fruit could potentially serve as
a food source for P. pectoralis during the fall and winter months when insect activity is low. Baccus et al. (2009) observed a diet consisting 88.4% of fruits and seeds in
winter, and 86.2% of fruits and seeds in fall, with a few individuals consuming Texas persimmon fruits in the winter months.
• Trap-line location, directionality, approximate arrangement and length was recorded for each trap-line during the project. This is essential as some trap-lines vary in number of traps (22 – 100), as
well as arrangement , i.e. some trap-lines were set up as web-array’s to estimate rodent density (Paramenter et al. 2003). Using ArcGIS software (ESRI 2011. ArcGIS Desktop: Version 10.2.
Redlands, CA: Environmental Systems Research Institute.), trap-lines were spatially referenced and plotted as poly-lines. Additionally by utilizing detailed aerial imagery, adjustments were made
to the trap-lines when appropriate to account for the surface distortion that is associated with map projection.
• For the purpose of this study it is important to consider the home range of this mouse and how it overlaps with the trap-line it was captured on, as a means to include habitat data from within its
home range. To do this, these trap-lines were buffered by the known approximate convex-polygon home range of P. pectoralis (A = 3,340 ± 935 m2) reported by Mullican and Baccus (1990). The
home range buffer creates an area of possible occurrence along the trap line that is necessary, as we are comparing the habitat within the buffer to abundance indices of the trap-line as a whole.
• These home range/trap-line buffers were then spatially overlaid with the known active vegetation series of DRSNA – BSU documented and mapped onsite by Keith (2011) and displayed in Figure
5. Based on preliminary data analysis, P. pectoralis has been captured within the following habitats: Lechuguilla-Sotol, Curly Mesquite-Sideoats Grama, Blackbrush, Ceniza, Ashe Juniper-Oak, and
Guajillo Series. These vegetation series are named by their most common plant species, other species associations within the vegetation series are described in more detail in Table 1.
GUAJILLO SERIES
RESOURCE DEPENDENT
SEASONAL SELECTION
• The Guajillo series is the most common vegetation series, covering 33% of DRSNA – BSU (Table 1.). The commonality of this habitat type may perhaps be causing this
association by shear dominance of the present plant communities, as this is another undocumented habitat affinity for this species. Although possible resources may be
provided by the associated indicator species listed in Table 1.
•Our data suggest that vegetative habitat selection by P. pectoralis is seasonal, and most likely dependent on the degree of resource availability within each vegetation
type. This highly mobile species is capable of dispersing to an area of greater resource availability, and furthermore the fluctuation of abundance indices within the
various habitat types described can be explained though the paradigm of trophic ecology. However fine-scale microhabitat analyses of P. pectoralis would provide greater
insights into these vegetative habitat preferences, taking into account abiotic as well as biotic habitat variables.
REFERENCES
1. BACCUS, J. T., J. M. HARDWICK, D.G. HUFFMAN, AND M. A. KAINER. 2009. Seasonal trophic ecology of the white-ankled mouse, Peromyscus pectoralis (Rodentia: Muridae) in central Texas. Texas Journal of Science 61:97118.
2. BACCUS, J.T., AND J.K. HORTON. 1984. Habitat utilization by Peromyscus pectoralis in central Texas. Pp. 7-26 in Festschrift for Walter W. Dalquest in honor of his sixty-sixth birthday (N.V. Horner, ed.). Midwestern State
University, Wichita Falls, Texas.
3. ETHEREDGE, D. R., M. D. ENGSTROM, AND R.C. STONE. 1989. Habitat discrimination between sympatric populations of Peromyscus attwateri and Peromyscus pectoralis in West-Central Texas. Journal of Mammalogy 70:300307.
4. GRIFFITH, G.E., S.A. BRYCE, J.M. OMERNIK, J.A. COMSTOCK, A.C. ROGERS, B. HARRISON, S.L. HATCH, AND D. BEZANSON. 2004. Ecoregions of Texas (color poster with map, descriptive text, and photographs): Reston, Virginia, U.S.
Geological Survey (map scale 1:2,500,000).
5. KEITH, E.L. 2011. Plant community, fuel model, and rare species assessment and baseline establishment of twenty vegetation monitoring plots at Devils River State Natural Area- Devils River Ranch unit in Val Verde
County, Texas. Raven Environmental Services, Huntsville, Texas.
6. KILPATRICK, C. W., AND W. CAIRE. 1973. First Record of the Encinal Mouse, Peromyscus pectoralis, for Oklahoma, and Additional Records for North-Central Texas. The Southwestern Naturalist, (3). 351.
7. MONJEAU, J. A., ROTELA, C. H., LAMFRI, M., MÁRQUEZ, J., SCAVUZZO, C. M., STANULESCU, M., AND ... E. G. RIAL. 2011. Estimating habitat suitability for potential hantavirus reservoirs in north-western Patagonia using satellite
imagery: Searching for the best predictive tools. Mammalian Biology, 76(4): 409-416.
8. MULLICAN, T. R., AND J. T. BACCUS 1990. Horizontal and vertical movements of the white-ankled mouse (Peromyscus pectoralis) in central Texas. Journal of Mammalogy 71:378-381.
9. OMERNIK, J. M. 1987. Ecoregions of the conterminous United States. Annals of The Association of American Geographers 77:118-125.
10. PARMENTER, R. R., YATES, T. L., ANDERSON, D. R., BURNHAM, K. P., DUNNUM, J. L., FRANKLIN, A. B., AND G. C. WHITE. 2003. Small-mammal density estimation: a field comparison of grid-based vs. web-based density
estimators. Ecological Monographs, 73(1), 1.
11. PETERSON, A.T. 2001. Predicting species’ geographic distribution based on ecological niche modeling. Condor, 103, 599–605.
12. SCHMIDLY, D. J. 1972. Geographic Variation in the White-Ankled Mouse, Peromyscus pectoralis. The Southwestern Naturalist, (2). 113.
13. SCHMIDLY, D. J. 1974. Peromyscus pectoralis. Mammalian Species 49:1-3.
ACKNOWLEDGMENTS
We would first like to thank the Texas Parks and Wildlife Department for funding associated with the survey of mammals, reptiles, and amphibians of Devils River State Natural Area-Big Satan Unit.
FIGURE 3. Map of the Devils River State Natural Area – Big Satan Unit
displaying the 15 active vegetation series present, as well as the developed
and disturbed areas identified by Keith (2011).
• The presence/absence of each vegetation series located within the trap-lines were used as my independent variables in this analysis. I used a multiple linear regression analysis within each of the
four seasonal groupings (winter, spring, summer, fall) to describe the linear relationship between the vegetative habitat variables generated and the abundance indices per trap-line. The best
model was generated per season using stepwise model selection by the Akaike information criterion (AIC). Analysis and assumption testing were conducted using R software.
REGRESSION
ANALYSIS
Further funds were provided by the CITR foundation of Angelo State University for a Graduate Research Fellowship to C. N. Morgan. We also thank the Park Superintendent of DRSNA – BSU, Joe
Joplin, as well as Mark Lockwood and David Riskind of Texas Parks and Wildlife Department for providing logistic support. We’d also like to thank Dr. Nicholas Negovetich for his assistance with the
statistical analysis. A special thanks to the many research assistants and colleagues for field work assistance, including Austin Osmanski, Grayson Allred, and countless other field assistants,
colleagues, and friends who have made fulfilling this research objective possible.