J. L. Boone, Ph.D., Ecology  
Laerm, J., and J. L. Boone. 1994. Mensural discrimination of four species of Peromyscus (Rodentia, Muridae) in the southeastern United States. Brimleyana, 21:107123.  
Table 1. Unstandardized discriminant function coefficients using one or two morphological characters of four Peromyscus species (P. gossypinus, P. leucopus, P. maniculatus, and P. polionotus) in the southeastern United States. Each sections contains the characters used, unstandardized discriminant coefficients, constants, and numbers of errors for each set of species. Discriminant scores for each pair of species have opposite signs, and this is indicated as one species greater than zero. Variables defined below.
Species Pair Skull only Skin and Skull    P. gossypinus vs. P. leucopus SL 0.927 Foot 0.593 MTL 3.732 SL 0.821 Constant 38.229 Constant 34.125 Pg scores > 0 Pg scores > 0 Errors: Pl 2; Pg 2 Errors: Pg 5; Pl 1 P. gossypinus vs. P. maniculatus SL 0.794 BNL 0.685 BD 2.123 BD 2.403 Constant 39.780 Constant 37.611 Pg scores > 0 Pg scores > 0 Errors: none Errors: Pg 1; Pm 0 P. gossypinus vs. P. polionotus SL 1.000 Tail 1.000 Constant 25.000 Constant 55.000 Pg scores > 0 Pg scores > 0 Errors: none Errors: none P. leucopus vs. P. maniculatus OC 2.523 Tail 0.165 BD 2.754 BNL 1.028 Constant 33.762 Constant 10.271 Pl scores > 0 Pm scores > 0 Errors: Pm 15; Pl 24 Errors: Pl 0; Pm 1 P. leucopus vs. P. polionotus SL 1.214 SL 0.953 MTL 2.636 Tail 0.085 Constant 37.389 Constant 27.251 Pl scores > 0 Pl scores > 0 Errors: Pp 1; Pl 2 Errors: Pl 3; Pp 0 P. maniculatus vs. P. polionotus SL 0.680 Tail 1.000 TTL 1.803   Constant 35.126 Constant 60.000 Pm scores > 0 Pm scores > 0 Errors: Pp 4; Pm 8 Errors: none


Methods One of us (JL) measured 14 cranial characters to the nearest 0.1 mm using dial calipers, and recorded three external measurements from specimen tags. We estimated age from pelage characters (no juvenile gray), tooth wear (significant wear on all major cusps), and degree of cranial suture fusion and only measured adults in age classes 4  6 (Schmidly 1973). We excluded specimens with missing data, juveniles, and subadults from all analyses. Mensural characters (Choate et al. 1973; DeBlase and Martin 1981) included: head and body length (body), tail length (tail), hind foot length (foot), greatest skull length (SL), basonasal length (BNL), rostral breadth (RB), nasal length (NL), interorbital constriction (OC), zygomatic breadth (ZB), bony palate length (PL), maxillary toothrow length (MTL), total toothrow length (TTL), palatal width (PW), pterygoid breadth (PB), bullar depth (BD), and anterior palatal (incisive) foramen length (PFL). We measured rostral length (RL) from the anteriormost point of the nasals to the anterior edge of the zygomatic arch, and body length was calculated as the difference between total and tail lengths. We excluded ear length due to predominance of missing data. Use of the discriminant function Discriminant analysis combines variables to generate a set
of linearly independent axes upon which specimens, after appropriate
transformation, can be plotted and their classification determined.
The appropriate transformation is to multiply each morphological
character variable (e. g., foot length, skull length) by its discriminant
function coefficient, sum the products, and add a constant (for
each axis separately). In general:
D1 = B10 + B11X1 + B12X2 + B13X3 + ... + B1nXn where D1 is the specimen's discriminant score on the first
axis, the B1i's are discriminant function coefficients estimated
from the data for the first axis (Bi0's are constants), and the
Xi's are the values of the original variables. This is done separately
for each axis, and the scores, D1, D2, ..., Dn, form the coordinate
of the specimen's location in the ndimensional discriminant space.
For example, to separate P. gossypinus from P. leucopus using
external and skull measurements, the appropriate
D = 34.125 + 0.593(foot) + 0.821(skull length). Which, given an unknown specimen with hindfoot and skull lengths
of 23.5 mm and 28.7 mm, respectively, and the coefficients of
these measurements from Table 3, becomes:
3.377 = 34.125 + 0.593(23.5) + 0.821(28.7). In this case, any positive value of D indicates P. gossypinus, and any negative value of D indicates a P. leucopus; thus this specimen is a P. gossypinus. Literature Cited Schmidly, D. J. 1973. Geographic variation and taxonomy of Peromyscus boylii from Mexico and the southern United States. J. Mamm. 54:111130. DeBlase, A. F., and R. E. Martin. 1981. A manual of mammalogy with keys of the families of the world. Second edition. Wm. Brown Co., Dubuque. Choate, J. R. 1973. Identification and recent distribution of whitefooted mice (Peromyscus) in New England. J. Mamm. 54:4149. 

Note: All distances, elevations, and other facts are approximate. ; Last updated 081123 

