Niche Pattern in a Forest‐Floor Small‐Mammal Fauna
Authors: Dueser Raymond D. , Shuggart H. H. 
Published: May 2006

This study examines the relationships among 4 small mammals species in 2nd—growth mesic forest on Walker Branch Watershed in eastern Tennessee, USA. Populations of Blarina brevicauda, Peromyscus leucopus, Ochrotomys nuttali and Tamias striatus were live—trapped on 9 0.36—ha grids during the summer of 1973. Eight measures of physical habitat structure were used in discriminant analysis of the microhabitats occupied by these 4 species. Three statistically significant discriminant functions were calculated. Each discriminant function is represented as an axis in a 3—dimensional discriminant space. These 3 axes are interpreted as vegetation type, vegetation structure and litter—soil surface characteristics. The positions of the species in the discriminant space characterize the microhabitat configurations of the species relative to the ecological properties attributed to the axes. Each species differs significantly from every other species on at least 1 axis. The observed species differences are conservative estimates of microhabitat (structural niche) segregation. We propose measures of niche position (i.e., exploitation speciality) and niche breadth based on the discriminant analysis. Species i is represented by a cloud of ni sample points in the discriminant space. Sample point j for species i lies the distance dij from the origin of the space. The average of these distances (°dj) represents the average "position" for species i relative to the origin. Because this origin represents the average of the microhabitats sampled on the watershed, and because the microhabitats actually occurring on the watershed are assumed to vary continuously, the likelihood of a species encountering favored microhabitat on Walker Branch decreases as °d increases. This ° is, thus, interpreted as an index of niche position relative to the average of the microhabitats sampled. Variability among the dij values for species i (vi) measures degree of specialization, a direct measure of niche breadth for species i. Our data indicate that °d and v are inversely related: breadth decreases as position becomes increasingly specialized. We incorporate measures of niche position, niche breadth and population abundance into an analysis of community "niche pattern." This niche pattern characterizes the 4 species as follows: Peromyscus is an abundant generalist, well—adapted to the watershed as a whole. Ochrotomys, the only other mouse, is a relatively rare specialist, poorly adapted to the watershed. Tamias occupies an intermediate position between Peromyscus and Ochrotomys, and exhibits intermediate abundance. Although we have little data for Blarina, this rare species appears to be poorly adapted to the watershed. Species differences in niche breadth appear to be determined more by the relative frequencies and carrying capacities of the species exploitation specialties than by the relative efficiencies with which the species exploit some critical limiting factor(s). Although we have no experimental evidence, the niche pattern observed for this community is consistent with an interference of competitive coexistence. The niche parameters of transient species which are infrequently encountered on Walker Branch are briefly discussed.