2007 NORTHEASTERN NATURALIST 14(1):139–144 Termite Resource Partitioning Related to Log Diameter Deborah A. Waller* Abstract - The termites Reticulitermes virginicus and R. flavipes are sympatric in forests along the eastern United States from Florida to Maryland. These congeners construct subterranean nests, forage on surface and buried wood, and appear to have very similar ecological requirements. In the present study, I examined host-wood selection by these species in a coastal forest over two years. Logs inhabited by R. virginicus had significantly greater diameters than those used by R. flavipes. It is not known whether this pattern resulted from species-specific differences in preference for host size or competition for preferred logs. Host-wood temperature did not differ for R. virginicus and R. flavipes. Introduction Coarse woody debris (CWD) is increasingly recognized as an important component of forest ecosystems through its role in nutrient cycling and carbon storage (Lockaby et al. 2002). Additionally, CWD supports a wide diversity of organisms as a source of food and habitat (Bate et al. 2004), including fungi (Heilmann-Clausen and Christensen 2004, Lindhe et al. 2004, Norden et al. 2004) and soil arthropods (Bouget and Duelli 2004, Jabin et al. 2004, Lockaby et al. 2002, Niemela 1997). However, the specific characteristics of fallen logs that may impact the diversity of organisms associated with them have been ignored until recently (Bate et al. 2004). Subterranean termites in the genus Reticulitermes are common inhabitants of dead wood in temperate forests (Waller and La Fage 1987). These insects are instrumental in degrading fallen trees and branches and they facilitate microbial and arthropod access to log interiors through their tunneling activities. Little is known about how termites find wood sources and whether specific log characteristics influence host selection. In the present study, I investigated downed logs for the presence of subterranean termites over a two-year period in southeastern Virginia. Two termite species native to this area, Reticulitermes virginicus (Banks) and R. flavipes (Kollar), nest in the soil and forage above ground in dead wood. These species are abundant in forests along the East Coast and are sympatric from Florida to Maryland (Weesner 1970). A third species, R. hageni Banks, shares this range (Weesner 1970), but I have never encountered R. hageni alates over three years of intensive research on this study site. Although termites play vital roles in wood decomposition, their foraging preferences are poorly understood. I recorded the diameter and temperature of CWD occupied by R. virginicus and R. flavipes over two years in a coastal forest. *Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529; dwaller@odu.edu. 140 Northeastern Naturalist Vol. 14, No. 1 Methods The study was conducted at the headquarters of the Virginia Coast Reserve near Nassawadox, VA, in a coastal pine forest. Every month from July 1993 through July 1995, I collected samples of foraging worker termites from ten logs on the property and brought them to the laboratory for species identification. Different logs were sampled every collection period by chopping into downed trunks and branches until termites were located. In the field, I measured log diameter to the nearest 0.1 cm at the widest point where termites were extracted. I also measured temperature with a Fisher thermometer probe at three locations within the wood where I found termites. The log species were not determined, but most were southern yellow pine, including Pinus taeda L. Termites were active in logs every month of the year, although in the winter they sometimes appeared quiescent and were occasionally surrounded by ice crystals. However, termites revived once they warmed up in the laboratory. Workers of R. virginicus and R. flavipes cannot be reliably separated using morphological characteristics. Identification using soldiers is more reliable, although there can be overlap in characters among species. However, the gut protozoan faunas of these two species differ significantly and can be used in termite species identification (Lewis and Forschler 2004, Yamin 1979). Reticulitermes flavipes harbors a diagnostic protozoan species, Dinenympha gracilis Leidy, which is absent in other Reticulitermes species (Lewis and Forschler 2004, Yamin 1979). Protozoan species in R. virginicus guts differ in proportion from those found in R. hageni (Lewis and Froschler 2004). In addition to using a morphological key to separate species by soldiers (Scheffrahn and Su 1994), I examined the gut protozoan fauna. For each termite sample collected, I chilled three termite workers to anesthetize them and removed their guts with forceps. Gut contents were macerated in 0.5% NaCl with neutral red dye and examined under a compound microscope at 400x magnification to identify protozoan species. Termites that contained the protozoan D. gracilis in their guts were identified as R. flavipes, and those without this protozoan were identified as R. virginicus (Lewis and Forschler 2004, Yamin 1979). Data analysis Two-factor analysis of variance (month x termite species) was performed using StatView statistical software (www.StatView.com/product/ index.shtml) to determine whether diameters of logs inhabited by termites changed seasonally or varied according to termite species. Mean log temperature was calculated from the three readings per log and similarly examined using two-factor analysis of variance. Results Reticulitermes virginicus inhabited logs with significantly greater diameters than those occupied by R. flavipes (F = 56.184; df = 1, 199; p = 0.0001) 2007 D.A. Waller 141 (Fig. 1). The mean log diameter inhabited by R. virginicus during the study was 16.7 ± 0.6 SE cm for 135 logs measured, while R. flavipes occupied 107 logs with a mean diameter of 9.9 ± 0.4 SE cm. Log diameter did not vary significantly over the two-year period (F = 1.362; df = 25, 199; p = 0.1258). In contrast, there was no temperature difference in logs inhabited by R. virginicus and R. flavipes (F = 2.432; df = 1, 199; p = 0.1205) (Fig. 2). However, log temperature varied significantly throughout the two years (F = 111.301; df = 25, 199; p = 0.0001) as expected in an environment with marked seasonality. The lowest mean temperature recorded in a log was 1.0 ºC ± 0.8 SE in January 1994 for R. virginicus, while the highest was 33.7 ºC ± 0.8 SE in July 1995, also for R. virginicus. Discussion Gause (1934) suggested that two species with identical niches cannot coexist indefinitely. In this study, R. virginicus inhabited logs with significantly larger diameters than did the congeneric R. flavipes, consistent with Gause’s Law. It is unclear why host-log diameter differed for these two species. The difference might be related to the preference of one or both species for hosts of a given diameter. Evans et al. (2005) found that drywood termites can estimate wood size by assessing the resonant frequency of the Figure 1. Diameter of logs inhabited by Reticulitermes virginicus and R. flavipes from July 1993–July 1995. 142 Northeastern Naturalist Vol. 14, No. 1 wood. This capability might be more important for drywood termites which live in discrete wood pieces than for subterranean termites that can forage on several different wood sources. One possibility is that log size is related to log temperature dynamics. Reproductive alates of R. flavipes perform mating flights earlier in the year than do those of R. virginicus. Perhaps smaller logs provide the appropriate temperatures for alate development during the winter months. Houseman et al. (2001) suggested that R. flavipes and R. hageni partition resources related to soil moisture and temperature in Texas. However, log temperature did not differ for R. virginicus and R. flavipes in the present study. Some insects have specific preferences for branch size (Hespenheide 1969, 1976). Wood-boring beetle size is correlated with host-branch size for the buprestid Agrilus (Hespenheide 1976). In the present study, the smaller termite species R. virginicus inhabited logs with greater diameters than the larger congener R. flavipes. Schiegg (2001) found greater species numbers and increased diversity of saproxylic Diptera and Coleoptera in tree limbs than in trunks in beech trees. These resources may support different insect communities, although Schiegg (2001) found significant overlap in species. In the present study, the origin of host wood was not identified, although it is likely that very large diameter logs represented fallen trunks while those with small diameters Figure 2. Mean temperature of logs inhabited by Reticulitermes virginicus and R. flavipes from July 1993–July 1995. 2007 D.A. Waller 143 derived from fallen limbs. 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