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.
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;
140 Northeastern Naturalist Vol. 14, No. 1
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).
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.
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.
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. Therefore differences in the wood characteristics
other than size of trunks versus limbs may have influenced host choice by R.
virginicus and R. flavipes.
Schiegg (2001) argued that sound forest management should leave tree
trunks and limbs on the forest floor to support insect diversity. The present
study provides support for this position because two congeneric termite
species foraged on logs of significantly different sizes throughout the year.
Given their importance in forest nutrient cycles, more information on these
species will benefit our understanding of forest ecosystems.
I thank Lisa Belitz, Tony Curtis, and Susan Morlino for assistance with this
study. I am grateful to the Virginia Coast Reserve for permission to use their
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