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2007 SOUTHEASTERN NATURALIST 6(3):491–504
Relationships Between an Introduced and Two Native
Dung Beetle Species (Coleoptera: Scarabaeidae) in Georgia
Orrey P. Young*
Abstract - Field collections, and laboratory observations and experiments, were
conducted in Tift County, GA, to determine possible interactions among the three
most abundant species of nocturnal scarab dung beetles. Light-trap data indicated
that Copris minutus occurred primarily in the winter and spring, Ateuchus histeroides
in the spring and summer, and Onthophagus gazella in the summer and fall. One of
the species, O. gazella, is a foreign introduction, and comparative laboratory food
procurement experiments revealed the superior ability of this species to obtain and
remove dung from the soil surface. A confrontation experiment also demonstrated
the behavioral dominance of O. gazella. A food-choice experiment indicated a more
restricted diet for O. gazella than for the other two species. Implications for the
future prospects of the two native species are discussed.
Present-day requirements are extensive for allowing a foreign insect to
be deliberately introduced into the United States. The Departments of Agriculture,
Health and Human Services, and Interior, as well as the Council on
Environmental Quality, all have data and analysis requirements and public
participation procedures that need to be completed before an insect species
can be released into the US (e.g., Young et al. 2000). This degree of
oversight, however, is a relatively recent phenomenon. A case in point is the
introduction of foreign dung beetles into the United States. In the early and
mid-1970s, several exotic scarab dung beetles were introduced into the
southeast and southwest US, one of which was Onthophagus gazella Fabricius,
for the purpose of improving the rate of dung removal from pastures
and to reduce populations of dung-breeding flies (Fincher 1981). Prior to its
introduction, an Environment Impact Statement or Environmental Assessment
(CEQ 1978) was not then required. Thus, the potential impact of these
introductions on the native dung arthropod community was not publicly
examined or discussed. The apparent assumption at the time was that there
were many vacant niches for introduced dung beetles to fill.
Field studies conducted after the initial introductions have indicated
the overwhelming success of O. gazella in establishment, range expansion,
and cow dung removal (Fincher et al. 1983, 1986). Onthophagus
gazella has become such a major component of the nocturnal cow dung
arthropod community that it is the candidate of choice when various
*United States Department of Agriculture,Agricultural Research Service, Southern
Grain Insects Research Laboratory, PO Box 748, Tifton, GA 31793. Current address
- 9496 Good Lion Road, Columbia, MD 21045; firstname.lastname@example.org.
492 Southeastern Naturalist Vol. 6, No. 3
control strategies for dung flies and parasitic nematodes are evaluated
(e.g., Fincher 1991, 1996).
Ateuchus histeroides Weber and Copris minutus (Drury) are two nocturnal
scarabs also occurring on cow dung in the southern United States
(Matthews 1961, Kohlman 1984). These two species and O. gazella cooccur
nocturnally in cow pastures and adjacent habitats in Tift County,
GA, one of the original O. gazella introduction sites (Fincher et al. 1983).
Although the nocturnal dung beetle community in the area probably exceeds
18 species of scarabs in at least 10 genera (Fincher et al 1969,
1970, 1971), these three species were the most common in light traps.
The purpose of the following collections, observations, and experiments
is to examine the relationships between these three species, emphasizing
their respective dung-removal capabilities and the resultant future prospects
for each species.
Materials and Methods
Procurement of live adult specimens and documentation of seasonal
occurrence of each of the three species was accomplished by the use of a
black-light trap during 1982 and 1983. This light trap was located 5 km SW
of Tifton, Tift County, GA, in a large residential yard immediately adjacent
to a garden, pine woods, and old fields, with a cow pasture about 1 km
distant. The light trap, with a 15-w flourescent black-light, was set once each
month, approximately mid-month, and operated for two consecutive nights
and the intervening day, during periods when rain was not predicted (and
which actually did not occur). Specimens were brought into the laboratory
and placed in large holding containers, refrigerated at 8 ºC for several hours
to slow movement, then sorted, counted, and finally sexed and aged if
possible. Beetles were then either released back in the light-trap area during
the July 1982–June 1983 period or maintained in holding containers for
Processing of dung
Cow dung was obtained from a Tifton pasture within 2 hours of deposition
and refrigerated in 500-cc sealed containers until needed. On the day of
each experiment, one container of cow dung was allowed to warm to room
temperature and then a portion was placed in a 50-cc graduated cylinder to
the top mark. A wooden dowel slightly smaller than the inside diameter of
the cylinder was used to compress the dung. Fluid was poured off, and the
process repeated until no fluids remained and the amount of dung remaining
was recorded. This procedure was repeated at the start of each experiment to
characterize the wet volume-compressed volume relationship of the dung
used for that experiment. This data would subsequently be employed at the
termination of the experiment.
2007 O.P. Young 493
The protocol for each dung-removal experiment involved the placing of
5 pairs of beetles of each of the three species in separate containers with a
specific volume of thawed and unpressed cow dung. The amount of dung
“removed” by the beetle pair was determined after 24 or 48 hours. Removal
was defined as the consumption or burial of dung; any dung which
remained on the soil surface, even if it had been dispersed by beetles, thus
was not removed. The experimental containers were metal cans (13 x 13
cm) with a fine mesh lid, filled with moistened soil packed to a depth of 10
cm. These were maintained at room conditions (ca. 22 ºC, 75% RH) and
local photoperiod. The various volumes of cow dung used in the experiments
were obtained by using a set of “cookie cutters,” fabricated with
aluminum strips to yield the required volumes of 5, 10, 20, and 40 cc. For
example, to obtain the 5-cc volume, the cutter required a circular strip 2.5
cm in diameter and 0.7 cm high, placed on a flat surface, and filled to the
top with dung. Beetles were maintained without food for the 48 hrs prior to
the start of each experiment, removed from the holding containers to the
experimental containers at 1700–1800 hrs, and offered a specific amount
of food at dusk, 1930–2030 h. After 24 or 48 hrs, beetles were transferred
back to the holding containers and the experimental container was assessed
for the amount of dung removed.
At the termination of each experiment, if there was no dung remaining
on the soil surface, then the degree of dung removal was 100%. If some
dung was remaining on the surface, an additional procedure was required.
The remaining surface dung was removed to a container, submerged in
water for 24 or 48 hrs, removed to a graduated cylinder, and compressed.
The resultant dung volume was then compared with the compressed volume
of the dung initially offered to the beetles. For example, at the
beginning of an experiment, a 50-cc volume of cow dung may have compressed
to 10 cc. If 10 cc of that uncompressed dung was offered to a group
of beetles, then 2 cc of that amount was compressed dung and the remained
8 cc was fluid. If dung collected on the soil surface at the termination of the
experiment was soaked and then compressed to 1 cc, then one-half of the
initial compressed material was buried and/or eaten by the beetles. Extrapolating
to the uncompressed volume, approximately 5 cc of the 10 cc
offered was removed by the beetles.
The volume of dung offered to the various beetles was calculated to be a
specific multiple of the combined volumes of the beetles in each container.
This technique was designed to relate the size (volume) of a beetle to the
amount of dung that it could remove. The values used for calculation of the
average length of each species are: C. minutus, 8–12.5 mm (Matthews
1961); A. histeroides, 6–7 mm (Ritcher 1966); and O. gazella, 6–11.5 mm
(Balthasar 1963). Values for the width and depth of the species are typically
not included in species descriptions, so approximate values were used. The
average values used for calculation of the volumes for each species are: C.
494 Southeastern Naturalist Vol. 6, No. 3
minutus, 10 mm L x 4 mm W x 3.5 mm D; A. histeroides , 6.5 x 4.5 x 3; and
O. gazella, 9 x 5 x 4. Computing the approximate volume of an individual
beetle (LxWxD) would be, for example C. minutus: 10 mm x 4 mm x 3.5 mm
= 0.010 m x 0.004 m x 0.003.5 m = 0.00000014 m3 = 0.14 cc (1 cc = 1 cm3 =
0.000001 m3). Volume values for the other species are: A. histeroides , 0.09
cc; and O. gazella, 0.18 cc. The 10 beetles in each experimental container
would thus have an approximate volume of 10 x volume in cc per individual
(e.g., C. minutus = 10 x 0.14 cc = 1.4 cc). If one individual of C. minutus
could remove the equivalent of its own volume in dung, then 10 individuals
should be able to remove 1.4 cc of dung. The smallest practical volume of
dung that could be utilized under the described experimental conditions was
5 cc, which represents about four times the volume of beetles (example C.
minutus) placed in each container. The four different volumes of dung used
in these experiments were 5, 10, 20, 40 cc, representing respectively about 4,
8, 16, and 32 times the volume of the group of C. minutus exposed to those
amounts of dung. The success of the three beetle species in removing dung
was expressed in several ways: as the amount and percent of dung removed
by each species, and as the relation between beetle volume and volume of
The ability of each species of beetle to remove dung was determined by
testing with four different volumes of dung. To accomplish this evaluation,
a group of 50 beetles of each species (5 male and 5 female per container
with soil, 5 containers) was first exposed to 5 cc of dung for 48 hrs, then
removed and held for 48 hrs without food, then exposed to 10 cc of dung
for 48 hrs, and so on for 20 cc and 40 cc of dung. The use of the same
beetles for each of the four tests was due to the limited availability of C.
minutus and A. histeroides. Copris minutus was tested by this procedure in
March, A. histeroides in May. An ample supply of O. gazella allowed for
the testing in July of two groups of 50 beetles, one terminated at 24 hrs and
one terminated at 48 hrs.
Non-dung feeding experiment
A single experiment was conducted in June 1982 to determine the ability
of O. gazella to survive on a non-dung diet, as identical experiments had
already been conducted with C. minutus and A. histeroides (Young 2005, in
press). A male and female pair of O. gazella was placed in a cylindrical glass
container (7 cm diam x 12 cm deep) with a fine mesh cover, packed with soil
to a depth of 8 cm, and maintained at laboratory conditions without food for
48 hrs. Fourteen additional replicates were prepared at the same time, and
after 48 hrs the 15 containers were separated into three sets of five each. One
set received 10 cc of thawed cow dung in each container, one set received
one coddled (killed in water at 90 ºC) Spodoptera frugiperda (J.E. Smith)
Lepidoptera: Noctuidae (fall armyworm; FAW) larva (5th instar, 30 mm) in
each container, and one set received no food. Containers were examined
every 3–5 days, with water mist and designated food added. The experiment
was terminated ten days after all beetles in the FAW set had died.
2007 O.P. Young 495
During 1982, all three species of beetles were exposed together to the
same potential food source on six occasions during the period April to
June. Two pairs of each species (12 beetles total) were denied food for 48
hrs, then released at 1200 hrs into a container (26 cm H x 40 cm L x 21 cm
W) with a fine mesh lid and packed with moistened soil from the light-trap
area to a depth of 14 cm. At 1600 hrs, a volume of fresh cow dung (10 cc)
was placed in the center of the container on the soil surface. Activity in the
container was recorded at several intervals for the next 48 hrs, when
the experiment was terminated and the amount of dung that had been
removed was determined.
Results and Discussion
Although the light-trap captures listed in Table 1 represent only one
location, sampled only twice each month, it does represent the general
pattern of adult occurrence for each species as reported elsewhere. Woodruff
(1973), using extensive records from throughout Florida, lists C.
minutus as occurring primarily from October to March. Kohlmann
(1984), in redescribing A. histeroides, used museum material collected in
the field primarily from May to September. Light-trap captures of O.
gazella over two seasons in Texas show largest captures in June to September,
with the total capture period from April to November (Fincher et
al. 1986). In other areas of Tift County, GA not adjacent to cow pastures,
A. histeroides co-occurs primarily with native Onthophagus species at
carrion, dung, rotting fungi, and dead arthropods (Young 1984). The
light-trap data in Table 1 suggests that C. minutus and A. histeroides
minimize interactions by seasonal separation. These two species have a
long evolutionary history of co-occurrence in the forest-open ecotone
areas of eastern United States (Matthews 1961, Kohlmann and Halffter
1988). Whether through previous competitive interactions, environmental
Table 1. Captures of three species of dung beetles at a black light trap, Tift County, GA, 1982–83.
Month Copris minutus Ateuchus histeroides Onthophagus gazella
July 0 229 1149
August 0 71 405
September 0 14 220
October 4 0 17
November 2 0 0
December 14 0 0
January 40 0 0
February 21 0 0
March 10 15 0
April 0 57 17
May 0 82 61
June 0 80 109
Totals 91 437 1978
496 Southeastern Naturalist Vol. 6, No. 3
constraints, or historical contingencies, the two species at the present
time do not appear to be directly affecting each other. These two species
in Tift County, however, do not have a long history of interactions with
O. gazella. Tift County is one of the original sites in the United States
where O. gazella was first introduced in 1975, with subsequent established
populations by 1978 (Fincher et al. 1983). The light-trap data
indicate overwhelming numbers of O. gazella occurring at the same time
and place as much smaller numbers of A. histeroides, suggesting potentially
negative impacts on A. histeroides if the same numerical dominance
of O. gazella occurred at food sources. The large numbers of O. gazella
in these light-trap collections are similar to those found in other locations.
In Texas over an entire year in one open pasture, 11,709 O. gazella
were captured in baited pitfall traps along with 40,079 individuals of 20
other species (Fincher et al. 1986).
Tables 2, 3, and 4 show the amount of dung removed in each of the
dung-volume experiments after 48 hrs for C. minutus, A. histeroides, and
O. gazella, respectively. Tables 2 and 3 both indicate a plateau pattern
beginning at 10 cc, where little if any additional dung is removed when
greater than 10 cc of dung is available. Table 4 does not show this pattern,
instead showing nearly complete removal for all dung volumes. These
differences between the species suggest that two different phenomena are
occurring. For C. minutus and A. histeroides (Tables 2 and 3), the initial
requirements of the beetles seem to be relatively small, leading to the
Table 2. Amount of dung removed by Copris minutus ( 5 pair/container, 5 replicates /dung size,
48 hours post exposure).
Container 5 cc 10 cc 20 cc 40 cc
1 1.5 2.5 2.5 2.5
2 2.5 3.0 3.5 3.0
3 2.5 3.5 3.5 3.5
4 3.0 4.0 4.5 4.5
5 3.0 4.5 6.0 6.5
Mean 2.5 3.5 4.0 4.0
% 50 35 20 10
Table 3. Amount of dung removed by Ateuchus histeroides ( 5 pair/container, 5 replicates /dung
size, 48 hours post exposure).
Container 5 cc 10 cc 20 cc 40 cc
1 3.5 5.0 5.5 5.5
2 3.5 5.0 6.0 5.5
3 4.0 6.0 6.0 6.0
4 4.0 6.5 7.0 6.0
5 5.0 7.5 8.0 7.0
Mean 4.0 6.0 6.5 6.0
% 80 60 32.5 15
2007 O.P. Young 497
possibility that food is being removed only for individual maintenance
needs and not for brood development. For O. gazella (Table 4), the large
amounts of dung removed would seem to exceed the amounts required just
for individual maintenance and suggests that dung is also being removed
for future progeny. The results of the confrontation experiment described
below support this supposition.
Table 4 presents for O. gazella the results of the 24-hr and 48-hr experiments
for the four dung volumes. The virtually complete removal of dung by
the five pairs in the 5-cc and 10-cc dung volume containers, as compared to
the less-than-complete removal in the 20-cc containers suggests that a 24-hr
“satiation” point is somewhere between 10 and 20 cc for the five pairs of
beetles. An additional 24 hrs for possible food removal in the 20 and 40 cc
containers does not substantially increase the amount of dung removed,
further suggesting a “satiation” point. As described elsewhere (Halffter and
Matthews 1966), dung scarab beetles of this type typically remain buried for
at least 48 hrs after acquiring food for themselves and for egg-laying. In
these experiments, the dung removed in the 20 and 40 cc containers between
24 and 48 hrs was probably accomplished by those few beetles that had not
acquired sufficient material in the first 24 hrs. If the 20 and 40 cc experiments
had been extended to 72 and 96 hrs, a more complete removal of dung
would be expected, as the beetles initially successful at removing dung at 24
hrs re-emerged for a new round of dung removal.
Table 5, which expresses the food removal results as a percentage of the
total body volume of each set of beetles, further supports the supposition that
Table 5. Removal of dung by three beetle species after 48 hrs, expressed as percent of total
beetle volume. Total volume of the ten beetles used in each test: Copris minutus—1.4 cc,
Ateuchus histeroides—0.9, cc, and Onthophagus gazella—1.8 cc.
Copris minutus Ateuchus histeroides Onthophagus gazella
Volume Volume % of Volume % of Volume % of
of dung removed (cc) beetle removed (cc) beetle removed (cc) beetle
5 cc 2.5 179 3.0 333 5.0 278
10 cc 3.5 250 4.5 500 9.9 550
20 cc 4.0 286 5.5 611 18.0 1000
40 cc 4.0 286 6.0 667 33.4 1855
Table 4. Amount of dung removed by Onthophagus gazella (5 pair/container, 5 replicates/ dung
size); two independent experiments, one terminated at 24 hrs, one at 48 hrs post exposure.
5 cc 10 cc 20 cc 40 cc
Container 24 hrs 48 hrs 24 hrs 48 hrs 24 hrs 48 hrs 24 hrs 48 hrs
1 4.5 5.0 9.5 9.5 14.5 17.5 20.5 26.0
2 4.5 5.0 9.5 10 15.5 18.0 22.0 26.0
3 5.0 5.0 9.5 10 16.0 18.0 23.0 29.5
4 5.0 5.0 10 10 17.0 19.5 27.5 31.5
5 5.0 5.0 10 10 19.5 20 31.0 36.0
Mean 4.9 5.0 9.7 9.9 16.5 18 24.8 29.4
% 98 100 97 99 82.5 90 62 73.5
498 Southeastern Naturalist Vol. 6, No. 3
O. gazella is acquiring more than just food for individual maintenance. A
reasonable amount of dung obtained for personal maintenance only, excluding
that required for brood development, appears to be about two to seven
times body volume, particularly given that the dung volume is ca. 80%
water, as seen for C. minutus and A. histeroides. The O. gazella results,
however, suggest that when a small amount (5 or 10 cc) of dung is available,
maintenance needs are satisfied first (550% of body volume). When an
amount well in excess of probable maintenance needs is available (40 cc),
the very large amount of dung removed (1633% of body volume) strongly
suggests acquisition for non-maintenance (i.e., reproductive) purposes. The
experimental procedures employed herein unfortunately do not directly
separate the two categories of dung removal: that required for individual
maintenance and that required for egg laying. Such an analysis would
require additional experiments with known age and sex individuals in mated
and unmated condition.
These removal experiments have attempted to quantify what was apparent
from field observations in Tift County: that O. gazella was far superior to
the native dung beetle species in removing cattle dung from the soil surface.
Figure 1, displaying the percent of dung removed in the different dungvolume
experiments for all three species, summarizes the results of these
experiments and further emphasizes the superiority of O. gazella in food
removal efficiency. Such superiority is perhaps not unexpected, given that
O. gazella is a specialist on cow dung and the other two species are more
generalist, consuming a variety of dung types as well as carrion and rotting
fungi (Young 2005, in press).
It is appropriate to ask how the results reported herein compare with
published attempts to document dung-removal efficiency. Miller (1954), in
South Georgia field observations involving human dung, determined the
relative abundance of each dung beetle species and then estimated how
much dung the various members of the community would remove. Though
Ateuchus lecontei and Copris minutus were among the most common
“buriers” (as opposed to “rollers”), they removed less than 2% of the
human dung. Bornemissza (1970) reported that in the laboratory one pair
of O. gazella could completely bury 100 cc of cow dung in 48 hrs, which
led him to state that this species was probably the “most efficient”
paracoprid beetle known. Macqueen and Beirne (1975) in laboratory studies
with Onthophagus nuchicornis (L.), an introduced invasive in British
Columbia, showed that in five days, two beetle pairs could only remove
about 25% of a 200-g cow dung pad. Fincher et al. (1981) in Georgia fieldplot
studies placed 1600 dung beetles of 11 species (excluding O. gazella)
with 200–300 g of cow dung, and in four days, obtained 78% burial.
Fincher (1981), in Texas field studies, documented an 82–88% burial of
artificially-deposited 2500-g cowpats within one week during the peak
activity period of O. gazella. Houston et al. (1984) documented in Texas
field studies that 22 pairs of O. gazella could not completely bury 1000-g
2007 O.P. Young 499
horse dung pads in 31 days. Collectively, these studies were not particularly
helpful in addressing the issue of O. gazella impact on native dung
beetles or providing an appropriate methodology for assessing potential
impacts. Hence, the present study attempts to develop a reasonably simple
and non-technical laboratory procedure that would allow comparisons of
dung-removal efficiencies for various species.
Non-dung feeding experiment with O. gazella
The single-dung and non-dung feeding experiment with O. gazella
(Table 6) was terminated after 32 days, with all beetles in the FAW set dead
by day 22, and no FAW larvae buried or consumed. Seventy percent of the
beetles in the dung set were alive on day 32, with ample amounts of cow
dung buried. The 10 beetles offered FAW larvae apparently starved to death;
the males died on average in 11 days, the females in 18 days. These survival
periods were not significantly different from those obtained from the set of
beetles denied food. By contrast, both C. minutus and A. histeroides have
been successfully maintained in the laboratory on a diet of dead lepidopteran
Figure 1. The amount of cow dung removed by three scarab species in containers
supplied with one of four different volumes of dung.
500 Southeastern Naturalist Vol. 6, No. 3
larvae, and in previous experiments, consumed dead FAW larvae and survived
as long on this diet as on a diet of cow dung (Young 2005, in press).
The published literature suggests that O. gazella is a specialist on cow dung
(i.e., Bornemissza 1970, Blume et al. 1974), and the preliminary experiment
described herein does not suggest otherwise.
The six trials conducted during April–June with all three species together
in the same container are typified by the description of the trial conducted on
15 May. The immediate action of the three species when placed together in
the container at 1200 hrs was to bury themselves in the soil. The placement
of cow dung in the container at 1600 hrs elicited no immediate response.
Local sunset was at about 1900 hrs, and beginning at 2030 hrs, beetles began
to appear, with all 12 present on the soil surface by 2130 hrs. At that time,
the four O. gazella were very rapidly walking over and around the dung pad
and the other eight beetles were more slowly walking in other parts of the
container. At 2330 hrs, all four O. gazella were below the soil surface and
most of the dung pad was buried. Small pieces of dung were scattered about
the soil surface, with three A. histeroides and one C. minutus in attendance,
and the other members of the two species below the soil surface. At 0700 hrs
the next day, all beetles were buried and no obvious dung was on the soil
surface. When viewed at 2300 hrs that night, all eight of the A. histeroides
and C. minutus were on the soil surface, but only one of O. gazella was
visible. The experiment was terminated the next morning and the soil excavated,
revealing two main O. gazella tunnels with several cow-dung brood
balls in side tunnels. Production of brood balls by O. gazella in only 14 cm
of soil is noteworthy, as previous studies indicate a preferred depth of 20–25
cm in moist sandy soil for brood-ball formation (Tyndale-Biscoe 1990).
Other tunnels were found with A. histeroides and C. minutus as occupants,
but no obvious cow dung was detected in those tunnels. It would appear that
the two pair of O. gazella obtained most of the cow dung, converting some
into brood balls for their progeny and probably consuming some. The other
two species may have consumed some dung, but did not acquire enough to
prepare brood material. The amount of dung placed in the container (10 cc)
Table 6. Survival period (days) of Onthophagus gazella in three feeding regimes, 1 pr/container,
5 replicates, terminated after 32 days.
No food Cow dung FAW larvae
Container Male Female Male Female Male Female
1 6 16 30 > 32 8 13
2 7 19 30 > 32 10 16
3 9 19 32 > 32 12 18
4 11 23 > 32 > 32 12 21
5 12 26 > 32 > 32 14 22
Mean 9 20.6 > 32 > 32 11.2 18
Combined mean 14.8 > 32 14.6
2007 O.P. Young 501
was chosen based on the concurrent experiment on dung removal (Table 4),
which indicated that five pairs of O. gazella alone could easily bury and/or
consume 10 cc of cow dung in 24 hrs, and do almost the same with 20 cc of
dung. The experiment thus was designed to see if individuals of C. minutus
and/or A. histeroides could outcompete O. gazella for that specific amount
of dung. They apparently could not. One obvious difference between the
species in this experiment was their rate of movement. It has been noted that
O. gazella pairs “work extremely rapidly” in removing cow dung from the
soil surface (Bornemissza 1970), and their movement in this experiment was
obviously faster than the other two species. Direct physical contact between
the species, such as fighting over a piece of dung, was not observed, suggesting
that C. minutus and A. histeroides, though equal in numbers to O.
gazella, were not sufficiently aggressive to contest O. gazella for a portion
of the cow dung.
The information presented in the food-removal experiments and the
confrontation experiment leads to the question: How do C. minutus and
A. histeroides survive in the face of apparently overwhelming numbers
and behavioral dominance of O. gazella when they co-occur at the same
site? The answer probably involves spatial and temporal separation and
the degree of food specialization. Copris minutus appears to be temporally
separated seasonally from both A. histeroides and the new invasive,
O. gazella, and thus probably is least affected by the presence of O.
gazella. Other Copris species in the area that occur as adults in the summer,
such as Copris fricator (Fabricius), have geographic and seasonal
overlap with O. gazella, but may possess habitat differences that reduce
the likelihood of competitive interactions (Matthews 1961). Ateuchus
histeroides, and its close congener A. lecontei (Harold) further to the
south, appear to be in direct competition with O. gazella, both temporally
and spatially. As indicated here, interactions with O. gazella may have a
negative impact on A. histeroides. Those impacts may be minimized by A.
histeroides utilizing a broader range of food items (Young, in press) and
a broader range of habitats (Kohlman 1984). As long as O. gazella remains
a cow-dung specialist active in open pastures, and A. histeroides
continues as a dung generalist active in wooded and ecotonal areas, there
should be minimal impacts. Those nocturnal scarab species occurring at
cow dung that may be most threatened by O. gazella are much larger,
such as Dichotomius carolinus (L.) (20–30 mm), Canthon vigilans
LeConte (16–22 mm), and Copris fricator (11–19 mm). These species
typically occur at a cow pad in low numbers (< 5; O.P. Young, pers.
observ.) and if outnumbered by the hundreds by O. gazella, might have
considerable difficulty obtaining food. Several co-occurring nocturnal
species of Onthophagus may also be threatened by the loss of available
food, but fortunately these species are all generalists and might have
minimal contact with O. gazella by utilizing food other than cow dung.
502 Southeastern Naturalist Vol. 6, No. 3
Even diurnal species could be affected by high population densities of the
nocturnal O. gazella, given the amount of dung this species can utilize
and the speed at which it can be removed.
The data and analysis presented herein does not fully answer the question
of possible interactions between C. minutus, A. histeroides, and O.
gazella. Additional information that would be necessary to complete that
analysis includes: (1) documentation of field co-occurrence of species pairs
and the trio, as determined by light traps and baited pitfall traps in several
different habitats; (2) more fine-grained examination of that co-occurrence,
particularly the timing of activity within the diel period; (3) elaboration of
the food requirements for each species, to include detailing consumption
and survival on a variety of potential food items, and documenting the
different food requirements for reproduction (food provisioned for larvae)
and for individual maintenance; and (4) observations of direct confrontations
between the species at a variety of potential food types and in various
density combinations, both in the field and in more controlled situations in
the lab. It should also be noted that the observations and experiments
reported herein were conducted 25 years ago, seven years after O. gazella
first appeared in the area. They are reported at this time because the impact
of introduced/invasive species on communities is a current topic of international
importance. The baseline of data provided by Fincher and colleagues,
plus this contribution, provide an excellent starting point for an analysis of
the long-term impact of an introduced/invasive species on an insect community
of significant economic importance. Thus, the status of O. gazella
and the dung beetle community in south Georgia in 2007 could be a valuable
contribution to the topic.
The field assistance of W. Wolfe and the laboratory assistance of C. Sharp, H.
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