Behavioral Ecology Vol. 11 No. 5: 486-494
© 2000 International Society for Behavioral Ecology
Ventilation of termite mounds: new results require a new model
Theodor Boveri Institut, Lehrstuhl für Tierökologie und Tropenbiologie, Am Hubland, 97074 Würzburg, Germany
Address correspondence to J. Korb at CSIRO, Entomology, GPO Box 1700, Canberra ACT 2601, Australia. E-mail: judith.korb{at}ento.csiro.au .
Received 30 May 1999; revised 28 August 1999; accepted 17 November 1999.
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ABSTRACT |
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In 1955, Lüscher proposed a ventilation mechanism for cathedral-shaped termite mounds to exchange respiratory gases. This mechanism was generally accepted, although it had never been tested critically. We tested this mechanism by investigating temperatures, CO2 concentrations, and air currents in and around two types of Macrotermes bellicosus mounds: cathedral-shaped mounds with many ridges and thin walls located in the savanna and dome-shaped mounds without ridges and with thick walls in the forest. These two mound shapes have two different mechanisms of ventilation, depending on the environmental temperature. In the savanna during the day, sun heats the air in the peripheral air channels inside the ridges of the mound above the central nest temperatures and produces a temperature gradient in the peripheral air channels with decreased temperatures at the top of the mound. This temperature gradient leads to convection currents with air rising inside the air channels of the ridges to the top of the mound, meanwhile exchanging CO2. In contrast, in the savanna during the night and generally in the forest, the temperatures inside the air channels are lower than those of the central nest, and no air currents rising upward inside the air channels were detected. The CO2 concentrations in the air channels of savanna mounds at night and forest mounds in general were higher than during the day in the savanna. Therefore, our data do not support Lüscher's proposed mechanism.
Key words: carbon dioxide, gas exchange, Ivory Coast, Macrotermes bellicosus, metabolism, termite mounds, thermoregulation.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Animals inhabiting natural cavities or self-constructed housings such as burrows often have problems ventilating these habitations to ensure sufficient gas exchange. In general, the ventilation systems are passive, driven by temperature or velocity gradients in air currents (Vogel, 1978
;
Vogel and Bretz, 1972;
Wenzel, 1990). Some species of
the fungus-cultivating termites, Macrotermitinae, construct elaborate mounds,
in which the colonies generate their own appropriate microclimate to a
considerable extent (e.g., Korb and
Linsenmair, 1998;
Lüscher,
1961; Ruelle,
1964). Although the problem of ventilating these mounds has long
been recognized (e.g.,
Grassé and
Noirot, 1958; Lüscher,
1955,
1956), and mound architecture
has often been interpreted as furthering ventilation (e.g.,
Bagine et al., 1989;
Collins, 1979;
Darlington, 1989), profound
investigations for closed mounds have been lacking.
Two general ventilation types can be distinguished according to mound
structure (Noirot, 1990): (1)
open ventilation systems in which the walls of the mounds have holes through
which air can stream in and out due to differences in wind velocity at
different mound heights (Darlington,
1984,
1997;
Geiger, 1965) or due to the
shape of the holes (Darlington,
1984; Weir, 1973)
or (2) closed ventilation systems in which the mounds have no holes and the
surface (wall) of the mounds is the exchange area between interior and
exterior of the mounds (Darlington,
1985,
1989).
In this study we examined the closed ventilation mechanism of two different
types of Macrotermes bellicosus (Smeathman) mounds in two different
habitats of the Comoé-National Park (CNP),
Ivory Coast (see also Korb and Linsenmair,
1998,
1999a,
b). In the savanna, mounds are
highly structured with many ridges (classified according to
Grassé and
Noirot, 1961, as nids en
cathédrale). The interior of these mounds
consists of a central, spherical nest, containing a central nursery region
with the royal cell, and surrounding fungus combs (i.e., the fungus garden).
This spherical nest is surrounded by a cavity, which at the apex of the nest
opens into a central shaft that extends to the top of the mound. Other air
channels rise at lower levels around the nest and run inside ridges of the
mound, directly below the mound surface (for further description, see
Korb, 1997:
Figure 4a,b). In contrast,
mounds in the gallery forest are dome shaped (classified according to
Grassé and
Noirot, 1961, as nids en
dôme). Similar to cathedral-shaped mounds,
these mounds consist of a central nest with a central shaft, but unlike the
former, the nest is surrounded by thick walls without ridges and without air
channels rising upward. Only occasionally do some small shafts rise up as
turrets beside the central shaft (see
Korb, 1997: Figure 4c,d).
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Lüscher
(1955) suggested the following
ventilation mechanism for closed, cathedral-shaped mounds such as those found
in the savanna. In M. bellicosus mounds, the central nest has a high
air humidity near saturation and a constant temperature of about 30°C
generated through the metabolism of the termites and fungi
(Korb, 1997;
Lüscher,
1961). Thus, Lüscher postulated that
air rises from the central nest inside the central shaft to the top of the
mound driven by convection currents. As temperatures in the peripheral air
channels of the ridges should be below those in the central shaft, air should
flow from the top of the mound into the air channels of the ridges. There,
descending air should exchange the respiratory gases through the thin mound
walls, before entering the nest again. Thus, the ridges are assumed to
function as the "lungs" of the mound.
In our study we wanted to empirically test
Lüscher's
(1955) hypothetical mechanism
for both mound types in the CNP because some temperature measurements
suggested that Lüscher's mechanism might not
apply to the cathedral-shaped savanna mounds
(Korb, 1997). Therefore, we
investigated the temporal and spatial distribution of temperatures and
CO2 concentrations in and around M. bellicosus mounds in
the savanna and the gallery forest to deduce their ventilation mechanisms. In
addition, the presence and absence of air currents was registered.
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METHODS |
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Study area
This study was done in Comoé-National Park (8°45' N, 3°49' W; elevation about 250 m, Ivory Coast; for more details, see FGU-Kronberg Bericht, 1979
; Poilecot,
1991). The study site was located within the Guinea savanna and
consisted of a mosaic of pathces of open to dense shrub savanna and gallery
forests along the main rivers. The area is characterized by marked dry and
rainy seasons of unpredictable lengths. Typically, the rainy season lasts from
April to October, peaking in August and September, with a relatively dry
period in June and July (total annual rainfall between 1992 and 1997: 700-1170
mm; Korb J, unpublished data).
CO2 concentrations and temperatures
During the transition from the dry to the rainy season in 1997, we examined
six cathedral-shaped mounds in the savanna and six dome-shaped mounds in the
gallery forest that were higher than 3.0 m. For each mound, we registered the
CO2 concentrations every 4 h for 24 h (starting at 0600 and ending
at 0200 h). At each sampling time, we took measurements at the four cardinal
compass directions at heights of 0.5 m, 1.0 m, 1.5 m, 2.0 m, and at top of the
mound, for cathedral-shaped mounds in the peripheral air channels of the
ridges, and for dome-shaped mounds in small channels inside the walls or air
channels inside the turrets. To perform each measurement, we drilled a small
hole into the mound wall, placed a tube from the gas analyzer into it, and
sealed the hole tightly with a piece of plastic film. The air from the air
channel was pumped at a constant flow rate of 1 ml/s to a nondifferential
infrared gas analyzer (BINOS 100.1 modified for field work by adaptation to 12
V and integrated installation of a filter against fine dust; Fisher Rosemount,
Hanau, Germany). Additional filters were installed to remove dust and
H2O (for further description, see
Korb and Linsenmair, 1999a).
After we removed the tube from the mound wall, the termites immediately closed
the hole. We could not determine concentrations in the center of the nest
because it was not possible to obtain gas samples from this region without
damaging the mounds considerably.
During all CO2 measurements, we continuously recorded the
temperatures (1) within the fungus combs, (2) within the air channels of the
mounds (height: 0.5 m; direction: north), and (3) of the air about 1 cm above
the mound surface (height: 0.5 m; direction: north) using thermistors
connected to a data logger (Squirrel 1200, Grant Instruments, Cambridge, UK;
measuring interval: 15 min; for further description, see
Korb and Linsenmair, 1998). In
addition, we determined the surface temperatures of the mounds at each
CO2-measuring point with an infrared thermometer (Cyclops S330;
Minolta, Germany) when measuring CO2 concentrations. Temperatures
at the mound surface are an indicator for the temperatures inside the air
channels (Korb J, unpublished data).
Air currents
To determine whether air actually circulated inside the mound with an easy
available and relatively nondestructive method, we carefully removed the tops
of ridges (cathedralshaped mounds) and turrets (dome-shaped mounds) of the
mounds and immediately closed the exposed part with clear plastic film. Water
should condense on the plastic sheet if air circulates because the air inside
the nest has a high humidity near saturation
(Korb, 1997), and so a
temperature drop or a pressure gain (e.g., due to circulation of air) at the
sheet should lead to condensation (compare to phase diagram; e.g.,
Atkins, 1993). We carried out
this procedure immediately after CO2 measurements at 1400 h and
2200 h (see above) in all four cardinal directions of a mound if ridges or
turrets were available (savanna: n = 24 at 1400 h and n = 24
at 2200 h; gallery forest: n = 19 at 1400 h and n = 19 at
2200 h).
Statistical analysis
The CO2 and temperature data were not normally distributed, so
we analyzed them using nonparametrical statistics. We used Bonferroni
corrections if the same data were analyzed repeatedly.
We examined the spatial distribution pattern of surface temperature and CO2 concentrations, respectively, with Wilcoxon paired rank tests by comparing the temperatures and CO2 concentrations at two different heights (of one direction) for each direction of each mound at each measuring time. Thus the sample size for each habitat was four directions (for the top of the mound one direction) multiplied by six mounds and six (three) sampling times.
We investigated the influence of temperature gradients between different mound heights on CO2 concentrations. First, we ranked the directions of each mound according to their temperature gradients for each sampling time. Then, we compared the CO2 concentrations between these ridges with different degrees of temperature gradients for each mound and sampling time with Friedmann two-way ANOVA. Thus, the sample size was six mounds multiplied by six (three) sampling times. Sample sizes were restricted at times due to a lack of ridges and turrets (especially in the forest mounds) in the corresponding directions and heights of a mound.
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RESULTS |
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Temporal course of CO2 concentrations and temperature conditions
In cathedral-shaped mounds of the shrub savanna (Figure 1), the concentrations of CO2 in the air channels declined during the day and increased during the night. Whereas during the night all sides of the mounds contained about the same concentrations of CO2, during the day the CO2 concentrations differed in different directions and shifted between air channels in a predictable manner consistent with the position of the sun. The air in the western side of the cathedral-shaped mounds had the most reduced CO2 concentrations in the mid-morning, all sides were reduced to their minimum concentrations in the mid-afternoon, and the eastern sides were lowest in the evening. During the night, the highest CO2 concentrations were measured inside the top of the mound, but during the day these declined compared with the other sampling heights; the lowest values were recorded at 1400 h.
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In the gallery forest (Figure 2) during the day and the night, the air from all sides of the dome-shaped mounds had similar and high concentrations of CO2. Thus, the distribution of CO2 concentrations inside the air channels resembled that of cathedral-shaped mounds during the night, although the absolute concentrations were much higher (0.25% versus 1.20%). During the day the CO2 concentrations declined a little (20%), but not so conspicuously as in savanna mounds (60%), and simultaneously on all sides. As found for cathedral-shaped mounds, the top of the mound had the highest CO2 concentrations during night and the lowest during the day when compared with the other sampling heights.
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Temporal temperature distribution patterns in and around the mounds corresponded with CO2 distribution patterns inside the mounds (Figure 3). Two phases can be distinguished: (1) When ambient air temperatures were higher than air channel temperatures and the latter higher than nest temperatures (1000-1800 h; Figure 3a), CO2 concentrations declined in cathedral-shaped mounds (Figure 1). (2) When the air channel temperatures were lower than the nest temperatures (1800-1000 h in cathedral-shaped mounds and 24 h per day in dome-shaped mounds; Figure 3a,b), CO2 concentrations were high in all sides of the mound (Figures 1 and 2).
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Air currents
Corresponding to these two phases, we detected humid air rising in the air
channels (by condensation of water on the lower side of the plastic film) only
when the temperatures in the air channels were higher than the nest
temperatures. (Condensation of water on the plastic film must be caused by a
pressure gain at the film, due to rising humid air, and could not be the
result of a temperature drop because the ambient air temperatures were higher
than the temperatures in the air channels during this time.) Air currents were
found only in the savanna. There were 14 films with condensation and 10
without when air channel temperatures were higher than those in the nest,
whereas there were zero films with condensation and 24 without when the
reverse was true for the savanna mounds. In the gallery forest, the air
channel temperatures were always lower than the nest temperatures, and no
films were ever wet (n = 38). Furthermore, air channels with air
currents (detected as above) had significantly higher concentrations of
CO2 when compared with air channels without air currents of the
same mound (Wilcoxon paired-rank test: n = 6; Z = -1.99,
p =.046).
This accordance in time between the two phases and the detectability of air currents suggested that (1) the uprise of air might be the result of increased air temperatures causing changed temperature gradients, and (2) CO2 was moved in these air currents. To test these hypotheses, we examined the temperature distribution pattern at different heights and sides of the mounds and their corresponding CO2 concentrations. The samples at 1000 h, 1400 h, and 1800 h were defined as day and at those at 2200 h, 0200 h, and 0600 h as night.
Spatial distribution pattern of temperatures along the mound
surface
In cathedral-shaped mounds during the day, temperatures at the mound
surface were significantly higher at a height of 2.0 m than at a height of
0.50 m, but not during the night (Wilcoxon paired-rank test: day: n =
72, Z = -2.08, p =.037; night: n = 68, Z =
-1.29, ns; Figure 4a). During
the day, temperatures at a height of 2.0 m were also significantly higher than
those at the top of the mound, whereas during the night the opposite was true
(Wilcoxon paired-rank test: day: n = 18, Z = -1.98,
p =.050; night: n = 17, Z = -3.57, p
<.001; Figure 4a).
In the gallery forest, during the day as well as during the night, temperatures at the mound surface did not differ between a height of 0.5 m and 2.0 m (Wilcoxon paired-rank test: day: n = 60, Z = -1.55, ns; night: n = 57, Z = -0.17, ns; Figure 4b). Temperatures at the mound's top were significantly higher than at a height of 2.0 m during the day and the night (Wilcoxon paired-rank test: day: n = 18, Z = -2.44, p =.015; night: n = 17; Z = -2.91; p =.004; Figure 4b).
Spatial distribution of CO2 inside the ridges of
mounds
CO2 concentrations in mounds were significantly lower at a
height of 2.0 m than at a height of 0.5 m for both habitats during the day,
whereas during the night CO2 concentrations were significantly
higher at a height of 2.0 m than at a height of 0.5 m in the savanna, and no
differences were found in the forest (Wilcoxon paired-rank test; savanna: day,
n = 72, Z = -5.76, p <.001; night, n =
68, Z = -2.97, p =.009; gallery: day, n = 60,
Z = -3.63, p <.001; night, n = 54, Z =
-2.43, ns; Figure 5a,b). In the
savanna during day and night, CO2 concentrations at the top of the
mound were significantly higher than at a height of 2.0 m, whereas in the
gallery forest they did not differ (Wilcoxon paired-rank test: savanna: day,
n = 18, Z = -2.81, p <.015; night, n =
17, Z = -3.22, p =.039; gallery: day, n = 17,
Z = -1.42, ns; night, n = 16, Z = -1.09, ns;
Figure 5a,b).
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CO2 concentrations in relation to temperature
gradients
In cathedral-shaped mounds during the day, ridges with the largest
temperature difference between the top of the mound and a height of 2.0 m
(i.e., where the top of the mound was relatively cooler than the surface at a
height of 2.0 m) had significantly higher CO2 concentrations than
ridges with a less pronounced temperature gradient (Friedmann two-way ANOVA;
rank 1 to rank 4: ridges with largest to smallest temperature gradient: day,
df = 3,18, 
2 = 12.52, p =.042;
Figure 6a). In contrast, in the
savanna during the night and in the gallery forest during day and night,
CO2 concentrations did not differ between ridges (Friedmann two-way
ANOVA; rank 1 to rank 4: ridges with largest to smallest temperature gradient:
savanna: night, df = 3,17, 2 = 1.76, ns; gallery: day, df =
3,18, 2 = 8.03, ns; night, df = 3,17, 2 =
2.19, ns; Figure 6a,b).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The aim of this study was to investigate the pattern of temperatures and CO2 concentrations in and at M. bellicosus mounds in time and space to deduce the ventilation mechanism of closed termite mounds and evaluate Lüscher's (1955
) hypothesis on their
ventilation. The detection of air currents rising upward inside the peripheral
air channels does not conform with Lüscher's
hypothesis, which suggests an uprise of air in the central shaft and
descending air inside the peripheral air channels. Instead, according to our
results (Figure 7), two types
of ventilation could be distinguished. They are the result of convection
currents and diffusion of CO2, both processes which depend on
temperature patterns.
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Externally driven ventilation: cathedral-shaped mounds in the savanna
during the day
In cathedral-shaped mounds during the day
(Figure 7a), the sun heats the
air inside the air channels via the mound surface with varying intensity in
different directions as the position of the sun changes during the course of
the day. This increase in temperature increases the diffusion rate of
CO2 (Atkins, 1993).
Surface temperatures became highest at a medium mound height probably due to
its greater exposure to solar radiation compared with the mound's tip and its
reduced mass compared with lower parts of the mound. As the temperature
differences increased between the cooler top of the mound and the warmer
surface at a medium mound height and between the cooler interior of the nest
and the heated air channels, convection currents became intensified inside the
air channels with highest CO2 diffusion rates at the medium mound
height. Warm air rises inside these peripheral air channels from a medium
mound height toward the cooler top of the mound. Greater convection currents
should occur inside ridges, with the most pronounced negative temperature
gradients pulling CO2-rich air from the nest into these ridges. As
the air rose upward inside the air channels, respiratory gases were partially
exchanged through the thin-walled ridges. As CO2 diffusion rates
increase with increasing temperature, CO2 concentrations in the air
channels were lowest at medium mound height. In ridges with less pronounced
negative temperature gradients, less intense convection currents probably
occurred which were not detectable with our method. These currents might drag
less air from the nest into the ridges and, due to lower velocity, air might
remain longer in the ridges, allowing a more effective exchange of respiratory
gases through the thin mound walls. Thus, these ridges had lower
CO2 concentrations than ridges with a more pronounced temperature
gradient. From the top of the mound air might descend inside the central shaft
to the nest because the temperature in the peripheral air channels is higher
than the nest temperature and lower than ambient temperature. This type of
ventilation can be called "externally driven ventilation" because
it is driven by temperature gradients generated by ambient temperatures via
local heating of the mound surface. It does not conform to
Lüscher's hypothesis.
Internally driven ventilation: cathedral-shaped mounds during the
night and forest mounds at all times
The second type of ventilation is more in accordance with
Lüscher's
(1955) hypothesis
(Figure 7b,d). It can be called
"internally driven ventilation" because it is driven by
temperature gradients generated by the metabolism of the termites and their
fungi (i.e., a thermosiphon).
In both habitats during the night, ambient temperatures were lower than the temperatures in the air channels, which were lower than the nest temperatures. Thus, humid air rich in CO2 might rise from the warm nest through the central shaft to the top of the mound and at the same time to the peripheral air channels driven by convection currents. There, respiratory gases might be exchanged. Water from the humid air of the nest might condense at the cooler mound walls. In addition, in cathedral-shaped mounds air might also descend from the top inside the peripheral air channels of all ridges, which is furthered by the higher temperatures at the top of the mound than at a medium mound height. (This is not possible in dome-shaped mounds because ridges are lacking; see below.) However, because air might also rise directly from the warmer nest to the cooler peripheral air channels, a circulation of air back to the nest (as suggested in Lüscher's hypothesis) seems unlikely, and air might instead be exchanged through the walls.
In contrast, mounds in the gallery forest during the day (Figure 7c) had higher ambient temperatures than the temperatures in the air channel which were—like during the night—lower than the nest temperatures. Thus, like during the night, air might rise from the nest to the top of the mound and to the air channels driven by convection currents. Water might condense at the mound walls and CO2 dissolve. However, during the day CO2 seems to be more effectively exchanged through the walls than during the night because the diffusion rates of CO2 increase with increasing temperature.
Although we have no systematic measurements of air currents at the top of the mounds, single observations confirmed that air rises up in the central shaft of mounds during the night in both habitats and during the day in forests. When the top of mounds were occasionally removed at these times in other experiments, a rise of warm air was observed (Korb J, personal observation).
General implications for ventilation of termite mounds
There are still many unanswered questions concerning the ventilation of
termite mounds, especially the importance of evaporation in relation to
convection currents as driving force. Nevertheless, our data clearly show that
the ventilation mechanism with air currents rising upward inside the central
shaft and downward inside the peripheral air channels of the ridges to enter
the nest again, as proposed by Lüscher
(1955), cannot be valid: In
externally driven ventilation, air currents rise upward inside the air
channels of the ridges and probably downward in the central shaft. In
internally driven ventilation air currents seem to rise upward inside the
central shaft. However, they probably do not circulate by descending inside
the peripheral air channels and entering the nest again either because
continuous peripheral air channels in ridges are lacking (as in the
dome-shaped mounds) or temperature gradients do not support it (as in the
cathedral-shaped mounds during the night).
Regarding ambient temperatures, the savanna of the CNP is an appropriate
habitat of M. bellicosus (Korb
and Linsenmair, 1999b) and typical for a savanna with
mound-building Macrotermitinae in general
(Korb, 1997). Thus, the
described externally driven ventilation ought to be the prevailing ventilation
mechanism for cathedral-shaped mounds. However, under cooler environmental
conditions, internally driven ventilation might occur, resulting in less
efficient gas exchange (see below). This might explain the higher
CO2 concentrations in Lüscher's study
(1961; 0.8-2.7%) than in this
study (<0.3 %). In dome-shaped mounds that are built by several species
(e.g., Darlington, 1985),
internally driven ventilation should always be common.
The externally driven ventilation seems to be more effective than the
internally driven ventilation, as CO2 concentrations were lower in
cathedral-shaped mounds in the savanna than in dome-shaped mounds in the
forest and within the cathedral-shaped mounds were lower during the day than
during the night. This is to be expected when considering (1) the available
surface for gas exchange, (2) the higher temperatures resulting in increased
diffusion rates, and (3) the circulation of air currents. During externally
driven ventilation, air circulates continuously from the nest through
peripheral air channels, and respiratory gases can be exchanged effectively
through the whole surface of the ridges. During internally driven ventilation,
air seems not to circulate within the mound, and, additionally, in the case of
the dome-shaped mounds the exchange area is almost exclusively limited to the
surface at the top of the mound. This limitation in gas exchange areas might
explain the occurrence of a large chimney (i.e., one tall central turret),
with the central shaft running inside, in the dome-shaped mounds of the
gallery forest (see Figure
7c,d). These mounds were closed, and thus the chimneys could not
serve to increase the gradient in wind velocity between the base and the top
of the mound that favors ventilation in open mounds (Darlington,
1984,
1997). However, in contrast to
the rest of the mound, the chimney had thin walls. Therefore, it might be the
main gas exchange structure and increases the available gas exchange area as
air can be exchanged when rising inside the central shaft to the top of the
mound.
In the CNP, the structure of the M. bellicosus mounds is an
adaptation to the environmental temperature constrained by the necessity of
gas exchange (Korb and Linsenmair,
1998,
1999a). In the relatively cold
gallery forest, the termites have to insulate their nests as much as possible
to reduce loss of heat (produced by the metabolism of the termites and their
fungi) to the environment and to maintain appropriate nest temperatures.
Therefore, they construct dome-shaped mounds with thick walls and reduced
surface areas (Korb and Linsenmair,
1998). However, this reduction in surface area is constrained by
the necessity for exchange of respiratory gases
(Korb and Linsenmair, 1999a).
In contrast, in the savanna the ambient temperatures are more appropriate and
the termites can construct cathedral-shaped mounds with large surfaces that
facilitate gas exchange (Korb and
Linsenmair, 1999a). Thus, ambient temperature influences the type
of ventilation directly by determing the temperature patterns in and around
the mound and indirectly by determining the mound structure.
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ACKNOWLEDGEMENTS |
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We thank Kouakou Kouadio Abdoulaye for assistance in the field, R. Leuthold, J. Darlington, and an anonymous referee for comments on the manuscript, and Q. Paynter and T. Evans for improving our English. D. Gutwerk provided valuable help when discussing the physical mechanisms of ventilation. Financial support was given by the German Academic Exchange Service (DAAD; D/931 15574), Volkswagen-Stiftung (Az I/64 102), and the University of Würzburg. The ministeries Eaux et Forêt and Recherche Scientifique de la Republique de Côte d'Ivoire gave permission for conducting research in Côte d'Ivoire (autorisation spéciale de recherche no.811; autorisation de recherche MRS/DPRF/AYK/j No 126/0).
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