Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Suzanne BP Holguin
5-15-03
Geog 810
Ants and Termites as Geomorphic Agents
According to J. Davis’ 312 Geomorphology class, geomorphology is the
“scientific study of the form of the earth’s surface, its landforms.” Davis also taught his
class that W. M. Davis described landforms to be the result of structure, process and time
(312 notes). Unfortunately, as David Butler (1995) notes, ‘structure, process and time’
are frequently presented as if they were “operative in a sterile, nonliving void.” Animals
are an obvious element of the earth’s landscape, yet animals and their impact are often
overlooked in geomorphic teachings.
Why have animals’ role in geomorphology been overlooked? According to
Butler (1995), many geomorphologists were trained in the earth and physical sciences,
rather than the biological sciences. This, Butler (1995) states, then translates into an
examination of how surface processes affect environmental and ecological systems rather
than how biological elements of the landscape affect systems and act as geomorphic
agents. Therefore, it is within the inter-disciplinary education of Geography that Butler
finds geomorphologists trained in, and more attentive to, scientific literature in the
biological sciences(1995).
David Butler’s frustration with Geomorphology, and the reluctance in the field to
acknowledge the fundamental role of animals as geomorphic agents of erosion,
transportation and deposition, led him to coin the new term, and field of study,
‘zoogeomorphology’ to specifically examine the role of animals as geomorphic agents
(1992, 1995). In Butler’s influential 1995 book Zoogeomorphology: animals as
geomorphic agents he presents an overview of how different animals alter their
environments over time. By using the term ‘animal,’Butler includes both endothermic
and ectothermic vertebrates as well as invertebrates, and places his emphasis on free-
ranging natural populations of animals, acknowledging “as natural as possible in such a
human-impacted world” (1995). According to Butler (1995), zoogeomorphic effects
specifically involve the movement of rock, soil or unconsolidated sediments from one
location to another, regardless of the size or range of movement. While we can imagine
the zoogeomorphic effects of a digging grizzly bear or a dam-modifying beaver, it may
be more difficult to visualize the impact of terrestrial invertebrates.
Most species of ants and termites are exceptional examples of zoogeomorphic
agents because they are eusocial insects. One of the evolutionary significant aspects of
ant and termite colonies is their internal organization, and their ability to differentiate
members into different castes. All of the more than 10,000 ant species and 2,200 termite
species are eusocial insects, meaning they have the following traits in common: 1.
cooperation in caring for the young; 2. reproductive division of labor; and 3. overlap of at
least two generations capable of contributing to colony labor (Oster and Wilson 1978). It
is quite interesting to note that 12 of the 13 known groups of insects that independently
evolved eusociality belong to the single order Hymenoptera (ants, bees and wasps) with
the thirteenth being the Isoptera (termites) (Oster and Wilson 1978). The requirement of
an overlap of at least two generations capable of contributing to colony labor, in
combination with reproductive division of labor and cooperative caring, translates into
the potential for huge colonies with thousands of workers capable of maintaining their
nests for decades.
Eusocial insects in general, and ants and termites specifically, have a significant
impact on the micro-geomorphology of their surroundings. Ants and termites construct
extensive and often massive nest systems in response to their need for food,
environmental control and social homeostasis (Wood and Sands 1978). As a result, they
can have a significant effect on the redistribution of soil particles, on physical and
chemical properties of the soil and consequently on vegetation (Wood and Sands 1978).
To summarize, termites and ants can contribute to soil erosion and denudation in 3 major
ways: 1. by removing the plant cover; 2. by digesting or removing organic material that
would otherwise be incorporated into the soil and enhance soil stability; and 3. by
bringing to the surface fine-grained material for subsequent wash and creep action (found
verbatim by multiple authors, each citing different authors as the originator, Butler 1995,
Mitchell 1988, Goudie 1995, Lee and Wood 1971). How do termites and ants alter their
surroundings?
Figure 1. Active termite nest and fresh aggregates from the subsoil. Source: Jungerius et al. 1999
To give an overview for both ant and termite nests, I have referred to J. Petal’s
1978 article entitled “The role of ants in ecosystems” and Wood and Sands 1978 article
entitled “The role of termites in ecosystems” both found within Production ecology of
termites and ants (ed. M. V. Brian). The construction of ant nests with above ground
mounds and systems of underground chambers and galleries modifies the physical and
chemical properties of both soil used for construction and the adjacent soils. Ant nests
are composed of a central site where the queen lives with a peripheral set of galleries and
chambers occupied by the workers, together forming an initially small nest capable of
being built into a complex network. Ant nests are constructed from the most readily
available materials. Hence, in rocky environments, nests are made of mineral materials,
while in forests, they consist mainly of woody materials. Just as with termites, ants use
their salivary secretions as a cementing agent to hold the materials together. Smaller
particles are raised from the deeper soil layers to the surface, while organic material is
moved further down. Chemically, while the pH of ants nests depend on the soil type,
even in almost neutral soils there is a slight increase or decrease in pH within the ant nest.
The geomorphic significance of ants rests in their aeration of the soil and the subsequent
creation of soils that allow rapid drainage and throughflow (Butler 1995).
Similar to ants, termite nests consist of one or more breeding centers from which
radiate a network of galleries to transport food, water, soil and as well as other
homeostatic tasks. Termite nests may be arboreal, epigeal (mounds) or subterranean.
The construction of the nests results in transport of soil either from deep or shallow
horizons to the soil surface, suggesting that modification of soils alter the soil profile,
texture, organic matter and nutrients. The nests are constructed from soil in combination
with excreta and saliva for their cementing qualities. Just as with ants, termites create
their nests using the materials found in their environment. Soil characteristics are an
important control of mound formation, and accordingly, much can be said about the earth
where termites are not found. Specifically, mounds tends to be rare on sands due to
insufficient binding material; on deeply cracking vertisols which are unstable; and on
shallow soils where there is a shortage of building material (Goudie 1996).
Wood and Sands note from their research that the sub-surface termite galleries
can be “so numerous as to collapse under-foot, leaving deep imprints” in the tropics
(1978). To begin to understand the magnitude of termite nests, a Kenyan mound revealed
the presence of 6 km of passage and 72,000 storage pits in an area of just 8,000 square
meters (Goudie 1996). Goudie revealed that termite mounds found in the Ivory Coast
reached a height of 1m between 2-3 years after their first appearance above ground, and
that a 3m mound would then be 8-10 years old. Though mounds are obviously
abandoned at times, in Queensland, Australia mounds are inhabited for 20-40 years!
(Goudie 1995). This associated dense network of galleries, it was suggested, must affect
porosity and aeration, infiltration, storage and drainage of water and growth of plant
roots, but in 1978 when Wood and Sands put forward these statements, none of these
important effects had been measured, only questioned. By 1996, Goudie more
confidently explains that termites found in huge numbers in fact do have a very high
biomass, create major structures, move large quantities of soil in the process of making
their nests, consume very appreciable amounts of litter and wood debris, create new soil
horizons, cover sands and stone lines, and probably exercise major control on the rate of
operation of such important physical processes as infiltration, surface wash, rain splash
detachment and soil creep (1996).
Through the formation of their extensive nests, ants and termites alter the micro-
geomorphology of their environments. Specifically, ants and termites increase
infiltration through the excavation of the chambers and galleries that form their nests.
Whereas the excavated holes a larger animal might make, such as a rodent, is referred to
as piping, the ant and termite literature refer to tunnels, with openings called macropores.
One of the earliest studies investigating water infiltration in termite nests was the 1986
article by Elkins et al. In the Chihuahuan desert ecosystem of Southern New Mexico,
Elkins et al. distinguish a mere 6 samples of both termite and termite free plots (treated
with insecticide). Elkins et al. used rainfall simulation at an average intensity of
124mm/h-1 to compare infiltration and run off on arid areas where subterranean termites
had been eliminated four years prior to the initiation of the study, compared with adjacent
areas populated by subterranean termites. Elkins et al. (1986) suggests that termites
could be an important element in the maintenance of hydrologic stability through
subsurface tunneling and soil profile disturbance.
Elkins et al. (1986) state that the most important finding in their study is that in
the absence of subterranean termites, “soil porosity is reduced thereby reducing water
infiltration.” This is an interesting way of twisting words so as not to imply there was
significance found in the water infiltration on termite plots, since it was lacking. Yet, the
authors suggest that in the northern Chihuahuan desert, subterranean termites are
“keystones” in the structure and function of that system (Elkins et al. 1986). Elkins
concludes that termite activity on watersheds in the Southwestern United States appear to
be a beneficial ecological process allowing greater short-term soil water storage, while
effectively checking erosional losses of soil and organic matter (1986).
While Elkins et al. (1986) recognizes that termites are a significant factor in the
regulation and maintenance of hydrologic responses, their early study falls short of
making a concrete connection between termites and infiltration rates. Over time, it is
intriguing to study the changes in experimental design and research concerning termites
and infiltration. Elkins et al. 1986 study begins to hint at the connection, yet falls short of
showing significance between termites and infiltration. As each researcher studies
previous experiments, we can trace the evolution of thought and experimentation,
increasing the levels of statistical significance, while always promoting termites as
fundamental components of soil-water economy and stability.
Ten years after Elkins’ study, and with a slight increase in thought regarding
experimental design, Mando et al. (1996) found termites to be the “most important soil
fauna in the Warm Seasonally-Dry Tropics” due to their impact on soil properties and
soil genesis. The experiment consisted of 4 plots, split in half to denote a Termite and
Non-Termite area. The plots were covered with a mulch of straw and wood to attract
termites, while half the plot, the Non-Termite sides were treated with an insecticide to
prevent termites from nesting. Insecticide was applied every two weeks, and after six
months, termites successfully inhabited the Termite side, while the Non-Termite side was
termite free. Mando et al. (1996) conducted “three [rain] simulation[s] of 60 minutes
duration” on each plot with an intensity of 50 mm/h. The second simulation was
conducted 24 hours after the first, and the third simulation was conducted 72 hours after
the second simulation (1986). During the rain simulations, the time between the
beginning of the simulation and the onset of ponding was called ponding time (PT), while
the elapsed time between the onset and the end of the runoff was called runoff time (RT),
which was recorded every five minutes. Therefore, the difference between rainfall
intensity and runoff intensity provided the cumulative infiltration and the infiltration rate
(Mando et al. 1996).
The results from Mando et al. (1996) demonstrate that termite nests do increase
infiltration, but at such a low sample size few of his results are statistically significant.
After six months, 88 (SD=5) open tunnels per square meter were found on the Termite
plots. According to Mando et al. (1996), cumulative infiltration after 30 minutes of
rainfall in the termite plots was higher than in Non-Termite plots, yet infiltration
decreased with increasing number of rain simulation. Since runoff measurements were
taken every 5 minutes, infiltration rates were also measured at half an hour, even though
technically the rain simulator was used for sixty minutes. While much of the experiment
lacks statistical significance, Mando et al. do demonstrate a trend between termite nests
and increased infiltration. Perhaps after only six months, termite nests are still in their
initial phases and are not well established. Additionally, a larger sample size would have
given the study more replications and hence more data.
Conveniently, Mando’s 1997 experiment combines three years worth of
infiltration data on a total of 24 Termite and 24 Non-Termite plots in a similar design to
his earlier study. Indeed, Mando found that termite activity resulted in a statistically
significant increase of water infiltration along with water storage and drainage. Mando
(1997) is sure that the “results prove that termite activity is a key element in the efficacy
of mulching to improve the infiltration capacity of crusted soil” because termites improve
infiltration through their tunnels excavated from soil.
It was the combination of termites and mulching in Mando’s 1997 study, which
increased the water storage capacity of the soil. Mando confirms that termite activity has
an effect on the soil water balance of crusted soils by increasing the infiltration amount,
soil water storage and drainage. The implications of Mando’s 1997 study are great,
suggesting that termite activity should be investigated and accounted for when
characterizing catchment hydrology and land management applications in the Sahel,
West Africa. Mando concludes by recommending the use of termites in soil and water
management techniques because of the “positive response of natural vegetation or crops .
. . due to termite effects” (1997).
The most complete and rational examination of termites and water infiltration was
performed by Leonard and Rajot entitled “Influence of termites on runoff and infiltration:
quantification and analysis” (2001). Having the benefit of so many previous studies,
Leonard and Rajot are able to build upon the growing literature on the subject, especially
from sahelian environments. The authors acknowledge that the harvesting activity of
termites results in the formation of dense networks of underground galleries and tunnels
that are connected to the soil surface by foraging holes, easily penetrated by water.
Leonard and Rajot (2001) recognize much of the work done by authors cited here as well,
and directly state that while it seems clear that termites increase infiltration, the authors
do not know if the effect will be large or not. Granted, this is not the most poignant
question, and perhaps the power of this question is lost in the poor translation of their
work, but nonetheless, their statement is important. The conditions under which many of
the past experiments had been performed are largely unnatural according to the authors
(2001). Specifically, Leonard and Rajot question the very high rainfall intensities of the
simulations (124mm/h-1, Elkins 1986) or high termite activity in a dense area that is not
representative of the surrounding environment (as in Mando 1997). The authors do
though, cite Mando’s 1997 article as the “most reliable result so far obtained on the
influence of termites on infiltration . . . increas[ing] by a factor of 1.5 due to the presence
of termites under 3 years of natural rainfall” (2001).
Leonard and Rajot (2001) state their study was performed under natural
conditions of rainfall, runoff and infiltration over the course of four consecutive years.
Once again, the experiment takes place in a sahelian environment, attracting termites to
crusted soil using a mulch. Six plots with five treatments in each were set up for a total
of 30 ‘sites’. The five different treatments in each block consisted of a control, which
was simply erosional soil, a mulch, mulch with insecticide, mulch with herbicide and
mulch with insecticide and herbicide. It should be noted that the authors realized at a
very late date in their research that the insecticide used also acted as an herbicide,
therefore preventing the ability to measure vegetation activity in the absence of termites.
In total then, there were 12 plots considered with termites, and 12 without.
Leonard and Rajot’s study was the first in my research to account for different
species of termites and their differing effect on the environment. Two species of termites
were predominant in the study, Macrotermes subhyalinus constructing above ground
mounds, while Odontotermes sp. excavated underground nests. Both of course include
dense networks of galleries near the soil surface. Of the many experiments performed,
water infiltration relates most to the current theme, and the authors used a rain simulation
of 40-mm for 1 hour. While the authors may boast of the natural-conditions of their
experiment, not only was the rain simulator used (of which the efficacy and reliability
was brought into question by a colleague in seminar) but methylene blue was added to
the water to colour the network of active galleries. The authors do not account for any
potential negative repercussions from using the rain simulator use or how methylene blue
might negatively affect the termite nests, perhaps disrupting the colony and therefore
creating an unnatural environment. In the end, it was determined from the methylene
blue that the galleries were only partially filled with water, not submerged (2001).
As expected, there is a relationship between the intensity of termite activity and
runoff, since the greater number of termite foraging holes reduced runoff (Leonard and
Rajot 2001). Yet, there is considerable variability which the authors must rationalize,
since the results showed that infiltration could be high with no macropores, and it was
also low at times despite the presence of macropores. The authors argue that although
infiltration increased with termite activity, at least 30 macropores per square meter were
necessary for significance. Perhaps, the authors suggest, even when the macropores are
closed or no longer visible, the infiltration capacity may still be high because the soil
crust has been destroyed (2001). In addition, when macropores are present their effect
may be imperceptible if they are located away from where the water concentrates
(Leonard and Rajot 2001). Leonard and Rajot (2001) conclude that while termites have
an influence on infiltration and runoff, it is difficult for them to quantify the effect due to
the high variability. The authors consider their study to be under natural conditions with
a large range of termite activity resulting in the infiltration increase by a “mean factor of
2-3,” similar to Mando (1997).
The fact that termites increase infiltration due to their extensive excavated
galleries seems somewhat obvious, even if designing an effective experiment is difficult.
What about the influence termites may have on the structure of the soil itself? Jungerius
et al. (1999) questioned the hypothesis that termites contribute to a stable microgranular,
or finely aggregated soil structure. Microaggregates, according to the authors, are often
very stable and give the soil a loamy texture, yet the origin and formation of the
microaggregates are not known (1999). Apparently, there is no clear relationship with
type of parent material, and microgranular soils have been found extensively on granites,
gneisses and sandstones, as well as dolomitic and phonolitic lava (Jungerius et al. 1999).
The authors chose to investigate termites and their role in microaggregate formation
because of the two ways termites can produce aggregates: 1. when soil is excavated and
carried in the mandibles and dumped on the surface or used in the above ground
formation of the nest, and 2. surface soil material passes through the intestinal system
when termites are feeding, and is excreted as fecal pellets (1999). Jungerius et al. (1999)
investigated the micoraggregates in the successive stages of the termite mound
development.
Above ground mounds or epigeal termite nests are “particularly numerous” on the
bottomlands of Kenya for two reasons mentioned by Jungerius: 1. occasional flooding
compels the termites to have their nests elevated to avoid inundation (an evolutionary
adaptation) and, 2. partly because the termite mounds have not been removed by
agricultural practices (1999). Though an ultimate and a proximate explanation is given,
the origin of raised termite mounds is not as pertinent as whether the authors indeed
found evidence to support their hypothesis. By combining stereomicroscopic and micro-
morphological techniques Jungerius et al. (1999) conclude that the structural units of
microgranular soil in the tropics could be formed by termites, even if their conclusion is
slightly hesitant. Termites produce stable microaggregates of about 0.6 mm in size, while
particles over 2 mm are not carried by termites and hence, coarse fragments gradually
concentrate at the bottom of the nest (Jungerius et al. 1999). The size of the
microaggregates are therefore, determined by the mandible size and ability of termites to
carry particles to the surface.
Since termites have been shown to alter their environments by increasing
infiltration and producing microaggregates (Elkins et al. 1986, Mando et al. 1996, Mando
1997, Leonard and Rajot 2001 and Jungerius et al. 1999) one must question the role of
ants in micro-geomorphologic change as well. Beginning with some of the earlier studies
of ant mound influences, Carlson and Whitford (1991) studied soils properties associated
with nest mounds of the western seed harvester ant, Pogonomyrmex occidentalis, near
Los Alamos, New Mexico. Of the 15 active nest sites selected for the soil study, Carlson
and Whitford found that ant mounds were significantly uniformly dispersed (perhaps for
territoriality reasons) with significantly higher concentrations of NO3, P and K (1991).
The ants excavated approximately 650kg/ha over the course of 3 months from June to
August in 1987. The authors’ results suggest that ants preferentially transport particles in
the order of gravel > sand > silt > clay, perhaps because at higher elevation gravel
mounds would be advantageous since gravel heats up quickly (Carlson and Whitford
1991). The authors decide, rather than demonstrate, that ant activities enhance soil
nutrient status, and that ants alter their environment according to changing needs.
Though much of the authors’ work is anecdotal, it suggests that further studies are needed
to better understand the role of ants and micro-geomorphology.
Dean and Yeaton begin their 1993 article acknowledging that the actions of any
animal that contributes to the movement of organic matter underground, (such as termites
or ants) must influence the local distribution of moisture and plant nutrients in the soil.
Specifically, in the southern Karoo, South Africa, nest mounds of the seed harvester ant,
Messor capensis, were hypothesized to contain more moisture, have a higher organic
matter content and an elevated nutrient status compared to surrounding areas (Dean and
Yeaton 1993). While the authors did successfully prove that nest mounds have an
elevated plant nutrient status compared to inter mound areas, strangely, the soils of seed
harvester ant nest mounds were actually significantly drier than soils in inter-mound
spaces! To explain this unexpected result, Dean and Yeaton suggest that soils at the base
of the mounds absorb water more quickly during rain than inter-mound soils, and the
authors state that “It is clear that nest-mound soils also dry out faster than inter-mound
soils” (1993).
Dean and Yeaton (1993) apply their results to the theories connecting infiltration
and ants nests, and recognize a trend. Nests of seed harvester ants may improve
infiltration by creating patches of less compacted, organic rich soils, ideal for plant
growth. While ant nests remained drier than inter mound soils, the authors suggest that
the infiltration ability of the nest-mound soils take up more water after it rains, and that
perhaps the soils below the nest mounds hold water at a greater depth than measured in
the study (Dean and Yeaton 1993).
Micromorphological characterizations of ant nests appear to be absent in the
literature, according to Wang et al. 1995. Therefore, their research objective was to
characterize the effect of L. neoniger Emery on physical and chemical soil modifications
while, 1. examining the geometry of nest castings and nest development; 2. describing,
measuring and interpreting micromorphological features of the nests from thin sections;
and 3. comparing selected chemical properties of ant crater rims and nests with that of
associated bulk soils. Ant nest casting are extensive and varied from 0.15 to 0.70m in
depth, while most of the galleries and chambers were concentrated in the upper 0.3m of
the soils profile (Wang 1995).
Concerning the micromorphological characteristics of the ant nest, Wang et al.
suggests that ants scavenge specifically for silt and colloidal material in addition to the
excavation materials to stabilize the nest walls. Nest walls are about 1 mm think and
have dark infillings of fine-sized soil materials (<0.25mm) between sand grains (1995).
Wang et al. (1995) found greater concentrations of silt and colloidal-sized materials,
rather than bulk soil, within the nest walls, while the outer edge of the wall appeared as
though it was intentionally arranged by the ants to have the flat surface facing the inside
of the nests. Wang et al. suspect that the ants are attempting to create a smooth path
within their nest! It appears that while excavating and constructing their nests, the ants
have rearranged and compacted the soil particles to a preferred orientation while using
specifically fine-particles as nest stabilizers (Wang et al. 1995).
Wang et al. concludes that the primary effect of the ants was mixing the upper
0.7m of soil (1995). Estimated soil turnover time ranges, for the upper 0.3 m soil from
approximately 1,000 – 2,800 years, and for soils between 0.3 and 0.7 m depths, estimated
soils turnover time ranges from approximately 9,000 – 24,000 years. Wang et al.
demonstrate the impact ant colonies can have on our environment and the rate at which
ants can alter the top soil.
For an investigation of the effects of seed harvester ants on the fertility, rainfall
infiltration, structural properties and water repellency of top soils in semi-arid rangeland
in SE Spain, we turn to Cammeraat et al. 2002. Of the 20 ant colonies located in the field
in June of 1997, nest mounds were found to have significantly lower pH than bulk soil
(Table 1). Electrical conductivity and concentrations of NO3-, NH4+, P, K, Mg and
organic C were significantly greater in soils from ant nest mounds (Cammeraat et al.
2002). Table 2 compares particle size distribution of soil samples taken from ant nests
and control sites, showing that all samples were “gravelly loamy sand” with differences
between the samples being small (Cammeraat et al. 2002). Infiltration rates were found
to be significantly higher on the ants’ nests when compared to the control area, where as
the same study performed a year later in 1998 resulted in infiltration rates being lower on
the nests. Cammeraat et al. conclude that ants’ nests act as sinks for water under slightly
humid to wet conditions, whereas under extremely dry conditions the infiltration is
reduced (2002).
Most of the research on ants and termites as agent of geomorphology has taken
place outside the United States. To bring the questions home, S. B. Vinson writes of the
invasion of the red imported fire ant to the southeastern United States (1997). Within six
months of colonization, a mound can reach about 7-15 cm across and 3-6 cm high,
containing several thousand ants (Vinson 1997). A mature fire ant colony may have
200,000-300,000 workers constructing a mound that may reach 30-50 cm in diameter and
over 35 cm high (Figure 2, Vinson 1997). The number of mounds per hectare range from
50-75, certainly suggesting geomorphic agents at work! Figure 3 is a great example of a
landscape altered by the presence of fire ants (Vinson 1997).
Figure 2 and 3 of fire ant nests, often 35 cm high, with over 500 mounds per hectare. Source: Vinson 1997
Fire ants are known for building large mounds at high densities throughout the
southeastern United States. According to Green et al. (1999) fire ants represent a new
soil-forming factor for the in the region, and hence, performed a study to quantify the
channel network geometry, clod density, aggregate stability and micromorphology of the
mounds on three texturally different soils to examine the moisture relationships in the
mounds (Green et al. 1999). Of significance to this paper, it was determined that the
fragile crust of the ant nests allowed more infiltration than the surrounding soils, with a
moisture content of up to 170% greater in the mound than in the adjacent soil shortly
after rainfall (Green et al. 1999). The authors determined that infiltrating water rapidly
drained from the mound and had the potential to be stored in the channels below the
mound. Interestingly, after one week of rainless conditions, moisture levels in the mound
and the upper part of the underlying soil were extremely low, much lower in fact than the
surrounding undisturbed soil (Green et al. 1999). The authors conclude that the mound
allows for more infiltration than undisturbed topsoil and more leaching within the mound.
Infiltrating water, according to Green et al. (1999), drains rapidly and can be stored in the
channels below the mound, as indicated by the occurrence of free water below mounds at
120, 81 and 46cm deep, while no free water was present in adjacent areas.
Green et al. (1999) recommend that as colonies relocate their mounds over time,
entire landscapes may be exposed to the greater leaching and soils may inherit new
macropores and soil aggregates. Imported fire ants affect their surrounding and hence
geomorphology by the creation of new macroporosity through their channel network as
well as aggregates and hence, alter the hydrology of the soil (Green et al. 1999). Green et
al. (1999) recommend that the presence of many mounds on the landscape may
noticeably alter the ecology and hydrology of the entire landscape, and therefore, the
imported fire ants represent a new soil-forming factor influencing the structure and
hydrology of the soils of the southeastern United States.
This research paper has demonstrated how effective ants and termites are as
geomorphic agents. It appears quite clear that ants and termites are certainly altering the
environment, even while on a micro-geomorphic scale. I found much more research than
expected, though much of the it fell short of statistical significance, repeatability and
application to the larger field. A more detailed analysis of a smaller set of experiments
would be an effective strategy to isolate one aspect of geomorphology, choosing from
infiltration, soil formation, microaggregates and nutrient changes. It is the goal of this
paper to introduce the subject of ants and termites as zoogeomorphic agents and to act as
a reference on the subject. The field of zoogeomorphology has been growing, and the
role of invertebrates as geomorphic agents has been increasingly recognized. As humans,
we often forget the significant role non-human animals have on the world, and as we
have learned, even the smallest invertebrates are capable of changing landscapes over
time.
Bibliography
Butler, David R. 1995. Zoogeomorphology: Animals as geomorphic agents.
Cambridge: Cambridge University Press.
___ 1992. The grizzly bear as an erosional agent in mountainous terrain. Zeitschrift fur
Geomorphologie 36(2): 167-189.
Cammeraat, L. H., S. J. Willott, S. G. Compton and L. D. Incoll. 2002. The effects of
ants’ nests on the physical, chemical and hydrological properties of a rangeland
soil in semi-arid Spain. Geoderma 105: 1-20.
Carlson, Stan R. and Walter G. Whitford. 1991. Ant mound influence on vegetation and
soils in a semiarid mountain ecosystem. American Midland Naturalist 26(1):
125-139.
Dean, W. R. J. and R. I. Yeaton. 1993. The effects of harvester ant Messor capensis
nest-mounds on the physical and chemical properties of soils in the southern
Karoo, South Africa. Journal of Arid Environments 25: 249-260.
Elkins, Ned Z., G. V. Sabol, T. J. Ward and W. G. Whitford. 1986. The influence of
subterranean termites on the hydrological characteristics of a Chihuahuan desert
ecosystem. Oecologia 68: 521-528.
Green, W. P., D. E. Pettry and R. E. Switzer. 1999. Structure and hydrology of mounds
of the imported fire ants in the southeastern United States. Geoderma 93: 1-17.
Goudie, Andrew. 1996. The geomorphology of the seasonal tropics. In The physical
geography of Africa, eds. W. M. Adams, A. S. Goudie and A. R. Orme. London:
Oxford University Press.
___ 1995. The changing Earth: rates of geomorphological processes. London:
Blackwell.
Jungerius, P. D., J. A. M. van den Ancker and H. J. Mucher. 1999. The contribution of
termites to the microgranular structure of soils on the Uasin Gishu Plateau,
Kenya. Catena 34: 349-363.
Leonard, J. and J. L. Rajot. 2001. Influence of termites on runoff and infiltration:
quantification and analysis. Geoderma 104: 17-40.
Mando, A. 1997. The impact of termites and mulch on the water balance of crusted
Sahelian soil. Soil Technology 11: 121-138.
Mando, A., L. Stroosnijder and L. Brussaard. 1996. Effects of termites on infiltration
into crusted soil. Geoderma 74:107-113.
Oster, George F. and Edward O. Wilson. 1978. Caste and ecology in the social insects.
New Jersey: Princeton University Press.
Petal, J. 1978. The role of ants in ecosystems. . In Production ecology of ants and
termites, ed. M. V. Brian, 293-325. London: Cambridge University Press.
Vinson, S. Bradleigh. 1997. Invasion of the red imported fire ant. American
Entomologist Spring: 23-39.
Wang, D., K. McSweeney, B. Lowery and J. M. Norman. 1995. Nest structure of ant
Lasius neoniger Emery and its implications to soil modification. Geoderma 66:
259-272.
Wood, T. G. and W. A. Sands. 1978. The role of termites in ecosystems. In Production
ecology of ants and termites, ed. M. V. Brian, 245-292. London: Cambridge
University Press.