Mound Building Activities Research Articles

Make the environment protect you from disease: elevated CO2 inhibits antagonists of the fungus-farming termite symbiosis

Fungus-farming termite colonies maintain monoculture fungus combs in underground chambers without apparent problems with diseases. Multiple lines of defense contribute to the suppression or removal of antagonists of the symbiosis, but the role of the termite-manipulated environment within mounds has yet to be tested. Specifically, termite mounds have extremely high levels of CO2 compared to atmospheric levels. We tested the effect of 5% CO2 on the growth of fungal crops from Macrotermes bellicosus colonies, generalist fungi that could challenge the symbiosis, as well as a specialist stowaway fungus, Pseudoxylaria. For sporulating fungi, we also quantified the effects on conidia production. We found that elevated CO2 significantly reduces mycelial growth and conidia production of the generalist fungi Aspergillus sp., Beauveria bassiana, and Metarhizium brunneum, whereas it overall had a net positive effect on the growth of the fungal crop Termitomyces and Pseudoxylaria; albeit, with variation between fungal strains within genera. Our findings point to elevated CO2 being of adaptive significance to the fungus-farming termite symbiosis as an additional layer of defense that helps keep termite fungus gardens free from fungal infections. The mound-building activities that make termites ecosystem engineers may thus also generate environmental conditions that impact the fate of fungi inhabiting the extended phenotypes that massive termite mounds represent.

Habitat-specific AMF symbioses enhance drought tolerance of a native Kenyan grass

The role of arbuscular mycorrhizal fungi (AMF) in enhancing plant tolerance to drought is well known. However, the degree to which AMF-plant symbioses are locally adapted has been suggested but is less well understood, especially at small spatial scales. Here, we examined the effects of two arbuscular mycorrhizal fungal communities on drought tolerance of Themeda triandra, a native African perennial bunchgrass. In our study area, mound building activities of Odontotermes sp. termites produce heterogeneous habitat, particularly with respect to water availability, and do so over small spatial scales (<50 m). Thus, plants and their AMF symbionts may experience identical climatic conditions but very different edaphic conditions. We hypothesized that AMF from off-mound areas, where plants experience drought more intensely than on termite mounds, would confer greater protection from drought conditions than AMF from termite mound soils. To test this, we conducted a greenhouse experiment in which we grew plants in soils that we inoculated with fungi from on or off termite mounds, or with a sterilized control inoculum. Our results reveal habitat-specific AMF effects on host stomatal functioning and growth. Contrary to our expectations, drought stressed grasses inoculated with AMF from termite mounds closed stomata less, and produced 60% more leaves than those inoculated with off-mound AMF, thus exhibiting higher levels of tolerance. Mound-inoculated plants that were drought stressed also produced more than twice as many leaves as non-inoculated plants. Longer-term productivity measurements indicate both on- and off-mound inoculated plants were able to recover to a greater extent than non-inoculated plants, indicating that AMF associations in general help plants recover from drought. These findings highlight the important role that AMF play in mitigating drought stress and indicate that AMF affect how plants experience drought in a small scale, habitat-specific manner.

Vegetation heterogeneity caused by an ecosystem engineer drives oviposition-site selection of a threatened grassland insect

Soil-disturbing ecosystem engineers play an important role in plant-species diversity in grasslands as they increase vegetation heterogeneity by creating gaps due to burrowing or mound-building activities. However, knowledge of the ecological importance of these microsites for arthropods is still rare. In this study, we analyse the role of ant-nest mounds of the yellow meadow ant (Lasius flavus) for oviposition-site selection of the silver-spotted skipper (Hesperia comma). Ant mounds were searched for H. comma eggs. Microclimatic and vegetation parameters were ascertained at occupied sites and control sites within the matrix vegetation. Furthermore, we analysed the habitat requirements of L. flavus by means of nest counting and the sampling of environmental parameters within different sites. L. flavus occurred most frequently in abandoned and less steep sites with deeper soils. Mean egg occupancy rates of H. comma on ant hills were 32 %, nearly twice as high as at control sites (18 %). In contrast to the surrounding vegetation, nest mounds were characterized by a lower vegetation cover and litter and a higher proportion of bare ground. Furthermore, they had a higher cover of host plants compared with control samples. These microhabitats offered the following essential key factors for the larval development of H. comma: (1) a suitable microclimate due to open vegetation and (2) a high amount of host plants. This study highlights the importance of L. flavus as an ecosystem engineer within central European grasslands because this species increases vegetation heterogeneity.

Island forming processes in the Okavango Delta, Botswana

The Okavango Delta in Botswana is a large (40,000km2) alluvial fan that is characterised by the presence of numerous tree-covered islands. Thought to originate from the mound-building activities of termites or through fluvial processes associated with development of scroll bars and inverted channels, islands have been shown to play an important role in the structure and functioning of the Delta through the creation of habitat diversity, focusing of nutrients, and disposal of toxic salts. This study investigates the processes responsible for the maintenance and growth of two such islands in the seasonal swamps. Transpiration by vegetation is shown to result in substantial increases in groundwater salinity beneath the islands, contributing to their growth through chemical precipitation. Detailed chemical analyses revealed that the precipitation of magnesian calcite and silica within the island soils contributes 30–40% of the total island volume. Isotopic analyses of carbonate samples show that vegetation plays an important role in providing carbon for carbonate precipitation. Variations in δ13C carbonate values appear to reflect the relative proportion of C3 to C4 plants on the island, with C4 species becoming more dominant toward island centres in response to increases in groundwater salinity. The study suggests that continued island growth is also related to the deposition of aerosols and the accumulation of dust preferentially on islands and possibly to ongoing termite activity. Tall trees that characterise the island margins trap dust carried from the floodplains, resulting particularly in the lateral growth of islands. Islands in the Okavango are considered to be the product of long-term aggradation processes, with the two islands studied estimated to be in the order of tens of thousands of years old.

Spatial distribution of ant mounds and effects on soil physical properties in wetlands of the Sanjiang plain, China

Ants constitute a dominant element of soil mesofauna due to their biomass, abundance, richness of species and distribution within terrestrial ecosystems. They are important regulators of soil aggregate structure as they translocate large amounts of soil from the bottom to the soil surface. In doing so, they form biogenic structures (BS) made up of aggregates of different sizes and characteristics, i.e. ant mounds. These BS have varying characteristics according to the ant species and the soil where they carry their activities. Ants are considered soil engineers because of their effects on soil properties, availability of resource and flow of energy and nutrients in soil. Thus, it is important to gain information on their distribution and abundance. Relatively little is known about the spatial distribution of mounds and their role in the soil physical properties in wetlands of the Sanjiang plain, China. We conducted a survey of ant mounds and measured the density, height, and diameter and material composition of different ant mounds. The ecological characteristics of wetlands that ant mounds wide occurrence were also investigated, including soil type, hydrology characters and plant composition. Differences in soil particle composition, bulk density and soil moisture between ant mound and natural meadow were measured to assess the influences of ant mounds on soil physical properties. We also studied the effects of ant mounds on the microtopography of meadows. Ant mounds were found mainly in the transition zone between terrestrial and aquatic habitats, with wetland type, including Calamagrostis augustifolia wet meadow, C. augustifolia marsh meadow, shrubs marsh meadow and Carex meyeriana– Carex appendiculata wetland, being a significant factor. Most of the mounds detected were inhabited by Lasius flavus Fabricius, Lasius niger Linnaeus and Formica sanguinea Latreille, which occupied 52.9%, 26.5% and 20.6% of the mounds surveyed, respectively. The density, height, diameter and mound composition were significantly different among the mounds of F. sanguinea Latreille, L. flavus Fabricius and L. niger Linnaeus. The average density and diameter of L. flavus mounds was significantly higher than those of other ant mounds. The average height of F. sanguinea mounds was highest among the mounds detected. Mound building activities changed soil particle size distribution, with the silt and clay content of mounds higher than for non-mound soil. Compared with adjacent, non-mound soil, the bulk density (0–30 cm) and water content (0–25 cm) of mound soil were significantly lower, but there were no significant differences between the mound soil of F. sanguinea Latreille and L. flavus Fabricius. The spatial distribution of ant mounds with different height and diameter also changed the micro-geomorphology of the soil surface, increasing the degree of fluctuation of the microtopography. The ant distribution characteristics and their ecological roles respond to a wide range of environmental alterations. The biogenic structures of ant and the specific environment associated with them have been defined as the “functional domain”, a sphere of influence that may significantly affect soil processes at certain spatial and temporal scales. Our results suggest that the distribution and structure of ant mounds can indicate wetland environmental changes, with mounds influencing ecosystem functions and enhancing wetland degradation.

The spatial extent of termite influences on herbivore browsing in an African savanna

Termite mounds form islands of fertility in savanna landscapes and create foraging hotspots for herbivores, but the magnitude and spatial extent of these influences is unknown. We mapped terrain, termite mound and woody vegetation three-dimensional (3-D) structure at 56 cm resolution across a large-scale (254 ha), long-term (34 years) herbivore exclusion experiment in the Kruger National Park, with the Carnegie Airborne Observatory (CAO). We compared vegetation 3-D structure in areas protected from herbivores with those accessible to herbivores, both on termite mounds and in the landscape matrix between termite mounds. Termite mound density was 1.1 ha −1 across the study area and mound size did not differ between protected and accessible areas. Woody vegetation canopy cover was ∼100% greater on protected than accessible mounds, but was only ∼20% greater in the protected inter-mound matrix when compared to the accessible matrix. Woody canopy height class distributions differed significantly between protected and accessible areas, with the tallest vegetation (>10 m) occurring on protected termite mounds. The impacts of herbivore browsing were evident at distances of up to 20 m from termite mound centres. Spatial analysis of mound distribution revealed that the sphere of termite mound influence constitutes ∼20% of the total landscape. Termite influences on herbivore browsing operate at scales much larger than the spatial extent of their mound building activities.

Documentation of Caddo Ceramic Vessel Sherds from the Shelby Site (41CP71) in the Vernon Holcomb Collection, Camp County, Texas

The Shelby site (41CP71) is an important Late Caddo period, Titus phase, religious and political center on Greasy Creek in the Northeast Texas Pineywoods. The site, occupied from the 15th century A.D. until at least the late 17th century A.D., is a large and well-preserved settlement with abundant habitation features as well as plant and animal remains, evidence of mound building activities in the form of a 1.5 m high structural mound, and a large community cemetery with at least 119 burial pits and perhaps as many as 200. The Shelby site is the nexus of one of a number of Titus phase political communities in the Big Cypress Creek stream basin. Nevertheless, very little is known archaeologically about the site—or the history of the Caddo’s settlement there—since almost all the work done at the site since it was discovered in 1979 has been by looters. Perttula and Nelson completed a limited amount of work in the village area in 2003, and Bob Turner and others worked in the 1.5 m high structural mound between 1985-1988, but an overall synthesis of the Caddo occupation at the Shelby site awaits more extensive professional archaeological investigations. One key step in any professional archaeological work that may be forthcoming at the site includes the documentation of Caddo material culture remains, especially Caddo ceramics, that are known to have come from the site, as they provide a record of the temporal, functional, and stylistic range of the ceramic vessels used and discarded at the site, as well as evidence of interaction and contact between different but contemporaneous Caddo groups. In August 2009, I had an opportunity to document a collection of Caddo ceramic sherds held by Vernon Holcomb from the Shelby site. He collected these sherds from the surface of the site some 25-30 years ago where they had been eroded out of the banks of a dry or intermittent stream branch that drains north to Greasy Creek.

Factors Affecting Distribution of the Mound-Building Ant &lt;I&gt;Lasius neoniger&lt;/I&gt; (Hymenoptera: Formicidae) and Implications for Management on Golf Course Putting Greens

Lasius neoniger (Emery), a cosmopolitan ant species, can be a serious pest when its mound-building activities occur on golf course putting greens and other closely mowed turfgrass sites. We mapped the distribution of 735 ant mounds on 30 sand-based putting greens of three golf courses. We then examined factors that might explain why >90% of the mounds on such greens were concentrated in a 2-m wide band just inside the perimeter. Root aphids (Homoptera: Aphididae) from which L. neoniger obtains honeydew were largely absent from high-sand root zone mix of greens but present in surrounding turfgrass on natural soil. Main ant nests, with brood, also were absent from sand-based greens but abundant in adjacent roughs. Although more root aphids were found within ant nests than away from nests, their numbers seem too low to be the main factor restricting the ants' distribution to edges of putting greens. In manipulative experiments, ants responded to low cut (scalped) turf and to sand-filled holes by increased mound building. We suggest that most ant mounds on sand-based greens are associated with subnests, used by foraging workers, which are connected to main nests located just outside the collar in natural soil. Encroachment of mounds into greens occurs when the polydomous colonies seasonally expand their foraging territories, accounting for mounds being concentrated around the perimeter. Control actions for L. neoniger on golf courses should focus on the perimeter of sand-based greens.

Vole mound effects and disturbance rate in a mediterranean plant community under different grazing and irrigation regimes

A factorial field experiment was used to assess the influence of soil-disturber mammals in the structure of a 9-year-old Mediterranean annual plant community subjected to different sheep grazing and irrigation regimes. We estimated the disturbance rate (mound building activity) by Mediterranean voles, their effects on vegetation and the mechanisms of these effects during a period of vole outbreak. The effects on vegetation were analysed at the levels of species, functional groups and plant community. Disturbance rate was high and voles can disturb the entire soil surface once every four or five years. The availability of certain trophic resources (perennial plants) appeared to drive vole expansion in the experimental plots and it was independent of the irrigation and grazing treatments. Mound building activities largely affected vegetation but conserved plot differences. Total vegetation cover, absolute cover of all functional groups, mean vegetation height and species richness were less on mounds than on undisturbed ground. These effects did not change the relative abundance of annuals, perennials, grasses and forbs. Only the relative abundance of small-seeded species decreased on mounds. As the proportion of these seeds was similar in both types of patches, we suggest that small-seeded species had more difficulties for germinating or emerging when they are buried during mound formation. Irrigation and sheep grazing promoted large changes in the vegetation parameters but these effects were, in general, similar on mounds and undisturbed ground. Our results show that the availability of germinable seeds may be the major limitation for mound revegetation, probably due to the scarcity of seeds existing at the depths from which soils are excavated. Our results also suggested a resource limitation on mounds. The results provide additional evidence that soil disturbances by small herbivore mammals exert relevant ecological effects on abandoned Mediterranean croplands. We discuss the ecological implications of vole mound-building activities for plant succession, plant species conservation and forage resource availability for livestock.

The role of biota in the initiation and growth of islands on the floodplain of the Okavango alluvial fan, Botswana

A group of islands of varying size on the floodplain of the Okavango alluvial fan, were studied to establish the processes which lead to the initiation and growth of islands. It was found that islands are initiated by the mound-building activities of the termite Macrotermes michaelseni. These termites import fine grained materials to use as a mortar for the construction of epigeal mounds. Their activities create a topographic feature, raised above the level of seasonal flooding, and also change the physical properties and nutrient status of the mound soil. Shrubs and trees are able to colonize these mounds, which results in increased transpiration. As a result, precipitation of calcite and silica from the shallow ground water occurs preferentially beneath the mounds, resulting in vertical and especially lateral growth, causing island expansion. © 1998 John Wiley & Sons, Ltd.

Evaluation of strychnine and zinc phosphide baits to control northern pocket gophers ( Thomomys talpoides) in alfalfa fields in Alberta, Canada

This study compared the effectiveness of Sanex 0.40% strychnine-treated oats, Fairview 0.37% strychnine-treated grains, and United Agri Products 2% zinc phosphide-treated oats to control northern pocket gopher ( Thomomys talpoides) populations in alfalfa fields in Alberta, Canada. The poison baits were tested during three phenological periods corresponding to the reproduction, summer juvenile dispersal, and early fall mound building activities. Overall, less than 17% of the pocket gopher populations were controlled by any poison bait during the reproduction and early fall periods. In summer, there was a significant difference ( P < 0.05) between poison baits as measured by the relative frequency of active and inactive burrow systems. The Sanex poison bait was significantly ( P < 0.05) more effective (36%) in terms of reduced pocket gopher activity than the other baits (≤ 15%). I suggest that the effectiveness of poison baits to control pocket gophers may be greater in mid-summer after hay harvest, when the young of the year disperse to establish their own burrow system. However, because of the overall poor performance of all tested poison baits in alfalfa fields, more research and development work based on animal behaviour should be carried out to improve bait acceptance.

Gopher Tortoise (Gopherus polyphemus) Effects on Soils and Vegetation in a Florida Sandhill Community

Burrowing and mound-building activities of gopher tortoises generated significant environmental heterogeneity in an oak-pine sandhill forest in Florida. Mounds were characterized by lower soil nutrient and organic matter concentrations, higher light intensities and greater diurnal temperature fluctuations than adjacent undisturbed areas. Temperatures during prescribed spring fires were significantly lower on mounds and near burrow openings relative to the surrounding undisturbed vegetation. Changes in plant species composition and relative abundances between recently abandoned mounds, old mounds and undisturbed areas indicated that mounds undergo microsuccession and contribute toward increased plant species diversity in the forest understory. Old mounds had the highest species richness per unit area. Mound size had no effect on plant population dynamics or community structure. Gopher tortoise disturbances increased the frequency of recruitment by seed relative to vegetative reproduction in the common rhizomatous forb, Pityopsis graminifolia.

The Woodland and Mississippian traditions in the prehistory of Midwestern North America

Cultural developments in Midwestern North America between 5000 and 400 B.P. are reviewed and related to two overlapping, but contrasting, cultural traditions: Woodland and Mississippian. Significant changes in prehistoric subsistence systems, settlement patterns, and sociopolitical organization are reviewed within a three-division framework, beginning with a Transitional period (5000–2000 B.P.) when Late Archaic and Early Woodland societies “settled into” different regions, constructed regional markers (cemeteries, mounds, earthworks), and established economic and social relations with both neighboring and more distant groups. This was followed by the Middle Woodland period (2000–1500 B.P.) that is associated with the Hopewell “climax” of long-distance exchange of exotic materials, mound building, and ceremonial activities, although all Middle Woodland groups did not participate in this “Hopewell interaction sphere.” In the Late Prehistoric period (1500–400 B.P.), the Woodland tradition persisted in some areas, while the Mississippian tradition developed from local Late Woodland societies elsewhere. Finally, the patterns of interaction between the two traditions are discussed.

Blue Grama and Buffalograss Patterns in and near a Prairie Dog Town

Highlight: Blue grama and buffalograss patterns differed in response to prairie dog mound building activities. While both species exhibited smaller pattern sizes within prairie dog towns compared to outside, but adjacent areas, the size of clumps and patches differed for the two species. Prairie dog activities caused a two-fold decrease in pattern size of blue grama by reducing size of clumps and patches. On the other hand, buffalograss patches were fi-agmented into small clumps which were not observed outside the town.