Burrowing Activity Research Articles

Effects of grazing and vegetation on Daurian Pika populations in northern Mongolia

Abstract Daurian Pika (Ochotona dauurica) are steppe-dwelling burrowing mammals with the potential to have large effects on central Asian grasslands due to their extensive range, propensity to occur at extremely high density, and roles as ecosystem engineers and important prey species. The few studies that have been done are mostly from northern China and Russia, while little research has been done in the majority of their range in Mongolia. We studied a population of Daurian Pika in the Darhad Valley of northern Mongolia, near the southern edge of the permafrost, where climate change is progressing rapidly. We evaluated pika populations at 87 random plots across a large 40 × 125 km area and assessed the impact of factors related to vegetation cover, grazing, and soils that predicted their occupancy and an index of their density (number of active burrows). We found that pikas were more likely to occur in areas with taller grass and higher forb cover, and burrow densities were higher in areas with low or moderate grazing and lower soil moisture. In summer, pikas mainly foraged on grass compared with forbs—while in fall, forbs appeared to be selected for in haypiles. Dense pika burrow systems had taller grasses and forbs in their immediate vicinity, suggesting that in some cases, pika could help promote plant growth for other grazers. Long-tailed Ground Squirrel (Urocitellus undulatus) was the second most abundant small mammal in our study sight and selected for areas with high cover of overgrazing indicator species and for short forbs, providing little evidence for competition with Daurian Pika. Our results suggest that shorter grass (~1 cm) can decrease pika occupancy by 75%, while heavy grazing may decrease burrow density by 66% in dry soils. With grazing pressure in Mongolia increasing dramatically since the 1990s, future research is strongly needed to assess the impacts of grazing on this keystone species.

Potential advantage of invasive estuarine worms over native species under exposure to relevant concentrations of graphene oxide: Behavioral and biochemical insights.

Technological development using graphene oxide (GO) has increased in the last years, leading to the release of this contaminant to final sinks, such as estuaries. Due to their potential to flocculate and deposit when interacting with high ionic strength media, GO poses a threat, especially to benthic organisms like polychaetes. In addition to chemical contamination, estuaries also face a severe threat from invasive species, which can cause irreversible damage to ecosystems. The combination of abiotic and biotic stressors may work together on native species, decreasing their resilience. Thus, this study aims to assess the effects of an abiotic stressor, GO nanosheets (0.001, 0.01, 0.1, 1, 10mg GO/Kg dw) on Hediste diversicolor (native species) and Arenicola marina (invasive species) through several behavioral assays and biochemical markers. The impact of invasive species A. marina (biotic factor) on H. diversicolor avoidance behavior was also evaluated. Obtained results demonstrated that H. diversicolor fled from lower GO contamination compartments to higher ones and that exposure to increased GO concentrations negatively impacted its burrowing activity. They were unable to escape from higher contamination compartments, but at the highest concentrations, the bioturbation activity was significantly higher, which may indicate that H. diversicolor tended to dwell deeper in the sediment. A. marina showed an escape behavior from compartments with higher GO concentrations. Additionally, this species' bioturbation activity significantly decreased when exposed to GO. Moreover, avoidance tests demonstrated that the presence of A. marina affected the behavior of H. diversicolor. Regarding oxidative stress, H. diversicolor seems to be more impacted than A. marina, since Lipid peroxidation levels were higher in all GO concentrations and Superoxide dismutase activity significantly increased in the lowest GO levels. Overall, H. diversicolor spatial distribution may be severely constrained under abiotic and biotic stress, while A. marina's higher foraging activity may promote its propagation in the estuary. Behavioral tests, combined with biochemical markers have shown to be relevant tools for the development of more environmental-realistic assessment and monitoring frameworks for estuaries.

Rescue and Translocation of Hispaniola Hutia (Plagiodontia aedium) in Pueblo Viejo, Cotuí Mining Concession Area.

Translocation of species is a common practice used in endangered species management and conservation plans, which can have the purpose of establishing new populations which are at risk of being wiped out, increase a species chance of survival or recovery, and to preserve genetic diversity. The present study details the rescue and relocation process of Hispaniola Hutia (Plagiodontia aedium) in the municipality of Cotuí, Dominican Republic. Data are presented for eight individuals, belonging to two different families, detailing capture methods, handling, reintroduction method, and behavior, as well as data on post-release monitoring for both families. It was found that the most efficient capture method was active capture by hand (6/8). The family groups were heterogeneous, although both families had in common the presence of a single adult male. The average weight of the individuals was 1.19 kg. Blood tests were carried out on the animals before being taken to the holding pens and compared with the values of other rodents, showing that hematic values for P. aedium were like those of another hutia species, Cynomys ludovicianus. During the period animals were held in pens before reintroduction, hutias showed trophic preferences for Clusia rosea and Guarea guidonea. The only supplementary food they consumed was Daucus carota. A fight was observed between members of different families during the acclimation period in the holding pen, between a subadult male and another dominant one, evidencing territorial behavior. Post-release monitoring of the families showed that the selection of habitat for relocation, based on the characterization of active burrows in the area, was successful in one of the two families relocated. One of the families abandoned the selected area for translocation during the monitoring. It is important to note that accurate population data of the targeted population, such as abundance and density, are necessary to guarantee the survival of the translocated animals in the new environment. The reintroduction method used in this study may serve as a baseline for future translocation projects for the species.

Digging for answers: defining the external architecture of the southern hairy-nosed wombats’ (Lasiorhinus latifrons) subterranean excavations

The southern hairy-nosed wombat (Lasiorhinus latifrons) is a large, nocturnal, herbivorous, burrowing marsupial, endemic to the semi-arid and arid regions of southern Australia. The active burrow of L. latifrons is used as the primary feature in population estimations. Therefore, accurate identification of an active burrow is vital, especially when other burrow-like structures exist. Entrance attributes such as width, height, the length and angle of the path leading to the entrance, and signs of wombat activity are indistinguishable between the different structures, making differentiation between them impossible without inspecting the structure beyond the entrance. Structures leading from entrances were identified in the field as possible burrows, blinds, and go-throughs. An unmanned aerial vehicle provided accurate images from immediately above 12 active wombat warren systems in the mid-north of South Australia, to support ground-truthing for mapping and verification of these structures. Active possible burrows (APB) were found to occur in proportionally lower numbers than the active non-burrow structures (ANBS) of blinds and go-throughs, varying in proportion from as high as 1:2 to as low as 1:11 (APB:ANBS). Defining an active burrow and other tunnels leading from an entrance increases accuracy in burrow identification used in population estimations, while recognising the existence of additional architectural features is vital to understanding the functional potential of L. latifrons as an ecosystem engineer.

Field Efficacy of Anticoagulant Rodenticide Towards Managing Rodent Pests in Jitra Rice Field, Kedah, Malaysia.

Frequent encounters with the greater bandicoot rats (Bandicota indica) following high rodent damage towards rice crops and lack of information on the species had encouraged this study to be conducted to test the relevance of using first- and second-generation rodenticide in a field efficacy test. This study also attempts to detect any sign of resistance of current rodent pest populations towards chlorophacinone (0.005%) and flucoumafen (0.05%) for the control of field rats predominant rice field agrosystem of the Kedah in northern peninsular Malaysia. Six different treatments over dry and wet rice planting season together with trapping exercise. The observation was evaluated based on the number of active burrows, counting tiller damage due to rodent attack and trapping index. The results indicated that flucoumafen gives better rodent control and has a better impact (p < 0.05) although chlorophacinone is still relevant to be applied (p < 0.05). Treatments during the off-planting season (September-February) are more effective compared to the main planting season (March-August). Rodent control during the early off-planting season is encouraged for better rodent management in the rice field and the use of bait stations to increase the weatherability of the baits.

Can repellent crops reduce the abundance of the common vole (Microtus arvalis) as a way to reduce crop damage?

The common vole is one of the most damaging rodents in agriculture. A number of methods are used to suppress its numbers and limit damage. One option is growing crops that are not suitable for voles; this might limit their numbers and distribution. Through long-term monitoring of common voles throughout the Czech Republic, their abundance in eleven crop types (annual, biennial and perennial crops) was evaluated through active burrow counts. Reference crops were selected from perennials and biennials and annual crops were selected as potential repellents. The perennial crops were clover with alfalfa, which serve as the primary habitat for voles. These crops are where voles are found in their highest densities, and from which they spread to the surrounding crops during periods of high abundance. The biennial winter rape was selected because it provides favourable conditions for voles to overwinter and multiply rapidly in the spring. Compared to perennial crops and winter rape, significantly lower numbers of voles were found in onions, poppy seeds and maize. Additionally, fewer voles were also found in mustard compared to perennial crops. Onion and poppy were the only crops to show a significantly lower abundance of voles in comparison to wheat. The annual crops tested are unattractive to voles and due to the cultivation practices used, they do not even have enough weeds as food. As profitable crops they can be cultivated over sufficiently large areas to potentially prevent the spread of voles to surrounding crops, especially during outbreak years.

How do plateau pikas use burrows during population reestablishment?

The construction of burrow systems is one of the most important challenges for burrowing animals, especially during population reestablishment. Efficient use of the existing resources could help improve the survival chances. To explore the strategies burrowing animals take in using the burrow resources, we conducted monthly field monitoring of the four features (Active burrows (AcB), abandoned burrows (AbB), latrine pits (LP), and shallow duck holes (SDH)) of plateau pika (Ochotona curzoniae) burrow systems after population extermination. The results indicated that the existing burrows were largely utilized in rebuilding their new burrow systems. The use rates of the four features were in the order of AcBs > AbBs > LPs > SDHs. More energy-saving measures were taken in using the existing burrows during population reestablishment than in the undisturbed natural ecosystems, including higher maintenance rates, higher transformation rates to AcBs, lower disappearing rates and new adding rates, especially in short time intervals; and burrows at the early breeding season are used more stable than at other times. Our study has implications for the population reestablishment of endangered burrowing animals.

Study of the influence of macro-structure and micro-structure on the mechanical properties of stag beetle upper jaw

Macrostructural control of stress distribution and microstructural influence on crack propagation is one of the strategies for obtaining high mechanical properties in stag beetle upper jaws. The maximum bending fracture force of the stag beetle upper jaw is approximately 154, 000 times the weight of the upper jaw. Here, we explore the macro and micro-structural characteristics of two stag beetle upper jaws and reveal the resulting differences in mechanical properties and enhancement mechanisms. At the macroscopic level, the elliptic and triangular cross-sections of the upper jaw of the two species of stag beetles have significant effects on the formation of cracks. The crack generated by the upper jaws with a triangular section grows slowly and deflects easily. At the microscopic level, the upper jaw of the two species is a chitin cross-layered structure, but the difference between the two adjacent fiber layers at 45° and 50° leads to different deflection paths of the cracks on the exoskeleton. The mechanical properties of the upper jaw of the two species of stag beetle were significantly different due to the interaction of macro-structure and micro-structure. In addition, a series of bionic samples with different cross-section geometries and different fiber cross angles were designed, and mechanical tests were carried out according to the macro-structure and micro-structure characteristics of the stag beetle upper jaw. The effects of cross-section geometry and fiber cross angle on the mechanical properties of bionic samples are compared and analyzed. This study provides new ideas for designing and optimizing highly loaded components in engineering. Statement of significanceThe upper jaw of the stag beetle is composed of a complex arrangement of chitin and protein fibers, providing both rigidity and flexibility. This structure is designed to withstand various mechanical stresses, including impacts and bending forces, encountered during its burrowing activities and interactions with its environment. The study of the upper jaw of the stag beetle can provide an efficient structural design for engineering components that are subjected to high loads. Understanding the relationship between structure and mechanical properties in the stag beetle upper jaw holds significant implications for biomimetic design and engineering.

Effects of Diel Oxygen Cycling and Benthic Macrofauna on Sediment Oxygen Demand

This field study examined how sediment macroinfauna change patterns of sediment oxygen demand (SOD) throughout a diel oxygen cycle. Sediments with a greater faunal presence would be expected to have greater overall SOD, and at night may alter their behavior and influence SOD depending on their response to low-oxygen stress. Dynamic faunal bioturbation or bioirrigation behavior would also result in corresponding variation in SOD values on short time scales. In situ flow-through benthic metabolism chambers were used to measure SOD at a high temporal resolution in discrete sediment patches. Sediments with more macroinfauna had greater average SOD over the diel cycle, consistent with previous studies. Where more macroinfauna were present, they drove greater SOD during nightly low oxygen, presumably by enhancing their burrowing and irrigation activities. SOD was also more variable on a sub-diel timescale in sediments with more macroinfauna. Sediment oxygen demand is dynamic and highly sensitive both temporally, on very short timescales, and spatially, in terms of resident fauna, and their interaction produces heretofore unaccounted complexity in patterns of SOD particularly in shallow coastal systems. Extrapolations of temporally and spatially limited SOD measurements to a system-wide scale that do not account for the short-term and spatially variable effects of fauna may produce imprecise and misleading estimates of this critical ecosystem function.

Grazing affects ecosystem traits by regulating plateau pika activities at the landscape scale

The mechanism underlying the effects of livestock grazing on grassland ecosystem traits has been greatly discussed. However, as a common small burrowing mammal on the Tibetan Plateau grasslands, the plateau pika's (Ochotona curzoniae) influence on alpine grassland ecosystem traits has rarely been investigated, especially beyond the plot scale. In this study, we flew an unmanned aerial vehicle (UAV) over a grassland landscape under grazing and nongrazing treatments. Mounted visible spectral remote sensing, in combination with field surveys, was utilized to explore how livestock and pika grazing modify grassland ecosystem traits at the landscape scale on the Tibetan Plateau (TP). Using object-oriented classification and partial least squares regression, we retrieved the pika burrow distribution and grassland ecosystem traits. Then, the relationships among livestock grazing, pika burrowing and ecosystem traits were evaluated. The results indicated that livestock grazing reduces the alpine meadow community height by 0.13 cm and the species number by 0.25 while increasing the vegetation coverage by 9.69 % and the aboveground biomass (AGB) by 10.07 g/m2. A lower statue grassland community with greater coverage caused by livestock grazing promotes pika burrowing. Pika burrow density increases 100/ha per 1.70 % increase in vegetation coverage, a 1.87 g/m2 increase in AGB or a 0.08 m decrease in community height. Under livestock grazing, both community structure and nutrients are more strongly associated with pika burrow density. The structural equation model demonstrated that livestock grazing regulates pika burrow density by moderating structural value and subsequently affecting nutritional value. Pika burrowing activity explains 40 % of the total variation in nutritional value. Our findings revealed an intrinsic linkage between mammal activities and alpine grassland ecosystems, which can provide guidelines for grassland management through pika population control by adjusting grazing intensity on the TP.

Drosophila immune cells transport oxygen through PPO2 protein phase transition

Insect respiration has long been thought to be solely dependent on an elaborate tracheal system without assistance from the circulatory system or immune cells1,2. Here we describe that Drosophila crystal cells—myeloid-like immune cells called haemocytes—control respiration by oxygenating Prophenoloxidase 2 (PPO2) proteins. Crystal cells direct the movement of haemocytes between the trachea of the larval body wall and the circulation to collect oxygen. Aided by copper and a neutral pH, oxygen is trapped in the crystalline structures of PPO2 in crystal cells. Conversely, PPO2 crystals can be dissolved when carbonic anhydrase lowers the intracellular pH and then reassembled into crystals in cellulo by adhering to the trachea. Physiologically, larvae lacking crystal cells or PPO2, or those expressing a copper-binding mutant of PPO2, display hypoxic responses under normoxic conditions and are susceptible to hypoxia. These hypoxic phenotypes can be rescued by hyperoxia, expression of arthropod haemocyanin or prevention of larval burrowing activity to expose their respiratory organs. Thus, we propose that insect immune cells collaborate with the tracheal system to reserve and transport oxygen through the phase transition of PPO2 crystals, facilitating internal oxygen homeostasis in a process that is comparable to vertebrate respiration.

Biphasic burrowing in Atlantic hagfish (Myxine limosa).

Myxine limosa is a burrowing species of hagfish that occurs in the western north Atlantic in areas with muddy substrate and at depths generally greater than 100 meters. Burrowing of M. limosa has been observed from submersibles, but little is known about the behavior of these animals within the substrate or the biomechanical mechanisms involved. Here we investigated burrowing in M. limosa by observing individuals as they burrowed through transparent gelatin. A photoelastic setup using crossed polarizers allowed us to visualize stress development in the gelatin as the hagfish moved through it. We found that M. limosa created U-shaped burrows in gelatin using a stereotyped, two-phase burrowing behavior. In the first ("Thrash") phase, hagfish drove their head and their anterior body into the substrate using vigorous sinusoidal swimming movements, with their head moving side-to-side. In the second ("Wriggle") phase, swimming movements ceased, with propulsion coming exclusively from the anterior, submerged portion of body. The Wriggle phase involved side-to-side head movements and movements of the submerged part of the body that resembled the "internal concertina" strategy used by caecilians and uropeltid snakes. The entire burrowing process took on average 7.6 minutes to complete and ended with the hagfish's head protruding from the substrate and the rest of its body generally concealed. Understanding the burrowing activities of hagfishes could lead to improved understanding of sediment turnover in marine benthic habitats, new insights into the reproductive behavior of hagfishes, or even inspiration for the design of burrowing robots.

Fate and partition of perfluoroalkyl acids (PFAAs) driven by particles in mangrove ecosystems: Mechanistic insights and environmental implications

A critical gap in understanding emerging pollutants in mangrove ecosystems should be addressed. Despite their ecological importance, the state of environmental quality in fragmented mangrove patches, especially emerging contaminants, remains largely uncharted. Our research presented an in-depth analysis of the distribution of perfluoroalkyl acids (PFAAs) across porewater, suspended particles, and sediment in these small, fragmented mangroves, revealing the mechanisms behind their distribution. The findings indicated that PFAA concentrations in sediments were generally lower than in suspended particles, except for C12–C14 perfluorinated carboxylic acids (PFCAs) and C4–C6 perfluorinated sulfonic acids (PFSAs). A comparison of contamination levels in different mangrove patches concurred with conventional water quality assessments and crab burrow surveys, showing that large artificially planted patches were less contaminated, while areas with intense human activity were more polluted. Notably, no significant differences were observed in the concentrations of long-chain PFAAs and PFCAs between patches (p > 0.1). Elevated crab burrowing activity and higher concentrations of perfluorobutanoic acid (PFBA) and perfluorohexane sulfonic acid (PFHxS) in suspended particles in low intertidal zones suggested that seafood, particularly crabs and shellfish, might be at risk of PFAA pollution. Rainfall-runoff was identified as the primary source of PFAA pollution in porewater and suspended particle systems in these areas. The transport of PFAAs and organic carbon in mangroves was influenced by the concentrations and properties of suspended particles. These insights were critical for developing targeted environmental management strategies to mitigate the impact of PFAAs and preserve the ecological integrity of mangrove ecosystems.

Can Hediste diversicolor Speed Up the Breakdown of Cigarette Butts in Marine Sediments?

Cigarette butts (CBs) are non-biodegradable harmful residues of synthetic origin and are widespread in marine environments around the world. Although environmental factors are often primarily responsible for the fragmentation of microplastics in the marine environment, biotic factors have recently been shown to be equally important in plastic debris. This study evaluates the role of the Hediste diversicolor polychaete in the fragmentation of CBs in the marine environment. Polychaetes were exposed to three concentrations of CB (0 (as the control), 0.25, and 1 butt L−1) at two different temperatures (15 °C and 23 °C) for 28 days. At each temperature, aquaria without polychaetes were used to study the effect of the burrowing activity of the polychaete on CB fragmentation. Toxicants analysed from exposed sediments increased their concentration in a dose-dependent manner to the CB concentration at a temperature of 15 °C but not at 23 °C. CBs did not directly decrease Hediste survival, but prolonged elevated temperatures increased the polychaetes’ susceptibility. The negative effects of CBs on burial success and burrowing behaviour could not be offset by the reduced start time caused by elevated temperatures. Regardless of temperature, both the weight loss and physical fragmentation of CBs buried in polychaete-contaminated sediments were significantly higher than those without Hediste, with no differences between the two concentrations tested. FTIR-ATR analysis used to evaluate CB degradation in relation to cellulose acetate decomposition showed a greater degradation of this compound in treatments with Hediste than in those without polychaetes (~2.75 times), but these differences were not significant. This study is a promising initial step for future research, as any factor that facilitates the fragmentation of this prevalent and hazardous waste must be carefully studied to extract the maximum benefit to help to reduce CBs in the marine environment.

Exposure to hull cleaning wastewater induces mortality through oxidative stress and cholinergic disturbance in the marine polychaete Perinereis aibuhitensis

While wastewater and paint particles discharged from the in-water cleaning process of ship hulls are consistently released into benthic ecosystems, their hazardous effects on non-target animals remain largely unclear. In this study, we provide evidence on acute harmful effects of hull cleaning wastewater in marine polychaete Perinereis aibuhitensis by analyzing physiological and biochemical parameters such as survival, burrowing activity, and oxidative status. Raw wastewater samples were collected during ship hull cleaning processes in the field. Two wastewater samples for the exposure experiment were prepared in the laboratory: 1) mechanically filtered in the in-water cleaning system (MF) and 2) additionally filtered with a 0.45 μm filter in the laboratory (LF). These wastewater samples contained high concentrations of metals (zinc and copper) and metal–based booster biocides (copper pyrithione and zinc pyrithione) compared to those analyzed in seawater. Polycheates were exposed to different concentrations of the two wastewater samples for 96 h. Higher mortality was observed in response to MF compared to LF–exposed polychaetes. Both wastewater samples dose-dependently decreased burrowing activity and AChE activity. Drastic oxidative stress was observed in response to the two wastewater samples. MDA levels were significantly increased by MF and LF samples. Significant GSH depletion was observed with MF exposure, while increased and decreased GSH contents were observed in LF-exposed polychaetes. Enzymatic activities of antioxidant components, catalase, superoxide dismutase, and glutathione S-transferase were significantly modulated by both wastewater samples. These results indicate that even filtered hull cleaning wastewater can have deleterious effects on the health status of polychaetes.

Consequences of plateau pika disturbance on plant-soil carbon and nitrogen in alpine meadows.

The presence of burrowing mammals can have extensive effects on plants and soils, creating bare soil patches in alpine meadows and potentially altering plant-soil carbon (C) and nitrogen (N). This study focuses on the plateau pika (Ochotona curzoniae) to examine the responses of plant-soil C and N to a small burrowing mammal from quadrat scale to plot scale. The density of active burrow entrances in disturbed plots was used as an indicator of the disturbance intensity of plateau pikas. The study found that the below-ground biomass (BGB) and its C and N, as well as soil C and N concentrations were significantly lower in bare soil areas than in vegetated areas and undisturbed plots. This shows that the quadrat scale limited the estimation of the C and N sequestration potential. Therefore, further research on the plot scale found that the disturbance by plateau pika significantly reduced plant biomass and BGB carbon stock. However, plateau pika did not affect soil C and N stocks or ecosystem C and N stocks. These findings suggest the bare soil patches formed by plateau pika caused plant and soil heterogeneity but had a trade-off effect on plant-soil C and N stocks at the plot scale. Nevertheless, moderate disturbance intensity increased the C and N sequestration potential in grassland ecosystems. These results provide a possible way to estimate how disturbance by small burrowing mammals affects C and N cycling in grassland ecosystems while accurately assessing the effects of small burrowing mammal densities on C and N in grassland ecosystems.

Abundance estimates of Gunnison's prairie dogs compared to the number of active burrows

AbstractReliable estimates of prairie dog (Cynomys spp.) population size and distribution are critical for assessing the status of prairie dogs and for selecting sites to reintroduce black‐footed ferrets (Mustela nigripes). The density of active prairie dog burrows has commonly been used as an index of prairie dog abundance. Indices derived from active burrow counts were developed for black‐tailed (C. ludovicianus) and white‐tailed (C. leucurus) prairie dogs, but their efficacy has not been evaluated for all prairie dog species and studies affirming their validity with robust abundance estimators are few. We indexed or estimated the abundance of Gunnison's prairie dogs (C. gunnisoni) in the Aubrey Valley, Arizona, USA, in 2006 at 2 different time periods using 4 different methods—maximum above ground counts (MAGC), minimum number known alive (MNKA), capture‐mark‐recapture (CMR), and mark‐resight—and compared these estimates to active burrow counts in 2005 and 2006. We found no positive relationship between active burrow counts and any abundance estimators. Mark‐resight estimates of abundance were greater than the MNKA and were positively correlated with both the MNKA (r2 = 0.30) and CMR estimates (r2 = 0.49). Both CMR estimates and MAGC were typically below the MNKA and therefore biased low. Our results indicated that more rigorous estimation methods may be necessary to accurately estimate prairie dog abundance and assess habitat quality for ferret conservation.

Occurrence and formation of clast-free circular depressions in the southern Namib Desert, Tsau ǁKhaeb (Sperrgebiet) National Park, Namibia

Circular depressions are concave, shallow depressions found on planar landscape surfaces in the southern Namib Desert. They occur on gravelly substrates with nearly level to very slightly inclined surfaces. The depressions range from 6 to 10 m in diameter with centers typically depressed 10–20 cm below the level of the surrounding terrain. Locations of individual circular depressions were mapped at one site using ground-based measurements and at three additional sites using Google Earth imagery. At all sites, circular depressions are highly overdispersed with densities ranging from approximately 10–20/ha and corresponding nearest neighbor distances of 17–24 m. Large fragments of weathered calcrete and stones occur on soil surfaces surrounding circular depressions, but not within the depressions. Circular depressions at one site contained active burrow systems of Brants’ whistling rat ( Paratomys brantsii). Bioturbation by these rodents contributes to the non-cohesive nature of the sandy substrate, which promotes aeolian deflation and formation of the depressions. Excavations of the burrow systems by the honey badger ( Mellivora capensis) in search of rodent prey can transfer large stones and calcrete fragments from the subsurface to the surface and subsequently move those materials about the surface. Even if such sequential, horizontal displacements are in random directions, such movements can eventually yield a central, clast-free area surrounded by a peripheral zone where the clasts accumulate once they have been displaced beyond the margin of the area to which the predator is drawn in search of rodent prey. A conceptual model consisting of a two-dimensional random walk of large clasts about the surface until they are displaced from the focal “arena” of rodent occupation provides a novel explanation for origin of a spatially organized pattern that is initiated through the random displacement of those materials. Comparable microtopographic patterning associated with bioturbation in other arid and semi-arid environments may have similar origins.

Earthworms and plants can decrease soil greenhouse gas emissions by modulating soil moisture fluctuations and soil macroporosity in a mesocosm experiment.

Earthworms can stimulate microbial activity and hence greenhouse gas (GHG) emissions from soils. However, the extent of this effect in the presence of plants and soil moisture fluctuations, which are influenced by earthworm burrowing activity, remains uncertain. Here, we report the effects of earthworms (without, anecic, endogeic, both) and plants (with, without) on GHG (CO2, N2O) emissions in a 3-month greenhouse mesocosm experiment simulating a simplified agricultural context. The mesocosms allowed for water drainage at the bottom to account for the earthworm engineering effect on water flow during two drying-wetting cycles. N2O cumulative emissions were 34.6% and 44.8% lower when both earthworm species and only endogeic species were present, respectively, and 19.8% lower in the presence of plants. The presence of the endogeic species alone or in combination with the anecic species slightly reduced CO2 emissions by 5.9% and 11.4%, respectively, and the presence of plants increased emissions by 6%. Earthworms, plants and soil water content interactively affected weekly N2O emissions, an effect controlled by increased soil dryness due to drainage via earthworm burrows and mesocosm evapotranspiration. Soil macroporosity (measured by X-ray tomography) was affected by earthworm species-specific burrowing activity. Both GHG emissions decreased with topsoil macropore volume, presumably due to reduced moisture and microbial activity. N2O emissions decreased with macropore volume in the deepest layer, likely due to the presence of fewer anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions, and endogeic earthworms may even reduce N2O emissions.

Initial observations of the impacts of infauna on portable free fall penetrometer measurements in sandy parts of Mobile Bay

The seabed surface provides habitat for abundant and diverse fauna, whose burrowing activities have been shown to modify geotechnical properties of surface sediments. Whether these impacts affect geotechnical properties on larger scales of traditional measurements has not been well studied. This study represents an initial attempt to assess whether infaunal activity affects seabed properties on a scale relevant for, and therefore, detectable in portable free fall penetrometer measurements. Specifically, we examine sediment strength profiles of the upper 10–70 cm of sandy (poorly graded sand and muddy sand) seabed sediments in Mobile Bay, Alabama, USA, hypothesizing that infauna create heterogeneity in sediment structure that would lead to variability in PFFP vertical profiles as well as among replicate measurements at a site. Sediments were composed predominantly of sands, with only 17% of the sites featuring sand contents < 97% and median grain sizes ranging from 0.0987 to 0.3457 mm. Sediment strength generally decreased with a decreasing sand content, but variability was not explained by sand content alone. PFFP impacts in sandier sites (> 97% sand) were limited to the surface few cm, but considerable vertical and spatial variability in muddy sands and lower strength at sites with abundant burrowing infauna suggest that infaunal activities may affect PFFP measurements in these sediments.