Low-productivity Environments Research Articles

Effect of an herbivorous subterranean rodent on vegetation in relation to primary productivity

AbstractSubterranean rodents modify the surrounding environment being classified, in some cases, as keystone species and/or ecosystem engineers. This role could be context‐dependent if the changes produced shift throughout the species distribution range and are stronger under certain environmental conditions. Our objective was to analyse whether the effect of Ctenomys mendocinus on vegetation cover is context‐dependent. Given that primary productivity may increase plants' ability to tolerate or compensate following herbivory, we hypothesize that the effect of C. mendocinus on vegetation cover will be context‐dependent along a primary productivity gradient, with smaller effects in highly productive environments and larger effects in less productive ones. We compared the effect of C. mendocinus on plant cover among four contrasting environments and found that it depended on primary productivity in a predictable manner. In low productivity environments, the rodent significantly reduces vegetation cover, while it has no discernible effect in highly productive ones. These findings suggest that the effect of C. mendocinus on plant cover depends on primary productivity level and highlights the importance of accounting for the underlying environmental factors that influence the intensity of C. mendocinus–plant interaction.

Long-term changes in herbivore community and vegetation impact of wild and domestic herbivores across Iceland

Changes in wild and domestic herbivore populations significantly impact extensive grazing systems, particularly in low productive environments, where increasing wild herbivore populations are perceived as a threat to farming. To assess the magnitude of these changes in Iceland, we compiled time series on herbivore populations from 1986 to 2020 and estimated changes in species densities, metabolic biomass, and consumption of plant biomass in improved lands and unimproved rangelands. We compared estimates of consumption rates to past and present net primary production. Overall, the herbivore community composition shifted from livestock to wildlife dominated. However, wild herbivores only contributed a small fraction (14%) of the total herbivore metabolic biomass and consumption (4–7%), and livestock dominated the overall herbivore biomass. These insights highlight the necessity of developing improved local integrated management for both wild and domestic herbivores where they coexist.

Assessment of Durum Wheat Cultivars’ Adaptability to Mediterranean Environments Using G × E Interaction Analysis

Aside from plant breeding and agricultural inputs, understanding and interpreting the Genotype × Environment (G × E) interaction has contributed significantly to the increase in wheat yield. In Central Macedonia, Greece, fifteen commercially important durum wheat cultivars and one landrace were tested in six cultivation environments classified into high- and low- productivity environments. This study aimed to identify the most productive and stable durum wheat genotypes across Mediterranean farming systems through a comparative examination of genotype plus genotype by environment (GGE) biplot alongside fifteen parametric and non-parametric stability models. In the organic (low productivity) environment, cultivar Zoi and the landrace Lemnos showed remarkable results, indicating a potential solution for biological agriculture. For the late-sowing (low productivity) environment, some widespread varieties such as Mexicali-81, Meridiano, and Maestrale had excellent performance, showing potential to overcome more adverse conditions during critical grain filling periods such as higher air temperature and deficient soil moisture, i.e., conditions that correlate with climate change. Evaluation of genotypes in all environments for a combination of high yield and stable production, showed that the best genotypes were G8 (Simeto), G2 (Canavaro), and G12 (Elpida). In the subgroup with the three high-productivity environments, G12 (Elpida), G8 (Simeto), and G6 (Mexicali-81) were the best genotypes, followed by G2 (Canavaro), while in the low-productivity subgroup, the G2 (Canavaro), G13 (Zoi) and G8 (Simeto) genotypes were the best.

Sediment Record of the Earliest Stage of the Evolution of Lake Kanozero (Sw Kola Peninsula): New Data for Regional Deglaciation Reconstructions and Relative Sea-Level Studies

The multi-proxy study of the lowermost part of the sediment sequence of Lake Kanozero (south-western part of the Kola Peninsula, ca. 53 m a.s.l.) revealed the evidences for marine waters penetration into the basin during the earliest stage of its evolution. The diatom analysis inferred the conditions of a large brackish-water basin. Sediments composition and very low organic content also supported large-basin and low-productivity environments. Based on the pollen study, this stage covers a cooling period preceding the Allerød (tentatively assigned to the Older Dryas) and the onset of the Allerød. Periglacial vegetation typical of the cold and dry climate prevailed in the area for the most of the period. The subsequent transition to the freshwater conditions inferred from the diatom study took place in the Allerød, according to the pollen data. Except for a minor decrease in the fine sand fraction, no other corresponding changes were observed in the sediment record suggesting no major shifts in sedimentary environments. In the late Allerød and throughout the Younger Dryas, Lake Kanozero remained a large, low-productive freshwater basin. Our results indicate that ice-free conditions with aquatic sedimentation in the Kanozero depression had already existed in the Older Dryas. This assumes earlier deglaciation of the study area than it was previously thought. The study also suggests that brackish conditions in the White Sea basin established earlier than reported before. While the previous studies found no signals of marine transgression above ca. 41 m a.s.l., our results indicate that the local marine limit in the study area exceeds ca. 53 m a.s.l.

Small particles and heterotrophic protists support the mesopelagic zooplankton food web in the subarctic northeast Pacific Ocean

AbstractA quantitative understanding of the mesopelagic zooplankton food web is key to development of accurate carbon budgets and geochemical models in marine systems. Here we use compound specific nitrogen stable isotope analysis of amino acids to quantify the trophic structure of the microzooplankton and mesozooplankton community during summer in the subarctic northeast Pacific Ocean during the EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign. Source amino acid values in particles and zooplankton provide strong evidence that basal resources for the mesopelagic zooplankton food web were primarily small (), suspended or slow‐sinking particles, but that surface organic matter delivered by vertically migrating zooplankton may have also been important. Comparisons of values of source and trophic amino acids provide estimates of food web length, which decrease significantly with depth and suggest that protistan microzooplankton are key components of the food web from the surface to at least 500. These results emphasize the importance of small particles as a source of carbon and nitrogen to mesopelagic communities in this region, support observations of an inverse relationship between zooplankton vertical migration and small particles as sources of carbon to deep‐sea food webs in low productivity environments, and document the role of heterotrophic protists as key trophic intermediaries in the mesopelagic zone at this location.

Early postglacial hunter-gatherers show environmentally driven “false logistic” growth in a low productivity environment

Studies that employ probability distributions of radiocarbon dates to study past population size often use exponential increase in radiocarbon dates with time as a standard of comparison for detecting population fluctuations. We show that in the case of early postglacial interior Scandinavia, however, the summed probability distribution of radiocarbon dates has best fit with a S-shaped logistic growth curve. Despite the logistic growth model having solid grounding in ecological theory, we further argue that what our data indicate is not logistic growth in the population ecological sense but “false logistic” growth that mainly follows from climatic and environmental forcing. In the initial postglacial phase, 9500–7500 BCE, human settlement was located almost exclusively along the Scandinavian Atlantic coast and the use of the mountainous interior remained low. Thereafter the formation of separate inland adaptations resulted in population growth in tandem with increasing climatic warming and environmental productivity. Some millennia later, when environmental productivity started to decrease after the Holocene Thermal Maximum, hunter-gatherer population size in interior Scandinavia reached a plateau that lasted at least 2000 years. Lowering productivity prevented any population growth that would be detectable in the available archaeological record.

Changes in invertebrate food web structure between high- and low-productivity environments are driven by intermediate but not top-predator diet shifts.

Predator-prey interactions shape ecosystem stability and are influenced by changes in ecosystem productivity. However, because multiple biotic and abiotic drivers shape the trophic responses of predators to productivity, we often observe patterns, but not mechanisms, by which productivity drives food web structure. One way to capture mechanisms shaping trophic responses is to quantify trophic interactions among multiple trophic groups and by using complementary metrics of trophic ecology. In this study, we combine two diet-tracing methods: diet DNA and stable isotopes, for two trophic groups (top predators and intermediate predators) in both low- and high-productivity habitats to elucidate where in the food chain trophic structure shifts in response to changes in underlying ecosystem productivity. We demonstrate that while top predators show increases in isotopic trophic position (<i>δ</i>¹⁵N) with productivity, neither their isotopic niche size nor their DNA diet composition changes. Conversely, intermediate predators show clear turnover in DNA diet composition towards a more predatory prey base in high-productivity habitats. Taking this multi-trophic approach highlights how predator identity shapes responses in predator-prey interactions across environments with different underlying productivity, building predictive power for understanding the outcomes of ongoing anthropogenic change.

Application of Stochastic Frontier to Agriculture in Ethiopia

ABSTRACT Farming is more than just a job of Ethiopia’s smallholder farmers, who live in a low productivity environment. This study employed stochastic frontier approach agricultural efficiency in Ethiopia. Furthermore, Tobit model results show that loss due to wild animals had a negative impact on technical efficiency, while slope of the land and off-farm income had a positive impact. Regarding to the determinants of allocative efficiency, uses of mobile have positive impacts and the off-/non-farm income have negative impacts. In terms of economic efficiency determinants, land slope has a positive influence, while loss due to wild animals and off-farm income have a negative influence. According to the study findings, farmers in the study area kill wild animals, such as monkeys, pigs, and apes, because the loss of wild animals has a high impact on agricultural production during the pre-harvest season. Thus to increase efficiency of farmers and boosting agricultural output, Ethiopian governments policies and strategies should be directed toward providing tourism, construction of soil bunds, tree planting, planting grass, fencing and use of natural fertilizer to maintain the fertility of steep slopes, and supporting farmers by providing network facilities for mobile users that boost farmers’ maize productive efficiency.

Genomic evaluation of milk yield in a smallholder crossbred dairy production system in India

BackgroundIndia is the largest milk producer globally, with the largest proportion of cattle milk production coming from smallholder farms with an average herd size of less than two milking cows. These cows are mainly undefined multi-generation crosses between exotic dairy breeds and indigenous Indian cattle, with no performance or pedigree recording. Therefore, implementing genetic improvement based on genetic evaluation has not yet been possible. We present the first results from a large smallholder performance recording program in India, using single nucleotide polymorphism (SNP) genotypes to estimate genetic parameters for monthly test-day (TD) milk records and to obtain and validate genomic estimated breeding values (GEBV).ResultsThe average TD milk yield under the high, medium, and low production environments were 9.64, 6.88, and 4.61 kg, respectively. In the high production environment, the usual profile of a lactation curve was evident, whereas it was less evident in low and medium production environments. There was a clear trend of an increasing milk yield with an increasing Holstein Friesian (HF) proportion in the high production environment, but no increase above intermediate grades in the medium and low production environments. Trends for Jersey were small but yield estimates had a higher standard error than HF. Heritability estimates for TD yield across the lactation ranged from 0.193 to 0.250, with an average of 0.230. The additive genetic correlations between TD yield at different times in lactation were high, ranging from 0.846 to 0.998. The accuracy of phenotypic validation of GEBV from the method that is believed to be the least biased was 0.420, which was very similar to the accuracy obtained from the average prediction error variance of the GEBV.ConclusionsThe results indicate strong potential for genomic selection to improve milk production of smallholder crossbred cows in India. The performance of cows with different breed compositions can be determined in different Indian environments, which makes it possible to provide better advice to smallholder farmers on optimum breed composition for their environment.

Generic Architecture for the Automatic Parametrization of Production Machine Assembly Programs

In a high-mix low volume production environment, time to market is a key factor. However, one bottleneck lies in the often times manual parametrization of machines for new or modified designs. A truly flexible manufacturing environment therefore requires a continuous data flow from the design stages to the shop floor. This paper presents a concept for the automated parameterization of machines at a large automotive plant. Therefore, this paper initially discusses the results of a stakeholder analysis. The stakeholders comprise of different departments related to the product design and manufacturing processes. The requirements resulting from the interviews conducted with the stakeholders are grouped and ordered by priority. Secondly a general architecture for the control interface is presented. It includes multiple submodules, which model the continuous data flow between the departments and the production systems. The first main step of the data flow is the transformation of the information which is presented in various styles depending on the source departments to structured and standardized data. Thereafter machine parameters are generated automatically by a submodule using the structured input data and inference rules. Finally, the architecture supports the automatic transfer of the machine readable output data to the assembly line. To test the architecture a prototype comprising of more than 100 robots in a live production environment is implemented. It allows for a continuous data flow from the design and productions planning department to the robots. This enables a flexible process control, which up to today has supported the fast roll out of more than 100 new product variants. In contrast to the conventional manual setup of the machines for operation, the prototype was able to show that the monetary and time expenditure could be reduced by 95 percent.

Carcasses attract invasive species and increase artificial nest predation in a desert environment

In addition to feeding on animal remains, many scavengers also function as predators. Carcasses may therefore affect local animal communities by attracting facultative scavengers and increasing predation risk for other species in the vicinity of the carcasses. This risk may be elevated in low productivity environments, especially where humans increase carcass production and where facultative scavengers include invasive species. In June and October 2018, we monitored experimentally placed red kangaroo (Osphranter rufus) carcasses and artificial bird nests in two different habitats in the Simpson Desert, Australia, to identify the nest predators attracted to the carcasses, and to determine how carcasses affect overall and predator-specific nest predation. We modelled our nests to approximate those of the ground nesting little buttonquail (Turnix velox) and the endangered night parrot (Pezoporus occidentalis). Native Corvus spp. and then invasive red foxes (Vulpes vulpes) were the top carcass visitors and nest egg predators. Carcass presence and open habitat increased overall nest predation and fewer artificial parrot nest eggs were depredated compared to those of quail. Open habitat and carcass presence only increased predator-specific nest predation by foxes, but corvid nest predation was highest in June 2018, and for the artificial quail nest types. Foxes were the main predator of eggs from night parrot nests. Our study shows that carcass provisioning by humans may have indirect, deleterious effects on ground nesting birds, and indicates that foxes might pose a greater threat to night parrot populations than previously recognised.

Larval quality and fecundity trade-offs are linked to the maternal environment in sea perch (Helicolenus percoides, Sebastidae)

Spatial differences in demographics and nutrition can result in variations in reproductive output and larval quality among marine subpopulations. We investigated how local differences in maternal provisioning influenced the quality and quantity of larvae in sea perch (Helicolenus percoides, Sebastidae), a long-lived, viviparous species, widely distributed around New Zealand, in order to determine how local differences in maternal provisioning influenced the quality and quantity of larvae. Subpopulations from Deep Cove within Fiordland, on the west coast, and the Otago shelf on the east coast of New Zealand's South Island were compared. We used fatty acid analysis of adult liver and gonad tissues to investigate potential spatial differences in maternal nutrition. Fatty acid analysis of larvae on the day of parturition, larval notochord length and oil globule volume on the day of parturition, change in length of cohorts of larvae and change in average size of the oil globule were used as proxies to establish differences in larval quality between the Deep Cove and Otago shelf subpopulations. Our results demonstrated a trade-off between fecundity and oil globule size, where sea perch from the Otago shelf were more fecund but provisioned their larvae with smaller oil globules than females from Deep Cove. We observed faster change in length and slower rates of change in size of the oil globule among cohorts of larvae produced by females from Deep Cove. The maternally provisioned concentrations of the key fatty acids docosahexaenoic acid (DHA) and arachidonic acid (ARA) were higher, and the eicosapentaenoic acid (EPA)/ARA ratio was lower among larvae produced by females from Deep Cove. The results indicated that potential visual and osmoregulatory advantages linked to these fatty acids are passed on to the offspring, necessary to survive in the low-light, low productivity environment of the inner fjords, characterised by high freshwater inputs. The results of the present study highlight the important link between the maternal environment and the quality and fitness of fish larvae.

Data driven automatic parameter inference for robotic assembly programs

In a high-mix low volume production environment, time to market is a key factor. However, one bottleneck lies in the often times manual parametrization of machines for new or modified designs. A truly flexible manufacturing environment therefore requires a continuous data flow from the design stages to the shop floor. This paper presents a concept for the automated parameterization of machines at a large automotive plant. It describes the interface requirements of the stakeholders involved as well as the overall system architecture. Finally, the paper presents first results of a prototype tested in serial production, spanning more than 100 machines.

Water quality and spatial and seasonal dynamics in the largest water supply reservoir in Brazil and implications for diatom assemblages

Abstract: Aim in this paper we investigated how spatial factors and seasonal dynamics influenced the diatom community in a tropical deep environment of low productivity waters in Brazil. Methods we used physical and chemical characteristics of the water and planktonic diatoms from 9 sampling stations during dry (austral winter) and wet (austral summer) seasons (N = 18) as the outline to identify water quality, spatial and seasonal patterns. To evaluate spatially and temporally integrated events from the recent past (approximately the last 5 years before sampling), and the species from diverse habitats of the system, we used diatoms from the surface sediment (top 2 cm, N = 9). Since we used the top 2 cm of surface sediment containing the dead diatoms that were deposited over recent past of the reservoir, seasonal sampling of the sediment was not needed. Results during the dry season heavily silicified long colonial planktonic diatom species associated mainly with higher mixing depth, pH, and transparency dominated the plankton, whereas in the wet season the reservoir became stratified, favoring planktonic solitary diatoms with high surface volume ratios. For the sediment, a general pattern emerged where planktonic species dominated in the deep sections of the reservoir, and the abundance of benthic species in shallow areas near the tributaries increased. Conclusions the diatom assemblages was mainly influenced by seasonal variations and mixing regime. Surface sediment samples provided longer-term information, and revealed habitat differentiation shaping diatom assemblages. Overall, the small centric planktonic Aulacoseira tenella (Nygaard) Simonsen stood out as the most abundant species in the entire reservoir in both, the plankton and the sediment, indicating that size and shape serve as adaptive strategies for buoyancy and nutrient uptake stand as a competitive advantage in deep low productivity environments.

Some like it hot, hungry tunas do not! Implications of temperature and plankton food web dynamics on growth and diet of tropical tuna larvae

Abstract Restricted to low-productivity environments near their thermal maxima, larval tunas may be threatened by warming global temperatures, yet our understanding of how they are constrained is limited. We examined blackfin tuna (Thunnus atlanticus, presumptive) diet and growth in the context of their prey and predators in the Straits of Florida in 2 years with contrasting summer conditions: low temperature (26.7–28.3°C)–high prey and high temperature (28.4–29.0°C)–low prey. In the cooler, high-prey conditions, larvae had 30% faster growth (0.45 mm d−1), fuller guts from predominantly feeding on calanoid copepods, and were 10× more abundant, dominating the larval fish assemblage. In contrast, in warm, low-prey conditions fewer, younger, and slower-growing (0.35 mm d−1) T. atlanticus fed predominantly on nauplii and had less full guts. Modelling individual growth across years revealed that growth peaked at an optimum of 28.5°C (5°C below known thermal maxima in the field) and high densities of predators selectively consumed slower-growing larvae. Low-prey availability may reduce the thermal optima of larvae, as growth and survival are diminished when low prey and high temperature coincide. Our results illustrate the importance of considering food web dynamics with temperature when predicting the response of organisms to ecosystem variability, particularly ongoing climate change.

Small mammal assemblage in beaver-modified habitats

One of the less studied positive interactions among organisms is facilitation. Facilitation may have significant impact on diversity of species especially in low productive environments. We studied the effects of well-known facilitator and ecosystem engineer, the North American beaver (Castor canadensis), on small mammal assemblages in the boreal zone. The small mammals, namely voles, mice, and shrews, were trapped over 2 years in ten beaver-modified habitats and in ten control sites. Contrary to our expectations, we did not observe any differences between species or individual numbers between beaver-modified and control sites. However, there were differences in species composition between sites; grass-eating field voles (Microtus agrestis) and invertebrate-eating shrews (Sorex araneus, Neomys fodiens) tended to be more common in beaver sites while forest-dwelling wood lemmings (Myopus schisticolor) and yellow-necked mice (Apodemus flavicollis) were only captured in control sites. The most common species in both habitats was the bank vole (Myodes glareolus), which is a generalist in its habitat requirements. The bank vole’s population structures were similar between the two habitat types. The actions of beavers in water bodies within boreal forests seem to have no effect on the small mammal diversity and their numbers at the regional scale but may have positive effect on them at the larger landscape level as beavers are increasing the overall habitat diversity in the landscape.

The global ecology of human population density and interpreting changes in paleo-population density

Explaining variation in human population density constitutes a basic research problem in human ecology and archaeological science. To contribute to this basic research problem, we build a graphic model and conduct a global analysis of the effects of ecological variables, controlling for technological differences, on human population density. Our results indicate that human population density displays a consistent relationship with ecological variables across productive technologies. Human population density peaks in high productivity environments with moderate levels of species richness and moderate to low levels of pathogens among hunter-gatherer, subsistence agricultural, and industrial societies. Population density is lower in low productivity environments as well as environments with high productivity, high species richness and high pathogen loads. The productive technologies associated with agriculture and industrial production impact human population density more than ecological variables, and shifts toward agriculture or industrial production may weaken the effect of net primary productivity on population density. These results illustrate the nature of the relationship between population density and ecological variables, which are partly driven by climate, and the results provide a basis for hypotheses that researchers can use to analyze the potential effects of climate change on material record estimates of human paleo-population density.

Maize prolificacy: A source of reproductive plasticity that contributes to yield stability when plant population varies in drought-prone environments

Reproductive plasticity, the ability of the plant to maintain the ratio between available resources and grain yield should be a useful trait to maintain the coupling between yield and resource availability under low-density management strategies adopted in drought-prone areas. Prolificacy could be an indicator of hybrid reproductive plasticity. The objective of this study was to assess the reproductive plasticity of modern prolific and non-prolific hybrids and its effect on grain yield and yield components in a drought-prone environment. Current hybrids of contrasting prolificacy were tested in shallow soil under different plant densities (2 to 6 pl m–2). Crops explored low productivity environments (average 5930 kg ha–1) and yield response to plant density was different between prolificacy groups. At 4 pl m–2 yield was similar between prolific and non-prolific hybrid groups. Prolificacy determined an increase in reproductive plasticity that significantly reduced the yield response to plant density. When plant density was reduced to 2 pl m–2 yield was maintained for the prolific hybrids while it was reduced more than 25% for the non-prolific ones. The reproductive plasticity of prolific hybrids was associated with an increased capacity of adjusting kernel number to available resources per plant. On the other hand, the increased reproductive plasticity of prolific hybrids did not present detectable yield penalties when plants were grown under stressful conditions (6 pl m–2). The lack of response to plant density of prolific hybrids could be interpreted as a reduction in the yield penalty of low-density management strategies. The reduction in plant density increases the ability of the crop to tolerate drought stress and therefore should increases yield stability in drought-prone areas.

Longest terrestrial migrations and movements around the world

Long-distance terrestrial migrations are imperiled globally. We determined both round-trip migration distances (straight-line measurements between migratory end points) and total annual movement (sum of the distances between successive relocations over a year) for a suite of large mammals that had potential for long-distance movements to test which species displayed the longest of both. We found that caribou likely do exhibit the longest terrestrial migrations on the planet, but, over the course of a year, gray wolves move the most. Our results were consistent with the trophic-level based hypothesis that predators would move more than their prey. Herbivores in low productivity environments moved more than herbivores in more productive habitats. We also found that larger members of the same guild moved less than smaller members, supporting the ‘gastro-centric’ hypothesis. A better understanding of migration and movements of large mammals should aid in their conservation by helping delineate conservation area boundaries and determine priority corridors for protection to preserve connectivity. The magnitude of the migrations and movements we documented should also provide guidance on the scale of conservation efforts required and assist conservation planning across agency and even national boundaries.

Denitrification is the main microbial N loss pathway on the Qinghai-Tibet Plateau above an elevation of 5000 m

Soil nitrogen (N) deficiency is the major factor contributing to low primary productivity on the Qinghai-Tibet Plateau. However, most of our understanding of N cycling is still based on human disturbed environments, and the microbial mechanisms governing N loss in low primary productivity environment remain unclear. This study explores three microbial N loss pathways in eight wetland and dryland soil profiles from the Qinghai-Tibet Plateau, at an elevation of above 5000 m with little human activity, using 15N isotopic tracing slurry technology, quantitative PCR, and high-throughput sequencing. No denitrifying anaerobic methane oxidation was detected. Anammox occurred in two of the wetland (n = 4) and dryland (n = 4) soil profiles, while denitrification widely occurred and was the dominant N loss pathway in all samples. Where denitrification and anammox co-occurred, both abundance and activity were higher in wetland than in dryland soils and higher in surface than in subsurface soils. In comparison with non-anammox sites, nitrate levels initiate anammox-related N cycling. High-throughput sequencing and network analysis of nirK, nirS, nosZ, and hzsB gene communities showed that Bradyrhizobiaceae (a family of rhizobia) may play a dominant role in N loss pathways in this region. Given the geological evolution and relatively undisturbed habitat, these findings strongly suggest that denitrification is the dominant N loss pathway in terrestrial habitats of the Qing-Tibet Plateau with minimal anthropogenic activity.