Direct Competition For Resources Research Articles

Darwin review: the evolution of virulence in human pathogens.

By definition, all pathogens cause some level of harm to their hosts. If this harm occurs while the pathogen is transmitting, it can negatively affect the pathogen's fitness by shortening the duration over which transmission can occur. However, many of the factors that increase virulence (i.e. harm to host) also promote transmission, driving the pathogen population towards an optimal state of intermediate virulence. A wider spectrum of virulence may be maintained among pathogen populations which are structured into multiple discrete strains though direct resource and immune-mediated competition. These various evolutionary outcomes, and the effects of medical and public health interventions, are best understood within a framework that recognizes the complex relationship between transmission and virulence in the context of the antigenic diversity of the pathogen population.

Implications of weakening of the United States Geological Survey Pesticide National Synthesis Project for Weed Scientists

Abstract Weeds are a significant threat to the production of agronomic, horticultural, and ornamental crops, as direct competition for resources can result in substantial yield shortfalls (WSSA 2023). A review of research data generated across the United States and Canada indicated that unmanaged weeds have the potential to reduce corn and soybean production by approximately 50%, even when other best management practices are applied (Soltani et al. 2016, 2017). The associated economic losses, which were estimated at 26.7 and 17.2 billion USD for corn and soybeans, respectively, would be catastrophic. Weeds can also interfere with crops, indirectly. For example, weeds may impede or delay harvest operations (Smith et al. 2000), reduce crop quality because of contamination (Moore et al. 2004), and serve as alternate hosts for pests and pathogens (Chen et al. 2011; Wisler and Norris 2005). Other habitats, such as rangelands, wetlands, and other natural and urban areas, are also affected by weedy and invasive plant species. Impacts of unwanted vegetation can include damage to infrastructure, damage to recreational space, altered water flow, degraded natural resources, reduced biodiversity and species displacement, and a loss of ecosystem services, among other effects (DiTomaso 2000; Jetter et al. 2021; Neal 2023; Vilà et al. 2011).

Knowledge of Cover Crop Seed Traits and Treatments to Enhance Weed Suppression: A Narrative Review

Cover crops, as either a living plant or mulch, can suppress weeds by reducing weed germination, emergence and growth, either through direct competition for resources, allelopathy, or by providing a physical barrier to emergence. Farmers implementing conservation agriculture, organic farming, or agroecological principles are increasingly adopting cover crops as part of their farming strategy. However, cover crop adoption remains limited by poor and/or unstable establishment in dry conditions, the weediness of cover crop volunteers as subsequent cash crops, and seed costs. This study is the first to review the scientific literature on seed traits of cover crops to identify the key biotic and abiotic factors influencing germination and early establishment (density, biomass, cover). Knowledge about seed traits would be helpful in choosing suitable cover crop species and/or mixtures adapted to specific environments. Such information is crucial to improve cover crops’ establishment and growth and the provision of ecosystem services, while allowing farmers to save seeds and therefore money. We discuss how to improve cover crop establishment by seed priming and coating, and appropriate seed sowing patterns and depth. Here, three cover crop families, namely, Poaceae, Brassicaceae, and Fabaceae, were examined in terms of seed traits and response to environmental conditions. The review showed that seed traits related to germination are crucial as they affect the germination timing and establishment of the cover crop, and consequently soil coverage uniformity, factors that directly relate to their suppressive effect on weeds. Poaceae and Brassicaceae exhibit a higher germination percentage than Fabaceae under water deficit conditions. The seed dormancy of some Fabaceae species/cultivars limits their agricultural use as cover crops because the domestication of some wild ecotypes is not complete. Understanding the genetic and environmental regulation of seed dormancy is necessary. The appropriate selection of cover crop cultivars is crucial to improve cover crop establishment and provide multiple ecosystem services, including weed suppression, particularly in a climate change context.

Weed-induced crop yield loss: a new paradigm and new challenges.

Direct competition for resources is generally considered the primary mechanism for weed-induced yield loss. A re-evaluation of physiological evidence suggests weeds initially impact crop growth and development through resource-independent interference. We suggest weed perception by crops induce a shift in crop development, before resources become limited, which ultimately reduce crop yield, even if weeds are subsequently removed. We present the mechanisms by which crops perceive and respond to weeds and discuss the technologies used to identify these mechanisms. These data lead to a fundamental paradigm shift in our understanding of how weeds reduce crop yield and suggest new research directions and opportunities to manipulate or engineer crops and cropping systems to reduce weed-induced yield losses.

Solanum carolinense L.

<i>Solanum carolinense</i> L.

Singleplex, multiplex and pooled sample real-time RT-PCR assays for detection of SARS-CoV-2 in an occupational medicine setting

For workplaces which cannot operate as telework or remotely, there is a critical need for routine occupational SARS-CoV-2 diagnostic testing. Although diagnostic tests including the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel (CDC Diagnostic Panel) (EUA200001) were made available early in the pandemic, resource scarcity and high demand for reagents and equipment necessitated priority of symptomatic patients. There is a clearly defined need for flexible testing methodologies and strategies with rapid turnaround of results for (1) symptomatic, (2) asymptomatic with high-risk exposures and (3) asymptomatic populations without preexisting conditions for routine screening to address the needs of an on-site work force. We developed a distinct SARS-CoV-2 diagnostic assay based on the original CDC Diagnostic Panel (EUA200001), yet, with minimum overlap for currently employed reagents to eliminate direct competition for limited resources. As the pandemic progressed with testing loads increasing, we modified the assay to include 5-sample pooling and amplicon target multiplexing. Analytical sensitivity of the pooled and multiplexed assays was rigorously tested with contrived positive samples in realistic patient backgrounds. Assay performance was determined with clinical samples previously assessed with an FDA authorized assay. Throughout the pandemic we successfully tested symptomatic, known contact and travelers within our occupational population with a ~ 24–48-h turnaround time to limit the spread of COVID-19 in the workplace. Our singleplex assay had a detection limit of 31.25 copies per reaction. The three-color multiplexed assay maintained similar sensitivity to the singleplex assay, while tripling the throughput. The pooling assay further increased the throughput to five-fold the singleplex assay, albeit with a subtle loss of sensitivity. We subsequently developed a hybrid ‘multiplex-pooled’ strategy to testing to address the need for both rapid analysis of samples from personnel at high risk of COVID infection and routine screening. Herein, our SARS-CoV-2 assays specifically address the needs of occupational healthcare for both rapid analysis of personnel at high-risk of infection and routine screening that is essential for controlling COVID-19 disease transmission. In addition to SARS-CoV-2 and COVID-19, this work demonstrates successful flexible assays developments and deployments with implications for emerging highly transmissible diseases and future pandemics.

Low resource availability drives feeding niche partitioning between wild bees and honeybees in a European city.

Cities are socioecological systems that filter and select species, therefore establishing unique species assemblages and biotic interactions. Urban ecosystems can host richer wild bee communities than highly intensified agricultural areas, specifically in resource-rich urban green spaces such as allotments and family gardens. At the same time, urban beekeeping has boomed in many European cities, raising concerns that the fast addition of a large number of managed bees could deplete the existing floral resources, triggering competition between wild bees and honeybees. Here, we studied the interplay between resource availability and the number of honeybees at local and landscape scales and how this relationship influences wild bee diversity. We collected wild bees and honeybees in a pollination experiment using four standardized plant species with distinct floral morphologies. We performed the experiment in 23 urban gardens in the city of Zurich (Switzerland), distributed along gradients of urban and local management intensity, and measured functional traits related to resource use. At each site, we quantified the feeding niche partitioning (calculated as the average distance in the multidimensional trait space) between the wild bee community and the honeybee population. Using multilevel structural equation models (SEM), we tested direct and indirect effects of resource availability, urban beekeeping, and wild bees on the community feeding niche partitioning. We found an increase in feeding niche partitioning with increasing wild bee species richness. Moreover, feeding niche partitioning tended to increase in experimental sites with lower resource availability at the landscape scale, which had lower abundances of honeybees. However, beekeeping intensity at the local and landscape scales did not directly influence community feeding niche partitioning or wild bee species richness. In addition, wild bee species richness was positively influenced by local resource availability, whereas local honeybee abundance was positively affected by landscape resource availability. Overall, these results suggest that direct competition for resources was not a main driver of the wild bee community. Due to the key role of resource availability in maintaining a diverse bee community, our study encourages cities to monitor floral resources to better manage urban beekeeping and help support urban pollinators.

Phytoplankton community structuring in the absence of resource-based competitive exclusion.

Under most natural marine conditions, phytoplankton cells suspended in the water column are too distantly spaced for direct competition for resources (i.e., overlapping cell boundary layers) to be a routine occurrence. Accordingly, resource-based competitive exclusion should be rare. In contrast, contemporary ecosystem models typically predict an exclusion of larger phytoplankton size classes under low-nutrient conditions, an outcome interpreted as reflecting the competitive advantage of small cells having much higher nutrient ‘affinities’ than larger cells. Here, we develop mechanistically-focused expressions for steady-state, nutrient-limited phytoplankton growth that are consistent with the discrete, distantly-spaced cells of natural populations. These expressions, when encompassed in a phytoplankton-zooplankton model, yield sustained diversity across all size classes over the full range in nutrient concentrations observed in the ocean. In other words, our model does not exhibit resource-based competitive exclusion between size classes previously associated with size-dependent differences in nutrient ‘affinities’.

Livestock displace European mouflon from optimal foraging sites

The conflict between free-ranging livestock and wildlife is a serious conservation concern across rural communities worldwide. Livestock may affect wild herbivores via direct competition for resources due to spatial and diet overlap or via behavioural interference. It is imperative that we disentangle the effects of livestock on wildlife behaviour to obtain an empirical basis able to stir management and conservation decisions. Here, we studied the effect of livestock presence on the habitat selection in a free-ranging European mouflon (Ovis aries musimon) population in Sardinia, where the species is under strict protection. We collected spatial data on mouflon and livestock during two consecutive years to investigate whether the mouflon selection of key feeding grassland sites was negatively impacted by the livestock presence. We found that mouflon preferably selected grassland, and its selection significantly increased when grass was of better quality (greener). We showed that livestock presence led to the displacement of mouflon from such preferred feeding sites, an effect clearly exacerbated by livestock proximity. We indeed found that the selection of grassland by mouflon dropped significantly when the distance between livestock and mouflon was below ~ 650 m, providing a useful management threshold indication. Livestock presence in close proximity displaced mouflon to sub-optimal habitat, and its effects may have negative impact on the population dynamic of this species which is already characterized by low female productivity within harsh Mediterranean environment. Our results give clear management indications aimed at better managing livestock grazing within natural areas to ultimately improve wildlife conservation.

New Technology Introduction Into an Existing Production Line Viewed From the Lens of a Sociotechnical Framework

Process changes, in manufacturing environments, can have a critical impact on the interface between social dynamics and technical systems if usability and performance are not factored into the project. Socio-technical frameworks allow us to analyze the introduction of new technology and the adaptation of social systems in manufacturing environments, where technological change is constant and is in direct competition for social, technical and capital resources within the organization. A case study method was chosen in an endeavor to collect, present, and analyze data that is being derived from the introduction of new machinery into an existing production line. The main overarching factor identified was organizational ‘fit’. This paper proposes that fit be used as a gauge for new technology introduction in existing production lines. If change can be designed and managed through a socio-technical framework, future expansion and intended improvements can be smoother and more effective.

Kin discrimination in allelopathy and consequences for agricultural weed control.

Among all biotic stress types (i.e. pathogens, pests and weeds), weeds have the largest potential for yield reduction (larger than the other two combined) (Oerke, 2006). Chemical control of weeds is coming under increasing pressure due to concerns about their health- and environmental impacts and increasing herbicide resistance of weeds. As a consequence there is an increased interest in ecological weed control, of which development of weed-suppressive crops can be an important part (Bastiaans, Paolini, & Baumann, 2008). In the current issue, Xu, Cheng, Kong, and Meiners (2021) for the first time, show that kin recognition (the ability of plants to distinguish genetically related individuals from strangers) can make rice plants more competitive against weeds potentially being a new strategy in ecological weed control. This article is protected by copyright. All rights reserved.

Plastic response to early shade avoidance cues has season-long effect on Beta vulgaris growth and development.

Early‐emerging weeds are known to negatively affect crop growth but the mechanisms by which weeds reduce crop yield are not fully understood. In a 4‐year study, we evaluated the effect of duration of weed‐reflected light on sugar beet (Beta vulgaris L.) growth and development. The study included an early‐season weed removal series and a late‐season weed addition series of treatments arranged in a randomized complete block, and the study design minimized direct resource competition. If weeds were present from emergence until the two true‐leaf sugar beet stage, sugar beet leaf area was reduced 22%, leaf biomass reduced 25%, and root biomass reduced 32% compared to sugar beet grown season‐long without surrounding weeds. Leaf area, leaf biomass, and root biomass was similar whether weeds were removed at the two true‐leaf stage (approximately 330 GDD after planting) or allowed to remain until sugar beet harvest (approximately 1,240 GDD after planting). Adding weeds at the two true‐leaf stage and leaving them until harvest (~1,240 GDD) reduced sugar beet leaf and root biomass by 18% and 23%, respectively. This work suggests sugar beet responds early and near‐irreversibly to weed presence and has implications for crop management genetic improvement.

Invasion drives plant diversity loss through competition and ecosystem modification

Abstract Although invasive plants increasingly contribute to the current biodiversity crisis, the mechanisms through which they impact native communities are still poorly understood. Community ecology theory has emphasized direct competitive displacement over common resources, but invasion‐driven ecosystem modifications, such as altered soil pH, might also have consequences for plant diversity. However, the relative importance of ecosystem modification compared to direct resource competition has rarely been tested. Here we studied the invasive vine Vincetoxicum rossicum across invaded meadows in southern Ontario, Canada. In each meadow site, we quantified: (a) the strength of impact on the resident plant community, (b) the potential for competition with resident species (as the degree of niche dissimilarity and competitive superiority to the residents based on their functional traits) and (c) the amount of ecosystem modification related to invasion. We found that impacts on plant biodiversity were more negative where the invader had greater potential to competitively displace species (because it had a similar niche as the residents or was competitively superior), but also where it strongly altered soil N pools, moisture and pH. Synthesis. Our case study suggests that while competition is undoubtedly an important driver of invasion impact, ecosystem modifications can have cascading effects on plant communities, thereby magnifying the impacts of biological invasions.

Phytoplankton community structuring and succession in a competition-neutral resource landscape

Phytoplankton community composition and succession affect aquatic food webs and biogeochemistry. Resource competition is commonly viewed as an important governing factor for community structuring and this perception is imbedded in modern ecosystem models. Quantitative consideration of the physical spacing between phytoplankton cells, however, suggests that direct competition for growth-limiting resources is uncommon. Here we describe how phytoplankton size distributions and temporal successions are compatible with a competition-neutral resource landscape. Consideration of phytoplankton-herbivore interactions with proportional feeding size ranges yields small-cell dominated size distributions consistent with observations for stable aquatic environments, whereas predator–prey temporal lags and blooming physiologies shift this distribution to larger mean cell sizes in temporally dynamic environments. We propose a conceptual mandala for understanding phytoplankton community composition where species successional series are initiated by environmental disturbance, guided by the magnitude of these disturbances and nutrient stoichiometry, and terminated with the return toward a ‘stable solution’. Our conceptual mandala provides a framework for interpreting and modeling the environmental structuring of natural phytoplankton populations.

Yield Losses Due to Weeds, Critical Period for Weed-crop Competition in Fenugreek (Trigonella foenum-graecum L.)

Background: Weed populations reduce crop yields by influencing the pattern of crop growth and development throughout the season and by directly competing with the crop for limiting precious resources, like light, water or nutrients. A number of the factors that influence magnitude of crop yield losses from weed interference include the timing of weed emergence relative to the crop, weed density, pattern of weed growth and development. Weed management is one among the foremost critical factors influencing crop yield. By providing a window of weed-free growth early within the season, the size advantage that crop seedlings have over weeds can be utilized to reduce the intensity of direct competition for resources at the stages of crop development when yield is being determined. Weeds are identified as a significance drawback since they create biotic stress in realizing the genetic yield potential of this valuable crop.Methods: A field experiment was carried out during the rabi season of 2010-11 to 2014-15 at ICAR- National Research Centre on Seed Spices, Ajmer, Rajasthan to estimate the yield losses because of weed infestation and to work out the critical period for weed control (CPWC) in fenugreek (Trigonella foenum-graecum L.). There were 14 treatments comprising of initial weedy periods of 15, 30, 45, 60, 75, 90 days after sowing (DAS) and weed free period upto 15, 30, 45, 60, 75, 90 DAS along with weedy till harvest (un-weeded check) and weed free till harvest (weed free check). The treatments were replicated three times in a randomized block design.Result: Maximum pod length (cm), number of pods/plant, number of seed/pod, test weight (g), seed yield (kg/ha), straw yield (kg/ha) and harvesting index (%) to the tune of 9.47, 41.2, 16.67, 12.60, 2297, 4954 and 31.73 were recorded at weed free throughout growth period. Weed infestation up to 30, 45, 60, 75, 90 DAS and weedy throughout growth period reduced the seed yield significantly to the magnitude of 567.3, 801.7, 913.3, 1253.3, 1393.7 and 1736.3 kg/ha. Yield losses in fenugreek increase from 2.95 kg/ha/day at 15 days weed infestation to 12.31 kg/ha/day at 135 days weed infestation. Maximum gross return (`104248/ha), net return (`67018/ha) were obtained at weed free throughout growth period with the B:C ratio 2.80 among the weed free treatments. The employment of response curves with weed free or weed competition period showed that seed yield of fenugreek were the highest with the field free from weeds throughout the growth period and the critical period of weed/fenugreek competition was 32 days after sowing and lies between 30-45 days after sowing. In regression approach for fenugreek seed yield and weed free or weed competition period the quadratic function was fitted to estimate the expected yields which had the high significant with the data recorded and have the highest values of R2. If we predict the seed yield losses based on the quadratic model for weed free period model, it declined from 42.04 at 0 DAS to 0.0% at 135 days. Similarly, weed infestation period model predicted the seed yield losses increased from 0.00 at 0 days weed infestation to 73.42% at 135 days. Critical period for weed competition in fenugreek was found to be 32 days after sowing. The CPWC is helpful for making decisions on the necessity for and timing of weed control.

Light Reflected from Different Plant Canopies Affected Beta vulgaris L. Growth and Development

Studies on crop response to light quality (red (R) to far-red (FR) light ratio) often recommend early weed removal to reduce the effects of shade avoidance responses on crop yield. However, it is unclear whether crops are able to distinguish reflected light quality of kin from that of nonkin. We evaluated the response of sugar beet (Beta vulgaris L.) to reflected FR light from sugar beet, common lambsquarters (Chenopodium album L.), Kentucky bluegrass (Poa pratensis L.), alfalfa (Medicago sativa L.), and bare soil (control) under outdoor conditions in 2016 and 2017. Treatments were completely randomized with 10 replications per treatment. The study methods ensured there was no direct resource competition. The reflected R:FR of plant species ranged from 0.06 (common lambsquarters) to 0.24 (sugar beet) compared to 0.7 for the bare soil. In 2016 and 2017, there were 2 to 4 more leaves in the sugar beet surrounded by soil compared to sugar beet surrounded by neighboring species. There was up to 47, 57, 43, and 23% reduction in sugar beet leaf area, shoot dry weight, root diameter, and root dry weight, respectively, due to reflected R:FR light from neighboring species. Sugar beet did not respond differently to reflected light quality of kin compared to nonkin.

Low spatial overlap between foraging shearwaters during the breeding season and industrial fisheries off the west coast of Portugal

Fisheries have impacted seabird populations worldwide, either via bycatch mortality or resource depletion. Understanding the overlap between seabird distributions and fisheries is an important element for bycatch risk assessment, though the drivers of variation in seabird-fishery overlap are not well understood for some seabird populations. Here, we quantified the spatial overlap between foraging Cory’s shearwaters Calonectris borealis during the breeding season and commercial fisheries operating within the Portuguese Exclusive Economic Zone. In addition, we evaluated whether overlap varied as a function of an individual’s boldness, sex or breeding stage. For this, we GPS tracked 361 foraging trips by 72 Cory's shearwaters nesting at Berlenga Island, Portugal, over 5 consecutive breeding seasons (2012-2016). Simultaneously, we used fishing effort data from Global Fishing Watch detailing the distribution of industrial fisheries within the temporal and spatial range of Cory's shearwater tracks. Although fishing vessels were present during 88.1% of foraging trips, Cory's shearwaters spent only on average 13.3% of the time foraging in the same areas as fisheries. Such low spatial overlap is likely driven by high prey availability near the colony and suggests low direct competition for resources. We also found variation in overlap with fisheries across the breeding period, with Cory's shearwaters spending approximately 11% more time foraging in the same areas as fixed gear and purse seine vessels during pre-laying than during chick-rearing. Surprisingly, no sex or boldness-related differences were found in the overlap with any fishing gear. Our findings have implications for understanding within population variation in the overlap between fisheries and seabirds and, in turn, bycatch risk.

Inter‐colony invasion between wild naked mole‐rat colonies

AbstractDespite published reports of inter‐colony aggression and invasion in the laboratory, direct aggressive competition for resources has not previously been considered as a driving force for the large colony size in naked mole‐rats (Heterocephalus glaber). We report evidence that wild colonies of naked mole‐rats invade neighbouring colonies and thus expand their territories. Furthermore, as has been observed in laboratory colonies, invading colonies may kidnap un‐weaned pups which can subsequently be incorporated into the workforce. This is convergent with the slave‐making ants and suggests that intergroup aggression between naked mole‐rat colonies may be a strong selective pressure for group living and extreme colony size.

At the Turn of the Tide: Space Use and Habitat Partitioning in Two Sympatric Shark Species Is Driven by Tidal Phase

Coexistence of ecologically similar species occupying the same geographic location (sympatry) poses questions regarding how their populations persist without leading to competitive exclusion. There is increasing evidence to show that micro-variations in habitat use may promote coexistence through minimising direct competition for space and resources. We used two sympatric marine predators that show high fidelity to a small, remote coral atoll as a model to investigate how temporally dynamic partitioning of space use may promote coexistence. Using novel methods (difference network analysis and dynamic space occupancy analysis), we revealed that even though blacktip reef sharks Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens both show focused use of the same atoll habitats, the spatio-temporal dynamics of their use was partitioned such that they only shared the same microhabitats 26% of the time. Moreover, the degree of overlap was strongly influenced by the tidal cycle, peaking at ~35% at higher tides as both species appear to target similar intertidal micro-habitats despite the increase in available space. Our work provides a rare example of how two marine predators with similar ecological roles and habitat preferences may coexist in the same place through dynamic segregation of habitat use in space and time, potentially reflecting adaptive behavioural traits for minimising interactions. The strong influence of small tidal variation on species habitat use and partitioning also raises concerns over how atoll ecosystem dynamics may be influenced by sea level rises that could alter tidal dynamics.

Interspecific interactions, movement patterns and habitat use in a diverse coastal shark assemblage

Sharks are a highly diverse predatory taxon and are regularly found in large, potentially competitive, assemblages. However, the mechanisms that enable long-term coexistence and factors that drive complementary movement are poorly understood. As interspecific interactions can have a large influence on survival and trophic linkages, research on shark assemblages could substantially increase our understanding of marine community dynamics. In this study, we used passive acoustic telemetry to compare the activity space size, spatial overlap and habitat use patterns of six co-occurring shark species from the same family in a tropical nearshore embayment. Our results indicated that all sizes of Rhizoprionodon taylori (a small-bodied, highly productive species) used significantly larger amounts of space (e.g., mean 95% KUD = 85.9 km2) than juveniles of large-bodied, less productive species (e.g., Carcharhinus amboinensis; 62.3 km2) that use nearshore areas as nursery areas. Most large, less productive species appeared risk averse by using less space, while the smaller more productive species took greater risk by roaming broadly. These movement strategies are likely a means of avoiding predation or gaining access to new or additional resources. Spatial overlap patterns varied substantially between species with overlap in core use areas ranging from 1.2 to 27.6%, but were consistent over time. Most species exhibited low spatial overlap, suggesting spatial partitioning to reduce interspecific competition. While a few species exhibited a high degree of spatial overlap (up to 60% of activity space extent), dietary diversity may reduce competition to support co-occurrence. These data suggest that complex interactions occur in communal nurseries in nearshore waters where species are in direct competition for resources at vulnerable life stages.