Relative Resource Availability Research Articles

Eco-enzymatic stoichiometry and microbial non-homeostatic regulation depend on relative resource availability during litter decomposition

The relationships between soil eco-enzymatic stoichiometry and substrate stoichiometry could be used to explain nutrient cycling processes regulated by microbial biomass stoichiometry. But what are the relationships between the stoichiometry of resources, microorganisms, and enzymes? We do not have a clear understanding yet, particularly in the different stages of litter decomposition. By analyzing the response of extracellular enzymatic stoichiometry to the imbalance between microbial and substrate stoichiometry, we explore the microbial-mediated litter transformation and microbial adaptation mechanisms in the transformation interface soil (TIS) layer. The results showed that soil microbial metabolism was limited by C and P during decomposition, peaking in the transition (middle) stage and then gradually decreasing. According to the judgment of microbial homeostasis (effect of substrate stoichiometry on microbial biomass stoichiometry), the microbial communities shift from homeostatic in the early stage to non-homeostatic in the middle stage and then return to homeostasis in the later stage. During the litter decomposition, the non-homeostatic period corresponded to the transition stage. That means severe microbial metabolic limitation is a potential determinant of microbial homeostasis. Soil microorganisms adapt and alleviate microbial metabolic limitations by adjusting extracellular enzyme activity and microbial non-homeostatic behavior when the available resources fail to satisfy microbial requirements.

Seasonal variation in impact of non‐native species on tropical seed dispersal networks

Abstract Invasive non‐native species can alter animal‐mediated seed dispersal interactions and ultimately affect the stability of recipient communities. The degree of such disturbances, however, is highly variable and depends on several factors, two of which have received little attention: the relative timing of native and non‐native fruiting phenologies, and the associated variation in relative resource availability across the fruiting period. Both are likely to alter plant–seed disperser interactions threatened by biological invasions. Here we investigated the impact of plant invasions on the seasonal dynamics of frugivory and seed dispersal networks across a large‐scale experimental setup and a plant invasion gradient on a tropical island. We recorded fruit and frugivore abundances, and plant–frugivore interactions across eight inselbergs (i.e. rocky outcrops) with different levels of plant invasion during 10 months on the island of Mahé, Seychelles. By combining four sampling methods of plant–frugivore interactions we constructed quantitative seed dispersal networks at all sites across two 5‐month seasons: the on‐peak and off‐peak fruiting season. Our findings showed that, by fruiting mostly synchronously with natives, non‐native plants compete with natives for dispersal services, predominantly carried out by native frugivores. Variation in native seed dispersal was driven by plant invasion and seasonality. Specifically, native seed dispersal declined with the degree of invasion; dispersal frequency increased with fruit abundance more strongly during the off‐peak fruiting season; and networks became increasingly specialised during off‐peak. These results indicated that during the main fruiting peak seed dispersal services were saturated, which likely intensified the competition between native and non‐native fruits. When resources were scarce during off‐peak fruiting season, native and non‐native frugivores were more selective in their fruit choice at sites dominated by non‐native plants. We showed that native plant and frugivore populations and native seed dispersal interactions were more vulnerable in invaded plant communities, where non‐native plants compete with natives for dispersal services potentially reducing native recruitment. As invasive non‐native plants dominate many ecosystems world‐wide, particularly on islands, our findings showed that controlling plant invasions in vulnerable native communities can be critical to maintain native ecosystem functions and biodiversity. Read the free Plain Language Summary for this article on the Journal blog.

Site suitability modeling with culturally-specific variables: A southern Northwest Coast case study

Site suitability modeling in archaeology has numerous applications in both research and cultural resource management contexts. However, oftentimes these models are built on limited or abstracted variables which do not adequately account for the human decision-making process. This approach uses seven culturally-specific variables from the southern Northwest Coast in order to develop a model of site suitability for Indigenous settlement in southern Oregon. The results of this model are validated through comparison with the location of 201 archaeological sites. The choice of variables also provides sufficient detail for patterns to emerge in the relationship between site type and relative resource availability. This study therefore demonstrates both the accuracy of models produced via this approach and its utility as a research tool for investigating archaeological settlement patterns.

Breakdown of the ideal free distribution under conditions of severe and low competition

Under the ideal free distribution (IFD), the number of organisms competing for a resource at different sites is proportional to the resource distribution among sites. The ideal free distribution of competitors in a heterogeneous environment often predicts habitat matching, where the relative number of individuals using any two patches matches the relative availability of resources in those same two patches. If a resource is scarce, access might be restricted to individuals with high resource holding potential, resulting in deviation from the IFD. The distribution of animals may also deviate from the IFD in the case of resource abundance, when social attraction or preference for specific locations rather than competition may determine distribution. While it was originally developed to explain habitat choice, we apply the habitat matching rule to microscale foraging decisions. We show that chickens feeding from two nondepleting feeders distribute proportionally to feeder space under intermediate levels of competition. However, chicken distribution between the feeders deviates from the IFD when feeder space is limited and competition high. Further, despite decreasing aggression with increasing feeder space, deviation from IFD is also observed under an excess supply of feeder space, indicating different mechanisms responsible for deviations from the IFD. Besides demonstrating IFD sensitivity to competition, these findings highlight IFD’s potential as a biological basis for determining minimal resource requirements in animal housing.Significance statementThe ideal free distribution (IFD) predicts how animals ought to distribute themselves within a habitat in order to maximize their payoff. Recent studies, however, have questioned the validity of the IFD concept following anomalous results. We studied the IFD in chickens by systematically varying the amount and distribution of space at two feed troughs. We show that when tested over a sufficiently large range, the distribution of birds depends on the overall resource availability. Furthermore, behavioral data suggest that distinctly different mechanisms account for deviations from the IFD at shortage and excess supply of feeder space, respectively.

Between personalized and racialized precision medicine: A relative resources perspective

Since the completion of the first human genome sequencing project in 2003, the potential for incorporating genomics into clinical practice in the pursuit of precision medicine has garnered a great amount of attention and interest. Existing literature presents a dichotomous view of the future of medicine: either precision medicine will replace race-based medicine or race-based medicine will persist despite developments in genetic research and genomic medicine. Drawing on interview data with 46 physicians and scientists in the USA, Canada, and Singapore who are conducting research or practicing precision medicine in the context of cancer treatment and prevention, this article attempts to contribute to the existing debate by proposing a ‘relative resources’ perspective to explain which approach will dominate in a particular healthcare setting. The author elaborates on the ‘heterogeneity of resources’ and suggests that the extent to which precision medicine will be personalized or racialized/ethnicized in the clinic will most likely be a function of the relative availability of resources – including but not limited to financial, human and computer informatics, and legal and infrastructural resources – at individual and collective levels in healthcare contexts.

Post-fire debris flows delay recovery and create novel headwater stream macroinvertebrate communities

Wildfire is one of the most important global agents of disturbance affecting terrestrial and riparian vegetation. Post-fire vegetation changes can alter stream resource pathways and cause channel reorganization and sediment-laden debris flows. Yet, little is known about macroinvertebrate community recovery following wildfire and debris flows and how these communities fit into the broader stream community mosaic. We examined the effects of wildfire and debris flows on relative resource availability and macroinvertebrate assemblages at 31 streams in Idaho, USA using a space-for-time study design. Wildfire and debris flows had no apparent effects on resource standing crop. However, macroinvertebrate communities among unburned, burned, and debris flow streams were quite different. Compared to unburned streams, biomass and density were higher at streams which experienced debris flows ~ 10 years post fire, but exhibited the near-complete absence of macroinvertebrates at streams with more recent debris flows. Stream macroinvertebrate communities impacted by debris flows were distinct compared to unburned and burned streams which did not experience debris flows. When found, differences in macroinvertebrate biomass, density, richness, and community structures were largely due to the incidence of debris flows. Debris flows removed the riparian vegetation, slowing its recovery, cascading to affect macroinvertebrate community structure into the long term.

Multichannel feeding by spider functional groups is driven by feeding strategies and resource availability

Multichannel feeding, whereby consumers feed across resource channels such as upon herbivore and detritivore resources, acts to link discrete compartments of a food web with implications for ecosystem functioning and stability. Currently however, we have little understanding which feeding strategies of consumers underlie multichannel feeding. We therefore link spider functional group and resource density‐dependent or density‐independent feeding strategies to multichannel feeding by quantifying not only consumer diet, but also the relative availability of resources. Here we analysed herbivore (green) and detritivore (brown) prey use by spider communities in grasslands, and tested if available prey biomass proportions were linked to observed spider dietary proportions.Different spider functional groups each linked green and brown resource channels, but while green prey were always consumed in proportion to their relative biomass, brown prey were consumed independently of proportion by some functional groups. Additionally, we found greater intraguild predation by cursorial spiders when green resources were relatively scarcer, suggesting green prey was preferred, and needed to be compensated for when rare. Overall, we observed a stronger consumer connection to the green than brown resource channel, yet this green connection was more variable due to greater range in green resource availability across grasslands and density‐dependent consumption on green prey. Consequently, multichannel feeding by spiders was determined by density‐dependent and density‐independent feeding strategies that varied by spider functional group and across resources channels. Our results demonstrate that the role of multichannel feeding by spiders in linking separate food web compartments is a dynamic component of food web structure in these wild grasslands.

Mixotrophy and intraguild predation – dynamic consequences of shifts between food web motifs

Mixotrophy is ubiquitous in microbial communities of aquatic systems with many flagellates being able to use autotroph as well as heterotroph pathways for energy acquisition. The usage of one over the other pathway is associated with resource availability and the coupling of alternative pathways has strong implications for system stability. We investigated the impact of dominance of different energy pathways related to relative resource availability on system dynamics in the setting of a tritrophic food web motif. This motif consists of a mixotroph feeding on a purely autotroph species while competing for a shared resource. In addition, the autotroph can use an additional exclusive food source. By changing the relative abundance of shared vs. exclusive food source, we shift the food web motif from an intraguild predation motif to a food chain motif. We analyzed the dependence of system dynamics on absolute and relative resource availability. In general, the system exhibits a transition from stable to oscillatory dynamics with increasing nutrient availability. However, this transition occurs at a much lower nutrient level for the food chain in comparison to the intraguild predation motif. A similar transition is also observed with variations in the relative abundance of food sources for a range of nutrient levels. We expect this shift in food web motifs to occur frequently in microbial communities and therefore the results from our study are highly relevant for natural systems.

Think ratio! A stoichiometric view on biodiversity–ecosystem functioning research

Ecological stoichiometry (ES) has become one of the most pervasive theoretical frameworks in environmental sciences and biology in the last two decades. ES allows predicting processes on all organizational levels from subcellular structures to ecosystems by relating the elemental composition and demand of organisms to the relative availability of resources. However, ES has been rarely used to understand and predict the relationship between biodiversity and ecosystem functioning (BEF), although ES would be ideally suited as it makes predictions on both population processes underlying biodiversity as well as on matter transformations underlying ecosystem processes. Here, we propose to link the two fields of research on ES and BEF relationships and highlight a number of potential avenues for further research. First, we cast a stoichiometric view on drivers of biodiversity change. Second, we address the stoichiometric underpinning of biodiversity–productivity relationships. Third, we discuss potential interactions between stoichiometry and diversity in a food web context.

Stoichiometric regulation of phytoplankton toxins

Ecological Stoichiometry theory predicts that the production, elemental structure and cellular content of biomolecules should depend on the relative availability of resources and the elemental composition of their producer organism. We review the extent to which carbon- and nitrogen-rich phytoplankton toxins are regulated by nutrient limitation and cellular stoichiometry. Consistent with theory, we show that nitrogen limitation causes a reduction in the cellular quota of nitrogen-rich toxins, while phosphorus limitation causes an increase in the most nitrogen-rich paralytic shellfish poisoning toxin. In addition, we show that the cellular content of nitrogen-rich toxins increases with increasing cellular N : P ratios. Also consistent with theory, limitation by either nitrogen or phosphorus promotes the C-rich toxin cell quota or toxicity of phytoplankton cells. These observed relationships may assist in predicting and managing toxin-producing phytoplankton blooms. Such a stoichiometric regulation of toxins is likely not restricted to phytoplankton, and may well apply to carbon- and nitrogen-rich secondary metabolites produced by bacteria, fungi and plants.

Resources supporting the food web of a naturally productive lake

A Bayesian mixing model and stable isotopes of carbon, nitrogen, and hydrogen were used to evaluate the extent to which six consumers (three fishes, two zooplankton, and a snail) in a naturally productive lake used terrestrial resources, epilimnetic and metalimnetic phytoplankton, benthic algae, and macrophytes. Resource use varied with consumer habitat use and feeding ability, but allochthony was consistently low (averaging 15% among consumers). The pelagic invertebrates Skistodiaptomus oregonensis and Chaoborus spp. relied on phytoplankton from the epilimnion (59% and 49%, respectively) and to a lesser extent from the metalimnion (28% and 26%, respectively); terrestrial resources comprised 9% and 18% of the diet of these consumers, respectively. The snail Helisoma trivolvis relied mainly on littoral resources (floating‐leafed macrophytes; 68% of diet), but terrestrial resources also constituted a substantial portion of its diet (21%). The fishes integrated among habitats more evenly than the other consumers, but pelagic resources formed the largest portion of their diets (Pimephales promelas = 64%, Lepomis gibbosus = 47%, and Perca flavescens = 47%). L. gibbosus was the fish with the most allochthonous diet (23%). The consumers of this productive lake were not highly dependent on allochthonous materials and tended to rely most heavily on local resources, including macrophytes.

Cultural Influences on Intertemporal Reasoning: An Annotated Bibliography

Abstract : This bibliography was produced as part of an Office of Naval Research project titled Cultural Influences on Intertemporal Reasoning. The project is intended to provide a platform of knowledge based on existing research that will improve our ability to field useful and meaningful decision support in cultures where the capacity for such support is either limited or nonexistent, with a focus on three non-Western cultures: Arab, Pashtun, and Somali culture. The focus of the project is on intertemporal reasoning and how the focal cultures differ in this respect from the West. What is meant by intertemporal reasoning? All cultures deal with time. How they understand it is a defining cultural characteristic. We use the term intertemporal reasoning to mean the psychosocial and cultural processes engaged when people are called upon to either integrate past experiences and events (history) or project forward to desired or undesired future states. Intertemporal reasoning can refer to how a culture deals with time itself as a phenomenon, or how events that either take place or have taken place are recalled, represented, and organized in terms of an explanation or history of the culture. Intertemporal reasoning includes how cultures ascribe meaning to events, including the meaning of the past and present in terms of the future. Intertemporality, as a cultural characteristic, describes differences between cultures that have importance for understanding social processes, such as decision making and planning, including the relationship between time and preferences, and the effects of time on cognitive processes. The bibliography is a collection of annotated entries that each of the three project researchers developed as part of their particular examination of the literature. Emphasis is on Arab culture, owing to the relative availability of resources published in English. Intended readers include those with an interest in this highly-focused aspect of non-Western cultures.

Effect of long‐term changes in relative resource availability on dietary preference of grazing sheep for perennial ryegrass and white clover

Three replicate paddocks, each of 0·235 ha, containing adjacent monocultures of perennial ryegrass or white clover [50:50 by ground area, 6 cm sward surface height (SSH) at start of experiment] were continuously stocked with three yearling and four mature non‐lactating, non‐pregnant Scottish halfbred ewes for 12 weeks. Herbage intake, grazing behaviour and dietary selection were measured on seven occasions. Clover SSH declined rapidly over the first 5 weeks then stabilized at 1·2–1·6 cm, whereas perennial ryegrass SSH rose slightly initially, then declined gradually. Animals initially included proportionately c. 0·6 white clover in their diet but, by the end of the experiment, this had fallen to 0·3. Total daily herbage intake declined over the 12 weeks from 1·8 kg dry matter (DM) day–1 at the start to 1·0 kg DM day–1. Total grazing time increased from 561 min day–1 to 649 min day–1 at the end of the experiment. The results suggest that, despite overall herbage depletion and a greater depletion of white clover than perennial ryegrass as a result of the initial partial preference for white clover, the animals traded‐off a reduced total intake and an increased grazing time in an attempt to maintain their initial preferred dietary composition.

Density-dependent habitat selection and the modeling of sperm whale (<i>Physeter macrocephalus</i>) exploitation

The monitoring and management of sperm whale (Physeter macrocephalus) populations have proved problematic. Studies of living animals indicate that movements are largely determined by resource availability, thus suggesting that density-dependent habitat selection may be a realistic framework within which to study sperm whale populations. A model, in which animals migrate between 2 × 2° squares at rates that depend on relative resource availability, was used to examine the effects of whaling on measures of sperm whale abundance. The model simulated four types of whaling: shore-based whaling, pelagic open-boat whaling by many boats, pelagic whaling by a fleet based around one factory ship, and pelagic whaling by a fleet sequentially exploiting different parts of the study area. Catch per unit effort was found to have little relationship with population size in any part of the study area for shore-based whaling and for pelagic whaling when the study area was sequentially exploited. Thus, in these circumstances, catch per unit effort should not be used as a measure of depletion. To give a reasonable assessment of depletion, visual or acoustic surveys must extend well beyond the areas being exploited.

Density-dependent habitat selection and the modeling of sperm whale (Physeter macrocephalus) exploitation

The monitoring and management of sperm whale (Physeter macrocephalus) populations have proved problematic. Studies of living animals indicate that movements are largely determined by resource availability, thus suggesting that density-dependent habitat selection may be a realistic framework within which to study sperm whale populations. A model, in which animals migrate between 2 × 2° squares at rates that depend on relative resource availability, was used to examine the effects of whaling on measures of sperm whale abundance. The model simulated four types of whaling: shore-based whaling, pelagic open-boat whaling by many boats, pelagic whaling by a fleet based around one factory ship, and pelagic whaling by a fleet sequentially exploiting different parts of the study area. Catch per unit effort was found to have little relationship with population size in any part of the study area for shore-based whaling and for pelagic whaling when the study area was sequentially exploited. Thus, in these circumstances, catch per unit effort should not be used as a measure of depletion. To give a reasonable assessment of depletion, visual or acoustic surveys must extend well beyond the areas being exploited.

A Multiattribute Optimization Model for Strategic Investment Decisions

AbstractStrategic investment decisions entail intertemporal resource allocation. Given relative resource availability and favourable environmental dynamics, effective strategic investment planning is a major determinant of overall corporate financial performance. This paper advances a methodology for optimizing intertemporal investment decisions through a consensus‐oriented process. This process entails identifying the strategic investment factors, their relative importance, and their assumed values relevant to the timing of each investment program. The paper also provides a methodology for determining the system's priority formulation as the model's objective function. This information generates an optimization matrix designated by investment programs and time. This matrix is then optimized through a hierarchical goal‐programming model that maximizes overall strategic investment decisions. The model was applied to a major capital investment program in the state of New York.RésuméLes décisions d'investissements stratégiques impliquent une allocation de ressources intertemporelles. étant donné la disponibilité relative des ressources et de bonnes dynamiques environnementales, une planification efficace des investissements stratégiques est le déterminant principal de l'ensemble des résultats financiers d'une entreprise. La présente recherche propose une méthodologie pour optimiser les décisions d'investissements intertemporels au moyen d'un processus orienté vers le consensus (consensus‐oriented). Ce processus comprend tout d'abord l'identification des facteurs d'investissements stratégiques, puis leur importance relative et leur valeur supposée en rapport avec l'échelonnage dans le temps de chaque programme d'investissement. Elle propose également une méthodologie pour déterminer la formulation de la priorité du système ainsi que la fonction objective du modèle. Cette information conduit à la construction d'une matrice d'optimisation par programmes et par temps d'investissement. Cette matrice est ensuite optimisée grǎce à un modèle de programmation à but hiérarchique qui maximise les décisions globales d'investissements stratégiques. Ce modèle à été appliqué à un programme d'investissement en immobilisations dans l'état de New York.

Plant chemical defense: monoterpenes and the growth-differentiation balance hypothesis

Recent studies of allocation to defensive chemicals in plants have provided insights into the ecological controls over plant defensive chemicals. Both developmental and ecological studies now suggest that we can understand the factors influencing allocation to defense by examining the relative availability of resources, external needs for chemical defense, and the internal demands for growth that plants face. These studies have also shed light on one of the more popular theories in plant evolutionary ecology, the growth-differentiation balance hypothesis of plant resource allocation.

Effects of alternate routings under variable lot-size conditions

SUMMARY Research into alternate routings suggests that basing process plans solely on machine and expected batch characteristics may be ignoring two important elements. (1) As actual batch quantities vary from their expected values, the balance between fixed and variable process components sometimes shifts, causing different machines to exhibit lower total processing costs. (2) As the most cost-effective machines become disproportionately loaded, the efficiency of the system may be served by considering alternative machines that are more generally available. The focus of this study is to investigate the significance of considering actual process quantity and relative resource availability under common conditions.

Pre-hatch and post-hatch brood amalgamation in North American Anatidae: a review of hypotheses

Two forms of brood amalgamation occur frequently in several species of North American waterfowl: (i) pre-hatch brood amalgamation, whereby a female lays her eggs in the nest of another female and the recipient thereafter provides all further care of the eggs and resulting offspring, and (ii) post-hatch brood amalgamation, whereby a female abandons or loses her young to another female after hatch, and the recipient subsequently tends the foster young. Some authors have viewed these behaviours as accidental or aberrant and of little evolutionary significance. More recently, a number of alternative hypotheses have been suggested. However, few of these hypotheses have been contrasted as viable alternatives and tested in the field, largely because an appropriate theoretical framework is lacking. We analyze the frequency of occurrence of brood amalgamation in North American anatids. We also review the hypotheses that have been proposed to explain these behaviours and erect a theoretical framework which applies to the evolution of both pre-hatch and post-hatch brood amalgamation, and which may apply to species other than those of the Anatidae. Finally, we show that the occurrence of brood amalgamation in North American waterfowl may be associated with low relative resource availability and K-type life-history traits.

Tannin, nitrogen, and cell wall composition of green vs. senescent Douglas-fir foliage : Within- and between-stand differences in stands of unequal density.

Tannin, cell wall, and nitrogen composition of green foliage and needle litter of similar-aged Douglas-fir (Pseudotsuga menziesii Mirb. Franco) from two stands differing in density and crown closure were compared. Trees in the closed-canopy stand had a lower basal area growth rate than those in the open-canopy stand. Stands did not differ in wood basal area/ha or forest floor C/N ratios, but the closed-canopy stand had a significantly larger accumulation of forest floor biomass and significantly higher levels of field-extractable nitrogen and nitrogen mineralization rates. Green foliage from trees in the closed-canopy stand had significantly lower nitrogen, astringency, and lignin contents, but higher cellulose concentration than trees in the open-canopy stand. These trends, inconsistent with the inverse relationship often observed between nitrogen and polyphenol contents of foliage, may result from differences in relative resource availability in the two stands. In contrast to green foliage, needle litter from the two stands had comparable contents of nitrogen, cellulose, and lignin, but astringency was significantly higher in litter from the closed-canopy stand. It is suggested that, within the constraints imposed by site conditions, evergreens may alter the tannin composition of senescing foliage, potentially affecting herbivory and decomposition differently.