Advantages and disadvantages of interference‐competitive ability and resource‐use efficiency when invading established communities

Invaders into established communities must overcome low resource availability. To establish, invaders must either appropriate resources from existing individuals through interference competition or efficiently use the small amount of resource that remains. Although both strategies may be important, they are rarely considered together and, in particular, resource‐use efficiency is often ignored in systems dominated by interference competition. To identify the traits that confer invasion success, we experimentally invaded resource patches in established communities with multiple species from two functional groups that differ in interference competitive ability and resource‐use efficiency. In contrast to previous assessments, we show that resource‐use efficiency can facilitate invasion in systems dominated by interference competition. Furthermore, large resource requirements can be a liability when establishing because interference competition is inherently costly and so cannot fully compensate for limitations in the primary resource. However, we also show that there is a tradeoff in performance among functional groups between small and large resource gaps. Our results suggest we modify the way we view and manage species invasion in systems dominated by interference competition.     

Is separating resource competition from allelopathy realistic?

Allelopathy and resource competition have often been suggested to explain plant-plant interference. Many studies have attempted to separate these two mechanisms of interference to demonstrate either as a probable cause of an observed growth pattern. We, however, are of the opinion that separating allelopathy from resource competition is essentially impossible in natural systems. Furthermore, any experimental design to separate allelopathy and resource competition will create conditions that will never occur in nature. In this article, the ecological interaction between allelopathy and resource competition in natural systems is discussed.     

Exergy-based accounting for land as a natural resource in life cycle assessment

Purpose

In life cycle assessment (LCA), literature suggests accounting for land as a resource either by what it delivers (e.g., biomass content) or the time and space needed to produce biomass (land occupation), in order to avoid double-counting. This paper proposes and implements a new framework to calculate exergy-based spatial explicit characterization factors (CF) for land as a resource, which deals with both biomass and area occupied on the global scale.

Methods

We created a schematic overview of the Earth, dividing it into two systems (human-made and natural), making it possible to account for what is actually extracted from nature, i.e., the biomass content was set as the elementary flow to be accounted at natural systems and the land occupation (through the potential natural net primary production) was set as the elementary flow at human-made systems. Through exergy, we were able to create CF for land resources for these two different systems. The relevancy of the new CF was tested for a number of biobased products.

Results and discussion

Site-generic CF were created for land as a resource for natural systems providing goods to humans, and site-generic and site-dependent CF (at grid, region, country, and continent level) were created for land as a resource within human-made systems. This framework differed from other methods in the sense of accounting for both land occupation and biomass content but without double-counting. It is set operationally for LCA and able to account for land resources with more completeness, allowing spatial differentiation. When site-dependent CF were considered for land resources, the overall resource consumption of certain products increased up to 77 % in comparison with site-generic CF-based data.

Conclusions

This paper clearly distinguished the origin of the resource (natural or human-made systems), allowing consistent accounting for land as a resource. Site-dependent CF for human-made systems allowed spatial differentiation, which was not considered in other resource accounting life cycle impact assessment methods.     

The functional trophic role of lotic primary consumers: generalist versus specialist strategies

1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well.
2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder-detritivore, scraper-herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems.
3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.     

The functional trophic role of lotic primary consumers: generalist versus specialist strategies

1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well.
2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder-detritivore, scraper-herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems.
3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.     

The dynamical implications of human behaviour on a social-ecological harvesting model

The dynamic aspects of human harvesting behaviour are often overlooked in resource management, such that models often neglect the complexities of dynamic human effort. Some researchers have recognized this, and a recent push has been made to understand how human behaviour and ecological systems interact through dynamic social-ecological systems. Here, we use a recent example of a social-ecological dynamical systems model to investigate the relationship between harvesting behaviour and the dynamics and stability of a harvested resource, and search for general rules in how relatively simple human behaviours can either stabilize or destabilize resource dynamics and yield. Our results suggest that weak to moderate behavioural and effort responses tend to stabilize dynamics by decreasing return times to equilibria or reducing the magnitude of cycles; however, relatively strong human impacts can readily lead to human-driven cycles, chaos, long transients and alternate states. Importantly, we further show that human-driven cycles are characteristically different from typical resource-driven cycles and, therefore, may be differentiated in real ecosystems. Given the potentially dramatic implications of harvesting on resource dynamics, it becomes critical to better understand how human behaviour determines harvesting effort through dynamic social-ecological systems.     

Degeneracy-Driven Self-Structuring Dynamics in Selective Repertoires

Numerous biological interactions, such as interactions between T cell receptors or antibodies with antigens, interactions between enzymes and substrates, or interactions between predators and prey are often not strictly specific. In such less specific, or “sloppy,” systems, referred to here as degenerate systems, a given unit of a diverse resource (antigens, enzymatic substrates, prey) is at risk of being recognized and consumed by multiple consumers (lymphocytes, enzymes, predators). In this study, we model generalized degenerate consumer-resource systems of Lotka–Volterra and Verhulst types. In the degenerate systems of Lotka–Volterra, there is a continuum of types of consumer and resource based on variation of a single trait (characteristic, or preference). The consumers experience competition for a continuum of resource types. This non-local interaction system is modeled with partial differential-integral equations and shows spontaneous self-structuring of the consumer population that depends on the degree of interaction degeneracy between resource and consumer, but does not mirror the distribution of resource. We also show that the classical Verhulst (i.e. logistic) single population model can be generalized to a degenerate model, which shows qualitative behavior similar to that in the degenerate Lotka–Volterra model. These results provide better insight into the dynamics of selective systems in biology, suggesting that adaptation of degenerate repertoires is not a simple “mirroring” of the environment by the “fittest” elements of population.     

Predictable quality of service atop degradable distributed systems

High performance and distributed computing systems such as peta-scale, grid and cloud infrastructure are increasingly used for running scientific models and business services. These systems experience large availability variations through hardware and software failures. Resource providers need to account for these variations while providing the required QoS at appropriate costs in dynamic resource and application environments. Although the performance and reliability of these systems have been studied separately, there has been little analysis of the lost Quality of Service (QoS) experienced with varying availability levels. In this paper, we present a resource performability model to estimate lost performance and corresponding cost considerations with varying availability levels. We use the resulting model in a multi-phase planning approach for scheduling a set of deadline-sensitive meteorological workflows atop grid and cloud resources to trade-off performance, reliability and cost. We use simulation results driven by failure data collected over the lifetime of high performance systems to demonstrate how the proposed scheme better accounts for resource availability.     

Statistical entropy analysis to evaluate resource efficiency: Phosphorus use in Austria

In a resource efficient economy, entropy generation must be kept low and high-entropy wastes should be transformed into low-entropy recycled products, thus saving natural resources. Based on this idea, statistical entropy analysis (SEA) was put forward as a method to evaluate material flow systems with respect to their ability to concentrate or dilute a substance throughout its life cycle using a single metric, relative statistical entropy (RSE). Whereas its application has so far been restricted to highly aggregated material flow systems or to assessments at plant or process level, in the present study the SEA method was adapted to assess the efficiency of resource use in material flow systems which consist of numerous resource flows and include multiple recycling loops. Phosphorus (P) use in Austria served as a case study to illustrate SEA-based resource efficiency assessment for different scenarios and over time. The evaluation enabled exploiting the outcomes of existing P flow studies in a straightforward way and produced additional insights related to the characteristics of resource use within the system. Changes in P management over time had a significant effect on the resource efficiency of P use. The RSE increased by 40% due to P use in Austria in the year 2000 compared to an increase of 30% in 2010. The generally favorable trend of statistical entropy (lower dissipation) in 2010 could be attributed mainly to lower dissipative emissions, more efficient bio-industry, and increasing P removal rates in waste water treatment, which overcompensated the negative impact of the ban of recycling of meat and bone meal (in 2001) on P use efficiency. Further, the SEA-based assessment applied to a scenario of optimized P management reflected the positive effects of measures to reduce emissions, enhance recycling, and reduce consumption of P on resource efficiency (50% lower RSE increase in the target system compared to the original state). In synthesis, this study shows that the SEA method is able to integrate various dimensions of resource use into a single indicator, which can serve as a basis to assess and improve the resource efficiency of macro-scale material flow systems.     

Cooperation can improve the resilience of common-pool resource systems against over-harvesting

Currently common-pool resource systems world-wide are under pressure due to overexploitation and environmental change. To ensure that these systems continue to provide vital ecosystem services it is necessary to sustain or increase their resilience against such pressure. One way of doing this may be to improve cooperation among agents who are heavily involved in common-pool resource systems, such as farmers, fishers, managers, and companies. Historical examples suggest that the persistence or collapse of common-pool resource systems may hinge on agents collaborating or not, but cooperation as a mechanism to improve resilience is not commonly included in existing models for studying resilience. Cooperation may be sustained through indirect reciprocity, i.e., cooperative behaviour by one agent that may be repaid by other agents. In this paper we develop a suite of agent-based models that represent an abstract version of a generic spatial common-pool resource system. This suite of models contains various mechanisms for cooperation based on trust. We investigate how the resilience of the models is affected by these mechanisms. The resilience of the models is assessed by applying various shocks which make it more difficult to gather resource, and measuring whether and how fast the agent population can recover from these shocks. The results suggest that although indirect reciprocity positively affects the level of cooperation in the system, cooperation could be common even without indirect reciprocity. It is shown that the presence of cooperation increases the resilience of the models against shocks.     

Deadlock Avoidance for Sequential Resource Allocation Systems: Hard and Easy Cases

Deadlock is a major problem for systems that allocate resources in real time. The key issue in deadlock avoidance is whether or not a given resource allocation state is safe: that is, whether or not there exists a sequence of resource allocations that completes all processes. Although safety is established as NP-complete for certain broad resource allocation classes, newly emerging resource allocation scenarios often exhibit unique features not considered in previous work. In these cases, establishing the underlying complexity of the safety problem is essential for developing the best deadlock avoidance approach. This work investigates the complexity of safe resource allocation for a class of systems relevant in automated manufacturing. For this class, the resource needs of each process are expressed as a well-defined sequence. Each request is for a single unit of a single resource and is accompanied by a promise to release the previously allocated resource. Manufacturing researchers have generally accepted that safety is computationally hard, and numerous suboptimal deadlock avoidance solutions have been proposed for this class. Recent results, however, indicate that safety is often computationally easy. The objective of this article is to settle this question by formally establishing the NP-completeness of safety for this class and investigating the boundary between the hard and easy cases. We discuss several special structures that lead to computationally tractable safety characteristics.     

A synthesis of subdisciplines: predator–prey interactions, and biodiversity and ecosystem functioning

The last 15 years has seen parallel surges of interest in two research areas that have rarely intersected: biodiversity and ecosystem functioning (BEF), and multispecies predator–prey interactions (PPI). Research addressing role of biodiversity in ecosystem functioning has focused primarily on single trophic‐level systems, emphasizing additive effects of diversity that manifest through resource partitioning and the sampling effect. Conversely, research addressing predator–prey interactions has focused on two trophic‐level systems, emphasizing indirect and non‐additive interactions among species. Here, we use a suite of consumer‐resource models to organize and synthesize the ways in which consumer species diversity affects the densities of both resources and consumer species. Specifically, we consider sampling effects, resource partitioning, indirect effects caused by intraguild interactions and non‐additive effects. We show that the relationship between consumer diversity and the density of resources and consumer species are broadly similar for systems with one vs. two trophic levels, and that indirect and non‐additive interactions generally do little more than modify the impacts of diversity established by the sampling effect and resource partitioning. The broad similarities between systems with one vs. two trophic levels argue for greater communication between researchers studying BEF, and researchers studying multispecies PPI.     

Discrete consumers,small scale resource heterogeneity,and population stability

We present a consumer-resource model in which individual consumers subsist on a continuum of resource distributed over a very large number of small “bite-sized” patches, each patch being sufficiently small that all its resource is eaten whenever a consumer visits. This form of consumer–resource interaction forces a heterogeneous distribution of resource among the patches, and may dampen out the large amplitude, consumer-resource cycles that are predicted by traditional models of well-mixed, spatially homogeneous systems. The resource equilibrium does not increase with enrichment, a prediction that distinguishes this model from models that invoke direct or indirect consumer density dependence as a stabilizing mechanism.     

Simple life-history omnivory: responses to enrichment and harvesting in systems with intraguild predation

This article analyzes the nature of top-down and bottom-up effects and alternative states in systems characterized by life-history omnivory. The analysis is based on a three-species food web with intraguild predation (IGP). The top predator population has juvenile and adult stages, which consume the basal resource and the intermediate prey, respectively; the prey consumes only the resource. The per capita reproduction of the adult predators depends on their consumption rate of prey, while the maturation rate of the juvenile predators depends on their resource consumption rate. Enriching the resource can increase or decrease the abundances of one or both of the two consumer species; an increased density is more likely in the intermediate species than in the systems where IGP is not based on stage differences. Alternative states that have or lack the predator occur frequently, particularly when the prey population is capable of reducing the resource to very low densities. These results differ from those of several other recent models of life-history omnivory. They suggest that life-history omnivory may be one of the primary reasons why exploited populations undergo sudden collapses and why collapsed populations fail to recover in spite of large reductions in the exploitation rate.     

Resources, competition and selfing: their influence on reproductive system evolution

Plant reproductive systems present a gradient of gender ranging from unisexuality to hermaphrodism. This variability in sex expression can be found within species and has been found to be influenced by external factors such as resource levels. The sexual strategy selected will depend not only on the number of pollen grains and seeds an individual can produce but also on the chance of success of this production. Production depends on trade-offs between female and male functions of hermaphrodites according to resource level and subsequent fate is influenced by selfing, inbreeding depression and competition among offspring. The goal of this study is to determine how interactions between these key parameters, resources availability, selfing and density-dependent competition within offspring influence the evolution of reproductive systems. We showed with a theoretical approach that (i) a change in resource level at the population level affects sexual strategies only in certain conditions; (ii) density-dependent seedling mortality disadvantages females compared to hermaphrodites and interacts strongly with resource level.     

GEMS: Gossip-Enabled Monitoring Service for Scalable Heterogeneous Distributed Systems

Gossip protocols have proven to be effective means by which failures can be detected in large, distributed systems in an asynchronous manner without the limitations associated with reliable multicasting for group communications. In this paper, we discuss the development and features of a Gossip-Enabled Monitoring Service (GEMS), a highly responsive and scalable resource monitoring service, to monitor health and performance information in heterogeneous distributed systems. GEMS has many novel and essential features such as detection of network partitions and dynamic insertion of new nodes into the service. Easily extensible, GEMS also incorporates facilities for distributing arbitrary system and application-specific data. We present experiments and analytical projections demonstrating scalability, fast response times and low resource utilization requirements, making GEMS a potent solution for resource monitoring in distributed computing.     

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents

Intraspecific variation in social systems is widely recognized across many taxa, and specific models, including polygamy potential, resource defense, and resource dispersion, have been developed to explain the relationship between ecological variation and social organization. Although mammals from temperate North America and Eurasia have provided many insights into this relationship, rodents from the Neotropics and temperate South America have largely been ignored. In this review we focus on reports documenting intraspecific variation in spacing systems, group size, and mating systems of caviomorphs. This large group of New World hystricognath rodents occupies a diverse array of habitats; thus, members of the same species potentially exhibit different social systems in response to different ecological conditions. Spatial patterns vary in response to a diverse array of factors, including predation, food availability, population density, and soil characteristics. Changes in group size typically correlate with changes in resource availability, particularly food. Mating systems generally reflect the ability of males to control access to females, which may depend on population density or food distribution. In general, social organization in caviomorphs fits predictions of resource-based models; however, most studies have been purely observational, involving small numbers of animals over short time periods and reporting qualitative rather than quantitative levels of ecological correlates. In future studies the use of molecular techniques and controlled, experimental manipulations can increase our understanding of intraspecific variation in caviomorph social systems. This understudied group of rodents offers excellent opportunities to provide insights into the influence of ecological conditions on behavior such as social systems.     

Resource abundance and the critical transition to cooperation

Cooperation is abundant in nature, occurring at all levels of biological complexity. Yet cooperation is continually threatened by subversion from noncooperating cheaters. Previous studies have shown that cooperation can nevertheless be maintained when the benefits that cooperation provides to relatives outweigh the associated costs. These fitness costs and benefits are not fixed properties, but can be affected by the environment in which populations reside. Here, we describe how one environmental factor, resource abundance, decisively affects the evolution of cooperative public goods production in two independent evolving systems. In the Avida digital evolution platform, populations evolved in environments with different levels of a required resource, whereas populations of Vibrio cholerae evolved in the presence of different nutrient concentrations. In both systems, cooperators and cheaters co‐existed stably in resource‐rich environments, whereas cheaters dominated in resource‐poor environments. These two outcomes were separated by a sharp transition that occurred at a critical level of resource. These results offer new insights into how the environment affects the evolution of cooperation and highlight the challenges that populations of cooperators face when they experience environmental change.     

Host specialist clownfishes are environmental niche generalists

Why generalist and specialist species coexist in nature is a question that has interested evolutionary biologists for a long time. While the coexistence of specialists and generalists exploiting resources on a single ecological dimension has been theoretically and empirically explored, biological systems with multiple resource dimensions (e.g. trophic, ecological) are less well understood. Yet, such systems may provide an alternative to the classical theory of stable evolutionary coexistence of generalist and specialist species on a single resource dimension. We explore such systems and the potential trade-offs between different resource dimensions in clownfishes. All species of this iconic clade are obligate mutualists with sea anemones yet show interspecific variation in anemone host specificity. Moreover, clownfishes developed variable environmental specialization across their distribution. In this study, we test for the existence of a relationship between host-specificity (number of anemones associated with a clownfish species) and environmental-specificity (expressed as the size of the ecological niche breadth across climatic gradients). We find a negative correlation between host range and environmental specificities in temperature, salinity and pH, probably indicating a trade-off between both types of specialization forcing species to specialize only in a single direction. Trade-offs in a multi-dimensional resource space could be a novel way of explaining the coexistence of generalist and specialists.