Resource Supply Rates Research Articles

Different measures of niche and fitness differences tell different tales

In modern coexistence theory, species coexistence can either arise via strong niche differences or weak fitness differences. Having a common currency for interpreting these mechanisms is essential for synthesizing knowledge across different studies and systems. However, several methods for quantifying niche and fitness differences exist, with little guidance on how and why these methods differ. Here, we first organize the available methods into three groups and review their differences from a conceptual point of view. Next, we apply four methods to quantify niche and fitness differences to one simulated and one empirical data set. We show that these methods do not only differ quantitatively, but affect how we interpret coexistence. Specifically, the different methods disagree on how resource supply rates (simulated data) or plant traits (empirical data) affect niche and fitness differences. We argue for a better theoretical understanding of what connects and sets apart different methods and more precise empirical measurements to foster appropriate method selection in coexistence theory.

Resource Heterogeneity, Not Resource Quantity, Plays an Important Role in Determining Tree Species Diversity in Two Species-Rich Forests

There is still considerable debate about the relative importance of resource heterogeneity and resource quantity in the maintenance of species diversity in a community. The resource heterogeneity hypothesis proposes that spatial heterogeneity of limiting resources and inter-specific differences in resource requirements will determine species richness. In contrast, the resource quantity hypothesis predicts that average resource supply rates contribute to species richness by their effects on plant density and stochastic population dynamics. However, the evaluation of the two hypotheses in observational studies is associated with a major methodological challenge as average resource supply rate often covaries with resource heterogeneity. Using a novel approach derived from the relationships between average resource supply rate, resource heterogeneity (calculated as the standard deviation of environmental factors) and plant density in the resource hypotheses, we evaluated the relative importance of resource quantity and resource heterogeneity with a variation partitioning model in Gutianshan (GTS) forest plot, China and Barro Colorado Island (BCI) forest plot, central Panama. We found that resource quantity explained much less of the variation in species richness than resource heterogeneity in both of GTS and BCI (44.5% vs 4.9% in GTS and 20.4% vs 0.8% in BCI at the 20×20 m scale, 57.5% vs 3.4% in GTS at the 40×40 m scale and 34.5% vs 2.6% in BCI at the 50×50 m scale). We also found that resource heterogeneity governed species richness in GTS, whereas spatial processes dominated species diversity in BCI. Moreover, most of the effect of resource heterogeneity and resource quantity on species richness overlapped with that of spatial processes. This result indicates that most effects of resources could also be explained by spatial processes, such as dispersal limitation. Therefore, resource heterogeneity and spatial processes, but not resource quantity played an important role in determining species diversity in these two old-growth forests. This is in contrast to the results of several manipulative studies, which found that resource quantity governed species diversity when one or a limited number of resources were considered. This suggests that the processes determining species richness along ecological gradients are complicated and determined by the interaction of various processes.

Bi-objective optimization algorithms for joint production and maintenance scheduling under a global resource constraint: Application to the permutation flow shop problem

Production scheduling and maintenance planning are two of the most important tasks that managers face before implementing their decisions on the shop floor. Another issue managers have to keep in mind is the proper allocation of various resources for production. These issues create difficulties in the planning process. In this paper, we propose a bi-objective model that integrates the three aforementioned issues and determines production scheduling, maintenance planning and resource supply rate decisions in order to minimize the make span and total production costs, which include total maintenance, resource consumption and resource inventory costs. Two meta heuristic methods were employed to find approximations of the Pareto optimal front in a permutation flow shop environment: The well-known non-dominated sorting genetic algorithm (NSGA-II) and a bi-objective adaptation of the particle swarm optimization (BOPSO). Additionally, a bi-objective randomized local search (BORLS) heuristic was developed in order to generate multiple non-dominated solutions along its search path. Two sets of computational experiments were conducted. In the first set, the performances of the two meta heuristics with purely random initial populations were compared, with results showing the superiority of BOPSO over NSGA-II. In the second set, the initial populations were enhanced with heuristically generated solutions from BORLS and the performances of BOPSO, NSGA-II and BORLS used as an independent search algorithm, were compared. In this instance, the algorithms performed evenly for large problems, with the BORLS method generating better solutions when total production cost is emphasized.

Using metabolic theory to assess structure and function in the deep-sea benthos, including microbial and metazoan dominance

Constraining seafloor carbon stocks and flows, and their links to biodiversity, remains a major global challenge, particularly in the deep ocean. We examine the density, biomass, respiration, and species richness size spectra of polychaetes from a time-series study (1991–2011) in the abyssal NE Pacific (Station M, 35°N, 123°W, 4000 m water depth). The spectra met the predictions of the metabolic theory of ecology (MTE) and were consistent with Damuth's rule of energetic equivalence. When combined via MTE, resource supply rate and habitat temperature have valuable predictive power for seafloor standing stocks. Intra-annual comparisons suggested seasonally variable resource acquisition rates and metabolism, consistent with the scope for specific dynamic action in polychaetes. Accepting and applying the assumptions of MTE, Damuth's rule, and 3/4-power mass-scaling of metabolism to the entire benthos, then two thirds of carbon remineralised at the seafloor might be attributable to metazoan invertebrates. This is contrary to the common finding of microbial dominance but may be resolved by considering (1) that only a fraction of microbial biomass may be metabolically active, and (2) that the metabolism of the largest members of the benthos could only be assessed at physical scales very much greater than are usually examined.

Seasonal resource conditions favor a summertime increase in North Pacific diatom\u2013diazotroph associations

In the North Pacific Subtropical Gyre (NPSG), an annual pulse of sinking organic carbon is observed at 4000 m between July and August, driven by large diatoms found in association with nitrogen fixing, heterocystous, cyanobacteria: Diatom–Diazotroph Associations (DDAs). Here we ask what drives the bloom of DDAs and present a simplified trait-based model of subtropical phototroph populations driven by observed, monthly averaged, environmental characteristics. The ratio of resource supply rates favors nitrogen fixation year round. The relative fitness of DDA traits is most competitive in early summer when the mixed layer is shallow, solar irradiance is high, and phosphorus and iron are relatively abundant. Later in the season, as light intensity drops and phosphorus is depleted, the traits of small unicellular diazotrophs become more competitive. The competitive transition happens in August, at the time when the DDA export event occurs. This seasonal dynamic is maintained when embedded in a more complex, global-scale, ecological model, and provides predictions for the extent of the North Pacific DDA bloom. The model provides a parsimonious and testable hypothesis for the stimulation of DDA blooms.

Covariations in ecological scaling laws fostered by community dynamics

Scaling laws in ecology, intended both as functional relationships among ecologically relevant quantities and the probability distributions that characterize their occurrence, have long attracted the interest of empiricists and theoreticians. Empirical evidence exists of power laws associated with the number of species inhabiting an ecosystem, their abundances, and traits. Although their functional form appears to be ubiquitous, empirical scaling exponents vary with ecosystem type and resource supply rate. The idea that ecological scaling laws are linked has been entertained before, but the full extent of macroecological pattern covariations, the role of the constraints imposed by finite resource supply, and a comprehensive empirical verification are still unexplored. Here, we propose a theoretical scaling framework that predicts the linkages of several macroecological patterns related to species' abundances and body sizes. We show that such a framework is consistent with the stationary-state statistics of a broad class of resource-limited community dynamics models, regardless of parameterization and model assumptions. We verify predicted theoretical covariations by contrasting empirical data and provide testable hypotheses for yet unexplored patterns. We thus place the observed variability of ecological scaling exponents into a coherent statistical framework where patterns in ecology embed constrained fluctuations.

Effects of Behavioural Strategy on the Exploitative Competition Dynamics.

We investigate a system of two species exploiting a common resource. We consider both abiotic (i.e. with a constant resource supply rate) and biotic (i.e. with resource reproduction and self-limitation) resources. We are interested in the asymmetric competition where a given consumer is the locally superior resource exploiter (LSE) and the other is the locally inferior resource exploiter (LIE). They also interact directly via interference competition in the sense that LIE individuals can use two opposite strategies to compete with LSE individuals: we assume, in the first case, that LIE uses an avoiding strategy, i.e. LIE individuals go to a non-competition patch to avoids competition with LSE individuals, and in the second one, LIE uses an aggressive strategy, i.e. being very aggressive so that LSE individuals have to go to a non-competition patch. We further assume that there is no resource in the non-competition patch so that individuals have to come back to the competition patch for their maintenance, and the migration process acts on a fast time scale in comparison with demography and competition processes. The models show that being aggressive is efficient for LIE's survival and even provoke global extinction of the LSE and this result does not depend on the nature of resource.

Resource-dependent attenuation of species interactions during bacterial succession.

Bacterial communities are vital for many economically and ecologically important processes. The role of bacterial community composition in determining ecosystem functioning depends critically on interactions among bacterial taxa. Several studies have shown that, despite a predominance of negative interactions in communities, bacteria are able to display positive interactions given the appropriate evolutionary or ecological conditions. We were interested in how interspecific interactions develop over time in a naturalistic setting of low resource supply rates. We assembled aquatic bacterial communities in microcosms and assayed the productivity (respiration and growth) and substrate degradation while tracking community composition. The results demonstrated that while bacterial communities displayed strongly negative interactions during the early phase of colonisation and acclimatisation to novel biotic and abiotic factors, this antagonism declined over time towards a more neutral state. This was associated with a shift from use of labile substrates in early succession to use of recalcitrant substrates later in succession, confirming a crucial role of resource dynamics in linking interspecific interactions with ecosystem functioning.

Scale‐dependent relationships between suspension‐feeding stream insects and water velocity in spatially heterogeneous flow environments

Summary Valuable insights about relationships between consumers and their resources have emerged from studies that investigated how these interactions vary with spatial scale. We conducted field studies to examine the scale-dependence of patterns of spatial variation in the densities of larval blackflies (Simulium tribulatum) and water velocity, a key variable determining resource supply rates to these passive suspension-feeders. We sought to answer two main questions: (i) How do patterns of spatial variation in water velocity and larval density change with scale? (ii) Does the relationship between larval density and water velocity vary with scale? We deployed artificial substrates on the bed of riffles and pools to assess spatial variation in water velocity and larval density at three spatial scales spanning four orders of magnitude: (i) among microhabitats within single substrates (centimetre scale); (ii) among substrates within individual riffles or pools (metre scale); and (iii) among riffles and pools (tens of metres scale). We used semi-cylindrical substrates that allowed us to estimate water velocities 1 mm above the substrate surface using a validated computational fluid dynamic model and measurements made with a 10-mm-diameter propeller flowmeter. On natural substrates (stones), we quantified fine-scale velocity variation (measured 1 mm above the stone using hot-film anemometry) and larval density at the two smallest scales. We used hierarchical regression models to partition variation in larval density and water velocity among spatial scales, and to measure the strength of relationships between larval density and water velocity at each scale. The distribution of spatial variation across scales was similar for both water velocity and larval density. The proportion of total variation differed markedly among scales, but variation did not increase monotonically with increasing spatial scale. The greatest proportional variation in velocity and density occurred at the smallest (among microhabitats) and largest (among riffles and pools) scales. The similar cross-scale distributions of variance for water velocity and larval density were not accompanied by consistent density–velocity relationships at all scales. At the smallest scale (i.e. among microhabitats on a single substrate), where spatial variation in velocity was large, there was a consistently strong positive relationship between larval density and water velocity. At the among-cylinder scale (within riffles or pools), where flow variation was smaller, the density–velocity relationship was strongly positive in pools but weakly negative in riffles. At the largest scale (among riffles and pools), the density–velocity relationship was positive among pools, and between riffles and pools, but was negative among riffles. Our results support the hypothesis that dispersal limitations may constrain the ability of larvae to reach preferred feeding sites at intermediate (among substrate) spatial scales. We believe the creative interplay of modelling, experiments and descriptive studies holds great promise for illuminating the causes and consequences of scale-dependence in resource tracking and habitat selection.

Phosphorus resource heterogeneity in microbial food webs

Food webs are often regulated by the bottom-up effects of resource supply rate. However, heterogeneity within a resource pool may also affect the structure and function of com- munities. To test this hypothesis, we measured the responses of aquatic microbial food webs in experimental mesocosms to the addition of 4 different phosphorus (P) sources: orthophosphate (PO4 3� ), 2-aminoethylphosphonate (AEP), adenosine triphosphate (ATP), and phytic acid (PA). Based on 16S rRNA gene sequencing, we found that P resource heterogeneity altered community assembly for bacteria and eukaryotic algae, suggesting that these microbial functional groups may be comprised of P-specialists. In contrast, cyanobacteria were relatively unaffected by our treatments, suggesting that these microorganisms may adopt a more generalist strategy for P- acquisition. Furthermore, our results revealed that P resource heterogeneity affected food web and ecosystem attributes such as nutrient concentrations, bacterial productivity, algal biomass, and ecosystem respiration. Lastly, we found no evidence for non-additive effects of resource het- erogeneity based on a treatment where a set of mesocosms received all 4 sources of P. Instead, our results support the view that there may be non-substitutable classes of P in aquatic ecosystems. Specifically, microbial food webs were more sensitive to P-containing biomolecules (PO4 3� and ATP) than P-containing structural or storage molecules (AEP and PA). Our results demonstrate that not all P resources are the same; although historically overlooked, P resource heterogeneity may have important implications for understanding and predicting the structure and function of aquatic communities.

Homeostasis and nutrient limitation of benthic autotrophs in natural chemostats

To explore how gradients in nutrient availability influence the stoichiometry of freshwater autotrophs, we sampled algal and submerged vascular plant tissues, as well as water for C : N : P ratios in 41 of north Florida's spring‐fed rivers, which are ideal natural laboratories because of unparalleled temporal stability in chemistry, temperature, and flow. Water chemistry across springs spanned a molar inorganic N : P gradient from 0.6 to 89.4, while repeated measurements within springs suggest low variation (coefficient of variation [CV] < 20%) over interannual timescales. We observed significant interspecific differences in stoichiometry suggesting different nutrient requirements, but there was negligible evidence that variation in nutrient supply influenced taxa presence or absence. Most importantly, we observed no plasticity in tissue stoichiometry for any taxa; homeostatic regulation coefficients (H) ranged from 4.8 to undefined (slope of log‐resource vs. log‐tissue ratios ≤ 0), suggesting strict homeostasis in this setting. To explore the paradox of plasticity in chemostat experiments vs. homeostasis in these natural chemostats, we adapted the Droop model to better represent benthic systems (i.e., where hydraulic and biomass turnover rates can be different) and to allow light limitation. Model results suggest increasing hydraulic turnover induces homeostasis and releases autotrophs from growth limitation by nutrients (i.e., inducing light limitation) over a large range of nutrient concentrations and element ratios, suggesting the resource supply rate in comparison with ecosystem demand, not concentration or element ratios, is the primary determinant of nutrient limitation, and thus a dominant control on autotroph stoichiometry. Our results suggest deviation between observed and taxa‐specific optimal stoichiometry may diagnose nutrient limitation.

Community disassembly and invasion of remnant native grasslands under fluctuating resource supply

Summary Native vegetation fragments embedded in anthropogenic landscapes are increasingly threatened by land‐use intensification. Managing disturbance regimes and nutrient inputs may help maintain species diversity in such remnants. Yet, it is unclear the extent to which changes in resource availability due to reduced capture by resident plants and/or increased supply rates may trigger native community disassembly and exotic invasions. We examined how mowing disturbance and N fertilizer addition affected plant community recovery after a burning event in a remnant corridor of tussock pampa grassland in Argentina. The percentage cover and richness of native and exotic plant functional groups were monitored over 4 years. According to the ‘fluctuating resource theory’, we expected invasion to be the highest when both light and N availability were increased simultaneously. Mowing delayed recovery by dominant C4 tussock grasses and promoted subordinate, native C3 grasses and exotic legumes, thus enhancing both native and exotic species richness. Fertilization induced a transient increase in native forbs but decreased total plant richness. Moreover, N addition to mowed grassland led to rapid invasion by short‐lived exotic forbs, which were then replaced by exotic perennial grasses. Exotic grasses eventually spread across the grassland corridor, although at different rates depending on the treatment, and in parallel to a generalized decline in native species cover. Synthesis and applications. Community disassembly patterns reflected differential responses of native and exotic functional groups to altered resource supply rates. Synergisms between canopy disturbances and N enrichment posed the greatest threat to preserving a pampa grassland remnant prone to invasion. Establishing buffer zones may be required to enhance the viability of corridor‐like grassland remnants in agricultural landscapes.

Quantitative food web analysis supports the energy-limitation hypothesis in cave stream ecosystems.

Energy limitation has long been the primary assumption underlying conceptual models of evolutionary and ecological processes in cave ecosystems. However, the prediction that cave communities are actually energy-limited in the sense that constituent populations are consuming all or most of their resource supply is untested. We assessed the energy-limitation hypothesis in three cave streams in northeastern Alabama (USA) by combining measurements of animal production, demand, and resource supplies (detritus, primarily decomposing wood particles). Comparisons of animal consumption and detritus supply rates in each cave showed that all, or nearly all, available detritus was required to support macroinvertebrate production. Furthermore, only a small amount of macroinvertebrate prey production remained to support other predatory taxa (i.e., cave fish and salamanders) after accounting for crayfish consumption. Placing the energy demands of a cave community within the context of resource supply rates provided quantitative support for the energy-limitation hypothesis, confirming the mechanism (limited energy surpluses) that likely influences the evolutionary processes and population dynamics that shape cave communities. Detritus-based surface ecosystems often have large detrital surpluses. Thus, cave ecosystems, which show minimal surpluses, occupy the extreme oligotrophic end of the spectrum of detritus-based food webs.

How ants drop out: ant abundance on tropical mountains.

In tropical wet forests, ants are a large proportion of the animal biomass, but the factors determining abundance are not well understood. We characterized ant abundance in the litter layer of 41 mature wet forest sites spread throughout Central America (Chiapas, Guatemala, Honduras, Nicaragua, and Costa Rica) and examined the impact of elevation (as a proxy for temperature) and community species richness. Sites were intentionally chosen to minimize variation in precipitation and seasonality. From sea level to 1500 m ant abundance very gradually declined, community richness declined more rapidly than abundance, and the local frequency of the locally most common species increased. These results suggest that within this elevational zone, density compensation is acting, maintaining high ant abundance as richness declines. In contrast, in sites above 1500 m, ant abundance dropped abruptly to much lower levels. Among these high montane sites, community richness explained much more of the variation in abundance than elevation, and there was no evidence of density compensation. The relative stability of abundance below 1500 m may be caused by opposing effects of temperature on productivity and metabolism. Lower temperatures may decrease productivity and thus the amount of food available for consumers, but slower metabolisms of consumers may allow maintenance of higher biomass at lower resource supply rates. Ant communities at these lower elevations may be highly interactive, the result of continuous habitat presence over geological time. High montane sites may be ephemeral in geological time, resulting in non-interactive communities dominated by historical and stochastic processes. Abundance in these sites may be determined by the number of species that manage to colonize and/or avoid extinction on mountaintops.

Factors associated with the success of native and nonnative species in an unfragmented arid-land riverscape

Native fish persistence is threatened by the establishment and spread of nonnatives. Identifying environmental and biotic factors associated with the success of co-occurring native fishes and nonnative taxa is central to identifying mechanisms responsible for native declines and nonnative expansion. We related physicochemical variables, food resources, and community composition to the success (secondary production) of native and nonnative fishes, tadpoles, and crayfish across six sites in three reaches (tributary, canyon, and valley) during 2008–2011 in the Gila River, New Mexico. Native fish success was greater than nonnative success across a range of physicochemical conditions, basal resource supply rates, and nonnative communities, although nonnative fish, tadpole, and crayfish success could approach or exceed that of native fishes in canyon habitats, a warm-water tributary, or in downstream valley sites, respectively. Native fish success was lowest in canyon reaches, when flathead catfish (Pylodictis olivaris) and common carp (Cyprinus carpio) were highly productive. These results demonstrate the potential for native fish persistence in the presence of nonnatives in physically unmodified streams, highlighting the importance of habitat preservation for native conservation.

Species-Specific Non-Physical Interference Competition among Mosquito Larvae

Individuals of different sex, size or developmental stage can compete differently and hence contribute distinctively to population dynamics. In species with complex life cycles such as insects, competitive ability is often positively correlated with larval developmental stage. Yet, little is known on how the development and survival of early-instars is influenced by interference from late-instar larvae, especially at low densities when exploitative competition is expected to be negligible. Furthermore, the specificity and mechanisms by which interference competition operates are largely unknown. We performed two complementary experiments aiming to quantify the competitive effects of late instar Ochlerotatus caspius on early instar larvae at low densities and under high resource supply rate. The first experiment examined the net effect of interference by 4th on 1st instar O. caspius larvae, relative to the effect of 1st instars on themselves. The second experiment examined the effect of species-specific, non-physical interference competition (i.e., cage larvae) by 4th on 1st instar O. caspius larvae at low or high densities. Specifically, we compared the responses of O. caspius larvae raised in the presence of caged con- or hetero-specific, Culiseta longiareolata, with that of larvae in the empty-cage control group. As expected, interference from late instar larvae had a net negative effect on the development rate of first instars. In contrast, the presence of caged con-specifics (non-physical interference) accelerated the development rate of O. caspius, however, this pattern was only evident at the low density. Notably, no such pattern was detected in the presence of caged hetero-specifics. These results strongly suggest the existence of species-specific growth regulating semiochemicals.

Zooplankton species richness–productivity relationship: Confronting monotonic positive and hump‐shaped models from a local perspective

AbstractThis study examined two models that are most frequently used to describe the relationship between species richness and productivity (SPR): monotonic positive and hump‐shaped models. We assessed zooplankton community diversity in response to algal productivity. The relationship between net primary productivity (NPP) and rarefied species richness was examined by fitting the data to two models and comparing them using the Akaike information criterion (AICc). Macrophyte banks with the highest net primary productivity had the highest zooplankton abundance. Our results pointed to a hump‐shaped model as the best fit to describe the relationship between zooplankton species richness and primary productivity (ΔAICc > 4). Thus, the diversity was lower at the extremes of productivity and higher at intermediate levels of productivity. We suggest that this relationship might occur because when the resource supply rates are low, environmental conditions are stressful, whereas a high availability of resources enhances competitive exclusion. Two observations supported this statement: (i) the total abundance of the community positively correlated with NPP (P < 0.05), indicating that less productive sites had few consumers and the raised productivity tended to favour the total abundance; (ii) NPP was negatively correlated with evenness (P < 0.05), indicating that productivity increased the dominance of certain species in the communities. Therefore, we challenged two of the models most frequently used to explain SPR, and discuss some mechanisms underlying a hump‐shaped SPR.

Theoretical Predictions for How Temperature Affects the Dynamics of Interacting Herbivores and Plants

Concern about climate change has spurred experimental tests of how warming affects species' abundance and performance. As this body of research grows, interpretation and extrapolation to other species and systems have been limited by a lack of theory. To address the need for theory for how warming affects species interactions, we used consumer-prey models and the metabolic theory of ecology to develop quantitative predictions for how systematic differences between the temperature dependence of heterotrophic and autotrophic population growth lead to temperature-dependent herbivory. We found that herbivore and plant abundances change with temperature in proportion to the ratio of autotrophic to heterotrophic metabolic temperature dependences. This result is consistent across five different formulations of consumer-prey models and over varying resource supply rates. Two models predict that temperature-dependent herbivory causes primary producer abundance to be independent of temperature. This finding contradicts simpler extensions of metabolic theory to abundance that ignore trophic interactions, and is consistent with patterns in terrestrial ecosystems. When applied to experimental data, the model explained 77% and 66% of the variation in phytoplankton and zooplankton abundances, respectively. We suggest that metabolic theory provides a foundation for understanding the effects of temperature change on multitrophic ecological communities.

Resource Stoichiometry and Consumers Control the Biodiversity-Productivity Relationship in Pelagic Metacommunities

Recent theory suggests that both biodiversity and productivity are constrained by resource supply rates and ratios and that resource stoichiometry is the key to understanding the relationship between biodiversity and productivity. We experimentally tested this theory using pelagic metacommunities. We amended existing predictions by explicitly considering evenness as an aspect of biodiversity and including control of algal biomass by consumption in addition to competition. The metacommunities received a different phosphorus (P) supply and the three patches within each metacommunity differed in their nitrogen (N) supply, which created different N∶P ratios (2, 16, and 128). All patches were inoculated with a phytoplankton assemblage consisting of five species, and half of the metacommunities received two ciliate species as consumers. At the level of the entire metacommunity, algal biomass increased with increasing P supply, whereas species richness and evenness decreased with increasing P supply. Without consumers, resource use efficiency (RUE; realized biomass per unit of P) increased with increasing richness and evenness. Consumer presence reduced overall biomass and richness and precluded a correlation between RUE and biodiversity. At the patch level, local evenness correlated with higher RUE at both imbalanced N∶P ratios (2 and 128) but not at a balanced N∶P ratio. In conclusion, overall P supply constrained realized biomass and altered diversity, whereas resource stoichiometry shaped the relationship between biodiversity and RUE.

The role of fluctuating resource supply in a habitat maintained by the competition‐colonization trade‐off

An exotic species can be a superior colonizer but inferior resource competitor relative to native species. Such species can spatially coexist for an extended period of time in a community maintained via competition-colonization (CC) trade-offs. Whether fluctuations in resource supply allow such exotic species to successfully invade and displace the native species or hold the coexistence is not previously explored, and it is the focus of this study. In this article, we model propagule-limited spatial competition explicitly linked with resource-competition within the framework of the classic CC-model, while time-dependent fluctuations in resource supply are considered in a sinusoidal function. The model predicts that if the amplitude of the fluctuations is greater than the average resource supply rate, there exist a range of values of fluctuation frequency that can allow the exotic species to successfully invade the habitat and to reduce the extent of native species. On the other hand, if the fluctuation amplitude is less than the average resource supply rate, such exotic species can coexist with the native species, independent of fluctuation frequencies. In addition, we found that at a constant resource supply rate, the exotic species can stably coexist with the native species at competitive equilibrium.