High-resource Environments Research Articles

Variation in root traits and phenotypic plasticity between native and introduced populations of the invasive plant Chromolaena odorata

Understanding intraspecific trait variations, particularly for invasive species that occupy large geographic areas with different resource conditions, can enhance our understanding of plant responses to changes in environmental resources. However, most related studies have focused on aboveground traits, while variations in root traits and responses to changes in resources during biological invasion have not been clarified. To fill this knowledge gap, we compared the root traits of Chromolaena odorata from 10 introduced populations in Southeast Asia and 12 native populations in North and Central America under different soil nutrients. The introduced populations of the invader exhibited greater resource-acquisitive root traits, characterized by reduced fine root diameter but increased proportions of absorbing root length and specific root length, compared to the native populations. Although nutrient addition significantly affected root traits, the introduced populations showed greater phenotypic plasticity in four traits (root / shoot ratio, specific root length, absorbing root length proportion, and branching intensity) than the native populations. Different root trait syndromes were observed between the introduced and native populations. These results indicate that after introduction, C. odorata may shift towards a more soil resource-acquisitive strategy and thus respond more positively to increased soils nutrients, thereby showing better performance in high-resource environments. This study provides a better understanding of how species respond to environment changes and reveals the factors underlying exotic plant invasion success.

The Late Miocene Talpidae (Eulipotyphla, Mammalia) from the Pannonian Region, Slovakia

AbstractCentral Europe is an area of high diversity for the Talpidae (Eulipotyphla, Mammalia) during the Late Miocene. The assemblages from Slovakia (Borský Svätý Jur, Krásno, Pezinok, Šalgovce, Studienka, Triblavina) are no exception with their abundant material representing eleven species. The uropsiline Desmanella is represented by D. rietscheli and D. dubia. Desmanini fossils are attributed to Archaeodesmana vinea, Archaeodesmana dissona new species, Gerhardstorchia biradicata, and Gerhardstorchia sp. The scalopines Proscapanus minor and P. austriacus are well recorded in the Vallesian localities and support the emergence of P. austriacus before the MN9/10 transition. Talpini and Urotrichini are especially rare and only represented by Talpa cf. T. minuta and Urotrichini gen. sp. indet. Finally, we identified the youngest occurrence of Desmanodon in Europe, D. cf. D. fluegeli, at the MN9 locality of Borský Svätý Jur. The high diversity in the Late Miocene Central European is partly explained by the co-occurrence of the competing Scalopini and Talpini during the Vallesian, indicating high resource environments. The decline of these tribes, followed by the success of the desmans during the Turolian, appears as a consequence of regional environmental changes.UUID: http://zoobank.org/a3eb532b-c341-489a-b0ff-ecf3f9466a76

Divergence in functional traits in seven species of neotropical palms of different forest strata.

Functional traits are morphological and physiological characteristics that determine growth, reproduction, and survival strategies. The leaf economics spectrum proposes two opposing life history strategies: species with an "acquisitive" strategy grow fast and exploit high-resource environments, while species with a "conservative" strategy emphasize survival and slow growth under low resource conditions. We analyzed intra and interspecific variation in nine functional traits related to biomass allocation and tissue quality in seven Neotropical palm species from understory and canopy strata. We expected that the level of resources of a stratum that a species typically exploits would determine the dominance of either the exploitative or conservative strategy, as well as degree of divergence in functional traits between species. If this is correct, then canopy species will show an acquisitive strategy emphasizing traits targeting a larger size, whereas understory species will show a conservative strategy with traits promoting efficient biomass allocation and survival in the shade. Two principal components (57.22% of the variation) separated palm species into: (a) canopy species whose traits were congruent with the acquisitive strategy and emphasized large size (i.e., diameter, height, carbon content, and leaf area), and (b) understory species whose traits were associated with efficient biomass allocation (i.e., dry mass fraction -DMF- and tissue density). As we unravel the variation in functional traits in palms, which make up a substantial proportion of the tropical flora, we gain a deeper understanding of how plants adapt to environmental gradients.

The Use and Non-Use of Technology During Hurricanes

Hurricanes can cause catastrophic damage; it is critical for those affected to access information about conditions, loved ones, and resources. Prior work in the HCI and CSCW communities has focused on how social media can be vital during natural disasters; non-social media technologies have been under-researched. To understand how technology other than social media can support or harm people during crises, we explore hurricane survivors' use and disuse of multiple kinds of technologies in online surveys with 138 US participants. We find substantial technology use supporting survivors' comfort and safety other than social media. We also observe that designing technologies for high-resource environments--as with many mainstream apps--causes users to decrease use of potentially critical technologies during utility outages, which are common during hurricanes. With themes of both (a) broad technology use and (b) conditions preventing technology use, we make recommendations for technical design, policy, and research to empower communities susceptible to hurricanes.

Antenatal corticosteroids: an updated assessment of anticipated benefits and potential risks

Antenatal steroid therapy is increasingly central to the obstetric management of women at imminent risk of preterm birth. For women likely to deliver between 24 and 34 weeks’ gestation, antenatal steroid therapy is standard of care, conveying sizable benefits and few risks in high-resource environments when appropriately targeted.Recent studies have focused on antenatal steroid use in periviable and late preterm populations, and in term cesarean deliveries. As a result, antenatal steroid therapy has now been applied from 22 weeks, to those delivered at 39+6 weeks estimated gestational age. There is also an increased appreciation that the vast majority of randomized control data informing the use of antenatal steroids derive from predominantly high-resource, Caucasian populations. Accordingly, a sizable amount of work has recently been undertaken to test if and how to safely use antenatal steroids in low- and middle-resource environments, wherein the often-high rates of preterm birth make these low cost, easily administered interventions an attractive proposition.It is likely underappreciated by the obstetric and neonatal communities that the overall efficacy of antenatal steroid therapy is highly variable (including when preterm risk is accurately assessed), that the treatment regimens employed are largely arbitrary, dosing is supra-pharmacological for effect, and the extent to which the benefit to risk balance is significantly and differentially modified by gestation. It is also very likely that the patients consented to receive these treatments are similarly unaware of the complex balance of potential benefits and harms. Although a small number of follow-up studies present a generally benign picture of long-term antenatal steroid risk, several large, population-based retrospective studies have identified associations between antenatal steroid use, childhood mental disease and newborn infections that warrant urgent attention.Of particular contemporary importance is emergent efforts to optimize antenatal steroid regimens based on the pharmacokinetics and pharmacodynamics of the agents themselves, the need for better targeting of these potent drugs, and clear articulation of the potential benefits and harms of antenatal steroid use at differing stages of pregnancy, and in different delivery contexts.

Pediatric Emergency Medicine Physicians' Perspectives on Emergency Care of Children With Medical Complexity: A Multi-institution Mixed-Methods Assessment.

Children with medical complexity (CMC) compose 1% of the pediatric population but account for 20% of pediatric emergency department (ED) visits. Previous descriptions of challenges and interventions to ensure quality of care are limited. Our objective was to elicit pediatric emergency medicine (PEM) physicians' perspectives on challenges and opportunities for improvement of emergency care of CMC, with a focus on emergency information forms (EIFs). We conducted a web-based survey of PEM physicians participating the American Academy of Pediatrics Section on Emergency Medicine Survey listserv. The survey was designed using an expert panel, and subsequently piloted and revised to an 18-item survey. Data were analyzed with descriptive statistics. One hundred fifty-one of 495 respondents (30%) completed the survey. Most respondents (62.9%) reported caring for >10 CMC per month. Whereas overall medical fragility and time constraints were major contributors to the challenges of caring for CMC in the ED, communication with known providers and shared care plans were identified as particularly helpful. Most respondents did not report routine use of EIFs. Anticipated emergencies/action plan was deemed the most important component of EIFs. Most PEM physicians view the care for CMC in the ED as challenging despite practicing in high-resource environments. Further research is needed to develop and implement strategies to improve care of CMC in the ED. Understanding experiences of providers in general ED settings is also an important next step given that 80% of CMC present for emergency care outside of major children's hospitals.

Disparities among crop species in the evolution of growth rates: the role of distinct origins and domestication histories.

Growth rates vary widely among plants with different strategies. For crops, evolution under predictable and high-resource environments might favour rapid resource acquisition and growth, but whether this strategy has consistently evolved during domestication and improvement remains unclear. Here we report a comprehensive study of the evolution of growth rates based on comparisons among wild, landrace, and improved accessions of 19 herbaceous crops grown under common conditions. We also examined the underlying growth components and the influence of crop origin and history on growth evolution. Domestication and improvement did not affect growth consistently, that is growth rates increased or decreased or remained unchanged in different crops. Crops selected for fruits increased the physiological component of growth (net assimilation rate), whereas leaf and seed crops showed larger domestication effects on morphology (leaf mass ratio and specific leaf area). Moreover, climate and phylogeny contributed to explaining the effects of domestication and changes in growth. Crop-specific responses to domestication and improvement suggest that selection for high yield has not consistently changed growth rates. The trade-offs between morpho-physiological traits and the distinct origins and histories of crops accounted for the variability in growth changes. These findings have far-reaching implications for our understanding of crop performance and adaptation.

Evolution of Bacterial Cross-Resistance to Lytic Phages and Albicidin Antibiotic.

Due to concerns over the global increase of antibiotic-resistant bacteria, alternative antibacterial strategies, such as phage therapy, are increasingly being considered. However, evolution of bacterial resistance to new therapeutics is almost a certainty; indeed, it is possible that resistance to alternative treatments might result in an evolved trade-up such as enhanced antibiotic resistance. Here, we hypothesize that selection for Escherichia coli bacteria to resist phage T6, phage U115, or albicidin, a DNA gyrase inhibitor, should often result in a pleiotropic trade-up in the form of cross-resistance, because all three antibacterial agents interact with the Tsx porin. Selection imposed by any one of the antibacterials resulted in cross-resistance to all three of them, in each of the 29 spontaneous bacterial mutants examined in this study. Furthermore, cross-resistance did not cause measurable fitness (growth) deficiencies for any of the bacterial mutants, when competed against wild-type E. coli in both low-resource and high-resource environments. A combination of whole-genome and targeted sequencing confirmed that mutants differed from wild-type E. coli via change(s) in the tsx gene. Our results indicate that evolution of cross-resistance occurs frequently in E. coli subjected to independent selection by phage T6, phage U115 or albicidin. This study cautions that deployment of new antibacterial therapies such as phage therapy, should be preceded by a thorough investigation of evolutionary consequences of the treatment, to avoid the potential for evolved trade-ups.

Electrochemical immunoplatform to unravel neurodegeneration and Alzheimer's disease through the determination of neurofilament light protein

Alzheimer's disease (AD) is a common neurodegenerative disorder associated with massive degradation of neuronal cell structure due to aging. In recent years, neurofilament light chain (NfL) arises as one of the most promising blood biomarkers for AD. Bioassays available for NfL determination in blood (ELISA kits or Simoa assays) require multiple steps, specialized personnel and expensive instrumentation of application limited to centralized and high-resource environments. With the aim of overcoming these drawbacks, this work reports the first magnetic microbeads (MBs)-based electrochemical bioplatform developed so far for the determination of NfL. The developed platform relies in a sandwich type immunoassay involving an HRP-secondary antibody to enzymatically label the detector antibody on the surface of commercial MBs functionalized with carboxylic acids. Amperometric transduction is carried out at screen-printed carbon electrodes (SPCEs) upon deposition of the magnetic bioconjugates on the working electrode surface using the H2O2/hydroquinone (HQ) system. This MBs-based immunoplatform provides a LOD value of 3.0 pg mL−1. The analytical performance is appropriate for the determination of NfL in plasma and brain tissues from AD patients using simple and short protocols (60 min) and requiring low amount of samples (5 µL raw plasma and 0.1 µg tissue extracts).

Allelic response of yield component traits to resource availability in spring wheat.

Investigation of resource availability on allele effects for four yield component quantitative trait loci provides guidance for the improvement of grain yield in high and low yielding environments. A greater understanding of grain yield (GY) and yield component traits in spring wheat may increase selection efficiency for improved GY in high and low yielding environments. The objective of this study was to determine allelic response of four yield component quantitative trait loci (QTL) to variable resource levels which were manipulated by varying intraspecific plant competition and seeding density. The four QTL investigated in this study had been previously identified as impacting specific yield components. They included QTn.mst-6B for productive tiller number (PTN), WAPO-A1 for spikelet number per spike (SNS), and QGw.mst-3B and TaGW2-A1 for kernel weight (KWT). Near-isogenic lines for each of the four QTL were grown in multiple locations with three competition (border, no-border and space-planted) and two seeding densities (normal 216 seedsm-2 and low 76 seedsm-2). Allele response at QTn.mst-6B was driven by changes in resource availability, whereas allele response at WAPO-A1 and TaGW2-A1 was relatively unaffected by resource availability. The QTn.mst-6B.1 allele at QTn.mst-6B conferred PTN plasticity resulting in significant GY increases in high resource environments. The gw2-A1 allele at TaGW2-A1 significantly increased KWT, SNS and GPC offering a source of GY improvement without negatively impacting end-use quality. QGw.mst-3B allelic variation did not significantly impact KWT but did significantly impact SPS. Treatment effects in both experiments often resulted in significant positive impacts on GY and yield component traits when resource availability was increased. Results provide guidance for leveraging yield component QTL to improve GY performance in high- and low-yield environments.

Corruption in global health: the open secret (personal opinion)

• The author is a physician and has served as Health Minister in her home country, Peru.• She reviews the role of leaders in low-resource settings in the development of corruption and extends her comments to high-resource environments.• She discusses 6 types of corruption: absenteeism, informal payments from patients, theft of money, supplies and medications, corruption in service provision, favouritism, and manipulation of data.

A growth-defense trade-off is general across native and exotic grasses.

High-resource environments typically favor quick-growing, poorly defended plants, while resource-poor environments typically favor slow-growing, well-defended plants. The prevailing hypothesis explaining this pattern states that, as resource availability increases, well-defended, slow-growing species are replaced by poorly defended, fast-growing species. A second hypothesis states that greater resource availability increases allocation to growth at the expense of defense, within species. Regardless of mechanism, if exotic species are released from enemies relative to natives, shifts in allocation to growth and defense both within and among species could differ by geographic provenance. To test whether resource availability alters growth or defense, within and among species, and whether any such effects differ between natives and exotics, we manipulated soil nutrient supply and access of aboveground insect herbivores and fungal pathogens under field conditions to individuals of six native and six exotic grass species that co-occurred in a North Carolina old field. The prevailing hypothesis' prediction-that species-level enemy impact increases with species' nutrient responsiveness-was confirmed. Moreover, this relationship did not differ between native and exotic species. The second hypothesis' prediction-that individual-level enemy impact increases with nutrient supply, after accounting for species-level variation in performance-was not supported. Together, these results support the idea, across native and exotic species, that plant species turnover is the primary mechanism underlying effects of nutrient enrichment on allocation to growth and defense in plant communities.

Inducible pesticide tolerance in Daphnia pulex influenced by resource availability.

Pesticides are a ubiquitous contaminant in aquatic ecosystems. Despite the relative sensitivity of aquatic species to pesticides, growing evidence suggests that populations can respond to pesticides by evolving higher baseline tolerance or inducing a higher tolerance via phenotypic plasticity. While both mechanisms can allow organisms to persist when faced with pesticides, resource allocation theory suggests that tolerance may be related to resource acquisition by the organism. Using Daphnia pulex, we investigated how algal resource availability influenced the baseline and inducible tolerance of D. pulex to a carbamate insecticide, carbaryl. Individuals reared in high resource environments had a higher baseline carbaryl tolerance compared to those reared in low resource environments. However, D. pulex from low resource treatments exposed to sublethal concentrations of carbaryl early in development induced increased tolerance to a lethal concentration of carbaryl later in life. Only individuals reared in the low resource environment induced carbaryl tolerance. Collectively, this highlights the importance of considering resource availability in our understanding of pesticide tolerance.

Effects of Short- and Long-Term Variation in Resource Conditions on Soil Fungal Communities and Plant Responses to Soil Biota.

Soil biota can strongly influence plant performance with effects ranging from negative to positive. However, shifts in resource availability can influence plant responses, with soil pathogens having stronger negative effects in high-resource environments and soil mutualists, such as arbuscular mycorrhizal fungi (AMF), having stronger positive effects in low-resource environments. Yet the relative importance of long-term vs. short-term variation in resources on soil biota and plant responses is not well-known. To assess this, we grew the perennial herb Asclepias speciosa in a greenhouse experiment that crossed a watering treatment (wet vs. dry treatment) with a manipulation of soil biota (live vs. sterilized soil) collected from two geographic regions (Washington and Minnesota) that vary greatly in annual precipitation. Because soil biota can influence many plant functional traits, we measured biomass as well as resource acquisition (e.g., root:shoot, specific leaf area) and defense (e.g., trichome and latex production) traits. Due to their important role as mutualists and pathogens, we also characterized soil fungal communities in the field and greenhouse and used curated databases to assess fungal composition and potential function. We found that the experimental watering treatment had a greater effect than soil biota origin on plant responses; most plant traits were negatively affected by live soils under wet conditions, whereas responses were neutral or positive in live dry soil. These consistent differences in plant responses occurred despite clear differences in soil fungal community composition between inoculate origin and watering treatments, which indicates high functional redundancy among soil fungi. All plants grown in live soil were highly colonized by AMF and root colonization was higher in wet than dry soil; root colonization by other fungi was low in all treatments. The most parsimonious explanation for negative plant responses in wet soil is that AMF became parasitic under conditions that alleviated resource limitation. Thus, plant responses appeared driven by shifts within rather than between fungal guilds, which highlights the importance of coupling growth responses with characterizations of soil biota to fully understand underlying mechanisms. Collectively these results highlight how short-term changes in environmental conditions can mediate complex interactions between plants and soil biota.

Relative importance of competition and plant-soil feedback, their synergy, context dependency and implications for coexistence.

Plants interact simultaneously with each other and with soil biota, yet the relative importance of competition vs. plant-soil feedback (PSF) on plant performance is poorly understood. Using a meta-analysis of 38 published studies and 150 plant species, we show that effects of interspecific competition (either growing plants with a competitor or singly, or comparing inter- vs. intraspecific competition) and PSF (comparing home vs. away soil, live vs. sterile soil, or control vs. fungicide-treated soil) depended on treatments but were predominantly negative, broadly comparable in magnitude, and additive or synergistic. Stronger competitors experienced more negative PSF than weaker competitors when controlling for density (inter- to intraspecific competition), suggesting that PSF could prevent competitive dominance and promote coexistence. When competition was measured against plants growing singly, the strength of competition overwhelmed PSF, indicating that the relative importance of PSF may depend not only on neighbour identity but also density. We evaluate how competition and PSFs might interact across resource gradients; PSF will likely strengthen competitive interactions in high resource environments and enhance facilitative interactions in low-resource environments. Finally, we provide a framework for filling key knowledge gaps and advancing our understanding of how these biotic interactions influence community structure.

Antenatal corticosteroids: an assessment of anticipated benefits and potential risks

Antenatal corticosteroids are standard of care for pregnancies at risk of preterm delivery between 24-34 weeks' gestational age. Recent trials demonstrate modest benefits from antenatal corticosteroids for late preterm and elective cesarean deliveries, and antenatal corticosteroids for periviable deliveries should be considered with family discussion. However, many women with threatened preterm deliveries receive antenatal corticosteroids but do not deliver until >34 weeks or at term. The net effect is that a substantial fraction of the delivery population will be exposed to antenatal corticosteroids. There are gaps in accurate assessments of benefits of antenatal corticosteroids because the randomized controlled trials were performed prior to about 1990 in pregnancies generally >28 weeks. The care practices for the mother and infant survival were different than today. The randomized controlled trial data also do not strongly support the optimal interval from antenatal corticosteroid treatment to delivery of 1-7 days. Epidemiology-based studies using large cohorts with >85% of at-risk pregnancies treated with antenatal corticosteroids probably overestimate the benefits of antenatal corticosteroids. Although most of the prematurity-associated mortality is in low-resource environments, the efficacy and safety of antenatal corticosteroids in those environments remain to be evaluated. The short-term benefits of antenatal corticosteroids for high-risk pregnancies in high-resource environments certainly justify antenatal corticosteroids as few risks have been identified over many years. However, cardiovascular and metabolic abnormalities have been identified in large animal models and cohorts of children exposed to antenatal corticosteroids that are consistent with fetal programming for adult diseases. These late effects of antenatal corticosteroids suggest caution for the expanded use of antenatal corticosteroids beyond at-risk pregnancies at 24-34 weeks. A way forward is to develop noninvasive fetal assessments to identify pregnancies across a wider gestational age that could benefit from antenatal corticosteroids.

The Role of the WFSA in Reaching the Goals of the Lancet Commission on Global Surgery.

The Role of the WFSA in Reaching the Goals of the Lancet Commission on Global Surgery.

Invasive Egg Predators and Food Availability Interactively Affect Maternal Investment in Egg Chemical Defense

Invasive species commonly predate the offspring of native species and eggs are the life stage most vulnerable to this predation. In many species with no maternal care, females can alter the phenotype of eggs to protect them, for instance through chemical defence. In ladybirds egg alkaloids deter predators, including invasive predatory species of ladybirds, but conversely may attract cannibals who benefit from the consumption of eggs with higher alkaloid levels. Invasive predators tend to be more abundant where resources are also abundant, but in high resource environments the maternal fitness benefits of sibling cannibalism are low. Consequently this presents a conflict for female ladybirds between the different factors that influence egg alkaloid level, as protecting her eggs from predators might come with the cost of inadvertently encouraging within-clutch cannibalism under circumstances where it is not beneficial. We investigated how the ladybird Adalia bipunctata addresses this trade-off experimentally, by measuring the quantity of alkaloids in eggs laid by ladybirds in environments that differed in levels of resource availability and perceived predation risk from an invasive predator Harmonia axyridis. Females did lay eggs with higher egg alkaloid levels under poor resource conditions, but only when predator cues were absent. The resulting negative correlation between egg number and egg alkaloid level under poor resource conditions indicates a trade-off between these two attributes of maternal investment, mediated by female response to offspring predation risk. This implies that selection pressures on mothers to adaptively adjust the risk of siblicide may outweigh the need to protect offspring from interspecific predation. Our results demonstrate that maternal effects are an important aspect of species’ responses to invasive predators, and highlight the value of studying maternal effects in the context of the multifaceted environments in which they occur.

Nonacademic Attributes Predict Medical and Nursing Student Intentions to Emigrate or to Work Rurally: An Eight-Country Survey in Asia and Africa.

AbstractWe sought to identify independent, nonacademic predictors of medical and nursing student intent to migrate abroad or from rural to urban areas after graduation in low- and middle-income countries (LMIC). This was a cross-sectional survey of 3,199 first- and final-year medical and nursing students at 16 training institutions in eight LMIC. Questionnaires assessed demographics, career intentions, and preferences regarding selected career, location, and work-related attributes. Using principal component analysis, student preferences were reduced into four discrete categories of priorities: 1) work environment resources, 2) location livability, 3) altruistic job values, and 4) individualistic job values. Students' preferences were scored in each category. Using students' characteristics and priority scores, multivariable proportional odds models were used to derive independent predictors of intentions to emigrate for work outside the country, or to work in a rural area in their native country. Students prioritizing individualistic values more often planned international careers (adjusted odds ratio [aOR] = 1.44, 95% confidence interval [CI] = 1.16-1.78), whereas those prioritizing altruistic values preferred rural careers (aOR = 1.82, 95% CI = 1.50-2.21). Trainees prioritizing high-resource environments preferentially planned careers abroad (aOR = 1.38, 95% CI = 1.12-1.69) and were unlikely to seek rural work (aOR = 0.60, 95% CI = 0.49-0.73). Independent of their priorities, students with prolonged prior rural residence were unlikely to plan emigration (aOR = 0.67, 95% CI = 0.50-0.90) and were more likely to plan a rural career (aOR = 1.53, 95% CI = 1.16-2.03). We conclude that use of nonacademic attributes in medical and nursing admissions processes would likely increase retention in high-need rural areas and reduce emigration "brain drain" in LMIC.

Field manipulations of resources mediate the transition from intraspecific competition to facilitation.

Population density affects individual performance, though its effects are often mixed. For sessile species, increases in population density typically reduce performance. Still, cases of positive density-dependence do occur in sessile systems and demand explanation. The stress gradient hypothesis (SGH) predicts that under stressful conditions, positive effects of facilitation may outweigh the negative effects of competition. While some elements of the SGH are well studied, its potential to explain intraspecific facilitation has received little attention. Further, there have been questions regarding whether the SGH holds if the stressor is a resource. Most studies of interactions between the environment and intraspecific facilitation have relied on natural environmental gradients; manipulative studies are much rarer. To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata. We found negative effects of density on colony performance in low resource environments, but mainly positive density-dependence in high resource environments. By adding resources, competition effects were reduced and the positive effects of facilitation were revealed. Our results suggest that resource availability mediates the relative strength of competition and facilitation in our system. We also suggest that intraspecific facilitation is more common than may be appreciated and that environmental variation may mediate the balance between negative and positive density-dependence.