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116 results for “Competition for resources”

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dryad32/100

Data from: Combined effects of natural enemies and competition for resources on a forest defoliator: a theoretical and empirical analysis

Explanations for the dynamics of insect outbreaks often focus on natural enemies, on the grounds that parasitoid and pathogen attack rates are high during outbreaks. While natural enemy models can successfully reproduce outbreak cycles, experiments have repeatedly demonstrated the importance of resource quality and abundance. Experiments, however, are rarely invoked in modeling studies. Here we combine mechanistic models, observational data, and field experiments to quantify the roles of parasitoid attacks and resource competition on the jack pine budworm, Choristoneura pinus. By fitting models to a combination of observational and experimental data, we show that parasitoid attacks are the main source of larval budworm mortality at low and intermediate budworm densities, but that resource competition is the main source of mortality at high densities. Our results further show that the effects of resource competition become more severe with increasing host tree age, and that the effects of parasitoids are moderated by strong competition between parasitoids for hosts. Allowing for these effects in a model of insect outbreaks leads to realistic outbreak cycles, while a host-parasitoid model without resource competition produces an unrealistic stable equilibrium. The effects of resource competition are modulated by tree age, which in turn depends on fire regimes. Our model therefore suggests that increases in fire frequency due to climate change may interact in complex ways with budworm outbreaks. Our work shows that resource competition can be as important as natural enemies in modulating insect outbreaks, while demonstrating the usefulness of high-performance computing in experimental field ecology.

opencc-zeroMay 2019View details →

dryad32/100

Data from: Teasing apart plant community responses to N enrichment: the roles of resource limitation, competition and soil microbes

Although ecologists have documented the effects of nitrogen enrichment on productivity, diversity and species composition, we know little about the relative importance of the mechanisms driving these effects. We propose that distinct aspects of environmental change associated with N enrichment (resource limitation, asymmetric competition, and interactions with soil microbes) drive different aspects of plant response. We test this in greenhouse mesocosms, experimentally manipulating each factor across three ecosystems: tallgrass prairie, alpine tundra and desert grassland. We found that resource limitation controlled productivity responses to N enrichment in all systems. Asymmetric competition was responsible for diversity declines in two systems. Plant community composition was impacted by both asymmetric competition and altered soil microbes, with some contributions from resource limitation. Results suggest there may be generality in the mechanisms of plant community change with N enrichment. Understanding these links can help us better predict N response across a wide range of ecosystems.

opencc-zeroDec 2015View details →

dryad32/100

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

1. 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 these 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. 2. 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. 3. To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata. 4. 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. 5. 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 act as mediators to the balance between negative and positive density-dependence.

opencc-zeroDec 2016View details →

dryad32/100

Exploitative competition for floral resources reduces sugar intake but differently impacts the foraging behaviour of two non-bee flower visitors

Identifying which behavioural strategies maximize individual fitness is a key objective in ecology. Organisms are known to adapt their foraging behaviour to their environment in response to abiotic and biotic constraints, such as the distribution of resources or the presence of competitors. For instance, bees are known to avoid recently visited flowers and thus focus their foraging on more rewarding patches. Whether other flower-visiting insects adapt their foraging behaviour in response to exploitative competition for floral resources remains unknown. Here, we asked if a predatory hoverfly (Episyrphus balteatus) and a parasitoid (Aphidius colemani) 1) are physiologically impacted by flower resource limitation following exploitation of flowers by a competitor (either the bumblebee Bombus terrestris or E. balteatus); 2) have the ability to discriminate flowers that were previously exploited by a competitor; and 3) modify their foraging behaviour accordingly. Episyrphus balteatus and A. colemani individuals foraging on previously exploited flowers were found to be less concentrated in sugar compounds, especially in fructose and glucose, suggesting that previously exploited flowers contained less available sugars. Nevertheless, individuals did not avoid previously exploited patches in the choice experiment. On the contrary, E. balteatus females preferentially landed on inflorescences that had previously been exploited by conspecifics (but not by B. terrestris), while A. colemani did not show preferences between inflorescences. However, female hoverflies spent more time feeding on unexploited patches, suggesting that exploited patches were resource limited. To our knowledge, this study provides the first evidence of the use of social cues among E. balteatus individuals in food foraging strategies. It also shows that even insects with tiny nectar requirements, such as parasitoids, can suffer from heavy exploitative competition. Such results may have applied consequences for the understanding of natural enemy conservation, in particular in agroecosystems where competition with honeybees may be important.

opencc-zeroNov 2021View details →

dryad32/100

Heterogeneity in resource competition covaries with individual variation in long-term social relationships

Resource competition among conspecifics is central to social evolution, as it serves as one of the primary selective pressures of group living. This is because the degree of competition for resources impacts the costs and benefits of social interactions. Despite this, how heterogeneity in resource competition drives variation in the type and quantity of long-term social relationships individuals foster has been overlooked. By measuring male mating competition and female foraging competition in a highly social, long-lived mammal, we demonstrate that individual variation in long-term intrasexual social relationships covaries with preferred habitat and experienced resource competition, and this effect differs based on the sex of the individual. Specifically, greater resource competition resulted in fewer social preferences, but the magnitude of the effect varied by both habitat and sex, whereas for social avoidances, both the directionality and magnitude of the effect of resource competition varied by habitat and sex. Together our work shows how fine-scale variation in individual socioecological niches (i.e., unique physical and social environments) can drive extensive variation in individual social behavior (here long-term relationships) within a population, thereby broadening current theories of social evolution.

opencc-zeroApr 2022View details →

dryad32/100

Intraspecific competition and temperature drive habitat-based resource polymorphism in brook charr

Intra- and interspecific competition, two density-dependent processes, are the two main driving forces suggested to promote habitat-based resource polymorphism, but very few studies have provided empirical support for this hypothesis. Furthermore, external drivers like temperature, an important environmental constraint in ectotherms, are often omitted when studying density-dependent habitat selection. Specifically, ambient temperature may have important effects on habitat-based resource polymorphism in ectotherms. Using mixed-effects modelling and isodar analyses, we quantified the effects of water temperature as well as intra- and interspecific competition on abundance and density-dependent habitat selection of brook charr (Salvelinus fontinalis) between littoral and pelagic habitats in 27 Canadian Shield lakes. We found that interspecific competition with white sucker (Catostomus commersonii) reduced brook charr abundances in both habitats but did not affect their density-dependent habitat selection. In contrast, the isodar analysis showed density-dependent habitat selection, confirming that intraspecific competition is a driver of brook charr habitat use in this system. Furthermore, brook charr preferred the littoral habitat at water temperatures below 20.8°C, but preferred the pelagic habitat above this threshold and no longer used the littoral habitat when its temperature was above ~22.2°C. By incorporating an external driver in the density-dependent habitat selection model, we show how the littoral temperature can shape brook charr distribution patterns between the littoral and pelagic habitats by acting as a thermal barrier and thus limiting the willingness of fish to use resources in the littoral habitat. This result suggests that global warming could constrain the diversifying effect of intraspecific competition and prevent resource polymorphism, a phenomenon that promotes adaptive radiation and speciation.

opencc-zeroOct 2022View details →

dryad32/100

Rapid evolution of ecological sexual dimorphism driven by resource competition

Sex differences in ecologically-important traits are common in animals and plants, and prompted Darwin to first propose an ecological cause of sexual dimorphism. Despite theoretical plausibility and Darwin's original notion, a role for ecological resource competition in the evolution of sexual dimorphism has never been directly demonstrated and remains controversial. I used experimental evolution in Drosophila melanogaster to test the hypothesis that resource competition can drive the evolution of sex differences in diet. Following just three generations of adaptation, offspring from flies evolved in low-resource, high-competition environments show elevated sexual dimorphism in diet preference compared to both the ancestor and populations evolved on high resource availability. This increased sexual dimorphism was the result of divergence in male sucrose intake and female yeast intake consistent with the differential nutritional requirements of the sexes. These results provide the first real-time direct evidence for evolution of sexual dimorphism driven by resource competition.

opencc-zeroOct 2022View details →

dryad32/100

Data from: The evolution of competitive ability for essential resources

Competition for limiting resources is among the most fundamental ecological interactions and has long been considered a key driver of species coexistence and biodiversity. Species' minimum resource requirements, their R*s, are key traits that link individual physiological demands to the outcome of competition. However, a major question remains unanswered - to what extent are species' competitive traits able to evolve in response to resource limitation? To address this knowledge gap, we performed an evolution experiment in which we exposed Chlamydomonas reinhardtii for approximately 285 generations to seven environments in chemostats which differed in resource supply ratios (including nitrogen, phosphorus and light limitation) and salt stress. We then grew the ancestors and descendants in common garden and quantified their competitive abilities for essential resources. We investigated constraints on trait evolution by testing whether changes in resource requirements for different resources were correlated. Competitive abilities for phosphorus improved in all populations, while competitive abilities for nitrogen and light increased in some populations and decreased in others. In contrast to the common assumption that there are trade-offs between competitive abilities for different resources, we found that improvements in competitive ability for a resource came at no detectable cost. Instead, improvements in competitive ability for multiple resources were either positively correlated or not significantly correlated. Using resource competition theory, we then demonstrated that rapid adaptation in competitive traits altered the predicted outcomes of competition. These results highlight the need to incorporate contemporary evolutionary change into predictions of competitive community dynamics over environmental gradients.

opencc-zeroMar 2020View details →

dryad32/100

Data from: Resource competition promotes tumour expansion in experimentally evolved cancer

Tumour progression involves a series of phenotypic changes to cancer cells, each of which presents therapeutic targets. Here, using techniques adapted from microbial experimental evolution, we investigate the evolution of tumour spreading - a precursor for metastasis and tissue invasion - in environments with varied resource supply. Evolutionary theory predicts that competition for resources within a population will select for individuals to move away from a natal site (i.e. disperse), facilitating the colonisation of unexploited resources and decreasing competition between kin. After approximately 100 generations in environments with low resource supply, we find that MCF7 breast cancer spheroids (small in vitro tumours) show increased spreading. Conversely, spreading slows compared to the ancestor where resource supply is high. Common garden experiments confirm that the evolutionary responses differ between selection lines; with lines evolved under low resource supply showing a plastic spreading phenotype. These differences in spreading behaviour between selection lines are heritable (stable across multiple generations), and show that the divergently evolved lines differ in their response to resource supply. It is possible that prolonged resource limitation itself causes a stable switch toward dispersal-like behaviour and an increased sensitivity to resource availability without the need for genetic change. Different clinical strategies may be needed depending on whether tumour progression is due to stable or plastic effects. This study highlights the effectiveness of experimental evolution approaches in cancer cell populations and demonstrates how simple model systems might enable us to observe and measure key selective drivers of clinically important traits.

opencc-zeroDec 2016View details →

dryad32/100

Divergent growth-differentiation balance strategies and resource competition shape mortality patterns in ponderosa pine

Dynamic resource availability leads to trade-offs among functions in plants. The growth-differentiation balance hypothesis (GDBH) predicts greater allocation of carbon to defense than growth when resources are scarce; with optimum defense production occurring at a point between the minimum and maximum growth rates. While the GDBH has been widely tested, consideration of phenotypic variation in rates for which defense is traded for growth and what this variation means for plant resistance remains rare. For defense, pines produce and store oleoresin in "resin ducts." Retrospective comparisons of resin ducts in pines have revealed that trees with greater numbers, sizes, or areas of xylem resin ducts are more likely to avoid or survive insect attacks. We used tree ring chronologies to quantify phenotypic variation in growth and resin duct defenses in pairs of living and bark beetle-killed Pinus ponderosa trees in southern New Mexico, USA, and to test the utility of the GDBH for explaining tree mortality. We also assessed the sensitivity of annual growth to climate and competitor density in years preceding mortality in each pair. Survivors had greater growth rates and total cross-sectional areas of resin ducts than trees killed by bark beetles. We did not observe a difference in climate-growth relationships among the groups, however, trees killed by bark beetles suffered negative effects of competition while survivors did not. Growth-defense trade-offs conformed to the GDBH's prediction of a quadratic relationship, however, the two groups significantly differed in the rate at which defense was traded for increasing levels of annual growth. Our results demonstrate that phenotypic variation in the trade-off between growth and defense could be used to characterize trees that were killed by or survived recent natural enemy epidemics. We hypothesize that the GDBH could be integrated with the characterization of phenotypic variation in growth-differentiation strategies—along with parsing of gene versus environment influences on phenotypes—at both local and landscape scales to increase our understanding of patterns of natural enemy impacts in plant populations.

opencc-zeroDec 2021View details →

zenodo32/100

Chat-GPT MT: Competitive for High- (but not Low-) Resource Languages

System outputs for the paper Chat-GPT MT: Competitive for High- (but not Low-) Resource Languages. Contains outputs for ChatGPT zero-shot and five-shot, GPT-4 five-shot, and Google Translate API

opencc-by-4.0Aug 2023View details →

dryad32/100