Ragan M Callaway

Ragan M Callaway
University of Montana | UMT

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284
Publications
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31,283
Citations
Citations since 2017
67 Research Items
12534 Citations
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Publications

Publications (284)
Article
Plant biodiversity-productivity relationships become stronger over time in grasslands, forests, and agroecosystems. Plant shoot and root litter is important in mediating these positive relationships, yet the functional role of plant litter remains overlooked in long-term experiments. We propose that plant litter strengthens biodiversity-ecosystem f...
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Vegetation pattern formation is a widespread phenomenon in resource-limited environments, but the driving mechanisms are largely unconfirmed empirically. Combining results of field studies and mathematical modeling, empirical evidence for a generic pattern-formation mechanism is demonstrated with the clonal shrub Guilandina bonduc L. (hereafter Gui...
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Earth’s dryland (hyper-arid, arid, semi-arid, and dry sub-humid) ecosystems face increasing aridity and invasion by exotic plant species. In concert, these global changes threaten the biodiversity, ecosystem functioning, and economic viability of drylands worldwide, with critical implications for environmental quality and human wellbeing. Positive...
Article
Year to year stability in crop production is a crucial aspect of feeding a growing global population. Evidence from natural ecosystems shows that increasing plant diversity generally increases the temporal stability of productivity; however, we have little knowledge of the mechanisms by which diversity affects stability. In fact, understanding the...
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An important hypothesis for how plants respond to introduction to new ranges is the evolution of increased competitive ability (EICA). EICA predicts that biogeographical release from natural enemies initiates a trade‐off in which exotic species in non‐native ranges become larger and more competitive, but invest less in consumer defences, relative t...
Preprint
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Interactions among plant species in extreme ecological systems are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat-sharing effects, in particular when microenvironmental heterogeneity and stress are high. Here, we address whether paired and random sampling methods...
Article
This article is a Commentary on Yu et al. (2022), 236: 1140–1153.
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Soil biota can determine plant invasiveness, yet biogeographical comparisons of microbial community composition and function across ranges are rare. We compared interactions between Conyza canadensis, a global plant invader, and arbuscular mycorrhizal (AM) fungi in 17 plant populations in each native and non-native range spanning similar climate an...
Article
Temporally heterogeneous environments may drive rapid and continuous plastic responses, leading to highly variable plasticity in traits. However, direct experimental evidence for such meta‐plasticity due to environmental heterogeneity is rare. Our objective was to investigate the effects of early experience with temporally heterogeneous water avail...
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Temporally dynamic resource supplies may alter or lead to fluctuations in competitive outcomes. Resource pulses have been theorized to promote incursion by exotic species with environments prone to higher resource fluctuations being more susceptible to invasion than those with more stable resource supplies. This is thought to be due, in part, to th...
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Positive interactions can drive the assembly of desert plant communities, but we know little about the species-specificity of positive associations between native shrubs and invasive annual species along aridity gradients. These measures are essential for explaining, predicting, and managing community-level responses to plant invasions and environm...
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Interactions among native and invasive species may affect management outcomes and goals. We implemented different mowing regimes to control the invasive Solidago gigantea and restore natural diversity, and also examined interactions between Solidago and a European native competitor, Tanacetum vulgare in the context of these regimes. Experimentally...
Article
This article is a Commentary on Oduor (2022), 233: 983–994.
Article
Allelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests t...
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Population and income growth are increasing global food demand at a time when a third of the world’s agricultural soils are degraded and climate variability threatens the sustainability of food production. Intercropping, the practice of growing two or more spatially intermingled crops, often increases yields, but whether such yield increases, their...
Article
Pollinators can drive indirect facilitative and competitive indirect interactions among plant species. Most work on indirect facilitation via pollinators has focused on “magnet species” which enhance the pollination success of their neighbors because they are disproportionately attractive. However, focusing on magnet species may overestimate the ge...
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Mixtures of species in natural or agricultural systems can increase the performance of individuals or groups relative to monocultures, often through facilitative mechanisms. Mechanisms include root communication by which plants can interrogate the identity of adjacent plants and respond negatively or positively. Alternatively, mixtures of species c...
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Insect pollinators have been relocated by humans for millennia and are, thus, among the world’s earliest intentional exotic introductions. The introduction of managed bees for crop pollination services remains, to this day, a common and growing practice worldwide and the number of different bee species that are used commercially is increasing. Bein...
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Interspecific facilitation contributes to the assembly of desert plant communities. However, we know little of how desert communities invaded by exotic species respond to facilitation along regional-scale aridity gradients. These measures are essential for predicting how desert plant communities might respond to concomitant plant invasion and envir...
Article
High biodiversity increases ecosystem functions; however, belowground facilitation remains poorly understood in this context. Here, we explore mechanisms that operate via ‘giving–receiving feedbacks’ for belowground facilitation. These include direct effects via root exudates, signals, and root trait plasticity, and indirect biotic facilitation via...
Article
Vegetation patterning in water-limited and other resource-limited ecosystems highlights spatial self-organization processes as potentially key drivers of community assembly. These processes provide insight into predictable landscape-level relationships between organisms and their abiotic environment in the form of regular and irregular patterns of...
Preprint
Full-text available
Aims Temporally heterogeneous environments have crucial influences on plant survival and growth, leading to greater variations in plasticity, but direct experimental evidence is rare. Our objective was to investigate how early experience with temporally heterogeneous water conditions may affect the subsequent performance and plasticity of plants in...
Article
After 25 years of biodiversity experiments, it is clear that higher biodiversity (B) plant communities are usually more productive and often have greater ecosystem functioning (EF) than lower diversity communities. However, the mechanisms underlying this positive biodiversity–ecosystem functioning (BEF) relationship are still poorly understood. The...
Article
The size and frequency of resource pulses can affect plant interactions and increase the abundance of invasive species relative to native species. We examined resource pulses generated during desiccation and rehydration of communities of native biological soil crust (biocrust) forming mosses, in the context of positive associations between biocrust...
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Significance Biodiversity is driven by complex associations among species, but ecologists often look only at competitive or facilitative interactions either independently or only for few species at a time. Using a large dataset of mountain ecosystems encompassing more than 2,000 species across the globe, we analyze the prevalence and importance of...
Article
Biological diversity depends on multiple, cooccurring ecological interactions. However, most studies focus on one interaction type at a time, leaving community ecologists unsure of how positive and negative associations among species combine to influence biodiversity patterns. Using surveys of plant populations in alpine communities worldwide, we e...
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1. Invasive species have the ability to rapidly adapt in the new regions where they are introduced. Classic evolutionary theory predicts that the accumulation of genetic differences over time in allopatric isolation may lead to reproductive incompatibilities resulting in decreases in reproductive success and, eventually, to speciation. However, exp...
Chapter
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This book contains 23 chapters divided into seven parts. Part I reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics; and reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to...
Chapter
This book contains 23 chapters divided into seven parts. Part I reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics; and reviews models, theories and hypotheses on how invasion performance and impact of introduced species in recipient ecosystems can be conjectured according to...
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Priority effects refer to the order or timing of species arrival, including how species that arrive early at a site either positively or negatively affect establishment, growth, or reproduction of species that arrive later. Despite the clear implications of priority effects for ecological restoration, there have been no reviews of how and where pri...
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Tolerance and suppression are distinct components of competition among plants, and recognizing how they affect competitive outcomes is important for understanding the mechanisms and consequences of competition. We used simulations informed by experimental trials to ask whether tolerance or suppression of competitors was more important for the survi...
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Aim and Location Positive interactions influence the assembly of plant communities globally, particularly in stressful environments such as deserts. However, few studies have measured the intensity and relative importance of positive interactions involving native and invasive species along aridity gradients. These measures are essential for predict...
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Exotic invasive plant species alter ecosystems and locally extirpate native plant species, and by doing so alter community structure. Changes in community structure may be particularly important if invaders promote species with certain traits. For example, the positive effects of most invaders on soil fertility may promote species with weedy traits...
Article
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Why only a small proportion of exotic species become invasive is an unresolved question. Escape from the negative effects of soil biota in the native range can be important for the success of many invasives, but comparative effects of soil biota on less successful exotic species are poorly understood. Studies of other mechanisms suggest that such c...
Article
Some invasive plant species rapidly evolve greater size and/or competitive ability in their non‐native ranges. However, it is not well known whether these traits transfer back to the native range, or instead represent genotype by environment interactions where traits are context‐specific to communities in the new range where the evolution occurred....
Article
When a nurse species facilitates the density of more than one species, strong indirect interactions can occur between the facilitated, or beneficiary, species, and these could lead to cascading interactive effects on community dynamics. In this context, negative effects of beneficiaries on the growth or reproduction of nurses are much more common t...
Article
This article is a Commentary on Zhang et al. (2020), 226: 244–253.
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Allelopathy, the release of chemicals by plants that inhibit the germination and growth of competing species, can be an important trait for invasive success. However, little is known about potential biogeographical differences in allelopathy due to divergent regional eco-evolutionary histories. To test this, we examined the allelochemical potential...
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Paterson’s curse (Echium plantagineum L. (Boraginaceae)), is an herbaceous annual native to Western Europe and northwest Africa. It has been recorded in Australia since the 1800’s and is now a major weed in pastures and rangelands, but its introduction history is poorly understood. An understanding of its invasion pathway and subsequent genetic str...
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Relatives often interact differently with each other than with nonrelatives, and whether kin cooperate or compete has important consequences for the evolution of mating systems, seed size, dispersal , and competition. Previous research found that the larger of the size dimorphic seeds produced by the annual plant Aegilops triuncialis suppressed ger...
Article
Background: Echium plantagineum a native of Europe and Africa, is a noxious invasive weed in Australia forming monocultural stands in pastures and rangelands. It produces a complex mixture of bioactive secondary metabolites including toxic pyrrolizidine alkaloids (PAs) that protect the plant from insect and livestock herbivory and naphthoquinones...
Article
Allelopathy, the release of chemicals by plants that inhibit the germination and growth of competing species, can be an important trait for invasive success. However, little is known about potential biogeographical differences in allelopathy due to divergent regional eco-evolutionary histories. To test this, we examined the allelochemical potential...
Article
Comparing genetic diversity, genetic differentiation and performance between native and non‐native populations has advanced our knowledge of contemporary evolution and its ecological consequences. However, such between‐range comparisons can be complicated by high among‐population variation within native and non‐native ranges. For example, native vs...
Article
Plant–soil feedbacks have important effects on plant communities, but most theory has been derived from experiments on intraspecific plant–soil feedbacks. Much less is known about how interspecific plant–soil feedbacks affect coexistence and plant communities, due in part to experimental and analytical challenges. Here, we propose a framework for e...
Article
1.Mosses often have positive effects on soil carbon and nitrogen cycling, but we know little about how environmentally determined cycles of desiccation and rehydration in mosses influence these processes. 2. In this context, we compared carbon and nitrogen in throughfall after precipitation passed through eight moss species that were either hydrate...
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Congeneric species with the same native and non-native ranges, but exhibiting different invasiveness, provide opportunities to assess the relative importance of factors contributing to successful invasions. For example, comparing the competitive ability of such congeners against other species from the native and non-native regions of invasive speci...
Article
1.Exotic plant species commonly exploit disturbances more successfully than native plants. This outcome is widely attributed to the fact that disturbance reduces biotic resistance from native plant competitors. However, biocrusts, communities of mosses, lichens and microorganisms, are a prominent component of semi‐arid grasslands occurring in the i...
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Seed predation can structure plant communities by imposing strong population controls on some species but not others. In this context, studies from various ecosystems report that native granivores selectively forage for seeds from native species over seeds from exotic invaders, which could disproportionately favor the establishment of invaders and...
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Aim: We studied the novel weapons hypothesis in the context of the broadly distributed tree species Eucalyptus globulus. We evaluated the hypothesis that this Australian species would produce stronger inhibitory effects on species from its non-native range than on species from its native range. Location: We worked in four countries where this speci...
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Invasive trees can cause catastrophic reductions in diversity in invaded grasslands and savannas. Such reductions often appear to be particularly severe in the new biogeographic ranges of these invaders. We present results of a field study that examined the effect of slash pine (Pinus elliottii), native to the southeastern US, on savanna groundcove...
Article
Invasive plant impacts vary widely across introduced ranges. We tested the hypothesis that differences in the eco‐evolutionary experience of native communities with the invader correspond with the impacts of invasive species on native vegetation, with impacts increasing with ecological novelty. We compared plant species richness and composition ben...
Article
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 sin...
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The importance of phenotypic plasticity for successful invasion by exotic plant species has been well studied, but with contradictory and inconclusive results. However, many previous studies focused on comparisons of native and invasive species that co‐occur in a single invaded region, and thus on species with potentially very different evolutionar...
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Seed predation and resource competition are fundamental biotic filters that affect the assembly of plant communities, yet empirical studies rarely assess their importance relative to one another. Here, we used rodent exclosures and experimental seed additions to compare how rodent granivory and resource competition affected the net establishment of...
Article
Premise of the study: Seed-level trade-offs of heterocarpic species remain poorly understood. We propose that seedlings emerging from seeds with a permanent pappus (dispersing seeds) are stronger competitors than those emerging from seeds without a pappus (nondispersing seeds) because dispersing seeds are larger and germinate faster than nondisper...
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Species-specific interactions can connect particular species to others, which has important implications for species interdependence and coexistence. However, species-specific effects of ecosystem engineers remain little explored, particularly in the alpine tropics. We investigated the effects of two cushion plants with subtle differences in morpho...
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Many species are characterized by high levels of intraspecific or ecotypic diversity, yet we know little about how diversity within species influences ecosystem processes. Using a common garden experiment, we studied how intraspecific diversity within the widespread and often dominant North American native Pseudoroegneria spicata (Pursh) Á. Löve. a...
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Despite the importance of arbuscular mycorrhizal (AM) fungi within terrestrial ecosystems, we know little about how natural AM fungal communities are structured. To date, the majority of studies examining AM fungal community diversity have focused on single habitats with similar environmental conditions, with relatively few studies having assessed...
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Scientific Reports 7 : Article number: 42792 10.1038/srep42792 ; published online: 17 February 2017 ; updated: 16 March 2017 In the original version of this Article, the legend of Figure 4 was incorrect: “Figure 4: There are two spelling problem in this image.
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Metabolic profiling can be successfully implemented to analyse a living system's response to environmental conditions by providing critical information on an organism's physiological state at a particular point in time and allowing for both quantitative and qualitative assessment of a specific subset(s) of key metabolites. Shikonins are highly reac...
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Echium plantagineum and E. vulgare are congeneric exotics first introduced to Australia in the early 1800 s. There, E. plantagineum is now highly invasive, whereas E. vulgare has a limited distribution. Studies were conducted to evaluate distribution, ecology, genetics and secondary chemistry to shed light on factors associated with their respectiv...
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During the past 100 years, studies spanning thousands of taxa across almost all biomes have demonstrated that competition has powerful negative effects on the performance of individuals and can affect the composition of plant communities, the evolution of traits, and the functioning of whole ecosystems. In this review, we highlight new and importan...
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High species diversity often enhances ecosystem function; however, the effects of diversity have not been commonly explored in the context of natural ecosystem variation. In intermountain grassland, it has been reported that Pinus ponderosa canopies and litter reduces the diversity of native species and increases the abundance of Bromus tectorum, a...
Article
How variation in factors controlling species abundance and distribution between native and non-native ranges compares to that within ranges remains poorly understood. We used a globally distributed ruderal, Centaurea solstitialis (Centaurea), to explore the possibility that the importance of those factors exhibits great variation between and within...
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Invasive species can rapidly adapt to conditions in non-native ranges, including changes in size and competitive ability. However, little is known about the heritability of such changes, and on the importance of hypothetical reintroductions in the maintenance of locally adapted traits. To test for this, we experimentally produced a cohort of Centau...
Article
Arbuscular mycorrhizal (AM) fungi can exert a powerful influence on the outcome of plant-plant competition. Since some exotic plants interact differently with soil biota such as AM fungi in their new range, range-based shifts in AM responsiveness could shift competitive interactions between exotic and resident plants, although this remains poorly s...
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Exotic invasive plants can exert strong selective pressure for increased competitive ability in native plants. There are two fundamental components of competitive ability: suppression and tolerance, and the current paradigm that these components have equal influences on a species' overall competitive ability has been recently questioned. If these c...
Article
Resistance and tolerance are two ways that plants cope with herbivory. Tolerance, the ability of a plant to regrow or reproduce after being consumed, has been studied less than resistance, but this trait varies widely among species and has considerable potential to affect the ecology of plant species. One particular aspect of tolerance, compensator...
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Bioactive plant secondary products are frequently the drivers of complex rhizosphere interactions, including those with other plants, herbivores and microbiota. These chemically diverse molecules typically accumulate in a highly regulated manner in specialized plant tissues and organelles. We studied the production and localization of bioactive nap...
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Plant community productivity can increase with increasing intraspecific genotypic diversity. Previous studies have attributed the genetic diversity-productivity pattern to differential resource use among genotypes, as many studies have found for species. But here we ask whether suppression of productivity at low intraspecific diversity by soil biot...
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Exotic plant invasion is often associated with dramatic increases in above-ground net primary productivity and soil nitrogen. However, most evidence for these increases comes from correlative studies of single species, leaving open the question of whether invasive plants drive these processes and whether they are consistent among invaders. We combi...