Publications by authors named "Andrew S MacDougall"

37 Publications

Globally, plant-soil feedbacks are weak predictors of plant abundance.

Ecol Evol 2021 Feb 27;11(4):1756-1768. Epub 2021 Jan 27.

Department of Biology University of British Columbia Kelowna BC Canada.

Plant-soil feedbacks (PSFs) have been shown to strongly affect plant performance under controlled conditions, and PSFs are thought to have far reaching consequences for plant population dynamics and the structuring of plant communities. However, thus far the relationship between PSF and plant species abundance in the field is not consistent. Here, we synthesize PSF experiments from tropical forests to semiarid grasslands, and test for a positive relationship between plant abundance in the field and PSFs estimated from controlled bioassays. We meta-analyzed results from 22 PSF experiments and found an overall positive correlation (0.12 ≤   ≤ 0.32) between plant abundance in the field and PSFs across plant functional types (herbaceous and woody plants) but also variation by plant functional type. Thus, our analysis provides quantitative support that plant abundance has a general albeit weak positive relationship with PSFs across ecosystems. Overall, our results suggest that harmful soil biota tend to accumulate around and disproportionately impact species that are rare. However, data for the herbaceous species, which are most common in the literature, had no significant abundance-PSFs relationship. Therefore, we conclude that further work is needed within and across biomes, succession stages and plant types, both under controlled and field conditions, while separating PSF effects from other drivers (e.g., herbivory, competition, disturbance) of plant abundance to tease apart the role of soil biota in causing patterns of plant rarity versus commonness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ece3.7167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7882948PMC
February 2021

Landscape modification and nutrient-driven instability at a distance.

Ecol Lett 2021 Mar 21;24(3):398-414. Epub 2020 Nov 21.

McGill University, 1205 Dr-Penfield Ave, Montreal, Quebec, H3A 1B1, Canada.

Almost 50 years ago, Michael Rosenzweig pointed out that nutrient addition can destabilise food webs, leading to loss of species and reduced ecosystem function through the paradox of enrichment. Around the same time, David Tilman demonstrated that increased nutrient loading would also be expected to cause competitive exclusion leading to deleterious changes in food web diversity. While both concepts have greatly illuminated general diversity-stability theory, we currently lack a coherent framework to predict how nutrients influence food web stability across a landscape. This is a vitally important gap in our understanding, given mounting evidence of serious ecological disruption arising from anthropogenic displacement of resources and organisms. Here, we combine contemporary theory on food webs and meta-ecosystems to show that nutrient additions are indeed expected to drive loss in stability and function in human-impacted regions. Our models suggest that destabilisation is more likely to be caused by the complete loss of an equilibrium due to edible plant species being competitively excluded. In highly modified landscapes, spatial nutrient transport theory suggests that such instabilities can be amplified over vast distances from the sites of nutrient addition. Consistent with this theoretical synthesis, the empirical frequency of these distant propagating ecosystem imbalances appears to be growing. This synthesis of theory and empirical data suggests that human modification of the Earth is strongly connecting distantly separated ecosystems, causing rapid, expansive and costly nutrient-driven instabilities over vast areas of the planet. Similar to existing food web theory, the corollary to this spatial nutrient theory is that slowing down spatial nutrient pathways can be a potent means of stabilising degraded ecosystems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ele.13644DOI Listing
March 2021

General destabilizing effects of eutrophication on grassland productivity at multiple spatial scales.

Nat Commun 2020 10 23;11(1):5375. Epub 2020 Oct 23.

Department of Ecology, Evolution, and Behavior, University of MN, St. Paul, MN, 55108, USA.

Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-19252-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7585434PMC
October 2020

Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties.

Glob Chang Biol 2020 Dec 22;26(12):7173-7185. Epub 2020 Sep 22.

Grupo de Investigaciones en Biología de la Conservación, INIBIOMA (CONICET-UNCOMA), Bariloche, Argentina.

Soil nitrogen (N) availability is critical for grassland functioning. However, human activities have increased the supply of biologically limiting nutrients, and changed the density and identity of mammalian herbivores. These anthropogenic changes may alter net soil N mineralization (soil net N ), that is, the net balance between N mineralization and immobilization, which could severely impact grassland structure and functioning. Yet, to date, little is known about how fertilization and herbivore removal individually, or jointly, affect soil net N across a wide range of grasslands that vary in soil and climatic properties. Here we collected data from 22 grasslands on five continents, all part of a globally replicated experiment, to assess how fertilization and herbivore removal affected potential (laboratory-based) and realized (field-based) soil net N . Herbivore removal in the absence of fertilization did not alter potential and realized soil net N . However, fertilization alone and in combination with herbivore removal consistently increased potential soil net N Realized soil net N , in contrast, significantly decreased in fertilized plots where herbivores were removed. Treatment effects on potential and realized soil net N were contingent on site-specific soil and climatic properties. Fertilization effects on potential soil net N were larger at sites with higher mean annual precipitation (MAP) and temperature of the wettest quarter (T.q.wet). Reciprocally, realized soil net N declined most strongly with fertilization and herbivore removal at sites with lower MAP and higher T.q.wet. In summary, our findings show that anthropogenic nutrient enrichment, herbivore exclusion and alterations in future climatic conditions can negatively impact soil net N across global grasslands under realistic field conditions. This is an important context-dependent knowledge for grassland management worldwide.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gcb.15308DOI Listing
December 2020

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands.

Glob Chang Biol 2020 Feb 3. Epub 2020 Feb 3.

Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.

Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature - herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local-scale herbivory, and its interaction with nutrient enrichment and climate, within global-scale models to better predict land-atmosphere interactions under future climate change.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gcb.15023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155038PMC
February 2020

Homogenization of freshwater lakes: Recent compositional shifts in fish communities are explained by gamefish movement and not climate change.

Glob Chang Biol 2019 Dec 6;25(12):4222-4233. Epub 2019 Oct 6.

Department of Integrative Biology, University Of Guelph, Guelph, ON, Canada.

Globally, lake fish communities are being subjected to a range of scale-dependent anthropogenic pressures, from climate change to eutrophication, and from overexploitation to species introductions. As a consequence, the composition of these communities is being reshuffled, in most cases leading to a surge in taxonomic similarity at the regional scale termed homogenization. The drivers of homogenization remain unclear, which may be a reflection of interactions between various environmental changes. In this study, we investigate two potential drivers of the recent changes in the composition of freshwater fish communities: recreational fishing and climate change. Our results, derived from 524 lakes of Ontario, Canada sampled in two periods (1965-1982 and 2008-2012), demonstrate that the main contributors to homogenization are the dispersal of gamefish species, most of which are large predators. Alternative explanations relating to lake habitat (e.g., area, phosphorus) or variations in climate have limited explanatory power. Our analysis suggests that human-assisted migration is the primary driver of the observed compositional shifts, homogenizing freshwater fish community among Ontario lakes and generating food webs dominated by gamefish species.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gcb.14829DOI Listing
December 2019

Food web rewiring in a changing world.

Nat Ecol Evol 2019 03 11;3(3):345-354. Epub 2019 Feb 11.

Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada.

Climate change is asymmetrically altering environmental conditions in space, from local to global scales, creating novel heterogeneity. Here, we argue that this novel heterogeneity will drive mobile generalist consumer species to rapidly respond through their behaviour in ways that broadly and predictably reorganize - or rewire - food webs. We use existing theory and data from diverse ecosystems to show that the rapid behavioural responses of generalists to climate change rewire food webs in two distinct and critical ways. First, mobile generalist species are redistributing into systems where they were previously absent and foraging on new prey, resulting in topological rewiring - a change in the patterning of food webs due to the addition or loss of connections. Second, mobile generalist species, which navigate between habitats and ecosystems to forage, will shift their relative use of differentially altered habitats and ecosystems, causing interaction strength rewiring - changes that reroute energy and carbon flows through existing food web connections and alter the food web's interaction strengths. We then show that many species with shared traits can exhibit unified aggregate behavioural responses to climate change, which may allow us to understand the rewiring of whole food webs. We end by arguing that generalists' responses present a powerful and underutilized approach to understanding and predicting the consequences of climate change and may serve as much-needed early warning signals for monitoring the looming impacts of global climate change on entire ecosystems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41559-018-0772-3DOI Listing
March 2019

The Neolithic Plant Invasion Hypothesis: the role of preadaptation and disturbance in grassland invasion.

New Phytol 2018 10 5;220(1):94-103. Epub 2018 Jul 5.

Instituto de Ciencias de la Tierra y Ambientales de La Pampa, CONICET-Universidad Nacional de La Pampa (UNLPam), Santa Rosa, 6300, Argentina.

A long-standing hypothesis is that many European plants invade temperate grasslands globally because they are introduced simultaneously with pastoralism and cultivation, to which they are 'preadapted' after millennia of exposure dating to the Neolithic era ('Neolithic Plant Invasion Hypothesis' (NPIH)). These 'preadaptations' are predicted to maximize their performance relative to native species lacking this adaptive history. Here, we discuss the explanatory relevance of the NPIH, clarifying the importance of evolutionary context vs other mechanisms driving invasion. The NPIH makes intuitive sense given established connections between invasion and agricultural-based perturbation. However, tests are often incomplete given the need for performance contrasts between home and away ranges, while controlling for other mechanisms. We emphasize six NPIH-based predictions, centring on trait similarity of invaders between home vs away populations, and differing perturbation responses by invading and native plants. Although no research has integrated all six predictions, we highlight studies suggesting preadaptation influences on invasion. Given that many European grasslands are creations of human activity from the past, current invasions by these flora may represent the continuation of processes dating to the Neolithic. Ironically, European Neolithic-derived grasslands are becoming rarer, reflecting changes in management and illustrating the importance of human influences on these species.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/nph.15285DOI Listing
October 2018

Herbivory and eutrophication mediate grassland plant nutrient responses across a global climatic gradient.

Ecology 2018 04 31;99(4):822-831. Epub 2018 Mar 31.

Department of Ecology, Evolution, and Behavior, University of MN, St. Paul, Minnesota, 55108, USA.

Plant stoichiometry, the relative concentration of elements, is a key regulator of ecosystem functioning and is also being altered by human activities. In this paper we sought to understand the global drivers of plant stoichiometry and compare the relative contribution of climatic vs. anthropogenic effects. We addressed this goal by measuring plant elemental (C, N, P and K) responses to eutrophication and vertebrate herbivore exclusion at eighteen sites on six continents. Across sites, climate and atmospheric N deposition emerged as strong predictors of plot-level tissue nutrients, mediated by biomass and plant chemistry. Within sites, fertilization increased total plant nutrient pools, but results were contingent on soil fertility and the proportion of grass biomass relative to other functional types. Total plant nutrient pools diverged strongly in response to herbivore exclusion when fertilized; responses were largest in ungrazed plots at low rainfall, whereas herbivore grazing dampened the plant community nutrient responses to fertilization. Our study highlights (1) the importance of climate in determining plant nutrient concentrations mediated through effects on plant biomass, (2) that eutrophication affects grassland nutrient pools via both soil and atmospheric pathways and (3) that interactions among soils, herbivores and eutrophication drive plant nutrient responses at small scales, especially at water-limited sites.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ecy.2175DOI Listing
April 2018

Context-dependent interactions and the regulation of species richness in freshwater fish.

Nat Commun 2018 03 6;9(1):973. Epub 2018 Mar 6.

Department of Integrative Biology, University Of Guelph, Guelph, Ontario, Canada, N1G 2W1.

Species richness is regulated by a complex network of scale-dependent processes. This complexity can obscure the influence of limiting species interactions, making it difficult to determine if abiotic or biotic drivers are more predominant regulators of richness. Using integrative modeling of freshwater fish richness from 721 lakes along an 11 latitudinal gradient, we find negative interactions to be a relatively minor independent predictor of species richness in lakes despite the widespread presence of predators. Instead, interaction effects, when detectable among major functional groups and 231 species pairs, were strong, often positive, but contextually dependent on environment. These results are consistent with the idea that negative interactions internally structure lake communities but do not consistently 'scale-up' to regulate richness independently of the environment. The importance of environment for interaction outcomes and its role in the regulation of species richness highlights the potential sensitivity of fish communities to the environmental changes affecting lakes globally.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-018-03419-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5840330PMC
March 2018

Local loss and spatial homogenization of plant diversity reduce ecosystem multifunctionality.

Nat Ecol Evol 2018 Jan 4;2(1):50-56. Epub 2017 Dec 4.

Department of Plant & Soil Sciences, University of Kentucky, Lexington, KY, 40546-0091, USA.

Biodiversity is declining in many local communities while also becoming increasingly homogenized across space. Experiments show that local plant species loss reduces ecosystem functioning and services, but the role of spatial homogenization of community composition and the potential interaction between diversity at different scales in maintaining ecosystem functioning remains unclear, especially when many functions are considered (ecosystem multifunctionality). We present an analysis of eight ecosystem functions measured in 65 grasslands worldwide. We find that more diverse grasslands-those with both species-rich local communities (α-diversity) and large compositional differences among localities (β-diversity)-had higher levels of multifunctionality. Moreover, α- and β-diversity synergistically affected multifunctionality, with higher levels of diversity at one scale amplifying the contribution to ecological functions at the other scale. The identity of species influencing ecosystem functioning differed among functions and across local communities, explaining why more diverse grasslands maintained greater functionality when more functions and localities were considered. These results were robust to variation in environmental drivers. Our findings reveal that plant diversity, at both local and landscape scales, contributes to the maintenance of multiple ecosystem services provided by grasslands. Preserving ecosystem functioning therefore requires conservation of biodiversity both within and among ecological communities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41559-017-0395-0DOI Listing
January 2018

A decade of insights into grassland ecosystem responses to global environmental change.

Nat Ecol Evol 2017 Apr 20;1(5):118. Epub 2017 Apr 20.

Department of Ecology, Evolution, and Behavior, University of Minnesota, 1479 Gortner Avenue, 140 Gortner Laboratory, Saint Paul, Minnesota 55108, USA.

Earth's biodiversity and carbon uptake by plants, or primary productivity, are intricately interlinked, underlie many essential ecosystem processes, and depend on the interplay among environmental factors, many of which are being changed by human activities. While ecological theory generalizes across taxa and environments, most empirical tests of factors controlling diversity and productivity have been observational, single-site experiments, or meta-analyses, limiting our understanding of variation among site-level responses and tests of general mechanisms. A synthesis of results from ten years of a globally distributed, coordinated experiment, the Nutrient Network (NutNet), demonstrates that species diversity promotes ecosystem productivity and stability, and that nutrient supply and herbivory control diversity via changes in composition, including invasions of non-native species and extinction of native species. Distributed experimental networks are a powerful tool for tests and integration of multiple theories and for generating multivariate predictions about the effects of global changes on future ecosystems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41559-017-0118DOI Listing
April 2017

Addition of multiple limiting resources reduces grassland diversity.

Nature 2016 09 24;537(7618):93-96. Epub 2016 Aug 24.

Swiss Federal Institute for Forest, Snow and Landscape Research, Community Ecology, Birmensdorf 8903, Switzerland.

Niche dimensionality provides a general theoretical explanation for biodiversity-more niches, defined by more limiting factors, allow for more ways that species can coexist. Because plant species compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature19324DOI Listing
September 2016

Climate modifies response of non-native and native species richness to nutrient enrichment.

Philos Trans R Soc Lond B Biol Sci 2016 05;371(1694)

Department of Ecology, Evolution, and Behavior, University of Minnesota, St Paul, MN 55108, USA.

Ecosystem eutrophication often increases domination by non-natives and causes displacement of native taxa. However, variation in environmental conditions may affect the outcome of interactions between native and non-native taxa in environments where nutrient supply is elevated. We examined the interactive effects of eutrophication, climate variability and climate average conditions on the success of native and non-native plant species using experimental nutrient manipulations replicated at 32 grassland sites on four continents. We hypothesized that effects of nutrient addition would be greatest where climate was stable and benign, owing to reduced niche partitioning. We found that the abundance of non-native species increased with nutrient addition independent of climate; however, nutrient addition increased non-native species richness and decreased native species richness, with these effects dampened in warmer or wetter sites. Eutrophication also altered the time scale in which grassland invasion responded to climate, decreasing the importance of long-term climate and increasing that of annual climate. Thus, climatic conditions mediate the responses of native and non-native flora to nutrient enrichment. Our results suggest that the negative effect of nutrient addition on native abundance is decoupled from its effect on richness, and reduces the time scale of the links between climate and compositional change.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2015.0273DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4843694PMC
May 2016

Comment on "Worldwide evidence of a unimodal relationship between productivity and plant species richness".

Science 2016 Jan;351(6272):457

Department of Ecology, Environment and Evolution, La Trobe University, Kingsbury Drive, Bundoora 3086, Victoria, Australia.

Fraser et al. (Reports, 17 July 2015, p. 302) report a unimodal relationship between productivity and species richness at regional and global scales, which they contrast with the results of Adler et al. (Reports, 23 September 2011, p. 1750). However, both data sets, when analyzed correctly, show clearly and consistently that productivity is a poor predictor of local species richness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.aad6236DOI Listing
January 2016

Integrative modelling reveals mechanisms linking productivity and plant species richness.

Nature 2016 Jan 13;529(7586):390-3. Epub 2016 Jan 13.

Department of Biology, Colorado State University, 1878 Campus Delivery, Fort Collins, Colorado 80526, USA.

How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature16524DOI Listing
January 2016

Spatially Heterogeneous Perturbations Homogenize the Regulation of Insect Herbivores.

Am Nat 2015 Nov 18;186(5):623-33. Epub 2015 Sep 18.

Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.

Anthropogenic influences on resources and consumers can affect food web regulation, with impacts on trophic structure and ecosystem processes. Identifying how these impacts unfold is challenging because alterations to one or both resources and consumers can similarly transform community structure, especially for intermediate consumers. To date, empirical testing of perturbations on trophic regulation has been limited by the difficulty in separating the direct effect of perturbations on species composition and diversity from those unfolding indirectly via altered feeding pathways. Moreover, disentangling the independent and interactive impacts of covarying stressors that characterize human-altered systems has been an ongoing analytical challenge. We used a large-scale metacommunity experiment in grasslands to test how resource inputs, stand perturbation, and spatial factors affect regulation of insect herbivores in tritrophic grassland food webs. Using path-model comparisons, we observed significant simplification of food web regulation on insect herbivores, shifting from mixed predator-resource regulation in unaltered mainland areas to strictly resource-based regulation with landscape perturbation and fragmentation. Most changes were attributed to homogenization of plant community caused by landscape fragmentation and the deterministic influence of eutrophication that reduced among-patch beta diversity. This led to a simplified food web dominated by fewer but more abundant herbivore taxa. Our work implies that anthropogenic perturbation relating to resources and spatial isolation can transform the regulation of food web diversity, structure, and function.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1086/683199DOI Listing
November 2015

Native and non-native ruderals experience similar plant-soil feedbacks and neighbor effects in a system where they coexist.

Oecologia 2015 Nov 25;179(3):843-52. Epub 2015 Jul 25.

Instituto de Ciencias de la Tierra y Ambientales de La Pampa, Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de La Pampa [INCITAP (CONICET-UNLPam)], Mendoza 109, 6300, Santa Rosa, La Pampa, Argentina.

Recent applications of coexistence theory to plant invasions posit that non-natives establish in resident communities through either niche differences or traits conferring them with fitness advantages, the former being associated with coexistence and the latter with dominance and competitive exclusion. Plant-soil feedback is a mechanism that is known to explain both coexistence and dominance. In a system where natives and non-natives appear to coexist, we explored how plant-soil feedbacks affect the performance of nine native and nine non-native ruderal species-the prevalent life-history strategy among non-natives-when grown alone and with a phytometer. We also conducted field samplings to estimate the abundance of the 18 species, and related feedbacks to abundances. We found that groups of native and non-native ruderals displayed similar frequencies of negative, positive, and neutral feedbacks, resulting in no detectable differences between natives and non-natives. Likewise, the phytometer exerted comparable negative impacts on native and non-native plants, which were unchanged by plant-soil feedbacks. Finally, feedbacks explained plant abundances only after removing one influential species which exhibited strong positive feedbacks but low abundance. Importantly, however, four out of five species with negative feedbacks were rare in the field. These findings suggest that soil feedbacks and plant-plant interactions do not confer an advantage to non-native over native species, but do contribute to the observed coexistence of these groups in the system. By comparing natives and non-natives with overlapping abundances and strategies, our work broadens understanding of the consequences of plant-soil feedbacks in plant invasion and, more generally, coexistence within plant communities.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00442-015-3399-yDOI Listing
November 2015

Plant species' origin predicts dominance and response to nutrient enrichment and herbivores in global grasslands.

Nat Commun 2015 Jul 15;6:7710. Epub 2015 Jul 15.

Department of Entomology, University of Maryland, College Park Maryland 20742, USA.

Exotic species dominate many communities; however the functional significance of species' biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms8710DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4518311PMC
July 2015

Grassland productivity limited by multiple nutrients.

Nat Plants 2015 Jul 6;1:15080. Epub 2015 Jul 6.

Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546, USA.

Terrestrial ecosystem productivity is widely accepted to be nutrient limited(1). Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)(2,3), the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized(4-8). However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nplants.2015.80DOI Listing
July 2015

Plant diversity predicts beta but not alpha diversity of soil microbes across grasslands worldwide.

Ecol Lett 2015 Jan 28;18(1):85-95. Epub 2014 Nov 28.

CSIRO Land and Water Flagship, Private Bag 5, Wembley, WA, 6913, Australia.

Aboveground-belowground interactions exert critical controls on the composition and function of terrestrial ecosystems, yet the fundamental relationships between plant diversity and soil microbial diversity remain elusive. Theory predicts predominantly positive associations but tests within single sites have shown variable relationships, and associations between plant and microbial diversity across broad spatial scales remain largely unexplored. We compared the diversity of plant, bacterial, archaeal and fungal communities in one hundred and forty-five 1 m(2) plots across 25 temperate grassland sites from four continents. Across sites, the plant alpha diversity patterns were poorly related to those observed for any soil microbial group. However, plant beta diversity (compositional dissimilarity between sites) was significantly correlated with the beta diversity of bacterial and fungal communities, even after controlling for environmental factors. Thus, across a global range of temperate grasslands, plant diversity can predict patterns in the composition of soil microbial communities, but not patterns in alpha diversity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ele.12381DOI Listing
January 2015

Herbivores and nutrients control grassland plant diversity via light limitation.

Nature 2014 Apr 9;508(7497):517-20. Epub 2014 Mar 9.

Instituto de Investigaciones Marinas y Costeras (IIMyC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Mar del Plata 7600 , Argentina.

Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature13144DOI Listing
April 2014

Eutrophication weakens stabilizing effects of diversity in natural grasslands.

Nature 2014 Apr 16;508(7497):521-5. Epub 2014 Feb 16.

Swiss Federal Institute for Forest, Snow and Landscape Research, 8903 Birmensdorf, Switzerland.

Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature13014DOI Listing
April 2014

Spatial variability in plant predation determines the strength of stochastic community assembly.

Am Nat 2013 Aug 20;182(2):169-79. Epub 2013 Jun 20.

Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.

High diversity is often poorly explained by trait-based deterministic models, in part because stochastic processes also influence community assembly. Testing how deterministic and stochastic processes combine to regulate diversity, however, has been limited by the spatial complexity of these interactions. Here, we demonstrate how spatial variability in small-mammal predation on plants, mostly by granivory, results in fine-scale switching between deterministically and stochastically regulated plant community assembly in an otherwise environmentally homogeneous tallgrass prairie. We initiated assembly with the uniform application of a 24-species mixture of prairie grasses and forbs, thereby setting the maximum level of diversity (γ-diversity). In field edges with higher densities of small mammals, traits reducing seed palatability deterministically produced homogeneous subsets of less palatable plant species within the first few months after planting (low α and β diversity). As small-mammal densities decreased in more open areas, assembly unfolded stochastically on the basis of which planted species happened to land at a given location (high α and β diversity). We used randomization models to validate that this higher β diversity was explained by true differences in community structure among plots rather than by the hidden effects of increasing α diversity. The net effect at the site level was a spatially structured array of prairie species, including a positive relationship between diversity and environmental suitability relating to reduced predator intensity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1086/670928DOI Listing
August 2013

Nutrients and defoliation increase soil carbon inputs in grassland.

Ecology 2013 Jan;94(1):106-16

Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.

Given the regulatory impact of resources and consumers on plant production, decomposition, and soil carbon sequestration, anthropogenic changes to nutrient inputs and grazing have likely transformed how grasslands process atmospheric CO2. The direction and magnitude of these changes, however, remain unclear in this system, whose soils contain -20% of the world's carbon pool. Nutrients stimulate production but can also increase tissue palatability and decomposition. Grazing variously affects tissue quality and quantity, decreasing, standing biomass, but potentially increasing leaf nutrient concentrations, root production, or investment in tissue defenses that slow litter decay. Here, we quantified individual and interactive impacts of nutrient addition and simulated grazing (mowing) on above- and belowground production, tissue quality, and soil carbon inputs in a western North American grassland with globally distributed agronomic species. Given that nutrients and grazing are often connected with increased root production and higher foliar tissue quality, we hypothesized that these treatments would combine to reduce inputs of recalcitrant-rich litter critical for C storage. This hypothesis was unsupported. Nutrients and defoliation combined to significantly increase belowground production but did not affect root tissue quality. There were no significant interactions between nutrients and defoliation for any measured response. Three years of nutrient addition increased root and shoot biomass by 37% and 23%, respectively, and had no impact on decomposition, resulting in a -15% increase in soil organic matter and soil carbon. Defoliation triggered a significant burst of short-lived lignin-rich roots, presumably a compensatory response to foliar loss, which increased root litter inputs by 33%. The majority of root and shoot responses were positively correlated, with aboveground biomass a reasonable proxy for whole plant responses. The exceptions were decomposition, with roots six times more decay resistant, and grazing impacts on tissue chemistry, with shoots undergoing significant alterations, while roots were unaffected. Because neither treatment affected concentrations of decay-resistant compounds in roots, the implied net effect is higher soil C inputs with potentially longer residency times. Areas managed with nutrients and moderate grazing in our study system could thus accumulate significantly more soil C than unmanaged areas, with a greater capacity to serve as sinks for atmospheric CO2.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1890/11-2070.1DOI Listing
January 2013

Regional contingencies in the relationship between aboveground biomass and litter in the world's grasslands.

PLoS One 2013 6;8(2):e54988. Epub 2013 Feb 6.

Department of Zoology, Oregon State University, Corvallis, OR, USA.

Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0054988PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3566150PMC
December 2013

Inversion of plant dominance-diversity relationships along a latitudinal stress gradient.

Ecology 2012 Jun;93(6):1431-8

Department of Integrative Biology, University of Guelph, Guelph, Ontario L9H 1X2, Canada.

Species interactions affect plant diversity through the net effects of competition and facilitation, with the latter more prevalent in physically stressful environments when plant cover ameliorates abiotic stress. One explanation for species loss in invader-dominated systems is a shift in the competition-facilitation balance, with competition intensifying in areas formerly structured by facilitation. We test this possibility with a 10-site prairie meta-experiment along a 500-km latitudinal stress gradient, quantifying the relationships among abiotic stress, exotic dominance, and native plant recruitment over five years. The latitudinal gradient is inversely correlated with abiotic stress, with lower latitudes more moisture- and nutrient-limited. We observed strong negative effects by invasive dominant grasses on plant establishment, but only in northern sites with lower-stress environments. At these locations, disturbance was critical for recruitment by reducing the suppressive dominant (invasive) canopy. In more stressful environments to the south, the impacts of the dominant invaders on plant establishment became facilitative, and diversity was more limited by seed availability. Disturbance prevented recruitment because seedling survival depended on a protective plant canopy, presumably because the canopy reduced temperature or moisture stress. Seed limitation was similarly prevalent in all sites. Our work confirms the importance of facilitation as an organizing process for plants in higher-stress environments, even with transformations of species composition and dominance. It also demonstrates that the mechanisms regulating diversity, including invader impacts, can vary within the same plant community depending on environmental context. Because limits on native plant recruitment are environmentally contingent, management strategies that seek to increase diversity, including invader eradication, must account for site-level variations in the balance between biotic and abiotic constraints.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1890/11-1290.1DOI Listing
June 2012

Productivity is a poor predictor of plant species richness.

Science 2011 Sep;333(6050):1750-3

Department of Wildland Resources and the Ecology Center, Utah State University, 5230 Old Main, Logan, UT 84322, USA.

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters(-2)) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1204498DOI Listing
September 2011

The invasive grass Agropyron cristatum doubles belowground productivity but not soil carbon.

Ecology 2011 Mar;92(3):657-64

Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1 Canada.

Root dynamics are among the largest knowledge gaps in determining how terrestrial carbon (C) cycles will respond to environmental change. Increases in productivity accompanying plant invasions and introductions could increase ecosystem C storage, but belowground changes are unknown, even though roots may account for 50-90% of production in temperate ecosystems. We examined whether the introduction of a widespread invasive grass with relatively high shoot production also increased belowground productivity and soil C storage, using a multiyear rhizotron study in 50-year-old stands dominated either by the invasive C3 grass Agropyron cristatum or by largely C4 native grasses. Relative to native vegetation, stands dominated by the invader had doubled root productivity. Soil carbon isotope values showed that the invader had made detectable contributions to soil C. Soil C content, however, was not significantly different between invader-dominated stands (0.42 mg C/g soil) and native vegetation (0.45 mg C/g soil). The discrepancy between enhanced production and lack of soil C changes was attributable to differences in root traits between invader-dominated stands and native vegetation. Relative to native vegetation, roots beneath the invader had 59% more young white tissue, with 80% higher mortality and 19% lower C:N ratios (all P < 0.05). Such patterns have previously been reported for aboveground tissues of invaders, and we show that they are also found belowground. If these root traits occur in other invasive species, then the global phenomenon of increased productivity following biological invasion may not increase soil C storage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1890/10-0631.1DOI Listing
March 2011