Showing papers by "Brian J. Enquist published in 2016"

Temperature mediates continental-scale diversity of microbes in forest soils

Abstract: Climate warming is increasingly leading to marked changes in plant and animal biodiversity, but it remains unclear how temperatures affect microbial biodiversity, particularly in terrestrial soils. Here we show that, in accordance with metabolic theory of ecology, taxonomic and phylogenetic diversity of soil bacteria, fungi and nitrogen fixers are all better predicted by variation in environmental temperature than pH. However, the rates of diversity turnover across the global temperature gradients are substantially lower than those recorded for trees and animals, suggesting that the diversity of plant, animal and soil microbial communities show differential responses to climate change. To the best of our knowledge, this is the first study demonstrating that the diversity of different microbial groups has significantly lower rates of turnover across temperature gradients than other major taxa, which has important implications for assessing the effects of human-caused changes in climate, land use and other factors.

Temperature response of soil respiration largely unaltered with experimental warming

Abstract: The respiratory release of carbon dioxide (CO2) from soil is a major yet poorly understood flux in the global carbon cycle. Climatic warming is hypothesized to increase rates of soil respiration, potentially fueling further increases in global temperatures. However, despite considerable scientific attention in recent decades, the overall response of soil respiration to anticipated climatic warming remains unclear. We synthesize the largest global dataset to date of soil respiration, moisture, and temperature measurements, totaling >3,800 observations representing 27 temperature manipulation studies, spanning nine biomes and over 2 decades of warming. Our analysis reveals no significant differences in the temperature sensitivity of soil respiration between control and warmed plots in all biomes, with the exception of deserts and boreal forests. Thus, our data provide limited evidence of acclimation of soil respiration to experimental warming in several major biome types, contrary to the results from multiple single-site studies. Moreover, across all nondesert biomes, respiration rates with and without experimental warming follow a Gaussian response, increasing with soil temperature up to a threshold of ∼25 °C, above which respiration rates decrease with further increases in temperature. This consistent decrease in temperature sensitivity at higher temperatures demonstrates that rising global temperatures may result in regionally variable responses in soil respiration, with colder climates being considerably more responsive to increased ambient temperatures compared with warmer regions. Our analysis adds a unique cross-biome perspective on the temperature response of soil respiration, information critical to improving our mechanistic understanding of how soil carbon dynamics change with climatic warming.

The energetic and carbon economic origins of leaf thermoregulation

Abstract: Leaf thermoregulation has been documented in a handful of studies, but the generality and origins of this pattern are unclear. We suggest that leaf thermoregulation is widespread in both space and time, and originates from the optimization of leaf traits to maximize leaf carbon gain across and within variable environments. Here we use global data for leaf temperatures, traits and photosynthesis to evaluate predictions from a novel theory of thermoregulation that synthesizes energy budget and carbon economics theories. Our results reveal that variation in leaf temperatures and physiological performance are tightly linked to leaf traits and carbon economics. The theory, parameterized with global averaged leaf traits and microclimate, predicts a moderate level of leaf thermoregulation across a broad air temperature gradient. These predictions are supported by independent data for diverse taxa spanning a global air temperature range of ∼60 °C. Moreover, our theory predicts that net carbon assimilation can be maximized by means of a trade-off between leaf thermal stability and photosynthetic stability. This prediction is supported by globally distributed data for leaf thermal and photosynthetic traits. Our results demonstrate that the temperatures of plant tissues, and not just air, are vital to developing more accurate Earth system models.

Observed forest sensitivity to climate implies large changes in 21st century North American forest growth.

Abstract: Predicting long-term trends in forest growth requires accurate characterisation of how the relationship between forest productivity and climatic stress varies across climatic regimes. Using a network of over two million tree-ring observations spanning North America and a space-for-time substitution methodology, we forecast climate impacts on future forest growth. We explored differing scenarios of increased water-use efficiency (WUE) due to CO2 -fertilisation, which we simulated as increased effective precipitation. In our forecasts: (1) climate change negatively impacted forest growth rates in the interior west and positively impacted forest growth along the western, southeastern and northeastern coasts; (2) shifting climate sensitivities offset positive effects of warming on high-latitude forests, leaving no evidence for continued 'boreal greening'; and (3) it took a 72% WUE enhancement to compensate for continentally averaged growth declines under RCP 8.5. Our results highlight the importance of locally adapted forest management strategies to handle regional differences in growth responses to climate change.

Cyberinfrastructure for an integrated botanical information network to investigate the ecological impacts of global climate change on plant biodiversity

Abstract: To answer many of the major questions in comparative botany, ecology, and global change biology it is necessary to extrapolate across enormous geographic, temporal and taxonomic scales. Yet much ecological knowledge is still based on observations conducted within a local area or even a few hundred square meters. Understanding ecological patterns and how plants respond to global warming and human alteration of landscapes and ecosystems necessitates a holistic approach. Such an approach must be conducted at a scale that is commensurate with the breadth of the questions being asked. Further, it requires identification, retrieval, and integration of diverse data from a global confederation of collaborating scientists across a broad range of disciplines. We propose to network core databases and data networks to create a novel resource for quantitative plant biodiversity science. The grand challenge is to assemble and share the world’s rapidly accumulating botanical information from plots and collections to create a distributed, web-accessible, readily analyzable data resource. With such a resource, we will answer major questions of direct relevance to plant ecology, plant evolution, plant geography, conservation, global change biology, and protection of biodiversity and ecosystem services. In particular, how does climate influence the distribution and abundance of plant species, how does the phylogenetic diversity of plants vary across broad environmental and climatic gradients, and how are plants assembled into ecological communities? While these and associated questions are at the core of many research endeavors in comparative botany and ecology, our past collective inability to integrate data on a large scale has significantly limited our ability to address these questions head on. This proposed Grand Challenge team will create a data resource of unprecedented size and scope together with the tools for its use, thereby empowering botanists and the general public to better address fundamental issues in plant ecology and global change biology. Although we will focus on plants of the New World, the infrastructure and protocols developed will be scalable to all geographic regions and all types of organisms. Future steps will enable cross-cutting linkages to emerging networks on plant genomics, physiology, and phylogeny, allowing us to address fundamental genetic and evolutionary questions at unprecedented spatial and temporal scales.

Towards Process-based Range Modeling of Many Species

Abstract: Understanding and forecasting species' geographic distributions in the face of global change is a central priority in biodiversity science. The existing view is that one must choose between correlative models for many species versus process-based models for few species. We suggest that opportunities exist to produce process-based range models for many species, by using hierarchical and inverse modeling to borrow strength across species, fill data gaps, fuse diverse data sets, and model across biological and spatial scales. We review the statistical ecology and population and range modeling literature, illustrating these modeling strategies in action. A variety of large, coordinated ecological datasets that can feed into these modeling solutions already exist, and we highlight organisms that seem ripe for the challenge.

A network approach for inferring species associations from co-occurrence data

Abstract: by broad-scale models, then stacking independent species distribution models to predict species assemblages (sensu Guisan and Rahbek 2011, Calabrese et al. 2014) will provide misleading predictions of fine-scale community assembly. Thus, a better understanding of species associations across scales could improve predictions of the dynamics of local community composition in changing environments. The goal of this paper is to improve the tools needed to detect interspecific associations from co-occurrence data. We first briefly describe the development of co-occurrence methods and then draw from different lines of research to present a more complete and flexible general framework for inferring species associations that overcomes multiple challenges faced by previous approaches.

Megafauna extinction, tree species range reduction, and carbon storage in Amazonian forests

Abstract: During the Late Pleistocene and early Holocene 59 species of South American megafauna went extinct. Their extinction potentially triggered population declines of large-seeded tree species dispersed by the large-bodied frugivores with which they co-evolved, a theory first proposed by Janzen and Martin (1982). We tested this hypothesis using species range maps for 257 South American tree species, comparing 63 species thought to be primarily distributed by megafauna with 194 distributed by other animals. We found a highly significant (p 95% following disperser extinction. A numerical gap dynamic simulations suggests that over a 10 000 yr period following the disperser extinctions, the average convex hull range size of large-seeded tree species decreased by ∼ 31%, while the estimated decrease in population size was ∼ 54%, indicating a likely greater decrease in species population size than indicated by the empirical range patterns. Finally, we found a positive correlation between seed size and wood density of animal-dispersed tree species implying that the Late Pleistocene and early Holocene megafaunal extinctions reduced carbon content in the Amazon by ∼ 1.5 ± 0.7%. In conclusion, we 1) provide some empirical evidence that megafauna distributed fruit species have a smaller mean range size than wind, water or other animal-dispersed species, 2) demonstrate mathematically that such range reductions are expected from megafauna extinctions ca 12 000 yr ago, and 3) illustrate that these extinctions may have reduced the Amazon's carbon storage capacity.

Re-growing a tropical dry forest: functional plant trait composition and community assembly during succession.

Abstract: NSF Graduate Research Fellowship; NSF CAREER Award; NSF ATB Award; Marie Curie International Outgoing Fellowship within the 7th European Community Framework Program (DiversiTraits project) [221060]; European Research Council (ERC) Starting Grant Project 'Ecophysiological and biophysical constraints on domestication in crop plants ' [ERC-StG-2014-639706-CONSTRAINTS]

Biogeographic patterns of soil diazotrophic communities across six forests in the North America

Abstract: Soil diazotrophs play important roles in ecosystem functioning by converting atmospheric N2 into biologically available ammonium. However, the diversity and distribution of soil diazotrophic communities in different forests and whether they follow biogeographic patterns similar to macroorganisms still remain unclear. By sequencing nifH gene amplicons, we surveyed the diversity, structure and biogeographic patterns of soil diazotrophic communities across six North American forests (126 nested samples). Our results showed that each forest harboured markedly different soil diazotrophic communities and that these communities followed traditional biogeographic patterns similar to plant and animal communities, including the taxa-area relationship (TAR) and latitudinal diversity gradient. Significantly higher community diversity and lower microbial spatial turnover rates (i.e. z-values) were found for rainforests (~0.06) than temperate forests (~0.1). The gradient pattern of TARs and community diversity was strongly correlated (r(2) > 0.5) with latitude, annual mean temperature, plant species richness and precipitation, and weakly correlated (r(2) < 0.25) with pH and soil moisture. This study suggests that even microbial subcommunities (e.g. soil diazotrophs) follow general biogeographic patterns (e.g. TAR, latitudinal diversity gradient), and indicates that the metabolic theory of ecology and habitat heterogeneity may be the major underlying ecological mechanisms shaping the biogeographic patterns of soil diazotrophic communities.

Variation and macroevolution in leaf functional traits in the Hawaiian silversword alliance (Asteraceae)

Abstract: Author(s): Blonder, B; Baldwin, BG; Enquist, BJ; Robichaux, RH | Abstract: The Hawaiian silversword alliance is a spectacular example of plant adaptive radiation. The lineage includes 33 species in three endemic genera (Argyroxiphium, Dubautia and Wilkesia) that occupy almost all major habitats of the Hawaiian archipelago. Here, we quantitatively explore functional diversification in the lineage by linking measurements of multiple leaf functional traits with climate niche and phylogenetic data. We show that leaf functional trait variation (i) spans much of the global angiosperm range, (ii) is best explained by a white-noise evolutionary model and (iii) is integrated in ways consistent with both the global leaf economics spectrum and the predictions of leaf venation network theory. Our results highlight the importance of functional diversification and integration in rapidly evolving plant lineages. They also provide compelling additional support for the view that the Hawaiian silversword alliance is one of the world's premier examples of adaptive radiation in plants. The Hawaiian silversword alliance includes 33 species in three endemic genera (Argyroxiphium, Dubautia, and Wilkesia) that occupy almost all major habitats of the Hawaiian archipelago (top row). We show that leaf functional trait variation in the lineage spans much of the global angiosperm range, is best explained by a white-noise evolutionary model, and is integrated in ways consistent with both the global leaf economics spectrum and the predictions of leaf venation network theory (bottom row). The results provide compelling support for the view that the silversword alliance is one of the world's premier examples of adaptive radiation in plants. Journal of Ecology

A plant growth form dataset for the New World

Abstract: This dataset provides growth form classifications for 67,413 vascular plant species from North, Central, and South America. The data used to determine growth form were compiled from five major integrated sources and two original publications: the Botanical Information and Ecology Network (BIEN), the Plant Trait Database (TRY), the SALVIAS database, the USDA PLANTS database, Missouri Botanical Garden's Tropicos database, Wright (2010), and Boyle (1996). We defined nine plant growth forms based on woodiness (woody or non-woody), shoot structure (self-supporting or not self-supporting), and root traits (rooted in soil, not rooted in soil, parasitic or aquatic): Epiphyte, Liana, Vine, Herb, Shrub, Tree, Parasite, or Aquatic. Species with multiple growth form classifications were assigned the growth form classification agreed upon by the majority (>2/3) of sources. Species with ambiguous or otherwise not interpretable growth form assignments were excluded from the final dataset but are made available with the original data. Comparisons with independent estimates of species richness for the Western hemisphere suggest that our final dataset includes the majority of New World vascular plant species. Coverage is likely more complete for temperate than for tropical species. In addition, aquatic species are likely under-represented. Nonetheless, this dataset represents the largest compilation of plant growth forms published to date, and should contribute to new insights across a broad range of research in systematics, ecology, biogeography, conservation, and global change science.

Examining variation in the leaf mass per area of dominant species across two contrasting tropical gradients in light of community assembly

Abstract: Leverhulme Trust; European Research Council [GEM-TRAITS (321131)]; Natural Environment Research Council [NE/J023418/ 1]; Division of Environmental Biology [1146206, 1457804]

Plant‐O‐Matic: a dynamic and mobile guide to all plants of the Americas

Abstract: Summary Advances in both informatics and mobile technology are providing exciting new opportunities for generating, disseminating, and engaging with information in the biological sciences at unprecedented spatial scales, particularly in disentangling information on the distributions and natural history of hyperdiverse groups of organisms. We describe an application serving as a mobile catalog of all of the plants of the Americas developed using species distribution models estimated from field observations of plant occurrences. The underlying data comprise over 3·5 million standardized observations of over 88 000 plant species. Plant-O-Matic, a free iOS application, combines the species distribution models with the location services built into a mobile device to provide users with a list of all plant species expected to occur in the 100 × 100 km geographic grid cell corresponding to the user's location. The application also provides ancillary information on species’ attributes (when available) including growth form, reproductive mode, flower color, and common name. Results can be searched and conditionally filtered based on these attributes. Links to externally sourced specimen images further aid in identification of species by the user. The application's ability to assemble locally relevant lists of plant species and their attributes on demand for anywhere in the Americas provides a powerful new tool for identifying, exploring, and understanding plant diversity. Mobile applications such as Plant-O-Matic can facilitate dynamic new approaches to science, conservation, and science education.

Corrigendum: Convergence of terrestrial plant production across global climate gradients

Abstract: Nature 512, 39–43 (2014); doi:10.1038/nature13470 It has come to our attention that in this Article, while translating the methods of Luo1 (originally written in Chinese), we did not appreciate that plant age (a) and stand biomass (Mtot) had been used to calculate net primary production (NPP). Thus,while the Luo data are appropriate for our analyses that used climate and environmental variables as predictors of NPP, they are not appropriate for those that use plant age and/or stand biomass as independent predictors as in our theoretical model.

Corrigendum: The energetic and carbon economic origins of leaf thermoregulation.

Abstract: Nature Plants 2, 16129 (2016); published 22 August 2016; corrected 26 August 2016. In the version of this Article originally published, the affiliation for Nate G. McDowell was incorrect. This has now been corrected.

Comment on Coomes et al. 'Scaling of xylem vessels and veins within the leaves

Abstract: [Coomes et al. (2008)][1] purport to test the predictions of the plant scaling model of [West et al. (1999)][2] by examining the scaling of xylem dimensions in 10 species of oaks ( Quercus spp.). While we commend their efforts to gather much needed data on the scaling of xylem dimensions in leaves,