About

Nathan Kraft is a professor in the Department of Ecology and Evolutionary Biology at UCLA. His research focuses on studying the ecological and evolutionary forces that structure communities, particularly plant systems. His projects integrate aspects of community ecology, biogeography, ecophysiology, and phylogenetics, with recent work centered on the forests of lowland Amazonia and annual plant communities in California. His research addresses species coexistence, plant responses to climate change, the distribution of diversity at broad spatial scales, and the assembly of regional biotas.

Research topics

• Biology
• Environmental science
• Ecology
• Atmospheric sciences
• Geology

Selected publications

• Spatial clustering modifies competition in a diverse annual plant community

  Proceedings of the National Academy of Sciences · 2026-01-16

  articleOpen accessSenior authorCorresponding

  Spatial patterns are widespread in nature, and their formation has been studied extensively. However, the effects of spatial aggregation on the strength of species interactions are less well understood, especially in diverse ecological communities. In a field experiment with annual grassland plants in California, we manipulated the spatial arrangement-but not the number or identity-of two competitors and measured how they jointly affected a focal individual. We found that focal plants produced more seeds when their competitors were clustered than when they were mixed. These results suggest that mixed competitors generally had a more negative effect than clustered competitors. However, the effect of clustering varied across the pairs of competitor species. Competitor species that exhibited greater differences in size and/or functional traits across the spatial arrangements resulted in larger effects of clustering on focal plant seed production. Additionally, a competitive hierarchy among our study species predicted the effects of clustered versus mixed competitors on focal plant seed production. Altogether, our work suggests that the spatial arrangement of competitors changes the realized strength of competition in diverse plant communities. Given the extensive variation in spatial aggregation in plant communities, this mechanism is likely to be a powerful but underappreciated force shaping competition in nature.

  PublisherDOI

• Author response for "Species functional traits affect regional and local dominance across western Amazonian forests"

  2025-10-18

  peer-review
  PublisherDOI

• Author response for "Competition contributes to quantitative mismatches between plant fitness and occurrence along environmental gradients"

  2025-04-17

  peer-reviewSenior author
  PublisherDOI

• Latitudinal scaling of aggregation with abundance and coexistence in forests

  Nature · 2025-02-26 · 21 citations

  articleOpen access

  The search for simple principles that underlie the spatial structure and dynamics of plant communities is a long-standing challenge in ecology1–6. In particular, the relationship between species coexistence and the spatial distribution of plants is challenging to resolve in species-rich communities7–9. Here we present a comprehensive analysis of the spatial patterns of 720 tree species in 21 large forest plots and their consequences for species coexistence. We show that species with low abundance tend to be more spatially aggregated than more abundant species. Moreover, there is a latitudinal gradient in the strength of this negative aggregation–abundance relationship that increases from tropical to temperate forests. We suggest, in line with recent work10, that latitudinal gradients in animal seed dispersal11 and mycorrhizal associations12–14 may jointly generate this pattern. By integrating the observed spatial patterns into population models8, we derive the conditions under which species can invade from low abundance in terms of spatial patterns, demography, niche overlap and immigration. Evaluation of the spatial-invasion condition for the 720 tree species analysed suggests that temperate and tropical forests both meet the invasion criterion to a similar extent but through contrasting strategies conditioned by their spatial patterns. Our approach opens up new avenues for the integration of observed spatial patterns into ecological theory and underscores the need to understand the interaction among spatial patterns at the neighbourhood scale and multiple ecological processes in greater detail. A unified framework is presented that integrates observed spatial patterns of individual trees in forests with ecological processes into a novel coexistence theory.

  PublisherOA PDFDOI

• Arbuscular mycorrhizal association regulates global root–seed coordination

  Nature Plants · 2025-08-19 · 6 citations

  articleOpen access
  PublisherOA PDFDOI

• Author response for "Competition contributes to quantitative mismatches between plant fitness and occurrence along environmental gradients"

  2025-06-06

  peer-reviewSenior author
  PublisherDOI

• Changes in flowering phenology with altered rainfall and the potential community impacts in an annual grassland

  American Journal of Botany · 2025-02-01 · 7 citations

  articleSenior author

  PREMISE: Shifts in the timing of life history events, or phenology, have been recorded across many taxa and biomes in response to global change. These phenological changes are often studied in a single species context, but considering the community context is essential for anticipating the cascading effects on biotic interactions that are likely to occur. Focusing on an annual grassland plant community, we examined how experimental changes in precipitation affect flowering phenology in a community context and explore the implications of these shifts for competitive interactions and species coexistence. METHODS: We experimentally manipulated rainfall with rainout shelters and recorded detailed flowering phenology data for seven annual species including two grasses and five forbs. We assessed how their first and peak flowering days were affected by changes in rainfall and explored how flowering overlap between competing species changed. RESULTS: Changes in rainfall shifted flowering phenology of some species, but sensitivity differed among neighboring species. Four of the seven species studied started and/or peaked flowering earlier in response to reduced water availability. The idiosyncratic shifts in flowering phenology have the potential to alter existing temporal dynamics that may be maintaining coexistence, such as temporal separation of resource-use among neighbors. CONCLUSIONS: Our results show how species-specific phenological consequences of global change can impact community dynamics and competition between neighboring plants and warrant future research.

  PublisherDOI

• Spatial clustering reveals the impact of higher-order interactions in a diverse annual plant community

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-07-18

  preprintOpen accessSenior author

  Abstract Spatial patterns are widespread in ecology, but their effects on species interactions remain unresolved, especially in diverse communities. In principle, the degree of spatial clustering could alter the concentration of higher-order interactions, which occur when one (or more) species modifies competition between two others. When species are well mixed, heterospecific neighbors have ample opportunity to modify a competitor’s interactions with other species. In contrast, species clustering can reduce the concentration of interspecific higher-order interactions. In a field experiment with annual grassland plants in California, we manipulated the spatial arrangement — but not the number or identity — of two competitors and measured how they jointly affected a focal individual. We found that focal plants produced more seeds when their competitors were clustered than when they were mixed. These results suggest that interspecific higher-order interactions generally had a stronger competitive (or weaker facilitative) effect than intraspecific ones. However, the effect of clustering varied across species. Larger differences in focal fecundity were correlated with competitors that had greater differences in size and/or functional traits between the spatial arrangements. Additionally, a competitive hierarchy among our study species predicted the effects of clustered versus mixed competitors on focal seed production. Altogether, our work suggests that the spatial arrangement of competitors changes the realized strength of competition in diverse plant communities by modifying the concentration of higher-order interactions. Given the extensive variation in spatial aggregation in plant communities, this mechanism is likely to be a powerful but underappreciated force shaping competition in nature. Significance Statement Plant species coexist in remarkably diverse assemblages throughout the world. Spatial patterns, including aggregation and intermixing, are also widespread in these communities. One potentially underappreciated mechanism that may structure the spatial dynamics of plant communities is interactions that uniquely occur in diverse systems, often called higher-order interactions. Here, we experimentally demonstrated that spatially mediated higher-order interactions operate among annual plants. These higher-order interactions, and their associated changes in competitor size and functional traits, were correlated with the competitive imbalance between competitors. Because both spatial aggregation and competitive hierarchies are widespread in nature, higher-order interactions emerging from their combination may be a more common driver of biodiversity patterns in plant communities than previously thought.

  PublisherDOI

• Species functional traits affect regional and local dominance across western Amazonian forests

  Journal of Ecology · 2025-12-09

  articleOpen access

  Abstract Several studies have documented dominance by few species in Amazonian forests. Dominant species tend to be either locally abundant (local dominants) or regionally frequent (widespread dominants) but rarely both (oligarchs). Here, we explore relationships between dominance and functional traits. We ask whether: (i) dominance is associated with specific functional profiles and (ii) dominance patterns (local vs. widespread dominants) are associated with different functional traits. We combined census data from 503 forest inventory plots across four lowland forest habitats in western Amazonia with trait information for ~2600 tree species, encompassing data collected in the focal plots and data from published sources. We considered traits that relate to leaf, wood, seed and whole‐plant strategies: specific leaf area (SLA), leaf area (LA), N content per unit leaf mass (LN), wood density (WD), seed mass (SM) and maximum diameter at breast height (DBH max ). Our results reveal that dominant species display different trait combinations depending on the habitat type. Taller dominant species exhibit higher regional frequency, associated with higher dispersal ability and lower local abundance, likely due to negative density dependence. Greater SM contributes to higher regional frequency of dominant species via greater dispersal by birds and mammals and seedling survival. Finally, traits related to resource conservation strategies, such as lower SLA, LA, LN and greater WD, favour higher local densities across most habitats, while the opposite pattern was linked to higher regional frequency. Synthesis . Our findings reveal that (i) dominance is associated with different functional traits depending on the habitat type, and (ii) different functional trait values define distinct dominance patterns. Our study exemplifies the potential of trait‐based approaches to illuminate the ecological mechanisms that may underlie dominance in tropical forests. Finally, accounting for both local abundance and regional frequency when studying dominance is likely to improve our understanding and forecasting of how different species will respond to global change drivers in western Amazonia.

  PublisherDOI

• Use and misuse of trait imputation in ecology: the problem of using out‐of‐context imputed values

  Ecography · 2025-02-03 · 6 citations

  articleOpen access

  Despite the progress in the measurement and accessibility of plant trait information, acquiring sufficiently complete data from enough species to answer broad‐scale questions in plant functional ecology and biogeography remains challenging. A common way to overcome this challenge is by imputation, or ‘gap‐filling' of trait values. This has proven appropriate when focusing on the overall patterns emerging from the database being imputed. However, some applications force the imputation procedure out of its original scope, using imputed values independently from the imputation context, and specific trait values for a given species are used as input for computing new variables. We tested the performance of three widely used imputation methods (Bayesian hierarchical probabilistic matrix factorization, multiple imputation by chained equations with predictive mean matching, and Rphylopars) on a database of tropical tree and shrub traits. By applying a leave‐one‐out procedure, we assessed the accuracy and precision of the imputed values and found that out‐of‐context use of imputed values may bias the estimation of different variables. We also found that low redundancy (i.e. low predictability of a new value on the basis of existing values) in the dataset, not uncommon for empirical datasets, is likely the main cause of low accuracy and precision in the imputed values. We therefore suggest the use of a leave‐one‐out procedure to test the quality of the imputed values before any out‐of‐context application of the imputed values, and make practical recommendations to avoid the misuse of imputation procedures. Furthermore, we recommend not publishing gap‐filled datasets, publishing instead only the empirical data, together with the imputation method applied and the corresponding script to reproduce the imputation. This will help avoid the spread of imputed data, whose accuracy, precision, and source are difficult to assess and track, into the public domain.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Higher order interactions, functional trait changes, and species coexistence in an annual plant community

  NSF · $627k · 2020–2025

• Functional traits and the mechanisms of species coexistence in an annual plant community

  NSF · $526k · 2016–2020

• Functional traits and the mechanisms of species coexistence in an annual plant community

  NSF · $530k · 2015–2016

Frequent coauthors

• Cyrille Violle

  Centre d'Écologie Fonctionnelle et Évolutive

  105 shared

• Brian J. Enquist

  Santa Fe Institute

  48 shared

• David D. Ackerly

  University of California, Berkeley

  33 shared

• Jens Kattge

  Max Planck Institute for Biogeochemistry

  29 shared

• Josep M. Serra‐Diaz

  Aarhus University

  29 shared

• Brody Sandel

  Santa Clara University

  28 shared

• Claire Fortunel

  25 shared

• Jens‐Christian Svenning

  Aarhus University

  25 shared

Labs

• 2023-2024 Undergraduate Research Lab AvailabilityPI

Education

• Ph.D., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2005

• M.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  2001

• B.S., Ecology and Evolutionary Biology

  University of California, Los Angeles

  1999