About

Judith Bronstein is a University Distinguished Professor in the Department of Ecology and Evolutionary Biology at the University of Arizona, a position she has held since 2012. Her research focuses on the ecology and evolution of interspecific interactions, particularly mutualisms, which are mutually beneficial relationships between species. Using a combination of field observations, experiments, and theoretical approaches, her work examines how population processes, abiotic conditions, and community context influence the net effects of these interactions on the fitness of each participating species. Her specific areas of interest include conflicts of interest between mutualists and their consequences for maintaining beneficial outcomes, the causes and consequences of cheating within mutualisms, context-dependent outcomes in both mutualisms and antagonisms, and the threats posed by human activities to mutualistic relationships. Her empirical research has recently concentrated on exploited pollination mutualisms in deserts, desert grasslands, and montane habitats in Arizona and Colorado. Throughout her career, she has contributed to developing a strong conceptual foundation for the study of mutualistic interactions.

Research topics

• Biology
• Ecology
• Sociology
• Evolutionary biology
• Zoology
• Genetics
• Botany
• Geography

Selected publications

• Author response for "Ants on flowers: Protective ants impose a low but variable cost to pollination, moderated by location of extrafloral nectaries and type of flower visitor"

  2025-03-17

  peer-review
  PublisherDOI

• Beyond mutualism: the nature of domesticator–domesticate interactions

  Trends in Ecology & Evolution · 2025-10-02

  reviewOpen accessSenior author

  The literature on domestication commonly calls the association between human domesticators and their plant and animal domesticates mutualistic, yet this designation is rarely examined critically. Here, we assess its validity based on the long-accepted ecological definition of mutualism and current evidence for origins, subsequent evolution, and present features of domesticator-domesticate interactions. We argue that it is difficult to wholly align these associations with standard concepts of mutualism. Instead, domesticator-domesticate interactions vary across domestication pathways and have changed throughout domestication timelines, spanning antagonism to commensalism to mutualism. We argue that the later stages of domestication in some intensively domesticated species form exploitative rather than mutualistic interactions. Moving away from conceptualizing domestication as mutualistic raises new questions regarding its ecology and evolution.

  PublisherDOI

• Ökosysteme. Über Risiken und Nebenwirkungen der Metapher

  Zeitschrift für Ideengeschichte · 2025-01-01

  article1st authorCorresponding

  «Kein Phänomen kann isoliert betrachtet werden, jedes wirkt sich auf alle Aspekte unseres Lebens aus. Wir müssen lernen, dass wir Teil des Ökosystems der Natur sind.» Diese schönen Sätze des kanadischen Architekten Arthur Erickson suggerieren eine große Sensibilität für die Umwelt. Sie schüren die Hoffnung, dass die Spezies Mensch sich auch neu und anders wahrnehmen könnte: als Teil der Natur, nicht als Herrscherin derselben. Alles, so legt Erickson nahe, sei mit allem verbunden. Doch in der Biologie ist «Ökosystem» ein definierter Begriff mit spezifischen Merkmalen, die seit mehr als sieben Jahrzehnten erforscht werden. Ist wirklich alles mit allem verbunden? Entspricht der von Erickson formulierte Gedanke der wissenschaftlichen Erkenntnis? Und falls nicht, ist das eigentlich ein Problem?

  PublisherDOI

• Review for "From friend to foe and back: coevolutionary transitions in the mutualism–antagonism continuum"

  2025-03-16

  peer-review1st authorCorresponding
  PublisherDOI

• A leaf‐surface fungus mediates interactions between leafcutter bees and the plants they cut to line their nests

  Ecology · 2025-10-01 · 2 citations

  articleSenior author

  Many insects damage leaves, a phenomenon that is foundational to their impacts on terrestrial ecosystems. Leaf traits, including chemistry, shape these interactions. In turn, leaf-surface (phylloplane) microbes can act directly or in concert with leaf chemistry to influence leaf choice, especially by insects whose reproductive success is tied to prolonged contact with leaf surfaces. Leafcutter bees (Megachile spp.) cut disks from leaves to line their nests, with leaves and their associated microbes forming the environment in which bees' offspring develop. We hypothesized that phylloplane microbial communities act in concert with leaf chemistry to mediate interactions between the leafcutter bee M. lippiae and the plants they cut. We surveyed phylloplane communities on rose (Rosa × hybrida, Rosaceae) leaflets that were cut versus not cut by wild M. lippiae. Microbial communities differed between cut and non-cut leaflets, with Aspergillus spp. overrepresented on cut leaflets, and Alternaria sp. and Bacillus sp. overrepresented on non-cut leaflets. Then, we inoculated rose leaves in the field to test the effect of these microbial taxa on cutting. When inoculated onto rose leaves, Alternaria and Bacillus had no effect on cutting, but Aspergillus resulted in twice as many cuts as on sham-inoculated leaves. To test whether Aspergillus could protect bee nests against pathogens, we grew Aspergillus with two pathogenic fungi: the generalist insect pathogen Beauveria bassiania and three strains of Ascosphaera that cause chalkbrood disease in bee larvae. Aspergillus did not inhibit the growth of Beauveria, but it markedly slowed the growth of Ascosphaera. To clarify whether these phylloplane microbes reflect differences in leaf chemistry or are instead independent cues that influence leaf cutting, we used liquid chromatography-mass spectroscopy to characterize the metabolome of cut and non-cut leaflets. Chemistry did not differ between cut and non-cut leaflets, nor did it vary as a function of microbial community composition. Our results suggest that Aspergillus, a common member of rose phylloplane communities, mediates interactions between leafcutter bees and roses, potentially affecting the fitness of both partners. This study reveals a previously unexplored role for phylloplane microbes in plant-insect associations.

  PublisherDOI

• Ants on flowers: Protective ants impose a low but variable cost to pollination, moderated by location of extrafloral nectaries and type of flower visitor

  Journal of Ecology · 2025-06-18 · 5 citations

  articleOpen access

  Abstract Throughout their lifetimes, individuals of most species engage in multiple mutualistic interactions simultaneously. These mutualisms can interfere with each other, leading to ecological costs that can influence the outcome of these interactions. Identifying factors that modulate these costs is pivotal to reaching a deeper understanding of the dynamics of mutualistic interactions. We investigated the ecological costs of protective ants on the pollination of plants with extrafloral nectaries (EFNs) and how plant traits and the type of pollinator can modulate them. We hypothesized that (1) ants negatively affect the patterns of flower visitation and plant reproductive performance and that (2) this effect is relatively higher for plants bearing EFNs close to inflorescences compared to those bearing EFNs only on vegetative tissues. Additionally, we hypothesized that (3) the effect of ants on flower visitation is contingent upon the type of flower visitor. To evaluate these hypotheses, we used a meta‐analytical approach based on 27 studies that assessed the effects of ants on patterns of floral visitation and plant reproductive performance. We found that ants impose a low, yet highly variable, cost to pollination. Specifically, ants have a strong negative effect on patterns of flower visitation, especially when the visitors are bees, but this does not translate into reduced plant reproductive performance. In fact, the reproductive success of plants with EFNs close to vegetative tissue is enhanced by ant presence. Finally, the negative effect of ants on flower visitors is stronger when EFNs are closer to inflorescences. Synthesis: Our results indicate that, in general, ants have a low impact on the pollination of EFN‐bearing plants. This pattern supports theoretical predictions that natural selection acts to lower the costs of protection mutualisms. Our macroscale evaluation further shows that plant traits such as EFN location, as well as the type of flower visitors, modulate this cost. The outcome of ant–pollinator interactions may affect the evolutionary trajectory of traits mediating defence and pollination in EFN‐bearing plants.

  PublisherOA PDFDOI

• The Study of Mutualism, Past, Present, and Future

  The American Naturalist · 2025-08-25 · 4 citations

  article1st authorCorresponding

  AbstractAfter a fitful start, the conceptual study of mutualism (mutually beneficial interspecific interactions) is now flourishing. In 1994, I reviewed the status of the field as reflected in the peer-reviewed literature; I also laid out directions for future research. Here, I look back on that assessment and offer an updated perspective on our understanding of mutualism. Most of the open questions I identified now have significant literatures of their own. New questions have sprung from each of these, and methodological innovations have made it more possible than ever before to obtain answers. I identify one astonishing gap from 1994: the absence of attention, either in journals or in my own synthesis, to the fate of mutualisms in a changing world. I offer a brief assessment of the now-massive literature on this topic. Finally, I suggest some directions in which the field as a whole might profitably move in the future.

  PublisherDOI

• Both costs and benefits determine the removal of <i>Datura</i> (Solanaceae) seeds by seed‐dispersing ants

  Ecology · 2025-11-01

  articleOpen accessSenior author

  Mutualisms confer both benefits and costs to participants, but costs have been largely ignored when considering how mutualisms function and evolve. Plants that are dispersed by ants produce seeds with attached nutrient-rich food rewards (elaiosomes). When ants approach a seed, they likely assess both the benefits (elaiosome mass) and costs (mass of the inedible seed) of moving it. We hypothesized that the masses of both the seed and elaiosome would affect diaspore removal rate, and predicted that when given a choice, ants would remove diaspores with higher benefits and diaspores with lower costs more quickly. To test these hypotheses, we manipulated the elaiosomes of Datura wrightii and Datura discolor (Solanaceae) and conducted choice experiments where we presented diaspores with variable benefits and costs to colonies of the seed-dispersing ant Novomessor cockerelli (Formicidae). D. discolor has a larger elaiosome-to-seed ratio since its seeds are half the mass of D. wrightii. Consistent with our hypotheses, ants removed seeds with heavier elaiosomes (larger rewards) and lighter seeds (lower costs) more quickly. Our study provides new evidence for seed dispersal costs by quantifying a cost of seed dispersal to ants and underscores the necessity of measuring both the benefits and costs of mutualistic interactions.

  PublisherOA PDFDOI

• Mutualism and division of labour: a mutual expansion of concepts

  Philosophical Transactions of the Royal Society B Biological Sciences · 2025-03-20 · 5 citations

  reviewOpen accessSenior author

  Division of labour within social groups and the interspecific relationships within mutualisms have traditionally been treated as separate research areas. In this opinion, we align terminologies and concepts between the two fields, by comparing within-group division of labour to the outsourcing of functions in mutualisms. Division of labour and interspecific outsourcing share fundamental similarities. Both are built from specialization of some individuals within the relationship on tasks or functions required for survival, growth and reproduction. Both also generate variable fitness outcomes. A key difference is that mutualisms generally generate direct fitness gain, while benefits from cooperative sociality often accrue from a mix of direct and indirect fitness. Additionally, the levels of physical and physiological specialization within many mutualisms expand far beyond the levels of differentiation seen in cooperative social groups, with the exception of reproductive division of labour. The consideration of between-species outsourcing in the context of division of labour allows expansion of our understanding of both fields and beyond, to consider general principles as drivers of division of labour, and role differences more broadly across levels of complexity.This article is part of the theme issue 'Division of labour as key driver of social evolution'.

  PublisherDOI

• Costs of floral larceny: A meta‐analytical evaluation of nectar robbing and nectar theft on animal‐pollinated plants

  Ecology · 2025-03-01 · 7 citations

  reviewOpen accessSenior author

  Mutualistic interactions are biological markets in which different species exchange commodities to mutual benefit. Mutualisms are, however, susceptible to exploitation, with some individuals taking without reciprocating. While it is generally assumed that exploiters will inflict fitness costs, evidence for such costs is mixed and difficult to generalize due to their context-dependent nature. Animal-pollinated flowers are commonly exploited by larcenists, non-pollinating animals that consume floral rewards often without transferring pollen. The impacts of larcenists on plant reproduction vary widely, suggesting they inflict differing costs on plants, but which types of floral larceny are most and least costly, and why, has received little attention. We employed a meta-analytical approach to explore the effects of flower larceny on nectar traits, pollinator visitation, and plant reproduction. We focused on the effects of two contrasting forms of larceny: primary nectar robbing-nectar consumption through holes constructed in the corolla rather than entering flowers legitimately-and nectar theft-nectar consumption by entering flowers but with no pollen transfer. We found that both robbing and theft had negative impacts on nectar quantity and quality, but that only theft negatively affected pollinator visitation rates. Similarly, robbers had no impact on either female or male reproductive success, whereas thieves consistently reduced both male and female reproductive success. These effects were not associated with plant mating systems nor with the identities of robbers and effective pollinators, challenging previous generalizations. This study provides a comprehensive evaluation of larcenists' costs to animal-pollinated plants, revealing that nectar theft is more detrimental to plant reproduction than nectar robbing. These results enhance our understanding of the intricate dynamics of mutualism exploitation in ecological and evolutionary contexts.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Context-Dependency in the Exploitation of Pollination Mutualisms

  NSF · $228k · 2014–2017

• DISSERTATION RESEARCH: Reinforcement of isolation between parasite host races

  NSF · $20k · 2016–2018

• Coevolution of Mutualism: Limits to Reproductive Success in a Fig/Pollinator Interaction

  NSF · $30k · 1994–1996

• ROW: Fig/Pollinator Interactions: Coevolution and Consequences of Flowering Phenology

  NSF · $150k · 1990–1994

Frequent coauthors

• Rebecca E. Irwin

  Rocky Mountain Biological Laboratory

  38 shared

• Sarah K. Richman

  ETH Zurich

  25 shared

• Goggy Davidowitz

  University of Arizona

  20 shared

• Régis Ferrière

  European Organization for Nuclear Research

  19 shared

• Elinor M. Lichtenberg

  University of North Texas

  17 shared

• Jacob M. Heiling

  Western Carolina University

  15 shared

• Takayuki Ohgushi

  Kyoto University

  12 shared

• Aviva Patel

  10 shared

Awards & honors

• Elected Fellow of the Ecological Society of America (2016)
• Pillar of Excellence Award, University of Arizona Honors Col…
• Named University Distinguished Professor, University of Ariz…
• Distinguished Service Award, National Science Foundation (20…
• Distinguished Career Teaching Award, College of Science, Uni…