Judith Bronstein
Professor, BIO5 Institute
Professor, Ecology and Evolutionary Biology
Professor, Entomology / Insect Science - GIDP
University Distinguished Professor
Primary Department
(520) 621-3534
Research Interest
Judith L. Bronstein is University Distinguished Professor of Ecology and Evolutionary Biology, with a joint appointment in the Department of Entomology. Dr. Bronstein’s large, active lab focuses on the ecology and evolution of interspecific interactions, particularly on the poorly-understood, mutually beneficial ones (mutualisms). Using a combination of field observations, experiments, and theory, they are examining how population processes, abiotic conditions, and the community context determine net effects of interactions for the fitness of each participant species. Specific conceptual areas of interest include: (i) conflicts of interest between mutualists and their consequences for the maintenance of beneficial outcomes; (ii) the causes and consequences of "cheating" within mutualism; (iii) context-dependent outcomes in both mutualisms and antagonisms; and (iv) anthropogenic threats to mutualisms. In addition, she is Editor-in-Chief of The American Naturalist, a leading international journal in ecology and evolution. An award-winning instructor, Dr. Bronstein teaches at both the undergraduate and graduate levels; she has also run a large training grant administered by BIO5 that places life sciences graduate students in public school classrooms around Tucson. She serves in leadership positions in the College of Science (including chairing the College of Science Promotion and Tenure Committee for 2013), at the University, and at the Arizona-Sonora Desert Museum, where she is a member of the Board of Trustees and Chair of the Science and Conservation Council.


Marazzi, B., Franklin, K., Sommers, P., Lopez, B., Bronstein, J., Bustamante Ortega, E., Burquez, A., Medellin, R., & Aslan, C. (2014). Plant biotic interactions in the Sonoran Desert: Conservation challenges and future directions.. Journal of the Southwest, 457-501.
Bshary, R., & Bronstein, J. L. (2004). Game Structures in Mutualistic Interactions: What Can the Evidence Tell Us About the Kind of Models We Need?. Advances in the Study of Behavior, 34, 59-101.


Currently, there is little information transfer between empiricists working on cooperative interactions between species (mutualism) and theoreticians who model possible scenarios for the evolution and maintenance of cooperation between unrelated individuals. Furthermore, both theoretical and behavioral approaches often fail to consider ecological parameters that influence behavior. Our goal is to present the wealth of empirical knowledge (both behavioral and ecological) on mutualistic systems in a structure that may facilitate communication between empiricists and theoreticians. We have chosen eight broad categories of mutualisms that have been intensely studied and that are relatively well understood. For each system, we assess possible states of 12 parameters that can help theoreticians to construct game structures of mutualisms that are built on current empirical knowledge. We point out how ecological variables may influence behavioral decisions in ways not identified by our parameters. Finally, we elucidate similarities between mutualistic systems with respect to game structures that may not be expected given the diversity of mutualisms with respect to ecological and evolutionary background. On the basis of these results, we promote an interactive approach with models based on empirical knowledge, amenable to further testing. © 2004 Elsevier Inc. All rights reserved.

Ness, J. H., Bronstein, J. L., Andersen, A. N., & Holland, J. N. (2004). Ant body size predicts dispersal distance of ant-adapted seeds: Implications of small-ant invasions. Ecology, 85(5), 1244-1250.


The services provided within a community can change as the species composition of that community changes. For example, ant-seed dispersal mutualisms can be disrupted in habitats dominated by invasive ants. We propose that this disruption is related to changes in mean ant body size, given that invasive ants are smaller than most native seed-dispersing ants. We demonstrate that the mean and maximum distances that ants transport seeds adapted for ant dispersal increase with worker body size, and that this relationship is an accelerating power function. This pattern is consistent among three ant subfamilies that include most seed-dispersing ants as well as most invasive ant species, is generalizable across ant species and communities, and is independent of diaspore mass. Using a case study, we demonstrate that both the mean body size of seed-collecting ants and seed dispersal distances are decreased in sites invaded by Solenopsis invicta, the imported red fire ant. Furthermore, we demonstrate that the mean size of seed-collecting ants at a seed depot or within a community is a useful predictor of mean seed dispersal distances at those sites. Last, we show that small seed-collecting ants and decreased seed dispersal distances are common features of sites occupied by invasive ants. The link between ant body size and seed dispersal distance, combined with the dominance of invaded communities by typically small ants, predicts the disruption of native ant-seed dispersal mutualisms in invaded habitats.

Bronstein, J. L. (1987). Maintenance of species-specificity in a Neotropical fig- pollinator wasp mutualism.. Oikos, 48(1), 39-46.


Specificity at different stages in the interaction was studied in a common neotropical fig, Ficus pertusa, particularly in relation to its sympatric congener F. tuerckheimii. 99% of pollinators arriving at sticky traps on flowering figs were the specialist species. Foreign pollinators virtually never entered F. pertusa syconia to oviposit or emerged from mature fruits. Pollinators arrive at F. pertusa trees in a one-day burst that is well timed with the presence of unpollinated syconia, providing evidence for the existence of a species-specific volatile attractant. Some nonpollinating wasps associated with F. pertusa appear to use the same attractant to locate the tree.-from Author

Ferriere, R., Bronstein, J. L., Rinaldi, S., Law, R., & Gauduchon, M. (2002). Cheating and the evolutionary stability of mutualisms. Proceedings of the Royal Society B: Biological Sciences, 269(1493), 773-780.

PMID: 11958708;PMCID: PMC1690960;Abstract:

Interspecific mutualisms have been playing a central role in the functioning of all ecosystems since the early history of life. Yet the theory of coevolution of mutualists is virtually nonexistent, by contrast with well-developed coevolutionary theories of competition, predator-prey and host-parasite interactions. This has prevented resolution of a basic puzzle posed by mutualisms: their persistence in spite of apparent evolutionary instability. The selective advantage of 'cheating', that is, reaping mutualistic benefits while providing fewer commodities to the partner species, is commonly believed to erode a mutualistic interaction, leading to its dissolution or reciprocal extinction. However, recent empirical findings indicate that stable associations of mutualists and cheaters have existed over long evolutionary periods. Here, we show that asymmetrical competition within species for the commodities offered by mutualistic partners provides a simple and testable ecological mechanism that can account for the long-term persistence of mutualisms. Cheating, in effect, establishes a background against which better mutualists can display any competitive superiority. This can lead to the coexistence and divergence of mutualist and cheater phenotypes, as well as to the coexistence of ecologically similar, but unrelated mutualists and cheaters.