I am currently seeking a PhD student for an NSF-funded research project on stream ecosystem ecology. See details below

Project: A doctoral position is available for an independent and motivated student with a background in ecology, environmental science, fisheries, or related fields. The student will participate in a collaborative, multi-institution NSF-funded research project to understand the patterns and drivers of organism size-structure in macroinvertebrate and fish food webs of stream ecosystems. The project aims to determine how individual metabolic scaling and trophic structure relate to the distribution of body sizes and energy flow in stream food webs. The student will have the opportunity to work in a variety of streams across North America within the National Ecological Observatory Network (NEON) and gain experience in the application of stable isotopes, respirometry, and Bayesian inferential frameworks. The position will be available starting in summer of 2026, but there is flexibility in the start date for fall 2026 for qualified applicants. The project leader, Dr. Jim Junker, works within a diverse and collaborative research group at the University of North Texas exploring aquatic ecosystems from biogeochemistry to food web ecology across a wide variety of scales. The lab group values diversity and seeks to build an inclusive lab environment. Compensation: Funds are available to support research activities and doctoral student salary and tuition. It is expected that support will come from a combination of research and teaching assistantships and that students will apply for appropriate fellowships and scholarships. Doctoral students on UNT assistantships are provided health insurance through the university’s health insurance plan. Eligibility: Candidates with a Master’s degree in a relevant field are preferred; however, consideration will be given to exceptional candidates with a Bachelor’s degree in a relevant field. Competitive candidates will have experience working in field settings; strong statistical and modelling skills, including experience in the R computing environment; and excellent interpersonal and writing skills. The position requires eligibility to operate a motor vehicle in the U.S. The student will be enrolled in the PhD program in the Department of Biological Sciences at the University of North Texas in Denton, TX. Application process: Application review will begin on February 10, 2026 and the position will remain open until filled. To apply, please send application materials to Dr. Jim Junker (<james.junker@unt.edu>) with the subject, “PhD application: aquatic ecosystem ecology”. Packets should include a single PDF with 1) cover letter describing your interest in the project, relevant experience, and career goals, 2) your CV, 3) the names and contact details of three (3) references, and 4) unofficial transcripts.

Ongoing projects

Size spectra of North American streams

Image of a size spectra showing the decline in abundance with body size. There are eight lines that from left to right change from red to blue. Under the lines there are organisms of different size with decreasing abundance with increasing size

Organism body size is a critical variable that is associated with numerous ecological attributes of organisms, including metabolic rate, movement, feeding interactions and trophic position, among others. As such, knowing information on the sizes of organisms can tell us a lot about ecosystem patterns and processes. For example, larger organisms use more energy, therefore fewer large individuals can be supported on a fixed energy source than smaller individuals on that same resource. Larger organisms, for the most part, eat individuals smaller then themselves. This project seeks to understand the patterns and drivers of organisms size distributions in streams of North America. We leverage a size-based theory of food webs, size spectra, to understand how energy flows up food webs from small organisms to larger predator species. In this work, we use data from the National Ecological Observatory Network (NEON) to explore how environmental variables such as temperature and basal resource availability control the distribution of individual body sizes in an ecosystem.

Relevant papers:

Pomeranz, J., J. R. Junker, V. Gjoni, and J. S. Wesner. (2024). Maximum likelihood outperforms binning methods for detecting differences in abundance size spectra across environmental gradients. Journal of Animal Ecology 93:267–280.DOI:10.1111/1365-2656.14044. PDF. LINK.

Wesner, J. S., J. P. F. Pomeranz, J. R. Junker, and V. Gjoni. (2024). Bayesian hierarchical modelling of size spectra. Methods in Ecology and Evolution 15:856–867. DOI:10.1111/2041-210X.14312. PDF. LINK.

Gjoni, V., J. P. F. Pomeranz, J. R. Junker, and J. S. Wesner. (2024). Size spectra in freshwater streams are consistent across temperature and resource supply. bioRxiv. LINK.

Gjoni, V., D. S. Glazier, J. Pomeranz, J. R. Junker, A. Smith, J. Woelber, S. Reynolds, T. Welch, and J. S. Wesner. 2025. Temperature and predation alter metabolic scaling without changing size-based community structure in freshwater macroinvertebrates. bioRxiv.LINK

Urbanization effects on stream water quality

Urbanization of stream environments is rapidly increasing globally. These changes often lead to shifts in the hydrology and ecology of these systems including the loss of important ecosystem services like clean water, food production, and recreation. Research in the group is using concentration-discharge (C-Q) relationships along with patterns of ecosystem metabolism to understand how streams transport and transform nutrients and materials delivered from the watershed. The rapidly expanding Dallas-Fort Worth metropolitan area provides a unique opportunity to explore gradients of urbanization and associated stream ecosystem in the largest inland metropolitan area of the U.S.

Population secondary production and toolsets for estimating secondary production

Secondary production, the accrual of heterotrophic biomass over time, is a comprehensive measure of population that incorporates individual growth, mortality, and reproduction. Because it is rooted in bioenergetic theory and incorporates detailed information of the entire life-cycle of organisms, it is also a very useful measurement for understanding the role of organisms in energy and nutrient cycles. Past and ongoing research in the lab has focused on understanding the drivers of secondary production from individuals to communities including the nutritional and thermodynamic controls on production dynamics. We also develop tools and statistical frameworks to estimate production to be able to best use the wealth of information collected in production studies.

Relevant papers and resources:

Junker, J. R.. secProd: a toolset for calculating secondary production of populations and communities.https://jimjunker1.github.io/secpRod/

Junker, J. R., W. F. Cross, J. P. Benstead, A. D. Huryn, J. M. Hood, D. Nelson, G. M. Gíslason, & J. S. Ólafsson. (2020). Resource supply governs the apparent temperature dependence of animal production in stream ecosystems. Ecology Letters 23(12):1809-1819. DOI:10.1111/ele.13608. PDF

Junker, J. R. & W. F. Cross. (2014). Seasonality in the trophic basis of a temperate stream invertebrate assemblage: Importance of temperature and food quality. Limnology and Oceanography 59(2):507-518. DOI:10.4319/lo.2014.59.2.0507. PDF

Past Projects