Research 

Our research  focuses on the functional attributes of stream ecosystems, how community composition influences ecosystem function and how ecological and evolutionary processes interact.  Much of our work focuses on the transport dynamics of various ecological entities (e.g. fine organic particles, nitrogen, phosphorus, organisms) and the potential for transport to longitudinally link ecosystems.  Our efforts have expanded recently to examine community and evolutionary topics and to better understand the functional consequences of management activities (e.g. land use change, riparian and stream restoration, etc.).  Although my research has focused on streams, I seek an understanding of these principles as generic processes active in all ecosystems.  Brief summaries of past and current research activities are included below. ​

From Ecosystems to Evolution: Harnessing elemental data to detect stoichiometry control-points and their consequences for organismal evolution.   NSF EPSCoR RII Track-2FEC
The supply of elements and energy governs biological activity from cellular to ecosystem scales.  Human activities profoundly impact the relative and absolute supply of elements to organisms and across the globe. Through this collaboration, we are combine ecological stoichiometry (ES) theory with ‘big data’ harvesting and analysis tools to build the research capability and human resource capacity across four EPSCoR jurisdictions (Nebraska, Wyoming, Arkansas, and Vermont). We will be using this unique database to investigate stoichiometric control of ecological phenomena occurring across scales that are currently difficult to investigate. 
For more information, check out this recent UNL press release. This is a recently funded project and several opportunities for graduate students, postdocs, and technicians are currently being advertised,   See the Opportunities page for more details.

StreamNET

Understanding how, when and where nutrients enter streams and lakes is critical to successfully managing Nebraska’s surface waters. This project meets this challenge, by building StreamNet, a novel network of high-frequency aquatic nutrient sensors with an easily accessible web application.  By combining innovative sensing technology with a user-driven web application, we hope to  provide novel information on nutrient conditions in Nebraska lakes and streams, leading to improved nutrient management techniques and, ultimately, improved water quality in the state.   This project is led by Dr. Jennifer Corman and also includes Dr Chris Chizinski, both from the School of Natural Resources at UNL .

The Prairie Corridor Project
The Thomas lab has partnered with other UNL faculty, the city of Lincoln, Nebraska, and our local natural resource district to characterize pollinator, plant and stream communities along the Haines Branch of Salt Creek.  Our partners are embarking on creating an intact tall-grass prairie corridor linking the city to the Audubon Society's Spring Creek Prairie, approximately 15 miles SW of Lincoln.   Our lab has been working to understand nutrient patterns along this corridor, variation in stream macroinvertebrates communities, changes in stream habitat, and rates of key ecological functions in selected sites spanning the proposed corridor.  This information will provide a baseline for assessing future changes that accompany future prairie and stream restoration activities that are currently being planned.

Eco-Evo Interactions in Trinidadian Streams

​I have been a member of a diverse research team initiated by an NSF – Frontiers in Biological Research (FIBR) award examining reciprocal feedbacks between evolution and ecosystem processes in nature (D.N. Reznick, lead PI).  Our focal species, the guppy (Poecilia reticulata), displays rapid evolution of body size, life histories and other traits when selective forces shift (e.g. high vs. low predation risk).  As a member of the ecosystem group, my laboratory has been responsible for designing, conducting and analyzing nitrogen isotope tracer experiments that quantitatively compare how the functional role of guppies in these food webs changes with local adaptation.   Associated papers include Bassar et al. 2010, El-Sabaawi et al. 2015, Collins et al. 2016, Simon et al. 2019  and Lopez-Sepulcre et al. 2020.  

EvoTRAC

The goal of this project, which we call “EvoTRAC” (Evolutionary and Ecological Variability in Organismal Trait Response with Altitude and Climate), is to experimentally quantify mechanisms of species and ecosystem sensitivity to warming and increased variation in precipitation, focusing on insects (mayflies, caddisflies, and stoneflies) in small streams in the Colorado Rockies and the Ecuadorian Andes. Theory predicts tropical stream species will be more physiologically sensitive to warming or greater variability in stream discharge than temperate species, and sensitivity should increase for species living in high elevations (alpine zones) versus lowland streams (foothills). We are testing this prediction by measuring the physiological tolerance of species to warming. We are also discovering new species and assessing the ability of species to move between streams as climate changes using landscape genomic techniques. Our ultimate goal is to provide a novel, integrative model for predicting species and stream ecosystem responses to climate shifts.  Collaborators on this project include LeRoy Poff (CSU), Cameron Ghalambor (CSU), Boris Kondratieff (CSU), Chris Funk (CSU), Alisha Shah (University of Montana), Brian Gill (Brown University), Kelly Zamudio (Cornell University), Alex Flecker (Cornell University),  Andrea Encalada (Universidad San Francisco de Quito [USFQ]), and Juan Guayasamin (USFQ).  Recent papers from this effort include Gill et al. 2016, Polato et al. 2018, Atkinson et al. 2018, Lessmean et al 2016, and Shah et al. 2017 and 2020.   This work is also featured in this article.    

The Stoichiometry of Nutrient Cycling

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 We have been interested in the coupling of nitrogen and phosphorus cycling in streams for quite some time.  Specifically,  we have been exploring how the availability of the element limiting biological production impacts the uptake and cycling of non-limiting elements (and vice versa).   Steve has participated in organized sessions, workshops and funded research efforts in California and Brazil focused on this topic.   Two papers from 2005 explore this topic in theory (Cross et al. and Schade et al.).  Those efforts led to empirical efforts funded by NSF and Brazil's Ciencias sem Frontieras program.  In the former, we worked with colleagues in California and Minnesota to examine how N and P spiraling interacted in N-limited streams in northern California that different in the amount of autotrophy occurring in the stream (e.g. Schade et al. 2010).  In the latter effort, we worked with colleagues at the State University of Rio de Janeiro to explore how this relationship played out in a tropical setting and whether nutrient additions and nutrient diffusing substrates lead to similar conclusions about nutrient limitation (Tromboni et al. 2018)  

Transport Dynamics of Fine Organic Particles

This research combined ecology and hydrology to address two dominant but competing characteristics of streams, downstream transport and in situ ecological processing. My dissertation examined the transport, deposition and re-suspension dynamics of fine organic particles in streams. Fine particulate OM is an important vector for distributing energy, contaminants and nutrients within streams (and their floodplain) at multiple spatial and temporal scales. Using field additions of radioactively-labeled natural detritus and inverse modeling, this research is one of the first studies to quantify organic particle deposition transport, deposition, and re-suspension in natural streams (Minshall et al. 2000, Thomas et al. 2001, Newbold et al. 2005).