There are two areas of ecology research that our lab is most interested in:
1) Macroscale patterns of and controls on ecological communities and food webs
As stream ecologists we are interested in watersheds, which include rivers, the smaller streams and tributaries that flow int them, and the surrounding area of land which drains the precipitation and runoff that ultimately becomes stream water. A central focus of stream ecology is to understand linkages between ecological processes occurring in the river or stream (and aquatic ecosystem) and its watershed (a terrestrial ecosystem). These “aquatic-terrestrial” linkages have been studied for decades and are known to be important. Energy produced in streams can feed animals in terrestrial food webs, and terrestrial energy can fuel stream food webs as well. Yet much of this work, including my own (Allen et al. 2012), has focused on processes occurring at the local or site scale. A central question that has been guiding research in our lab has been to ask how the relative magnitude and balance of these linkages varies geographically. There are several projects by different members my lab that are answering this question in different ways.
What regional and continental scale processes control the patterns of aquatic insect prey fluxes from streams to terrestrial food webs? The dissertation of Darin Kopp, PhD candidate in our lab, is focused on how the describing the flow of emergent adult aquatic insects from rivers and streams (important prey for birds and other terrestrial predators) into watersheds at the scale of the contiguous US. Thus far we have found that the geometry of these stream networks is an important predictor of how much of the watershed receives a significant contribution of aquatic insect prey (Kopp and Allen, in press).
How do dams modify the relative importance of aquatic and terrestrial energy sources in stream food webs? Michelle Busch, a PhD student in my lab, is studying how the importance of terrestrial energy (primarily falling tree leaves) in stream food webs can be impacted by dams in rivers. Busch is conducting a comparative field study on four different rivers in southeastern Oklahoma to test the hypothesis that this terrestrial food source is lost in rivers downstream of dams, making the food web more reliant on stream algae instead of terrestrial-derived organic matter.
How does the structure and function of stream food webs vary in different terrestrial biomes? Dr. Daniel Nelson, is leading several projects focused on aquatic-terrestrial linkages. One project is a large comparative field study of stream food webs spanning the deserts of the Southwest US the grasslands of the North American Great Plains, and the deciduous forests of Southeastern US. The hypothesis we are testing is that the importance of terrestrial energy in aquatic food webs increases as terrestrial productivity increases from deserts to grasslands to forests. One manuscript from this project found that the stream taxa that are reliant on terrestrial energy sources (leaf shredding primary consumers) increased as leaf-litter became more abundant across this climate gradient (Nelson et al., in review). Finally, Dr. Nelson also led a large experiment at the Aquatic Research Facility at OU, where we manipulated food web structure of artificial streams from “green” algae-based food webs to “brown” leaf litter-based food webs. We are investigating which food web types are most resilient to warming and drying, two ecological stressors that are becoming more common in an era of anthropogenic change.
Allen, D. C., C. C. Vaughn, J. F. Kelly, J. T. Cooper, M. H. Engel. 2012. Bottom-up biodiversity effects increase resource subsidy flux between ecosystems. Ecology 93(10): 2165-2174.
Kopp, D. A. and D. C. Allen. Stream Network Geometry and the Spatial Influence of Aquatic Insect Subsidies across the Contiguous US. In press. Ecosphere.
Nelson, D., D. A. Kopp, and D. C. Allen. Regional vs. local controls on community structure across a broad climate gradient. In review. Freshwater Science.
2) A macrosystems approach to studying stream drying
Community ecologists are often interested in how abiotic (climate, geomorphology, hydrology) factors act as a set of filters that control which species can persist in a given location. The effect of drying not been strongly considered as an abiotic factor that might structure stream ecosystems. The second major focus of ongoing research in our lab is comprised of two different projects focused on stream drying. This work is advancing basic ecology research and also relevant to ongoing policy debates on environmental protections for streams that dry (Marshall et al 2018). There are two goals of this research area: 1) to understand how drying affects stream ecosystems, and 2) to understand how this effect varies geographically.
Dry Rivers Research Coordination Network. The Dry Rivers RCN is an NSF-funded collaborative network of ecologists and hydrologists who study streams that dry or cease to flow (often collectively called intermittent rivers and ephemeral streams, or IRES). The goal of our network is to synthesize existing data on IRES, particularly those in the US, and to generate reviews and conceptual papers that advance the field. We are in our second year of the project and have recruited more than 30 participants to participate in our first workgroup. We are currently working on several different projects that focus on linking the streamflow regime (flow frequency, duration, timing, and magnitude) to the structure and function of stream ecosystems. We are using stream flow data collected across the contiguous US to investigate how river drying patterns vary geographically, and are compiling ecological data to investigate how variation in these drying patterns affects the biological organization of streams
StreamCLIMES. StreamCLIMES (sCaling cLimate, connectIvity, and coMmunitiEs in Streams) is an NSF-funded collaborative Macrosystems Biology project that spans 6 different institutions (Northern Arizona University, University of Arizona, University of California Berkeley, University of Louisiana Lafayette, University of Oklahoma, and Virginia Tech). This project will be one of the first coordinated studies on stream drying across the southern US, an area where drying is common and human demand for water is increasing. We are in the first year of this project and are studying 10 watersheds in different eco-climatic domains in the southern US. First, we will be establishing 100 field sites where we will monitor drying patterns and sample for benthic macroinvertebrates for 3 years. We are working closely with the National Ecological Observatory Network (NEON), as 9 of these 10 regions houses a NEON site. PIs from each institution will be playing a fundamental role in leading different aspects of the empirical research to build a project that spans genetic, population, community and ecosystem levels of biological organization. Second, we will be developing hydrological models for the study systems that will model stream drying patterns under different climate scenarios, including climate change and different climate oscillation patterns (El Niño Southern Oscillation etc.). Third, we will be integrating hydrological model outputs, the field-based empirical data that we collect, and other spatial datasets to explore how spatio-temporal variation in drying patterns from different climate scenarios affects stream ecosystems at the river network, regional, and continental scales.
Allen, D. C., K. E. McCluney, S. R. Elser, and J. L Sabo. 2014. Water as a trophic currency in dryland food webs. Frontiers in Ecology and the Environment 12(3): 156-160.
Marshall, J. C., V. Acuña, D. C. Allen, N. Bonada, A.J. Boulton, S. M. Carlson, C. N. Dahm, T. Datry, C. Leigh, P. Negus, J. S. Richardson, S. Sabater, R. J. Stevenson, A. L. Steward, R. Stubbington, K. Tockner, R. Vander Vorste. 2018. Protecting U.S. temporary waterways. Science. 361: 856.
StreamCLIMES is a collaborative research project that will study the effects of drying on stream ecosystems across the southern US. Collaborators include Michael Bogan at the University of Arizona, Katie Costigan at the University of Louisiana Lafayette, Meryl Mims at Virginia Tech, Ben Ruddell and Abe Springer at Northern Arizona University, Albert Ruhi at the University of California Berkeley, Robert Pastel at Michigan Tech University, and Tom Neeson and Yang Hong at the University of Oklahoma.
The Dry Rivers Research Coordination Network is a network of ecologists and hydrologists who study streams that do not always flow. Collaborators on this project include Katie Costigan, Kate Boersma, Michael Bogan, Thibault Datry, Ken Fritz, Sarah Godsey, Stephanie Kampf, Meryl Mims, Julian Olden, Albert Ruhi, Adam Ward, Margaret Zimmer, Emily Bernhardt, Walter Dodds, Jay Jones, and others. You can follow us on twitter @DryRiversRCN. This project is jointly funded by the National Science Foundation Divisions of Biology and Geosciences and will run from 2018-2022.
Surveys for non-native crayfish in southeastern Oklahoma
Crayfish are large-bodied benthic omnivores that are ecologically important components to both lentic and lotic ecosystems. Crayfish are also among the most notorious invasive aquatic species in freshwater ecosystems and have been reported not only to displace native crayfish species but also to impact other aquatic organisms, including fish. We will determine the current distribution and population status of native and invasive crayfish species in southeastern Oklahoma rivers where sportfish (i.e. smallmouth bass and other sunfishes) depend on crayfish as a substantial part of their diet. We will conduct surveys for native and invasive crayfishes in 80 sites in the Kiamichi, Little, Glover and Mountain Fork Rivers. From these surveys, we will identify areas where invasive crayfish coexist with native crayfish. Second, we will conduct a comparative field study at 12 study sites that span a natural gradient of invasive crayfish densities to investigate diets of native and invasive crayfish species using stable isotopes. This project is funded by the Oklahoma Department of Wildlife Conservation, and will run from 2019-2022.
The Hunt for the Ozark Emerald
The Ozark Emerald (Somatochlora ozarkensis) a regionally endemic dragonfly and identified as a Tier II species of greatest conservation need by the Oklahoma Department of Wildlife Conservation. We will conduct adult surveys and aquatic macroinvertebrate sampling with the primary focus being the discovery of Ozark Emerald larvae, which are unknown from the wild. Sampling will help determine the habitat of larval Ozark Emeralds and what macroinvertebrate species co-occur with them. We also will survey crayfish communities at the study sites, with special attention toward the Kiamichi Crayfish (Orconectes saxatilis), a Tier I species, and the Mena and Ouachita Mountain Crayfish (O. menaeand Procambarus tenuis), both Tier II species. Second, we will compile crayfish data from previous research projects in the Ouachita Mountains/West Gulf Coastal Plain Region. Allen Lab postdoc Dr. Daniel Nelson will be leading this project, and odonate specialist Brenda Smith from the Oklahoma Biological Survey is also a co-PI on the project. This project is funded by the Oklahoma Department of Wildlife Conservation, and will run from 2018-2021.
Chasing the Peppered Shiner
The Oklahoma Department of Wildlife Conservation has identified the Peppered Shiner, Notropis perpallidus, as a Tier I species of greatest conservation need. This is a very rare species restricted to a relatively small geographic region in a few rivers in the south-central United States, and it has not been collected in Oklahoma since 1991. Here we will collaborate with Dr. Bill Matthews, renowned fish ecologist and Professor Emeritus at the University of Oklahoma, to conduct targeted surveys for Peppered Shiner in the Kiamichi, Little, Glover, and Mountain Fork Rivers in southeast Oklahoma. This project is funded by the Oklahoma Department of Wildlife Conservation and will run from 2018-2020.