About

Daniel C Allen is a faculty member at The Pennsylvania State University, leading the Allen Lab. His research focuses on understanding stream ecosystems, particularly how large-scale environmental variations such as stream drying impact these ecosystems. His work involves spatial modeling and ecological analysis to explore the effects of climate change and anthropogenic influences on freshwater habitats. As a professor, he contributes to advancing ecological knowledge and environmental management through his research and mentorship.

Research topics

• Computer Science
• Ecology
• Geography
• Environmental science
• Geology
• Biology
• Sociology
• Cartography
• Water resource management
• Environmental resource management
• Physics
• Climatology
• Meteorology
• Environmental planning
• Physical geography
• Geotechnical engineering
• Mechanics

Selected publications

• Aridity Drives Streamflow, Network Connectivity and Climate Change Impacts in Non‐Perennial Stream Networks

  Ecohydrology · 2025-12-01

  article

  ABSTRACT Non‐perennial streams are globally prevalent. These streams are vital components of ecosystems, yet their drying patterns and resulting impacts on hydrologic connectivity remain poorly understood at the watershed scale. Aridity is a dominant driver of stream drying, but its influences on hydrologic connectivity have not been fully explored. In this study, we investigated the role of aridity in shaping streamflow and connectivity patterns in non‐perennial stream networks that span the continental United States aridity gradient. Using hydrologic models, we simulated daily streamflow and stream network connectivity under current and future climate scenarios. Our findings support previous research showing that aridity and streamflow are strongly linked. We also found that connectivity was related to aridity, although this relationship was weaker. Under the future climate scenario, mean runoff increased in most watersheds in the future, while mean connectivity decreased in the majority of watersheds. This difference is an indicator of the complex relationship between streamflow and connectivity. Aridity was a strong predictor of changes in very high and very low connectivity periods that resulted from climate change, but aridity did not predict changes in mean connectivity. Arid watersheds tended to experience more high connectivity days due to climate change while humid networks tended to have more low connectivity days. By modelling climate impacts at the network scale and across a broad hydroclimatic gradient, we highlight the importance of considering context‐dependent changes in network connectivity in river flow management and watershed conservation plans.

  PublisherDOI

• rTMS Implementation in ELFT (East London Foundation Trust): A Prospective Clinical Study

  BJPsych Open · 2025-06-01

  articleOpen access

  Aims: To evaluate the effectiveness and safety of repetitive transcranial magnetic stimulation (rTMS) in treating treatment-resistant depression (TRD), with a focus on changes in depression severity measured by the Montgomery–Åsberg Depression Rating Scale (MADRS) and the Hamilton Depression Rating Scale (HAMD). Methods: A prospective clinical trial was conducted with 15 patients diagnosed with TRD, defined as having failed at least two adequate antidepressant trials. rTMS was administered using a left dorsolateral prefrontal cortex (DLPFC) protocol, with sessions delivered five times per week over six weeks for the majority of participants. Depression severity was assessed using MADRS and HAMD scores both before and after treatment. Adverse events were monitored throughout the study. Paired t-tests were used to analyse changes in MADRS and HAMD scores, with statistical significance set at p<0.05. Effect sizes were calculated using Cohen’s d. Results: The average MADRS score decreased from 35.33 pre-intervention to 24.67 post-intervention, reflecting a mean reduction of 10.67 points and a large effect size (Cohen’s d=1.23). Similarly, HAMD scores decreased from 22.83 to 13.67, with a mean reduction of 9.17 points and a large effect size (Cohen’s d=0.98). While most patients demonstrated significant improvement, one patient experienced worsening symptoms. Adverse events were generally mild, with 7 patients reporting no side effects and 4 reporting mild pain at the stimulation site. Conclusion: rTMS appears to be an effective and well-tolerated treatment option for reducing depressive symptoms in patients with TRD. The significant reductions in MADRS and HAMD scores, along with large effect sizes, support the potential of rTMS as a therapeutic intervention for this population. Further research with larger sample sizes, including the use of a control group, is needed to confirm these findings and explore the long-term efficacy of rTMS in managing TRD.

  PublisherOA PDFDOI

• Shared leadership can promote success in collaborative research networks in ecology

  Functional Ecology · 2025-07-21

  articleOpen access1st authorCorresponding

  Abstract While collaborative science is becoming the norm in ecology, many ecologists participating in collaborations are less aware of the body of research that studies the processes by which collaborative teams organize and communicate. Here, we discuss how we successfully used a shared leadership model in the Dry Rivers Research Coordination Network. We discuss how this model promoted our success in different stages of the project, using the Tuckman model of team development: forming, storming, norming, performing and adjourning. Shared leadership in the forming phase helped us recruit a diverse membership from different scientific disciplines. In the storming and norming phases, shared leadership was especially useful in ensuring that all voices were heard in establishing group norms that promoted adhesion among and investment by RCN members. Shared leadership in the performing phase was crucial in providing opportunities for early career members to lead projects, and in the adjourning phase we reflected upon our entire collaboration to identify that shared leadership was crucial to our success, generating the thesis for this commentary. It is our hope that others may find this discussion of our experience in implementing a shared leadership model useful in developing their own fruitful collaborations. Read the free Plain Language Summary for this article on the Journal blog.

  PublisherOA PDFDOI

• Reviews and syntheses: Variable inundation across Earth's terrestrial ecosystems

  Biogeosciences · 2025-02-24 · 7 citations

  articleOpen accessCorresponding

  Abstract. The structure, function, and dynamics of Earth's terrestrial ecosystems are profoundly influenced by how often (frequency) and how long (duration) they are inundated with water. A diverse array of natural and human-engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans extreme events to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human-engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks and approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting changes in VIE function in response to global change. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth's VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via unifying conceptual models in which the impacts of variable inundation are studied across multi-dimensional environmental space.

  PublisherOA PDFDOI

• The Role of Fuh's Parameter in Predicting Global Water Budget Deficits and Runoff Ratio Sensitivity

  2024-07-11

  preprintOpen access

  As patterns of precipitation and evapotranspiration change, human water security and aquatic ecosystem health depend on understanding how catchment characteristics interact with climate to control river flow and water budget imbalances. We compiled estimates of precipitation, actual and potential evapotranspiration, temperature, and river discharge for over 1,148 catchments during the 2001-2020 period and used these estimates to calculate water budget imbalances as well as changes in runoff ratio and numerous river flow properties including timing, magnitude, and variability of flow. We found that that the parameter from Fuh’s equation (m) was a powerful predictor of hydrologic sensitivity to climate fluctuations, but not necessarily the magnitude of these changes. Specifically, water budget imbalances were almost entirely explained by two catchment properties: m and aridity. Runoff ratio sensitivity to temporal fluctuations in wetness index were also best explained by m, compared to a host of other catchment characteristics tested. In contrast to its predictive power for sensitivity, m was a poor predictor of total changes in runoff ratio. A subsequent correlational analysis between changes in runoff ratio and 66 geographic, climatic, land use, and human impact metrics, found that fluctuations in climate were a far more powerful predictor of changes in runoff ratio (and a suite of other flow properties) than m, indicating that at the global scale, the magnitude of changes in climate dominate the idiosyncratic catchment-level responsiveness to changes in climate, emphasizing the paramount importance of addressing climate change in protecting freshwater resources.

  PublisherDOI

• Global patterns of allochthony in stream–riparian meta‐ecosystems

  Ecology Letters · 2024-03-01 · 20 citations

  articleOpen access1st authorCorresponding

  Ecosystems that are coupled by reciprocal flows of energy and nutrient subsidies can be viewed as a single "meta-ecosystem." Despite these connections, the reciprocal flow of subsidies is greatly asymmetrical and seasonally pulsed. Here, we synthesize existing literature on stream-riparian meta-ecosystems to quantify global patterns of the amount of subsidy consumption by organisms, known as "allochthony." These resource flows are important since they can comprise a large portion of consumer diets, but can be disrupted by human modification of streams and riparian zones. Despite asymmetrical subsidy flows, we found stream and riparian consumer allochthony to be equivalent. Although both fish and stream invertebrates rely on seasonally pulsed allochthonous resources, we find allochthony varies seasonally only for fish, being nearly three times greater during the summer and fall than during the winter and spring. We also find that consumer allochthony varies with feeding traits for aquatic invertebrates, fish, and terrestrial arthropods, but not for terrestrial vertebrates. Finally, we find that allochthony varies by climate for aquatic invertebrates, being nearly twice as great in arid climates than in tropical climates, but not for fish. These findings are critical to understanding the consequences of global change, as ecosystem connections are being increasingly disrupted.

  PublisherOA PDFDOI

• Asynchronous movement patterns between breeding and stopover locations in a long-distance migratory songbird

  Avian Conservation and Ecology · 2024-01-01 · 2 citations

  articleOpen access

  The species-specific migratory patterns and strategies of many songbirds remain unknown or understudied, as research in animal ecology is biased toward the breeding period, with the fewest studies on the migratory period across taxa. Identifying large-scale spatiotemporal migratory patterns is challenging, as individuals within a species may vary in their migratory behavior and strategies. The Yellow Warbler (<em>Setophaga petechia</em>) is a Nearctic-Neotropical migrant that is relatively well studied during the breeding season, but its species-wide migratory patterns remain understudied. Our aim in studying Yellow Warbler movement ecology was to characterize temporal migration patterns during fall migration. We sought to determine the temporal migration pattern among breeding locations, as determined by the hydrogen stable isotope values in feather samples collected at disjunct (~2000 km) stopover sites in the Gulf of Maine (n = 50) and the Gulf of Mexico (n = 150). We used a similarity matrix to group individuals into a geographic cluster by breeding location, which was then used as the response variable in a modeling analysis. Our results provide evidence that Yellow Warblers exhibit an asynchronous, type 1 temporal migration pattern with southern breeding populations initiating migration prior to northern populations. Using hydrogen isotopes, we identified the temporal migration patterns between geographic clusters, representing an individual’s breeding location, and stopover sites along the Gulf of Maine and Gulf of Mexico, which fills a gap in understanding Yellow Warbler migration ecology.

  PublisherOA PDFDOI

• Biogeochemical and community ecology responses to the wetting of non-perennial streams

  Nature Water · 2024-09-19 · 16 citations

  articleOpen access
  PublisherOA PDFDOI

• Author response for "Global patterns of allochthony in stream–riparian meta‐ecosystems"

  2024-01-16

  peer-review1st authorCorresponding
  PublisherDOI

• Human activities shape global patterns of decomposition rates in rivers

  Science · 2024-05-30 · 31 citations

  articleOpen access

  Rivers and streams contribute to global carbon cycling by decomposing immense quantities of terrestrial plant matter. However, decomposition rates are highly variable and large-scale patterns and drivers of this process remain poorly understood. Using a cellulose-based assay to reflect the primary constituent of plant detritus, we generated a predictive model (81% variance explained) for cellulose decomposition rates across 514 globally distributed streams. A large number of variables were important for predicting decomposition, highlighting the complexity of this process at the global scale. Predicted cellulose decomposition rates, when combined with genus-level litter quality attributes, explain published leaf litter decomposition rates with high accuracy (70% variance explained). Our global map provides estimates of rates across vast understudied areas of Earth and reveals rapid decomposition across continental-scale areas dominated by human activities.

  PublisherOA PDFDOI

Recent grants

• RCN: Intermittent River Research Coordination Network (IRRCN): Integrating Intermittent River Ecology and Hydrology

  NSF · $500k · 2018–2021

• Collaborative Proposal: MSB-FRA: Scaling Climate, Connectivity, and Communities in Streams

  NSF · $937k · 2022–2024

• NSF Postdoctoral Fellowship in Biology for FY 2011

  NSF · $119k · 2012–2014

• Collaborative Proposal: MSB-FRA: Scaling Climate, Connectivity, and Communities in Streams

  NSF · $1.4M · 2019–2022

• RCN: Intermittent River Research Coordination Network (IRRCN): Integrating Intermittent River Ecology and Hydrology

  NSF · $327k · 2021–2024

Frequent coauthors

• Caryn C. Vaughn

  Oklahoma Biological Survey

  39 shared

• Darin Kopp

  University of Oklahoma

  34 shared

• Thibault Datry

  Universidade Federal do Ceará

  26 shared

• Flavia Tromboni

  University of Koblenz and Landau

  26 shared

• Arial J. Shogren

  University of Alabama

  25 shared

• Lillian McGill

  University of Washington

  20 shared

• Aimee H Fulerton

  NOAA National Marine Fisheries Service

  20 shared

• Ryan M. Burrows

  University of Melbourne

  19 shared

Labs

• THE ALLEN LAB at The Pennsylvania State UniversityPI

Education

• Ph.D., Ecology

  University of California, Davis

  2007

• M.S., Ecology

  University of California, Davis

  2002

• B.S., Biology

  University of California, Davis

  1999