Poulsen John R.

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John R.

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Now showing 1 - 4 of 4
  • Article
    Employing plant functional groups to advance seed dispersal ecology and conservation
    (Oxford University Press, 2019-02-17) Aslan, Clare E. ; Beckman, Noelle G. ; Rogers, Haldre S. ; Bronstein, Judith L. ; Zurell, Damaris ; Hartig, Florian ; Shea, Katriona ; Pejchar, Liba ; Neubert, Michael G. ; Poulsen, John R. ; Hille Ris Lambers, Janneke ; Miriti, Maria ; Loiselle, Bette ; Effiom, Edu ; Zambrano, Jenny ; Schupp, Eugene W. ; Pufal, Gesine ; Johnson, Jeremy ; Bullock, James M. ; Brodie, Jedediah ; Bruna, Emilio ; Cantrell, Robert Stephen ; Decker, Robin ; Fricke, Evan ; Gurski, Katherine ; Hastings, Alan ; Kogan, Oleg ; Razafindratsima, Onja ; Sandor, Manette ; Schreiber, Sebastian ; Snell, Rebecca ; Strickland, Christopher ; Zhou, Ying
    Seed dispersal enables plants to reach hospitable germination sites and escape natural enemies. Understanding when and how much seed dispersal matters to plant fitness is critical for understanding plant population and community dynamics. At the same time, the complexity of factors that determine if a seed will be successfully dispersed and subsequently develop into a reproductive plant is daunting. Quantifying all factors that may influence seed dispersal effectiveness for any potential seed-vector relationship would require an unrealistically large amount of time, materials and financial resources. On the other hand, being able to make dispersal predictions is critical for predicting whether single species and entire ecosystems will be resilient to global change. Building on current frameworks, we here posit that seed dispersal ecology should adopt plant functional groups as analytical units to reduce this complexity to manageable levels. Functional groups can be used to distinguish, for their constituent species, whether it matters (i) if seeds are dispersed, (ii) into what context they are dispersed and (iii) what vectors disperse them. To avoid overgeneralization, we propose that the utility of these functional groups may be assessed by generating predictions based on the groups and then testing those predictions against species-specific data. We suggest that data collection and analysis can then be guided by robust functional group definitions. Generalizing across similar species in this way could help us to better understand the population and community dynamics of plants and tackle the complexity of seed dispersal as well as its disruption.
  • Article
    Inorganic carbon speciation and fluxes in the Congo River
    (John Wiley & Sons, 2013-02-14) Wang, Zhaohui Aleck ; Bienvenu, Dinga Jean ; Mann, Paul J. ; Hoering, Katherine A. ; Poulsen, John R. ; Spencer, Robert G. M. ; Holmes, Robert M.
    Seasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville-Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge-correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO2*, the sum of dissolved CO2 and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11–61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO2* and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO2 at a rate of ~109 mol m−2 yr−1. The basin-wide DIC yield was ~8.84 × 104 mol km−2 yr−1. The discharge normalized DIC flux to the ocean amounted to 3.11 × 1011 mol yr−1. The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers.
  • Article
    Advancing an interdisciplinary framework to study seed dispersal ecology
    (Oxford University Press, 2019-08-19) Beckman, Noelle G. ; Aslan, Clare E. ; Rogers, Haldre S. ; Kogan, Oleg ; Bronstein, Judith L. ; Bullock, James M. ; Hartig, Florian ; Hille Ris Lambers, Janneke ; Zhou, Ying ; Zurell, Damaris ; Brodie, Jedediah ; Bruna, Emilio ; Cantrell, Robert Stephen ; Decker, Robin ; Effiom, Edu ; Fricke, Evan ; Gurski, Katherine ; Hastings, Alan ; Johnson, Jeremy ; Loiselle, Bette ; Miriti, Maria ; Neubert, Michael G. ; Pejchar, Liba ; Poulsen, John R. ; Pufal, Gesine ; Razafindratsima, Onja ; Sandor, Manette ; Shea, Katriona ; Schreiber, Sebastian ; Schupp, Eugene W. ; Snell, Rebecca ; Strickland, Christopher ; Zambrano, Jenny
    Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant’s life history and environmental variability that ultimately influences a population’s ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity.
  • Article
    The biogeochemistry of carbon across a gradient of streams and rivers within the Congo Basin
    (John Wiley & Sons, 2014-04-30) Mann, Paul J. ; Spencer, Robert G. M. ; Dinga, Bienvenu J. ; Poulsen, John R. ; Hernes, P. J. ; Fiske, Gregory J. ; Salter, M. E. ; Wang, Zhaohui Aleck ; Hoering, Katherine A. ; Six, J. ; Holmes, Robert M.
    Dissolved organic carbon (DOC) and inorganic carbon (DIC, pCO2), lignin biomarkers, and theoptical properties of dissolved organic matter (DOM) were measured in a gradient of streams and rivers within the Congo Basin, with the aim of examining how vegetation cover and hydrology influences the composition and concentration of fluvial carbon (C). Three sampling campaigns (February 2010, November 2010, and August 2011) spanning 56 sites are compared by subbasin watershed land cover type (savannah, tropical forest, and swamp) and hydrologic regime (high, intermediate, and low). Land cover properties predominately controlled the amount and quality of DOC, chromophoric DOM (CDOM) and lignin phenol concentrations (∑8) exported in streams and rivers throughout the Congo Basin. Higher DIC concentrations and changing DOM composition (lower molecular weight, less aromatic C) during periods of low hydrologic flow indicated shifting rapid overland supply pathways in wet conditions to deeper groundwater inputs during drier periods. Lower DOC concentrations in forest and swamp subbasins were apparent with increasing catchment area, indicating enhanced DOC loss with extended water residence time. Surface water pCO2 in savannah and tropical forest catchments ranged between 2,600 and 11,922 µatm, with swamp regions exhibiting extremely high pCO2 (10,598–15,802 µatm), highlighting their potential as significant pathways for water-air efflux. Our data suggest that the quantity and quality of DOM exported to streams and rivers are largely driven by terrestrial ecosystem structure and that anthropogenic land use or climate change may impact fluvial C composition and reactivity, with ramifications for regional C budgets and future climate scenarios.