title: Distribution drivers and physiological responses in geothermal bryophyte communities.
abstract: Our ability to explain community structure rests on our ability to define the importance of ecological niches, including realized ecological niches, in shaping communities, but few studies of plant distributions have combined predictive models with physiological measures.
  
  
  
  Using field surveys and statistical modeling, we predicted distribution drivers in geothermal bryophyte (moss) communities of Lassen Volcanic National Park (California, USA). In the laboratory, we used drying and rewetting experiments to test whether the strong species-specific effects of relative humidity on distributions predicted by the models were correlated with physiological characters.
  
  
  
  We found that the three most common bryophytes in geothermal communities were significantly affected by three distinct distribution drivers: temperature, light, and relative humidity. Aulacomnium palustre, whose distribution is significantly affected by relative humidity according to our model, and which occurs in high-humidity sites, showed extreme signs of stress after drying and never recovered optimal values of PSII efficiency after rewetting. Campylopus introflexus, whose distribution is not affected by humidity according to our model, was able to maintain optimal values of PSII efficiency for 48 hr at 50% water loss and recovered optimal values of PSII efficiency after rewetting.
  
  
  
  Our results suggest that species-specific environmental stressors tightly constrain the ecological niches of geothermal bryophytes. Tests of tolerance to drying in two bryophyte species corresponded with model predictions of the comparative importance of relative humidity as distribution drivers for these species.
authors.affiliation: Portland State University, Center for Life in Extreme Environments and Department of Biology, P.O. Box 751, Portland, Oregon 97207-0751, USA.
authors.forename: Estefanía Llaneza
authors.initials: EL
authors.lastname: García
authors.affiliation: Portland State University, Center for Life in Extreme Environments and Department of Biology, P.O. Box 751, Portland, Oregon 97207-0751, USA.
authors.forename: Todd N
authors.initials: TN
authors.lastname: Rosenstiel
authors.affiliation: Portland State University, Center for Life in Extreme Environments and Department of Biology, P.O. Box 751, Portland, Oregon 97207-0751, USA.
authors.forename: Camille
authors.initials: C
authors.lastname: Graves
authors.affiliation: Portland State University, Center for Life in Extreme Environments and Department of Biology, P.O. Box 751, Portland, Oregon 97207-0751, USA.
authors.forename: Erin E
authors.initials: EE
authors.lastname: Shortlidge
authors.affiliation: Portland State University, Center for Life in Extreme Environments and Department of Biology, P.O. Box 751, Portland, Oregon 97207-0751, USA eppley@pdx.edu.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Eppley
mesh_terms: D044002:Bryophyta / Q000502:physiology* / Q000528:radiation effects; D002940:Circadian Rhythm / Q000502:physiology; D003890:Desiccation; D005453:Fluorescence; D059207:Geothermal Energy; D006813:Humidity; D008027:Light; D012044:Regression Analysis; D013045:Species Specificity; D013696:Temperature
keywords: GIS; bryophyte; desiccation; physiological ecology; plant; temperature