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Growth and ecological impacts of an invasive bryophyte in Hawaii: the strange tale of Sphagnum palustre
David Beilman1, Stephanie Joe1 ,2, Schubert Olivia1, Margaret McCain1
1
University of Hawaii at Manoa, Honolulu, HI, USA, 2Oahu Army Natural Resources Program, Honolulu, HI, USA
Sphagnum palustre was transplanted from the wet rainforests of the Kohala Mountains of Hawaii Island to Mt.
Kaala on the island of Oahu where it has since been an aggressive invader. Growth-in-length during 2011-2013
on Kaala was more rapid during the dry season and was equal to about 4 cm per year, which was about 25%
faster than at a site in its native range on Hawaii Island. Estimated Net Primary Production, however, was similar
in both populations. Measurements of radiocarbon in accumulated biomass showed that a 39-cm-thick deposit
and 4.728 kg m-2 of Sphagnum litter has accumulated over the last 14 years at a central location on Kaala. Over
this same time, about 17cm and 7.237 kg m-2 accumulated at a site in the Kohala mountains. Soil respiration
measured using soil collars and dark chambers during six site visits revealed that Sphagnum-invaded areas of
Kaala had depressed rates of CO2 emission relative to native soil despite the addition of significant amounts of
dead Sphagnum biomass. Soils with invasive Sphagnum were observed to be modest sources of CH4, particularly
during the dry season, whereas native soils on Kaala were modest methane sinks, revealing a switch in
ecosystem function with invasion. Climate-mediated differences in plant growth and phenotype seem to be
promoting the spread and ecosystem impact of this invasive bryophyte on a Hawaiian mountain.
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Pleistocene sea-level changes as a predictor for insular species richness?
Kenneth Rijsdijk1, Sietze Norder1, Rudy Otto2, Brent Emerson3, Emiel Van Loon1, Ben Warren4, Even Tjørve5,
Sergio Ávila9, Kostas Triantis6, Robert Whittaker7, Christophe Thébaud8, Tommy Hengl10, Vincent Florens11,
Justin Gerlach12, Henry Hooghiemstra1, Erik De Boer1, Claudia Baider11, Gerard Oostermeijer1, Menno
Schilthuizen13, José María Fernández-Palácios2, Owen Griffiths
1
Institute for Biodiversity and Ecosystem Dynamics & Institute for Interdisciplinary Studies, University of
Amsterdam, Amsterdam, The Netherlands, 2Instituto Universitario de Enfermedades Tropicales y Salud Pública.
de Canarias (IUETSPC), Universidad de La Laguna, Lalaguna, Spain, 3Island Ecology and Evolution Research
Group, IPNA-CSIC, Lalaguna, Spain, 4Institut für Systematische Botanik, Universität Zürich, Zürich, Switzerland,
5
Lillehammer University College, Lillehammer, Norway, 6National and Kapodistrian University of Athens, Athens,
Greece, 7Biodiversity, Ecosystems and Conservation research cluster, Biodiversity institute, School of Geography
and the environment, Oxford, UK, 8Laboratoire Evolution et Diversite Biologique, UMR 5174 (UPS, CNRS, ENFA),
Toulouse, France, 9Faculdade de Ciências da Universidade do Porto and CIBIO, Centro de Investigação em
Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Pólo dos Açores and Departamento de
Biologia, Univ, Açores, Portugal, 10ISRIC – World Soil Information, Wageningen, The Netherlands, 11Biosciences
at Faculty of Science, University of Mauritius, Mauritius, Mauritius, 12University Museum of Zoology, Cambridge,
UK, 13NCB Naturalis, Leiden, The Netherlands, 14La Vanille Crocodile Park Farms, La Vanille, Mauritius
Pleistocene sea level change significantly altered surface areas and degree of isolation of oceanic islands. Sea
level falls during glacial periods led to increase of surface areas, emergence of guyots and a between islands
within archipelagos was well as the distance to nearby continents, whereas interglacial sea level rises led to
opposite effects. We test the hypothesis that the dynamics of such changes explains at least partly present day
species richness. To this end we modelled the effect of sea level change for one glacial-interglacial cycle and
derived unique metrics for each of 68 islands that describe maximum palaeo-area (pA), surface-area change(AC),
maximum palaeo-distance and distance change. We then used these metrics along with present area, present
distance, present altitude and island age as predictors for present-day gastropod richness in linear mixed models.
We found when including continental oceanic islands (Seychelles) in our data set that pA and AC are significant
predictors for species richness for nearly all chorological classes. When excluding the Seychelles we found pA
remains the only significant predictor for endemic richness. In addition we found for the Canarian islands that
islands that were formerly merged share significantly more species and multiple endemics than islands that had
remained separated. We conclude that changes in the configuration f islands and archipelagos through time likely
play a key role in determining current species richness through its influence on the ecological and evolutionary
processes underlying community dynamics.
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