Browsing by Author "Ah-Peng, Claudine"

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    Bryophytes in the hydrological cycle and climate change implications : A case study of La Réunion cloud forest
    (2012) Cardoso, Anabelle Williamson; Hedderson, Terry A; Ah-Peng, Claudine; Flores, Olivier; West, Adam
    Bryophytes are able to intercept atmospheric water over the entire surface of their shoot and, once intercepted, this water forms a vital part of the hydrological cycle of their surrounding ecosystems. To investigate the role of bryophytes in the hydrological cycle, our study, conducted in the biodiversity hotspot of the tropical montane cloud forest of La Réunion, focused on two leafy liverwort species, Mastigophora diclados and Bazzania decrescens. We evaluated liverwort biomass, water storage capacity, atmospheric or cloud water interception, and photosynthetic response to desiccation. We found that B. decrescens stored approximately double the mean and maximum litres of water per hectare despite occupying less than half the volume of M. diclados. Despite this decreased water storage capacity, we found that M. diclados had a greater ability to intercept atmospheric moisture than B. decrescens, which had similar interception ability to the control. These interception abilities affected water flux in the two liverwort species. We found that this variation in water flux had an effect on photosynthesis. Both species displayed a significant relationship between photosynthesis and water content. We found that both species showed a loss of photosynthesis at very low and very high water contents with the optimal water content for photosynthesis corresponding to the in situ water content of the liverworts. The abundance of both species and their cloud water interception ability together with the wide range of photosynthetic tolerance of M. diclados and the large water storage capacity and slow desiccation rate of B. decrescens make both liverwort species ecologically important in the forest's hydrological cycle. Anthropogenic climate change threatens this ecosystem as the cloud that these species are so dependent on is predicted to lift. Our findings tie the liverworts very closely to their environment and therefore show support for the idea that bryophytes are excellent early warning signals for predicted climate changes.
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    Climatic specialisation: an explanation for the range size and distribution of bryophytes on a tropical island elevational gradient
    (2020) Figenschou, Laura Kristina; Hedderson,Terry Albert; West, Adam; Ah-Peng, Claudine
    Are species physiologically specialised to the specific climatic conditions in their habitats and can this explain their distributions? This thesis addresses this question using a very specific system: bryophytes on the elevational gradient of Piton des Neiges, Réunion Island. Bryophytes are expected to be specialised to fairly narrow conditions of drought, temperature and insolation, which restrict their geographic range. However, little is known about the mechanisms that connect bryophytes with climatic factors. In this thesis I test the idea of ecophysiological specialisation using reciprocal transplant experiments, along with direct laboratory measurements of species' responses to desiccation and temperature. In these experiments I use species restricted to low, mid or high elevation, as well as widespread species found along most of the gradient. The transplant experiment revealed a trend of upslope survival of restricted species, with species from all sites performing best at their elevation of origin and the site above, and badly at lower elevations. Despite macroclimate being found as an important factor shaping bryophyte range size and distribution, the effect of microhabitat could not be ignored. This was especially true for the widespread species, which showed a strong effect of microhabitat placement in the transplant experiment. Desiccation tolerance was found to increase with elevation in range-restricted species, but widespread species showed little difference in their sensitivity to desiccation, regardless of elevation of origin. Range-restricted species from low elevation were more sensitive to low temperatures and had higher optimum temperatures for photosynthesis than mid- and high-elevation species. Widespread species had narrower ranges of temperature tolerances than range-restricted species, and did not differ in their response to temperature, regardless of elevation of origin. The results of these experiments corresponded well with the climatic conditions that these species habitually experience – with extremes at the gradient peripheries and intermediate conditions in between. This thesis showed that specialisation to both macro- and microclimatic conditions can be attributed as a main driver of bryophyte range size and distribution on the elevational gradient of Piton des Neiges, Réunion Island. This research adds to the body of knowledge on the physiological responses of tropical bryophytes, which is important for species' distribution modelling. Furthermore, it provides insight into the factors that shape bryophyte distribution, critical for biodiversity management under climate change scenarios.
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    Diversity and biogeography of Madagascan bryophytes with an analysis of taxic and functional diversity along an elevational gradient in Marojejy National Park
    (2018) Marline, Lovanomenjanahary; Hedderson, Terry A J; Ah-Peng, Claudine
    A central goal of ecology is to understand the influence of biodiversity on ecosystem functioning and the processes that determine the composition and diversity of biological assemblages. In this thesis, I investigate the regional and global context of the bryophytes of Madagascar, an ecologically important but poorly studied group, and the factors affecting epiphytic bryophyte diversity, distribution and assemblage of communities along an elevational gradient in Marojejy National Park, north-eastern Madagascar. Firstly, based on literature reviews and available herbarium data, I examined the bryophytes of Madagascar through a historical, floristic and phytogeographic synthesis. Secondly, the ecological survey of bryophytes from a range of diversity and functional perspectives provided insight on: (1) the pattern of species richness and range-size distribution of epiphytic bryophytes and the factors affecting the distribution patterns. (2) The variations in species composition between sites. I documented how the two components of beta-diversity (turnover and nestedness) are influenced by elevational variation. (3) The relationship between bryophyte species functional diversity and community assembly based on a morphological trait-based approach. I tested how bryophyte species functionally interact with their abiotic and biotic environments and how habitat filtering and niche differentiation influence bryophyte assemblages along an elevational gradient. The bryoflora of Madagascar, with its 1188 species and infraspecific taxa is relatively rich and highly diversified. Along the Marojejy elevational gradient, 254 epiphytic bryophytes species including 157 liverworts and 97 mosses were reported. Species richness distribution has a hump-shaped pattern along the elevational gradient, with a richness peaking at mid-elevation, 1250 m. My results suggest that middomain-effect was the most effective in predicting species richness, but environmental variables such as mean temperature, relative humidity, vapour deficit pressure and canopy height also play important roles in shaping richness pattern. Throughout the gradient, species dissimilarity due to replacement (species turnover) contribute the most to variation in species composition between sites. Both habitat filtering and niche differentiation were found to be involved in structuring species abundances within the studied communities. This combination of biogeographic, taxic, and community ecology approaches, is the first detailed study on the bryoflora of Madagascar and contributes to the direct application of bryological data to conservation planning for Madagascar’s unique ecosystems.
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    The diversity of ground bryophyte communities along an altitudinal gradient on La Réunion island
    (2011) Lane, Wade Howard; Hedderson, Terry A; Ah-Peng, Claudine; Slingsby, Jasper A
    Aim: To compare the α, β and phylogenetic diversity of the ground bryophyte communities along a tropical altitudinal gradient in order to determine which processes govern these assemblages. Location: La Réunion island (55°39'E; 21 °00'S), in the western Indian Ocean. Methods: The ground bryophyte communities were surveyed along the eastern slope of Piton des Neiges (350 - 3050 m). α, β and phylogenetic diversity along the altitudinal gradient was determined and graphically presented. Results: The α diversity had two distinct peaks at 1150 - 1350 m and at 2750 m, these corresponded to a dominance in liverwort and moss species, respectively. The phylogenetic diversity along the altitudinal gradient was far greater than is predicted from the null models suggesting that ground bryophyte communities are structured according to "environmental filters". The mid-domain effect and mass effect could not be used to describe the changing diversity along the altitudinal gradient, however a correlation analysis revealed temperature and relative humidity influences the changing a diversity. Main Conclusions: In conclusion both ecological and evolutionary processes structure the ground bryophyte communities.