Role of aspect in terrestrial and intertidal distributional patterns, and ecological processes
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Understanding better the impact of climate and changing environmental conditions on species and ecosystems has become one of the pressing research priorities. In addition, a need for more realistic field-based climate change experiments and focus on community and ecosystem functioning has grown in the last decade. The main aim of this PhD work was to study the effect of mainly temperature variation on species and ecosystems, by studying small-scale aspect (slope orientation) on both intertidal gullies and hedgerows/road verges in SW England. Such paralleled studies between terrestrial and marine ecosystem are sparse. I especially investigated (1) abiotic variations, (2) species distribution and richness, (3) species physiology (osmotic regulation) and phenology (gonad development), (4) leaf-litter decomposition as a key ecological process, and (5) comparison of conspecific species with different biogeographic origins, all between north- and south-facing aspects in both ecosystems. In both the intertidal and terrestrial ecosystems, south-facing slopes were much warmer (annual mean) and experienced more hot extreme events (more intense and frequent) than the opposite north-facing slopes; which corrobotate some future predictions by the IPCC. In addition, south-facing terrestrial slopes were significantly drier than the north-facing ones. Abundance and richness was greater on cooler north- than south-facing aspect on the rocky shore at all studied levels of organisation. Osmotic regulation did not seem to explain distributional change between two closely related limpet species, suggesting that other ecosphysiological or behavioural thermoregulation are factors involved. There was no variation with aspect in soil mesofauna, little variation in decomposition process, while greater differences were detected in terrestrial plants at most levels of organisation, except at the community level. This work showed that intertidal gullies and road verges are good systems to study the impact of temperature variations on ecosystem patterns and processes, and that aspect seem to buffer temperature extremes, offering refugia for cold-adapted and moist-tolerant species on the cooler and moister habitats (e.g. north-facing aspect). Aspect influenced species distribution at different levels (community, taxonomic, functional, species, and biogeographic origins), and differences between north- and south-facing aspects were more marked, however, on the intertidal than on land. In the future, slope aspect could be at interest for the conservation and management sector as a way to locally buffer global warming.
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