摘要:

Mainly on the basis of the distribution patterns of 42 species of the recently revised genusCladopkora(Chlorophyceae) in the north Atlantic Ocean, it appeared possible to distinguish 10 phytogeographic distribution groups of wide applicability.Experimentally determined critical temperatures limiting essential events in the life histories of 17 benthic algal species were used to infer possible phytogeographic boundaries; these appeared to fit closely the phytogeographic boundaries derived from field‐distribution data. For a temperate species, at least six different boundaries can be postulated and should be checked in the northern hemisphere: (1) the ‘northern lethal boundary’ (corresponding to the lowest winter temperature which a species can survive); (2) the ‘northern growth boundary’ (corresponding to the lowest summer temperature which, over a period of several months, permits sufficient growth); (3) the ‘northern reproductive boundary’ (corresponding to the lowest summer temperature permitting reproduction over a period of several months); (4–6) the corresponding southern boundaries. Photoperiodic responses may influence the temperature responses.Many phytogeographic boundaries appear to be of a composite nature. For instance, the southern boundary ofLaminaria digitatafollows the European 10°C February isotherm (which corresponds to the highest winter temperature permitting fertility in the female gametophyte, i.e. to the ‘southern reproductive boundary’), and the American 19°C summer isotherm (corresponding to the ‘southern lethal boundary’).Thus, experimental evidence supports the validity of eight of the following 10 distribution groups (for distribution groups 2 and 6, such evidence could not be found): (1) the amphiatlantic tropical‐to‐warm temperate group, with a north‐eastern extension (examples:Gracilaria foliiferaandCentroceras clavulalum); (2) the amphiatlantic tropical‐to‐warm temperate group, with a north‐western extension (example:Hypnea musciformis); (3) the amphiatlantic tropical‐to‐temperate group (example:Sphacelaria rigidula =furcigera);(4) the amphiatlantic temperate group: theCladophora rupestristype (examples:Callithamnion hookeri, Dumontia contorta; Laminaria saccharinais transitional to type 10,I., digitatato types 5 and 10); (5) the amphiatlantic temperate group: theCl. albidatype (examples:Scytosiphon lomentaria, Petalonia fascia);(6) the tropical western Atlantic group; (7) the north‐east American tropical‐to‐temperate group (example:Gracilaria tikvahiae);(8) the north‐east American temperate group and the corresponding Japanese temperate group (examples:Campylaephora hypneoidesandSargassum muticum);(9) the warm‐temperate Mediterranean‐Atlantic group, and the corresponding warm‐temperate Californian group (examples:Saccorhiza polyschides, Laminaria hyperborea, I., ockroleuca, Macrocystis pyrifera, Hedophyllum sessile);(10) the Arctic group (examples:Saccorhiza dermatodeaandSphacelaria arctica).Distribution groups 6, 9 and 10 have comparatively narrow temperature ranges with a span of 18 22°C between their lethal boundaries and of 5 12°C between their reproductive or growth boundaries. These narrow temperature ranges limit the species in these groups to the tropics; the temperate coasts on the eastern sides of the north Pacific and north Atlantic Oceans and in the southern hemisphere; and to the Arctic, respectively. The narrow temperature ranges of group 9 make the species in this group unfit for life on the western temperate coasts of the north Pacific and north Atlantic Oceans, where algae must cope with annual temperature fluctuations of more than 20°C.Conversely, algae in group 8 (containing the numerous Japanese endemic species) are characterized by wide temperature spans (e.g. 29°C between ‘lethal boundaries’, 12–19°C between ‘growth and/or reproductive boundaries’) and must be potentially capable of occupying wide latitudinal belts on temperate coasts along the east sides of the north Pacific and north Atlantic Oceans. Algae ‘escaped’ from Japan, such asSargassum muticum, conform to this picture. Apparently Japanese algae do not have the capacity for long distance dispersal. The corresponding east American coasts (30–45 N) harbour very few endemic species, probably as a result of the adverse nature of these sediment coasts for benthic macroalgae and their functioning as a barrier to latitudinal displacements of the flora during glaciations.The remaining distribution groups (1,2,3,4,5,7) are characterized by wide temperature spans and wide distributions, often in both the Atlantic and Pacific Oceans and in both hemispheres.Six temperate species (in distribution groups 4, 5 and 9) with an amphiaequatorial distribution have similar winter‐temperature maxima permitting reproduction and corresponding with winter isotherms of 15–17°C; their upper lethal temperatures are more dissimilar and correspond with summer isotherms of 20–30°C. Their amphiaequatorial distribution can be explained by assuming glacial temperature drops along east Pacific and east Atlantic equatorial coasts in narrow belts of intensifie

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02035.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The three extant Divisions comprising the bryophytes extend, as fossils, well back into Palaeozoic time. Bryophyte origin is part of the rise of terrestrial, vascularized, plants with sporopollenin‐walled spores in the Silurian. Before the end of Carboniferous time, bryophyte lines were widely present. Separation of Gondwana and Laurasia by the Permian Tethys Sea and subsequent widespread desert episodes fragmented an already diversified bryoflora subjecting it to intense selective pressure. The cool, mesic climate of southern Gondwana provided a refugium for austral bryophytes. Warmer and drier climates of the Permo‐Triassic Laurentian‐Laurasia favoured drought‐adapted or niche‐specific groups creating marked systematic discontinuities. The Angaran wet, probably cool, temperate region provided refuge for basic stock for much of today's rich holarctic and wet ‘tropical’ bryofloras. Climatic changes, correlated with tectonic events and the rise of angiosperms, opened habitats favourable for a diversity explosion. Despite demonstrated potential for long‐distance dispersal, modern distributions are mostly linked with total floras or establishment on islands prior to niche saturation. Remnants of Gondwanan bryoflora persist in high southern latitudes as disjunctions with the possibility that the folded ranges of the African Cape have been an insular fragment at higher latitudes becoming attached shortly after angiosperm diversification. Floras of southern India and east Africa have common features but the Himalayan flora shows evidence that the Gondwanan flora of the Indian plate was lost during the movement through desert and tropical latitudes; neotropical and palaeotropical floras are distinctive. Much of the northern Australian bryoflora is recently Malesian‐derived while the southeast shows strong austral influence and commonality with New Zealand. Tropical Pacific island floras are mostly Malesian‐derived but with both holarctic and austral elements present as in Hawaii and the Society Islands. Holarctic bryoflora is circum‐polar with temperate areas of Euro‐American and far eastern elements floristically bound by disjunct and vicariad species. Kroeber Coefficients of Correlation differ as Pacific island floras are compared and Guttman‐Lingoes Smallest Space Coordinates indicates floristic subgroups within Polynesia. Although these and other mathematical treatments yield potentially promising results, the methods are yet unrefined and there is some uncertainty whether characteristics of numbers or of organisms are i

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1982.tb02036.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY