Concepts Of Biogeography Research Articles

Paleoclimatic relicts and climatic disjunctions in the Flora of Northern Portugal

Climate is generally considered the main factor determining the global distribution of plant and animal species.
 Climate changes, depending on their rapidity and intensity, can give rise to events of (local, regionalor global) extinction, redistribution of flora and fauna, population genetic divergence, ecotype differentiation or even speciation. That is, climate changes reflect on both ecosystem structure and function, as well as on spatial organisation of the borders between biogeographic units, and eventually also on the genesis of both ecosystems and biogeographic units itsel.
 Specific physical conditions working at a local scale (microclimate), such as rocky cliffs, watercourses or special types of rock, can enable the persistence of species in territories where the macroclimate is no longer appropriate for their occurrence. There are also those species whose taxonomic independence occurred under climate conditions which were very different from the current ones, and then became adapted to the plant communities developing under the new climate. If these species are common extant taxa elsewhere, they are called climatic disjunctions, but if their distribution is nowadays very restricted, they are known as climatic relicts.
 A related concept is the one of "biogeographic relict". Traditionally, a biogeographic relict is anendemic taxon, with limited distribution range, descending of another taxon that was once widely distributed. Like many other concepts in Biogeography and Ecology, the concept of biogeographic relict depends on both space and time scales. Also, taxonomic entities of lower rank (the species and infra-specific ranks) are no more than useful abstractions, often very hard to relate to genetic distances. Therefore, we think it is possible to extend the concept of"relict" to the population level, at different biogeographic dimensions and time scales, as long as it is possible to relate current distribution patterns of those populations with specific palaeoclimatic periods and events. Within this wide concept of "relict", isolated populations of plants which are common in other biogeographic territories are here interpreted as climatic disjunctions. On the other hand, in order to keep the "taxon biogeographic relict" concept, we think it is more appropriate, on a small spatial scale, to speak of relict populations of a given taxon, or then, of territorial (local) relict, as long as thc specific biogeographic scale is referred.
 Their specific survival conditions, the potential uniqueness of their genetic information, and the biogeographic significance of the plant communities they live in, give climatic relicts and disjunctians a remarkable conservation value. They are also precious sources of information concerning past climates.
 ln this paper, we present a preliminary list of palaeoclimatic relicts and climatic disjunctions of the Northern Portugal flora. We recognise three main types of relicts occurring in the territory: I)Palaeoclimatic relicts (xerophytic and mesophytic subtypes); 2) Würmian temperate climatic disjunctions; and 3) Pre-würmian mediterranean climatic disjunctions. ln this first approach, we only listed those taxa whose isolated populations are clearly related to specific palaeoclimatic periods and events. For each taxon, we present information on ecology and distribution in Portugal. We also address the conservation status of these relict populations and discuss future perspectives for their long-term preservation in the territory.

Changing Concepts in Biogeography

The continuing goal of biogeography is to explain the structure, function, and history of animals and plants in relation to their geographic ranges and to correlate these results with phylogenetic systems. Because of their num­ bers, insects represent a significant part of biogeography. However, our much greater knowledge of vertebrates until recently has resulted in an inordinate emphasis on birds and mammals. Insect biogeography, however, has been carefully surveyed in the Annual Review of Entomology in articles by Gressitt (10), Munroe (32), and again Gressitt (11), reviewing the litera­ ture up to 1972. This review is not organized along the lines of others cited above, nor does it claim to be complete in covering the expanding field of either general or regional publications on biogeography of insects. Such restraint must be exercised in view of the ever increasing number of relevant publications, which is evident from the tremendous growth of the Zoological Record during the last decade. In addition, however, there is a growing conviction that much basic work of alpha and beta taxonomy (26) has to be done or redone for most groups of insects, and that many statements and theories, hitherto undisputed, now seem preliminary and premature. The following survey, therefore, is limited to the presentation of some impressively chang­ ing concepts of biogeography and to acknowledging the altered situation of entomology in the last decade.