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Isolated Stands (isolated + stand)
Selected AbstractsLimited Reintroduction Does Not Always Lead to Rapid Loss of Genetic Diversity: An Example from the American Chestnut (Castanea dentata; Fagaceae)RESTORATION ECOLOGY, Issue 3 2007Sarah A. M. Pierson Abstract In restoring species, reasons for introducing limited numbers of individuals at different locations include costs of introduction and maintenance, limited founder supply, and risk "bet hedging." However, populations initiated from few founders may experience increased genetic drift, inbreeding, and diversity loss. We examined the genetic diversity of an isolated stand of more than 5,000 American chestnut trees relative to that of the 9 surviving stand founders (out of 10 total) planted in the 1880s. We used minisatellite DNA probes to reveal 84 genetic markers (circa 24 loci) among the nine founders, and their genetic diversity was compared with three separate plots of descendant trees, as well as with two natural stands. The descendants were circa 7.3% more heterozygous than the founders (mean estimated H= 0.556 vs. 0.518, respectively; p < 0.0001). Genetic differentiation was not pronounced (FST < 0.031), and no markers, including those at low frequency among the founders, were lost in the descendants. The founders and natural transects were not significantly different in H or similarity (mean proportion of bands shared). Special planting or mating protocols for establishment of a vigorous American chestnut population from a low number of founders may not be required to avoid strong effects of genetic drift and inbreeding. These results demonstrate that loss of genetic diversity following reintroduction of a limited number of founders is not always inevitable, such as this case where the species is highly outcrossing, expression of heterozygous advantage may occur, the original founders remain as gene contributors over generations, and the establishing population expands constantly and rapidly. [source] Welche Bedeutung hat die sexuelle Reproduktion für den Erfolg der Art Calamagrostis epigejos (L.) Roth?FEDDES REPERTORIUM, Issue 3-4 2003A. Grüttner Dr. Als Quellen der Variabilität im Potential der sexuellen Reproduktion fanden sich Unterschiede in der Keimungsgeschwindigkeit (entspelzte Karyopsen keimten rascher und synchroner), bei den Keimraten und vor allem bei der Zahl keimfähiger Diasporen pro Rispe. Von den anderen abweichend zeigten kleine isolierte Bestände geringere Keimraten und brachten , wohl bedingt durch Selbstinkompatibilität , kaum keimfähige Diasporen hervor. Bei gezielter Suche fanden sich Keimlinge auf offenen, zumindest leicht tonhaltigen Rohböden. Das Wachstum der Keimlinge stagnierte und keiner von über 6000 überlebte bis zum nächsten Jahr. Da Bewässerung die Entwicklung auf dem selben Substrat sehr förderte, war offenbar Wassermangel für das geringe Wachstum ausschlaggebend. Die erfolgreiche generative Etablierung ist also auf den Zufall günstiger Witterungsphasen oder Standorte angewiesen. Auch im Frühjahr waren noch keimfähige Diasporen in aufrechten Rispen nachweisbar, sodass sich der Diasporenfall mehr oder weniger über das gesamte Jahr erstreckt. Im Zusammenspiel mit dem Fehlen von Dormanz ermöglicht das die Nutzung nicht vorhersagbarer günstiger Witterungsphasen. Bei einem Kulturversuch kamen einzelne Individuen auch mit schwierigen Substraten gut zurecht, auf denen die Mehrzahl kümmerte. Danach ergibt sich die standörtliche Breite der Art C.,epigejos als Summe sehr unterschiedlicher Reaktionsnormen der Individuen. Die angeführten Befunde unterstreichen insgesamt die Bedeutung der sexuellen Reproduktion und der genetischen Diversität für den Erfolg der Art. Is sexual reproduction important to the success of Calamagrostis epigejos (L.) Roth? Calamagrostis epigejos is very common in Central Europe and occupies an extraordinary wide range of habitats. As up to now nearly no reports exist on spontaneous seedling emergence, we aimed to investigate several aspects of sexual reproduction, thereby refering to contrasting habitat types. Components in the variability of the potential of sexual reproduction were differences in germination speed and rates and, above all, number of germinable seeds per panicle. Unlike the others, small isolated stands produced very low numbers of germinable seeds, probably caused by selfincompatibility. Our search for seedlings was successful at several sites , all distinguished by raw soil, a certain clay content, and little cover of vegetation and plant litter. The seedlings grew very slowly and none of more than 6000 survived the first year. Additional water enabling much better growth indicates the necessity of favorable weather or favorable habitats (with constant water supply) for successful seedling establishment. Seed dispersal nearly all around the year, combined with the lack of dormancy, allows to make use of the unpredictable opportunities of suitable weather periods. A growth experiment on different substrates demonstrated: the more extreme the conditions, the more differentiated the amount of biomass achieved by each of 20 genets. Some genets grew well even on substrates where most others stagnated. This outcome suggests the wide range of habitats covered by C. epigejos to be the result of the genetic diversity, which in turn is maintained by sexual reproduction and avoidance of inbreeding. [source] Ancestry and divergence of subtropical montane forest isolates: molecular biogeography of the genus Abies (Pinaceae) in southern México and GuatemalaMOLECULAR ECOLOGY, Issue 10 2008JUAN P. JARAMILLO-CORREA Abstract The genus Abies has a complex history in southern México and Guatemala. In this region, four closely related species, Abies flinckii, A. guatemalensis, A. hickelii, and A. religiosa, are distributed in fragmented and isolated montane populations. Range-wide genetic variation was investigated across species using cytoplasmic DNA markers with contrasted inheritance. Variation at two maternally inherited mitochondrial DNA markers was low. All species shared two of the nine mitotypes detected, while the remaining seven mitochondrial DNA types were restricted to a few isolated stands. Mitochondrial genetic differentiation across taxa was high (GST = 0.933), it was not related to the taxonomic identity (amova; P > 0.05) of the populations, and it was not phylogeographically structured (GST , NST). In contrast, variation at three paternally inherited chloroplast DNA microsatellites was high. Chloroplast genetic differentiation was lower (GST = 0.402; RST = 0.547) than for mitochondrial DNA, but it was significantly related to taxonomy (amova; P < 0.001), and exhibited a significant phylogeographical structure (GST < RST). Different analyses of population structure indicated that A. flinckii was the most divergent taxon, while the remaining three species formed a relatively homogeneous group. However, a small number of the populations of these three taxa, all located at the limits of their respective ranges or in the Transverse Volcanic Belt, diverged from this main cluster. These trends suggest that the Mesoamerican Abies share a recent common ancestor and that their divergence and speciation is mainly driven by genetic drift and isolation during the warm interglacial periods. [source] Spatial and temporal variation in the fruiting phenology of palms in isolated standsPLANT SPECIES BIOLOGY, Issue 1 2008GREGORY H. ADLER Abstract Fruiting phenologies of two species of palms, Astrocaryum standleyanum L. H. Bailey and Attalea butyracea (Mutis ex L. f) Wess. Boer, isolated on eight small (1.7,3.7 ha) forested islands in the Panama Canal were studied over a 33-month period. Individual palms were permanently marked with numbered aluminum tags and censused each month for the presence of ripe fruits. The dataset consisted of 1106 monthly observations of palms with ripe fruits among the 634 marked individuals. Mean densities of palms of reproductive size varied widely among islands, ranging from a low of 0.3 ha,1 for A. standleyanum and 3.5 ha,1 for A. butyracea to a high of 44.9 ha,1 for A. standleyanum and 33.7 ha,1 for A. butyracea. Both species showed distinctly seasonal periods of fruiting activity that varied in duration between the two species and among years. The timing of fruiting by A. standleyanum was highly synchronous among islands, whereas inter-island synchrony in A. butyracea was less pronounced. The percentages of marked individuals that fruited varied widely among islands and years. Results indicated that these palms responded to both spatially and temporally variable conditions that promoted fruit production. We suggest that pollinator abundances are a crucial factor affecting reproductive output. Conditions that favor successful reproduction and seed dispersal, such as pollinator activity and the attraction of dispersal agents, may be the ultimate factors that have influenced the reproductive phenologies of these two species of palms. [source] Impacts of Restored Patch Density and Distance from Natural Forests on Colonization SuccessRESTORATION ECOLOGY, Issue 4 2003Hans Jacquemyn Abstract The reduction and fragmentation of forest habitats is expected to have profound effects on plant species diversity as a consequence of the decreased area and increased isolation of the remnant patches. To stop the ongoing process of forest fragmentation, much attention has been given recently to the restoration of forest habitat. The present study investigates restoration possibilities of recently established patches with respect to their geographical isolation. Because seed dispersal events over 100 m are considered to be of long distance, a threshold value of 100 m between recent and old woodland was chosen to define isolation. Total species richness, individual patch species richness, frequency distributions in species occurrences, and patch occupancy patterns of individual species were significantly different among isolated and nonisolated stands. In the short term no high species richness is to be expected in isolated stands. Establishing new forests adjacent to existing woodland ensures higher survival probabilities of existing populations. In the long term, however, the importance of long-distance seed dispersal should not be underestimated because most species showed occasional long-distance seed dispersal. A clear distinction should be made between populations colonizing adjacent patches and patches isolated from old woodland. The colonization of isolated stands may have important effects on the dynamics and diversity of forest networks, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stands. [source] Conservation genetics of endangered flying squirrels (Glaucomys) from the Appalachian mountains of eastern North AmericaANIMAL CONSERVATION, Issue 2 2005Brian S. Arbogast We assessed the genetic status of two endangered subspecies of the northern flying squirrel (Glaucomys sabrinus) that are restricted to isolated stands of high elevation spruce-fir and adjacent spruce-fir-hardwood ecotonal habitat in the Appalachian Mountains of eastern North America. We used mitochondrial DNA (mtDNA) and allozyme data to estimate levels of genetic variability in the two subspecies of interest and then evaluated this information in the context of large-scale phylogeographical structure and overall genetic variability for the entire species and for the closely related and partially sympatric southern flying squirrel (Glaucomys volans). This broader analysis involves much of North America's northern coniferous forest biome, together with the deciduous forest biome of eastern North America. Our results support the evolutionary distinctness of the endangered Appalachian populations of G. sabrinus. These populations possess several private alleles and have levels of genetic variability that are substantially lower than those observed in conspecific populations found elsewhere. However, the endangered Appalachian populations of G. sabrinus have higher levels of genetic variability than those observed in populations of G. volans from across eastern North America. These results highlight the utility of evaluating the conservation genetics of small and isolated populations within a broad-scale comparative evolutionary and biogeographical framework. [source] | ||||||||||