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Genetic diversity in relation to secondary succession of forest tree communities

Wehenkel C., Corral-Rivas J., Hernandez-Diaz J.

Polish Journal of Ecology

2011

Vol. 59, nr 1

45-54

Forest succession is a fundamental ecological process, which has significant implications for the biological, biophysical, and biogeochemical processes in an ecosystem. Genetic diversity is not only a product of the number of species present in a given area, but also of successional change from colonization of gaps by pioneer species to mature climax forest. Genetic diversity should be higher in earlier successional stages than in later stages because high environmental predictability in later successional stages favours low genetic diversity. In the present study the relationship between secondary succession and genetic diversity was explored in eight stands of characteristic tree communities in the Thuringian forest area (Germany). Each of the eight stands was subdivided into six plots in a grid of 40 x 40 m to detect as much as possible tree species and genetic variants within the forest tree community and successionspecific structures. To define secondary succession, the mean Ellenberg indicator values for light and nitrogen in the herb layer, weighted for coverage, as well as the percentage of climax tree species in naturally regenerated stands were used. All species and genotype diversities based on the investigated tree species were calculated by the so-called Hill numbers. The results showed that the Gregorius's Covariation (C) of secondary succession with the transspecific genotype diversity as well as the transspecific genotype diversity per species for the enzyme systems AAT, HEK, PGI, MDH, IDH as well as the AFLP trait was statistically significant in several relationships. The transspecific genotype diversities were often significantly greater in the earlier successional stages than in the later stages. Selection effects during replacement of light and nitrogen demanding species and plant communities by more economical and competitive species such as Abies alba Mill. and Fagus sylvatica L. probably dominated in the study. Based on the results of the study, we conclude that genetic diversity may be an essential attribute of stages of secondary succession that should be further explored because of its relation to adaptability and ecological stability.

Variability changes in the ammonite family Dactylioceratidae during the Lower Toarcian

Morard A., Guex J.

Volumina Jurassica

2006

Vol. 4, no. 1

194-195

The comparison of successive dactylioceratid samples collected in the Moroccan Middle-Atlas, the Spanish Betic Cordillera, the Lusitanian Basin and the Causses Basin, allowed us to better characterize the range of variability of these forms from the very base of the Toarcian to the Lower-Middle Toarcian transition. From a biostratigraphic point of view, the Tethyan subgenus Eodactylites (Schmidt-Effing 1972) clearly precedes the NW European subgenus Orthodactylites – as recorded in the Lusitanian Basin succession for example, the latter then giving rise to the Dactylioceras s.s. Both early subgenera can be distinguished morphologically, and separated in a number of “species”, although isolated specimens may be difficult to identify. The main point is that Eodactylites, as well as early Orthodactylites form complete series of continuous covariation, the latter progressively branching into two main lineages in the Semicelatum Subzone. Following the occurence of some rare forerunners, known from the Middle-Upper Domerian, the evolution of the macroconch representatives of this ammonite family can be summarised in three main steps: 1. A sudden “mass apparition” of Eodactylites defines the base of the Toarcian. Their variability spectrum is immediately quite large, with a covariation series between a densely ornamented, somewhat involute and compressed pole (E. mirabile) and a more robust very evolute form with distant primary ribs and possible tuberculation (E. pseudocommune). 2. Ornamental variability tends to disappear in the outer whorls of Orthodactylites, whereas their inner whorls still display a wide covariation series (from slightly compressed forms with dense simple ribs to stout pantuberculate ones), as already noted by Howarth (1962). Intermediate forms seem to disappear in the Semicelatum Subzone. 3. Two lineages are then clearly distinct, one leading from isocostate to variocostate non tuberculate serpenticones (Dactylioceras s.s.), the second developing depressed whorls prone to tuberculation, particularly in inner whorls (Nodicoeloceras). A further diversification occurs at the Lower-Middle Toarcian transition (Guex 1971). In this new evolutionary frame, divergent views on the taxonomy of the Toarcian Dactylioceratidae can eventually be reconciled, as different authors in the past based their classification schemes only on a limited portion of the succession presented here.