Análisis de la vegetación arbórea en la provincia florística de Tehuacán-Cuicatlán

The arboreal vegetation of a portion of the Tehuacán-Cuicatlán Valley is analyzed. An altitudinal gradient was followed along the leeward slopes of the Sierras de Juarez and Zongolica (Sierra Madre Oriental). Multivariate analysis techniques, ordination (principal component analysis and reciprocal averaging) and classification (informationanalysis program CENOSIS 2) were used. The results allow the definition of "groups" identifiable with vegetation types defined from a physiognomic-structural view point; however, the analysis performed shows that the arboreal vegetation of the study area possesses a variability and heterogeneity not detected by previous descriptive physiognomic studies. The importance of human disturbance and other factors (e.g. biotic interactions) affecting the structure and composition of the plant communities of the study area is discussed . The analysis techniques are compared with regards to their efficiency in handling high levels of vegetational heterogeneity , being the classification technique the most efficient one. Finally, some considerations judged interesting for future investigations are proposed.

Comparative morphometrics and relative growth of Cherax quadricarinatus (Von Martens, 1868) males and females

The relative growth of Cherax quadricarinatus (Von Martens, 1868) males and females under laboratory conditions was analysed using eight somatic measurements. The allometry of each measurement was estimated in relation to total length. The morphometrics were analysed using the original values, as well as normalized data from each group. Two multivariate analyses were carried out: reciprocal averaging and principal components. The results showed that the two sexes have a similar relative growth. However, differences between the sexes were recorded with respect to shape, though not to size. This was observed through the reciprocal averaging analysis after normalization of the individuals in each group. The morphometric variables that differentiated the sexes were the width and length of the chela, followed by the length of the abdomen. Thus, this analysis was useful to determine the shape differences between the sexes in culture.

An ordination approach to the quantification of smokers' readiness to change 1This research was supported by a grant from Société de Tabacologie, Paris, and partially supported by La Ligue Nationale Contre le Cancer.

The paper argues that the problem of estimating a “readiness-to-change” score for smokers from processes of change measures is closely related to dating problems in archaeology. It amounts to finding a joint ordination of both smokers (“sites”) and processes of change (“tools”) in a common space, so that smokers be located close to processes they use most, in some sense. Properties of Correspondence Analysis as a reciprocal averaging technique are first briefly summarized, and its capability of recovering nonlinear structures is recalled. Application to processes of change data in smoking cessation leads to a solution which first axis is interpreted as a cognitive-behavioral continuum. Processes are shown to be scaled in a way that is in good convergence with longitudinal data previously reported ( Prochaska et al., 1991 ), and subjects' locations to be significantly related to actual quitting. Finally, it is shown how new responses profiles could be projected on the obtained solution to get a practical estimation of probability to quit.

Mallomonadacean (Chrysophyceae) assemblages and their relationships with limnological characteristics in 38 Adirondack (New York) lakes

The siliceous scales of 30 mallomonadacean taxa were identified and counted from the surficial sediments of 38 Adirondack lakes. The scales were usually abundant and were always well preserved. The Adirondack flora is typical of acidic to circumneutral oligotrophic lakes. Common taxa include Mallomonas acaroides, M. caudata, M. crassisquama, M. hamata, M. pseudocoronata, M. punctifera, Synura echinulata, S. petersenii, S. sphagnicola, S. spinosa, and Chrysosphaerella longispina. The abundance of certain species (e.g., Mallomonas hindonii, M. hamata) appears to be a reliable indication of acidic waters. Reciprocal averaging (RA) ordination was used to determine if distribution of the mallomonadacean assemblages corresponded with major environmental gradients. Correlations between the first RA axis scores and lakewater pH (r2 = 0.63) and related factors (log10 alkalinity, r2 = 0.66; pCa, r2 = 0.39; pMg, r2 = 0.43) were strongest. Relationships were weaker with average depth, summer epilimnion temperature, elevation, NO3, and total Al, and were not statistically significant with conductivity, color, Secchi disc transparency, total P, chlorophyll a, SO4, and Si. Cluster analysis grouped both lakes and taxa into categories best explained by their pH-related characteristics. Analysis of surficial sediment from lakes with known limnological characteristics is a useful approach for the study of the ecology and taxonomy of the Mallomonadaceae. Our data demonstrate that mallomonadacean distributions reflect lake conditions and, therefore, are potentially useful indicators in limnological and paleolimnological studies.

Community Gradients in the Scotian Shelf Zooplankton

The structure of the zooplankton community of the Scotian Shelf was investigated during eight cruises between August 1978 and September 1980. An inshore–offshore community gradient correlated with temperature, salinity, and distance to shore was the strongest pattern revealed by reciprocal averaging. Zooplankton taxa were grouped as inshore (characterized by Arctic species), intermediate (the dominant shelf species), or offshore (expatriate species) on the basis of reciprocal averaging results and correlations with environmental variables. Recurrent group analysis revealed a pattern consistent with that of reciprocal averaging. A shelf recurrent group was always present, dominated by the "core" species: Calanus finmarchicus, Metridia lucens, Pseudocalanus minutus, Oithona similis, and Limacina retroversa; related shelf edge/slope groups were also present. Substantial differences between cruises were apparent in both reciprocal averaging and recurrent group analysis results and appeared to be related to aperiodic changes in hydrographic conditions. Aperiodic incursions of slope water may represent an energy supplement (as nutrients or zooplankton prey species) or an energy loss if expatriate species exploit the shelf community.