Spatio temporal population dynamics of the invasive diatom Didymosphenia geminata in central-southern Chilean rivers.

We document the distribution of Didymosphenia geminata in central-southern Chilean rivers and identify the chemical and physical factors associated with its presence/absence (p/a). Repeated surveys in five successive years provided evidence that D. geminata could be nearing a biogeographic equilibrium in the region. D. geminata databases from extensive biological and environmental surveys in 187 rivers, within ten catchments, south of 38°S commenced in November 2010 and ran through May 2013. In addition, data from two other field surveys were used. The sites evenly distributed latitudinally were climatically characterized. The recent sampling program, following a published species distribution model, was designed to explore D. geminata distribution within thirteen catchments (34°S-48°S). An extensive river survey in 2014 (spring-summer) and in 2015 (autumn) included the p/a, and relative abundance of D. geminata cells in phytobenthos and in the drift. These p/a results showed that the probability of re-encountering D. geminata cells at sites where the species was previously found was significantly high while the probability of finding D. geminata cells at sites previously without the species was significantly low. This suggests that the distribution of D. geminata cells among suitable habitats was nearing completion. The relative abundance of D. geminata cells in the phytobenthos versus in the drift indicates seasonality with higher proportion of cells in the phytobenthos during the spring-summer than during the autumn. During the final surveys, principal component analysis of chemical and physical characteristics of rivers showed significant differences between rivers with and without D. geminata. Based on our observations of the distribution of D. geminata cells among rivers with suitable habitat conditions and the fluctuating rate of spread between rivers, we conclude that D. geminata is probably in the ending stage of its spatial demographic expansion in Chile surmounting the different barriers of the invasive process.

[Digital image processing: fundamental techniques and applications in biological research]. / Procesamiento de imágenes digitales: técnicas fundamentales y aplicaciones en la investigación en biología.

Digital image processing represents a relatively new but very dynamic domain. Its importance is still growing due to the rapid development in related computer equipment. In this paper basics concepts are introduced and a survey of problems and methods is presented. Starting with techniques used for the capture of data, it continues with techniques applied to coding new data, image enhancement and pattern recognition. Special attention is given to pattern recognition techniques which provide the basics for classification of data according to established criteria. Finally, two applications are presented; the reconstruction of 3-D volumes from serial cutting and a survey of chlorophyll concentration on Lake Aculeo using remote images obtained by the LANDSAT satellite.