Ángel Puerto Martín

A SIS Epidemiological Model Based on Cellular Automata on Graphs

The main goal of this work is to introduce a new SIS epidemic model based on a particular type of finite state machines called cellular automata on graphs. The state of each cell stands for the fraction of the susceptible and infected individuals of the cell at a particular time step and the evolution of these classes is given in terms of a local transition function.

Influencia sobre la diversidad de los valores de importancia considerados en el muestreo

SUMMARY An analysis is made of the variatons undergone by diversity on considering six variables of different importance: density, cover, biomass, abundance as a function of density, abundance as a function od cover and frequency. The example proposed includes thirty communities grouped into six types; three of these were typical communities of herbaceous species of the semiarid regions of Western Spain and the other three show different intensities of lignous species. It is concluded that the abundances and frequency are of little interest for the calculation of diversity. Density, cover and biomass form a continuous series which, in the order mentioned, display a greater range of variation between extreme values (positive aspect) and a strong decrease of the influence of richness versus equitability (negative aspect). Owing to this antithesis in quality, cover is chosen as the best parameter or defining diversity.

Análisis de una microtransección relacionada con la profundidad del suelo

espanolLa microheterogeneidad del medio se relaciona con frecuencia con la distribucion de las especies. En este trabajo se estudia una transeccion de corto recorrido, tomando como base de diferenciacion la profundidad del suelo. Se concluye que hay una acomodacion del nicho de las especies de acuerdo con la misma, aunque tambien pueden influir otras causas, tales como: a) El alejamiento de los afloramientos rocosos. b) Pequenos cambios en la profundidad, cuando esta es inferior a 20 cm. c) Los cambios rapidos de profundidad, que determinan desplazamientos de las especies. d) La existencia de zonas de transicion, antes de que se alcance el pastizal tipico. EnglishThe microheterogeneity of the environment is frecuently related to species distribution. In this study a short distance transection is analysed using soil depth as a basis of differentiation. It is concluded that there exists a niche accomodation of species related to soil depth, althoug the same could also be influenced by other factors like: a) The distance from rock outcrops. b) Small changes in soil depth, when soil depth is below 20 cm. c) Rapid changes of soil depth that determine shifts of species. d) The existance of transition zones prior to the formation of a typical grassland.