Caracterización de las poblaciones de los principales cerambícidos xilófagos en las masas de quercíneas del suroeste español y su incidencia en el estado fitosanitario de las mismas

Resumen

The dehesa is a silvopastoral system in the Iberian Peninsula of high economic and ecological value which, due to the great richness and diversity of its flora and fauna, has been recognized as protected habitat in the EEC directive (CD 92/43/EEC of 21 May 1992) and listed among the top 34 biodiversity hotspots. One of the most serious challenges faced by the dehesa system during the last decades is the so-called "Z.5 seca"or oak-decline. Among other factors, current decline in the Quercus Mediterranean woodlands is due to three xylophage cerambycids: Cerambyx we/ensii Küster, C. cerdo L. and Prinobius myardi Musant. The xylophage cerambycids of the Cerambyx group find themselves in a different position. The C. cerdo appears in Annex II in the Berne Convention as a protected species, where it is catalogued as a "species of EC interest" and its preservation linked with "the establishment of a consistent network of special areas of conservation". This protected status is also found in the corresponding transposition into national law: Annex II in the Real Decreto 1193/1998. Likewise, the International Union for the Conservation of Nature (IUCN, 1996) classifies the C. cerdo as a vulnerable species. Nevertheless, the main borer beetles in the dehesas of western Andalusia are C. we/ensii and P. myardi. The latter is practically unknown and both have no conservation status. Knowledge about the biology and behavioral patterns of these two species is irregular and imprecise. I have designed a Capture-Mark-Recapture sampling procedure for this Dissertation Thesis as the populations under study are open. Chapter 2 contains a detailed description of the research design and methodology for the sampling procedure. I undertook fieldwork during May, June, July and August in the years 2002-2009, collecting data samples from 4099 individuals: 3480 C. welensii and 619 P. myardi. By means of binary coding, I reconstructed the life histories for each of the cited individuals. In this respect, I made use of the Jolly-Seber (JS), Cormack-Jolly-Seber (CJS) and Time Since Marked (TSM) population model types as these models best explain the behavior of species. By means of the POPAN formulation, I calculated the following population parameters: survival rate (Phi), recapture (p), proportions of transient present in the sample (x),proportions of transient present in the overall population and population size (N). I have made use of the Degree Days Phenology Model (DD) in order to delve into the relationship between the species under analysis and their environment. More specifically, I aimed for establishing the correlation between temperature and insect development. In this Dissertation Thesis, I propose a method that is based on DD models and determines the influence of ambient temperature for the flight period of the C. we/ensii and P. myardi species. The method hereby proposed is iterative and consists in the repetition of the estimation procedure readjusting the input variables (initial date and minimum and maximum development threshold) until we have smallest root mean square error (RMSE). Once obtained the cited variables, I proceed to calculate the thermal constants for cumulative percentage of emergence (CPE) 1-99% at 10% intervals. Chapters 3 and 4 show how the TSM population model selected and the scrutiny of the estimated variables (Phi, p, x, T & N) prove the existence of two individual groups among the populations of C. we/ensii and P. myardithat develop differing vital strategies. In the case of the C. we/ensii population, their vital strategy involves both male and female individuals. I also prove that one of the species is much commoner than the other in our fieldwork area and that each species shows distinctive behavioral patterns. As regards the phenology model here adopted, I prove its utility and also validate the DD-based variables proposed: initial date and minimum and maximum development threshold. Finally, I also provide the thermal constants for the corresponding PVA in the two cited species as these may produce more accurate trapping, sampling and monitoring campaigns concerning the populations involved in the near future.