Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks

Espelta J.M., Cortés P., Molowny-Horas R., Retana J. (2009) Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks. Oecologia. 161: 559-568.
Enllaç
Doi: 10.1007/s00442-009-1394-x

Resum:

The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0%) as in Q. ilex (20.0%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60%) than in Q. ilex (21%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects. © Springer-Verlag 2009.

Llegeix més

Els alzinars Manuals de gestió d’hàbitats.

Espelta JM, Gracia M, Molowny R, Ordoñez JL, Retana J, Vayreda J et al (2009) Els alzinars Manuals de gestió d’hàbitats. Diputació de Barcelona. Barcelona. 181 pp.

Floristic homogenization by native ruderal and alien plants in north-east Spain: The effect of environmental differences on a regional scale

Pino J., Font X., de Cáceres M., Molowny-Horas R. (2009) Floristic homogenization by native ruderal and alien plants in north-east Spain: The effect of environmental differences on a regional scale. Global Ecology and Biogeography. 18: 563-574.
Enllaç
Doi: 10.1111/j.1466-8238.2009.00458.x

Resum:

Aim: To evaluate the relative potential contribution of native ruderals and aliens to plant homogenization at a regional scale, after taking into account the effect of diverse environmental distances. Location: Catalonia (north-east Spain) Methods: We have used the flora module of the BDBC project (Catalonian Database of Biodiversity), which provides information on plant species distribution per 10 × 10 km Universal Transverse Mercator (UTM) cell. Pairwise floristic similarities of: (1) total, (2) native non-ruderal, (3) native ruderal, and (4) alien vascular plant species have been calculated for a particularly well-sampled subset of UTM cells, using a modified version of the Simpson index. These similarities have been compared per UTM pair using Mantel tests, before and after considering their relative association with geographical, climatic and landscape distances from linear regression models. The floristic similarity of both total and native non-ruderal species was also correlated with the proportion of alien and native ruderal species after discounting the effects of environmental distances. Results: The proportion of variance explained by environmental correlates was highest for the floristic similarity of native non-ruderal plants and lowest for that of aliens. In all plant groups, climatic distance was the main significant variable of species similarity. Geographical distance was only significant for total and native non-ruderal species and was of secondary importance in both cases. Landscape distance was not significant in any case. Similarities among both aliens and native ruderals were significantly higher than among native non-ruderals, but these differences disappeared after removing the effect of environmental distances. Main conclusions: Species similarity between sites may depend on differences in environmental factors other than geographical distance. This has to be taken into account when exploring the implications for biotic homogenization. In the case of Catalonian flora, the potentially homogenizing effect of native ruderal and alien species seems to be associated with their lower dependence on geographical distance and climatic factors compared with those of native, non-ruderal species. © 2009 Blackwell Publishing Ltd.

Llegeix més