Dead wood of arborescent Euphorbia plants in the Macaronesian islands and Morocco has a diverse fauna of wood-boring beetles. Thirty-eight species were found in four species groups of Euphorbia, including 29 species of scolytine bark beetles, six species of cossonine weevils, two species of Laemophloeidae and one of Monotomidae. All scolytines (but not cossonines and cucujoids) have narrow host preferences, using only one host group for feeding and reproduction. The number of islands on which each species was found was also limited, resulting in geographically distinct guilds for each Euphorbia host. The majority of species (26) were found on the E. lamarckii species complex, followed by E. balsamifera (13) and the succulents E. canariense (12) and E. echinus (3), while only two species were found on the rare montane species, E. longifolia, in Madeira. Up to six or seven species could be found in a single branch of E. lamarckii and E. canariense, respectively, but more than half of the plants had fewer than three species. Putative niche partitioning was indicated by the alternative utilization of different tissues in E. balsamifera and different moisture preferences in the succulent E. canariense. Several unusual features of bark beetle reproductive biology were also observed, including infrequent communal nesting and very small broods. Taken together with the phylogenetic, geographical and biological data now available for most species associated with dead Euphorbia, several of the beetle guilds should provide promising model systems for studying of species interactions and community structure.
In this study two important factors that are thought to govern interspecific variation in pollen-ovule ratios were examined. First, the effect of habitat disturbance on variation in pollen-ovule ratio was determined. The second factor studied was the pollination type, used as a surrogate for the efficiency of pollination. Because seed mass is known to be strongly correlated with the pollen-ovule ratio it was also included in the analyses to examine if a possible effect of habitat disturbance or pollination type is still valid after accounting for the effect of seed mass. Furthermore, phylogenetically comparative methods were used to investigate whether the correlations between traits were maintained through evolutionary history or are only present in recent species data, i.e. in analyses that do not consider phylogenetic relationships between species. In conflict with the reproductive assurance hypothesis, habitat disturbance did not have a significant effect on interspecific pollen-ovule ratio variation. In contrast, pollination type accounted for a significant proportion of the variation in pollen-ovule ratios, even after taking into account the strong effect of seed mass. General results do not differ between the cross-species and phylogenetic comparative approaches. The results both accord with the predictions of the sex allocation theory and the proposition that the chance of a pollen grain reaching a stigma governs the pollen-ovule ratio.