•Inter-plant variability better explains secondary sexual dimorphism.•Flower and leaf Nitrogen cocentration was higher in females than in males.•Females would adopt a quality investment strategy ...while males adopt a quantity one.
Inter-plant variability (i.e., differences between individuals within population) may be a significant and rather neglected source of variation for addressing the occurrence of secondary sexual dimorphism in plants, especially in long-lived species. However, secondary sexual dimorphism (SSD) in plants is generally analyzed through the comparison of position metrics alone, mainly by the mean values of the male and female samples. Here we analyzed SSD in the dioecious tree Lithraea molleoides by a traditional comparison of position metrics and by taking into account inter-plant variability through a bootstrapping procedure i.e., by selecting randomly and one at a time, a female and a male from the sample and comparing them. This procedure was repeated several times and then the mean of those differences and the confidence intervals were calculated. Our results showed that inter-plant variability contribute to SSD, particularly in nutrient allocation to leaves and flowers. Some floral traits, on the other hand, were higher in males irrespective of inter-plant variability (i.e., flower number and flower mass). Accordingly, males produce more than twice as many flowers as females and their flowers had 22% more biomass than female’s flowers. On the other side, females had 20% more floral N concentration per unit dry mass (floral Nmass) and had more leaf N concentration per unit dry mass (leaf Nmass) than males when inter-plant variability was considered. This differences in nutrient concentration could lead to a higher herbivory in females than in males given a higher leaf nutritional quality. Thus, the quantification of inter-plant variability seems crucial for detecting inter-sexual differences, which may have important ecological and evolutionary implications.
Urbanisation is one of the main drivers of insect species loss worldwide. However, its impacts on ecological interactions involving insects still deserve further research, especially seed predation ...and parasitism of seed predators.
Here, we evaluated the seed predation rate by the specialist bruchid beetle Pseudopachymerina spinipes and its parasitism rate in the native tree Vachellia caven (Fabaceae) along an urbanisation gradient in Cordoba (Argentina). Since resource availability can influence these ecological interactions, we also investigated whether seed and prey availability could affect seed predation and parasitism rates, respectively.
We sampled trees in 10 sampling sites along an urbanisation gradient estimated by the Normalised Difference Vegetation Index (NDVI) within a 100 m radius. In our system, sites with low NDVI, beyond representing the low amount of vegetation cover, also indicate high surface temperature and low availability of host trees.
Seed predation in V. caven and the parasitism rate of P. spinipes were significantly reduced with increasing urbanisation. Notably, seed availability at the pod level did not affect seed predation rate, while prey availability was negatively correlated with parasitism rate.
These findings suggest a deleterious effect of urbanisation on the studied antagonistic interactions, giving no support to the idea of resource limitation effects.
We evaluated how urbanisation degree and resource availability per pod affect the seed predation rate of a native Fabaceae tree by a specialist bruchid beetle and its parasitism rate. Seed predation rate and parasitism rate significantly decreased with increasing urbanisation. Seed number per pod did not affect seed predation, but prey availability negatively influenced the parasitism rate. Our results suggest a deleterious effect of urbanisation on the studied antagonistic interactions, giving no support to the idea of resource limitation effects.
