Morphological Traits of Two Seed-Feeding Beetle Species and the Relationship to Resource Traits.

Morphological traits are useful to investigate insect sex-related differences in body size and to reveal differences in resource use. It has been suggested that as the resource increases, so does the body size of organisms interacting with the resource, highlighting the crucial role of resource quality and quantity in determining the morphological traits of organisms interacting with the resource. Here, we describe morphological traits of two species of Bruchinae, Merobruchus terani (Kingsolver 1980) and Stator maculatopygus (Pic 1930), consuming seeds of Senegalia tenuifolia (Fabaceae: Mimosoideae). We evaluated the influence of monthly sample and sampling sites on tibia and femur length and biomass. In addition, we tested two predictions in which body size related to resource amount and body size related to longevity. Males of M. terani were heavier than females, whereas the two sexes of S. maculatopygus did not differ in biomass. Both species had larger body sizes in the late ripe-fruit stage. With respect to sampling sites, biomass of M. terani did not differ, whereas S. maculatopygus did differ in biomass. Merobruchus terani showed a positive relationship with seed traits, whereas S. maculatopygus showed no relationship. At the same time, fruit traits showed a negative effect on morphological traits for both beetle species. The longevity experiment, performed using only M. terani, showed an equal longevity and seed consumption rate for both sexes. Our study indicates that different species, interacting in the same system and performing similar functional behaviors, respond differently to the same resource.

The interplay among prey preference, nutrient enrichment and stability in an omnivory system.

Food webs usually display an intricate mix of trophic interactions where multiple prey are common. In this context omnivory has been the subject of intensive analysis regarding food web stability and structure. In a three species omnivory setting it is shown that the modeling of prey preference by the top predator may exert a strong influence on the short as well as on the long term dynamics of the respective food web. Clearly, this has implications concerning the stability and the structure of omnivory systems under disturbances such as nutrient enrichment.