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[en] A morphological, molecular, and behavioural characterization of Rhionaeschna galapagoensis is presented, based on a series of specimens and observations from San Cristóbal Island, Galápagos, including both adults and larvae. Several of the characters proposed earlier to distinguish between the adults of this species and its closest relative, R. elsia, are found to be variable, but the presence of a black band over the fronto–clypeal suture is confirmed as a good diagnostic character. The ultimate instar larvae of R. galapagoensis is described for the first time, and diagnosed from its closest relatives by a combination of characters, including the acute angle between the prothoracic apophyses, absence of lateral spines on abdominal segment 6, and length of cerci relative to paraprocts. Molecular analysis confirmed that R. galapagoensis and R. elsia are sister species, and showed that their genetic distance is the closest among the analyzed species, which is to be expected given the young age of the Galápagos Islands. The larvae of R. galapagoensis were very common and widespread in the mountain streams and a pond in the southwest of San Cristóbal. Swarms of tens of individuals formed at sunrise in the coastal vegetation, together with adults of Tramea cf. cophysa, feeding on small flying insects. Males showed patrolling behaviour on small sections of the streams and at a pond. Only one copulation was observed, lasting 10 minutes. Females oviposited alone on floating vegetation in running and standing waters. Our observations corroborate that R. galapagoensis and R. elsia are two parapatric species, morphologically and genetically close. In San Cristóbal, R. galapagoensis had large populations, apparently not threatened. (Author)
[en] Herbivorous insects are remarkably species-diverse, and the cause of such diversity remains a classical issue in the fields of ecology and evolution. The traditional explanation for the huge diversity of such insects is that repeated dietary changes over evolutionary time provided opportunities for speciation, thereby enhancing the diversification rate. A different view suggests that herbivore diversity became saturated over time, with factors affecting the points of dynamic equilibrium of species diversity within each lineage (and thus associated with maintenance of species diversity) being the determinants of the diversity evident today. Thus, both generation and maintenance processes, and their relative importance, are critical for understanding the diversity of herbivorous insects. Furthermore, the neutral theory of biodiversity and biogeography has recently gained attention as an alternative explanation for the generation and maintenance of diversity, as opposed to adaptive processes centred around host specificity. However, these possible routes toward herbivore diversity have rarely been evaluated in parallel, and the work of various groups has become both segmentalised and complicated, compromising any comprehensive understanding of the issue. Thus, in the present paper, I briefly review our knowledge of herbivore diversity and the major relevant studies. The aim was to share knowledge, creating a common starting point from which future discussions among researchers may be generated. It may be that no single approach can resolve the many remaining questions on herbivore diversity. However, an improved understanding of such diversity can be achieved by combining knowledge gained in studies of both the generation and maintenance of diversity.
[en] In laboratory experiments we obtain that the apparent growth rate of the population becomes larger than one under the normal condition, triggered by the external perturbation as the removal of individuals. The changed growth rate is stable for a while. We also propose a simple model of population dynamics allowing both matching and mis-matching the trend of the external perturbation, and show that the growth rate of the model population is changeable and stable to some extent