Daniel Otte

Simple Versus Elaborate Behavior in Grasshoppers an Analysis of Communication in the Genus Syrbula

The species in the genus Syvbula possess more elaborate courtship behavior than other Orthoptera. This fact is difficult to explain because other species living in similar situations possess very simple behavior. Pair formation is achieved through the attraction of females to stridulating males, or through reciprocal stridulating and approaching between males and females. Occasionally females attract males by singing spontaneously. The two Syrbula species live together in parts of Texas. Reproductive isolation is ensured and needless sexual interactions are prevented by call differences; i.e., females respond only to the songs of their own species. Elaborate courtship is omitted when pairs are formed through an exchange of calling signals. However, in the presence of sexually unreceptive females, males perform elaborate courtship behavior. The movements of appendages are mostly synchronous suggesting they are controlled by a single command from the brain; however, some asymmetry of movements exists (the appendages on the two sides of the body assume different positions and may be out of phase with one another) indicating a more complicated control system than exists in the European species, GomPhocerus rufus. Males assume a position nearly parallel to the female during courtship and the near appendages perform one set of movements and the far appendages a different set. Each side of the body can perform both sets of movements. Intermale rivalry takes several forms: stealing of females by non-calling or non-courting males, the production of male-identifying or male-spacing signals and, possibly, chorusing. The causes for the evolution of elaborate behavior are unknown. It may have evolved due to sexual selection or due to the fact that females of Syrbula require some special sort of priming before each mating. Selection for reproductive isolation does not usually seem to result in elaboration of courtship in grasshoppers. Sexual dimorphism is pronounced and its importance may lie in sexual or species recognition.

Species Richness Patterns of New World Desert Grasshoppers in Relation to Plant Diversity

The numbers of grasshopper species in North and South American deserts are compared. The Sonoran Desert of Arizona has a significantly richer fauna than the floristically similar Monte Desert of Argentina. Recruitment of species through immigration and colonization may be greater in North America where the deserts have richer source areas. Niche space differentes do not adequately account for the different diversities. South American deserts may also have fewer species because they were more strongly affected by Pleistocene events than their North American counterparts. Evidence that North American deserts are older is also discussed.

Plant preference and plant succession

SummaryThe theory that early successional plants and annual plants will be less well defended against generalist herbivores than later successional plants and perennial plants, because they avoid herbivores by escaping in space and time, is evaluated. The theory is not supported in the ecosystem examined. The correlation between level of preference and the ability of plants to support growth and survival is examined and shown to be high.