Monte Lloyd

Comparative nutrient extraction from forages by grazing bovids and equids: a test of the nutritional model of equid/bovid competition and coexistence

SummaryRuminants are unevenly distributed across the range of body sizes observed in herbivorous mammals; among extant East African species they predominate, in numbers and species richness, in the medium body sizes (10–600 kg). The small and the large species are all hind-gut fermenters. Some medium-sized hind-gut fermenters, equid perissodactyls, coexist with the grazing ruminants, principally bovid artiodactyls, in grassland ecosystems. These patterns have been explained by two complementary models based on differences between the digestive physiology of ruminants and hind-gut fermenters. The Demment and Van Soest (1985) model accounts for the absence of ruminants among the small and large species, while the Bell/Janis/Foose model accounts both for the predominance of ruminants, and their co-existence with equids among the medium-sized species (Bell 1971; Janis 1976; Foose 1982). The latter model assumes that the rumen is competitively superior to the hind-gut system on medium quality forages, and that hind-gut fermenters persist because of their ability to eat more, and thus to extract more nutrients per day from high fibre, low quality forages. Data presented here demonstrate that compared to similarly sized grazing ruminants (bovids), hind-gut fermenters (equids) have higher rates of food intake which more than compensate for their lesser ability to digest plant material. As a consequence equids extract more nutrients per day than bovids not only from low quality foods, but from the whole range of forages eaten by animals of this size. Neither of the current nutritional models, nor refinements of them satisfactorily explain the preponderance of the bovids among medium-sized ungulates; alternative hypotheses are presented.

THE PERIODICAL CICADA PROBLEM. I. POPULATION ECOLOGY

Periodical cicadas, Magicicada spp., have the longest life cycles known for insects. In anyone population, all but a tiny fraction are the same age. The nymphs suck juices from the roots of deciduous forest trees in eastern United States (see Marlatt, 1907, for a complete account of the life cycle). Mature nymphs finally emerge from the ground, become adults, mate, lay their eggs, and die within the same few weeks of every seventeenth (or, in the South, every thirteenth) year. Not one species does this, but three. There are three separate and distinct species that occur together over most of the range of periodical cicadas (Alexander and Moore, 1962) and, wherever the species coexist, they are invariably synchronized. In different re-

Self Regulation of Adult Numbers by Cannibalism in Two Laboratory Strains of Flour Beetles (Tribolium Castaneum)

Two strains of flour beetles, though different in reproductive potential, maintain similar equilibrium densities when their populations are confined. A simple mathematical model shows that this result is to be expected in a population system dominated by cannibalism, provided the rates of cannibalism do not differ and the predatory adults do not become satiated. See full-text article at JSTOR

17-YEAR CICADAS EMERGING AFTER 18 YEARS: A NEW BROOD?

eight weeks, by their tiny progeny. Originally we assumed that case (1) but not (2) had occurred in northern Kentucky. Periodical cicadas had appeared in 1970 (Brood X) and 1974 (Brood XIV). However, we later received word from friends that there had been a substantial emergence there in 1975. We revisited our study area and found that this was indeed the case. We then chose one of our study sites (Mason) reported in the earlier paper (Lloyd and White, 1976) and made another collection of twigs along the forest edge adjacent to the previous years collection. We have now counted and measured these eggnests and report the results herewith, along with additional data obtained by digging in an area 2 km away, which also had cicadas emerging in all three years. An unexpected finding of interest is that one of the three synchronized speciesMagicicada septendecula-made up a disproportionately large share of the delayed emergence in 1975. This suggests that M. septendecula is a relatively poor competitor, which may be related to the fact that it is usually the rarest of the three species emerging together. Evolution, 33(4), 1979, pp. 1193-1199

Spontaneous, field tested and tethered flight in healthy and infected Magicicada septendecim L.

SummaryFlight capabilities of healthy and fungus infected Magicicada septendecim L. (Homoptera: Cicadidae) were compared using 3 complementary techniques: 1) observations of spontaneous flights, 2) field-tested flights, and 3) tethered flights in which endurance was measured. Spontaneous flight distances are much lower than those obtained on field tested fliers. While healthy individuals flew significantly greater distances than did individuals bearing conidia or resting spores of the fungus, Massospora cicadina Peck, the two groups-healthy versus conidia and resting spores pooled-did not differ in flight speed or flight endurance. The magnitude of each of the 3 flight indicators is much lower than those of most dispersing insects, suggesting that this periodical cicada species is a relatively poor disperser.Nevertheless, and contrary to the results of one published study, cicadas flew long distances in single flights, also they often took many flights. Our data help to explain how periodical cicadas can invade new, sometimes distant, habitat each generation. Since infected individuals have both the speed and the endurance of healthy individuals, we conclude that the conspicuous absence of the fungus from early successional, manmade, and second growth habitat is due either to the inability of resting spores of this fungus to survive in recently plowed or fertilized soils or to an intrinsic aversion to flight of infected individuals.