No description available.

It is now well established that certain chemical compounds, administered to animals in early pregnancy, can adversely influence the development of the fetus, resulting in congenital malformations. Recently, it bas been shown that thalidomide, a sedative drug, may induce skeletal defects in the offspring of treated females when administered in the early stages of pregnancy. McColl, Globus and Robinson (1963) reported that certain skeletal defects could be produced in the offspring of Sprague-Dawley rats following chronic oral administration of thalidomide. Notable among the defects produced were malfomations of the sternum. [...]

This work sets out to describe the socio-ecological niches of otonya irroratus, Rhabdomys pumilio and Praomys natalensis in the Natal midlands. This objective necessitated a broad-based approach in which aspects of the ecological niches, and the social behaviour and social organization of the three species were investigated in field (habitat and trapping) and laboratory (experimental and observational) studies, during the period January 1976-May 1978. To test the assumption that the commonly sympatric O. irroratus, R. pumilio and P. natalensis are primarily adapted to habitats which differ mainly in respect of water availability, an attempt was made to define their positions on a mesic/xeric continuum. The results suggest that in terms of the parameters measured (responses to water and cover availability, and to food and water deprivation), O. irroratus is more nearly mesically adapted than is R. pumilio, with P. natalensis positioned between the two extremes. However, in the case of P. natalensis it is apparently of overriding importance that this species is adapted to disturbed habitats. The mesic habitats preferred by O. irroratus are often of limited size, but resource availability within these areas is apparently high and stable. Extensive areas of suitable habitat are available to R. pumilio, but availability of resources is seasonally variable. The disturbed habitats preferred by P. natalensis arise unpredictably in nature and, depending on the rate of ecological succession, may be short-lived; hence availability of resources to this species is highly unpredictable. Social behaviour was studied by means of dyadic encounters in the laboratory. Communication in O. irroratus, R. pumilio and P. natalensis appears to be dominated by auditory, visual and olfactory signals respectively, although O. irroratus also has well developed visual signals in its communicatory repertoire. These differences are explained mainly in terms of patterns of diel activity and habitat preferences: R. pumilio is adapted to bright light, and its visual signals are subtle; O. irroratus is adapted to dim light, and its visual signals involve gross changes in posture, while the use of loud, low frequency vocalizations would allow conspecifics to know their precise location in relation to one another in dense vegetation; P. natalensis is nocturnal, and hence appears to emphasize olfactory (and possibly ultrasonic) communication, which would permit transfer of information in the dark. O. irroratus is overtly highly aggressive, but agonism is ritualized; ritualization of aggression has probably evolved to allow high densities of this species to exploit limited areas of prime habitat. R. pumilio is less overtly aggressive than O. irroratus, but aggression tends to be unritualized; direct aggression probably acts as a spacing mechanism, and is possible in view of the large areas of habitat available to this species. Agonism is poorly developed and ritualized in P. natalensis, permitting high sociability and group formation in this species, and maximum exploitation of locally abundant resources. Social organization was studied in the field (trapping studies) and by means of dyadic encounters in the laboratory. The social system of O. irroratus appears to include temporal territoriality, which would permit animals to live in close spatial association (in small areas of habitat) while seldom actually meeting. Hierarchical ranking occurs in male O. irroratus and R. pumilio, with competition in both most likely being for mating opportunities. Breeding females of these two species are intrasexually territorial, in the case of Q. irroratus thereby providing dispersing young with adequate space for establishment of a home-range in prime habitat, and in R. pumilio protecting the young against conspecific female aggression until dispersal. R. pumilio tends to aggregate in mesic refuge habitats in winter, which apparently reflects the seasonality of resource availability to this species in drier environments. P. natalensis is colonial, an adaptation facilitating maximum exploitation of temporarily abundant resources in transitory disturbed habitats. In response to intense courtship by the male, female R. pumilio appear to undergo reflex ovulation; this strategy would maximize the chances of fertilization occurring during occasional meetings between males and females. Courtship intensity is low in P. natalensis, and presumably because the colonial social system of this species ensures frequent association between potential mates, females appear to ovulate spontaneously. Sexual activity was not observed in O. irroratus. The life-history tactics of the three species are such that o. irroratus and P. natalensis respectively appear to be K- and r-selected, with R. pumilio falling between these two extremes on an r-K continuum. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1982.

This thesis presents the results of a 3 year field study on the behavioural ecology of the mara on the Valdés Peninsula in Argentina. The main goal was to investigate why the mara's social system incorporates both monogamy and communal denning, a combination unknown in other mammals. The research techniques used were behavioural observations and radio-tracking. Radio-tracking of 9 maras revealed that pairs were continually moving into new areas, suggesting that their ranging behaviour is adapted to an irregular pattern of resource distribution. Two maras had prevailing ranges of 35 ha and moved yearly over about 200 ha. Ranges floated around a geographic centre. One constraint on the animals' movements may be the need to stay near a den site for pupping. Maras were diurnal, and spent on average 46% of the day grazing. Ranges may overlap up to 33%, but range use between neighbouring pairs were negatively correlated suggesting that animals were avoiding each other--pairs may be occupying floating territories. Evidence that maras are monogamous in the wild is presented. The factors leading to monogamy are argued to be: (i) females are irregularly dispersed because of the distribution of food; and (ii) the brevity of the female's oestrus (1-2 hrs). A male attempting to mate polygynously would have difficulties in finding and securing a female; thus males may do best by staying with one female to ensure a successful mating. Males may enhance their reproductive success by watching for predators so that their females can spend more time feeding to meet the energetic demands of lactation and gestation. During the pupping season, August to January, groups of 1 to 22 pairs gather at single dens. Several dens may be located near each other to form denning communities. Most pairs produce only one litter a year and there is a peak of births in September and October. Pairs visit the den once a day for a period of 5-6 weeks to nurse their young. Den sites are not limited; and the reason maras den communally appears to be the increased protection from predators accruing to pups and adults in larger groups. Two possible routes are suggested in the evolution of the mara's social system: (i) from a monogamous starting point it has become advantageous to creche pups; or (ii) ancestral maras were more colonial and probably polygynous, but have been forced to space out because of changes in the distribution of food, which has led to monogamy. Finally, maras were compared with other caviomorph rodents, lagomorphs, and monogamous ruminants and were shown to be most similar to the latter in their adaptations to the environment a remarkable example of convergent evolution.

Many studies have reported deficient or intermittent patterns of natural regeneration in temperate deciduous woodland. The present study aimed to assess the relative impact of herbivore-mediated plant mortality on the natural regeneration dynamics of representative tree species (Acer pseudoplatanus, Betula pendula, Fraxinus excelsior, Ilex aquifolium, Sorbus aucuparia, Taxus baccata and Ulmus glabra) in representative temperate deciduous woodland (Shipley Wood and Derwent Gorge, County Durham). Sapling density and the density, spatial association and size distribution of adult tree populations varied significantly between tree species and study sites, reflecting contrasting patterns of current and historical regeneration. Rates of post-dispersal seed predation and seedling herbivory were quantified using field-based 'cafeteria' trials. Rodents were the principal agents responsible for seed predation, whereas seedling herbivory was attributable to a mixed suite of herbivores including invertebrates, rodents and larger mammals. Rates of seed predation and seedling herbivory varied significantly between tree species, most likely reflecting individualistic, trade-off responses to chemical and physical attributes. Fine-scale spatial variation most likely reflected the preferential foraging of rodents beneath protective vegetation cover. There was no consistent evidence to support the hypothesis that dispersed seeds may escape disproportionately high offspring mortality beneath parent plants resulting from increased herbivore activity. Natural seedling density varied significantly between years and between tree species, according to the abundance of viable seeds produced by conspecific adult trees. Although seedling survivorship varied significantly between species, the survivorship of each species was similar between years and between cohorts of the same year. Canopy cover, field layer cover or correlated factors were significant determinants of seed germination and seedling emergence, establishment and survival, according to age- and species-specific tolerances. In relative terms, patterns of natural regeneration were primarily herbivore- limited (Acer and Taxus), microsite-limited (Betula, Fraxinus, Ilex and Ulmus) or limited by herbivores and microsites (Sorbus). The availability of viable seeds may have also limited the recruitment of Ilex, Sorbus, Taxus and Ulmus. Vegetative expansion, mast seeding, seed bank regeneration and repeated, prolonged reproduction may have reduced the actual impact of herbivory on natural regeneration, such that long-lived iteroparous tree species were unlikely to have been critically dependent on current recruitment.

No description available.

Thesis (Ph. D.)--Michigan State University. Neuroscience Program, 2008. / Title from PDF t.p. (viewed on Mar. 26, 2009). Includes bibliographical references (p. 109-119). Also issued in print.

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 20-25). Also available in electronic format on the Internet.

Thesis (M.A.)--University of North Carolina Wilmington, 2009. / Title from PDF title page (February 22, 2010) Includes bibliographical references (p. 55-58)

Thesis (Ph. D.)--University of Wisconsin--Madison, 1962. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 97-100).