Cross-sectional morphometric data on a population of semifree-ranging squirrel monkeys,Saimiri sciureus (Iquitos)

Demography of squirrel monkeys (Saimiri sciureus) in captive environments and its effect on population growth

Understanding which life-history variables have the greatest influence on population growth rate has great ecological and conservation importance. Applying models of population regulation and demographic mechanisms can aid management and conservation of both wild and captive populations. By comparisons of sensitivity, elasticity, and life-table response analyses, we identified demographic processes that were most likely to produce changes in population size (via prospective analyses) and the traits that actually influenced population changes (via retrospective analyses) among sexes, zoological facilities, and generations of captive squirrel monkey populations (Saimiri sciureus). Variation in life-history traits occurs within each group analyzed. Those traits that vary the most include age at maturity, age at last reproduction, and fertility. Zoos with increasing population growth rates maintain earlier ages of maturity, later ages of last reproduction, high rates of juvenile and adult survival, and most importantly greater fertility, reflecting shorter inter-birth intervals. Using prospective analyses, juvenile and adult survivals were predicted to be demographic traits with the greatest effect on population growth. Surprisingly, and despite predictions, retrospective analyses revealed that fertility was the life-history characteristic trait that contributed the most to changes in population size.

Age and seasonal effects on predator-sensitive foraging in squirrel monkeys (Saimiri sciureus): a field experiment

A field experiment was conducted to examine the effect of perceived predation risk on the use of foraging areas by juvenile and adult primates under different conditions of local food abundance. Wild squirrel monkeys, Saimiri sciureus, were observed in an experiment conducted during the dry and the wet seasons at a site in Eastern Amazonia, Brazil. Animals were presented with feeding platforms that differed in food quantity and exposure to aerial predators through varying vegetative cover. In the dry season, juveniles and adults chose platforms based solely on food quantity. However, in the wet season, juveniles foraged preferentially on high-reward platforms only if cover level also was high (i.e., potentially offered greater concealment from predators). In contrast, adults showed the same pattern of platform use regardless of season. These results indicate that age and local resource availability based on seasonality affect whether primates forage in a predator-sensitive manner. Juveniles may be more sensitive to predation risk when foraging, and individuals may take fewer risks when resource abundance is high in their environment.

The relationship between maximum jumping performance and hind limb morphology/physiology in domestic cats (Felis silvestris catus)

A critical role of functional morphology is to demonstrate form—function relationships that can then be used by evolutionary biologists to infer the evolutionary history of the structure in question. Tests of theoretical expectations about the effects of many aspects of morphology/physiology on locomotor performance have had very mixed results. If systems such as jumping can be shown to reliably predict performance from morphology, this would provide a foundation upon which hypotheses for the evolutionary origin of certain morphologies can be generated. The present study examined whether a relationship exists between maximum takeoff velocity(TOV) and several carefully chosen morphological and physiological traits in domestic cats (Felis silvestris catus). Based on the contributions of extensor muscle work to increasing the kinetic and potential energy of the center of mass (CM) during takeoff, we predicted that maximum TOV would be dependent upon relative limb length, relative extensor muscle mass, body mass and the percentage of fast-twitch muscle fibers. Both maximum TOV and this series of traits were measured in 18 cats. We found that variation in cat maximum TOV is significantly explained by both hind limb length and fat mass relative to lean body mass, but not by extensor muscle mass relative to lean mass or fast-twitch fiber content. The effect of body fat mass is pervasive because it reduces the proportion of muscle mass/body mass and thus increases the muscle work invested in increasing the CM potential energy as compared with kinetic energy during takeoff.

Grandmother hypothesis and primate life histories

The adaptive significance of midlife menopause in human females has long engaged the attention of evolutionary anthropologists. In spite of extensive debate, the problem has only recently been examined in the context of primate life histories. Here I extend those investigations by comparing life history traits in 16 primate species to test predictions generated from life history theory. In humans, late ages of maturity and higher than expected birth rates are systematically associated with extended postmenopausal longevity. Links among these adjustments on the primate pattern can explain how selection could slow somatic senescence without favoring extension of the fertile span. This conclusion is consistent with the observation that our fertile spans are similar to those of other pongids. The shape of the argument herein demonstrates the utility of life history theory for solving problems of adaptive evolution in female life history traits, with consequences for broader arguments regarding human evolution.

Body mass in comparative primatology

Data are presented on adult body mass for 230 of 249 primate species, based on a review of the literature and previously unpublished data. The issues involved in collecting data on adult body mass are discussed, including the definition of adults, the effects of habitat and pregnancy, the strategy for pooling data on single species from multiple studies, and use of an appropriate number of significant figures. An analysis of variability in body mass indicates that the coefficient of variation for body mass increases with increasing species mean mass. Evaluation of several previous body mass reviews reveals a number of shortcomings with data that have been used often in comparative studies.

Limb bone allometry in primates: a test of the elastic similarity model

Morphometric data on postcranial elements of ten species of Old World primates are used to test the elastic similarity model of limb scaling. The data are divided into three groupings to exclude as much variation due to differences in locomotor adaptation as possible. The data on skeletal diameters fits the model reasonably well. The length results, however, are generally not in conformity with the model's predictions.