Tephrochronology

Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly

Optimal foraging and fitness in Columbian ground squirrels

Optimal diets were determined for each of 109 individual Columbian ground squirrels ( Spermophilus columbianus ) at two sites in northwestern Montana. Body mass, daily activity time, and vegetation consumption rates for individuals were measured in the field, along with the average water content of vegetation at each ground squirrel colony. I also measured stomach and caecal capacity and turnover rate of plant food through the digestive tract for individuals in the laboratory to construct regressions of digestive capacity as a function of individual body mass. Finally, I obtained literature estimates of average daily energy requirements as a function of body mass and digestible energy content of vegetation. These data were used to construct a linear programming diet model for each individual. The model for each individual was used to predict the proportion of two food types (monocots and dicots) that maximized daily energy intake, given time and digestive constraints on foraging. Individuals were classified as “optimal” or “deviating”, depending on whether their observed diet was significantly different from their predicted optimal diet. I determined the consequences of selecting an optimal diet for energy intake and fitness. As expected, daily energy intake calculated for deviators (based on their observed diet proportion) was less than that for optimal foragers. Deviating foragers do not appear to compensate for their lower calculated energy intake through other factors such as body size or physiological efficiency of processing food. Growth rate, yearly survivorship, and litter size increase with calculated energy intake, and optimal foragers have six times the reproductive success of deviators by age three. Optimal foraging behavior, therefore, appears to confer a considerable fitness advantage.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47783/1/442_2004_Article_BF00318534.pd

Sociality of Columbian ground squirrels in relation to their seasonal energy intake

Seasonal energy intake was estimated for ten populations of Columbian ground squirrels ( Spermophilus columbianus ) in northwestern Montana. We calculated daily energy intake for an average ground squirrel in each population using measurements of feeding time, consumption rates of different vegetation types (monocots vs. dicots), and the proportion of monocots and dicots in the diet. These daily energy intakes were multiplied by the length of the plant growing season for each population to estimate seasonal energy intake, i.e. over the ground squirrel active season. Amicable interaction rates measured for each population varied with seasonal energy intake, but not with environmental heterogeneity, sex ratio, or the ratio of adults to juveniles. In particular, amicable interactions among adult-juvenile and juvenile-juvenile pairs increased as seasonal energy intake decreased. The proportion of females breeding as yearlings increased as seasonal energy intake increased. This suggests that “harsh” environments reduce the energy available for juvenile growth and development, leading to delayed dispersal and age at first reproduction. These responses may promote the formation of kin groups and increased amicable interactions within those groups. The length of the plant growing season may determine environmental “harshness” across elevational gradients, but at a particular elevation, “harshness” may depend on factors determining daily food intake.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47787/1/442_2004_Article_BF00317200.pd

Repairing broken trust between leaders and followers: How violation characteristics temper apologies

This study examines the conditions under which apologies help to elicit forgiveness and restore trust following trust violations between leaders and followers. The intentionality and severity of violations are examined in a critical incident study and a laboratory study. The results support a model in which forgiveness mediates the relation of apology quality and trust. More importantly, the moderation–mediation model shows that apology quality influenced forgiveness and subsequent trust following violations that were moderate in severity–intentionality combination. The effect of apologizing affects trust directly without forgiveness when the severity–intentionality combination held minor or extreme intensity. The results suggest a range in which apologies are effective and enrich understanding of the conditions under which trust can be recovered through an apology–forgiveness process in leader–follower relationships. The contribution of the study lies in elucidating that the combination of severity and intentionality of leaders’ trust violations has greater importance than either one separately