Adaptive sex allocation by brood reduction in antechinuses

Antechinuses (Dasyuridae: Marsupialia) exhibit dramatic interpopulation variation in the sex ratio at birth, a pattern which has previously been interpreted in terms of both local resource competition and Trivers/Willard effects. However, Antechinus stuartii usually fail to wean all the young that attach to their teats. At least in captivity, this is because they often eat their young. In free-living populations, brood reduction affects sons and daughters differently. Mothers virtually always wean some daughters. The probability that a daughter will be weaned declines with the number of daughters in the pouch. The health or quality of the mother does not affect the number of daughters weaned. By contrast, mothers tend to wean all or none of their sons. A strong correlate of infanticide against sons is senescence. Old mothers rarely invest in sons, and produce low-quality daughters. Mothers suffer a direct cost (mortality during lace lactation) of male-biased litters. Coupled with data on prenatal sex allocation, these results support the conjoint influence of local resource competition and the Trivers-Willard effect. However, they suggest that in populations where females are largely semelparous, the population optimum generated by local resource competition may be unattainable, because of the importance of producing at least one daughter. These observations support recent theoretical claims that the sex ratio at the population level is not easily predicted, but suggest that the diversity of mammalian sex allocation tactics has been underestimated.     

Responses of pikas (Ochotona princeps,Lagomorpha) to naturally occurring terrestrial predators

Summary The responses of individually marked pikas (Ochotona princeps) to terrestrial predators were investigated in 1980 and 1981 in the Rocky Mountains of Colorado. Pikas uttered short call vocalizations in a variety of contexts: preceding or following an individual's movement, and in response to conspecifics, other nonpredaceous mammals and predators. Adult pikas apparently discriminated contexts in which predators were present by short calling more frequently and for longer duration compared with calling in nonpredator contexts. Short calls uttered by juveniles were similar in all contexts.Adults responded differently to two types of terrestrial predators: weasels and pine martens. Pikas called less frequently in response to weasels than to martens and avoided weasels more often than martens. They delayed the initiation of calling following the first sighting of a weasel more often than to martens. Weasels were determined to be more effective predators of pikas than martens, and these asymmetries in behavior and alarm vocalizations may indicate that responses reduce an individual's risk of predaton by weasels.Both male and female pikas called in response to predators, and residents called more often than nonresidents. The possible function of predator-related vocalization in pikas is discussed. It is suggested that calls to predators may function to warn local residents, which in pikas are usually closely related.     

Impacts of Dams on Flow Regimes in Three Headwater Subbasins of the Columbia River Basin,United States1

Moore, Johnnie N., Alicia S. Arrigoni, and Andrew C. Wilcox, 2012. Impacts of Dams on Flow Regimes in Three Headwater Subbasins of the Columbia River Basin, United States. Journal of the American Water Resources Association (JAWRA) 48(5): 925‐938. DOI: 10.1111/j.1752‐1688.2012.00660.x Abstract: We compared long‐term changes in flow regimes resulting from climate change with those resulting from dams in three matched pairs of natural and modified headwater subbasins of the Columbia River. Based on the analysis of 12 flow‐regime metrics, we found that damming had minimal effect on most quantity of flow metrics, but major effect on timing of flow metrics, especially those representing “spring runoff.” In all modified subbasins, “spring runoff” metrics occurred much earlier than natural flow (up to ～44 days earlier for April‐July flows). Storage capacity modulated the magnitude of timing of flow‐metric changes, with the largest storage capacity leading to the most change. However, even in subbasins with low storage capacity, we found significant change in most timing of flow metrics. We also found that damming, especially in subbasins with higher storage capacity, overwhelmed climate variability in all basins for most flow metrics. This shows that reservoir operations need to be modified to more closely match the natural timing of flow regimes to promote positive ecologic response in modified rivers, even in basins where quantity of flow metrics have not changed substantially as a result of damming.