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This book takes a fresh approach to some of the classic questions in ecology. In particular, what determines where a species lives and what determines its abundance? Despite great progress in the twentieth century much more remains to be done before we can provide full answers to these questions so that reliable predictions can be made as to what will be found in unstudied areas or times. We believe that the methods described and deployed in this book point the way forward. The core message of the book is that key insights come from understanding what determines population growth rate (pgr). We believe that application of this approach will make ecology a more predictive science.
No abstract is provided for this article.
No abstract is provided for this article.
In cooperatively breeding birds, where helpers of both sexes assist with the provisioning and upbringing of offspring who are not their own, males tend to contribute more than females to rearing young. This sex difference has been attributed to paternity uncertainty, but could also occur because males contribute more where they are likely to remain and breed in their group of origin. In contrast to most birds, female meerkats ( Suricata suricatta ) are more likely to breed in their natal group than males. We show that female meerkat helpers contribute more to rearing young than males and that female helpers feed female pups more frequently than males. Our results suggest that sex differences in cooperative behavior are generated by sex differences in philopatry and occur because females derive greater direct benefits than males from raising recruits to their natal group. These findings support the view that direct, mutualistic benefits are important in the evolution of specialized cooperative behavior.
Temporal changes in phenological traits arising as a consequence of recent rapid environmental change have been widely demonstrated in animal populations. Increasingly, studies are seeking to understand the impact of changes in such traits on individual fitness and population dynamics, with the ultimate aim of predicting population persistence or extinction under different climate scenarios. Here, we examined the effects of environmental change on maternal reproductive traits in a wild population of red deer ( Cervus elaphus ) and sought to explain why, despite a rapid advance in offspring birth dates, we observed no apparent consequences for offspring fitness. By using path analysis, we identified both direct and indirect paths along which changes in environmental conditions affected birth date, birth mass, juvenile survival, and female fecundity. In general, warmer temperatures were associated with earlier birth dates and greater birth mass, and higher rainfall was associated with reduced juvenile survival and reduced female fecundity. We also examined concurrent effects of population density, maternal age, and reproductive history, and found that temporal stasis in average trait values, at least in part, could be explained by antagonistic roles of direct and indirect effects of changing climate and increasing population density. Identification of the many mechanisms that contribute to the dynamics of phenotypic traits is challenging; this study demonstrates the need to consider both climatic and demographic variation in order to understand the fitness consequences of changes in phenological traits.
Measures of glucocorticoid stress hormones (e.g. cortisol) have often been used to characterize conflict between subordinates and dominants. In cooperative breeders where subordinates seldom breed in their natal group and assist in offspring rearing, increases in subordinate glucocorticoid levels may be caused by conflict among subordinates as well as by the energetic costs of helping behavior and fluctuations in food availability may exacerbate these effects. During a 6-year study of Kalahari meerkats (Suricata suricatta), we investigated how social, environmental, and individual characteristics influenced subordinate plasma cortisol levels. Subordinate females, who are often the target of aggression from dominant females, had higher cortisol levels when the dominant female in their group was pregnant while the cortisol levels of subordinate males were unaffected by the reproductive state of dominant females. Subordinates of both sexes had higher cortisol levels if they belonged to groups 1) where neither of the dominant breeders in the group were their parents, 2) that contained a high proportion of subordinate females, or 3) that were either very large or very small, especially when the weather was cold and dry. Subordinates in groups containing young pups had higher cortisol levels. Finally, cortisol levels were higher in subordinates of both sexes if they were lighter for their age or had lost little body mass the night prior to sampling. Our results show that both social conflict and cooperative behavior can elevate glucocorticoid levels in subordinates and that both effects can be modified by variation in weather and food availability.
The Allee effect describes a scenario in which populations at low numbers are affected by a positive relationship between population growth rate and density, which increases their likelihood of extinction. The importance of this dynamic process in ecology has been under-appreciated and recent evidence now suggests that it might have an impact on the population dynamics of many plant and animal species. Studies of the causal mechanisms generating Allee effects in small populations could provide a key to understanding their dynamics.
There is no information and therefore no consensus on how chloroquine should be administered to persons with severe malaria. Although widely considered dangerous, parenteral chloroquine is extensively used. We studied the acute disposition and toxicity of intravenous (iv), intramuscular (im), subcutaneous (sc), and oral chloroquine in 60 adult Zambian patients hospitalized with falciparum malaria. Plasma concentration profiles after parenteral administration were characterized by wide fluctuations between peak and trough values. Absorption of im and sc chloroquine was rapid, with a median time to peak concentration of 30 min and a peak plasma concentration five times higher than after oral administration. The pharmacokinetic data suggest that the acute toxicity of parenteral chloroquine is related to transiently high concentrations in blood and result from incomplete distribution out of a relatively small central compartment. Parenteral chloroquine may be administered safely by simply giving smaller, more-frequent doses than are currently used or, in the case of iv administration, by using continuous infusion.
