No abstract is provided for this article.
Population dynamics and evolutionary change are linked by the fundamental biological processes of birth and death. This means that population growth may correlate with the strength of selection, whereas evolutionary change can leave an ecological signature. We decompose population growth in an age-structured population into contributions from variation in a quantitative trait. We report that the distribution of body sizes within a population of Soay sheep can markedly influence population dynamics, accounting for up to one-fifth of observed population growth. Our results suggest that there is substantial opportunity for evolutionary dynamics to leave an ecological signature and visa versa.
The current decline of the highly endangered African wild dog (Lycaon pictus) may be partly due to the population dynamics induced by their social system. African wild dogs are obligate co-operators, and their need for helpers could generate inverse density dependence at the pack level. We show, through a mathematical model, that this can create an Allee effect, leading to a lower population size and a higher risk of population extinction, compared to populations with direct density dependence. This is due to three different processes. All three processes can increase population extinction individually and probably occur simultaneously in African wild dogs. First, inverse density dependence causes significantly higher rates of pack extinction. Second, it also increases the probability of failure to colonize territories by founders. Third, the Allee effect at the pack level (with a critical number of individuals), generates an Allee effect at the population level (with a critical number of packs). These three processes are likely to apply to other obligate co-operative breeders. Furthermore, our results suggest that habitat fragmentation and destruction, as well as increased human pressure, increase the effects of inverse density dependence. Direct and indirect anthropogenic effects may thus be more detrimental to obligate co-operative breeders than to other species.
"Pharmacokinetics of Three Commercial Antivenoms in Patients Envenomed by the Malayan Pit Viper, Calloselasma Rhodostoma, in Thailand" published on Mar 1990 by The American Society of Tropical Medicine and Hygiene.
No abstract is provided for this article.
Although differences in breeding lifespan are an important source of variation in male fitness, the factors affecting the breeding tenure of males have seldom been explored. Here, we use cross-species comparisons to investigate the correlates of breeding lifespan in male mammals. Our results show that male breeding lifespan depends on the extent of polygyny, which reflects the relative intensity of competition for access to females. Males have relatively short breeding tenure in species where individuals have the potential to monopolize mating with multiple females, and longer ones where individuals defend one female at a time. Male breeding tenure is also shorter in species in which females breed frequently than in those where females breed less frequently, suggesting that the costs of guarding females may contribute to limiting tenure length. As a consequence of these relationships, estimates of skew in male breeding success within seasons overestimate skew calculated across the lifetime and, in several polygynous species, variance in lifetime breeding success is not substantially higher in males than in females.
At the recent Financial Times Conference on Telecommunications and the European Business Market: the Perspectives for Change, two of the contributors examined the question of whether companies should “make” their own private telecommunications network, or “buy” a publicly-offered service. The topic is not only interesting as a case study of “make or buy”, but is especially timely in the specific field of telecommunications in Europe. In June 1987, the European Commission issued its Green Paper on telecommunications liberalisation and rationalisation of Europe's equipment manufacturers. Current difficulties include national regulatory powers, cross subsidies, lack of common standards, and lack of agreement on standards, frequencies and tariff principles. Not least, rapid changes in the technology itself has turned telecommunications into a Strategic competitive asset for companies. The two authors of these articles argue from slightly different perspectives; White as a major user developing into a provider, and Wilson as an adviser and provider. Both are convinced that the make or buy decision is an over-simplification; there are other, intermediate, options. Both agree that which ever decision is taken, it is likely to be the most important one in information technology that companies make in the next few years.
