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Low Fecundity (low + fecundity)
Selected AbstractsMating Effort and Cryptic Sperm Choice in Scorpionflies: Male Investment Strategy vs.ETHOLOGY, Issue 12 2008Female Control In this study, we examined which sex controls sperm transfer during copulation in scorpionflies. Therefore male scorpionflies were doubly mated to females of high and low fecundity to explore whether they allocate sperm according to female quality. While mating order had no effect males transferred sperm at higher rates when mating with low-quality instead of high-quality females. As there is no obvious benefit from providing low-fecundity females with more sperm, we suggest a condition-dependent female ability to counteract sperm transfer. Therefore, we disabled females at the beginning of copulations using the insecticide Propoxur which leads to total paralysis caused by tremors. While the provoked muscle contractions led to significantly smaller numbers of sperm transferred, Propoxur treatment had no effect on males. We suggest female counteracting of sperm transfer to be adaptive by decreasing the relative amount of sperm transferred by low-quality males and increasing the proportion of offspring sired by high-quality males. [source] Adaptation, migration or extirpation: climate change outcomes for tree populationsEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 1 2008Sally N. Aitken Abstract Species distribution models predict a wholesale redistribution of trees in the next century, yet migratory responses necessary to spatially track climates far exceed maximum post-glacial rates. The extent to which populations will adapt will depend upon phenotypic variation, strength of selection, fecundity, interspecific competition, and biotic interactions. Populations of temperate and boreal trees show moderate to strong clines in phenology and growth along temperature gradients, indicating substantial local adaptation. Traits involved in local adaptation appear to be the product of small effects of many genes, and the resulting genotypic redundancy combined with high fecundity may facilitate rapid local adaptation despite high gene flow. Gene flow with preadapted alleles from warmer climates may promote adaptation and migration at the leading edge, while populations at the rear will likely face extirpation. Widespread species with large populations and high fecundity are likely to persist and adapt, but will likely suffer adaptational lag for a few generations. As all tree species will be suffering lags, interspecific competition may weaken, facilitating persistence under suboptimal conditions. Species with small populations, fragmented ranges, low fecundity, or suffering declines due to introduced insects or diseases should be candidates for facilitated migration. [source] The ecology and evolutionary endocrinology of reproduction in the human femaleAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue S49 2009Virginia J. Vitzthum Abstract Human reproductive ecology (HRE) is the study of the mechanisms that link variation in reproductive traits with variation in local habitats. Empirical and theoretical contributions from biological anthropology, physiology, and demography have established the foundation necessary for developing a comprehensive understanding, grounded in life history theory (LHT), of temporal, individual, and populational variation in women's reproductive functioning. LHT posits that natural selection leads to the evolution of mechanisms that tend to allocate resources to the competing demands of growth, reproduction, and survival such that fitness is locally maximized. (That is, among alternative allocation patterns exhibited in a population, those having the highest inclusive fitness will become more common over generational time.) Hence, strategic modulation of reproductive effort is potentially adaptive because investment in a new conception may risk one's own survival, future reproductive opportunities, and/or current offspring survival. The hypothalamic-pituitary-ovarian (HPO) axis is the principal neuroendocrine pathway by which the human female modulates reproductive functioning according to the changing conditions in her habitat. Adjustments of reproductive investment in a potential conception are manifested in temporal and individual variation in ovarian cycle length, ovulation, hormone levels, and the probability of conception. Understanding the extent and causes of adaptive and non-adaptive variation in ovarian functioning is fundamental to ascertaining the proximate and remote determinants of human reproductive patterns. In this review I consider what is known and what still needs to be learned of the ecology of women's reproductive biology, beginning with a discussion of the principal explanatory frameworks in HRE and the biometry of ovarian functioning. Turning next to empirical studies, it is evident that marked variation between cycles, women, and populations is the norm rather than an aberration. Other than woman's age, the determinants of these differences are not well characterized, although developmental conditions, dietary practices, genetic variation, and epigenetic mechanisms have all been hypothesized to play some role. It is also evident that the reproductive functioning of women born and living in arduous conditions is not analogous to that of athletes, dieters, or even the lower end of the "normal range" of HPO functioning in wealthier populations. Contrary to the presumption that humans have low fecundity and an inefficient reproductive system, both theory and present evidence suggest that we may actually have very high fecundity and a reproductive system that has evolved to be flexible, ruthlessly efficient and, most importantly, strategic. Yrbk Phys Anthropol 52:95,136, 2009. © 2009 Wiley-Liss, Inc. [source] Sources of variation in fecal cortisol levels in howler monkeys in belizeAMERICAN JOURNAL OF PRIMATOLOGY, Issue 7 2010Alison M. Behie Abstract High cortisol levels are known to cause low fecundity and increased mortality; thus, the prospect of using cortisol as a measure of population health is an exciting one. However, because so many factors can interact to influence cortisol release, it can be difficult to interpret what exactly is creating changes to cortisol levels. This study investigates variation in fecal cortisol levels in a population of black howlers (Alouatta pigra) from 350 fecal samples collected from 33 individuals in more than 4 years. A general linear mixed model revealed that cortisol varied significantly with fruit availability and contact with tourists. When fruit availability was low, cortisol increased, likely because when fruit availability is low monkeys eat less fruit, thus obtaining less sugar. This result may simply reflect cortisol's metabolic function of mobilizing glucose. It also indicates that these monkeys may be experiencing periods of food stress throughout the year, which was earlier thought to be minimal for a primarily folivorous species. Presence of tourists was the only other factor found to lead to high cortisol; with exposure to tourists increasing stress levels. These results highlight the importance of understanding how physiological factors can influence cortisol, making it easier to interpret results and determine the external social or ecological stressors that may increase cortisol. Am. J. Primatol. 72:600,606, 2010. © 2010 Wiley-Liss, Inc. [source] Life-history traits associated with fragmentation vulnerability of lizards in the Thousand Island Lake, ChinaANIMAL CONSERVATION, Issue 4 2009Y. Wang Abstract Following habitat fragmentation, the remnant faunal community will undergo a period of species loss or ,relaxation.' Theory predicts that species with particular life-history traits, such as a small population size, small geographical range, low fecundity and large body size, should be more vulnerable to fragmentation. In this study, we investigated the relationships between the above life-history traits and the fragmentation vulnerability index (the number of islands occupied) of five lizard species inhabiting recently isolated land-bridge islands in the Thousand Island Lake, China. Data on life-history traits were collected from field surveys (population density) and from the literature (body size, clutch size and geographical range size). The species,area relationships for lizards sampled from the mainland versus on the islands differed significantly (i.e. the number of species inhabiting islands was decreased relative to similar-sized areas on the mainland), indicating that species extinction has occurred on all of the study islands following isolation. For the fragmentation vulnerability index, model selection based on Akaike's information criterion identified natural density at mainland sites as the best correlate of vulnerability to fragmentation, supporting the hypothesis that rare species are most vulnerable to local extinction and will be lost first from fragmented landscapes. In contrast, there was little evidence for an effect of lizards' snout,vent length, clutch size or geographical range size on fragmentation vulnerability. Identification of species traits that render some species more vulnerable to fragmentation than others has important implications for conservation and can be used to aid direct management efforts. [source] Reef shark declines in remote atolls highlight the need for multi-faceted conservation actionAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010Nicholas A. J. Graham Abstract 1.The decline of large-bodied predatory species in the oceans is a concern both from a sustainability perspective and because such species can have important ecological roles. Sharks are particularly vulnerable to fishing as their life histories are characterized by late age at maturity, large body size, and low fecundity. 2.Substantial shark population declines have been documented for a number of coastal and pelagic systems, with high population abundance limited to a few remote locations. The relative abundance and composition of reef shark populations are assessed from 1975 to 2006 at a remote, largely uninhabited, group of atolls in the central Indian Ocean; the Chagos Archipelago. 3.Number of sharks observed per scientific dive declined from a mean of 4.2 in the 1970s to 0.4 in 2006, representing a decline of over 90%. Silvertip sharks displayed an increase in abundance from 1996, whereas blacktip and whitetip reef sharks were rarely encountered in 2006. 4.Poaching in the archipelago, is the most likely cause of these declines, highlighted by a number of illegal vessels containing large numbers of sharks arrested since 1996. The data highlight that shark populations, even in remote, otherwise pristine, marine areas, are vulnerable to distant fishing fleets, and a range of strategies will need to be used in concert for their conservation. Copyright © 2010 John Wiley & Sons, Ltd. [source] Managing global shark fisheries: suggestions for prioritizing management strategiesAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2005Michael J. Barker Abstract 1.Over the past two decades the number of fisheries targeting shark resources has increased dramatically. A combination of factors, including relatively slow growth rate, low fecundity and late age of maturity, result in low recovery rates from exploitation for most shark species. This, in turn, is reflected in the poor record of sustainability of shark fisheries. 2.One of the greatest challenges is to find a way to deal with the substantial levels of shark bycatch taken in many non-target fisheries. Poor general recording of shark landings and paucity of shark landing data at the species level also undermine the development of effective shark management strategies.3. This paper reviews the problems that must be faced worldwide if shark resources are to be managed sustainably and lays out a comprehensive set of prioritized management strategies to facilitate the sustainable management of global shark fisheries. It is acknowledged that the majority of sharks are harvested in developing countries and that the management of shark resources in developing and developed countries will need to incorporate different management strategies relevant to local socio-economic agendas. The management recommendations deal with methods to improve the global regulation of fisheries, ways to improve global conservation ethics and encourage active participation in management, as well as means by which specific management strategies may be implemented. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||