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Only Likely (only + likely)
Selected AbstractsMating signal partitioning in multi-species assemblages: a null model test using frogsECOLOGY LETTERS, Issue 3 2003Andrew A. Chek Abstract Competitive partitioning of ,community' signal space has long been suggested to underlie diversification of mating signals. Selection or competitive exclusion is expected to reduce overlap of signals, minimizing destructive interference or reducing mismating. We used null models backed by simulation of type I and II error rates to test for evidence of structuring within 11 frog advertisement call assemblages. Within three assemblages, we found significant over-dispersion and regularity-of-spacing in dominant frequency and in pulse rate, consistent with a signal interference hypothesis and signal confusion hypothesis, respectively. Observed partitioning could represent signal evolution or could result from selection on assemblage composition. Most assemblages showed no acoustic partitioning possibly because: (i) partitioning is more readily apparent in female preference, calling times or sites, rather than call attributes; (ii) assemblages have not yet accommodated recently arrived species, or are compositionally unstable so that acoustic accommodation cannot occur; and (iii) evidence of partitioning is only likely where the acoustic space is densely packed. [source] Constraints on recovery: using molecular methods to study connectivity of aquatic biota in rivers and streamsFRESHWATER BIOLOGY, Issue 4 2007JANE M. HUGHESArticle first published online: 2 MAR 200 Summary 1. The ,Field of Dreams Hypothesis' states ,if we build it, they will come', referring to the assumption that if habitats are restored, species will recolonise them. However, the ability of a species to recolonise a restored site will depend not only on the appropriate habitat being present, but also on the ability to get there. This is likely to depend on both the species' dispersal behaviour and the position of a site in the landscape. 2. Animals with good potential for dispersal are more likely to be able to disperse to newly restored sites. Similarly, sites in lowland streams with limited altitudinal differences between sites may be easier to reach than upstream sites. This is because upstream sites are connected to one another via lowland streams that have different characteristics and therefore may be difficult for animals to traverse. 3. In this paper, genetic data from a range of freshwater species that have been analysed in my laboratory are used to assess the importance of life cycle and position in the landscape (i.e. upland versus lowland streams) on connectivity patterns (and thus recolonisation potential) among populations. 4. In general, contemporary dispersal across catchment boundaries is negligible, except for aquatic insects with an adult flight stage. Dispersal among streams within catchments appears to be more limited than was predicted from knowledge on life histories, except for fish in lowland rivers and streams. 5. As predicted, dispersal of fish, crustaceans and molluscs among streams within catchments is significantly greater in lowland rivers than in upland streams. 6. Overall, these analyses suggest that, with the exception of most insects, and fishes in lowland rivers, natural recolonisation of restored sites is only likely from sites within the same stream. If a species has disappeared from the whole stream, then restoration of habitat alone may not be sufficient for its re-establishment. [source] Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainmentFRESHWATER BIOLOGY, Issue 2 2004Marc Schallenberg Summary 1. Wind-induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas-tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light-limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light-limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity. [source] Breeding performance, age effects and territory occupancy in a Bonelli's Eagle Hieraaetus fasciatus populationIBIS, Issue 2 2008JOSÉ A. MARTÍNEZ Bonelli's Eagle Hieraaetus fasciatus is one of the most endangered birds of prey in Europe. Despite mounting interest and research, several questions regarding the conservation implications of territory occupancy and site-dependent population regulation remain insufficiently explored for this species. Here, we report on a 12-year study of the territorial structure of a Bonelli's Eagle population in southeastern Spain. No signals of population decline were found in the breeding population, as mean annual productivity was stable and the presence of mixed-age pairs in the population decreased with the years. However, the average proportion of subadults occupying territories was larger than that observed in other Spanish populations. Contrary to the predictions of a despotic distribution model, we found no significant relationship between occupancy rates and breeding parameters. Our results showed significant variations in productivity attributable to differences in the quality of individuals (i.e. mixed versus adult pairs), but no variability among territories per se (i.e. caused by habitat heterogeneity). Moreover, coexistence with intraguild species did not have any significant effect on productivity, although the proximity of Eagle Owls Bubo bubo affected the occupation rate of territories. Finally, our population does not appear to experience site-dependent population regulation, as a positive relation between mean annual productivity and density was found. The threat posed by changes in land use in the study area leads us to suggest that strict protection of current territories is necessary to ensure population persistence, and we suggest that a significant population increase is only likely if new or deserted territories become available. [source] Expansionary Fiscal Shocks and the US Trade Deficit,INTERNATIONAL FINANCE, Issue 3 2005Christopher J. Erceg In this paper, we use a dynamic general equilibrium model of an open economy to assess the quantitative effects of fiscal shocks on the trade balance in the United States. We examine the effects of two alternative fiscal shocks: a rise in government consumption, and a reduction in the labour income tax rate. Our salient finding is that a fiscal deficit has a relatively small effect on the US trade balance, irrespective of whether the source is a spending increase or tax cut. In our benchmark calibration, we find that a rise in the fiscal deficit of 1 percentage point of gross domestic product (GDP) induces the trade balance to deteriorate by 0.2 percentage point of GDP or less. Noticeably larger effects are only likely to be elicited under implausibly high values of the short-run trade price elasticity, or of the share of liquidity-constrained households in the economy. From a policy perspective, our analysis suggests that even reducing the current US fiscal deficit (of 3% of GDP) to zero would be unlikely to narrow the burgeoning US trade deficit significantly. [source] Using data in legacy fundraising: a practical approachINTERNATIONAL JOURNAL OF NONPROFIT & VOLUNTARY SECTOR MARKETING, Issue 4 2009Nigel Magson Legacies provide a major source of income to charities, and their importance is only likely to increase with the passing on of the baby-boomer generation. Legacy fundraising is a long-term process, based on developing relationships with donors over time. Data have a key role to play in the development of these relationships, allowing legacy fundraisers to measure and track their donors, and to contribute to the development of effective fundraising strategies. This paper discusses the effective collection and use of data in legacy fundraising, from consolidating data, to analysing the results and building legacy targeting models. The authors discuss how these principles have been applied in UK-based charity, Help the Aged, in conjunction with their Data Agency, Tangible Data (formerly Talking Numbers) and to give practical advice on how they may be implemented in other organisations. Copyright © 2009 John Wiley & Sons, Ltd. [source] Deferred Harvests: The Transition from Hunting to Animal HusbandryAMERICAN ANTHROPOLOGIST, Issue 2 2001Michael S. Alvard We define animal husbandry as prey conservation. Conservation is rare among extant hunters and only likely to occur when prey are highly valued, private goods. The long-term discounted deferred returns from husbandry must also be greater than the short-term returns from hunting. We compare the returns from hunting and husbanding strategies as a function of prey body size. Returns from husbanding are estimated using a maximum sustainable yield (MSY) model. Following Charnov (1993), allometric analyses show that the MSY is nearly independent of prey body size. The opportunity costs of husbanding are measured as prey standing biomass times the discount rate. Since standing biomass scales positively with body size, the opportunity costs of husbanding are greater for larger animals. An evolutionary discount rate is estimated following Rogers (1994) to be between 2.4% and 6%. Using these values, the prey body size for which hunting and meat-only husbanding provide the same return is approximately 40kg. Animals greater than 40kg are predicted to be hunted, [animal husbandry, evolutionary ecology, allometry, hunting, Neolithic transition] [source] Rapid actions of oestrogen on gonadotropin-releasing hormone neurons; from fantasy to physiology?THE JOURNAL OF PHYSIOLOGY, Issue 21 2009Allan E. Herbison Oestradiol (E2) exerts critical homeostatic feedback effects upon gonadotropin-releasing hormone (GnRH) neurons to maintain fertility. In the female, E2 has both negative and positive feedback actions to suppress and stimulate GnRH neuron activity at different times of the ovarian cycle. This review summarizes reported rapid E2 effects on native embryonic and adult GnRH neurons and attempts to put them into a physiological perspective. Oestrogen has been shown to rapidly modulate multiple processes in embryonic and adult GnRH neurons including intracellular calcium levels, electrical activity and specific second messenger pathways, as well as GnRH secretion itself. Evaluation of in vivo data suggests that there is no essential role for rapid E2 actions in the positive feedback mechanism but that they may comprise part of the negative feedback pathway. Adult GnRH neurons are only likely to be exposed to E2 from the gonads via the circulation with appropriate physiological E2 concentrations in the rodent being 10,50 pm for negative feedback ranging up to 400 pm for positive feedback. Although most studies to date have examined the effects of supraphysiological E2 levels on GnRH neurons, there is accumulating evidence that rapid E2 actions may have a physiological role in suppressing GnRH neuron activity. [source] | |||||||||||||