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Resource Value (resource + value)
Selected AbstractsEffects of Predation Threat on the Structure and Benefits from Vacancy Chains in the Hermit Crab Pagurus bernhardusETHOLOGY, Issue 11 2009Mark Briffa Vacancy chains occur when individuals occupy discrete re-useable resource units, which once abandoned by the current owner can then be occupied by a new owner. In order to enter the newly vacated resource the new owner must first vacate its current resource unit, such that a vacancy chain consists of a series of linked moves between resource units of different value, equivalent to different ,strata' in the chain. Vacancy chains may represent an important route by which resources are distributed through populations. Indeed, the arrival of a new resource has the potential to initiate a series of moves propagating beyond the individual that encounters the new resource unit. Thus, the chain participants as a whole may experience ,aggregate benefits' from the arrival of the new resource unit. The extent of these benefits, however, may not necessarily be evenly distributed between all chain participants; some individuals could receive greater than average benefits by moving through more than one stratum (,skipping') and some individuals could experience a reduction in resource value by moving to a resource unit of lower quality than that occupied initially (a ,backward move'). Such moves represent deviations from the ,ideal' vacancy chains assumed by theory. Here we analyse the aggregate benefits and benefits to individuals participating in vacancy chains of empty gastropod shells in the hermit crab Pagurus bernhardus. We also investigate the effect of predation risk on these two levels of benefits and on chain structure. Adding a new shell at the top of the chain causes an overall increase in shell quality after 24 h but the distribution of benefits between strata in the chain varies with the presence and absence of the predator cue. Although there was significant concordance between chain structure in the presence and absence of the predator cue, the structure was significantly different from an ideal vacancy chain in the absence but not the presence of the predator cue. [source] Does Host Value Influence Female Aggressiveness, Contest Outcome and Fitness Gain in Parasitoids?ETHOLOGY, Issue 4 2007Marlene Goubault Intraspecific competition for resources is common in animals and may lead to physical contests. Contest outcomes and aggressiveness can be influenced by the resource holding potential of contestants but also by their perception of the resource value (RV). Competitors may assess resource quality directly (real RV) but may also estimate it according to their physiological status and their experience of the habitat quality (subjective RV). In this article, we studied contests between females of the solitary parasitoid Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae) when exploiting simultaneously a host, a Delia radicum L. (Diptera: Anthomyiidae) pupa. We tested the effect of factors modifying host value on the occurrence of agonistic behaviours, contest outcomes and host exploitation. The factors tested were: the quality of the previous habitat experienced by females, female egg load, host parasitism status and the stage reached by the owner female in her behavioural oviposition sequence. Females successfully protected their host against intruders during its exploitation, but not after oviposition, and their aggressiveness did not seem to be influenced by their perception of the RV. The fact that the host is subsequently parasitized by the opponent females appears to mainly depend on the host selectiveness of females. [source] Male Competition over Access to Females in a Spider with Last-Male Sperm PrecedenceETHOLOGY, Issue 5 2003Daniela Schaefer Agonistic behaviour between male cellar spiders (Pholcus phalangioides) was investigated to test whether (1) size difference determines which male achieves access to the female, (2) males are able to monopolize access to the female until egg laying and whether (3) female resource value increases before egg laying because of last-male sperm precedence. We further investigated whether (4) there is variation in time and energy spent on courtship and copulation depending on the degree of sperm competition, i.e. with or without rival present. In three experimental settings we introduced two males of either different or similar sizes, or a single male to a female. The mating units were constantly video-observed until the females produced their first egg sac. Experience, ownership and female resource value in terms of body size was controlled. Our results show that larger males achieve almost exclusive access to females. Size symmetrical settings resulted in increased fighting activity and duration but dominance did not influence mating success. If copulations were disturbed by the rival male, copulations were terminated earlier in symmetrical settings compared with asymmetrical settings. In 94.8% of trials only one copulation took place, suggesting that the copulating male successfully monopolized access to the female. Males confronted with a rival copulated longer but courted significantly shorter than lone males. Although the last male to copulate sires 88% of the offspring in P. phalangioides, neither fighting nor courtship activity increased before the female laid a batch of eggs. This suggests that males have no indication of the timing of oviposition. [source] Male,male combats in a polymorphic lizard: residency and size, but not color, affect fighting rules and contest outcomeAGGRESSIVE BEHAVIOR, Issue 3 2009Roberto Sacchi Abstract Theoretical models predict that the outcome of dyadic agonistic encounters between males is influenced by resource-holding potential, resource value, and intrinsic aggressiveness of contestants. Moreover, in territorial disputes residents enjoy a further obvious competitive advantage from the residency itself, owing to the intimate familiarity with their territory. Costs of physical combats are, however, dramatically high in many instances. Thus, signals reliably reflecting fighting ability of the opponents could easily evolve in order to reduce these costs. For example, variation in color morph in polymorphic species has been associated with dominance in several case studies. In this study, we staged asymmetric resident-intruder encounters in males of the common wall lizard Podarcis muralis, a species showing three discrete morphs (white, yellow, and red) to investigate the effects of asymmetries in color morph, residency, and size between contestants on the outcome of territorial contests. We collected aggression data by presenting each resident male with three intruders of different color morph, in three consecutive tests conducted in different days, and videotaping their interactions. The results showed that simple rules such as residency and body size differences could determine the outcome of agonistic interactions: residents were more aggressive than intruders, and larger males were competitively superior to smaller males. However, we did not find any effect of color on male aggression or fighting success, suggesting that color polymorphism in this species is not a signal of status or fighting ability in intermale conflicts. Aggr. Behav. 35:274,283, 2009. © 2009 Wiley-Liss, Inc. [source] Paternity and social rank in wild chimpanzees (Pan troglodytes) from the Budongo Forest, UgandaAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010Nicholas E. Newton-Fisher Abstract We analyzed patterns of paternity and male dominance rank in the Sonso community of wild East African chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda. Our major objective was to determine whether and how social rank influenced paternity success. We successfully genotyped 52 individuals at up to nine microsatellite loci, using DNA extracted from fecal samples. Of 24 offspring analyzed, we identified sires for 21. Paternity success was significantly correlated with social rank, with alpha males siring a disproportionate number of offspring. However, both middle- and low-ranking males also fathered offspring, and the priority-of-access model provided a relatively poor prediction of which males would be successful and under what circumstances. The concentration of paternities among only seven males and the tendency for high-ranking males to sire offspring of multiparous females suggest that both individual variation in male quality and the resource value of particular females may be mediating factors. In comparison with other chimpanzee studies, our results support the hypothesis that larger male cohort size reduces the ability of the alpha male to monopolize females, though within our study, male number did not affect the success of the alpha. Successful sires were not necessarily those who achieved the highest mating success with the females whose offspring they sired, but were those who demonstrated higher investment by spending significantly more time in association with these females. Finally, we estimate extra-group paternity at 0,5%, supporting other evidence that the community serves as the primary reproductive unit in chimpanzees. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source] Local Participation in Natural Resource Monitoring: a Characterization of ApproachesCONSERVATION BIOLOGY, Issue 1 2009FINN DANIELSEN conservación; evaluación de la biodiversidad; esquemas de monitoreo; intereses locales; manejo de recursos naturales Abstract:,The monitoring of trends in the status of species or habitats is routine in developed countries, where it is funded by the state or large nongovernmental organizations and often involves large numbers of skilled amateur volunteers. Far less monitoring of natural resources takes place in developing countries, where state agencies have small budgets, there are fewer skilled professionals or amateurs, and socioeconomic conditions prevent development of a culture of volunteerism. The resulting lack of knowledge about trends in species and habitats presents a serious challenge for detecting, understanding, and reversing declines in natural resource values. International environmental agreements require signatories undertake systematic monitoring of their natural resources, but no system exists to guide the development and expansion of monitoring schemes. To help develop such a protocol, we suggest a typology of monitoring categories, defined by their degree of local participation, ranging from no local involvement with monitoring undertaken by professional researchers to an entirely local effort with monitoring undertaken by local people. We assessed the strengths and weaknesses of each monitoring category and the potential of each to be sustainable in developed or developing countries. Locally based monitoring is particularly relevant in developing countries, where it can lead to rapid decisions to solve the key threats affecting natural resources, can empower local communities to better manage their resources, and can refine sustainable-use strategies to improve local livelihoods. Nevertheless, we recognize that the accuracy and precision of the monitoring undertaken by local communities in different situations needs further study and field protocols need to be further developed to get the best from the unrealized potential of this approach. A challenge to conservation biologists is to identify and establish the monitoring system most relevant to a particular situation and to develop methods to integrate outputs from across the spectrum of monitoring schemes to produce wider indices of natural resources that capture the strengths of each. Resumen:,El monitoreo de tendencias en el estatus de especies o hábitats es rutinario en los países desarrollados, donde es financiado por el estado o por grandes organizaciones no gubernamentales y a menudo involucra a grandes números de voluntarios amateurs competentes. El monitoreo de recursos naturales es menos intenso en los países en desarrollo, donde las agencias estatales tienen presupuestos pequeños, hay menos profesionales o amateurs competentes y las condiciones socioeconómicas limitan el desarrollo de una cultura de voluntariado. La consecuente falta de conocimientos sobre las tendencias de las especies y los hábitats presenta un serio reto para la detección, entendimiento y reversión de las declinaciones de los recursos naturales. Los tratados ambientales internacionales requieren que los signatarios realicen monitoreos sistemáticos de sus recursos naturales, pero no existe un sistema para guiar el desarrollo y la expansión de los esquemas de monitoreo. Para ayudar al desarrollo de tal protocolo, sugerimos una tipología de categorías de monitoreo, definidas por el nivel de participación local, desde ningún involucramiento local con el monitoreo realizado por investigadores profesionales hasta un esfuerzo completamente local con el monitoreo llevado a cabo por habitantes locales. Evaluamos las fortalezas y debilidades de cada categoría de monitoreo, así como su sustentabilidad potencial en países desarrollados o en desarrollo. El monitoreo basado localmente es particularmente relevante en los países en desarrollo, donde puede llevar a decisiones rápidas para resolver amenazas clave sobre sus recursos naturales, puede facultar a las comunidades locales para un mejor manejo de sus recursos naturales y puede refinar las estrategias de uso sustentable para mejorar la forma de vida local. Sin embargo, reconocemos que la precisión y exactitud del monitoreo llevado a cabo por comunidades locales en situaciones diferentes requiere de mayor estudio y los protocolos de campo requieren de mayor desarrollo para obtener lo mejor del potencial de este método. Un reto para los biólogos de la conservación es la identificación y establecimiento del sistema de monitoreo más relevante para la situación particular, así como el desarrollo de métodos para integrar los resultados de una gama de esquemas de monitoreo para producir índices de recursos naturales más amplios que capturen las fortalezas de cada uno. [source] Challenging Neo-Malthusian Deforestation Analyses in West Africa's Dynamic Forest LandscapesPOPULATION AND DEVELOPMENT REVIEW, Issue 1 2000Melissa Leach Many influential analyses of West Africa take it for granted that ,original' forest cover has progressively been converted and savannized during the twentieth century by growing populations. By testing these assumptions against historical evidence, exemplified for Ghana and Ivory Coast, this article shows that these neo-Malthusian deforestation narratives badly misrepresent people,forest relationships. They obscure important nonlinear dynamics, as well as widespread anthropogenic forest expansion and landscape enrichment. These processes are better captured, in broad terms, by a neo-Boserupian perspective on population,forest dynamics. However, comprehending variations in locale-specific trajectories of change requires fuller appreciation of social differences in environmental and resource values, of how diverse institutions shape resource access and control, and of ecological variability and path dependency in how landscapes respond to use. The second half of the article présents and illustrates such a "landscape structuretion" perspective through case studies from the forest,savanna transition zones of Ghana and Guinea. [source] | ||||||||||