New Individuals (new + individual)

Distribution by Scientific Domains

Selected Abstracts

Dempster,Shafer models for object recognition and classification

A.P. Dempster
We consider situations in which each individual member of a defined object set is characterized uniquely by a set of variables, and we propose models and associated methods that recognize or classify a newly observed individual. Inputs consist of uncertain observations on the new individual and on a memory bank of previously identified individuals. Outputs consist of uncertain inferences concerning degrees of agreement between the new object and previously identified objects or object classes, with inferences represented by Dempster,Shafer belief functions. We illustrate the approach using models constructed from independent simple support belief functions defined on binary variables. In the case of object recognition, our models lead to marginal belief functions concerning how well the new object matches objects in memory. In the classification model, we compute beliefs and plausibilities that the new object lies in defined subsets of an object set. When regarded as similarity measures, our belief and plausibility functions can be interpreted as candidate membership functions in the terminology of fuzzy logic. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 283,297, 2006. [source]

Comparative dynamics of gestalt odour formation in two ant species Camponotus fellah and Aphaenogaster senilis (Hymenoptera: Formicidae)

Alain Lenoir
Abstract. Ant colonies experience continuous shifts in worker populations, which may affect odour composition in the nest. A major question regarding the dynamics of gestalt formation is that of the speed at which the scent of a new individual will be incorporated into the gestalt. It is predicted from the gestalt model of colony odour that workers have to exchange recognition cues continuously to maintain themselves within the gestalt and become well integrated within their colony. Using radioactive tracers the rates of transfer were measured between a labelled donor ant and one or 10 recipient ants, as a close approximation to the within-nest situation. The labelled hydrocarbons were first transferred to a small number of individuals and progressively to all the individuals of the group so that the distribution of hydrocarbon transfer rate approached a normal distribution. Furthermore, in Camponotus fellah Dalla Torre, which performs trophallaxis, homogeneity was reached more rapidly than in Aphaenogaster senilis Mayr, which does not show this behaviour. In the latter species, the gestalt seems to be maintained mainly by allogrooming. These experiments were accompanied by behavioural observations to ascertain the respective importance of trophallaxis and allogrooming in the behavioural time-budget of the ants. In A. senilis, allogrooming was more frequent than in ants that trophallax, which corroborates the role of allogrooming in the establishment of the gestalt in this species. [source]

Habitat selection as a source of inter-specific differences in recruitment of two diadromous fish species

Summary 1For aquatic species with highly dispersive offspring, the addition of new individuals into an area (recruitment) is a key process in determining local population size so understanding the causes of recruitment variability is critical. While three general causative mechanisms have been identified (the supply of individuals, habitat selection and mortality), we have a limited understanding of how variation in each is generated, and the consequences this may have for the spatial and temporal distribution of recruits. 2We examined whether active habitat selection during settlement could be the cause of variability in populations of two diadromous fish species using a field survey and laboratory-based choice experiments. If larval behaviour is important, we predicted there would be inter-specific differences in abundance between sites during the survey, and that larvae would prefer water collected from sites with higher conspecific abundances during the experiments. 3During the field survey, significant differences were detected between two rivers (the Cumberland and Grey), with one species (Galaxias maculatus) found in higher abundances at one site (the Cumberland River) while comparable numbers of a closely related species (Galaxias brevipinnis) were caught at both sites. Laboratory choice experiments were conducted to determine whether larval preferences during settlement could be the cause of these differences. G. maculatus larvae showed a preference for freshwater over saltwater, indicating that the fish may be responding to reduced salinities around river mouths during settlement. The results of a second experiment were consistent with the notion that larval preferences could be the mechanism driving differences in the populations of the two rivers, with G. maculatus preferring water collected from the Cumberland River while G. brevipinnis did not prefer water from either river. 4These results demonstrate that active habitat selection may be important in establishing spatial patterns of larvae at settlement, and that multiple cues are likely to be involved. This study also demonstrates that the behaviours exhibited by individuals can strongly influence the structure and dynamics of populations of aquatic species with complex life cycles. [source]


S. L. Kong
Recruitment, the entry of new individuals into a population, was investigated by a clearing experiment along the shore of A Ma Wan (AMW) in Ping Chau, Hong Kong SAR, China. Two types of clearing, with all the existing vegetation removed (cleared) and with the top 2 to three mm of the rock surface removed (hammered), were carried out monthly in AMW from November 1997 to June 1999. Observations were made one month after clearing and on a monthly basis thereafter. The number of algal species present on the cleared areas and their percentage cover were recorded. The experimental results showed that more algal species were recruited during March and April in 1998 (n=10) but in 1999, the number of species was found higher in February and March (n=8). Species richness dropped after May (more obvious in 1998), indicating that recruitment greatly declined in summer. A tuft complex composed of several filamentous algal species dominated over the others in all clearing areas (coverage mostly over 90%) but recruits of Caulerpa peltata, Colpomenia sinuosa, Enteromorpha sp., Hypnea charoides, Padina spp., Sargassum sp., Spyridia filamentosa, Ulva sp., etc. also were observed during the study period. Generally, there were no significant differences in terms of species richness and composition of the recruits between the two treatments (cleared vs. hammered) as well as with the controls. This implied that algae in AMW were more likely to be recruited de novo from elsewhere rather than regenerated from remnants of the previous year's growth. [source]

Metapopulation dynamics across gradients , the relation between colonization and extinction in shaping the range edge

OIKOS, Issue 10 2009
Beáta Oborny
We study the dynamics of a metapopulation in which the rates of colonization and/or extinction change along an environmental gradient. Spatially explicit simulations are applied to compare two cases: in parent-dependent colonization (PDC) the rate of colonization is limited by the production of new individuals; in offspring-dependent colonization (ODC) it is limited by the success of establishment of the offspring. Thus, PDC depends on the quality of the parent's site, while ODC is dependent on the offspring's site. We combine PDC and ODC in a spatially implicit model. We study the steady-state distribution of a metapopulation, and ask whether the local densities of occupied sites at each position x along the gradient could be predicted from the local rates of colonization c(x) and extinction e(x). This prediction is not trivial, since the sites are connected, enabling a flow of individuals from more favorable to less favorable sites. The results show that at ODC a single parameter, c(x)/e(x), is sufficient for the prediction. Therefore, different species and geographic regions can be directly compared by appropriate rescaling: choosing the local average lifetime of occupancy, 1/e(x), for a time unit at each point along the gradient. This permits generalizations about the shape of range edges, and can help to predict the position of the boundary of a species' distribution. At PDC, rescaling is not possible: the whole profile of c(x) and e(x) along the gradient has to be taken into consideration. Nevertheless, rescaling gives a good approximation when the parent-dependent component of colonization does not change abruptly across space. [source]

Reestablishment of the Southern California Rocky Intertidal Brown Alga, Silvetia compressa: An Experimental Investigation of Techniques and Abiotic and Biotic Factors That Affect Restoration Success

Stephen G. Whitaker
Previous research has indicated that many rocky intertidal macrophyte communities in southern California, and other locations around the world, have shifted from larger, highly productive, fleshy seaweeds toward a smaller, less productive, disturbance-tolerant flora. In widespread decline are ecologically important, canopy-forming, brown seaweeds, such as the southern California rockweed species Silvetia compressa. Restoration efforts are common for depleted biogenic species in other habitats, but restoration within rocky intertidal zones, particularly on wave-exposed coasts, has been largely unexplored. In two phases, we attempted to restore Silvetia populations on a southern California shore by transplanting live plants and experimentally investigating factors that affect their survival. In Phase I, we implemented a three-way factorial design where juvenile Silvetia thalli were transplanted at four sites with a combination of simulated canopy and herbivore exclusion treatments. Transplant survival was low, although enhanced by the presence of a canopy; site and herbivore presence did not affect survival. In Phase II, we used a two-way factorial design, transplanting two size classes of rockweeds (juveniles and reproductive adults) on horizontal and partially shaded, north-facing vertical surfaces at a target location where this rockweed has been missing since at least the 1970s. Transplant survival was moderate but lower than natural survival rates. Larger thalli exhibited significantly higher survival rates than smaller thalli in both the transplanted and naturally occurring populations, particularly on vertical surfaces. Higher mortality on horizontal surfaces may have been due to differences in desiccation stress and human trampling. Transplanting reproductive adults resulted in the subsequent recruitment of new individuals. [source]