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Spatial Isolation (spatial + isolation)
Selected AbstractsDistribution patterns of the Q and B biotypes of Bemisia tabaci in the Mediterranean Basin based on microsatellite variationENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2007B. Simón Abstract At least five of the biotypes described in the Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) complex are known to be present in the Mediterranean Basin area. Only two of them, however, are economically relevant, that is, biotypes B and Q. Biological and genetic differences between the two biotypes have been well studied, but less is known about their patterns of genetic variation and population structure. To address these issues, a study was undertaken based on variation at six microsatellite loci among a subset of nine B. tabaci populations (five belonging to the Q and four to the B biotype). The data obtained show that (i) these loci showed considerable polymorphism in the Q and B biotypes populations although the presence of null alleles can obscure the picture; (ii) the Iberian-Q, Canarian-Q, and Egyptian-B populations exhibit heterozygosity excess as a result of bottleneck events; (iii) the low genetic differentiation between the Israeli, Iberian Peninsula, and Italian populations suggest that these populations share a common gene pool; (iv) the genetic distances between the Canarian-Q population and the geographically close population from Morocco indicates spatial isolation and a limited gene flow; and finally (v) the microsatellite data for the B populations indicate that the whiteflies from Egypt and Israel have a close phylogenetic relationship, but the source of these biotype B invasions into the Mediterranean area remains unknown. [source] Responses of Snow Voles, Chionomys nivalis, Towards Conspecific Cues Reflect Social Organization during Overwintering PeriodsETHOLOGY, Issue 11 2002Juan J. Luque-Larena Among microtine rodents, reaction to chemical cues from conspecifics is assumed to reflect social and spatial relationships. Generally, strong attraction of particular odours correlates with non-aggressive behaviour and high spatial tolerance towards odour donors, whereas weak attraction correlates with greater levels of aggression and spatial segregation. In the present study, we examined whether winter odour preferences of the snow vole Chionomys nivalis, a rock-dwelling microtine principally found at high-mountainous regions, differ from that of other vole species, owing to their different social organization during overwintering periods. The social structure of C. nivalis over the winter period is relatively unusual among vole species in that they become nomadic and solitary. In odour choice trials under laboratory conditions, we found that both males and females avoided zones with conspecific odours of both sexes in comparison with unscented control zones or own odours. These results are consistent with the elevated levels of intraspecific aggression and spatial isolation of C. nivalis during overwintering periods. Furthermore, scent-elicited self-grooming increased when their own odour was offered against conspecific cues. This, in combination with an active avoidance of conspecific odours, might functionally contribute to minimize direct confrontations between solitary individuals, thereby reducing the risks of aggressive encounters during overwintering periods. [source] Distribution of aquatic vascular plants in lowland rivers: separating the effects of local environmental conditions, longitudinal connectivity and river basin isolationFRESHWATER BIOLOGY, Issue 3 2005BENOÎT O. L. DEMARS Summary 1. Changes in species distributions along rivers have rarely been observed independently of changes in environmental conditions and meaningful comparison between different catchments is made difficult by the limited geographical distribution of species. This study presents a new approach to quantify the effect of the spatial structure of lowland river networks on aquatic plant distribution and to explore the potential underlying processes using species life-history characteristics. 2. Twenty-five species of aquatic vascular plants recorded in 62 sites across five calcareous river basins were used to investigate (i) the temporal turnover of plant species, (ii) the habitat utilisation of species, (iii) the trade-offs between different plant life-history characteristics and (iv) the relationship between species life-history characteristics and habitat utilisation. 3. The annual plant turnover within a 3-year period was, although significant, extremely low. It suggests that results from spatial surveys conducted over 3 years should not be undermined by temporal changes. 4. Spatial connectivity along and between rivers was more important than in-channel physical characteristics in shaping species assemblages. Neither chemical factors (ammonium, phosphate) nor extrinsic biotic competitors (filamentous green algae) significantly influenced plant distribution. 5. The most common combinations of life-history characteristics were neither related to environmental conditions nor to spatial isolation. Instead, they could reflect natural selection processes associated with larger scales than those considered in this study. 6. Plant distribution was most strongly related to the dispersal and regeneration abilities of the plants, supporting the hypotheses relating to longitudinal connectivity. The hypothesis that different growth forms would be associated with different in-channel physical features was not verified. As expected, there were no substantial differences in plant life-history characteristics between river basins. [source] Single host trees in a closed forest canopy matrix: a highly fragmented landscape?JOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2007J. Müller Abstract:, Whether trees represent habitat islands and therefore are influenced by similar biogeographic processes as ,real' islands is controversial. For trees in highly fragmented landscapes the impacts of spatial isolation on arthropod communities have already been demonstrated. However, we have almost no evidence that in large forests the arthropod communities on single trees in a closed canopy matrix are influenced by similar processes. In the present study the influence of spatial isolation on the specialized oak crown fauna was analysed in a large broadleaved forest area in northern Bavaria, Germany. The dependence of specialists on the proportion of oaks in the surrounding forest was investigated by using flight interception traps (67 on oak, 19 on beech). As target species, saproxylic and herbivorous Coleoptera and Heteroptera were sampled. The following two hypotheses were tested: (1) The proportion of oak specialists differs for oaks in beech forests and oaks in oak forests. (2) The proportion of oak specialists increases with the proportion of oaks in the surrounding forest. For all species groups, the proportion of oak specialists was higher in oak crowns than in beech crowns. Herbivorous beetles and true bugs showed a higher proportion of specialists in oak forests than on single oaks in beech forests. The proportion of herbivorous oak specialists increased significantly with increasing numbers of adjacent oak trees, while saproxylic Coleoptera showed no relationship to oak density. For herbivorous Coleoptera a threshold of higher proportion occurred where >30% oak was present, and for Heteroptera a first threshold was identified at values >70% and a second at >30%. This indicates that larger habitat patches within a closed forest canopy matrix support larger populations of herbivorous oak specialists. Hence, similar effects of spatial isolation might occur in a closed forest as have already been shown for highly fragmented open landscapes. [source] Do linear landscape elements in farmland act as biological corridors for pollen dispersal?JOURNAL OF ECOLOGY, Issue 1 2010Anja Van Geert Summary 1.,Habitat fragmentation in agricultural landscapes has reduced the population sizes of many plant species while increasing their spatial isolation. Restoration or maintenance of the connectivity by gene flow between the fragmented patches may be determinant to sustaining viable populations, especially for insect-pollinated species. Functional biological corridors facilitating pollen flow between remnants in a human-dominated matrix might achieve this. 2.,Dye dispersal was investigated for the extremely fragmented insect-pollinated herb Primula vulgaris, using fluorescent dye particles as pollen analogues, in a study site comprising 20 populations, of which 13 pairs were physically connected by a linear landscape elements (LLEs, ditches), and 11 pairs were not connected by an LLE. The dye deposition events were used to fit a model of pollen dispersal at the landscape level. We examined whether existing LLEs in the intensively used agricultural landscape act as functional corridors for pollen dispersal. The effects of LLE length and size and plant density of the recipient population on the dispersal patterns were tested. 3.,Dye dispersal showed a leptokurtic decay distribution, with 80% of the dye transfers occurring at less than 85.1 m, and a maximal distance of 1010.8 m. The mean distance travelled by fluorescent dye particles based on the dye dispersal model was , = 87 m. 4.,Dye dispersal between populations was found to be significantly higher when populations were connected by an LLE, than when populations were unconnected. For the group of population pairs connected by an LLE, dye deposition significantly decreased with the distance to dye source, but was not related to recipient population size and plant density. 5.,Synthesis. Our study is, to our knowledge, the first to demonstrate that existing LLEs in an intensively used farmland may act as functional biological corridors facilitating pollen dispersal through pollinator movements. The maintenance or restoration of a network of populations connected by LLEs, but also by other landscape structures (e.g. population relays in vegetation patches and networks of small elements allowing indirect connections) should be strongly encouraged. [source] Invasion Possibility and Potential Effects of Rhus typhina on Beijing MunicipalityJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2008Guangmei Wang Abstract Rhus typhina, an alien species introduced from North America, was identified as a main afforestation species in Beijing municipality. However, its invasiveness is still at odds. To clarify this problem, we applied the North American Screening System and the Australian Screening System to preliminarily predict its invasion possibility. Both screening systems gave the same recommendation to "reject". The geographical distribution was surveyed, with the population features of R. typhina against the native plant communities being assessed. With anthropogenic assistance, R. typhina has been scattered on almost all habitats from downtown to mountains, including roadsides, farmlands and protected areas. As a clonal shrub, R. typhina possessed a high spreading rate, varying from 6.3 m/3 years at sterile habitats to 6.7 m/3 years at fertile ones. Significantly lower species richness, individual density and diversity were observed in the R. typhina community than those of the native Vitex negundo Linn.var. heterophylla (Franch.) Rehd. community at both sterile and fertile habitats. Continual wide plantation of R. typhina may further foster its population expansion, which helps the species to overcome spatial isolation. The fact that each root fragment can develop into a new individual makes R. typhina very difficult to be eradicated once established. From a biological point of view, we believe that R. typhina is a plant invader in Beijing. We therefore suggest the government should remove the name of R. typhina from the main tree species list in afforesting Beijing. [source] RAPD variation and population genetic structure in Prunus mahaleb (Rosaceae), an animal-dispersed treeMOLECULAR ECOLOGY, Issue 9 2000Pedro Jordano Abstract We examined the patterns of random amplified polymorphic DNA (RAPD) variation among seven Prunus mahaleb (Rosaceae) populations extending over , 100 km2 to examine local differentiation in relation to spatial isolation due to both geographical distance and differences in elevation. No less than 51.4% of the RAPD loci were polymorphic, but very few were fixed and among-population variation accounted for 16.46% of variation in RAPD patterns. Mean gene diversity was 0.1441, with mean Nei's genetic diversity for individual populations ranging between 0.089 and 0.149. Mean GST value across loci was 0.1935 (range, 0.0162,0.4685), giving an average estimate for Nm of 1.191. These results suggest extensive gene flow among populations, but higher GST and lower Nm values relative to other outcrossing, woody species with endozoochorous dispersal, also suggest a process of isolation by distance. The combined effect of both geographical and elevation distances and nonoverlapping flowering and fruiting phenophases on the GST matrix was partially significant, revealing only marginal isolation of the P. mahaleb populations. The matrix correlation between estimated Nm values among populations and the geographical + elevation distance matrices (r = ,0.4623, P = 0.07), suggests a marginal trend for more isolated populations to exchange less immigrants. Long-distance seed dispersal by efficient medium-sized frugivorous birds and mammals is most likely associated to the high levels of within-population genetic diversity. However, vicariance factors and demographic bottlenecks (high postdispersal seed and seedling mortality) explain comparatively high levels of local differentiation. [source] Populations do not become less genetically diverse or more differentiated towards the northern limit of the geographical range in clonal Vaccinium stamineum (Ericaceae)NEW PHYTOLOGIST, Issue 2 2008Sarah B. Yakimowski Summary ,,Geographically peripheral populations are expected to exhibit lower genetic diversity and higher differentiation than central populations because of their smaller size and greater spatial isolation. In plants, a shift from sexual to clonal asexual reproduction may further reduce diversity and increase differentiation. ,,Here, these predictions were tested by assaying 36 inter-simple sequence repeat (ISSR) polymorphisms in 21 populations of the woody, clonal plant Vaccinium stamineum in eastern North America, from the range center to its northern limit where it has ,threatened' status. Populations decline in frequency, but not size or sexual reproductive output, across the range. ,,Within-population diversity did not decline towards range margins. Modest genetic differentiation among populations increased slightly towards range margins and in small populations with high clonal propagation and low seed production, although none of these trends was significant. Low seed production and high clonal propagation were not associated with large-scale clonal spread. ,,By combining demographic and genetic data, this study determined that increased population isolation, rather than reduced population size, can account for the weak increase in genetic differentiation at range margins. [source] Wild grapevine: silvestris, hybrids or cultivars that escaped from vineyards?PLANT BIOLOGY, Issue 3 2010Molecular evidence in Sardinia Abstract Vitis vinifera ssp. silvestris, the spontaneous subspecies of V. vinifera L., is believed to be the ancestor of present grapevine cultivars. In this work, polymorphism at 13 SSR loci was investigated to answer the following key question: are wild plants (i) true silvestris, (ii) hybrids between wild and cultivated plants or (iii) or ,escapes' from vineyards? In particular, the objective of the present study was to identify truly wild individuals and to search for possible hybridization events. The study was performed in Sardinia, the second largest island in the Mediterranean Sea, which is characterized by a large and well-described number of both grape cultivars and wild populations. This region was ideal for the study because of its spatial isolation and, consequently, limited contamination from outside material. The results of this study show that domesticated and wild grapevine germplasms are genetically divergent and thus are real silvestris. Pure lineages (both domesticated and wild) show very high average posterior probabilities of assignment to their own clusters, with a low level of introgression. [source] Breeding behavior and its possible consequences for gene flow in Taraxacum sect.PLANT SPECIES BIOLOGY, Issue 2 2010Erythrosperma (H. Lindb.) Dahlst. Abstract Studies of pollen, seed set and experimental hybridizations were carried out to clarify breeding behavior and gene flow pathways in Taraxacum sect. Erythrosperma. Seeds from hybridization (106 samples), open pollinated (34) and bagged (43) capitula were analyzed for breeding system using a flow,cytometric seed screen. In the section Erythrosperma, diploids are obligate sexuals, mostly allogamous; however, autogamy also occurs (in 28% of unpollinated capitula). Triploids are apomicts with residual sexuality (in 13% of capitula pollinated by pollen of diploids). Pollen of diploids in Taraxacum is usually approximately the same size (regular pollen). In our study, in the section Erythrosperma, many diploids (24%) produced pollen grains of different sizes (irregular pollen) and one plant produced no pollen. The pollen of triploids is either irregular (33%) or the triploids produce no pollen (67%). Consequently, the method of ploidy level assessment on the basis of pollen characteristics is not suitable for Taraxacum sect. Erythrosperma. Low potential for polyploid hybrid formation between diploid maternal plants and polyploid pollen donors, considerable tendency to autogamy and no evidence of the formation of diploid progeny by polyploid maternal plants (facultative apomixis) indicates low intensity of gene flow within Taraxacum sect. Erythrosperma. This, together with a lower population density and spatial isolation of ploidy levels, is expected to result in a lower rate of formation of new apomictic lineages. Thus, Taraxacum sect. Erythrosperma appears evolutionarily more stable and taxonomically less complicated than sect. Ruderalia. The present study supports the agamospecies concept of Taraxacum sect. Erythrosperma. [source] Effects of Forest Fragmentation on Pollinator Activity and Consequences for Plant Reproductive Success and Mating Patterns in Bat-pollinated Bombacaceous Trees,BIOTROPICA, Issue 2 2004Mauricio Quesada ABSTRACT Forest fragmentation and the resulting spatial isolation of tree species can modify the activity of pollinators and may have important implications for the reproductive success and mating systems of the plants they pollinate. The objectives of this study were to (1) evaluate the effect of forest fragmentation on pollinator activity in bat-pollinated bombacaceous trees and (2) determine the effects of forest fragmentation on reproductive success and mating systems of bombacaceous trees. We studied these parameters in three bombacaceous tree species in tropical seasonal forest of Chamela, Jalisco, Mexico, and Osa and Guanacaste, Costa Rica. For Ceiba aesculifolia, more visits were observed in fragments by both Glossophaga soricina and Leptonycteris curasoae. For Ceiba grandiflora, Musonycteris harrisoni visited flowers exclusively in forest and G. soricina visited more flowers in forest than in fragments; no difference was shown by L. curasoae. For Ceiba pentandra in Chamela, no differences were found in visitation by G. soricina between forest and fragments; L. curasoae visited significantly more flowers in forest. Ceiba pentandra received more visits by Phyllostomus discolor than G. soricina in Guanacaste, whereas no bat visitors were observed in Osa. Total mean flower production was greater in fragments than forest for C. aesculifolia, whereas no difference was observed for C. grandiflora. Fruit set was greater in forest than in fragments for C. grandiflora, whereas no difference was observed for C. aesculifolia. Outcrossing rates were high for C. aesculifolia and C. grandiflora in Chamela, and for C. pentandra in Guanacaste, independent of tree habitat, while C. pentandra in Osa showed a mixed-mating system. The effects of forest fragmentation on bat pollinators, plant reproductive success, and mating patterns varied depending upon the bombacaceous species. This variability was associated with the effects that forest fragmentation may have on differences in flowering patterns, bat foraging behavior, and plant self-incompatibility systems. RESUMEN La fragmentatión de bosques y el aislamiento espacial, producto de este fenómeno, pueden modificar la actividad de los polinizadores y pueden tener implicaciones importantes sobre el éxito reproductivo y los sistemas de apareamiento de las plantas que polinizan. Los objetivos de este estudio consisten en: (1) evaluar los efectos de la fragmentatión de bosque sobre la actividad de los polinizadores de árboles de Bombacaceas, y (2) determinar los efectos de la fragmentación sobre el éxito reproductivo y el sistema de apareamiento de árboles de Bombacaceas. Evaluamos estos parámetros en 3 especies de árboles de esta familia en bosques estacionales en Jalisco, México y Guanacaste y Osa, Costa Rica. Las flores de Ceiba aesculifolia fueron mas visitadas en fragmentos por Glossophaga soricina y Leptonycteris curasoae. En Ceiba grandiflora, Musonycteris harrisoni visitó flores exclusivamente en el bosque y G. soricina visitó mas flores en el bosque que en los fragmentos mientras que no hubo diferencias para L. curasoae. En Chamela, no hubo diferencias en la tasa de visitas de flores entre bosque y fragmentos para G. soricina en Ceiba pentandra mientras que L, curasoae visitó más flores en el bosque. En Guanacaste, C, pentandra recibio mas visitas de Phyllostomus discolor que de G. soricina mientras que no hubo visitas por murcielagos en Osa. La produccion total promedio de flores fue mayor en los fragmentos que en el bosque para C. aesculifolia mientras que no hubo diferencias para C. grandiflora. La proba-bilidad de que una flor produzca fruto fué mayor en el bosque que en los fragmentos para C. grandiflora pero no hubo diferencias en C. aesculifolia. La tasa de exocruzamiento fue aha para C. aesculifolia y C. grandiflora en Chamela, y para C. pentandra en Guanacaste, mientras que C. pentandra en Osa mostró un sistema de apareamiento mixto. Los efectos de la fragmentación de bosques sobre la polinización por murciélagos, la reproducción de plantas y sus patrones de apareamiento varían dependiendo de la especie de Bombacaceae. Esta variabilidad está asociada a los efectos que la fragmentación de bosques puede tener sobre diferencias en los patrones de floración, el comportamiento de forrajeo de los polinizadores, y los sistemas de incompatibilidad de las plantas. [source] The Nightly Round: Space, Social Capital, and Urban Black NightlifeCITY & COMMUNITY, Issue 2 2010Marcus Anthony Hunter Using data generated from participant observation and semistructured interviews, I consider the ways in which nightlife, or what might be imagined as the nightly round,a process encompassing the social interactions, behaviors, and actions involved in going to, being in, and leaving the club,is used to mitigate the effects of social and spatial isolation, complementing the accomplishment of the daily round. Through an analysis of the social world of The Spot, I argue that understanding the ways in which urban blacks use space in the nightclub to mediate racial segregation, sexual segregation, and limited social capital expands our current understanding of the spatial mobility of urban blacks as well as the important role of extra-neighborhood spaces in such processes. Further, I highlight the ways that urban blacks use space in the nightclub to leverage socioeconomic opportunities and enhance social networks. While I found that black heterosexual and lesbian and gay patrons used space in similar ways at The Spot, black lesbians and gays were more likely to use the club as a space to develop ties of social support. El recorrido de todas las noches: espacio, capital social y la vida nocturna de las personas de raza negra residentes en las ciudades (Marcus Anthony Hunter) Resumen Usando datos generados a partir de la observación participante y entrevistas semi-estructuradas, analizo las formas en que la vida nocturna o lo que podemos imaginar como el recorrido nocturno -un proceso que abarca las interacciones sociales, conductas y acciones incluidas en el ir hacia, estar en y salir de los clubes de baile- es utilizado para mitigar los efectos del aislamiento social y espacial, complementando así el logro de las actividades realizadas durante el día. A través del análisis del mundo social del club "The Spot", sostengo que estudiar las formas en que las personas de raza negra residentes en las ciudades utilizan el espacio en los clubes nocturnos para mediar la segregación racial y sexual y su limitado capital social, contribuye a expandir nuestra comprensión de la movilidad espacial de las personas de raza negra residentes en las ciudades al igual que el importante rol de los espacios extra-barriales en estos procesos. Además, enfatizo las maneras en que este conglomerado utiliza el espacio en los clubes nocturnos para mejorar sus oportunidades socio-económicas y ampliar sus redes sociales. Mis resultados indican que aunque las y los clientes heterosexuales, lesbianas y gays de raza negra de "The Spot" utilizaban el espacio de manera similar, las lesbianas y gays de raza negra eran más propensos a utilizar el club como un espacio para desarrollar redes de apoyo social. [source] | ||||||||||||||||||||||