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Sampling Scale (sampling + scale)
Selected AbstractsApplication of the New Keystone-Species Concept to Prairie Dogs: How Well Does It Work?CONSERVATION BIOLOGY, Issue 6 2000Natasha B. Kotliar This prompted Power et al. (1996) to refine the definition: keystone species have large effects on community structure or ecosystem function (i.e., high overall importance), and this effect should be large relative to abundance (i.e., high community importance). Using prairie dogs (Cynomys spp.) as an example, I review operational and conceptual difficulties encountered in applying this definition. As applied to prairie dogs, the implicit assumption that overall importance is a linear function of abundance is invalid. In addition, community importance is sensitive to abundance levels, the definition of community, and sampling scale. These problems arise largely from the equation for community importance, as used in conjunction with removal experiments at single abundance levels. I suggest that we shift from the current emphasis on the dualism between keystone and nonkeystone species and instead examine how overall and community importance vary (1) with abundance, (2) across spatial and temporal scales, and (3) under diverse ecological conditions. In addition, I propose that a third criterion be incorporated into the definition: keystone species perform roles not performed by other species or processes. Examination of how these factors vary among populations of keystone species should help identify the factors contributing to, or limiting, keystone-level functions, thereby increasing the usefulness of the keystone-species concept in ecology and conservation. Although the quantitative framework of Power et al. falls short of being fully operational, my conceptual guidelines may improve the usefulness of the keystone-species concept. Careful attention to the factors that limit keystone function will help avoid misplaced emphasis on keystone species at the expense of other species. Resumen: Se ha sugerido que el concepto de especie pilar no sea usado más en ecología y conservación, principalmente debido a que el concepto ha sido pobremente definido. Esto instigó a Power et al. (1996) a refinar la definición: las especies pilar tienen grandes efectos en la estructura de una comunidad o la función de un ecosistema (alta importancia en lo general), y este efecto debe ser grande en relación con la abundancia (alta importancia en la comunidad). Usando los perros de pradera (Cynomys spp) como ejemplo, revisé las dificultades operativas y conceptuales encontradas durante la aplicación de esta definición. Al aplicarse a perros de pradera, la suposición implícita de que la importancia en lo general es una función lineal de la abundancia es inválida. Además, la importancia en la comunidad es sensible a los niveles de abundancia, a la definición de comunidad y a la escala de muestreo. Estos problemas surgen, en gran medida, de la ecuación para la importancia en la comunidad, al ser usada conjuntamente con experimentos de remoción a un solo nivel de abundancia. Sugiero que el énfasis actual en la dualidad sobre especies pilares/no pilares cambie para examinar cómo varía la importancia en lo general y en la comunidad; (1) con la abundancia, (2) a lo largo de escalas espaciales y temporales, y (3) bajo diversas condiciones ecológicas. Además, propongo que sea incorporado un tercer criterio en la definición: las especies pilar llevan a cabo funciones no llevadas a cabo por otras especies o procesos. El análisis de cómo varían estos factores entre poblaciones de especies pilar ayudará a identificar los factores que contribuyen, o limitan las funciones a nivel pilar, incrementando con ello la utilidad del concepto de especie pilar en ecología y conservación. Aunque el marco de trabajo cuantitativo de Power et al. no llega a ser completamente operacional, mis guías conceptuales pueden mejorar la utilidad de este concepto. Una atención especial a los factores que limitan el funcionamiento pilar ayudaría a evitar un énfasis mal ubicado en especies pilar a costa de otras especies. [source] Micro-scale Systematic Sampling of Soil: Heterogeneity in Populations of Fusarium oxysporum, F. solani, F. roseum and F. moniliformeJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2000M. C. Rodríguez-Molina Abstract The variability of Fusarium spp. density in soil was studied in a field located in Badajoz (south-western Spain). The upper 40 cm of each side of a 1 m × 1 m × 1 m pit were sampled intensively, taking soil samples from points 10 cm apart. The species isolated were F. oxysporum, F. solani, F. roseum and F. moniliforme. For all four sides of the pit population densities of F. oxysporum, F. solani and F. roseum significantly decreased with increasing soil depth and for all the four layers significant differences were detected between sides of the pit. Horizontal variability also occurred on a smaller sampling scale: when a layer of a side was sampled, densities might be significantly different between points in the layer. However, no clear trend in horizontal variability was observed for any species. These findings demonstrate that Fusarium spp. populations were heterogeneously distributed in this reduced soil volume. Zusammenfassung Die Variabilität der Dichte von Fusarium spp. im Boden wurde in einem Feld in Badajoz (Südwestspanien) untersucht. Die oberen 40 cm jeder Seite einer 1 m × 1 m × 1 m großen Grube wurden intensiv beprobt, wobei im Abstand von jeweils 10 cm Bodenproben entnommen wurden. Aus den Proben wurden F. oxysporum, F. solani, F. roseum und F. moniliforme isoliert. An allen vier Seiten der Grube nahmen die Populationsdichten von F. oxysporum, F. solani und F. roseum mit zunehmender Bodentiefe signifikant ab. Bei allen vier Schichten wurden signifikante Unterschiede zwischen den Seiten der Grube festgestellt. Bei kleinerem Beprobungsmaßstab wurde auch horizontale Variabilität festgestellt: Wenn eine Schicht einer Seite beprobt wurde, unterschieden sich die Dichten zwischen den einzelnen Punkten der Schicht teilweise signifikant. Für keine Art war jedoch eine deutliche Tendenz bei der horizontalen Variabilität feststellbar. Die Ergebnisse zeigten, daß die Populationen von Fusarium spp. in diesem kleinen Bodenvolumen heterogen verteilt waren. [source] Patterns of vegetative growth and gene flow in Rhizopogon vinicolor and R. vesiculosus (Boletales, Basidiomycota)MOLECULAR ECOLOGY, Issue 8 2005ANNETTE M. KRETZER Abstract We have collected sporocarps and tuberculate ectomycorrhizae of both Rhizopogon vinicolor and Rhizopogon vesiculosus from three 50 × 100 m plots located at Mary's Peak in the Oregon Coast Range (USA); linear map distances between plots ranged from c. 1 km to c. 5.5 km. Six and seven previously developed microsatellite markers were used to map the approximate size and distribution of R. vinicolor and R. vesiculosus genets, respectively. Genetic structure within plots was analysed using spatial autocorrelation analyses. No significant clustering of similar genotypes was detected in either species when redundant samples from the same genets were culled from the data sets. In contrast, strong clustering was detected in R. vesiculosus when all samples were analysed, but not in R. vinicolor. These results demonstrate that isolation by distance does not occur in either species at the intraplot sampling scale and that clonal propagation (vegetative growth) is significantly more prevalent in R. vesiculosus than in R. vinicolor. Significant genetic differentiation was detected between some of the plots and appeared greater in the more clonal species R. vesiculosus with ,ST values ranging from 0.010 to 0.078*** than in R. vinicolor with ,ST values ranging from ,0.002 to 0.022** (*P < 0.05, **P < 0.01, ***P < 0.001). When tested against the null hypothesis of no relationship between individuals, parentage analysis detected seven likely parent/offspring pairs in R. vinicolor and four in R. vesiculosus (, = 0.001). Of these 11 possible parent/offspring pairs, only two R. vinicolor pairs were still supported as parent/offspring when tested against the alternative hypothesis of being full siblings (, = 0.05). In the latter two cases, parent and offspring were located at approximately 45 m and 28 m from each other. Challenges to parentage analysis in ectomycorrhizal fungi are discussed. [source] Universal fitting formulae for baryon oscillation surveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Chris Blake ABSTRACT The next generation of galaxy surveys will attempt to measure the baryon oscillations in the clustering power spectrum with high accuracy. These oscillations encode a preferred scale which may be used as a standard ruler to constrain cosmological parameters and dark energy models. In this paper we present simple analytical fitting formulae for the accuracy with which the preferred scale may be determined in the tangential and radial directions by future spectroscopic and photometric galaxy redshift surveys. We express these accuracies as a function of survey parameters such as the central redshift, volume, galaxy number density and (where applicable) photometric redshift error. These fitting formulae should greatly increase the efficiency of optimizing future surveys, which requires analysis of a potentially vast number of survey configurations and cosmological models. The formulae are calibrated using a grid of Monte Carlo simulations, which are analysed by dividing out the overall shape of the power spectrum before fitting a simple decaying sinusoid to the oscillations. The fitting formulae reproduce the simulation results with a fractional scatter of 7 per cent (10 per cent) in the tangential (radial) directions over a wide range of input parameters. We also indicate how sparse-sampling strategies may enhance the effective survey area if the sampling scale is much smaller than the projected baryon oscillation scale. [source] The effect of the sampling scale on zooplankton community assessment and its implications for the conservation of temporary ponds in south-west SpainAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2007Khalid Fahd Abstract 1.The zooplankton (rotifer and microcrustacean) assemblages of temporary ponds in the Doñana National Park (south-west Spain) have been compared in two surveys of contrasting scales that resulted in the same number of samples: an extensive survey of 36 ponds sampled in May 1998 (or widespread survey) and a survey of nine ponds sampled four times over 2 years (or cumulative survey). 2.The total number of microcrustacean and rotifer taxa was larger in the cumulative survey (43 and 41 taxa, respectively) than in the widespread survey (39 and 34, respectively). Crustacean assemblages became less alike throughout the cumulative survey. 3.The presence of invertebrates (Coleoptera, Odonata, Heteroptera and crayfish) and aquatic vertebrates (fish and salamanders) was recorded as an estimate of potential predator impact on zooplankton. Several pond features (water depth, conductivity, pH, chlorophyll a concentration, distance to the nearest permanent pond and to the marsh) were also measured in both surveys. 4.A combination of these environmental factors was more strongly related to the similarity matrices derived from the zooplankton assemblages of the cumulative survey (Rho=0.7) than to those of the widespread survey (Rho<0.4). The distance of ponds to the marsh was an important factor in explaining this correlation as well as the strongest factor in the ordination of crustacean assemblages following a CCA. 5.Predation by exotic fish in long-hydroperiod ponds where overflow drains to the nearby marsh (fish source) is the mechanism likely to explain the changes in crustacean composition recorded in the cumulative survey. 6.The cumulative survey was more suitable for the study of zooplankton diversity as it rendered a higher number of taxa and gave more insight into the mechanisms that explain taxon richness. Thus, conservation strategies in temporary habitats require a scale of observation that includes long temporal changes. Copyright © 2006 John Wiley & Sons, Ltd. [source] Occupancy frequency distributions: patterns, artefacts and mechanismsBIOLOGICAL REVIEWS, Issue 3 2002MELODIE A. McGEOCH ABSTRACT Numerous hypotheses have been proposed to explain the shape of occupancy frequency distributions (distributions of the numbers of species occupying different numbers of areas). Artefactual effects include sampling characteristics, whereas biological mechanisms include organismal, niche-based and metapopulation models. To date, there has been little testing of these models. In addition, although empirically derived occupancy distributions encompass an array of taxa and spatial scales, comparisons between them are often not possible because of differences in sampling protocol and method of construction. In this paper, the effects of sampling protocol (grain, sample number, extent, sampling coverage and intensity) on the shape of occupancy distributions are examined, and approaches for minimising artefactual effects recommended. Evidence for proposed biological determinants of the shape of occupancy distributions is then examined. Good support exists for some mechanisms (habitat and environmental heterogeneity), little for others (dispersal ability), while some hypotheses remain untested (landscape productivity, position in geographic range, range size frequency distributions), or are unlikely to be useful explanations for the shape of occupancy distributions (species specificity and adaptation to habitat, extinction,colonization dynamics). The presence of a core (class containing species with the highest occupancy) mode in occupancy distributions is most likely to be associated with larger sample units, and small homogenous sampling areas positioned well within and towards the range centers of a sufficient proportion of the species in the assemblage. Satellite (class with species with the lowest occupancy) modes are associated with sampling large, heterogeneous areas that incorporate a large proportion of the assemblage range. However, satellite modes commonly also occur in the presence of a core mode, and rare species effects are likely to contribute to the presence of a satellite mode at most sampling scales. In most proposed hypotheses, spatial scale is an important determinant of the shape of the observed occupancy distribution. Because the attributes of the mechanisms associated with these hypotheses change with spatial scale, their predictions for the shape of occupancy distributions also change. To understand occupancy distributions and the mechanisms underlying them, a synthesis of pattern documentation and model testing across scales is thus needed. The development of null models, comparisons of occupancy distributions across spatial scales and taxa, documentation of the movement of individual species between occupancy classes with changes in spatial scale, as well as further testing of biological mechanisms are all necessary for an improved understanding of the distribution of species and assemblages within their geographic ranges. [source] | ||||||||||