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Sampling Intensity (sampling + intensity)
Selected AbstractsFunctional trait variation and sampling strategies in species-rich plant communitiesFUNCTIONAL ECOLOGY, Issue 1 2010Christopher Baraloto Summary 1. ,Despite considerable interest in the application of plant functional traits to questions of community assembly and ecosystem structure and function, there is no consensus on the appropriateness of sampling designs to obtain plot-level estimates in diverse plant communities. 2. ,We measured 10 plant functional traits describing leaf and stem morphology and ecophysiology for all trees in nine 1-ha plots in terra firme lowland tropical rain forests of French Guiana (N = 4709). 3. ,We calculated, by simulation, the mean and variance in trait values for each plot and each trait expected under seven sampling methods and a range of sampling intensities. Simulated sampling methods included a variety of spatial designs, as well as the application of existing data base values to all individuals of a given species. 4. ,For each trait in each plot, we defined a performance index for each sampling design as the proportion of resampling events that resulted in observed means within 5% of the true plot mean, and observed variance within 20% of the true plot variance. 5. ,The relative performance of sampling designs was consistent for estimations of means and variances. Data base use had consistently poor performance for most traits across all plots, whereas sampling one individual per species per plot resulted in relatively high performance. We found few differences among different spatial sampling strategies; however, for a given strategy, increased intensity of sampling resulted in markedly improved accuracy in estimates of trait mean and variance. 6. ,We also calculated the financial cost of each sampling design based on data from our ,every individual per plot' strategy and estimated the sampling and botanical effort required. The relative performance of designs was strongly positively correlated with relative financial cost, suggesting that sampling investment returns are relatively constant. 7. ,Our results suggest that trait sampling for many objectives in species-rich plant communities may require the considerable effort of sampling at least one individual of each species in each plot, and that investment in complete sampling, though great, may be worthwhile for at least some traits. [source] Relationship between sampling intensity and precision for estimating damage to maize caused by rodentsINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2007Loth S. MULUNGU Abstract In this study we aimed to determine the relationship between sampling intensity and precision for estimating rodent damage. We used the systematic row sampling technique to provide data to achieve precision and accuracy in estimations of rodent damage in maize fields at the planting and seedling stages. The actual rodent damage to maize in 15 fields, each 0.5 ha in size, in Morogoro, Tanzania, was established at the seedling stage. These data were used to simulate the sampling intensities that would provide precision and accuracy. The variations between estimates were plotted against the sampling intervals. The results of this study show that the relationship between average standardized variances and sampling intervals is linear. The heterogeneous distribution of damage in some plots caused variations in the accuracy of the estimates between plots, but a sampling interval of five rows consistently produced estimates with a variance of less than 10%. We provide a standard curve that will allow a decision to be made on the sampling intensity as a function of required precision using the systematic row sampling technique in maize fields. [source] A re-examination of the expected effects of disturbance on diversityOIKOS, Issue 3 2000Robin L. Mackey Disturbance is often cited as one of the main factors determining patterns of species diversity. Several models have predicted qualitatively that species richness should be highest at intermediate intensities and/or frequencies of disturbances, but none indicate whether this effect should be strong (statistically accounting for much variability in diversity) or only subtle. Empirical evidence on the point is very mixed. This study examines Markov models of the dynamics of six real communities. We derive the predicted changes in species richness and evenness when these communities are subjected to quantified disturbance frequency and intensity gradients. We also use several different sampling intensities (i.e. numbers of individuals counted) to determine how this affects richness-disturbance relationships. Our models predict that peaked responses of diversity to disturbance should be less common than monotonic ones. Species richness should vary, on average, by only 3% over gradients of no disturbance to complete disturbance. In the most extreme case, richness varied two-fold over this gradient. Moreover, richness may increase monotonically, decrease monotonically, or be a peaked function of disturbance, interacting in a non-intuitive fashion with both the sampling intensity and the community in question. These results are broadly consistent with a review of published richness-disturbance relationships. Evenness varies somewhat more strongly along disturbance gradients, but the effect is still small. We conclude that extant models provide little reason to believe that disturbance should play more than a subtle role in determining patterns of diversity in nature, contrary to most contemporary literature. [source] Quantifying root lateral distribution and turnover using pine trees with a distinct stable carbon isotope signatureFUNCTIONAL ECOLOGY, Issue 1 2005K. JOHNSEN Summary 1In order to help assess spatial competition for below-ground resources, we quantified the effects of fertilization on root biomass quantity and lateral root distribution of mid-rotation Pinus taeda trees. Open-top chambers exposed trees to ambient or ambient plus 200 µmol mol,1 atmospheric CO2 for 31 months. 2Tank CO2 was depleted in atmospheric 13C; foliage of elevated CO2 trees had ,13C of ,42·9, compared with ,29·1 for ambient CO2 trees. 3Roots 1 m from the base of elevated CO2 -grown trees had more negative ,13C relative to control trees, and this difference was detected, on average, up to 5·8, 3·7 and 3·7 m away from the trees for 0,2, 2,5 and >5 mm root-size classes, respectively. Non-fertilized tree roots extended as far as fertilized trees despite the fact that their above-ground biomass was less than half that of fertilized trees. 4These results are informative with respect to root sampling intensity and protocol, and the distances required between experimental manipulations to evaluate below-ground processes of independent treatments. 5Fine-root turnover has usually been estimated to range from weeks to 3 years, representing a major avenue of carbon flux. Using a mixing model we calculated that 0,2 mm roots had a mean residence time of 4·5 years indicating relatively slow fine-root turnover, a result that has major implications in modelling C cycling. [source] Relationship between sampling intensity and precision for estimating damage to maize caused by rodentsINTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2007Loth S. MULUNGU Abstract In this study we aimed to determine the relationship between sampling intensity and precision for estimating rodent damage. We used the systematic row sampling technique to provide data to achieve precision and accuracy in estimations of rodent damage in maize fields at the planting and seedling stages. The actual rodent damage to maize in 15 fields, each 0.5 ha in size, in Morogoro, Tanzania, was established at the seedling stage. These data were used to simulate the sampling intensities that would provide precision and accuracy. The variations between estimates were plotted against the sampling intervals. The results of this study show that the relationship between average standardized variances and sampling intervals is linear. The heterogeneous distribution of damage in some plots caused variations in the accuracy of the estimates between plots, but a sampling interval of five rows consistently produced estimates with a variance of less than 10%. We provide a standard curve that will allow a decision to be made on the sampling intensity as a function of required precision using the systematic row sampling technique in maize fields. [source] Undersampling bias: the null hypothesis for singleton species in tropical arthropod surveysJOURNAL OF ANIMAL ECOLOGY, Issue 3 2009Jonathan A. Coddington Summary 1Frequency of singletons , species represented by single individuals , is anomalously high in most large tropical arthropod surveys (average, 32%). 2We sampled 5965 adult spiders of 352 species (29% singletons) from 1 ha of lowland tropical moist forest in Guyana. 3Four common hypotheses (small body size, male-biased sex ratio, cryptic habits, clumped distributions) failed to explain singleton frequency. Singletons are larger than other species, not gender-biased, share no particular lifestyle, and are not clumped at 0·25,1 ha scales. 4Monte Carlo simulation of the best-fit lognormal community shows that the observed data fit a random sample from a community of ~700 species and 1,2 million individuals, implying approximately 4% true singleton frequency. 5Undersampling causes systematic negative bias of species richness, and should be the default null hypothesis for singleton frequencies. 6Drastically greater sampling intensity in tropical arthropod inventory studies is required to yield realistic species richness estimates. 7The lognormal distribution deserves greater consideration as a richness estimator when undersampling bias is severe. [source] Nested assemblages of Orthoptera species in the Netherlands: the importance of habitat features and life-history traitsJOURNAL OF BIOGEOGRAPHY, Issue 11 2007M. A. Schouten Abstract Aim, Species communities often exhibit nestedness, the species found in species-poor sites representing subsets of richer ones. In the Netherlands, where intensification of land use has led to severe fragmentation of nature, we examined the degree of nestedness in the distribution of Orthoptera species. An assessment was made of how environmental conditions and species life-history traits are related to this pattern, and how variation in sampling intensity across sites may influence the observed degree of nestedness. Location, The analysis includes a total of 178 semi-natural sites in the Pleistocene sand region of the Netherlands. Methods, A matrix recording the presence or absence of all Orthoptera species in each site was compiled using atlas data. Additionally, separate matrices were constructed for the species of suborders Ensifera and Caelifera. The degree of nestedness was measured using the binmatnest calculator. binmatnest uses an algorithm to sort the matrices to maximal nestedness. We used Spearman's rank correlations to evaluate whether sites were sorted by area, isolation or habitat heterogeneity, and whether species were sorted by their dispersal ability, rate of development or degree of habitat specificity. Results, We found the Orthoptera assemblages to be significantly nested. The rank correlation between site order and sampling intensity was high. The degree of nestedness was lower, but remained significant when under- and over-sampled sites were excluded from the analysis. Site order was strongly correlated with both size of sample site and number of habitat types per site. Rank correlations showed that species were probably ordered by variation in habitat specificity, rather than by variation in dispersal capacity or rate of development of the species. Main conclusions, Variation in sampling intensity among sites had a strong impact on the observed degree of nestedness. Nestedness in habitats may underlie the observed nestedness within the Orthoptera assemblages. Habitat heterogeneity is closely related to site area, which suggests that several large sites should be preserved, rather than many small sites. Furthermore, the results corroborate a focus of nature conservation policy on sites where rare species occur, as long as the full spectrum of habitat conditions and underlying ecological processes is secured. [source] Spatial distribution of populations of solitarious adult desert locust (Schistocerca gregaria Forsk.) on the coastal plain of SudanAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2004Gebremedhin Woldewahid Abstract 1,Densities of solitarious adult desert locusts were measured on regular grids of up to 126 sample sites in the southern part of the coastal plain of Sudan during the winters of 1999/2000 and 2000/2001. Geostatistical procedures were used to characterize spatial dependence of locust density, to evaluate the possibility of estimating locust densities at unvisited sites, based on information obtained at surveyed sites, and to create density maps. 2,Sample variograms indicate that population densities were spatially correlated over ranges from 5 to 24 km. The range of spatial correlation decreased as dry conditions towards the end of the rainy season concentrated the locusts in contracting areas of sufficient humidity and availability of green vegetation. The rather small ranges of spatial correlation indicate that sampling needs to be conducted at a refined scale (< 24 km between sample points) to avoid missing hot spots of desert locust. 3,Locust densities were highly correlated with cover abundance of the wild plant Heliotropium arbainense and cultivated millet, Pennisetum typhoidum. The association of locusts with these host plants can be used to target sampling and enhance detection chance. 4,The relationship between sampling intensity and kriging variance was explored. Implications for monitoring of desert locust are discussed. [source] Modelling species diversity through species level hierarchical modellingJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 1 2005Alan E. Gelfand Summary., Understanding spatial patterns of species diversity and the distributions of individ-ual species is a consuming problem in biogeography and conservation. The Cape floristic region of South Africa is a global hot spot of diversity and endemism, and the Protea atlas project, with about 60 000 site records across the region, provides an extraordinarily rich data set to model patterns of biodiversity. Model development is focused spatially at the scale of 1, grid cells (about 37 000 cells total for the region). We report on results for 23 species of a flowering plant family known as Proteaceae (of about 330 in the Cape floristic region) for a defined subregion. Using a Bayesian framework, we developed a two-stage, spatially explicit, hierarchical logistic regression. Stage 1 models the potential probability of presence or absence for each species at each cell, given species attributes, grid cell (site level) environmental data with species level coefficients, and a spatial random effect. The second level of the hierarchy models the probability of observing each species in each cell given that it is present. Because the atlas data are not evenly distributed across the landscape, grid cells contain variable numbers of sampling localities. Thus this model takes the sampling intensity at each site into account by assuming that the total number of times that a particular species was observed within a site follows a binomial distribution. After assigning prior distributions to all quantities in the model, samples from the posterior distribution were obtained via Markov chain Monte Carlo methods. Results are mapped as the model-estimated probability of presence for each species across the domain. This provides an alternative to customary empirical ,range-of-occupancy' displays. Summing yields the predicted richness of species over the region. Summaries of the posterior for each environmental coefficient show which variables are most important in explaining the presence of species. Our initial results describe biogeographical patterns over the modelled region remarkably well. In particular, species local population size and mode of dispersal contribute significantly to predicting patterns, along with annual precipitation, the coefficient of variation in rainfall and elevation. [source] Species discovery in marine planktonic invertebrates through global molecular screeningMOLECULAR ECOLOGY, Issue 5 2010ERICA GOETZE Abstract Species discovery through large-scale sampling of mitochondrial diversity, as advocated under DNA barcoding, has been widely criticized. Two of the primary weaknesses of this approach, the use of a single gene marker for species delineation and the possible co-amplification of nuclear pseudogenes, can be circumvented through incorporation of multiple data sources. Here I show that for taxonomic groups with poorly characterized systematics, large-scale genetic screening using a mitochondrial DNA marker can be a very effective approach to species discovery. Global sampling (120 locations) of 1295 individuals of 22 described species of eucalanid copepods identified 15 novel evolutionarily significant units (ESUs) within this marine holoplanktonic family. Species limits were tested under reciprocal monophyly at the mitochondrial (mt) gene 16S rRNA, and 13 of 15 lineages were reciprocally monophyletic under three phylogenetic inference methods. Five of these mitochondrial ESUs also received moderate support for reciprocal monophyly at the independently-inherited nuclear gene, internal transcribed spacer 2 (ITS2). Additional support for the utility of mt DNA as a proxy for species boundaries in this taxon is discussed, including results from related morphological and biogeographic studies. Minimal overlap of intra-ESU and inter-ESU 16S rRNA genetic distances was observed, suggesting that this mt marker performs well for species discovery via molecular screening. Sampling coverage required for the discovery of new ESUs was found to be in the range of >50 individuals/species, well above the sampling intensity of most current DNA Barcoding studies. Large-scale genetic screening can provide critical first data on the presence of cryptic species, and should be used as an approach to generate systematic hypotheses in groups with incomplete taxonomies. [source] On the usage and measurement of landscape connectivityOIKOS, Issue 1 2000Lutz Tischendorf This paper examines the usage and measurement of "landscape connectivity" in 33 recent studies. Connectivity is defined as the degree to which a landscape facilitates or impedes movement of organisms among resource patches. However, connectivity is actually used in a variety of ways in the literature. This has led to confusion and lack of clarity related to (1) function vs structure, (2) patch isolation vs landscape connectivity and, (3) corridors vs connectivity. We suggest the term connectivity should be reserved for its original purpose. We highlight nine studies; these include modeling studies that actually measured connectivity in accordance with the definition, and empirical studies that measured key components of connectivity. We found that measurements of connectivity provide results that can be interpreted as recommending habitat fragmentation to enhance landscape connectivity. We discuss reasons for this misleading conclusion, and suggest a new way of quantifying connectivity, which avoids this problem. We also recommend a method for reducing sampling intensity in landscape-scale empirical studies of connectivity. [source] A re-examination of the expected effects of disturbance on diversityOIKOS, Issue 3 2000Robin L. Mackey Disturbance is often cited as one of the main factors determining patterns of species diversity. Several models have predicted qualitatively that species richness should be highest at intermediate intensities and/or frequencies of disturbances, but none indicate whether this effect should be strong (statistically accounting for much variability in diversity) or only subtle. Empirical evidence on the point is very mixed. This study examines Markov models of the dynamics of six real communities. We derive the predicted changes in species richness and evenness when these communities are subjected to quantified disturbance frequency and intensity gradients. We also use several different sampling intensities (i.e. numbers of individuals counted) to determine how this affects richness-disturbance relationships. Our models predict that peaked responses of diversity to disturbance should be less common than monotonic ones. Species richness should vary, on average, by only 3% over gradients of no disturbance to complete disturbance. In the most extreme case, richness varied two-fold over this gradient. Moreover, richness may increase monotonically, decrease monotonically, or be a peaked function of disturbance, interacting in a non-intuitive fashion with both the sampling intensity and the community in question. These results are broadly consistent with a review of published richness-disturbance relationships. Evenness varies somewhat more strongly along disturbance gradients, but the effect is still small. We conclude that extant models provide little reason to believe that disturbance should play more than a subtle role in determining patterns of diversity in nature, contrary to most contemporary literature. [source] Improving the assessment of species compositional dissimilarity in a priori ecological classifications: evaluating map scale, sampling intensity and improvement in a hierarchical classificationAPPLIED VEGETATION SCIENCE, Issue 4 2010B.E. Lawson Abstract Question: Can species compositional dissimilarity analyses be used to assess and improve the representation of biodiversity patterns in a priori ecological classifications? Location: The case study examined the northern-half of the South-east Queensland Bioregion, eastern Australia. Methods: Site-based floristic presence,absence data were used to construct species dissimilarity matrices (Kulczynski metric) for three levels of Queensland's bioregional hierarchy , subregions (1:500 000 scale), land zones (1:250 000 scale) and regional ecosystems (1:100 000 scale). Within- and between-class dissimilarities were compiled for each level to elucidate species compositional patterns. Randomized subsampling was used to determine the minimum site sampling intensity for each hierarchy level, and the effects of lumping and splitting illustrated for several classes. Results: Consistent dissimilarity estimates were obtained with five or more sites per regional ecosystem, 10 or more sites per land zone, and more than 15 sites per subregion. On average, subregions represented 4% dissimilarity in floristic composition, land zones approximately 10%, and regional ecosystems over 19%. Splitting classes with a low dissimilarity increased dissimilarity levels closer to average, while merging ecologically similar classes with high dissimilarities reduced dissimilarity levels closer to average levels. Conclusions: This approach demonstrates a robust and repeatable means of analysing species compositional dissimilarity, determining site sampling requirements for classifications and guiding decisions about ,lumping' or ,splitting' of classes. This will allow more informed decisions on selecting and improving classifications and map scales in an ecologically and statistically robust manner. [source] Combined definition of seed transfer guidelines for ecological restoration in the French PyreneesAPPLIED VEGETATION SCIENCE, Issue 1 2010S. Malaval Abstract Question: Can genetic tools combined with phytogeography help to define local plants and how geographically close the source population should be to the restoration site? Location: Subalpine and alpine French Pyrenees. Methods: The main phytogeographic boundaries in the French Pyrenees described by different authors were studied and this geographic pattern was compared with the results of genetic analysis for the four Pyrenean plants studied (Trifolium alpinum, Festuca eskia, Festuca gautieri and Rumex scutatus), based on random amplified polymorphic DNA (RAPD) marker analysis, unweighted pair-group method with arithmetic averages (UPGMA) analysis and Mantel correlograms comparing geographic and genetic distances. Results: The genetic analysis allowed definition of two main evolutionarily significant units (ESUs) for the plants under study. Although the limit between the two zones was slightly variable according to the species considered, an eastern and a western ESU was consistently observed. This delineation was concordant with the main phytogeographic boundaries of the French Pyrenees. Conclusion: RAPD markers and associated Mantel correlograms can be useful to draw ESUs for individual species when the sampling intensity is relatively dense, and similarities were revealed between species sharing the same distribution range. This delineation allowed integration of infraspecific plant variation in the management of natural resources for revegetation in the Pyrenees. Nevertheless, caution is needed for the establishment of seed pools in order to maximize genetic diversity in each of the pools during collection and production. [source] | |||||||||||||