Magnitude Of Spatial Variation Research Articles

Spatial structure in ecological communities – a quantitative analysis

The spatial structure of communities has recently gained much attention in ecology. Spatial structure comprises an important element in communities, but the literature lacks a thorough investigation about possible among‐organism or among‐ecosystem differences in the degree of spatial structure. Here, I conducted a quantitative review to determine if the degree of spatial structure varied predictably between the major organism types and ecosystems. Spatial structure was quantified as the relative fraction of community variation explained purely by spatial variables (fraction S/E). I integrated data from 322 variation partition analyses both in a generalized linear model (GLM) and using a boosted regression tree method, and showed that a mean of 11.0% of the variation in community composition was explained purely by spatial variables. Across all taxa, a body size–S/E relationship was positive. In GLM, fraction S/E increased highly significantly with study extent, it was highest among terrestrial taxa and higher in ectotherms than in homoiotherms. Spatial structure was also higher in omnivores than in autotrophs. These results suggest that the degree of spatial structure is jointly driven by extrinsic factors such as study extent and ecosystem type, and intrinsic factors such as body size, thermoregulation and interactions between body size and dispersal mode. These results should be important not only for basic research, but also conservation and bioassessment programs would benefit from the information about the magnitude of spatial variation in nature.SynthesisSpatial processes comprise an important element in most ecological communities, but the degree to which spatial structure varies across organisms or ecosystems is poorly known. Here, a quantitative review of 322 variation partition analyses indicated that spatial component varied predictably across ecological communities – it was driven by study extent and ecosystem type as well as by species traits such as body size and thermoregulation. These results give deep insights into the magnitude of spatial variation in nature and should be highly beneficial for conservation and bioassessment programs that are built on the information about how communities vary in space.

Geostatistical analysis of fruit yield and detachment force in coffee

The aim of this study was to use geostatistical analysis to evaluate the spatial variation in the detachment force of coffee fruit and coffee yield by variograms and kriging for precision agriculture. This study was conducted at Brejao farm, Tres Pontas, Minas Gerais, Brazil. The detachment force of green and mature coffee fruit was measured with a prototype dynamometer and georeferenced. The yield data were obtained from manual harvesting and were georeferenced. The data were evaluated by variograms estimated by residual maximum likelihood (REML), which provided a satisfactory approach for modeling all the variables with a small sample size. Spherical and exponential models were fitted, the first provided the better fit to mature fruit detachment force and the latter provided the better fit to coffee yield and green fruit detachment force. They were used to describe the structure and magnitude of spatial variation in the variables studied. Kriged estimates were obtained with the best fitting variogram models and mapped. The statistical and geostatistical analyses enabled us to characterize the spatial variation of the detachment force of green and mature coffee fruit and coffee yield and to visualize the spatial relations among these variables. The precision agriculture techniques used in this paper to collect, map and analyze the variables studied will help coffee farmers to manage their fields. Maps of coffee yield will enable farmers to apply nutrients site-specifically and manage harvesting either manually or mechanically. In addition, maps of detachment force of coffee fruit can enable farmers to harvest coffee selectively by choosing the appropriate places and the right time to start. This will improve the quality of the final product and also increase profits.

Geographic and temporal variation in the ant-seed dispersal assemblage of the perennial herb Helleborus foetidus L. (Ranunculaceae)

Spatio-temporal variations in the composition of the animal interactive assemblages may result in variations in selective pressures on the plants. In ant–seed dispersal mutualisms, the study of the magnitude of spatial and temporal variation of ant assemblages is rarely studied, limiting inferences and generalizations on the evolution of this mutualism. Here, we describe the ant–disperser assemblage of the myrmecochorous herb Helleborus foetidus in 14 populations across the Iberian Peninsula, and dissect the variation in the assemblage into spatial and temporal components as a first step to evaluate the evolutionary potential of this interaction. The ant–visitor assemblage of H. foetidus was mainly represented by species of Formicinae and it was highly diverse and variable in composition and function. Ants behaving as legitimate dispersers and those with mixed behaviour numerically dominated the assemblage compared with elaiosome consumers. The magnitude of the spatial variation was higher than the temporal variation, suggesting that the relative frequency of each functional group will be more foreseeable among years in each population than among populations. At the expense of further analysis of the effects of such variation on dispersal success, we can envisage a selection mosaic scenario, where local adaptive responses of plants might arise as a result of local variations in the specific composition and function of the assemblage. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 135–150.

Spatial variation in demography and population growth rate: the importance of natal location

1. Understanding the pattern and magnitude of spatial variation in demography and population growth rate (lambda) is key to understanding the structure and dynamics of natural populations. However, such spatial variation is challenging to quantify. We use>20 years of individual life-history data to quantify small- and large-scale spatial variation in demography and lambda within a single population of red-billed choughs Pyrrhocorax pyrrhocorax on Islay, Scotland. Critically, we demonstrate a major importance of an individual's natal rather than current location in driving observed spatial variation. 2. Breeding success (the number of offspring fledged per breeding attempt) varied among individual chough nest sites but did not vary on a larger spatial scale across Islay. 3. The proportion of fledglings observed to survive to recruiting age varied markedly among individual nest sites and also varied more widely across Islay. Spatial capture-mark-recapture models defined two discrete geographical regions where fledgling survival differed significantly: choughs fledged in region 'BGE' were more likely to survive than choughs fledged in region 'CNSW' as both subadults and adults. 4. The asymptotic lambda attributable to breeding attempts in region BGE exceeded unity, and exceeded that attributable to breeding attempts in region CNSW. Relatively productive and unproductive regions therefore exist within this population. 5. Spatial variation in adult survival was better explained by an individual's natal region than the region where that individual settled to breed. Spatial variation in lambda would consequently have remained undetected had survival been measured across resident breeders rather than across individuals fledged in each region. Furthermore, breeding success was a weak predictor of a nest site's estimated productivity of recruits. 6. We therefore describe marked spatial variation in demography and lambda within a single population of a territorial vertebrate, mediated partly by long-term links between an individual's natal location and its subsequent life-history. Life-long monitoring of individuals of known origin may therefore be necessary to identify accurately subpopulations of intrinsically high and low lambda.

The Strength and Structure of the Coronal Magnetic Field

I discuss a method for determining the strength and spatial structure of the coronal magnetic field by observations of the Faraday rotation of a radio galaxy which is in conjunction with the Sun. Given a knowledge of the plasma density in the outer corona, and the magnetic field sector structure (both independently available), the strength of the coronal field can be determined, as well as the magnitude of spatial variations on scales of 1000 km to several solar radii. Such knowledge is crucial for testing computational models of the solar corona, which are prominently featured in this meeting. Results are presented from observations with the Very Large Array radio telescope of the radio galaxy 3C228 on August 16, 2003, when the line of sight to the source was at heliocentic distances of 7.1−6.2R ⊙. The observations are consistent with a coronal magnetic field which is proportional to the inverse square of the distance in the range 6 ≤ r ≤ 10R ⊙, and has a value of 39 mG at 6.2R ⊙. The Faraday rotation is uniform across the source, indicating an absence of strong plasma inhomogeneity on spatial scales up to 35,000 km.

Spatial variability in soil properties on slow-forming terraces in the Andes region of Ecuador

Due to severe land degradation problems, soil conservation is a matter of major concern in the Ecuadorian Andes. Slow-forming terraces, a variation of hedgerow agro-forestry systems composed by contour grass barrier strips, can be considered as the most frequently used technique in Andean rural communities of Ecuador. However, due to shallow soils, terrace development often has the disadvantage causing gradients in soil properties from the upper to the lower elevations within the terrace. The main objectives of this study were to assess (i) spatial variability in soil properties on slow-forming terraces in the Andes and (ii) implications of variability for the management of this soil conservation technique. In order to measure spatial variability, soil sampling (0–15 cm) was carried out in bands following the contour, which were located every 1 m beginning at the highest point of elevation and including the lowest point on the terrace. Soil properties, such as pH(H 2O), pH(NaF), organic carbon, total nitrogen, NO 3 −, P, K, exchangeable aluminium, P fixation, exchangeable bases, cationic exchange capacity, base saturation and texture, were monitored on eight terraces, having slopes from 15 to 30%, a length of 4–8 m and soils ranging from Cambisols to Phaeozems, in the Ecuadorian Andes (Gima, Azuay). Terraces, which were 2–4 years, were managed in a traditional or more intensified way (i.e. without or with the application of organic manure). Bufferstrips were composed by (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability was analysed by stepwise multiple regression analysis, where position on the terrace was the independent variable and soil property was the dependent variable. Factor analysis was carried out in order to compare spatial variability patterns of the terraces and formulate management strategies. High spatial variability in soil properties was found. Although spatial variation was site dependent, it was clear that soil fertility increased from the upper to the lower part of the terraces. The present study shows that management strategy could influence the pattern and magnitude of spatial variation. Site-specific soil fertility improvement is suggested as means to combat variation caused by tillage erosion in slow-forming terraces.

Habitat structure, resources and diversity: the separate effects of surface roughness and macroalgae on stream invertebrates.

Habitat structure has pervasive effects on community composition and diversity, with physically complex habitats often containing more species than physically simple ones. What factors or mechanism drive this pattern is little understood, but a complicating problem is that different sources of habitat structure can be confounded in both surveys and experiments. In this study, we carried out an experiment in which two sources of habitat structure, attached macroalgae and substrate surface texture, were separately manipulated to discern their joint and separate effects upon the diversity and composition of colonizing macroinvertebrates in a stony, upland stream. Because stream algae vary markedly in abundance in both space and time, we also sampled the epilithon of stream stones at two spatial scales on eight dates over 2 years to gain some preliminary data on how stream algae vary between individual substrata over time. Experimental substrata had either a smooth (siltstones, sandstones, crystal-poor felsic volcanics, plain paving bricks) or rough (granodiorites, crystal-rich felsic volcanics, sand-blasted paving bricks) surface. We allowed these substrata to be colonized naturally by macroalgae, mostly the filamentous red alga Audouinella hermannii. Half of each of the rough and smooth substrata were selected at random and the macroalgae gently sheared off. All substrata were defaunated with a household insecticide with little field persistence, set out randomly through the study riffle, and invertebrates allowed to colonize them for 14 days. Some substrata were sampled immediately to check the efficacy of faunal and algal removals, which proved to be successful. Experimental results showed that both surface texture and macroalgae increase species richness independently of each other. Surface texture had no effect on densities, while macroalgae increased colonization densities, but rarefaction showed that both sources of habitat structure increased species richness above values expected simply on the basis of the numbers of colonists. However, reference stones with high macroalgal cover had the same species richness as those with low cover, suggesting that the effects of macroalgae on species richness are transient relative to those associated with surface texture. Epilithon samples taken at different times suggest that the magnitude of spatial variation in plant growth alters with time. If plants generally recolonize rough surfaces more quickly than smooth, then the effects of habitat structure on macroinvertebrates ought to be strongest after major disturbances during growing seasons of plants.

Geographic variation in polyphenolic levels of Northeastern Pacific kelps and rockweeds

Brown algal polyphenolic compounds are secondary metabolites whose functions may include protecting plants from pathogens or damage by UV radiation, and deterring feeding by herbivores. We present here the first analysis of spatial variation (at scales from tens of meters to hundreds of kilometers) in concentration of these compounds in two orders of brown algae from the northeastern Pacific Ocean. In kelps (order Laminariales), variation among sites was significant in only 25% of species examined and was consistent within families (high in the Alariaceae and low in the Laminariaceae and Lessoniaceae). In rockweeds (order Fucales, family Fucaceae), site variation was high in three of four species examined. Both the proportion of high polyphenolic kelp species and the magnitude of spatial variation within species from both kelps and rockweeds were much higher than would have been predicted from previous studies in other regions. In one kelp (Laminaria groenlandica), significant differences between sites occurred at scales of only tens of meters. No latitudinal clines were observed. Differences in phenolic concentrations of kelps spanned nearly an order of magnitude in one species, Hedophyllum sessile. Phenolic levels were significantly higher in members of the Fucales than the Laminariales, but showed no significant differences between intertidal and subtidal species.

Spatial and Temporal Variations in Surface Albedo of a Subarctic Landscape Using Surface-based Measurements and Remote Sensing

Spatial and temporal variation in summertime albedo of a subarctic landscape near the Hudson Bay coast is examined using ground-based measurements and Landsat Thematic Mapper (TM) imagery. Temporal variation in surface albedo was determined using an extensive data set from six tower sites with multiple years of data. Four distinct patterns in evolution of the seasonal trend in daily albedo were discovered for the six sites and appeared to be related to vegetation and surface moisture characteristics. All sites showed an albedo response to solar zenith angles greater than 60 degrees, at smaller zenith angles hourly albedo was a good representation of daily values.TM imagery from a dry year (1984) and a wet year (1991) were used to derive maps of albedo for the study area. Spatial variation of albedo was examined within representative training areas centered on the six tower sites. The magnitude of spatial variation in albedo was typically less than 0.04 for all sites. Spatial variability was slightly greater in the wet year. A one pixel transect of albedo across the study area showed the largest difference between lakes and terrestrial surfaces. However, within the terrestrial zones, alternating patches of open forest and tundra and differences in wetness create a coherent pattern in albedo across the landscape.

Adult emergence phenology in checkerspot butterflies: the effects of macroclimate, topoclimate, and population history.

The prediction of adult emergence times in insect populations can be greatly complicated by microclimatic gradients, especially in circumstances where distributions of juveniles along those gradients vary from year to year. To investigate adult emergence patterns in topographically heterogeneous habitats, we built a model of postdiapause development of the Bay checkerspot butterfly, Euphydryas editha bayensis. The model uses slope-specific insolation as the rate-controlling variable, and accounts for both solar exposure of the habitat and cloud cover. Instar-specific larval mass gains per unit of insolation were determined from mark-recapture experiments. A small correction for daily low temperatures was used to calibrate the model to five years of field data on larval mass. The model predicted mean mass of 90% of larval samples within 4 clear days over a 70-120 day growing season. The magnitude of spatial variation in emergence times across habitat slopes is greater than annual variation in emergence times due to yearly weather conditions. Historical variation (yearly shifts in larval distributions across slopes) is an important determinant of mean population emergence dates. All of these factors need to be considered in understanding adult emergence phenology in this butterfly and in other insects inhabiting heterogeneous thermal environments. Such an understanding can be useful in managing insect populations for both pest control and conservation.

Effects of a pipeline right-of-way on sediment yields in the Spring Creek watershed, Alberta

Very few data are available on the sediment yield of Alberta watersheds especially in the northern portion of the province. In the 175 000 km2 Peace River basin, which covers about 25% of Alberta, sediment data are collected regularly at only four stations. One of these is the 112.7 km2 Spring Creek watershed. In 1977 a pipeline was installed near the mouth of Spring Creek, disturbing an area of about 5000 m2 near the stream channel. The effects of this were to increase local sediment yields by over 1600 Mg in a 4 month period. This compares with regional averages for the Peace River basin of 18–88 Mg∙km−2∙year−1. The study indicates the magnitude of spatial variation of sediment production and shows some effects of geotechnical activities on sediment yields.