Quadrat Counts Research Articles

Drastic decline of an extensive eelgrass bed in Nova Scotia due to the activity of the invasive green crab (Carcinus maenas)

In 2001–2002, there were severe declines of eelgrass (Zostera marina) in estuaries along the Nova Scotia coast of the southern Gulf of St. Lawrence. We examined the relationship between the recent invasion of European green crabs (Carcinus maenas) and the eelgrass decline in Benoit Cove in Tracadie Harbour. The abnormally abundant eelgrass wrack consisted mainly of entire shoots, not the usual blades. Three separate methods yielded similar estimates of the rate of shoot removal from the eelgrass beds (direct quadrat counts, “mark–recapture” of tagged shoots in the eelgrass bed, and rate of shoot appearance in the shore wrack). From 14 July to 8 September 2002, the shoot density in the bed fell by about 75 %. Similar rates of decline occurred in crab enclosures (4.4 crabs m−2) placed in the eelgrass bed. Green crab foraging, involving the tearing of shoots and the digging of large pits, was the reason for the drastic decline of the eelgrass bed in Benoit Cove. It is clear that an invasion of green crabs to a region where they had not previously existed can both destroy eelgrass beds and restrict their recovery.

FOREST SPECIES CLASSIFICATION BASED ON STATISTICAL POINT PATTERN ANALYSIS USING AIRBORNE LIDAR DATA

Abstract. The paper investigated the effectiveness of point pattern methods in the application of forest species classification using airborne LiDAR data. The forest stands and individual trees in our study area were classified as either shade tolerant or intolerant species. The purpose of adopting the point pattern methods is to develop new features to effectively characterize the pattern of internal foliage distribution of forest stands or individual trees. Three methods including Quadrat Count, Ripley's K-function, and Delaunay Triangulation were applied, and six feature groups were derived for a stand or tree sample. Feature selection was performed based on the derived features in order to find the best ones for the following classification procedure, which was implemented by two supervised and two unsupervised methods. These newly derived features were proved effective for the classification. The highest classification accuracy 97% was achieved at stand level and 90% at individual tree level. The sensitivity of classification accuracy to the number of features used was also investigated in this paper.

Spatial Analysis of High Resolution Aerial Photographs to Analyze the Spread of Mountain Pine Beetle Infestations

Mountain pine beetle (Dendroctonus Ponderosae) infestations in Western Canada have reached alarming proportions. The spread of attacks has significantly impacted pine tree stocks, the forest ecosystem in general and the overall socio-economic condition of residents in communities that depend on the forest industry. The ability to track these attacks and anticipate their trajectories will allow forest managers to target intervention measures and improve mitigation efforts. Spatial analysis methods are well suited to characterize the dynamics of the mountain pine beetle attacks. This study implemented a multi-scale spatiotemporal analysis to describe the patterns of three consecutive attack years (2000-2002) for a 19 km2 study site in British Columbia, Canada. In the first stage, baseline complete spatial randomness (CSR) was examined using average nearest neighbour analysis and quadrat counts on infestation data extracted from 19 cm resolution black and white aerial photographs. In the second stage, global and local Moran’s I spatial autocorrelation statistics, Getis-Ord General G global high/low clustering and Getis-Ord G_i^* test statistic techniques were used to evaluate the spread patterns over time. The results show a significant clustering of attack sites in the first two years, with considerable changes in the attack spread in the third year. These changes were independent of the two levels of spatial resolution used. Knowledge about infestation patterns can be used to anticipate needed social and environmental assistance for affected communities. Further, the information can aid overall sustainable forestry management.

Study of initial stages of thin film growth by means of computer simulation and image analysis: Advanced atomistic modelling

A method of computer experiment was used for a study of nucleation and initial stages of three-dimensional film growth. In the first part of the experiment, the simulated structures with given parameters were generated by a model combining the molecular dynamics and Monte Carlo approaches. In the second part, the acquired structures were analysed by means of morphological methods. The ‘Quadrat Counts’ method and Voronoi tessellation were used and compared. The influence of individual modelled parameters such as deposition rate, contact angle and condensation coefficient was studied and discussed. The used morphological methods were also applied on the TEM images of indium films in order to compare the obtained results.

Irrigation frequency influences establishment of silvery thread moss (Bryum argenteum Hedw.) and rooting of creeping bentgrass (Agrostis stolonifera L.) on simulated golf greens

The encroachment of moss on creeping bentgrass (Agrostis stolonifera L.) golf greens is a significant problem throughout the world. Although chemical control products for moss exist many are not registered for this use in Europe and Canada. As a result turfgrass managers must rely on cultural methods to manage moss encroachment. A survey of 15 golf courses in southwestern Ontario positively identified silvery thread moss (Bryum argenteum Hedw.) (STM) as the primary species of moss present. In order to determine the effects of irrigation practices on STM establishment two independent greenhouse experiments were conducted in which the quantity and frequency of irrigation were altered. Pots containing creeping bentgrass were inoculated with STM and irrigated at either 75% or 100% open pan evaporation (Eo) and at 1-, 2-, 4-, or7-day intervals. Volumetric water content was measured in the top 5.7 cm of the pots to confirm that changes in water availability were a result of irrigation practices. Between the two levels tested, irrigation quantity had no effect on the presence of STM. In the first experiment irrigation at 1-day and 2-day intervals had significantly more STM invasion than irrigation at 4- and 7-day intervals. In the second experiment point quadrat counts showed that irrigating at both 1-day and 2-day intervals resulted in significantly more STM and that the most moss was observed with the daily irrigation regime. Root data were also collected to determine the effect of irrigation practices on root mass. The daily irrigation treatments in both experiments had reduced root mass although in the first experiment only the root mass below 12 cm was lower. In the second experiment the total root mass was highest for the 4-day irrigation interval with the 2- and 7-day intervals having intermediate root mass and daily irrigation resulting in the least.

A test for space limitation with an application to recently settled lobsters

Space limitation in larval settlement can play an important role in the population dynamics of marine species. A novel statistical test for space limitation based on quadrat counts of individuals is described. The test is based on identifying a significant relationship between the relative dispersion of quadrat counts and overall mean density. An application to a time series of quadrat counts of recently settled American lobsters Homarus americanus covering the period 1993–2007 in Casco Bay, Maine, USA (43°45′N; 69°58′W), is presented. For this data set, the null hypothesis that space is not limiting could not be rejected (P = 0.10).

Pitfall trapping bias and arthropod body mass

Abstract. 1. Pitfall trapping is one of the most widely used arthropod sampling techniques. However, relative species abundance in pitfall trap catches differs from that found using quadrat samples. This difference, here termed bias, reflects the fact that pitfall trap catch is influenced not only by abundance but also by other factors, including activity, which may be linked to body size. Here, we investigate whether the bias affecting pitfall trap catches of a particular species is related to the typical body mass of individuals of that species.2. Data were extracted from five studies where pitfall trapping bias was quantified and covered 32 species of spiders and carabid beetles. Bias was expressed as the ratio of biomass captured by pitfall traps to that measured by quadrat counts (four field studies), or as the product of mean speed of movement and probability of capture per trap encounter, at standard density (one laboratory study).3. Pitfall trapping bias and body mass were strongly related on a log–log scale, with log(body mass) explaining 78% of the variation in log(bias) (P < 0.0001). There was no significant effect of arthropod group (spiders, carabids) or study location (field, laboratory).4. A method is proposed to correct pitfall catches of each of a group of species, based on the typical body mass of an individual of each species. This approach may remove much of the bias in pitfall trap data and so improve the value of this type of data in studies of arthropod communities.

Quadrat Count, June 2011

Quadrat Count, June 2011

Analysis of electroperforated materials using the quadrat counts method

The electroperforation distribution in thin porous materials is investigated using the quadrat counts method (QCM), a classical statistical technique aimed to evaluate the deviation from complete spatial randomness (CSR). Perforations are created by means of electrical discharges generated by needle-like tungsten electrodes. The objective of perforating a thin porous material is to enhance its air permeability, a critical issue in many industrial applications involving paper, plastics, textiles, etc. Using image analysis techniques and specialized statistical software it is shown that the perforation locations follow, beyond a certain length scale, a homogeneous 2D Poisson distribution.

Study of initial stages of thin film growth by means of atomistic computer simulation and image analysis

Nucleation and initial stages of three-dimensional film growth were studied by a computer experiment. The experiment consisted of two parts – preparation of simulated thin-film structures and computational analysis of their images. The simulated structures were generated by a model combining the molecular dynamics and Monte Carlo approaches. The analysis of the obtained structures was based on the ’Quadrat Counts’ method, which proved to be one of the most promising algorithms of image processing. The results obtained by image analysis of simulated thin films were discussed and the most suitable algorithms were suggested for the analysis of experimentally prepared films.

Application of the quadrat counts method to the analysis of the spatial breakdown spots pattern in metal gate/MgO/InP structures

The breakdown spots spatial distribution in NiSi/MgO/InP structures is analyzed using the quadrat counts method, a classical statistical technique aimed to evaluate the deviation from complete spatial randomness. The spots appear as black dots spread over the gate electrode area and are the result of important local thermal effects occurring during the current runaway associated with the formation of the percolation paths across the dielectric film. Using image analysis techniques and specialized statistical software it is shown that the spots’ locations follow a homogeneous 2D Poisson distribution, what can be regarded as an indirect indicator of the quality and uniformity of the samples under investigation.

Does Bird Predation Enhance the Impact of Green Muscle® (Metarhizium acridum) used for Grasshopper Control?*

A study at Khelcom, Central Senegal, from September 2008 till June 2009 tested two different dose rates (25 and 50 g conidia/ha) of the mycoinsecticide Green Muscle® (Metarhizium acridum) and an untreated control, against grasshoppers in a field trial on nine 400-ha plots in three blocks. The study area was a deforested sylvo-pastoral reserve, 12.5% cultivated, whereas the remainder was fallow or grassland in succession. Grasshopper densities were calculated by executing transect and quadrat counts on plots. The grasshopper community structure was assessed by systematic sweep-net sampling on plots. From these data grasshopper biomass on plots was calculated for each sampling date. Bird numbers were counted on the same transects by the Distance Sampling technique and their densities calculated from Effective Strip Widths (ESW). Energetic requirements of individual bird species were calculated from digestibility-corrected Field Metabolic Rates (FMRs) and for acridivorous species their daily intake of grasshoppers was calculated. Grasshopper densities were very high, with up to 90 ind./m2 in September and 30–35 ind./m2 in October. Numbers and biomass decreased on treated plots as grasshoppers became infected, and remained significantly different from control plots for three months (until January). The relative importance of grasshopper consumption by birds increased between October (high grasshopper densities) and December (medium densities) from an initial 0.06 (±0.03) %/day to a ceiling of 1.6 (±0.9)% per day. Total grasshopper removal during the dry season was 70 %, whereas during the rainy season this was < 1%. Birds specifically captured large and medium-bodied grasshoppers, but rarely small-bodied species, whose numbers initially increased. These findings were corroborated by field observations and by analysis of regurgitated pellet contents of Montagu's Harriers, i.e., small-bodied grasshoppers were only 1.4 – 2.6% of all grasshoppers taken, whereas they constituted 61 – 68% of random samples from the field. Densities of acridivorous Palaearctic migratory birds, in particular White Stork, Ciconia ciconia, Montagu's Harrier, Circus pygargus and Lesser Kestrel, Falco naumanni, were very high and unprecedented elsewhere. Their numbers largely exceeded the 1% criterion for international importance.

Analysis of spatial pattern of settlements in the federal capital territory of Nigeria using vector-based GIS data

Human settlements are important, seemingly static but dynamic, features of the cultural landscape that have attracted several studies due to the important role they play in human life. This paper examined the spatial distribution of settlements in the Federal Capital Territory (FCT) of Nigeria. The analysis uses vector based GIS data derived from the 1989 political map of the FCT. Map composition was done with ArcView 3.2a software and the nearest neighbour statistics was computed using the pattern analysis function of Ilwis 3.0 software. The result of the quadrat count analysis yielded a variance mean ratio of 1.34 to show that the settlements of the FCT were clustered in space as opposed to the subjective findings of some authors, which suggested that the settlements were evenly spread. Analysis of the degree of clustering reveals that 51 per cent of all settlement pair has a separation of less than four kilometres, 63 per cent has a separation of less than five kilometres, 79 per cent has less than six kilometres while 97 per cent has a separation of less then nine kilometres. It was thus found out that, for 80 per cent of all settlements in the point map, one nearest neighbour can be found within a radius of 2 kilometres. Also, for 68 per cent of the settlements, three nearest neighbours can be found while for 60 per cent of the settlements, six nearest neighbours can be found within a radius of 2 kilometres. Analysis of the distance at which neighbours could be found revealed that the probability of finding six neighbours becomes 1 at a distance of one kilometre. This indicates that, we are 100 per cent sure of finding 6 nearest neighbours within a distance of one kilometre radius on the map.

Electrical properties of nanocomposites near percolation threshold – dynamics

The paper deals with analysis of morphology and electrical properties of (nano)composite films. It describes a computer simulation tool for morphological and transport analysis of the films. Two models of composite structures are prepared — a hard disk and soft disk model. Their morphology is studied by the covariance, Quadrat Counts method, and Voronoi tessellation. Some specific characteristics of the methods are introduced. The electric properties are studied by the Monte Carlo simulations via tunnel charge transport. The results for d.c. conductivity as well as in case of changing voltage are done.

Variability and community organization in moderately exposed tropical rocky shore algal communities as influenced by different consumer groups

AbstractTropical rocky shores have been described as diverse and having a complex variety of consumers. This wide array of consumers has been studied to shed light on the different roles of consumers, particularly grazers on rocky shores and how they affect the relative abundance and distribution of sessile algal prey. One of the aims of ecology is to clarify factors that regulate and structure the abundance, growth and relationship of predators and preys in each habitat. Grazing is known as one of the most important determinants of growth and distribution of rocky shore communities. In this study a comparison between the different effects of fishes, crabs and molluscan herbivores on the relative abundances of microalgae and macroalgae from micro (hundreds of microns) to medium (tens of meters to kilometers) scales of spatial variability was conducted. At the start of the experiment several hypotheses were forwarded: 1) that herbivores will reduce the density of microalgae and macroalgal cover causing a barren appearance and ultimately reducing algal diversity where grazing intensity is highest across treatments, sites and shores; 2) and where grazing pressure is low, algal cover and diversity will be high; 3) and that fishes and crabs contribute significantly to maintaining a high grazing pressure in the area and that fishes control the algal assemblage in benign environments. These were evaluated by exclusion experiments and quadrat counts to determine the effects of grazers on different functional groups of algae. Microalgal density was assessed indirectly by measuring chlorophyll a from rock chips taken from the treatment plots. Microspatial variability of different sites was assessed by scoring digital micrographs of rock chips also taken from treatment plots. Algal cover of treatment plots was assessed by using digital photos taken during forthnightly visits in all sites. The univariate and multivariate results show significant differences across treatments, sites and shores and even significant temporal differences. Microalgal abundance and erect algal cover in fenced plots were significantly different compared to the other treatments. Grazer removal effectively caused a completely different algal assemblage to develop through time in cage and fenced treatments while maintaining a mostly barren cover in most open and control set-ups. Species which are not typically present in shores have grown inside cage and fenced treatments during the period of manipulation. Molluscan herbivores are the most effective grazers in these shores and control the relative distribution of algae by restricting the recruitment success of algal sporelings particularly erect macroalgae. Herbivorous fishes and crabs do not directly influence algal sporelings since the early stages of algae are too small for them to handle. But both consumers complement the removal of turf forming algae. The observed over all grazing effects show that molluscs have greater impact than fishes and crabs combined; the effect of either fishes or crabs are equal. Hence, the impact of crabs and fishes on these shores are minimal, mainly affecting turf forming algae. Moreover, the observed spatial variability in algal assemblage from micro to medium scales is mainly driven by high grazing intensity. Thus, grazing acts as a highly effective top down control mechanism in these shores during the cool winter season.

Variability and community organization in moderately exposed tropical rocky shore algal communities as influenced by different consumer groups

Tropical rocky shores have been described as diverse and having a complex variety of consumers. This wide array of consumers has been studied to shed light on the different roles of consumers, particularly grazers on rocky shores and how they affect the relative abundance and distribution of sessile algal prey. One of the aims of ecology is to clarify factors that regulate and structure the abundance, growth and relationship of predators and preys in each habitat. Grazing is known as one of the most important determinants of growth and distribution of rocky shore communities. In this study a comparison between the different effects of fishes, crabs and molluscan herbivores on the relative abundances of microalgae and macroalgae from micro (hundreds of microns) to medium (tens of meters to kilometers) scales of spatial variability was conducted. At the start of the experiment several hypotheses were forwarded: 1) that herbivores will reduce the density of microalgae and macroalgal cover causing a barren appearance and ultimately reducing algal diversity where grazing intensity is highest across treatments, sites and shores; 2) and where grazing pressure is low, algal cover and diversity will be high; 3) and that fishes and crabs contribute significantly to maintaining a high grazing pressure in the area and that fishes control the algal assemblage in benign environments. These were evaluated by exclusion experiments and quadrat counts to determine the effects of grazers on different functional groups of algae. Microalgal density was assessed indirectly by measuring chlorophyll a from rock chips taken from the treatment plots. Microspatial variability of different sites was assessed by scoring digital micrographs of rock chips also taken from treatment plots. Algal cover of treatment plots was assessed by using digital photos taken during forthnightly visits in all sites. The univariate and multivariate results show significant differences across treatments, sites and shores and even significant temporal differences. Microalgal abundance and erect algal cover in fenced plots were significantly different compared to the other treatments. Grazer removal effectively caused a completely different algal assemblage to develop through time in cage and fenced treatments while maintaining a mostly barren cover in most open and control set-ups. Species which are not typically present in shores have grown inside cage and fenced treatments during the period of manipulation. Molluscan herbivores are the most effective grazers in these shores and control the relative distribution of algae by restricting the recruitment success of algal sporelings particularly erect macroalgae. Herbivorous fishes and crabs do not directly influence algal sporelings since the early stages of algae are too small for them to handle. But both consumers complement the removal of turf forming algae. The observed over all grazing effects show that molluscs have greater impact than fishes and crabs combined; the effect of either fishes or crabs are equal. Hence, the impact of crabs and fishes on these shores are minimal, mainly affecting turf forming algae. Moreover, the observed spatial variability in algal assemblage from micro to medium scales is mainly driven by high grazing intensity. Thus, grazing acts as a highly effective top down control mechanism in these shores during the cool winter season.

The alien invasive land snail &lt;i&gt;Theba pisana &lt;/i&gt;in the West Coast National Park: Is there cause for concern?

The distribution, abundance, size distribution and diurnal activity patterns of invasive land snails, Theba pisana, in the West Coast National Park (WCNP), South Africa, were investigated. The park was divided into 1 km2 grids, within each of which five 1 m2 quadrat counts of live snails were recorded. Of 106 grids sampled, 19% contained live snails. The average density of snails was 4.04 m-2 ± 24.9, significantly lower than in disturbed habitats adjacent to the park (57 m-2 ± 96.25), but very high densities were recorded at two sites. Snails were most abundant along roadsides and densities decreased dramatically with distance from roads. T. pisana in the WCNP appear to have an annual lifecycle, breeding in autumn to winter and growing to adult size of about 14 mm diameter by the end of the following summer. Snails were observed on a wide variety of endemic and introduced plant species and appeared to have a catholic diet. They are active mostly at night and especially during periods of high humidity, irrespective of temperature. Given the very high densities that T. pisana can attain at some sites, plus their apparently catholic feeding habits, their potential impact on the vegetation of the park is cause for concern and should be further investigated. Control of the main colonies should also be considered.

Visualization of spatial patterns and temporal trends for aerial surveillance of illegal oil discharges in western Canadian marine waters

This paper examines the use of exploratory spatial analysis for identifying hotspots of shipping-based oil pollution in the Pacific Region of Canada’s Exclusive Economic Zone. It makes use of data collected from fiscal years 1997/1998 to 2005/2006 by the National Aerial Surveillance Program, the primary tool for monitoring and enforcing the provisions imposed by MARPOL 73/78. First, we present oil spill data as points in a “dot map” relative to coastlines, harbors and the aerial surveillance distribution. Then, we explore the intensity of oil spill events using the Quadrat Count method, and the Kernel Density Estimation methods with both fixed and adaptive bandwidths. We found that oil spill hotspots where more clearly defined using Kernel Density Estimation with an adaptive bandwidth, probably because of the “clustered” distribution of oil spill occurrences. Finally, we discuss the importance of standardizing oil spill data by controlling for surveillance effort to provide a better understanding of the distribution of illegal oil spills, and how these results can ultimately benefit a monitoring program.

Spatial statistics of pitting corrosion patterning: Quadrat counts and the non-homogeneous Poisson process

This paper presents a stochastic analysis of spatial point patterns as effect of localized pitting corrosion. The Quadrat Counts method is studied with two empirical pit patterns. The results are dependent on the quadrat size and bias is introduced when empty quadrats are accounted for the analysis. The spatially inhomogeneous Poisson process is used to improve the performance of the Quadrat Counts method. The latter combines Quadrat Counts with distance-based statistics in the analysis of pit patterns. The Inter-Event and the Nearest-Neighbour statistics are here implemented in order to compare their results. Further, the treatment of patterns in irregular domains is discussed.

Testing the spatial significance of weed patterns in arable land using Mead’s test

SummaryThere is a need in weed science for statistical tests for patchiness and spatial pattern. The objective of this study was to investigate the performance of Mead’s test for detecting patterns in synthetic data and in real weed counts made in maize, and making a first assessment of its applicability in ecological studies on weeds. In an extension to Mead’s test, made here for the first time, we merge original quadrat count data into rectangular cells of m by n quadrats. Care was taken to rule out the effect of starting point on the test result. Using the synthetic data, we demonstrate the ability of the test to detect both patchiness and homogeneity as deviations from randomness. The first deviation results in right‐sided significance, and the second in left‐sided significance of the test. Analysis of the real weed patterns demonstrated patchiness at many scales for five of the six investigated species and lack of any deviation from randomness in the sixth: Taraxacum officinale. The latter was the only wind dispersing species in the dataset. No deviation towards homogeneity was found in any of the real weed species at any scale. All patchy patterns showed anisotropy, being elongated in the direction of field traffic. As it turns out, Mead’s test is well suited to detect departures from randomness in observed weed patterns and enhances the suite of diagnostic tools that can be employed by weed ecologists.