Quadrat Research Articles

Abundance estimation of rocky shore invertebrates at small spatial scale by high-resolution digital photography and digital image analysis

We have tested both the usefulness of high-resolution digital photography for data acquisition and digital image analysis, by non-supervised classification and high pass filter, for recognition and abundance estimation of benthic intertidal organisms. These digital tools were compared with visual scan and photo quadrat conventional methods. The comparison was done using 40 quadrats (10×5 cm) randomly selected along a 5-m transect on the rocky shore of the Pemaquid Point, Maine, USA. ANOVA for repeated measures was used to test differences among methods. Monte Carlo simulation analysis was used to explore differences among methods over a large set of data ( n=100, 500, 1000 quadrats). Differences among methods were observed when 40 quadrats were used. Tukey multiple comparison test showed that abundance estimation from visual scan, photo quadrat and digital image analysis by high pass filter do not differ significantly among them but differ from non-supervised classification results. Due to its accurate estimation, high pass filter (Prewitt) method was chosen as the most reliable digital method to estimate species abundance. Monte Carlo simulation of visual scan, photo quadrat and high pass filter results showed significant differences when the number of quadrats was larger. These results showed that the combined use of digital photography and digital image analysis techniques for the acquisition and analysis of recorded data is a powerful method for the study of intertidal benthic organisms. Results produced using these techniques were similar than those produced by conventional methods but were obtained in a much-reduced time.

Point vs. photo quadrat estimates of the cover of sessile marine organisms

Point and photo quadrats were used to estimate the percent cover of organisms in three moderately layered intertidal assemblages in central california. Photo quadrats were done by photographing and mapping 30 × 50 cm areas with and without overstories moved aside. Photographs were projected over a grid of 100 dots and the organism under each dot recorded. Point quadrats were done by recording successive contacts of a pointed rod lowered vertically at 50 random locations within the same areas sampled with photo quadrats. Point quadrats produced 1.6–2.3 times higher total cover estimates, higher individual cover estimates for almost every taxon sampled, a higher number of total taxa, but lower precision than photo quadrats. While commonly called point quadrats, grids of intersecting lines or dots on transparent sheets are probably more similar in accuracy to photo quadrats. We suggest calling such devices grid quadrats to distinguish them from true point quadrats where actual contact is made with the organisms being sampled. Except for monolayered assemblages with few species in large patches, or in studies where only the overstory is of interest, point quadrats give a more accurate measure of cover than do photo quadrats, and take only slightly more time in the field.

Les conséquences d’un supplément alimentaire sur la dynamique des populations de rongeurs au Sénégal. I. Le cas de Mastomys erythroleucus en zone sahélo-soudanienne

The Mastomys erythroleucus population of a sahelo-sudanian woodland has been studied from August 1976 to October 1979 on two quadrats : a control quadrat (QC) 2.5 ha in size, and a provisioned quadrat (QA) 4 ha in size, where food pellets were regurlarly provided twice a week since September 1976 (yearly food supplement : 120 kg/ha/yr). The following changes were observed on the provisioned quadrat : (1) an increased population density, (2) an increased production of young, and (3) an improvement of their survival rate. Two further changes were also noticed : (4) while the number of immigrants was not significantly different on the two quadrats during the experiment, the duration of their stay was greater on the provisioned area than on the control area, and (5) the size of the resident females home ranges was decreased. Whereas the experimental increase in food availability and predictibility triggered in this case an increase in Mastomys erythroleucus population density through a better recruitment, it was not influential in preventing the population decline which took place at a similar rate on both quadrats in 1977.

Quadrat Inventory of Pheasant Trends in Oregon

Quadrat Inventory of Pheasant Trends in Oregon