Point Count Sampling Research Articles

Traditional Agriculture and the Conservation of Biological Diversity in Crete, Greece

The biological diversity in traditional agroecosystems and potential diversity loss associated with land use change in upland Crete was investigated. Using transects, plots and point count sampling methods, the dominant vegetation types and land uses, floristic diversity, breeding birds, and key biophysical attributes of remnant traditional agroecosystems in three upland catchments were identified. Eight vegetation/land use types were observed, including: chestnut stands, old olive groves, maquis, phrygana, intensively cropped parcels, rock walls and hedges, woodlands, and intensive olive groves. Eighty-three native plant species in traditional agroecosystems were recorded, the majority of which were shade intolerant perennial herbs and shrubs adapted to grazing and browsing. The vegetation types/land uses were distributed in a complex mosaic across the landscape, exhibited a wide range of light conditions, structural attributes, percent ground cover, soil organic matter levels, and provided breeding habitat for at least 19 bird species. Traditional farming, grazing and forestry are declining throughout the northern Mediterranean. Woodlands and intensive olive monocultures have replaced diverse land use mosaics and contain less biological diversity than traditional agroecoystems. The conservation of Mediterranean floristic diversity necessitates understanding disturbance regimes and may require maintaining the land use practices and mosaics associated with traditional cultivation practices and livestock grazing.

Effects of point count protocol on bird abundance and variability estimates and power to detect population trends

Abstract We used a three-year point-count data set from Hoosier National Forest, Indiana, to evaluate alternative point-count sampling strategies for detecting songbird declines. Repeated-measures ANOVA indicated that mean abundance estimates increased with increasing count radius (P < 0.0001, each species), and coefficients of variation (CVs) decreased. Mean abundance estimates increased with longer count duration (6-, 8-, and 10-min) for only two of 13 species, and CVs did not necessarily decrease. The power to detect a 5% annual population trend increased with more survey points, more visits per point, and more years of surveys. Managers can use observer time most efficiently by employing counts of short duration. Counts using a larger radius will reduce CVs and therefore provide potentially better annual estimates of abundance and power to detect changes over a period of years. The design of the study and nature of the variability in bird abundance will determine whether increasing the number of point...

REVISIT SCHEDULE DOES NOT AFFECT RESULTS OF POINT COUNTS

We compared two fixed-radius point count sampling regimes using two abundant breeding species, the Dark-eyed Junco (Junco hyemalis) and the Chestnut-sided Warbler (Dendroica pensylvanica), in a forested landscape in the southern Appalachian mountains of Virginia. The same 20 points were counted three times under each of two revisiting schedules, either hourly or weekly, and the maximum and mean number of males recorded. Revisit schedule had no detectable effect on numbers of either species recorded, regardless of whether the fixed radius was 50 or 100 m or whether count duration was 5 or 10 min. For juncos, the maximum number of birds detected using an hourly revisit schedule with a 100-m fixed-radius count circle and a 5-min or 10-min count duration provided close matches to the density estimated by intensive territory mapping of this color-banded population (0.398 males/ha or 0.298 males/ha respectively, versus 0.325 known breeding males/ha). When revisiting count stations is desirable, the use of a 1-h revisit schedule provides an economical way to increase number of visits, with no apparent reduction in precision or accuracy of the estimate.

Refining the Use of Point Counts at the Scale of Individual Points in Studies of Bird-Habitat Relationships

Useful sampling guidelines have recently been provided to improve the precision of bird population parameter estimates from point count data. Less attention has been given, however, to the issue of accuracy or completeness of counts at each sampling point. While it may not be critical in studies that compare average counts among study plots, completeness of counts at the level of individual points may pose several problems in studies that assess relationships between response variables (species' occurrence or abundance) and explanatory variables (vegetation structure, size and isolation of the fragment, proportion of interior habitat) on a point by point basis. Reliability of models in such studies is greatly dependent on the accuracy of counts at each point. We examined how bias of incomplete counts could be minimised through refinements of the point-count method. Six forest types of the northeastern deciduous forest in Quebec (Canada) were intensively surveyed during an entire breeding season. Census performances of the point-count method for measuring species richness at individual points were assessed by resampling the original data set for a simulated census protocol of two visits at a point. Effects of daily variation, time of season, time of day, and count duration were tested. Census performances of counts conducted the same day were significantly poorer than counts from different days. Census performances were influenced by the time of season during which counts were conducted. When pooled across habitats, census performances for counts that combined visits at the beginning and at the end of the breeding season were significantly better than counts that were concentrated in either one of these periods. The 05:00 to 08:30 morning period yielded the best results for five of the six habitats. Census performances in open field were, however, significantly better during the first sampling period (04:30), suggesting that bird censuses in open habitats could be initiated before sunrise. Longer counts (25 and 20 min) greatly improved species richness estimates at a point. For studies that focus on comparisons at the scale of individual points, longer counts are preferable to short counts (15 and 10 min). We stress the importance of the scale (study plots or individual points) at which statistical analyses of point count data are conducted in the decision-making process of point count sampling procedures.

Optimal Allocation of Point-Count Sampling Effort

Both unlimited and fixed-radius point counts only provide indices to population size. Because longer count durations lead to counting a higher proportion of individuals at the point, proper design of these surveys must incorporate both count duration and sampling characteristics of population size. Using information about the relationship between proportion of individuals detected at a point and count duration, we present a method of optimizing a point-count survey given a fixed total time for surveying and travelling between count points. The optimization can be based on several quantities that measure precision, accuracy, or power of tests based on counts, including (1) mean-square error of estimated population change; (2) mean-square error of average count; (3) maximum expected total count; or (4) power of a test for differences in average counts. Optimal solutions depend on a function that relates count duration at a point to the proportion of animals detected. We model this function using exponential and Weibull distributions, and use numerical techniques to conduct the optimization. We provide an example of the procedure in which the function is estimated from data of cumulative number of individual birds seen for different count durations for three species of Hawaiian forest birds. In the example, optimal count duration at a point can differ greatly depending on the quantities that are optimized. Optimization of the mean-square error or of tests based on average counts generally requires longer count durations than does estimation of population change. A clear formulation of the goals of the study is a critical step in the optimization process.

Application of stereological analysis of cell volume to isolated myocytes in culture with and without adrenergic innervation

A three-dimensional analysis to evaluate structural changes in cultured cardiac myocytes following adrenergic innervation was performed using stereological techniques formerly limited to cells in tissue and organs. Cell volumes were calculated for two groups of cells at 96 hours in culture: isolated myocytes and myocytes innervated with adrenergic neurons. Relative and absolute volumes of the nucleus, cytoplasm, and cell were quantified by systematically sampling sections throughout the cell and by point count sampling techniques. Volumetric estimates were similarly determined for the mitochondria, sarcomeres, and other cellular components in the cytoplasm. Data were analyzed with ANOVA and randomized block design to control for variation among the cultures. Adrenergic innervation produced a 44% increase in cell volume, X +/- SEM, (3,344 +/- 196 microns3 to 4,816 +/- 400 microns3, P = 0.007). The absolute volume of mitochondria significantly increased after innervation (521 +/- 42 microns3 to 744 +/- 54 microns3, P less than 0.01). Absolute sarcomere volume did not change significantly (750 +/- 92 microns3 to 642 +/- 1061 microns3, P = 0.14). Other cellular components, defined as all cytoplasmic components except mitochondria and sarcomeres, significantly increased with innervation (1,739 +/- 166 microns3 to 3,097 +/- 338 microns3, P = 0.02). The relative volume of the nucleus and the cytoplasm in the cell remained unchanged following innervation. However, the relative volume of mitochondria decreased by 6%, the percent of the cytoplasm occupied by the sarcomeres decreased by 44%, and the volume occupied by the other cellular components increased by 22%. These findings support the use of stereological analysis as a means to quantify cell volumes of cultured myocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Sedimentology and Clast Orientations of the 18 May 1980 Southwest-Flank Lahars, Mount St. Helens, Washington

ABSTRACT Three lahars that resulted from the flow transformation of an milled pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic Mount St. Helena eruption of 18 May 1980 deposited about 1 106 m3 of massive, poorly sorted, poorly graded volcaniclastic sediment on the southwest flank (SWF). Mean peak flow velocities over a 5-km radius ranged from more than 30 m/s in the proximal area (mean slope angle of 13°) to about 5 m/s in the distal area (mean slope angle of 4° 9); the lahars rapidly decelerated as deposition occurred on forested slopes. Average yield strength of the SWF lahars ranged from 9,000 to 12,000 dn/cm2; Bingham viscosity ranged from 2.8 103 to 50 103 poises. Average flow density of the SWF lahars was about 2.0 g/cm3. To determine the grain-size distribution of the SWF lahars, spot sampling of deposit matrix from vertical exposures was supplemented with point-count sampling of larger particles. Results from these analyses indicate that downflow changes in mean gram size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4 mm, and occur only in the basal portion of the deposits; both mean grain size and sorting coefficient increase slightly with distance. The deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting Fabric analyses of clast long axes indicate strong planar orientations parallel to flow surfaces. An eigenvalue analysis demonstrates the occurrence of both flow-parallel long-axis orientations with upstream dips and flow-transverse orientations. Similar clast fabric results were obtained for deposits of the North Fork Toutle River lahar. However, the mean clast long-axis dip in the SWF lahars is significantly shallower than the mean clast long-axis dip in the North Fork Toutle lahar, and is more like clast long-axis dips reported for tills and other sediment flows. The data from the SWF lahars indicate that lahar clast fabric may be more complex and variable than previously suggested.