Straight Transect Research Articles

Weeds in Florida Sugarcane as Host Plants for Three Species of Rice Stink Bugs (Hemiptera: Pentatomidae)

Weeds in Florida Sugarcane as Host Plants for Three Species of Rice Stink Bugs (Hemiptera: Pentatomidae)

Identification of the non-tree vegetation of opada forest reserve for conservation

Objectives of study: to identify the non-tree vegetation of Opada Forest Reserve (OFR) and provide comprehensive vegetation data for monitoring, conservation and management of present biodiversity. OFR is about 215.76km2 in size. Its map was gridded at an interval of one degree and each grid was 3.61 km2. Using a table of random numbers, ten of the grids were randomly selected. Within each grid, straight line transects of 2km long were randomly laid using Global Positioning System, to locate transects in the right grids and prismatic compass to maintain straight transects, 25m × 25m quadrates were taken at regular intervals of 500m. Each transect accommodated four quadrats which were 40 altogether. 1m2 sub-plots were located at the four corners of the quadrates for identification and counting of species. There were 160 sub-plots for this assessment. About 48- grass species, 12- climbers, 37- herbs, 4- shrubs and 5- sedges were identified.

Carrion subsidies provided by fishermen increase predation of beach‐nesting bird nests by facultative scavengers

AbstractMany predators are also scavengers that feed on carrion and human refuse. Therefore, the availability of carrion can elevate the abundance or activity of facultative scavengers, amplifying predation pressure on prey. On Australian beaches, fishermen often discard fish carcasses that could attract facultative scavengers, both native, such as Australian ravens Corvus coronoides, and invasive, such as European red foxes Vulpes vulpes, and result in elevated rates of predation on wildlife. We tested whether the presence of fish carcasses increased the risk of depredation for nearby nests of beach‐nesting birds by deploying artificial nests in 12 subsidized and 12 control patches, spaced 1 km apart, on a beach. We placed a fish carcass in each subsidized patch, but not at control patches. In each patch, we placed two artificial nests, which resembled red‐capped plover Charadrius ruficapillus nests, 80 m apart and 40 m from carcasses at subsidized patches. Nest predators were identified from tracks and predator activity near subsidized and control nests was measured by counting tracks crossing a straight transect (220 m). The activity of a native predator, the Australian raven, was 17 times higher near (<80 m) nests with fish carcasses than nests without carcasses. After 72 h, 96% of nests near carcasses were depredated compared with 30% of nests without carcasses. Ravens were identified as the culprit for 80% of depredated nests. Although other predators were present in the study area, they did not depredate artificial nests in this experiment. Previous studies have highlighted the effects of permanent and/or large‐scale food resources on scavenger abundance and impact. A key management implication of our study is that even small, sparsely distributed, temporally irregular food subsidies, provided by humans, can elevate the activity and predatory impacts of facultative scavengers.

Canine fecal contamination in a metropolitan area (Milan, north-western Italy): prevalence of intestinal parasites and evaluation of health risks.

Intestinal parasites of dogs represent a serious threat to human health due to their zoonotic potential. Thus, metropolitan areas presenting high concentrations of pets and urban fecal contamination on public areas are at sanitary risk. Major aim of this survey was to determine prevalence of zoonotic parasites in dog fecal samples collected from public soil of Milan (north-western Italy). Differences in parasites prevalence distribution were explored by a geographical information system- (GIS-) based approach, and risk factors (human density, sizes of green parks, and dog areas) were considered. The metropolitan area was divided into 157 rectangular subareas and sampling was performed following a 1-kilometer straight transect. A total of 463 fecal samples were analyzed using centrifugation-flotation technique and ELISA to detect Giardia and Cryptosporidium coproantigens. A widespread fecal contamination of soil was highlighted, being fecal samples found in 86.8% of the subareas considered. The overall prevalence of intestinal parasites was 16.63%. Zoonotic parasites were found, such as Trichuris vulpis (3.67%), Toxocara canis (1.72%), Strongyloides stercoralis (0.86%), Ancylostomatidae (0.43%), and Dipylidium caninum (0.43%). Giardia duodenalis was the most prevalent zoonotic protozoa (11.06%), followed by Cryptosporidium (1.10%). Faeces from subareas characterized by broad green areas showed to be particularly prone to infection.

Detection of Climate-Sensitive Zones and Identification of Climate Change Indicators: A Case Study from the Bavarian Forest National Park

We determined the climate-sensitive zones along an altitudinal gradient in a low mountain range forest, the Bavarian Forest National Park in south-eastern Germany, and studied which vascular plant species are likely to respond to climate change. Plants were recorded on 273 plots along four straight transects. The composition of the plant species and their environmental correlates were detected using unconstrained correspondence analysis (DCA) with post-hoc correlation of axes against site variables. We tested the effect of site variables on species composition using maximally selected rank statistics, which allow the simultaneous identification of a threshold and assessment of its significance. Species turnover within the vascular plant community along the altitudinal gradient was assessed using the same method on the basis of the DCA sample scores. Using geostatistical models of local temperature and Bayesian methods with binomial errors that account for spatial structure, we tested the influence of temperature on selected single vascular plant species and assessed the suitability of the species as climate change indicators. Temperature was the most important factor explaining the variability in vascular plant community composition, which changed discretely along the altitudinal gradient, with a climate-sensitive zone found between 1,100 and 1,200 m a.s.l. The distribution of ten species with their lower or upper altitudinal limit in this zone was significantly driven by temperature. To track vegetation responses to climate change effectively, we suggest a three-level monitoring program, flexible with regard to the volume of required sampling effort.

Counting elephants in Montane forests: some sources of error

AbstractThe dung count method is widely used to estimate elephant numbers in forests. It was developed in the lowland forests of Central Africa but it is also used in Montane forests in eastern Africa. Using data collected on Mount Kenya and computer simulations, this paper explores the following issues associated with dung surveys in Montane forests: High rainfall at 3000 m altitude on Mount Kenya was expected to accelerate dung pile decay but no significant difference was found between 3000 and 2500 m where less rain falls, possibly because high rainfall at 3000 m is counteracted by lower temperatures; Physical obstacles make it difficult to walk long, straight transects in Montane forests. Deviating from a straight line pushes the distribution of distance measurements from dung piles to the transect centre line (pdist) towards a negative exponential (NE), which complicates data analysis and may give inaccurate estimates. Using short transects largely alleviate this problem; Analysis of dung count simulations shows that the expected sightability curve of pdist pushes towards a NE with increasing numbers of obstacles blocking the view, even along perfectly straight transects; Extrapolating measured dung density to map area on Mount Kenya resulted in an underestimate of c. 13%. An unstratified correction of map area to ground area for Montane areas would be biased because of the strong tendency for elephants to avoid steeply sloping areas.

SHIPBOARD LINE TRANSECT SURVEYS OF CRABEATER SEAL ABUNDANCE IN THE PACK‐ICE OFF EAST ANTARCTICA: EVALUATION OF ASSUMPTIONS

AbstractWe examine the extent to which the assumptions underlying line transect sampling are satisfied in shipboard surveys of crabeater seals (Lobodon carcinophaga) hauled out on the Antarctic pack‐ice. Measurement of the perpendicular distance of seal groups from the ship with an electronic inclinometer fitted to a rifle stock was unbiased. Crabeater seals showed little movement in response to the approaching ship. Movement away from the ship by seals close to the ship's track was partially responsible for a relative lack of sightings close to the transect‐line, but otherwise had little effect on the sighting histogram. Minor deviations from the transect direction to avoid running over seals violated the assumption of uniform distribution of groups, and contributed to a relative lack in sightings close to (<40 m) the transect‐line. We estimate that 5%‐10% of seal groups close to the transect‐line were not sighted by bridge observers prior to passing abeam of the ship, but most of these missed groups were likely to have been sighted some distance behind‐abeam. Shipboard transects provided a biased sample of four environmental features known to be related to crabeater seal abundance because of logistical difficulties in the ship traversing along straight transects through thick ice. Calculation of transect length L from successive GPS locations was mildly sensitive to the frequency of locations. We provide analytical recommendations to reduce or eliminate the effect of assumption violation when present and hence minimize bias in abundance estimation.

Effects of Human Handling of Seeds on Seed Removal by Rodents

Many studies have examined seed removal by rodents without regard to possible biases from inadvertent olfactory cues left by the researcher. I compared removal rates of seeds that had direct contact with human skin (scent treatment) with those that had no direct contact (no-scent treatment). Seeds of two species were alternated at 5 m intervals along a straight transect in a native grassland in northwestern Illinois. Each treatment had 100 seeds, equally divided among two woodland species that are regularly dispersed by birds into grasslands. Seeds were monitored for removal for 30 d. The rate of seed removal was significantly faster for the scent than no-scent treatment. At the end of the study 88% of scented seeds had been removed compared with 55% of the no-scent seeds. Researchers should minimize unintentional olfactory cues during seed removal studies in order to get more accurate estimates of the impact of seed removers.

Variation in hydroacoustic abundance of pelagic fish

The variation in hydroacoustic abundance of pelagic fish was studied in Baltic coastal areas. Comparisons between zigzag transects and straight transects in the middle of a study area showed no consistent differences and neighbouring areas had generally similar abundances. The layout of transects and the exact boundaries chosen for a study in our open area are thus not crucial to the result. However, increasing the length of hydroacoustic transects within an area (increased degree of coverage) decreases the coefficient of variation between replicates. The average coefficient of variation (CV) between replicates from one night along a single transect was 20%, while for replicates from different nights the CV value was on average 29%. This implies that day-to-day migration between the study area and its surroundings influences hydroacoustic assessments less than the factors causing variation between replicates from the same night. These relations, however, differ between areas. In a sheltered bay, the CV between nights was 9% at a high degree of coverage. In a more open area the value was 20–30% and increased coverage had small effects on the variation between nights. Thus, in a relatively closed area, a high degree of coverage increases the reliability of the assessment, while in a more open area it might be more important to increase the study area (decreases effects of migration) or to record data on several nights. The precision in hydroacoustic assessment of fish is as good as or even better than recorded assessments for zooplankton, pelagic mysids, macrobenthos, meiobenthos, shallow water fish and gill net catches of littoral fish.

Guidelines for Line Transect Sampling of Biological Populations

Practical field procedures for conducting line transect surveys to estimate the size or density of biological populations are presented and discussed. Assumptions required for valid line transect surveys are specified. We emphasize that it is crucial to conduct observations along straight transects and obtain accurate measurements of distances and sighting angles. It is most important to conduct the survey in such a way as to maximize the probability that all objects on the centerline are found.