scholarly journals A Post-hurricane Quantitative Assessment of the Red-bellied Racer (Alsophis rufiventris) on Saba and Comparison with St. Eustatius

2021 ◽  
Author(s):  
Hannah Madden ◽  
Lara Mielke
Keyword(s):  
Detection Probability ◽  
Distance Sampling ◽  
Line Transect ◽  
Vegetation Types ◽  
Elevational Gradients ◽  
Study Region ◽  
Entire Study ◽  
Prior Literature ◽  
High Conservation ◽  
Dutch Caribbean

We estimated occupancy, abundance (lambda), detection probability, density/ha and abundance of a regionally endemic snake in the Colubrid family on the Dutch Caribbean island of Saba in 2021, four years after hurricanes Irma and Maria impacted the island. Line transect surveys were conducted at 74 sites covering 6.7 ha. The proportion of sites occupied was estimated at 0.74 (min 0.48, max 0.90), with occupancy varying between vegetation types and across elevational gradients. Similarly, lambda was estimated at 1.61 (min 0.7, max 3.7) but varied between vegetation types and elevational gradients. Detection probability was estimated at 0.15 (min 0.10, max 0.21). Using Distance sampling, we estimated 10.9 (min 7.3, max 16.2) racers/ha, with a total population estimate of 4,917 (min 2,577, max 6,362) across the entire study region (438.6 ha.) Based on anecdotal observations from Saban residents and prior literature describing the pre-hurricane population as abundant (at least 2.0 racers/hour), we posit that the population experienced a hurricane-induced decline but may have since recovered, though not to previous levels (1.28 racers/hour). Nevertheless, our results suggest that racer densities on Saba are currently higher than those on St. Eustatius. Despite this, given the species extremely limited extant range and the presence of invasive species on both islands, prevention of local extirpation should be a high conservation priority.

Historical analysis of changes in land use and carbon stock of vegetation in south and southeast Asia

1991 ◽  
Vol 21 (1) ◽  
pp. 91-110 ◽  
Author(s):  
Elizabeth P. Flint ◽  
John F. Richards
Keyword(s):  
Land Use ◽  
Carbon Content ◽  
Carbon Stock ◽  
Demographic Data ◽  
Standing Stock ◽  
Carbon Equivalent ◽  
Vegetation Types ◽  
Study Region ◽  
Entire Study ◽  
Ecological Zones

A time series (1880, 1920, 1950, 1980) of estimates of land use and carbon content of vegetation is presented for a contiguous area of 1.7 × 106 km2 in northern India, Bangladesh, and Burma. This was developed using sequential bookkeeping models, which systematically incorporate official agricultural and forest statistics with ecological, botanical, historical, geographical, and demographic data. For 149 administrative units, aggregated into 39 ecological zones, we estimated area and carbon content for each of the following land-use categories: net cultivated area, settled–built-up area, forest–woodland, interrupted woods, grass–shrub complexes, barren – sparsely vegetated areas, wetlands, and surface water. Dominant patterns of land-use change were deforestation, agricultural expansion, and wetland clearance, but significant regional and temporal disparities were observed. For the entire study region, the estimated standing stock of carbon in biomass declined by 2.62 Gt over the century. Release by periods was 911 Mt for 1880–1920, 750 Mt for 1920–1950, and 964 Mt for 1950–1980. Forest–woodland and interrupted woods vegetation released carbon equivalent to over 90% of the total release. Both conversion of forest to other vegetation types and reduction over time of biomass within vegetation types contributed significantly to decreases in total standing carbon stock during the period.

scholarly journals Getting the Most From Surveys: How Method Selection and Method Modification Impact Butterfly Survey Data

2021 ◽  
Author(s):  
Katherine C Kral-O’Brien ◽  
Adrienne K Antonsen ◽  
Torre J Hovick ◽  
Ryan F Limb ◽  
Jason P Harmon
Keyword(s):  
Species Richness ◽  
New Species ◽  
Count Data ◽  
Distance Sampling ◽  
Line Transect ◽  
Similar Species ◽  
Method Selection ◽  
M 10 ◽  
Sampling Procedures

Abstract Many methods are used to survey butterfly populations, with line transect and area surveys being prominent. Observers are typically limited to search within 5 or 10 m from the line, while observers are unrestricted in larger specified search regions in area surveys. Although methods differ slightly, the selection is often based on producing defendable data for conservation, maximizing data quality, and minimizing effort. To guide method selection, we compared butterfly surveys using 1) line versus area methods and 2) varying width transects (5 m, 10 m, or unrestricted) using count data from surveys in North Dakota from 2015 to 2018. Between line and area surveys, we detected more individuals with area surveys, even when accounting for effort. However, both methods accumulated new species at similar rates. When comparing transect methodology, we detected nearly 60% more individuals and nine more species when transect width increased from 5 m to unrestricted, despite similar effort across methodology. Overall, we found line surveys slightly less efficient at detecting individuals, but they collected similar species richness to area surveys when accounting for effort. Additionally, line surveys allow the use of unrestricted-width transects with distance sampling procedures, which were more effective at detecting species and individuals while providing a means to correct count data over the same transect length. Methods that reduce effort and accurately depict communities are especially important for conservation when long-term datasets are unavailable.

Harbor porpoise (Phocoena phocoena) recovery in the inland waters of Washington: estimates of density and abundance from aerial surveys, 2013–2015

2016 ◽  
Vol 94 (7) ◽  
pp. 505-515 ◽  
Author(s):  
Thomas A. Jefferson ◽  
Mari A. Smultea ◽  
Sarah S. Courbis ◽  
Gregory S. Campbell
Keyword(s):  
Puget Sound ◽  
Distance Sampling ◽  
Line Transect ◽  
Inland Waters ◽  
San Juan ◽  
Phocoena Phocoena ◽  
Harbor Porpoise ◽  
San Juan Islands ◽  
Juan De Fuca ◽  
Harbor Porpoises

The harbor porpoise (Phocoena phocoena (L., 1758)) used to be common in Puget Sound, Washington, but virtually disappeared from these waters by the 1970s. We conducted systematic aerial line-transect surveys (17 237 km total effort) for harbor porpoises, with the goal of estimating density and abundance in the inland waters of Washington State. Surveys in Puget Sound occurred throughout the year from 2013 to 2015, and in the Strait of Juan de Fuca and the San Juan Islands (and some adjacent Canadian waters) in April 2015. We used a high-wing, twin-engine Partenavia airplane and four observers (one on each side of the plane, one looking through a belly port, and one recording data). A total of 1063 harbor porpoise groups were sighted. Density and abundance were estimated using conventional distance sampling methods. Analyses were limited to 447 harbor porpoise groups observed during 5708 km of effort during good sighting conditions suitable for line-transect analysis. Harbor porpoises occurred in all regions of the study area, with highest densities around the San Juan Islands and in northern Puget Sound. Overall, estimated abundance for the Washington Inland Waters stock was 11 233 porpoises (CV = 37%, 95% CI = 9 616 – 13 120). This project clearly demonstrated that harbor porpoises have reoccupied waters of Puget Sound and are present there in all seasons. However, the specific reasons for their initial decline and subsequent recovery remain uncertain.

The importance of survey design in distance sampling: field evaluation using domestic sheep

2011 ◽  
Vol 38 (3) ◽  
pp. 221 ◽  
Author(s):  
Tom A. Porteus ◽  
Suzanne M. Richardson ◽  
Jonathan C. Reynolds
Keyword(s):  
Population Size ◽  
Survey Design ◽  
Distance Sampling ◽  
Field Evaluation ◽  
Stage I ◽  
Stage Ii ◽  
Line Transect ◽  
Domestic Sheep ◽  
Management Decisions ◽  
Mobile Species

Context Sampling methods to estimate animal density require good survey design to ensure assumptions are met and sampling is representative of the survey area. Management decisions are often made based on these estimates. However, without knowledge of true population size it is not possible for wildlife biologists to evaluate how biased the estimates can be if survey design is compromised. Aims Our aims were to use distance sampling to estimate population size for domestic sheep free-ranging within large enclosed areas of hill country and, by comparing estimates against actual numbers, examine how bias and precision are impaired when survey design is compromised. Methods We used both line and point transect sampling to derive estimates of density for sheep on four farms in upland England. In Stage I we used limited effort and different transect types to compromise survey design. In Stage II we increased effort in an attempt to improve on the Stage I estimates. We also examined the influence of a walking observer on sheep behaviour to assess compliance with distance sampling assumptions and to improve the fit of models to the data. Key results Our results show that distance sampling can lead to biased and imprecise density estimates if survey design is poor, particularly when sampling high density and mobile species that respond to observer presence. In Stage I, walked line transects were least biased; point transects were most biased. Increased effort in Stage II reduced the bias in walked line transect estimates. For all estimates, the actual density was within the derived 95% confidence intervals, but some of these spanned a range of over 100 sheep per km2. Conclusions Using a population of known size, we showed that survey design is vitally important in achieving unbiased and precise density estimation using distance sampling. Adequate transect replication reduced the bias considerably within a compromised survey design. Implications Management decisions based on poorly designed surveys must be made with an appropriate understanding of estimate uncertainty. Failure to do this may lead to ineffective management.

scholarly journals The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys

2008 ◽  
Vol 35 (4) ◽  
pp. 275 ◽  
Author(s):  
Rachel M. Fewster ◽  
Colin Southwell ◽  
David L. Borchers ◽  
Stephen T. Buckland ◽  
Anthony R. Pople
Keyword(s):  
Survey Design ◽  
Distance Sampling ◽  
High Mobility ◽  
Line Transect ◽  
Transect Line ◽  
Aerial Surveys ◽  
Pack Ice ◽  
Capture Recapture ◽  
Distance Data ◽  
Crabeater Seals

Line-transect distance sampling is a widely used method for estimating animal density from aerial surveys. Analysis of line-transect distance data usually relies on a requirement that the statistical distribution of distances of animal groups from the transect line is uniform. We show that this requirement is satisfied by the survey design if all other assumptions of distance sampling hold, but it can be violated by consistent survey problems such as responsive movement of the animals towards or away from the observer. We hypothesise that problems with the uniform requirement are unlikely to be encountered for immobile taxa, but might become substantial for species of high mobility. We test evidence for non-uniformity using double-observer distance data from two aerial surveys of five species with a spectrum of mobility capabilities and tendencies. No clear evidence against uniformity was found for crabeater seals or emperor penguins on the pack-ice in East Antarctica, while minor non-uniformity consistent with responsive movement up to 30 m was found for Adelie penguins. Strong evidence of either non-uniformity or a failure of the capture–recapture validating method was found for eastern grey kangaroos and red kangaroos in Queensland.

Ecological thresholds and the status of fire-sensitive vegetation in western Arnhem Land, northern Australia: implications for management

2009 ◽  
Vol 18 (2) ◽  
pp. 127 ◽  
Author(s):  
Andrew C. Edwards ◽  
Jeremy Russell-Smith
Keyword(s):  
National Parks ◽  
Fire History ◽  
Fire Management ◽  
Fire Regime ◽  
Vegetation Types ◽  
Northern Australia ◽  
Study Region ◽  
Ecological Thresholds ◽  
Arnhem Land ◽  
The Status

The paper examines the application of the ecological thresholds concept to fire management issues concerning fire-sensitive vegetation types associated with the remote, biodiversity-rich, sandstone Arnhem Plateau, in western Arnhem Land, monsoonal northern Australia. In the absence of detailed assessments of fire regime impacts on component biota such as exist for adjoining Nitmiluk and World Heritage Kakadu National Parks, the paper builds on validated 16-year fire history and vegetation structural mapping products derived principally from Landsat-scale imagery, to apply critical ecological thresholds criteria as defined by fire regime parameters for assessing the status of fire-sensitive habitat and species elements. Assembled data indicate that the 24 000 km2 study region today experiences fire regimes characterised generally by high annual frequencies (mean = 36.6%) of large (>10 km2) fires that occur mostly in the late dry season under severe fire-weather conditions. Collectively, such conditions substantially exceed defined ecological thresholds for significant proportions of fire-sensitive indicator rain forest and heath vegetation types, and the long-lived obligate seeder conifer tree species, Callitris intratropica. Thresholds criteria are recognised as an effective tool for informing ecological fire management in a variety of geographic settings.

Short visits reveal consistent patterns of interyear and intercolony variation in seabird nestling diet and performance

2002 ◽  
Vol 80 (12) ◽  
pp. 2190-2199 ◽  
Author(s):  
D F Bertram ◽  
T Golumbia ◽  
G K Davoren ◽  
A Harfenist ◽  
J Brown
Keyword(s):  
Growth Performance ◽  
Large Scale ◽  
Southern Oscillation ◽  
Large Contribution ◽  
Fish Prey ◽  
Study Region ◽  
Entire Study ◽  
Nestling Growth ◽  
Nestling Development ◽  
Nestling Diet

To investigate the utility of short visits to seabird colonies to gauge nestling growth performance and diet, in 4 consecutive years (1995–1998) we measured nestling development and diet of Rhinoceros Auklets (Cerorhinca monocerata) at three colonies in British Columbia: Seabird Rocks, Triangle Island, and SGaang Gwaii (Anthony Island). In all years, nestlings of a given wing length on Triangle Island were significantly smaller than those on Seabird Rocks or SGaang Gwaii. Meals were also significantly lighter on Triangle Island than on Seabird Rocks or SGaang Gwaii; meals on the latter two islands were indistinguishable in mass. Retarded nestling development and small meal size on Triangle Island likely reflect the large contribution of rockfish (Sebastes spp.) to nestling diet on that colony alone. The intercolony differences in nestling performance appear to reflect the strong influence of local fish prey populations. Nonetheless, a united decline in performance in 1996 and subsequent increase on all colonies suggest the influence of large-scale ocean climate phenomena on our entire study region and beyond. We did not, however, observe noticeable effects of the 1997–1998 El Niño Southern Oscillation event on nestling growth performance or diet. We discuss the utility of our short-visit techniques for seabird-monitoring programs.

scholarly journals Estimating abundance of the Endangered onager Equus hemionus onager in Qatruiyeh National Park, Iran

Oryx ◽  
2013 ◽  
Vol 47 (2) ◽  
pp. 266-272 ◽  
Author(s):  
Mahmoud-Reza Hemami ◽  
Moslem Momeni
Keyword(s):  
Growth Rate ◽  
Protected Area ◽  
National Park ◽  
Natural Populations ◽  
Distance Sampling ◽  
Line Transect ◽  
Management Interventions ◽  
Equus Hemionus ◽  
Wild Ass ◽  
Semi Arid

AbstractHistorically, the onager or Persian wild ass Equus hemionus onager, endemic to Iran, was widespread on the arid and semi-arid central steppes but only two natural populations remain. We estimated the population density of the onager in Qatruiyeh National Park using line transect distance sampling. Transects were surveyed on three plains in the Park and the results compared with total counts conducted by the Department of Environment. Our estimate (109 onagers per 100 km2; 95% confidence interval 67–179) is similar to that obtained by the total counts (137 onagers per 100 km2). Distance sampling is therefore a promising method for estimating the abundance of the onager. Using the annual censuses performed by the Department of Environment over the last 13 years we estimated that the population has a growth rate of 0.09. During the same period the onager population in the Touran Protected Complex has experienced a severe decline. The high density of onagers within the National Park indicates the unsuitability of adjacent habitats, including Bahram-e-Goor Protected Area, for this species. Lack of sufficient security and poorly distributed water sources appear to be the main reasons discouraging onagers from entering the Bahram-e-Goor Protected Area. We recommend and describe management interventions that could potentially assist in maintaining the last surviving onager populations in Iran.

scholarly journals Spatial Paradigms in Road Networks and Their Delimitation of Urban Boundaries Based on KDE

2020 ◽  
Vol 9 (4) ◽  
pp. 204 ◽  
Author(s):  
Yuying Lin ◽  
Xisheng Hu ◽  
Mingshui Lin ◽  
Rongzu Qiu ◽  
Jinguo Lin ◽  
...  
Keyword(s):  
Spatial Data ◽  
Rural Areas ◽  
Urban Areas ◽  
Critical Role ◽  
Road Networks ◽  
Spatial Data Analysis ◽  
Easy Method ◽  
Study Region ◽  
Entire Study ◽  
Depth Analysis

An in-depth analysis of urban road network distribution plays a critical role in understanding the urbanization process. However, effective ways to quantitatively analyze the spatial paradigms of road networks are still lacking, and few studies have utilized road networks to rapidly identify urban areas of a region. Thus, using a fast-developing region in the south-eastern costal region of China, Fuzhou City, as a case, we introduced kernel density estimation (KDE) to characterize road networks and quantified the area’s spatial heterogeneity using exploratory spatial data analysis (ESDA) and semivariance analysis (SA). The results show that there is an uneven spatial distribution of the networks both at the regional and downtown levels. At the regional level, there is a conspicuous polarization in the road distribution, with the KDE being much higher in the urban areas than in the rural areas; at the downtown level, the KDE gradually decreases from the center to the periphery. Quantitatively, the ranges of the spatial dependence of the networks are approximately 25 km for the entire study region and 12 km for the downtown area. Additionally, the spatial variations vary among different directions, with greater variations in the northeast–southwest and the southeast–northwest directions compared with the other directions, which is in line with the urban sprawl policy of the study area. Both the qualitative and quantitative results show that the distribution of road networks has a clear urban–rural dual structure, which indicates that road networks can be an active tool in identifying the urban areas of a region. To this end, we propose a quick and easy method to delimit urban areas using KDE. The extraction results of KDE are better than those of the index-based built-up index (IBI), indicating the effectivity and feasibility of our proposed method to identify the urban areas in the region. This research sheds new light on urbanization development research.

scholarly journals Analysis of soil and vegetation patterns in semi-arid Mediterranean landscapes by way of a conceptual water balance model

2008 ◽  
Vol 12 (3) ◽  
pp. 899-911 ◽  
Author(s):  
I. Portoghese ◽  
V. Iacobellis ◽  
M. Sivapalan
Keyword(s):  
Water Balance ◽  
Soil Water ◽  
Water Holding Capacity ◽  
Sensitivity Analyses ◽  
Vegetation Types ◽  
Study Region ◽  
Mediterranean Landscapes ◽  
Soil Water Holding Capacity ◽  
Water Holding ◽  
Semi Arid

Abstract. This paper investigates the impact of various vegetation types on water balance variability in semi-arid Mediterranean landscapes, and the different strategies they may have developed to succeed in such water-limited environments. The existence of preferential associations between soil water holding capacity and vegetation species is assessed through an extensive soil geo-database focused on a study region in Southern Italy. Water balance constraints that dominate the organization of landscapes are investigated by a conceptual bucket approach. The temporal water balance dynamics are modelled, with vegetation water use efficiency being parameterized through the use of empirically obtained crop coefficients as surrogates of vegetation behavior in various developmental stages. Sensitivity analyses with respect to the root zone depth and soil water holding capacity are carried out with the aim of explaining the existence of preferential soil-vegetation associations and, hence, the spatial distribution of vegetation types within the study region. Based on these sensitivity analyses the degrees of suitability and adaptability of each vegetation type to parts of the study region are explored with respect of the soil water holding capacity, and the model results were found consistent with the observed affinity patterns.

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