Movement patterns and study area boundaries: influences on survival estimation in capture–mark–recapture studies

The inability to account for the availability of individuals in the study area during capture–mark–recapture (CMR) studies and the resultant confounding of parameter estimates can make correct interpretation of CMR model parameter estimates difficult. Although important advances based on the Cormack–Jolly–Seber (CJS) model have resulted in estimators of true survival that work by unconfounding either death or recapture probability from availability for capture in the study area, these methods rely on the researcher's ability to select a method that is correctly matched to emigration patterns in the population. If incorrect assumptions regarding site fidelity (non‐movement) are made, it may be difficult or impossible as well as costly to change the study design once the incorrect assumption is discovered. Subtleties in characteristics of movement (e.g. life history‐dependent emigration, nomads vs territory holders) can lead to mixtures in the probability of being available for capture among members of the same population. The result of these mixtures may be only a partial unconfounding of emigration from other CMR model parameters. Biologically‐based differences in individual movement can combine with constraints on study design to further complicate the problem. Because of the intricacies of movement and its interaction with other parameters in CMR models, quantification of and solutions to these problems are needed. Based on our work with stream‐dwelling populations of Atlantic salmon Salmo salar, we used a simulation approach to evaluate existing CMR models under various mixtures of movement probabilities. The Barker joint data model provided unbiased estimates of true survival under all conditions tested. The CJS and robust design models provided similarly unbiased estimates of true survival but only when emigration information could be incorporated directly into individual encounter histories. For the robust design model, Markovian emigration (future availability for capture depends on an individual's current location) was a difficult emigration pattern to detect unless survival and especially recapture probability were high. Additionally, when local movement was high relative to study area boundaries and movement became more diffuse (e.g. a random walk), local movement and permanent emigration were difficult to distinguish and had consequences for correctly interpreting the survival parameter being estimated (apparent survival vs true survival).     

Ecological and methodological factors affecting detectability and population estimation in elusive species

Although mark-recapture methods are among the most powerful tools for monitoring wildlife populations, the secretive nature of some species requires a comprehensive understanding of the factors that affect capture probability to maximize accuracy and precision of population parameter estimates (e.g., population size and survivorship). Here, we used aquatic snakes as a case study in applying rigorous mark-recapture methods to estimate population parameters for secretive species. Specifically, we used intensive field sampling and robust design mark-recapture analyses in Program MARK to test specific hypotheses about ecological and methodological factors influencing detectability of two species of secretive aquatic snakes, the banded watersnake (Nerodia fasciata), and the black swamp snake (Seminatrix pygaea). We constructed a candidate set of a priori mark-recapture models incorporating various combinations of time- and sex-varying capture and recapture probabilities, behavioral responses to traps (i.e., trap-happiness or trap-shyness), and temporary emigration, and we ranked models for each species using Akaike's Information Criterion. For both banded watersnakes and black swamp snakes we found strong support for time-varying capture and recapture probabilities and strong trap-happy responses, factors that can bias population estimation if not accommodated in the models. We also found evidence of sex-dependent temporary emigration in black swamp snakes. Our study is among the first comprehensive assessments of factors affecting detectability in snakes and provides a framework for studies aimed at monitoring populations of other secretive species. © 2010 The Wildlife Society.     

Comparability of macroinvertebrate biomonitoring indices of river health derived from semi-quantitative and quantitative methodologies

Aquatic macroinvertebrates have been the basis for one of the primary indicators and a cornerstone of lotic biomonitoring for over 40 years. Despite the widespread use of lotic invertebrates in statutory biomonitoring networks, scientific research and citizen science projects, the sampling methodologies employed frequently vary between studies. Routine statutory biomonitoring has historically relied on semi-quantitative sampling methods (timed kick sampling), while much academic research has favoured fully quantitative methods (e.g. Surber sampling). There is an untested assumption that data derived using quantitative and semi-quantitative samples are not comparable for biomonitoring purposes. As a result, data derived from the same site, but using different sampling techniques, have typically not been analysed together or directly compared. Here, we test this assumption by comparing a range of biomonitoring metrics derived from data collected using timed semi-quantitative kick samples and quantitative Surber samples from the same sites simultaneously. In total, 39 pairs of samples from 7 rivers in the UK were compared for two seasons (spring and autumn). We found a strong positive correlation (r_s = +0.84) between estimates of taxa richness based on ten Surber sub-samples and a single kick sample. The majority of biomonitoring metrics were comparable between techniques, although only fully quantitative sampling allows the density of the community (individual m⁻²) to be determined. However, this advantage needs to be balanced alongside the greater total sampling time and effort associated with the fully quantitative methodology used here. Kick samples did not provide a good estimate of relative abundance of a number of species/taxa and, therefore, the quantitative method has the potential to provide important additional information which may support the interpretation of the biological metrics.     

Open removal models with temporary emigration and population dynamics to inform invasive animal management

Removal sampling data are the primary source of monitoring information for many populations (e.g., invasive species, fisheries). Population dynamics, temporary emigration, and imperfect detection are common sources of variation in monitoring data and are key parameters for informing management. We developed two open robust‐design removal models for simultaneously modeling population dynamics, temporary emigration, and imperfect detection: a random walk linear trend model (estimable without ancillary information), and a 2‐age class informed population model (InfoPM, closely related to integrated population models) that incorporated prior information for age‐structured vital rates and relative juvenile availability. We applied both models to multiyear, removal trapping time‐series of a large invasive lizard (Argentine black and white tegu, Salvator merianae) in three management areas of South Florida to evaluate the effectiveness of management programs. Although estimates of the two models were similar, the InfoPMs generally returned more precise estimates, partitioned dynamics into births, deaths, net migration, and provided a decision support tool to predict population dynamics under different effort scenarios while accounting for uncertainty. Trends in tegu superpopulation abundance estimates were increasing in two management areas despite generally high removal rates. However, tegu abundance appeared to decline in the Core management area, where trapping density was the highest and immigration the lowest. Finally, comparing abundance predictions of no‐removal scenarios to those estimated in each management area suggested significant population reductions due to management. These results suggest that local tegu population control via systematic trapping may be feasible with high enough trap density and limited immigration; and highlights the value of these trapping programs. We provided the first estimates of tegu abundance, capture probabilities, and population dynamics, which is critical for effective management. Furthermore, our models are applicable to a wide range of monitoring programs (e.g., carcass recovery or removal point‐counts).     

Gear type,species composition and economic value of fisheries in the mangroves of Pak Phanang,Thailand

Fishing gear and methods, catch composition, annual catch numbers and the monetary value of fisheries based in the mangroves of Pak Phanang, Nakhon Si Thamarat province, Thailand, were studied from September 2004 to February 2005. The fishing gear and methods were surveyed by visual observation and interviews. Sample catches were taken for each type of fishing gear and method. Semi-closed questionnaire surveys were conducted among fishers, local traders, local administrative officers and related organizations to derive information on utilized species, gear and methods, fisher and fishery status, and trading and catch price. The Pak Phanang mangrove fishery has three types of multi-species capture gear: channel traps, gill nets and lift nets. It also has three kinds of single-species (group) gear/methods: crab traps, catfish hooks and hand capture using a long tail fishing boat. A total of 57 fish species in 27 families, and 23 shell fish species in 8 families were recorded from the catch samples. Penaeid shrimp (25%), and ambassid (31%) and mugilid (24%) fishes were the abundant groups in the channel traps, while ariid (36%) and mugilid (19%) fishes were abundant in the lift net catches. Ambassid (42%) fish dominated the gill net catches. Species richness (number of species) varied depending on sampling month and type of fishing gear. The total annual catch and its monetary value were estimated to be 442–551 tons and US $368,038–733,973, respectively. The estimated annual catch per unit area of mangrove was 63–79 kg ha⁻¹, which generated a market value of US $368,038–733,973, respectively. The estimated annual catch per unit area of mangrove was 63–79 kg ha⁻¹, which generated a market value of US 52–105.     

Detection of stored-wheat beetle species and estimation of population density using unbaited probe traps and grain trier samples

Field studies were conducted in order to compare the effectiveness of unbaited probe traps and grain trier samples in the detection of several beetle species. On June 15, 1997, fourteen probe traps were placed in three steel bins containing wheat in Central Greece. Two of them were inserted in the central zone of the bulk, five in the half of the bin radius (median zone) and seven near the bin wall (distal zone). From June 30 up to and including January 1998, the traps were checked for adult beetles every fifteen days (15 sampling dates in total). On each date, samples were also taken from spots adjacent to trap locations, using a grain trier. The mean temperatures recorded near the bulk surface decreased by an average of 1.16 °C per sampling date. Twenty-four species, belonging to 14 families of Coleoptera were found. The most abundant species in the traps were Cryptolestes ferrugineus and Tribolium castaneum, while Sitophilus oryzae was the most abundant in the samples. Significantly greater numbers of adults were found in traps than in samples, during the whole sampling period; traps also detected adults in most locations while in the corresponding samples no adults were found. Significantly higher numbers of adults were found in the central sampling zone, using both devices. Taylor's power law parameters showed that in both sampling methods the most abundant species showed aggregated spatial patterns. Although the correlation coefficient values between trap catches and number of adults per trier sample differ significantly from zero (P < 0.01) in a high number of sampling dates, it can be concluded that traps are poor indicators of population density. The accuracy provided as a percentage of the mean, decreases exponentially with the increase of the mean value. Based on traps, the desired accuracy level (35%) is not achievable even in higher mean values or even with high numbers of traps. On the contrary, with trier samples it is possible to estimate population density with a relatively low number of sampling units. Significant differences in the required number of sampling units (sample size) were noted among species.     

Spatial distribution,sampling efficiency and Taylor's power law. 2. Interpreting density-dependent sampling efficiency

1. The intimate relationship between sampling efficiency and Taylor's power law (TPL) was investigated with gypsy moth sample data. The data were used to compute sampling efficiency directly and indirectly by TPL.
2. Comparison of TPLs and efficiency plots of male and female pupae confirmed the identities linking TPL with sampling efficiency. Divergence of sex-specific TPL plots indicated local scale density-dependent sex ratio.
3. Egg mass sample data confirmed the sampling efficiency and TPL identities provided the same variance and mean vectors were used to compute TPLs. Small differences in sample numbers destroy the identities but approximate efficiency estimates are still obtainable from the TPLs. Sampling efficiency of timed walks, fixed area and variable area surveys were estimated and ranked.
4. Rescaling moth catches per trap to number per unit volume changes slope, intercept and correlation coefficient while stretching the pattern of data points. Comparison of absolute density estimates over two different time intervals showed density-dependent variation declining with increasing sample interval.
5. Fitting power laws by ordinary dependent regression is less efficient than fitting by geometric mean regression and produces biased regression parameters. The significance of this for the analysis and interpretation of ecological sample data generally is discussed.

     

Application of Rapid Bioassessment Protocols (RBP) for benthic macroinvertebrates in Brazil: comparison between sampling techniques and mesh sizes

This study is part of the effort to test and to establish Rapid Bioassessment Protocols (RBP) using benthic macroinvertebrates as indicators of the water quality of wadeable streams in south-east Brazil. We compared the cost-effectiveness of sampling devices frequently used in RBPs, Surber and Kick-net samplers, and of three mesh sizes (125, 250 and 500 microm). A total of 126,815 benthic macroinvertebrates were collected, representing 57 families. Samples collected with Kick method had significantly higher richness and BMWP scores in relation to Surber, but no significant increase in the effort, measured by the necessary time to process samples. No significant differences were found between samplers considering the cost/effectiveness ratio. Considering mesh sizes, significantly higher abundance and time for processing samples were necessary for finer meshes, but no significant difference were found considering taxa richness or BMWP scores. As a consequence, the 500 microm mesh had better cost/effectiveness ratios. Therefore, we support the use of a kick-net with a mesh size of 500 microm for macroinvertebrate sampling in RBPs using family level in streams of similar characteristics in Brazil.     

Evaluating Abundance Estimate Precision and the Assumptions of a Count-Based Index for Small Mammals

ABSTRACT Conservation and management of small mammals requires reliable knowledge of population size. We investigated precision of mark-recapture and removal abundance estimates generated from live-trapping and snap-trapping data collected at sites on Guam (n = 7), Rota (n = 4), Saipan (n = 5), and Tinian (n = 3), in the Mariana Islands. We also evaluated a common index, captures per unit effort (CPUE), as a predictor of abundance. In addition, we evaluated cost and time associated with implementing live-trapping and snap-trapping and compared species-specific capture rates of selected live- and snap-traps. For all species, mark-recapture estimates were consistently more precise than removal estimates based on coefficients of variation and 95% confidence intervals. The predictive utility of CPUE was poor but improved with increasing sampling duration. Nonetheless, modeling of sampling data revealed that underlying assumptions critical to application of an index of abundance, such as constant capture probability across space, time, and individuals, were not met. Although snap-trapping was cheaper and faster than live-trapping, the time difference was negligible when site preparation time was considered. Rattus diardii spp. captures were greatest in Haguruma live-traps (Standard Trading Co., Honolulu, HI) and Victor snap-traps (Woodstream Corporation, Lititz, PA), whereas Suncus murinus and Mus musculus captures were greatest in Sherman live-traps (H. B. Sherman Traps, Inc., Tallahassee, FL) and Museum Special snap-traps (Woodstream Corporation). Although snap-trapping and CPUE may have utility after validation against more rigorous methods, validation should occur across the full range of study conditions. Resources required for this level of validation would likely be better allocated towards implementing rigorous and robust methods.     

Estimating survival of a streamside salamander: importance of temporary emigration,capture response,and location

Estimating survival for highly secretive aquatic animals, such as stream salamanders, presents numerous challenges. Salamanders often spend a considerable time in refugia where they are difficult to capture. Few studies have calculated vital rates for stream salamanders, yet the need is substantial as they are threatened by a wide range of land-use stressors, especially urban development. In this study, we used 34 months of continuous field samples collected at an urban and undisturbed stream and robust design mark-recapture analysis to evaluate the importance of temporary emigration, capture response, and location on survival estimates of the salamander Desmognathus fuscus. We constructed a set of candidate models incorporating combinations of time- and location-varying capture and recapture probabilities, capture responses, temporary emigration, and survival estimates and ranked models using Akaike’s Information Criterion. We found strong support for month-specific capture probabilities, recapture probabilities, temporary emigration and a negative behavioral response to capture in the majority of months. We found no support for variation in capture probabilities, recapture probabilities, and temporary emigration between locations. However, we found that location strongly influenced survival estimates. Specifically, survival estimates were significantly higher at the undisturbed site than at the urban site. Our results emphasize the importance of estimating capture probabilities, recapture probabilities, capture response, and temporary emigration when evaluating survival in highly secretive aquatic animals. Failure to account for these population parameters will likely yield biased estimates of survival in freshwater animal populations.     

Binomial sampling to estimate rust mite (Acari: Eriophyidae) densities on orange fruit

Binomial sampling based on the proportion of samples infested was investigated for estimating mean densities of citrus rust mite, Phyllocoptruta oleivora (Ashmead), and Aculops pelekassi (Keifer) (Acari: Eriophyidae), on oranges, Citrus sinensis (L.) Osbeck. Data for the investigation were obtained by counting the number of motile mites within 600 sample units (each unit a 1-cm2 surface area per fruit) across a 4-ha block of trees (32 blocks total): five areas per 4 ha, five trees per area, 12 fruit per tree, and two samples per fruit. A significant (r2 = 0.89), linear relationship was found between ln(-ln(1 -Po)) and ln(mean), where P0 is the proportion of samples with more than zero mites. The fitted binomial parameters adequately described a validation data set from a sampling plan consisting of 192 samples. Projections indicated the fitted parameters would apply to sampling plans with as few as 48 samples, but reducing sample size resulted in an increase of bootstrap estimates falling outside expected confidence limits. Although mite count data fit the binomial model, confidence limits for mean arithmetic predictions increased dramatically as proportion of samples infested increased. Binomial sampling using a tally threshold of 0 therefore has less value when proportions of samples infested are large. Increasing the tally threshold to two mites marginally improved estimates at larger densities. Overall, binomial sampling for a general estimate of mite densities seemed to be a viable alternative to absolute counts of mites per sample for a grower using a low management threshold such as two or three mites per sample.     

Surber and kick sampling: a comparison for the assessment of macroinvertebrate community structure in streams of south-western Australia

Macroinvertebrate community structure was compared in benthic samples taken by Surber and kick methods from a lotic system in south-western Australia. Eleven sites were sampled concurrently in winter, spring and summer 1987.Surber samples contained fewer individuals and more taxa, particularly those with a low frequency of occurrence. This was attributed to the lower surface area, but greater intensity of Surber sampling. It is proposed that the Surber method is more suited to taking cryptic and closely adherent taxa in sites with a highly heterogeneous substratum.Percentage similarity between paired Surber and kick samples was determined by Sorensen's and Czekanowski's coefficients, with mean values of 66% and 60% for June, 61% and 49% for September and 66% and 49% for December respectively. Ordination demonstrated a division of upland from lowland sites on axis 1, with a separation of paired-samples on axis 2. This pattern held across qualitative and quantitative datasets, with and without a downweighting on rare taxa. At each level of classification fewer paired-samples separated in qualitative than quantitative datasets.Kick sampling provided a substantial saving in costs over Surber sampling, particularly when qualitative data were utilised, making the method suitable for routine, biological monitoring. However, the initial use of replicated Surber sampling, particularly in areas that have not been previously sampled is recommended for environmental impact studies to detect rare taxa, that may be endangered.     

Effects of reducing sample size on density estimates of citrus rust mite (Acari: Eriophyidae) on citrus fruit: simulated sampling

The consequence of reducing sample size on the accuracy and precision of estimates of citrus rust mite, Phyllocoptruta oleivora (Ashmead), densities on oranges was investigated. The sample unit was a 1-cm2 surface area on fruit. Sampling plans consisting of 360, 300, 200, 160, 80, 48, 36, or 20 samples per 4 ha were evaluated through computer simulations by using real count data from 32 data sets of 600 sample units per 4 ha. The original and reduced sampling plans were hierarchical with different numbers of sample areas per 4 ha, trees per area, fruit per tree, and samples per fruit. Individual estimates (n=100 simulations per data set) using each plan were sometimes considerably below or above target densities. In an original set of count data with a mean of six mites per cm2, simulations of 36 samples per 4 ha produced individual estimates ranging from one to 16 mites per cm2, whereas 80 samples per 4 ha produced estimates ranging from two to 10 mites per cm2. The plans consisting of 36 or more samples were projected to provide precision levels of 0.25 (SEM/mean) or better at densities of five or more mites per cm2 based on log-data, a projection that needs to be verified under real-grove situations. Each plan consistently provided mite detection in these sampling simulations except those consisting of 20 or 36 samples, which sometimes failed to detect mites when the target density was less than five mites per cm2. The study provided insight into the probable precision, accuracy and detection thresholds for eight candidate sampling plans varying from relatively low to high resource input.     

Effect of sampling scale on the assessment of epiphytic bacterial populations

Bacterial populations on above-ground plant surfaces were estimated at three different biological scales, including leaflet disks, entire leaflets, and whole plants. The influence of sample scale on the estimation of mean bacterial population size per unit and per gram and on the variability among sampling units was quantified at each scale. Populations were highly variable among sampling units at every scale examined, suggesting that there is no optimal scale at which sample variance is reduced. The distribution of population sizes among sample units was sometimes, but not consistently, described by the lognormal. Regardless of the sampling scale, expression of population sizes on a per gram basis may not reduce variance, because population size was not generally a function of sample unit weight within any single sampling scale. In addition, the data show that scaling populations on a per gram basis does not provide a useful means of comparing population estimates from samples taken at different scales. The implications of these results for designing sampling strategies to address specific issues in microbial ecology are discussed. Correspondence to: L.L. Kinkel     

Fish stock assessment in lakes based on mass removal

The efficiency of mass removal of fishes can potentially be assessed using catch statistics collected during intensive fishing periods. The calculations are based on the general assumption that a decline in population size will produce a decline in catch per unit effort (cpue). When the removal is efficient it is possible to estimate the population size both at the beginning of the fishing period and after the removal.
Two examples are based on the winter seine net fishing of vendace ( Coregonus albula ) in Lake Pyhäjärvi, SW Finland in (1) 1983–1984 and (2) 1989–1990. The effects of the error in catch composition samples and random changes in probabilities of capture during the removal period on the final estimates of initial stock sizes are also examined.
The precision of the population estimates shown here was greatly influenced by the violation of the underlying assumption that the probability of capture is equal for all members of the target age group. In any case, particular attention should be paid to optimizing the sampling programme so that it will reveal the best information on the exploited stock with the resources in hand.     

Use of the Robust Design to Estimate Seasonal Abundance and Demographic Parameters of a Coastal Bottlenose Dolphin (Tursiops aduncus) Population

As delphinid populations become increasingly exposed to human activities we rely on our capacity to produce accurate abundance estimates upon which to base management decisions. This study applied mark–recapture methods following the Robust Design to estimate abundance, demographic parameters, and temporary emigration rates of an Indo-Pacific bottlenose dolphin (Tursiops aduncus) population off Bunbury, Western Australia. Boat-based photo-identification surveys were conducted year-round over three consecutive years along pre-determined transect lines to create a consistent sampling effort throughout the study period and area. The best fitting capture–recapture model showed a population with a seasonal Markovian temporary emigration with time varying survival and capture probabilities. Abundance estimates were seasonally dependent with consistently lower numbers obtained during winter and higher during summer and autumn across the three-year study period. Specifically, abundance estimates for all adults and juveniles (combined) varied from a low of 63 (95% CI 59 to 73) in winter of 2007 to a high of 139 (95% CI 134 to148) in autumn of 2009. Temporary emigration rates (γ'') for animals absent in the previous period ranged from 0.34 to 0.97 (mean  =  0.54; ±SE 0.11) with a peak during spring. Temporary emigration rates for animals present during the previous period (γ'''') were lower, ranging from 0.00 to 0.29, with a mean of 0.16 (± SE 0.04). This model yielded a mean apparent survival estimate for juveniles and adults (combined) of 0.95 (± SE 0.02) and a capture probability from 0.07 to 0.51 with a mean of 0.30 (± SE 0.04). This study demonstrates the importance of incorporating temporary emigration to accurately estimate abundance of coastal delphinids. Temporary emigration rates were high in this study, despite the large area surveyed, indicating the challenges of sampling highly mobile animals which range over large spatial areas.     

Improving our understanding of demographic monitoring: avian breeding productivity in a tropical dry forest

The ratio of juvenile to adult birds in mist‐net samples is used to monitor avian productivity, but whether it is a “true” estimate of per capita productivity or an index proportional to productivity depends on whether capture probability is not age‐dependent (true estimate) or age difference in capture probability is consistent among years (index). Better understanding of the processes affecting age‐ and year‐specific capture probabilities is needed to advance the application of constant‐effort mist‐netting for monitoring and conservation, particularly in many tropical settings where capture rates are often low. We ranked members of the avian community by capture frequencies, determined if temporary emigration influenced the availability of birds to be captured, and assessed the distribution of birds relative to mist‐nets and the parity between capture‐based productivity estimates and number of fledglings in nest plots in a tropical dry forest in Puerto Rico in 2009 and 2010. Few captures characterized the community of 25 resident species and, when estimable, capture probabilities were low, particularly for juveniles (typically < 0.1). Negative trends in capture probability, temporary emigration, and the distribution of birds suggest that avoidance of mist‐nets influenced capture rates in our study. Increasing mist‐net coverage or moving mist‐nets between sampling periods could increase capture rates. The number of fledglings observed in nest plots (25 ha/plot) did not correlate well with capture‐derived estimates (20 ha/net stations), suggesting the presence of immigrants or failure to find all nests. Our results suggest that indices of breeding productivity from mist‐netting data may track temporal changes in productivity, but such data likely do not reflect “true” productivity in most cases unless age‐specific differences in capture probability are incorporated into estimates. Pilot studies should be conducted to evaluate capture rates and the spatial extent sampled by mist‐nets to improve sampling design and inferences before informing decisions.     

Efficient,Noninvasive Genetic Sampling for Monitoring Reintroduced Wolves

ABSTRACT Traditional methods of monitoring gray wolves (Canis lupus) are expensive and invasive and require extensive efforts to capture individual animals. Noninvasive genetic sampling (NGS) is an alternative method that can provide data to answer management questions and complement already-existing methods. In a 2-year study, we tested this approach for Idaho gray wolves in areas of known high and low wolf density. To focus sampling efforts across a large study area and increase our chances of detecting reproductive packs, we visited 964 areas with landscape characteristics similar to known wolf rendezvous sites. We collected scat or hair samples from 20% of sites and identified 122 wolves, using 8–9 microsatellite loci. We used the minimum count of wolves to accurately detect known differences in wolf density. Maximum likelihood and Bayesian single-session population estimators performed similarly and accurately estimated the population size, compared with a radiotelemetry population estimate, in both years, and an average of 1.7 captures per individual were necessary for achieving accurate population estimates. Subsampling scenarios revealed that both scat and hair samples were important for achieving accurate population estimates, but visiting 75% and 50% of the sites still gave reasonable estimates and reduced costs. Our research provides managers with an efficient and accurate method for monitoring high-density and low-density wolf populations in remote areas.     

Spatial distribution,sampling efficiency and Taylor's power law

1. A relationship between sampling efficiency and Taylor's power law (TPL) is derived and illustrated with data from gypsy moth samples taken in Pennsylvania. 2. It is shown that attractant traps such as pheromone and light traps may exhibit density‐dependent sampling efficiency which can influence the parameters of TPL. 3. Comparison of the light trap and pheromone trap sample data with those of a standardised suction trap enables the attractant traps to be standardised. 4. Rescaling male moth catches per trap to number per unit volume increases the slope, intercept and correlation coefficient while stretching the pattern of data points. 5. Density‐dependent sampling efficiency of attractant traps shows how TPL is sensitive to spatial aggregation behaviour as well as other life‐history variables.     

Comparing clustered sampling designs for spatially explicit estimation of population density

Spatially explicit capture–recapture methods do not assume that animals have equal access to sampling devices (e.g., detectors), which allows for gaps in the sampling extent and nonuniform (e.g., clustered) sampling designs. However, the performance (i.e., relative root mean squared error [RRMSE], confidence interval coverage, relative bias and relative standard error) of clustered detector arrays has not been thoroughly evaluated. I used simulations to evaluate the performance of various detector and cluster spacings, cluster configurations (i.e., number of detectors arranged in a square grid), sampling extents and number of sampling occasions for estimating population density, the relationship between detection rate and distance to a detector from the animal's center of activity (σ) and base detection rates, using American black bears (Ursus americanus) as a case study. My simulations indicated that a wide range of detector configurations can provide reliable estimates if spacing between detectors in clusters is ≥1σ and ≤3σ. A number of cluster configurations and occasion lengths produced estimates that were unbiased, resulted in good spatial coverage, and were relatively precise. Moreover, increasing the duration of sampling, establishing large study areas, increasing detection rates and spacing clusters so that cross-cluster sampling of individuals can occur could help ameliorate deficiencies in the detector layout. These results have application for a wide array of species and sampling methods (e.g., DNA sampling, camera trapping, mark-resight and search-encounter) and suggest that clustered sampling can significantly reduce the effort necessary to provide reliable estimates of population density across large spatial extents that previously would have been infeasible with nonclustered sampling designs.