A new cost‐effective approach to survey ecological communities

Surveying ecological communities often means the tedious work of collecting detailed information on each species within each sampling unit (e.g. trap, transect, quadrat). In this paper, we first argue that presence–absence and abundance data are the two extremes of a spectrum of data formats. By counting individuals of each species within a sampling unit until either a predefined (user‐defined) number of individuals is reached or all individuals of the species are counted, all intermediate cases can be generated. By independently correlating each intermediate case with the complete abundance data, we show that it is not necessary to count all individuals to recover the patterns of variation characterizing a community data table. When the same procedure is applied in combination with different distance coefficients such as the Hellinger, chord, χ², percentage difference or modified Gower, or the distance between species profiles, an even lower number of individuals per species need to be counted within a sampling unit for the patterns of variation defining a community to be recovered. By applying the same counting procedure to data collected during a pilot study, we show that the maximum number of individuals that need to be counted within a sampling unit for a species can be estimated from a pilot study containing as little as 3% of randomly selected sampling units throughout the complete survey area. An example of how to apply this new counting method is presented, using data from a boreal forest Carabidae community sampled in northwestern Alberta, Canada.     

On the estimation of species richness based on the accumulation of previously unrecorded species

Estimation of species richness of local communities has become an important topic in community ecology and monitoring. Investigators can seldom enumerate all the species present in the area of interest during sampling sessions. If the location of interest is sampled repeatedly within a short time period, the number of new species recorded is typically largest in the initial sample and decreases as sampling proceeds, but new species may be detected if sampling sessions are added. The question is how to estimate the total number of species. The data collected by sampling the area of interest repeatedly can be used to build species accumulation curves: the cumulative number of species recorded as a function of the number of sampling sessions (which we refer to as “species accumulation data”). A classic approach used to compute total species richness is to fit curves to the data on species accumulation with sampling effort. This approach does not rest on direct estimation of the probability of detecting species during sampling sessions and has no underlying basis regarding the sampling process that gave rise to the data. Here we recommend a probabilistic, nonparametric estimator for species richness for use with species accumulation data. We use estimators of population size that were developed for capture‐recapture data, but that can be used to estimate the size of species assemblages using species accumulation data. Models of detection probability account for the underlying sampling process. They permit variation in detection probability among species. We illustrate this approach using data from the North American Breeding Bird Survey (BBS). We describe other situations where species accumulation data are collected under different designs (e.g., over longer periods of time, or over spatial replicates) and that lend themselves to of use capture‐recapture models for estimating the size of the community of interest. We discuss the assumptions and interpretations corresponding to each situation.     

Diversity of Chrysomelidae (Coleoptera) in Galicia, Northwest Spain: Estimating the Completeness of the Regional Inventory

The diversity of Chrysomelidae (Coleoptera) in Galicia, Northwest Spain was examined. A long-term sampling was conducted during 1996–2001 and 267 species were collected, but including bibliographic citations a total of 276 species were recorded. As a result of this study the regional inventory has grown from 83 taxa cited before 1998 to the current 276 species. Species accumulation models were used to measure the inventory completeness and estimate the actual species richness of Chrysomelidae occurring in Galicia. Estimates were generated by analyzing both the rarefaction curve from the long-term sampling and the cumulative number of species recorded from Galicia since 1866. Values of total richness predicted by these different methods range between 290 and 323 species. Therefore, it seems that between 85 and 95% of the leaf beetle fauna was recorded and thus the inventory has reached an acceptable level of completeness.     

Inferring host specificity and network formation through agent-based models: tick–mammal interactions in Borneo

Patterns of host–parasite association are poorly understood in tropical forests. While we typically observe only snapshots of the diverse assemblages and interactions under variable conditions, there is a desire to make inferences about prevalence and host-specificity patterns. We studied the interaction of ticks with non-volant small mammals in forests of Borneo. We inferred the probability of species interactions from individual-level data in a multi-level Bayesian model that incorporated environmental covariates and advanced estimates for rarely observed species through model averaging. We estimated the likelihood of observing particular interaction frequencies under field conditions and a scenario of exhaustive sampling and examined the consequences for inferring host specificity. We recorded a total of 13 different tick species belonging to the five genera Amblyomma, Dermacentor, Haemaphysalis, Ixodes, and Rhipicephalus from a total of 37 different host species (Rodentia, Scandentia, Carnivora, Soricidae) on 237 out of 1,444 host individuals. Infestation probabilities revealed most variation across host species but less variation across tick species with three common rat and two tree shrew species being most heavily infested. Host species identity explained ca. 75 % of the variation in infestation probability and another 8–10 % was explained by local host abundance. Host traits and site-specific attributes had little explanatory power. Host specificity was estimated to be similarly low for all tick species, which were all likely to infest 34–37 host species if exhaustively sampled. By taking into consideration the hierarchical organization of individual interactions that may take place under variable conditions and that shape host–parasite networks, we can discern uncertainty and sampling bias from true interaction frequencies, whereas network attributes derived from observed values may lead to highly misleading results. Multi-level approaches may help to move this field towards inferential approaches for understanding mechanisms that shape the strength and dynamics in ecological networks.     

Species richness and composition assessment of spiders in a Mediterranean scrubland

Intensive fieldwork has been undertaken in Portugal in order to develop a standardized and optimized sampling protocol for Mediterranean spiders. The present study had the objectives of testing the use of semi-quantitative sampling for obtaining an exhaustive species richness assessment of spiders and testing the effects of day, time of day, collector and sampling method on the collected species richness and composition of a Mediterranean scrubland. The collecting summed 224 samples corresponding to one person-hour of effective fieldwork each. In total, 115 species were captured, of which 110 were recorded inside a delimited one-hectare plot, corresponding to more than 70% of the about 160 estimated species. Although no estimator reached the asymptote, the Michaelis-Menten curve behaviour indicates that the estimated richness should be accurate. Most different sampling approaches (day, time of day, collector and sampling method) were found to influence richness, abundance or composition of the samples to some extent, although sampling method had the strongest influence whereas “collector” showed no effect at all. The results support the idea that the only variables that need to be controlled in similar protocols are the sampling methods and the time of day when each method is executed. We conclude that populations in structurally simple habitats present narrower peaks of adult abundance, which implies higher percentages of juveniles in samples. Finally, results also indicate that habitats with a relatively simple structure like scrublands may require as much sampling effort, in order to reach similar proportions of captured species in relation to the estimated richness, as habitats that are much more complex.     

Detection probability and Pasteurellaceae surveillance in bighorn sheep

We investigated the influence of detection probability (i.e., the probability of detecting the disease or organism of interest) on the repeatability of results reported from bacterial culture tests used to demonstrate the presence of species in the Pasteurellaceae family that infect bighorn sheep (Ovis canadensis). We also estimated occupancy probabilities (i.e., the probability an individual bighorn in a herd is infected) for each cultured biovariant and examined the effects of detection probability on the number of samples needed to detect the Pasteurellaceae biovariants from within an individual sheep as well as from within a herd. We collected 5-15 samples from free-ranging bighorns in Colorado, using oropharyngeal swabs or swabs of lungs, and submitted these swabs either immediately or after 2 days for bacterial culture. We saw significant variability in results for repeated samples from each of the sheep, and detection probabilities were ≤ 0.71 for all Pasteurellaceae biovariants cultured. The delayed (≥ 2 days) sample submission reduced both the microbial diversity detected and the detection probability for the biovariants characterized when compared to samples submitted immediately. Oropharyngeal sampling had higher detection probabilities of the individual biovariants than did lung swabs, and there was a difference in the biovariants detected between oropharyngeal and lung sampling. Depending on the biovariant of interest, estimates of occupancy probabilities ranged from 0.37-0.89, and we estimated that three to >30 swab samples were necessary to obtain a 95% confidence of detecting the cultured biovariants if they were present in an individual sheep. We estimated that the optimal sample sizes to detect the observed biovariants within a sheep herd with a 95% confidence ranged from sampling two bighorns twice to sampling 40 individuals once. Detection probability impacts the results reported from bacterial cultures for Pasteurellaceae in bighorn sheep, and confounding effects of the detection process should be addressed to improve the rigor of surveillance.     

Can Malaise traps be used to sample spiders for biodiversity assessment?

Malaise traps are typically used to sample a range of flying insect groups; however non-target taxa such as spiders may also be collected in large numbers. In this study, spiders were sampled in peatlands and wet grasslands and catches in Malaise and pitfall traps were compared in order to determine the adequacy of Malaise traps for use in spider biodiversity assessment. Overall, the number of species and individuals caught in Malaise and pitfall traps were comparable, although more species were sampled in Malaise traps in locations with a greater structural diversity of the vegetation. The spider fauna sampled by the Malaise traps differed from that of the pitfall traps, but both methods consistently separated the species assemblages by biotope. These results demonstrate that Malaise traps are effective at sampling spiders and indicate that they can be used in biodiversity assessment. In addition the complementary species sampled by each method mean that employing both techniques will be useful where a full inventory of the species is required. The authors do not suggest that Malaise traps should be used solely to sample spiders; however, if traps are set to collect insects, identification of the spiders sampled may reduce the need to employ additional sampling techniques.     

Constant tree species richness along an elevational gradient of Mt. Bokor,a table-shaped mountain in southwestern Cambodia

Some previous studies along an elevational gradient on a tropical mountain documented that plant species richness decreases with increasing elevation. However, most of studies did not attempt to standardize the amount of sampling effort. In this paper, we employed a standardized sampling effort to study tree species richness along an elevational gradient on Mt. Bokor, a table-shaped mountain in southwestern Cambodia, and examined relationships between tree species richness and environmental factors. We used two methods to record tree species richness: first, we recorded trees taller than 4 m in 20 uniform plots (5 × 100 m) placed at 266–1048-m elevation; and second, we collected specimens along an elevational gradient from 200 to 1048 m. For both datasets, we applied rarefaction and a Chao1 estimator to standardize the sampling efforts. A generalized linear model (GLM) was used to test the relationship of species richness with elevation. We recorded 308 tree species from 20 plots and 389 tree species from the general collections. Species richness observed in 20 plots had a weak but non-significant correlation with elevation. Species richness estimated by rarefaction or Chao1 from both data sets also showed no significant correlations with elevation. Unlike many previous studies, tree species richness was nearly constant along the elevational gradient of Mt. Bokor where temperature and precipitation are expected to vary. We suggest that the table-shaped landscape of Mt. Bokor, where elevational interval areas do not significantly change between 200 and 900 m, may be a determinant of this constant species richness.     

Temporal variation in species-area curves for invertebrates in clumps of an intertidal mussel

We examined the temporal variation in the relationships between the number of invertebrate species, and of total individuals inhabiting clumps of the intertidal mussel Brachidontes rostratus and the area of the clumps We collected clumps in four seasons - autumn, winter, spring and summer - from a rocky shore in south-eastern Australia Positive curvilinear relationships between species number and area were recorded for all seasons but fewer species for a given area were found in autumn and summer compared with winter and spring These species-area relationships were different from those predicted from a passive sampling model (Random Placement Model) Positive relationships between number of individuals and area were also recorded but these did not vary between seasons There was no short-term difference (i e between phases of tide and day) in species or individual number in clumps Seasonal variation, and small-scale spatial unpredictability in recruitment patterns are potentially important determinants of species numbers in this system The seasonal differences we have recorded for mussel clumps suggest that future studies on island systems particularly in marine habitats should consider temporal variation in species-area relationships and that conclusions from previous comparisons of species-area curves based on one-off sampling must only be tentative     

A stochastic model for the spatial distribution of species based on an aggregation–repulsion rule

The heterogeneity associated with the spatial distribution of organisms is an awkward problem in ecology because this heterogeneity directly depends on the sampling scale. To specify the scope of the influence of sampling scale on the level of species aggregation, we need data sets that entail excessive sampling costs in situ. To find a solution for this problem, we can use models to simulate patterns of organisms. These models are often very complex models that take into account heterogeneity of habitats and displacement or longevity of studied species. In this article, we introduce a new stochastic model to simulate patterns for one taxon and we want this model to be parsimonious, i.e., with few parameters and able to simulate observed patterns. This model is based on an aggregation–repulsion rule. This aggregation–repulsion rule is defined by two parameters. On a large scale, the number of aggregates present on the pattern is the first parameter. On a smaller scale, the level of aggregation–repulsion among individuals is determined by a probability distribution. These two parameters are estimated from field data set in a robust way so that the simulated patterns reflect the observed heterogeneity. We apply this model to entomological data: four Diptera families, namely the Sciaridae, Phoridae, Cecidomyiidae, and Empididae. The field data for the Phoridae family are used to simulate sampling using different trap sizes. We record changes in the coefficient of variation (C) as a function of the sampling scale, and we can suggest to ecologists emergence traps of 0.6 m², in other words a square 77 × 77 cm trap, to obtain a C value under 20%. Received: February 28, 2000 / Accepted: October 14, 2000     

How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model

The fossil record is a rich source of information about biological diversity in the past. However, the fossil record is not only incomplete but has also inherent biases due to geological, physical, chemical and biological factors. Our knowledge of past life is also biased because of differences in academic and amateur interests and sampling efforts. As a result, not all individuals or species that lived in the past are equally likely to be discovered at any point in time or space. To reconstruct temporal dynamics of diversity using the fossil record, biased sampling must be explicitly taken into account. Here, we introduce an approach that uses the variation in the number of times each species is observed in the fossil record to estimate both sampling bias and true richness. We term our technique TRiPS (True Richness estimated using a Poisson Sampling model) and explore its robustness to violation of its assumptions via simulations. We then venture to estimate sampling bias and absolute species richness of dinosaurs in the geological stages of the Mesozoic. Using TRiPS, we estimate that 1936 (1543–2468) species of dinosaurs roamed the Earth during the Mesozoic. We also present improved estimates of species richness trajectories of the three major dinosaur clades: the sauropodomorphs, ornithischians and theropods, casting doubt on the Jurassic–Cretaceous extinction event and demonstrating that all dinosaur groups are subject to considerable sampling bias throughout the Mesozoic.     

Estimating mountain goat abundance using DNA from fecal pellets

Non-invasive collection of tissue samples to obtain DNA for microsatellite genotyping required to estimate population size has been used for many wildlife species but rarely for ungulates. We estimated mountain goat (Oreamnos americanus) population size on a mountain complex in southwestern British Columbia by identification of individuals using DNA obtained from fecal pellet and hair samples collected during 3 sampling sessions. We identified 55 individuals from 170 samples that were successfully genotyped, and estimated a population of 77 mountain goats (SE = 7.4). Mean capture probability was 0.38 (SE = 0.037) per session. Our technique provides one of the first statistically rigorous estimates of abundance of an ungulate species using DNA derived primarily from fecal pellets. Our technique enables managers to obtain minimum counts or population estimates of ungulates in areas of low sightability that can be used for conservation and management. © 2011 The Wildlife Society.     

Estimating species – area relationships by modeling abundance and frequency subject to incomplete sampling

Models and data used to describe species–area relationships confound sampling with ecological process as they fail to acknowledge that estimates of species richness arise due to sampling. This compromises our ability to make ecological inferences from and about species–area relationships. We develop and illustrate hierarchical community models of abundance and frequency to estimate species richness. The models we propose separate sampling from ecological processes by explicitly accounting for the fact that sampled patches are seldom completely covered by sampling plots and that individuals present in the sampling plots are imperfectly detected. We propose a multispecies abundance model in which community assembly is treated as the summation of an ensemble of species‐level Poisson processes and estimate patch‐level species richness as a derived parameter. We use sampling process models appropriate for specific survey methods. We propose a multispecies frequency model that treats the number of plots in which a species occurs as a binomial process. We illustrate these models using data collected in surveys of early‐successional bird species and plants in young forest plantation patches. Results indicate that only mature forest plant species deviated from the constant density hypothesis, but the null model suggested that the deviations were too small to alter the form of species–area relationships. Nevertheless, results from simulations clearly show that the aggregate pattern of individual species density–area relationships and occurrence probability–area relationships can alter the form of species–area relationships. The plant community model estimated that only half of the species present in the regional species pool were encountered during the survey. The modeling framework we propose explicitly accounts for sampling processes so that ecological processes can be examined free of sampling artefacts. Our modeling approach is extensible and could be applied to a variety of study designs and allows the inclusion of additional environmental covariates.     

Integrating Modern Vegetation and Ethnographic Data to Understand Dietary Choices in the Past: the Case of the Southern Paiute,Utah

Ethnographic information on dietary plants can be cast into an ecological framework by using vegetation sampling techniques. Lists of ethnobotanical species become the basis of a dietary inventory that applies to a regional assemblage of vegetation types in a landscape associated with an archaeological site. But such lists are usually derived from many sources often without biogeographic or temporal reference. In effect, the dietary inventory represents potential food plants that may ultimately be found in archaeological deposits. The dietary palette, however, is composed of plant species that actually occur within the greater landscape of an archaeological site and that may or may not be known from the ethnographic record. Vegetation sampling provides a quantitative assessment of the dietary palette in the local ecosystem by using standard metrics, such as plant cover, basal area, density, and even productivity. By comparing vegetation data to the dietary inventory and archaeobotanical record, general patterns of foraging behavior as predicted by behavioral ecology are verified. This study of the Southern Paiute in south-central Utah also compares the plant species composition of modern and ancient landscapes, emphasizing a lack of correspondence between the dietary inventory and the dietary palette, as well as with the archaeobotanical record. Our example is from North Creek Shelter, a well-stratified archaeological site on the Colorado Plateau.     

Comparing two methods for estimating floral resource availability for insect pollinators in semi-natural habitats

Pollinator and flowering plant interactions play a critical role in maintaining most terrestrial ecosystems, including agroecosystems. Although estimates of floral resource availability are essential to understand plant–pollinator relationships, no generally accepted methodology exists to date. We compared two methods for sampling floral resources in a single meadow. About every three days, we recorded species lists of insect-pollinated plants with abundance categories assigned to each species (hereafter referred to as scanning) and we counted the flowering shoots in 36 2 × 2 m quadrats (hereafter quadrat sampling). These methods were compared with respect to (i) the number of species detected, (ii) estimated floral resource abundance, and (iii) temporal changes in flowering. With scanning, we found more potential nectar-plant species and species were found earlier than with quadrat sampling. With the latter, abundant species were found with higher probability than the scarce. Flower abundances were correlated between the two methods. We predicted that a cover of 6.3 ± 3.6% should be used for an appropriate estimate of flower abundance in our study site, although the optimal cover probably varies across different habitats. Furthermore, flower abundance changed 6% per day compared to the flowering peak. Overall, scanning seems to be more appropriate for detecting presence and the timing of species, while quadrats may provide higher resolution for abundance estimates. Increased sampling coverage and frequency may enhance research accuracy and using scanning and quadrat sampling simultaneously may help to optimize research effort. We encourage further development of sampling protocols.     

植物空间分布格局中邻体距离的概率分布模型及参数估计

最近邻体法是一类有效的植物空间分布格局分析方法,邻体距离的概率分布模型用于描述邻体距离的统计特征,属于常用的最近邻体法之一。然而,聚集分布格局中邻体距离(个体到个体)的概率分布模型表达式复杂,参数估计的计算量大。根据该模型期望和方差的特性,提出了一种简化的参数估计方法,并利用遗传算法来实现参数优化,结果表明遗传算法可以有效地估计的该模型的两个参数。同时,利用该模型拟合了加拿大南温哥华岛3个寒温带树种的空间分布数据,结果显示:该概率分布模型可以很好地拟合美国花旗松(P.menziesii)和西部铁杉(T.heterophylla)的邻体距离分布,但由于西北红柏(T.plicata)存在高度聚集的团簇分布,拟合结果不理想;美国花旗松在样地中近似随机分布,空间聚集参数对空间尺度的依赖性不强,但西北红柏和西部铁杉空间聚集参数具有尺度依赖性,随邻体距离阶数增加而变大。最后,讨论了该模型以及参数估计方法的优势和限制。     

Optimizing Diversity Assessment Protocols for High Canopy Ants in Tropical Rain Forest

The canopies of tropical rain forests support highly diverse, yet poorly known, animal and plant communities. It is vital that researchers who invest the time needed to gain access to the high canopy are able efficiently to survey the animals and plants that they find there. Here, we develop diversity assessment protocols for one of the most ecologically important canopy animal groups, the ants, in lowland dipterocarp rain forest in Sabah, Malaysia. We design and test a novel trap (the purse‐string trap) that can be remotely collected, thus avoiding disturbance to ants. We compare this modified trap with two other methods for surveying canopy ants: precision insecticide fogging and baited pitfall trapping. In total, we collected 39,351 ants belonging to 173 species in 38 genera. Fogging collected the most individuals and species, followed by purse‐string trapping with baited pitfall trapping catching the fewest. Fogging also resulted in samples with a different species composition to purse‐string trapping and baited pitfall trapping, which were not different from one another. Using a ‘greedy algorithm’, which guides the selection of inventory methods in order to maximize new species discovered per researcher‐hour, we show that projects allocating fewer than 132 researcher‐hours to canopy ant collection and identification should sample exclusively using fogging. Those with more time should use a combination of methods. This prioritization technique could be used to accelerate species discovery in future rapid biodiversity assessments. Abstract in Malay is available in the online version of this article.     

Estimating the abundance of rare and elusive carnivores from photographic-sampling data when the population size is very small

Conservation and management agencies require accurate and precise estimates of abundance when considering the status of a species and the need for directed actions. Due to the proliferation of remote sampling cameras, there has been an increase in capture–recapture studies that estimate the abundance of rare and/or elusive species using closed capture–recapture estimators (C–R). However, data from these studies often do not meet necessary statistical assumptions. Common attributes of these data are (1) infrequent detections, (2) a small number of individuals detected, (3) long survey durations, and (4) variability in detection among individuals. We believe there is a need for guidance when analyzing this type of sparse data. We highlight statistical limitations of closed C–R estimators when data are sparse and suggest an alternative approach over the conventional use of the Jackknife estimator. Our approach aims to maximize the probability individuals are detected at least once over the entire sampling period, thus making the modeling of variability in the detection process irrelevant, estimating abundance accurately and precisely. We use simulations to demonstrate when using the unconditional-likelihood M ₀ (constant detection probability) closed C–R estimator with profile-likelihood confidence intervals provides reliable results even when detection varies by individual. If each individual in the population is detected on average of at least 2.5 times, abundance estimates are accurate and precise. When studies sample the same species at multiple areas or at the same area over time, we suggest sharing detection information across datasets to increase precision when estimating abundance. The approach suggested here should be useful for monitoring small populations of species that are difficult to detect.     

Diversity of social wasps (Hymenoptera: Vespidae) in Cerrado fragments of Uberlândia, Minas Gerais State, Brazil

Studies of species survey are important to know the available natural resources and to get useful information about the ecological characteristics of a specific area. There are not studies, on this issue, related to social wasps, in the Triangulo Mineiro region. The present study describes the diversity of species found in fragments of the cerrado region in Uberlandia, MG, and their temporal distribution. The field study was conducted from October 2003 to September 2004, and 43 samplings were carried out using active searching (24) and point sampling (19) methodologies. Twenty-nine species were found in 10 genera, Polybia and Polistes corresponding to 51.5% of the total listing. Mischocyttarus cerberus styx Richards represented 26.5% of the total individuals recorded by active searching and Agelaia pallipes (Olivier) corresponded to 57.6% by point sampling. Two species had their first record for the state of Minas Gerais: Polybia striata (Fabricius) and M. cerberus styx. The studied fragments presented a high level of diversity (H' = 0.66 to 1.16), a large number of rare species and a few common species. To collect the more common species the point sampling method was satisfactory while active searching was better to collect the rarer species. The active searching methodology was more efficient than point sampling, however some species could only be collected by point sampling. These factors showed that in order to carry out a wasp survey, a combination of different collection methodologies seems to be more appropriate.     

Underestimated spider diversity in a temperate beech forest

We used canopy fogging to study the high (20–26 m), intermediate (13–19 m) and low (5–6 m) strata in three European beech patches (Fagus sylvatica) in nine months (2005–2007) and estimate species richness and diversity of arboreal spiders. Eight species (10%) were previously unseen in European beech trees, and one of these is likely a new species. Moreover, two species are on the Bavarian red list. Our results revealed that the high stratum of the old-growth trees provided unique resources and possessed the greatest diversity and evenness, whereas intermediate and low strata had high similarity in respect to diversity, dominance, species, and family composition. Since the majority of beech forests consists of mature and young trees in Central Europe, and old-growth forests are rarely preserved, we recommend young beech be used in a sampling protocol for rapid biodiversity assessment. However, adding samples from the two higher strata to the lowest stratum (55 species), almost doubled the estimated species richness (102 species). This suggests that the lower stratum alone does not represent a true image of the total canopy fauna inventory in this, and likely other, beech stands. To complete this comprehensive inventory in European beeches, the Chao1 predicted that additional sampling would be needed in the highest stratum, where there is a high probability to find previously undetected species in a next survey. Our study clearly shows that neglecting the crowns of the largest, tallest trees risks underestimating the overall spider diversity in Central European forests.