Efficient sampling of ground-dwelling arthropods using pitfall traps in arid steppes

Pitfall trapping is probably the most frequently used method for sampling ground-dwelling arthropods. While the capture of specimens in pitfall traps largely depends on the number of individuals in the sampled area, trap design and trapping effort for a given environment, can also affect sampling success. The aim of this study was to determine the best pitfall trapping design for collecting ground-dwelling arthropods in the wind-blown and cold arid steppe areas of Patagonia. We tested four designs of traps, six types of preservative and different times of activation as well as the quantity of traps. Both preservation attributes and sampling efficiency differed between different trap designs and fluids compared. We conclude that in order to obtain reliable data on the structure of a community of ground-dwelling arthropods in Patagonia, at least three pitfall traps per experimental unit are required. In addition, traps should be opened for a minimum of 10 days filled with 300 ml of 30% ethylene glycol. We also suggested the use of a simple trap design (i. e. without funnel or roof). We believe these findings will contribute to more appropriate sampling of the ground dwelling fauna of Patagonia as well as other arid areas, leading to more reliable diversity studies.     

Comparison of pitfall traps and litter bags for sampling ground-dwelling arthropods

Abstract:  For their simplicity and effectiveness, pitfall traps have become a standard technique to measure the activity and relative abundance of ground-dwelling arthropods. Permeable screen or mesh bags filled with plant material, referred to as litter bags, have also recently been employed as a complementary sampling technique for epigeal taxa. The anticipated need for increased field research on arthropod populations, particularly in transgenic crops with insecticidal properties, suggests that a relative assessment of both sampling methods could contribute to the design of future studies. Comparisons among pitfall traps, and litter bags placed above- or below-ground indicated that above-ground litter bags most frequently succeeded in collecting certain groups of arthropods associated with moisture and sheltered areas, including centipedes (Chilopoda) and beetle larvae (Carabidae, Staphylinidae). Conversely, pitfall traps most often captured taxa considered active at ground level, such as adult carabids or harvestmen (Opiliones). For taxa collected in >40% of all three trap types, bootstrap confidence intervals for the coefficient of variation (CV; used to assess precision or sampling efficiency) showed that above-ground litter bags were significantly more precise than pitfall traps for sampling elongate springtails (Collembola) and adult rove beetles (Staphylinidae), but only during the first year of sampling. While below-ground litter bags often appeared similar to one or both of the other trap types, in no case were below-ground litter bags best based on frequency of collection or CV. Though differences were not always consistent between years, results suggest that the additional effort required to sample using litter bags may be justified for the collection of some ground-dwelling taxa.     

Comparison of reptile sampling in Iran with pitfall versus double-ended funnel traps

In north Khorasan province, Iran, we compared the effectiveness of two types of traps for collecting reptiles: funnel traps and pitfall traps. Three stations were monitored over three 10-day periods and in total 544 individuals (including 200 recaptures) belonging to 5 species and 4 families of lizards (Lacertidae) were collected. Funnel traps with 280 captures were more efficient than pitfall traps with 264 captures, but the differences between the two traps are not significant. Three species were captured most often in the three different stations respectively: station 1, Bunopus crassicauda (22% relative frequency); station 2, Eremias fasciata (29% relative frequency); and station 3, Trapelus agilis (32% relative frequency). Shannon species richness indices were higher for pitfall than funnel traps (i.e., 1.45 vs. 1.40), but the difference was not significant. Pitfall traps were better for capturing species that search widely for food, while the funnel traps preferentially captured species that climb plants, such as Trapelus agilis. We recommend using both types of trap to capture the various types of species in any one region.     

Sampling epigeal arthropods: an evaluation of fenced pitfall traps using mark-release-recapture and comparisons to unfenced pitfall traps in arable crops

The efficiency of fenced pitfall traps for estimating the density of commonly occurring epigeal predatory beetles was examined using mark-release-recapture. Most beetles of those recovered were recaptured within one week of their release. For seven of the ten species tested recapture rates were over 70%, with higher rates for the larger species. The predatory arthropod species composition captured using fenced pitfall traps was compared to unfenced pitfall traps in winter wheat, spring barley and winter oilseed rape. Compositional analysis revealed that the dominance structure of seven carabid beetle (Coleoptera: Carabidae) taxa differed between the trap types and month of sampling in winter wheat and spring barley, but differences were small with the exception of a few taxa. Linear relationships between the two techniques were found for some carabid and rove beetles (Coleoptera: Staphylinidae). The dominance structure of seven linyphiid spider (Araneae: Linyphiidae) taxa differed between the two trap types in wheat but not barley, although large differences were restricted to two taxa. No linear relationships between the two techniques were found for any of the Linyphiidae examined. Rove beetles were more effectively sampled using the fenced compared to unfenced pitfall traps.     

Influence of carrion smell and rebaiting time on the efficiency of pitfall traps to dung beetle sampling

Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) are very useful insects, as they improve the chemo-physical properties of soil, clean pastures from dung pads, and help control symbovine flies associated with bovine cattle. Their importance makes it fundamental to sample and survey them adequately. The objectives of the present study were to determine the influence of decaying insects trapped in pitfalls on the attractiveness of Moura pig Sus scrofa L. (Suidae) and collared peccary Tayassu tajacu (L.) (Tayassuidae) dung used as baits to lure dung beetles, and to establish how long these baits remain attractive to dung beetles when used in these traps. Some dung beetle species seemed to be able to discriminate against foul smell from decaying insects within the first 24 h, hence decreasing trap efficiency. This was more evident in peccary dung-baited traps, which proved to be the least attractive bait. Attractiveness lasted only 24 h for peccary dung, after which it became unattractive, whereas the pig dung bait was highly attractive for 48 h, after which its attractiveness diminished but was not completely lost.     

A comparison of pitfall traps with bait traps for studying leaf litter ant communities.

A comparison of pitfall traps with bait traps for sampling leaf litter ants was studied in oak-dominated mixed forests during 1995-1997. A total of 31,732 ants were collected from pitfall traps and 54,694 ants were collected from bait traps. They belonged to four subfamilies, 17 genera, and 32 species. Bait traps caught 29 species, whereas pitfall traps caught 31 species. Bait traps attracted one species not found in pitfall traps, but missed three of the species collected with pitfall traps. Collections from the two sampling methods showed differences in species richness, relative abundance, diversity, and species accumulation curves. Pitfall traps caught significantly more ant species per plot than did bait traps. The ant species diversity obtained from pitfall traps was higher than that from bait traps. Bait traps took a much longer time to complete an estimate of species richness than did pitfall traps. Little information was added to pitfall trapping results by the bait trapping method. The results suggested that the pitfall trapping method is superior to the bait trapping method for leaf litter ant studies. Species accumulation curves showed that sampling of 2,192+/-532 ants from six plots by pitfall traps provided a good estimation of ant species richness under the conditions of this study.     

Hypogaeic pitfall traps: methodological advances and remarks to improve the sampling of a hidden ant fauna

Ant assemblages present a great vertical stratification, with microhabitats showing strong differences in relation to species composition. Among the microhabitats, the hypogaeic has been poorly studied. Hypogaeic or subterranean ants live in the deeper soil layers, which make the sampling logistics and operability a difficult work. The fact that the hypogaeic ant fauna is diversified and abundant, with low similarity to ant assemblages in other microhabitats, has promoted the development of several collecting techniques to sample this hidden ant fauna. Here, we verify the ability of hypogaeic pitfall traps to sample subterranean ants. In addition, we propose methodological advances and remarks about the use of this ant sampling technique.     

Few beetle species can be detected with 95% confidence using pitfall traps

False absences in wildlife surveys make it difficult to identify metapopulation processes, increase uncertainty of management decisions and bias parameter estimates in habitat models. Despite these risks, the number of species that can be detected with a certain probability in a community survey has rarely been examined. I sampled beetles over 5 months using pitfall trap grids at three rainforest locations in Tasmania, Australia. I compared detection probability for dispersed and clustered sampling schemes using a zero‐inflated binomial model and a simpler occurrence method to calculate the probability of detection. After excluding extremely rare species, I analysed 12 of 121 species. Only three to six species could be detected with 95% probability using a sampling effort that is frequently applied in ecological studies. A majority of common species had a mid summer peak in detection probability meaning that survey effort could be reduced from 5 to 2 months with only a small reduction in data quality. Most species occurred at only a proportion of sample points within locations. Despite the implied spatial structuring, three small grids within a location detected 10 of 12 species as effectively as large, dispersed grids. This study warns that as little as 5% of the beetle fauna may have a 95% probability of detection using the frequently applied pitfall trap method, highlighting a substantial limitation in our ability to accurately map the distributions of ground invertebrates. Whether very large sample sizes can overcome this limitation remains to be examined.     

The digging‐in effect on ant studies with pitfall traps: influence of type of habitat and sampling time

Pitfall traps are among the most common sampling methods used for the study of ants. There are many types of traps and many possible ways of using them. The various methodologies may introduce biases in sampling. One possible bias may be caused by the digging‐in effect (DE), resulting in higher catches of ants immediately after traps are set in the ground which subsequently decline. In this study, we performed two experiments to verify the consequences of the DE for ants in a Mediterranean ecosystem. In the first experiment we distinguished between two types of habitats: closed and open (i.e., with or without shrub or tree cover). The second experiment was carried out in a homogeneous pasture where the time of prevalence of the DE was verified, investigating the duration of the effect. The results indicate differences between communities in the first 24 h after setting of the traps, which had disappeared after 48 h. This does not dismiss the possibility of certain species being affected either positively (increase in captures) or negatively (decrease). Changes in species composition, determining whether the DE was manifested or not, differed among habitat types.     

Behavioural responses of three linyphiid spiders to pitfall traps

The behaviour of three linyphiid spider species (Araneae: Linyhiidae) towards pitfall traps was investigated in an experimental arena. Capture efficiencies were low with a mean of between 16 and 57 traps being encountered before spiders were caught. Survival time, trap encounter rate, trap entry rate and reactions towards vegetation were all found to be species-specific. These behaviours are considered to affect differentially pitfall trap efficiency and may partially explain the lack of clear relationship between pitfall trap catch and density found in published studies.     

A comparison of water traps, cylindrical sticky traps and suction traps for sampling thysanopteran populations at different levels

Thysanoptera drifting over and around a wheat field were trapped using black, green and white water traps, black cylindrical sticky traps and suction traps. Certain Taeniothrips spp., Thrips spp., and Aeolothrips spp. were strongly attracted to white but not to green or black; Limothrips cerealium Hal., Chirothrips manicatus Hal., and Stenothrips gramium Uzel were not markedly attracted to any of these colours. At crop level suction traps gave more consistent catches² than either sticky or water traps; at higher levels, catches from sticky traps were more consistent than those from water traps. Up to 48 ft the aerial density of all species decreased with height but the rapidity of the decrease differed between species.

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Sommaire Les Thysanoptères qui flottaient autour et au-dessus d'un champ de blé étaient attrapés par le moyen de pièges à l'eau noirs, verts ou blancs, de pièges cylindriques qui étaient visqueuz et noirs et d'aspirateurs. De certaines espèces des genres Taeniothrips, Thrips et Aeolothrips étaient très attirées par le blanc mais pas par le vert ni le noir: les espèces Limothrips cerealium Hal., Chirothrips manicatus Hal., et Stenothrips gramium Uzel n'étaient pas notablement attirées par chacune de ces couleurs. Au niveau des épis les données obtenues avec les aspirateurs étaient plus justes que ne l'étaient celles obtenues avec les pièges à glu ou les pièges à eau: plus haut les pièges à glu indiquaient des données plus justes que les pièges à eau. Jusqu'à quinze mètres environ de hauteur la densité aérienne de toutes les espèces diminuaient progressivement, mais la rapidité de la diminution était différente entre les espèces.

     

Use of infochemicals to attract carrion beetles into pitfall traps

When the bodies of small vertebrates start to decay shortly after death, a number of organosulfur compounds are produced, including methanethiol, dimethylsulfide (DMS), dimethyldisulfide (DMDS), dimethyltrisulfide (DMTS), and S-methyl thioacetate. These molecules appear to attract various necrophagous animals. We tested the roles of DMS, DMDS, and DMTS (in order of decreasing volatility) as attractants of carrion beetles (Coleoptera: Silphidae: Nicrophorinae) in a field experiment in an agricultural landscape in southern Bohemia, Czech Republic. We collected a total of 362 adult Nicrophorus vespillo (L.) that were attracted to 220 baited pitfall traps in a 3-day experiment. Sets of traps baited with DMTS were more successful in catching N. vespillo than sets baited with a blank. Traps containing DMDS had higher trapping success than traps containing DMS. In addition, trapping success strongly increased using DMTS in the presence of DMDS but not of DMS, suggesting a synergistic effect of DMDS and DMTS. We observed similar patterns between males and females in response to the infochemicals tested.     

笼捕法和陷阱法对森林小型兽类多样性监测效率比较

<正>小型兽类包括食虫目(Insectivora)、啮齿目(Rodentia)、翼手目(Chiroptera)、兔形目(Lagomorpha)等,物种数量多,分布广,适应能力强,对环境变化敏感,因此其群落组成和种群数量变化可较好地反映生境变化的质量和人类活动的干扰程度(肖治术等,2002;李俊生等,2003;仝磊和路纪琪,2010)。小型兽类多样性一直是生物多样性和生态环境监测与评价的重要指示类群之一(周立志和马勇,2002)。统计动物毛发、粪便、巢穴、叫声、足迹等动物痕迹以及直接观察等方法已被广泛用于兽类物种监测和种群密度估计(Eberhardt and Van Etten,1956;Bider,1968;Gannon     

A mathematical model of a crocodilian population using delay-differential equations

The crocodilia have multiple interesting characteristics that affect their population dynamics. They are among several reptile species which exhibit temperature-dependent sex determination (TSD) in which the temperature of egg incubation determines the sex of the hatchlings. Their life parameters, specifically birth and death rates, exhibit strong age-dependence. We develop delay-differential equation (DDE) models describing the evolution of a crocodilian population. In using the delay formulation, we are able to account for both the TSD and the age-dependence of the life parameters while maintaining some analytical tractability. In our single-delay model we also find an equilibrium point and prove its local asymptotic stability. We numerically solve the different models and investigate the effects of multiple delays on the age structure of the population as well as the sex ratio of the population. For all models we obtain very strong agreement with the age structure of crocodilian population data as reported in Smith and Webb (Aust. Wild. Res. 12, 541-554, 1985). We also obtain reasonable values for the sex ratio of the simulated population.     

Why are pitfall traps so rare in the natural world?

Prey capture by trapping is uncommon taxonomically, and generally requires highly evolved cognitive powers (humans) or specialist self-secreted materials (for example, spiders and caddisfly larvae). The most notable exception to this is the conical traps dug by antlion larvae. The relative uncommonness (taxonomically and ecologically) of such pitfall traps has been described as an unexplained mystery in recent publications. Here we suggest some potential routes that might lead to resolution to this mystery. We argue that although such pitfall traps have numerous benefits and are relatively cheap and easy to construct, they may suffer two significant disadvantages relative to, for example, spiders’ webs. First, pitfall traps may require a quite specialist microhabitat. Second, antlion pitfall traps may only work to retain all but the smallest prey if the antlion is present at the bottom of the pit. Thus, antlion may be more functionally tied to their trap than spiders and (since traps are much more visually conspicuous than their owners) this may make them vulnerable to predators and parasitoids that cue on the traps. Both these hypothesised drawbacks are speculative in the absence of a strong body of data and so we discuss how both potential costs could be explored empirically.