Spatial distribution patterns and implications for conservation ofScrophularia takesimensis (Scrophulariaceae), an endangered endemic species on Ulleung Island, Korea

As part of an on-going effort to conserve endangered and endemicScrophularia takesimensis (Scrophulariaceae), we analyzed its spatial distribution patterns by applying an index of dispersion, plant-to-all-plant distances, and the varying quadrat size method. Three indices — Dispersion, Morisita, and Standardized Morisita — all revealed clumping with small aggregates, and distances between aggregates were more or less regular. The asymptote level occurred at a distance of 20 to 30 m; the distance showing 90% of cumulative frequency coincided with 20 to 21 m; 95%, 24 to 25 m; and 99%, 31 to 32 m. The 20 m× 20 m and 40 m×40 m quadrats contained 25 and 40 plants, respectively. We conclude that this number of individuals and size of area are the minimum required for the conservation of this species.     

Seasonal distribution and some features of the biology of spiny lumpfish <Emphasis Type="Italic">Eumicrotremus asperrimus</Emphasis> (Cyclopteridae,Scorpaeniformes) in the northwestern part of the Sea of Japan

According to data of 1981–2007, it was shown that the migration of spiny lumpfish Eumicrotremus asperrimus from wintering grounds to the coast begins in spring, with the onset of water warming. During summer and autumn, E. asperrinus feeds, concentrating in the bathymetric range of 100–300 m. With the start of winter water cooling, it migrates for wintering to depths larger than 500 m. Main aggregations of E. asperrimus were found off the coasts of Northern Primorye. Catches included specimens with a length of 3–16 cm; however, the overwhelming majority (95%) had a length of 5–10 cm, with the domination of two size groups: 6–7 and 9 cm. The spawning of E. asperrimus is apparently highly extended in time and occurs in the spring-summer period in shallow waters. Similarly to other representatives of the genus Eumicrotremus, E. asperrimus is a planktonphage with a narrow food specialization. Off the coasts of Primorye, in the summer period it feeds almost on one species—hyperiid Themisto japonica—with a value of diurnal diet averaging 6.7% of the body weight. According to an expert estimate, the biomass of E. asperrimus in the northwestern part of the Sea of Japan may comprise no less than 5000 t.     

Critical nuclear DNA size and distribution associated with S phase initiation

Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology and autoradiography grain patterns between middle G₁ and middle S phases: Our results show two distinct [³H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size (reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near the nuclear periphery.     

Bryophytes, lichens and phanerogams in an alvar grassland: relationships at different scales and contributions to plant community pattern

The relationship between bryophytes and lichens versus phanerogams has been investigated in three stands of a limestone grassland community, along three transects of 500 10 X 10 cm plots. Ordination axes resulting from Detrended Correspondence Analysis for bryophytes and lichens versus phanerogams were correlated using Spearman rank correlation coefficient. The effect of grain (sample plot) size on relationships between species along the gradient and on the correlation between the layers formed by bryophytes and lichens (cryptogams) and phanerogams, and with environmental variables has been as well examined. Values for light, moisture, pH and nitrogen have been derived from the vegetation itself with the help of Ellenberg indicator values. The relative position of species in the ordination space is more or less the same until grain size 3 (10 x 40 cm) for cryptogams and phanerogams and until grain size 2 (10 × 20 cm) for all-species together. Therefore, it is suggested that sample plot sizes of 10 × 10 cm to 10×20 cm are appropriate as units for field experiments testing interactions between cryptogams and phanerogams. The respective layers were weakly correlated and the correlation between them increased with increase in grain size. The correlation of DCA axis 1 from the ordination of cryptogams, phanerogams and all-species with the environmental factors was weak and similar in order of magnitude. Only the environmental variables which were strongly correlated with the DCA axis 1 increased in correlation at larger grain sizes. The ordinations of cryptogams, phanerogams and all-species were correlated along DCA axis 1 with pH in all investigated stands and at almost all grain sizes. Multi-species patches have been detected by pattern analysis (PASFRAN) on DCA sample scores from ordinations of cryptogams, phanerogams and combined matrices. Multi-species patterns with sizes between 20-240 cm. composed by bryophytes and lichens and by phanerogams have been found. Complex patterns formed by cryptogams and phanerogams together, which are different in size than those in the separate layers, suggest that bryophytes + lichens and phanerogams may interact with each other.     

Distribution and some features of biology of rock greenling <Emphasis Type="Italic">Hexagrammos lagocephalus</Emphasis> in Pacific waters off the northern Kuril Islands and southeastern Kamchatka

Based on materials of trawl studies performed from 1992 to 2002 off the Pacific coast of Kamchatka and the northern Kuril Islands in the framework of the integrated (VNIRO, KamchatNIRO, Sakh-NIRO) program on the study of fishery resources of the continental slope, data on the distribution and biology of rock greenling Hexagrammos lagocephalus were analyzed. It was elucidated that this species is extremely eurybathic; the range of its seasonal vertical migrations embraces depths of 1–2 m in summer, and in the spawning period and up to 665 m in winter. The spatial distribution has a mosaic pattern, maximum concentrations were recorded at the slope and shelf of the Shumshu Island and the southern extremity of Kamchatka. The size, weight, and sex composition, and the maturation and feeding of the rock greenling are considered. Maximum fish sizes in trawl catches are 58 cm and 2.63 kg; sex composition is characterized by the domination of females in all size groups (79%). The bulk of feeding consisted of Cephalopoda, small crustaceans—Amphipoda and Isopoda—as well as the eggs of fish and Gastropoda. With an increase in sizes, the greenling passes from feeding on small benthic organisms to larger movable forms.     

Structure and use of distance calls in wild bonobos (Pan paniscus)

We report the physical structure and use of a distance call (high-hoot) by wild bonobos (Pan paniscus).Although spectrographic analyses reveal high structural variability, the total sample can be subdivided according to the composition of units—the presence or absence of an initial segment—and the range of the lowest harmonic. Analyses of samples from male—female pairs,vocalizing simultaneously and in close proximity, reveal that both animals utter calls in more or less precise temporal alternation but with different spectral ranges. Whether these differences are gender-specific or related to other factors, such as age or the social relations between particular individuals, is not clear. We suggest that (a) individuals of the same party may coordinate their vocal activity on both the temporal and the spectral level and (b) high hootings stimulate emission of equal vocalizations by members of other parties and may increase cohesion among community members. Comparison of a restricted number of spectrograms from known individuals indicates that bonobos may be able to adjust spectral parameters of one type of distance calls (high- hoot) according to corresponding calls of conspecifics.     

Space use of common genets<Emphasis Type="Italic">Genetta genetta</Emphasis> in a Mediterranean habitat of northeastern Spain: differences between sexes and seasons

The seasonal home range size and spatial relationships of 16 adult genetsGenetta genetta Linnaeus, 1758 (6 males and 10 females) were estimated in a Mediterranean habitat of northeastern Spain. Genets minimum density was estimated as 0.98/km². Mean annual home range was 113.1 ha in males and of 72.0 ha in females. Males had larger home ranges than females in all seasons, but differences were only significant in winter. Home range size changed seasonally and showed a similar pattern in both sexes, with lower values in summer (males — 41.2 ha, females — 29.0 ha) and maximum ones in spring (males — 78.8 ha, females — 56.1 ha). Animals displayed spatial fidelity throughout the year. Core areas (MCP50) represented 27% and 19% of total home range size for males and females, respectively. Resting home ranges (based on locations of inactive animals) were 9 times lower than overall home range size. Individuals of the same sex overlapped less than individuals of different sexes, especially with regard to core areas, which showed almost no overlap. The results obtained suggest that (1) different factors are likely to affect the space use of genets, such as body mass, food abundance and reproductive cycle; (2) genets use space in a heterogeneous way, with areas of greater activity than others within their home range; (3) there was intrasexual segregation with regard to space use.     

Population Decline of Loggerhead Turtles: Two Potential Scenarios for Fethiye Beach,Turkey

Based on nesting data over a 12-year period (1993–2004), this study points to a negative population trend of the loggerhead turtle population at Fethiye beach, Turkey. The number of nests fluctuated from a maximum of 186 in 1995 to a minimum of 58 in 2004. Successively smaller peaks at 3-year intervals were followed by successively smaller troughs. Two analyses—one representing a dampened oscillation, the other retaining the period and the amplitudes of the nesting cycles—predict that nest number will drop to about 40–50 by 2015, i.e. to about 22–27% of its highest value. This drop at Fethiye does not correspond with a visible increase at neighboring beaches, leading to the interpretation that the number of nesting turtles here is declining. Moreover, the carapace size of emerging adult females is apparently decreasing, as are clutch sizes. Such a potential negative trend at a key Turkish nesting beach is cause for concern, an incentive for continued study, and a call for more coordinated and effective conservation programs in this region of the Mediterranean.     

Bomb <Superscript>14</Superscript>C enrichment indicates decadal C pool in deep soil?

Studies of changes in soil organic carbon (SOC) stocks normally limit their focus to the upper 20–30 cm of soil, yet 0–20 cm SOC stocks are only ∼40% of 0–1 m SOC. Accounting for only the upper 20–30 cm of SOC has been justifiable assuming that deeper SOC is unreactive since it displays ¹⁴C-derived mean residence times of hundreds or thousands of years. The dramatic increase in the ¹⁴C content of the atmosphere resulting from thermonuclear testing circa 1963 allows the unreactivity of deep SOC to be tested by examining whether deep soils show evidence of ‘bomb-¹⁴C’ incorporation. At depths of 40–100 cm, a well-studied New Zealand soil under stable pastoral management displays progressive enrichment of over 200‰ across samplings in 1959, 1974 and 2002, indicating substantial incorporation of bomb ¹⁴C. This pattern of deep ¹⁴C enrichment—previously observed in 2 well-drained California grassland soils—leads to the hypothesis that roots and/or dissolved organic C transport contribute to a decadally-reactive SOC pool comprising ∼10–40% of SOC below 50 cm. Deep reactive SOC may be important in the global C cycle because it can react to land-use or vegetation change and may respond to different processes than the reactive SOC in the upper 20–30 cm of soil.     

Demographic Structure of Zanzibar Red Colobus Populations in Unprotected Coral Rag and Mangrove Forests

More than half of the global population of the endangered Zanzibar red colobus (Procolobus kirkii) live outside the single major protected area on Zanzibar Island. We present data on the 2 largest, discrete subpopulations living in unprotected areas at extremes of the species’ range. We compare the size and structure of 11 groups, specifically 6 core groups inhabiting interior, mature forest with 5 peripheral groups living in disturbed/degraded edge habitats. Groups living in southern mangrove forest—a species-poor but more productive and less seasonal habitat than coral rag thicket—had larger group sizes and more heterogeneous age structure, were more stable, and had higher rates of infant survival than did groups in northern coral rag. Group size ranged from 5.5 ± 1.6 SD (the smallest reported for this species) in edge coral rag to 31.2 + 1.9 SD in core mangroves. Edge groups were significantly smaller than core groups in northern coral rag while in the south, where all groups had access to mangroves, we found no significant difference in mean group size between edge and core areas. Groups using mangroves exhibited frequent social play, an indicator of habitat quality, and had a higher ratio of births per female per year. We suggest that mangroves are an important refuge and possibly source habitat for Zanzibar red colobus. We urge the conservation of mangrove and remaining coral rag in the unprotected areas described here in an effort to sustain this endemic species throughout its range.     

Resource patch size and flexible foraging in white-faced capuchins (Cebus capucinus)

White-faced capuchins (Cebus capucinus)on Barro Colorado Island, Panama, have a flexible foraging strategy. Typically, foraging party size is small and individuals feed dispersed from one another. When seasonal fruiting of large volume trees occurs, the majority of the group forages simultaneously. As C. capucinusdo not display a rigorous dominance structure and there are few indications that individuals or coalitions monopolize food patches,individuals are expected to display scramble strategies instead of high frequencies of contest competition. I recorded foraging party size (simultaneous foragers), the total number of animals to feed successively, and the diameter at breast height (DBH) of fruit trees used in two habituated troops. Individuals in each group spent a substantial amount of time — 65 and 48% of foraging time for each group — foraging in party sizes of one. Monkeys predominantly foraged alone in small trees (0- to 20- cm DBH), successively in medium trees (21- to 60- cm DBH), and simultaneously in large trees (>61- cm DBH). They used small trees more frequently than all other tree classes. In medium-sized trees, although fruit was plentiful, space was limited. In these trees Cebusforaged successively. In large-volume trees, space and fruit were abundant and several individuals fed together. As the DBH of fruiting trees increased, the average foraging party size increased exponentially. Cebus capucinusat Barro Colorado Island modify their foraging party size to adapt to the seasonal patterns of fruit production.     

The taxonomy of neolithic man and its phylogenetic relationship to later paleolithic man and modern man in China

In approaching the taxonomy of Neolithic Man and its phylogenetic relationship to Later Paleolithic Man and Modern Man in China, the statistical methods used here are Penrose's shape distance and PCA (Principal Component Analysis). The scattergram based on principal component scores, combines the dendrogram based on Penrose's shape distance, and takes the male taxonomy into main consideration, but takes the female taxonomy — as a reference only because the differentiations in physical characteristics among male populations generally are rather larger than those among the female populations. Thus according to this scattergram, Neolithic Man in China can be divided into two large groups: the Northern China group, and the Southern China group. The theory is that in Hengzhen there exist some blood mixtures between the Southern China Group and the Northern China Group (especially the third subgroup) of Neolithic Man. Later Paleolithic Man of China — Liujiang and Upper-Cave Man — can also clearly distinguished from the rest of Neolithic Man in China in the scattergram, and can be considered as two different local types of Later Paleolithic Man. So-called “Negro-Australoid” racial traits can themselves be doubtlessly traced back to Later Paleolithic Man of China — Liujiang and Upper-cave Man. These traits are the intrinsic characteristics of Neolithic Man in China and only then is there slight difference in the extent of the manifestation of these traits in the population.     

Feeding interactions and diet of carnivorous fishes in the Shelikhov Bay of the Sea of Okhotsk

The food spectra, trophic statuses, and feeding interrelations of three most abundant benthic carnivorous fish species inhabiting the Shelikhov Bay—the Pacific cod Gadus macrocephalus, the great sculpin Myoxocephalus polyacanthocephalus, and the Okhotsk sculpin M. ochotensis—are considered based on materials collected during the complex survey of the RV Professor Kaganovsky of the TINRO-Center, in September 2004. It was found that these species were facultative predators with wide food spectra. The significance of prey objects in the diet of the Okhotsk sculpin was as follows: crustaceans, fish, and mollusks. Great sculpin and Pacific cod preyed mostly on fish, then on crustaceans, and mollusks. Pacific cod ate equal proportions of fish and decapods. All the species had age-related variability of diet. The potential competition of great sculpin and Okhotsk sculpin for food was mitigated by the difference in the depths of their ranges, as well as by morphological (body size) and behavioral peculiarities in the areas where their habitats overlapped, and in microecosystems. The most probable competition was among Pacific cod 30–60 cm long and Okhotsk sculpin 20–50 cm in length, as well as among cod and great sculpins of all sizes.     

On the recombinational origin of protein-sequence-subunit structure

Since 1929 the concept that proteins are built from subunits of certain standard size (Svedberg 1929) has been revisited several times, each time with a new demonstration that, indeed, there are certain preferred protein sizes. According to recent estimates the overrepresented sizes are close to multiples of 125 amino acid (aa) residues for eukaryotes and 150 residues for prokaryotes. To explain these preferences, a hypothesis is suggested, and quantitatively developed, on the recombinational nature of this regularity. The protein-coding sequences are assumed to evolve at some early stage via recombinational events—insertions of DNA circles of a certain optimal size. The contour lengths of the protein-coding DNA circles had to be simultaneously divisible by three and, to minimize torsional constraint, by the DNA helical repeat. With these two conditions satisfied, the calculated contour lengths of the DNA circles, 250–500 base pairs (bp), turn out to correspond well to known optimal DNA circularization sizes and to the predicted range of the protein sequence subunit sizes: 80–170 as residues, which covers experimentally observed values. The subunit size is found to be strongly influenced by the helical repeat of DNA. The sizes 125 and 150 as are derived when the corresponding helical repeats of DNA are set within fractions of promilles from the 10.54 by/turn value. This fits to the experimentally estimated mean for natural mixed DNA sequences, 10.53–10.57 by/turn. The suggested recombinational mechanism thus not only gives a qualitative explanation for the observed underlying order in the protein sequences but also quantitatively links the observed protein sequence sizes with the optimal DNA circularization size and with the helical repeat of DNA. It also offers a versatile molecular model of early protein evolution by fusion and insertion of preexisting proteins of standard subunit sizes.     

Effects of patch size on colonisation in estuaries: revisiting the species-area relationship

The effects of patch size on the colonisation and succession of intertidal invertebrates and algae were investigated in an estuary near Sydney, New South Wales, Australia. The specific aim was to test explicitly for the presence of a species-area relationship, and examine whether this could be explained by the random placement hypothesis (i.e. that the number of species per unit area was the same on patches of different sizes). In addition, I tested the extent to which differences in numbers of species reflected differences in the composition of assemblages. Wooden panels of three different sizes (10 × 10 cm, 20 × 20 cm and 40 × 40 cm) were placed in the field on intertidal oyster leases in each of two different experimental trials: spring (October 1994) and summer (January 1995). Independent replicate measures of the number of colonising species on panels were obtained after different periods of time, up to 25 months. I also obtained measures of abundance of individual species and composition of assemblages on panels of different sizes. This allowed specific tests of the hypothesis that the size of the patch being colonised is important in structuring these assemblages. The strength of the species-area relationship increased through time on panels submersed in October, but the trend was reversed for panels submersed in January. There was a significant interaction between factors of patch size and time of submersion for multivariate measures of differences in composition among replicates. The random placement hypothesis was supported in certain situations, but not in others. When rejected, it was for different reasons on panels submersed in the two different trials. Panels initiated in October tended to have proportionally greater numbers of species per unit area on larger panels, while the panels initiated in January tended to have more species per unit area on smaller panels. There was an identifiable relationship between differences in numbers of species and differences in species composition for panels submersed in October. This was not true, however, for panels submersed in January, where the species-area relationship did not hold after longer periods. The succession of organisms through time was, overall, more important in structuring the assemblages than was the size of the patch being colonised. The species-area relationship should not necessarily be regarded as a truism – it did not always hold in this system. The initial timing of experiments with respect to recruitment and succession influenced the results. Received: 16 March 1998 / Accepted: 5 October 1998     

Being Barbie: the size of one's own body determines the perceived size of the world

A classical question in philosophy and psychology is if the sense of one's body influences how one visually perceives the world. Several theoreticians have suggested that our own body serves as a fundamental reference in visual perception of sizes and distances, although compelling experimental evidence for this hypothesis is lacking. In contrast, modern textbooks typically explain the perception of object size and distance by the combination of information from different visual cues. Here, we describe full body illusions in which subjects experience the ownership of a doll's body (80 cm or 30 cm) and a giant's body (400 cm) and use these as tools to demonstrate that the size of one's sensed own body directly influences the perception of object size and distance. These effects were quantified in ten separate experiments with complementary verbal, questionnaire, manual, walking, and physiological measures. When participants experienced the tiny body as their own, they perceived objects to be larger and farther away, and when they experienced the large-body illusion, they perceived objects to be smaller and nearer. Importantly, despite identical retinal input, this "body size effect" was greater when the participants experienced a sense of ownership of the artificial bodies compared to a control condition in which ownership was disrupted. These findings are fundamentally important as they suggest a causal relationship between the representations of body space and external space. Thus, our own body size affects how we perceive the world.     

The influence of aggregate size and drannage potential on germination of barley seeds in flooded soil

Emergence and growth of barley was severely decreased by short periods (less than 24 hours) of pre-emergence waterlogging at 20°C. The extent of damage depended on a combination of duration of waterlogging, soil water potential and aggregate size. Potentials of less than—4kPa prevented loss of plants developing in aggregates of less than 2 mm diameter after a transitory period of waterlogging although some shoot and root damage occurred. By comparison seeds growing in soil consisting of aggregates greater than 2 mm in diameter were not damaged by transitory waterlogging even when drainage only occurred at−0.8kPa. The severity of damage increased with the period of waterlogging. A criterion obtained as the product of mean size grade and water potential gave a single value (−4NM⁻¹) below which emergence was satisfactory. Waterlogging halfway through germination gave more severe damage than near sowing date or near emergence.     

Neuronal nitric oxide synthase immunopositive neurons in cat vestibular complex: a light and electron microscopic study

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase–antiperoxidase–diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups—small (with diameter less than 15 μm), medium-sized (with diameter from 15 to 30 μm), large type I (with diameter from 30 to 40 μm), and large type II (with diameter greater than 40 μm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups—small (with diameter less than 15 μm), medium-sized (with diameter from 15 to 30 μm), and large (with diameter greater than 30 μm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.     

The scale-dependent importance of habitat factors and dispersal limitation in structuring Great Lakes shoreline plant communities

Niche-based and neutral models of community structure posit distinct mechanisms underlying patterns in community structure; correlation between species’ distributions and habitat factors points to niche assembly while spatial pattern independent of habitat suggests neutral assembly via dispersal limitation. The challenge is to disentangle the relative contributions when both processes are operating, and to determine the scales at which each is important. We sampled shoreline plant communities on an island in Lake Michigan, varying the extent and the grain of sampling, and used both distance-based correlation methods and variance partitioning to quantify the proportion of the variation in plant species composition that was attributable to habitat factors and to spatial configuration independent of habitat. Our results were highly scale dependent. We found no distance decay of plant community similarity at the island scale (1−33 km). All of the explained variation (32%) in species composition among samples at this scale was attributed to habitat factors. However, at a site intensively sampled at a smaller scale (5−1,200 m), similarity of species composition did decay with distance. Using a coarse sampling grain (transects), habitat factors explained 40% of the variation, but the purely spatial component explained a comparable 22%. Analyzing plots within transects revealed variation in species composition that was still jointly determined by habitat and spatial factors (18 and 11% of the variance, respectively). For both grain sizes, most of the habitat component was spatially structured, reflecting an abrupt alongshore transition from sandy dunes to cobble beach. Space per se explained more variation in species composition at a second site where the habitat transition was more gradual; here, habitat acted as a less selective filter, allowing the signal of dispersal limitation to be detected more readily. We conclude that both adaptation to specific habitat factors and habitat-independent spatial position indicative of dispersal limitation determine plant species composition in this system. Our results support the prediction that dispersal limitation—a potentially, but not necessarily, neutral driver—is relatively more important at smaller scales.     

Prey size selection and distance estimation in foraging adult dragonflies

To determine whether perching dragonflies visually assess the distance to potential prey items, we presented artificial prey, glass beads suspended from fine wires, to perching dragonflies in the field. We videotaped the responses of freely foraging dragonflies (Libellula luctuosa and Sympetrum vicinum—Odonata, suborder Anisoptera) to beads ranging from 0.5 mm to 8 mm in diameter, recording whether or not the dragonflies took off after the beads, and if so, at what distance. Our results indicated that dragonflies were highly selective for bead size. Furthermore, the smaller Sympetrum preferred beads of smaller size and the larger Libellula preferred larger beads. Each species rejected beads as large or larger than their heads, even when the beads subtended the same visual angles as the smaller, attractive beads. Since bead size cannot be determined without reference to distance, we conclude that dragonflies are able to estimate the distance to potential prey items. The range over which they estimate distance is about 1 m for the larger Libellula and 70 cm for the smaller Sympetrum. The mechanism of distance estimation is unknown, but it probably includes both stereopsis and the motion parallax produced by head movements.