Average Straight-line Distance Research Articles

Spatial Ecology of Eastern Copperheads in Fragmented and Unfragmented Habitats

We quantified and compared movement and microhabitat use of Eastern Copperheads (Agkistrodon contortrix) in fragmented and unfragmented habitats to determine the effects of fragmentation on movement and habitat use. We used thread bobbins to track movement and calculate straight-line distance (SLD) moved, total distance (TDM) moved, and occupied area for individual snakes. Microhabitat use was characterized by quantifying number of trees, woody vegetation stems, herbaceous vegetation stems, percent grass coverage, and percent canopy coverage at each location a snake was observed, and at an equal number of randomly selected locations. Neither SLD nor TDM differed between fragmented and unfragmented habitats. Overall average SLD moved was 24.1 m and TDM was 39.6 m over 48 h. Although SLD and TDM did not differ between sites, mean occupied area ± standard error was significantly greater at the unfragmented (2,310.9 ± 272.7 m) compared with the fragmented site (1,025.9 ± 314.9 m). Microhabitat features were similar between the fragmented and unfragmented sites, and herbaceous vegetation and high canopy cover were associated with locations where snakes were observed at both sites. It is likely that Eastern Copperheads can persist in a variety of habitats in the southeastern United States because their preferred microhabitat features are widely distributed and common in both fragmented and unfragmented environments, demonstrating that they retain characteristics of a habitat specialist within heterogeneous environments suitable for generalists.

Cyprus wheatears Oenanthe cypriaca likely reach sub-Saharan African wintering grounds in a single migratory flight

Long-distance migratory flights with multiple stop-overs, multiple wintering sites, and small-scale connectivity in Afro-Palearctic migrants are likely to increase their vulnerability to environmental change and lead to declining populations. Here we present the migration tracks and wintering locations of the first six Cyprus Wheatears to be tracked with geolocators: a species with high survival and a stable population. We therefore predicted a non-stop flight from Cyprus to sub-Saharan wintering grounds, a single wintering area for each individual and a wide spread of wintering locations representing low migratory connectivity at the population level. The sub-Saharan wintering grounds in South Sudan, Sudan and Ethiopia were likely reached by a single flight of an average straight-line distance of 2,538 km in ca. 60 hours, with an average minimum speed of 43.1 km/h. The high speed of migration probably ruled out stop-overs greater than a few hours. Cyprus Wheatears migrated from Cyprus in mid-late October and most probably remained at a single location throughout winter; three out of five birds with available data may have used a second site <100 km away during February; all returned between the 7 – 22nd March when accurate geolocation data are not possible due to the equinox. Wintering locations were spread over at least 950 km. There were no tag effects on survival. Cyprus Wheatears showed a migratory strategy in accordance with their observed high survival rate and demonstrated a routine flight range that allows much of the Mediterranean and the Sahara to be crossed in a rapid two and a half-day flight. This article is protected by copyright. All rights reserved.

Short-length routes in low-cost networks via Poisson line patterns

In designing a network to link n points in a square of area n, we might be guided by the following two desiderata. First, the total network length should not be much greater than the length of the shortest network connecting all points. Second, the average route length (taken over source-destination pairs) should not be much greater than the average straight-line distance. How small can we make these two excesses? Speaking loosely, for a nondegenerate configuration, the total network length must be at least of order n and the average straight-line distance must be at least of order n1/2, so it seems implausible that a single network might exist in which the excess over the first minimum is o(n) and the excess over the second minimum is o(n1/2). But in fact we can do better: for an arbitrary configuration, we can construct a network where the first excess is o(n) and the second excess is almost as small as O(log n). The construction is conceptually simple and uses stochastic methods: over the minimum-length connected network (Steiner tree) superimpose a sparse stationary and isotropic Poisson line process. Together with a few additions (required for technical reasons), the mean values of the excess for the resulting random network satisfy the above asymptotics; hence, a standard application of the probabilistic method guarantees the existence of deterministic networks as required (speaking constructively, such networks can be constructed using simple rejection sampling). The key ingredient is a new result about the Poisson line process. Consider two points a distance r apart, and delete from the line process all lines which separate these two points. The resulting pattern of lines partitions the plane into cells; the cell containing the two points has mean boundary length approximately equal to 2r + constant(log r). Turning to lower bounds, consider a sequence of networks in satisfying a weak equidistribution assumption. We show that if the first excess is O(n) then the second excess cannot be

Short-length routes in low-cost networks via Poisson line patterns

In designing a network to link n points in a square of area n, we might be guided by the following two desiderata. First, the total network length should not be much greater than the length of the shortest network connecting all points. Second, the average route length (taken over source-destination pairs) should not be much greater than the average straight-line distance. How small can we make these two excesses? Speaking loosely, for a nondegenerate configuration, the total network length must be at least of order n and the average straight-line distance must be at least of order n 1/2, so it seems implausible that a single network might exist in which the excess over the first minimum is o(n) and the excess over the second minimum is o(n 1/2). But in fact we can do better: for an arbitrary configuration, we can construct a network where the first excess is o(n) and the second excess is almost as small as O(log n). The construction is conceptually simple and uses stochastic methods: over the minimum-length connected network (Steiner tree) superimpose a sparse stationary and isotropic Poisson line process. Together with a few additions (required for technical reasons), the mean values of the excess for the resulting random network satisfy the above asymptotics; hence, a standard application of the probabilistic method guarantees the existence of deterministic networks as required (speaking constructively, such networks can be constructed using simple rejection sampling). The key ingredient is a new result about the Poisson line process. Consider two points a distance r apart, and delete from the line process all lines which separate these two points. The resulting pattern of lines partitions the plane into cells; the cell containing the two points has mean boundary length approximately equal to 2r + constant(log r). Turning to lower bounds, consider a sequence of networks in satisfying a weak equidistribution assumption. We show that if the first excess is O(n) then the second excess cannot be

TERRESTRIAL HABITAT USE BY NESTING PAINTED TURTLES IN LANDSCAPES WITH DIFFERENT LEVELS OF FRAGMENTATION

As part of a comprehensive study of the effects of landscape change on the demography of aquatic turtles, we investigated the use of upland habitats by adult female painted turtles (Chrysemys picta) during the nesting season. We intentionally selected three ponds that were surrounded by a range of land uses and development (e.g., road density ranged from 0.9 to 7.3 km/km2). Terrestrial locations of transmitter-equipped turtles (n = 8) and unmarked females that were incidentally encountered (n = 10) were recorded to: i) determine the distance traveled to nesting habitat, ii) estimate the frequency that female turtles crossed roads to reach nesting habitat, and iii) examine how the abundance of potential nesting habitat affected distance traveled. Average straight-line distance from shoreline to the site a female turtle was encountered ranged from 54 to 115 m for the three ponds. We estimated that marked turtles made five road crossings and two turtles were killed by vehicles. Distance traveled was negatively correlated with the abundance of nesting habitat near a pond. Although adult females are probably less vulnerable when nesting occurs near pond shores, nests created near pond edges may be more vulnerable to predation. As a result, providing additional nesting habitat away from roads and other potential sources of mortality may enhance recruitment among local turtle populations.

Associations between incisor and mandibular condylar movements during maximum mouth opening in humans

This study evaluated the common clinical assumption that condylar translation and mouth opening at the incisor are closely related. The sample studied comprised 27 adult females (23–35 years), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements (straight-line distances and curvilinear pathways) were recorded in three dimensions (3D) for 20 s with an optoelectric (Optotrak®) jaw-tracking system while each participant performed multiple maximum opening cycles. Masticatory analysis and multilevel statistical programs computed the 3D movements of the incisors and condylar hinge axis during opening and closing. The incisor point moved an average straight-line distance of 46.6 mm during opening and 45.9 mm during closing; the lengths of the opening and closing curvilinear pathways were 48.6 and 47.7 mm, respectively. The condyles moved average straight-line distances of 11.9 and 12.2 mm during opening and closing, respectively. The condyles’ curvilinear pathways during opening and closing were 14 and 14.6 mm, respectively. Ranges of condylar movement varied widely between individuals. The straight-line distances and curvilinear pathways were highly correlated for the incisors ( R=0.98) and the condyles ( R=0.98). Neither the straight-line distances nor curvilinear pathways of the incisors were correlated with those of the condyles. Incisor straight-line distances and curvilinear pathways were moderately correlated with mandibular rotation ( R between subjects=0.82 and R between repeats=0.88). During repeated openings, both condylar and incisor excursions increased, but during repeated closings only incisor excursions increased. It is concluded that (1) maximum incisor opening does not provide reliable information about condylar translation and its use as a diagnostic indicator of condylar movement should be limited, (2) healthy individuals may perform normal opening with highly variable amounts of condylar translation, (3) the straight-line distances of the incisor and condyles provide adequate information about the length of the curvilinear pathway, and (4) variation in maximum incisor opening is largely explained by variation in the amount of mandibular rotation.

Aspects of the ranging pattern in a group of wild woolly monkeys (Lagothrix lagothricha).

A group of woolly monkeys (Lagothrix lagothricha), studied for 1,800 hr from June 1984 until September 1987 in the eastern Colombian Amazon, used a home range of about 760 ha, 90% of which overlapped the ranges of three other groups. Home range use varied throughout the year, correlating in part with variations in fruit production. The home range exhibited a nonexclusive "core area" in the floristically most diverse part of the home range, although the majority of the home range was entered at a much lower frequency. Within the study area woolly monkeys occurred at a density of 5.5 individuals/km2. The average day range was 2,880 m, and the average straight line distance between sleeping sites was 896 m. Day ranges differed significantly across months, but the only significant correlation tested was a positive relation with time spent "moving" in the activity budget. Comparisons with three other Amazonian sites where woolly monkeys have been studied reveal considerable variation. Soil fertility, plant community differences, and other factors seem to influence ranging patterns. © 1996 Wiley-Liss, Inc.

Summer Movements of Female Moose and Dispersal of Their Offspring

Fifty-seven radio-equipped moose (Alces alces) in central Sweden were located during the 3 summers of 1980-83. Forty-two were cows (≤2 years old) and 15 were calves (5 males and 10 females) when captured. Aerial tracking was conducted ≤1 time/week. No significant differences in average size of summer home ranges were found between age classes. All cows returned to the same summer range each spring. Consecutive summer home ranges overlapped from 1 to 100%. Ten of 14 radio-equipped calves accompanied their cow to summer ranges. The 1st indications of separation between cow and offspring were recorded from 7 to 29 May. The average straight line distance between cow and offspring successively increased from separation to mid-June when it became relatively constant (1.5-2.0 km). One of 10 calves that completed the migration together with the cow abandoned its mother's home range completely. Adult female offspring continued to reside near their yearling home range during consecutive summers.

Movements of Tagged American Lobsters, Homarus americanus, off Southwestern Nova Scotia

A total of 4304 American lobsters (Homarus americanus) were tagged and released in inshore areas off southwestern Nova Scotia and on northwest Browns Bank during June–August 1975. Of the 424 lobsters recaptured within 5.4 yr of release, 385 had known recapture locations. For all release areas the average straight-line distance traveled by mature ([Formula: see text]carapace length) lobsters (15.6 km) was significantly greater than for immature (59–94 mm carapace length) lobsters (4.7 km). Most (69.3%) of the immature lobsters (N = 212) were recaptured less than 18.5 km (10 naut mi) from the release sites; for mature lobsters (N = 173) this percentage was 40.5%. Previous tagging studies off southwestern Nova Scotia revealed little evidence of long-distance movement; our study, however, shows that mature lobsters can move long distances. Many (19.7%) of the mature lobsters were recaptured more than 92.6 km (50 naut mi) from the release sites. The overall direction of travel was south, in both an east and west direction, with many lobsters moving greater than 50 km from coastal Nova Scotia and Browns Bank into the Gulf of Maine and to the slopes of the continental shelf. Thirteen lobsters moved from Browns Bank to inshore areas of southwestern Nova Scotia. The evidence of the long-distance interchange of a portion of the mature adults between southwestern Nova Scotia and the adjoining continental shelf suggests that lobsters in these areas could belong to a single stock.

Denning Habits of Striped Skunks (Mephitis mephitis)

Thirty-six striped skunks were located in the field a total of 1627 times. There was a general shift from underground, upland dens in winter to aboveground, lowland dens in summer. Significant intraspecific contact occurred through concurrent and sequential use of underground dens and hollow logs. Den-sharing occurred only between the 3rd week in October and the 1st week in April. Both males and females changed den locations frequently. The average straight line distance between successive den sites was 0.48 km.

Biology of Striped Skunks on a Southwestern Lake Erie Marsh

Striped skunks were studied on and near a 2083-acre marsh in northwestern Ohio in 1967 and 1968. The breeding season ranged from 12 February to 25 March, and the young were born from mid-April to mid-May. Most young skunks became self-sufficient in midAugust. The adult sex ratio averaged 0.8 male per female. Seventy-one per cent of the skunks examined were under 1 year old. Daily activity usually began within 60 min after sunset. Adult males and pregnant females were difficult to capture in the late spring and summer. Decreasing barometric pressure was significantly related to skunk captures. The average straight line distance between capture locations was 0.5 mile for adult males and females and 0.2 and 0.4 miles for juvenile males and females, respectively. Home ranges varied from 31 to 114 acres. The density of skunks in late summer was 12 per square mile. Skunks temporarily used the numerous dens on the dikes. Most of the 93 blue-winged teal and mallard nests observed were destroyed by predators, but skunks destroyed only 13 %. Waterfowl nesting areas surrounded by deep channels or over 0.5 mile from areas frequented by skunks were relatively safe from skunk predation.

Movements, Growth and Survival of Marked and Tagged Lobsters Liberated in Egmont Bay, Prince Edward Island

The average straight line distance between release and recapture points of 253 tagged lobsters free 10 to 12 months was 7.3 nautical miles (13.5 km). Carapace-length growth increments per moult among 870 punch-marked lobsters recovered from the fishing grounds were independent of size and averaged 0.47 inches (11.9 mm) for males and 0.42 inches (10.7 mm) for females. Weight increments per moult varied from 4.0 to 7.5 ounces (113–213 g) for males and from 3.3 to 5.4 ounces (94–153 g) for females. Of the males, 17.8% moulted twice; of the females, 7.4%. Survival over a 10-month period was estimated to be 76.4%.