Differences In Dispersal Distances Research Articles

Tumbleweed Dispersal in Florida Sandhill Baptisia (Fabaceae)

MEHLMAN, D. W. (Department of Biological Science, Florida State University, Tallahassee, FL 32306). Tumbleweed dispersal in Florida sandhill Baptisia (Fabaceae). Bull. Torrey Bot. Club 120: 60-63. 1993.-Tumbleweed dispersal of Baptisia lanceolata (Walt.) Ell. and B. lecontei T.&G. was studied at a Florida sandhill site. The sandhill habitat is characterized by an open canopy of pines with a low ground cover of grasses, forbs, and shrubs. Plants tagged in the late fall were followed through the winter and early spring. The above-ground part of almost all plants examined broke off at the base and plants moved a maximum of 120 m from the growing site. Significant differences in dispersal distance were found between survey dates, and the mean distance moved increased throughout the period. Dispersed plants were concentrated in certain compass quadrants, consistent with wind-aided plant movement. Baptisia lanceolata plants that moved the farthest had fewer pods remaining on them. Wind-aided dispersal of the entire plant appears to be a viable method of long-distance dispersal in these two species.

Demography of an Increasing Population of Sparrowhawks

SUMMARY (1) The recolonization of an area in east-central England by sparrowhawks Accipiter nisus (L.) was studied after the local population had been eliminated, almost certainly by organochlorine pesticides. Over a 10-year period, nest numbers increased rapidly to begin with and then more slowly, with a mean rate of 21% per year. (2) Over the whole 10 years, the estimated annual survival of breeders was at least 76% for males and 74% for females, and mean productivity was 2*1 young per nest. Throughout, the breeding population contained a large proportion of first-year birds, with an overall figure of 35% of all male breeders and 25% of all female breeders. As the breeding population grew, young raised in the area tended to disperse ever greater distances from their natal sites. (3) Comparison of the increasing population with stable and decreasing populations in southern Scotland showed that differences in population trend were associated mainly with differences in the recruitment of new breeders (greatest in the increasing and lowest in the decreasing population) and in age of first breeding (earliest in the increasing and latest in the decreasing population). There were also differences in dispersal distances (shorter in the increasing population), and in the annual survival of breeders (greater in the increasing population). In contrast, differences in breeding success between areas were slight, and non-significant.

Natal Dispersal in the Nuthatch

Between 1970 and 1983, more than 1500 Nuthatch nestlings were banded in an area of about 400 km2. By regular trapping sessions at feeding sites and checking of roosting and breeding birds, 55 of them were recaptured within the study area (3.6%). Dispersal distances varied between 36 m and 11 km, with a median around 1 km. We found no difference in dispersal distance between males and females, nor between young from early and late broods. The absence of a sexual bias in dispersal is explained by the symmetry in territorial behaviour of the sexes. An analysis of movements after the first recapture showed no evidence for dispersal after the birds' first summer.

Pollen flow in Psiguria warscewiczii: a comparison of Heliconius butterflies and hummingbirds.

Pollen dispersal by male and female Heliconius butterflies and hermit hummingbirds was examined in a natural population of the tropical vine Psiguria warscewiczii. Fluorescent dyes were used to track flowers visited by individual pollinators. Mean distance of pollen dispersal was significantly higher by males than by female Heliconius. Butterflies dispersed pollen greater distances than did hummingbirds. There were no significant differences in dispersal distance among species of Heliconius. The number of flowers or plants to which dye was dispersed was greater for Heliconius than for hummingbirds.The home range behavior and site specificity exhibited by Heliconius, together with the preference by most Heliconius species in the study site for Psiguria led us to examine the relationship between the butterflies' home range and its daily foraging among Psiguria. A Heliconius mark-recapture program was conducted simultaneously with the dye program. This study showed that individual butterflies, for which extensive recaptures were made, visited an area of Psiguria plants on any one day that corresponded to the area in which those butterflies were caught or observed. The area over which a butterfly moved was termed its home range; within home ranges relative movement by butterflies was estimated as the mean distance between sequential captures. This estimate differed significantly among species of Heliconius; males of all species moving greater distances than females.

Adult Nomadism in Tengmalm's Owl Aegolius funereus

To test the hypotheses that Tengmalm's Owl is 'nomadic', we examined Swedish ring recoveries of adults and juveniles marked during the breeding season. There was no clear difference in dispersal distance between adults and juveniles. In two cases, adults nested a few 100 m from the sites where they bred during one and two preceding years, respectively. There was one clear case of adult nomadism: an owl captured on the nest breed two years later 510 km away. This may be the longest distance recorded between two breeding sites in the same bird.