Differences In Dispersal Distances Research Articles

Spatial and temporal variation in the distribution of burrowing mayfly nymphs (Ephemeroptera: Hexagenia limbata and H. rigida) in western Lake Erie

In the early 1990s, burrowing mayfly species reappeared in sediments of the western basin of Lake Erie after an absence of over 30years due to episodic hypoxia at the sediment–water interface. Long-term monitoring of adult mayflies at shoreline areas had revealed that Hexagenia rigida was more abundant than Hexagenia limbata during the initial recolonization period, but was gradually replaced by H. limbata. We hypothesized that this shift in dominance would be confirmed by the distribution and abundance of nymphs. We identified nymphs collected each spring throughout western Lake Erie from 1997 to 2004. The relative abundances of H. rigida and H. limbata nymphs exhibited the same temporal sequence as adults. Furthermore, the number of sites in the western basin in which H. rigida occurred decreased as the occurrence frequency of H. limbata increased. H. limbata were dominant in the basin by 2004. Hexagenia limbata nymphs persisted in the center-most part of the basin, whereas H. rigida did not, possibly due to differences in tolerance to hypoxia. There were no significant differences in body size between the two populations. Differences in dispersal distance from source populations and the timing and success of egg hatching likely accounted for the initial colonizing success of H. rigida, but the differential ability of H. limbata eggs to overwinter in sediments and possible tolerance of nymphs to hypoxia has possibly led to its current dominance in the western basin.

Correlates and Fitness Consequences of Natal Dispersal in Swainson's Hawks

Natal dispersal is an important, yet often poorly studied, process in population ecology. Natal dispersal can affect population structure and individual fitness. We examined correlates of natal dispersal distances of a population of Swainson's Hawk (Buteo swainsoni) in northern California that has been monitored from 1979 to 2010. We examined the effects of sex, number of offspring fledged, population density, primary productivity around a nest site, and annual trends on dispersal from the natal site to the breeding site of individuals recruited into the breeding population. Female Swainson's Hawks dispersed farther than males. Natal dispersal was negatively correlated with primary productivity and was positively correlated with population density around the nest site. We found no correlation between natal dispersal distance and lifetime reproductive success of those individuals recruited into the breeding population, indicating no fitness costs of increased dispersal. We examined the potential genetic contributions to dispersal distance by examining differences in dispersal distance between full siblings. We found that the dispersal difference between siblings was significantly more similar than would be expected by chance. However, we detected no relationships between paternal or maternal natal dispersal distances and natal dispersal of offspring, although sample sizes were limited. We conclude that observed similarities in siblings' natal dispersal distance were likely a result of similarities in unmeasured environmental variables rather than of a genetic mechanism of natal dispersal. Perinatal conditions seemed to have significant effects on distances offspring dispersed, but increased natal dispersal had no apparent consequences on fitness.

Melanin-based coloration predicts natal dispersal in the barn owl, Tyto alba

Searching for a suitable breeding site is an important decision in the life of most animals. The decisions where to settle and how far to travel before doing so depend on many factors. Individual differences in dispersal distance could result from different strategies (e.g. specialists versus generalists), which might result in similar reproductive success in different habitats, or different competitive abilities to acquire a territory close to the natal site. The barn owl is polymorphic in melanic coloration, which is associated with many physiological and behavioural traits such as habitat choice, stress response and docility, raising the possibility that the coloration is also related to dispersal. We studied natal dispersal (from rearing site to site of first breeding attempt) and breeding dispersal (from one breeding site to the next) in barn owls using a long-term data set. Darker reddish individuals moved further than paler individuals during natal dispersal, but not during breeding dispersal. A cross-fostering experiment showed that the colour of the biological and foster parents had no influence on dispersal distance. The distance dispersed by parents and same-sex offspring was correlated, whereas natal and breeding dispersal were not repeatable within individuals, indicating that they are two different processes. Given that the distance travelled in natal dispersal appears to be heritable, the underlying genes might be coupled to those related to coloration. We discuss hypotheses to explain the potential adaptive function of the link between coloration and natal dispersal. ► We studied natal and breeding dispersal distances in barn owls. ► Natal dispersal differs between individuals of different colour. ► Natal dispersal is correlated between parent and offspring. ► Genes related to coloration might be related to dispersal.

Pollen productivity estimates strongly depend on assumed pollen dispersal

Past plant abundance may be reconstructed from pollen data if dispersal distances of pollen and pollen productivities of each taxon are known. Using surface sediment samples from small and medium sized, closed and near circular lakes from lowland Central Europe, we tested the validity of three pollen dispersal models by comparing empirical pollen data from each lake with simulated pollen data derived from applying various pollen dispersal models to vegetation data from rings situated up to 100 km from each site. Pollen assemblages simulated with a Lagrangian stochastic (LS) model best fit real pollen assemblages, simulations with the commonly used Prentice model on pollen dispersal underestimated the amount of pollen arriving from distances larger than 10 km and overestimated the differences in dispersal distances between lighter ( Pinus) and heavier ( Fagus, Picea) pollen grains. The LS model appeared to provide more appropriate simulations. Pollen productivity estimates (PPEs) calculated for the data set showed that the choice of the dispersal model has great impact on the results. If derived with the Prentice model, PPEs for Fagus and Picea are three times higher than with the LS model. Studies on pollen productivities thus need to consider the apparent limitations of the Prentice model. We suggest an alternative approach, which uses simulations instead of the extended R-value model, to calculate PPEs. The approach is flexible in the use of dispersal functions and produced consistent results for two independent data sets from small and medium sized lakes.

Dispersal, Band Encounters, and Causes of Death in a Reintroduced and Rapidly Growing Population of Peregrine Falcons

Abstract Dispersal is a key parameter for understanding demography and is consequently critical to conservation management. Peregrine Falcons (Falco peregrinus) in eastern North America exemplify a population that collapsed to extirpation and, subsequent to reintroduction, experienced a rapid, dispersal-based expansion back into its former range. To understand how dispersal and its correlates may be impacting falcon demography and encounter rates, we looked for (a) patterns of sex- and site-based differences in the dispersal movements of Peregrine Falcons from Pennsylvania, U.S.A.; (b) trends in density dependence in dispersal distances; (c) linkages between natal- and breeding-site characteristics; and (d) causes of death of Peregrine Falcons. Female peregrines showed significantly greater natal dispersal distances (337.7 ± 164.5 km; n = 24) than did males (161.4 ± 177.7 km; n = 21), but there were no statistically significant differences in dispersal distances of all birds or in breeding-site select...

Leftovers in seed dispersal: ecological implications of partial seed consumption for oak regeneration

Summary 1. Successful seed dispersal by animals is assumed to occur when undamaged seeds arrive at a favourable microsite. Most seed removal and dispersal studies consider only two possible seed fates, predation or escape intact. Whether partial consumption of seeds has ecological implications for natural regeneration is unclear. We studied partial consumption of seeds in a rodent‐dispersed oak species. 2. Fifteen percent of dispersed acorns were found partially eaten in a field experiment. Most damage affected only the basal portion of the seeds, resulting in no embryo damage. Partially eaten acorns had no differences in dispersal distance compared to intact acorns but were recovered at farther distances than completely consumed acorns. 3. Partially eaten acorns were found under shrub cover unlike intact acorns that were mostly dispersed to open microhabitats. 4. Partially eaten acorns were not found buried proportionally more often than intact acorns, leading to desiccation and exposure to biotic agents (predators, bacteria and fungi). However, partial consumption caused more rapid germination, which enables the acorns to tolerate the negative effects of exposure. 5. Re‐caching and shrub cover as microhabitat of destination promote partial seed consumption. Larger acorns escaped predation more often and had higher uneaten cotyledon mass. Satiation at seed level is the most plausible explanation for partial consumption. 6. Partial consumption caused no differences in root biomass when acorns experienced only small cotyledon loss. However, root biomass was lower when acorns experienced heavy loss of tissue but, surprisingly, they produced longer roots, which allow the seeds to gain access sooner to deeper resources. 7. Synthesis. Partial consumption of acorns is an important event in the oak regeneration process, both quantitatively and qualitatively. Most acorns were damaged non‐lethally, without decreasing both dispersal distances and the probability of successful establishment. Faster germination and production of longer roots allow partially eaten seeds to tolerate better the exposure disadvantages caused by the removal of the pericarp and the non‐buried deposition. Consequently, partially consumed seeds can contribute significantly to natural regeneration and must be considered in future seed dispersal studies.

Dispersal ofRhyzopertha dominica(Coleoptera: Bostrichidae) in Different Habitats

The lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), a serious pest of stored cereal grains, is widely distributed and has been collected in different habitats in North America, such as those from agricultural and nonagricultural settings. Our objective was to study the dispersal distances and direction of dispersal by R. dominica after external marking using fluorescent powder, releasing marked beetles, and recapturing adults using pheromone traps in distinctively different ecological habitats, wooded sites and open grasslands, for 2 consecutive yr. The recapture rate of marked beetles ranged from 6 to 26% in both sites and was generally higher in the wooded site than the open field site for both years. There was a significant difference in dispersal distances between wooded and open sites. Mean dispersal distances in the wooded site ranged from 337 to 375 m, whereas in the open site, they varied from 261 to 333 m. Trap captures for both marked and feral beetles were related to the ambient temperature such that increase in trap captures occurred with increasing temperature. Significant differences were observed for directional movement of R. dominica in both sites and indicated that most beetles dispersed in the northwest direction. Correlation analyses showed that the relationship between numbers of marked-released-recaptured beetles significantly decreased with increasing trap distances. Understanding dispersal distances and directions provide insight to flight behavior of R. dominica and to the relationship between ecologically diverse breeding habitats. Knowledge of R. dominica habitat ecology outside of grain storage facilities may be useful in designing suitable management tactics to minimize the onset of infestations in grain storages.

Population genetic structure of raccoons (Procyon lotor) inhabiting a highly fragmented landscape

The raccoon ( Procyon lotor (L., 1758)), a generalist mesocarnivore, has thrived in anthropogenically fragmented landscapes. In this study we utilized 13 microsatellites to analyze the population genetic structure in raccoons occupying an agriculturally fragmented habitat. Our analyses revealed low, but significant, levels of genetic structure (FST = 0.022, P < 0.001) among 645 raccoons inhabiting 29 spatially distinct habitat patches (neighborhoods). We found no evidence for the presence of either isolation by distance or barriers. However, spatial autocorrelation revealed evidence for social structure at the raccoon-neighborhood scale. About 30% of the variance in levels of social structure among raccoon neighborhoods was explained by effects of habitat-patch size and the percentage of land cover represented by forest around the individual habitat patch. We found strong evidence of sex-biased dispersal using direct (parentage analysis) and indirect (relatedness and assignment indices) genetic estimators. However, our analysis revealed that among dispersing raccoons there was no difference in dispersal distance between sexes and that dispersal events are randomly distributed with respect to distance. Our study provides evidence that demographic and behavioral processes affecting raccoon spatial organization may be most critical at very fine scales of biological organization, such as within individual habitat patches.

Clumped versus scattered: how does the spatial correlation of disturbance events affect biodiversity?

In this study, we systematically explore the effects of rate and spatial correlation (level of clumping) of disturbance events on a community of sessile species differing in their life history traits. A spatially explicit individual-based model shows that long-term coexistence is very sensitive to spatial correlation when the trade-off in life history traits includes differences in dispersal distances. Highest biodiversity emerges at highly correlated disturbances of intermediate rates. Diversity peaks shift to larger rates when clumping decreases. Scattered disturbances lead to competitive exclusion. Interestingly, we observed additional peaks in the diversity–disturbance curves at certain levels of clumping. Thus, subject to the differences in life history traits, particular combinations of disturbance rate and spatial correlation may enable subsets of species to coexist, which opens new possibilities for explaining diversity. Our results suggest that observation of high biodiversity under spatially correlated disturbances points to a competition–colonisation trade-off, which includes dispersal distances.

Male‐biased dispersal in a tropical Australian snake (Stegonotus cucullatus, Colubridae)

Sex-based differences in dispersal distances can affect critical population parameters such as inbreeding rates and the spatial scale of local adaptation. Males tend to disperse further than females in mammals, whereas the reverse is true for birds; too few reptiles have been studied to reveal generalities for that group. Although reptiles are most diverse and abundant in the tropics, few tropical reptiles have been studied in this respect. We combine data from a long-term (10-year) mark-recapture study with genetic information (based on nine microsatellite markers) on slatey-grey snakes (Stegonotus cucullatus, Colubridae) in the Australian wet-dry tropics. Males attain larger body sizes than females, and both genetic and mark-recapture data show that males also disperse further than females. Recapture records show that hatchling males dispersed away from their release points whereas hatchling females did not, and adult males moved further than adult females. In the genetic analysis, males contributed less to overall FST and relatedness than did females (F(STm) = 0.0025, F(STf) = 0.0275, P < 0.001; r(m) = 0.0053; r(f) = 0.0550; P < 0.001). Spatial autocorrelation analyses within the largest population revealed a similar pattern, with spatial structuring stronger for females than males. Overall, our genetic analyses not only supported the mark-recapture data, but also extended our insights by revealing occasional long-distance dispersal not detected by the mark-recapture study.

Effective pollen dispersal is enhanced by the genetic structure of an Aesculus turbinata population

Summary 1 Studies using highly informative genetic markers (e.g. microsatellites) have revealed effective movement of genes through pollen grains from more distant sources into offspring than those inferred on the basis of physical pollen movement alone. In order to identify the factors that cause such effective pollen movement in tree populations, analyses of the genetic structure of reproductive trees and parentage analyses for seedlings and saplings were conducted in a 110-ha population of Aesculus turbinata, a tall deciduous tree species that is pollinated by insects and has large seeds that are dispersed by gravity and small mammals. 2 By analysing genotypes of seed coats, which are identical to those of the seed parents, and of leaves from seedlings, pollen donors and seed parents were identified for seedlings. Differences in size and dispersal mode between pollen and seeds caused a significant difference in dispersal distances. Reflecting the restricted seed dispersal (25.3 m on average), there was significant positive relatedness between reproductive trees standing within 150 m of each other. 3 The percentage of self-pollinated offspring decreased from 8.3% at the seedling stage to 0.56% at the sapling stage. The disappearance of out-crossed individuals during the stage between seedling and sapling seemed to be associated with the spatial distance separating their parents: the proportion of juvenile trees that died was higher for those that originated from out-crosses between adults standing within 100 m of each other, where positive relatedness was found between adult trees. Consequently, the deaths of individuals arising from self-pollination events and from crosses between reproductive trees that were spatially adjacent caused longer effective pollen movement for the offspring that survived. The distance between the two parents of a tree, which indicates the distance of effective pollen movement, increased from 179.9 m for seedlings to 288.9 m for saplings. 4 The genetic structure of the adult population of A. turbinata affected the survival of offspring through biparental inbreeding depression, and, then, removal of individuals resulting from crosses between related adults in turn promoted effective pollination over longer distances.

Seed dispersal of Korean pine Pinus koraiensis labeled by two different tags in a northern temperate forest, northeast China

AbstractTwo types of tagging methods, i.e., a 1 × 3‐cm tin tag attached to seed with a 10‐ to 12‐cm metal wire (total weight 0.32 g) and a 2 × 4‐cm white plastic tag fastened to seed with an identical metal wire (total weight 0.57 g) were used to study their effects on seed dispersal of Korean pine by small rodents. A total of 600 seeds were released to assess four main points: (1) difference in seed survival rates, (2) difference in caching behaviors of small rodents, (3) difference in dispersal distances, and (4) proportion of seed missing. The results demonstrated that seed removal for wire‐plastic‐tagged seeds was faster than that for wire‐tin‐tagged seeds. There was no apparent difference in the proportion of seeds eaten in situ (42% and 52% for wire‐plastic‐tagged seeds and wire‐tin‐tagged seeds, respectively). We found 41% and 1% of seeds were moved and hoarded for wire‐plastic‐tagged seeds and wire‐tin‐tagged seeds, respectively. However, 2.33% and 14% of seeds were missing, and their ultimate fates were not known for wire‐plastic‐tagged seeds and wire‐tin‐tagged seeds, respectively. We found the wire‐plastic‐tagged seeds easier to track than the wire‐tin‐tagged seeds due to the fact that the white plastic tags were more salient than the tin tags in field environments. The average dispersal distances were 4.11 ± 2.40 m and 3.01 ± 2.06 m for wire‐plastic‐tagged seeds and wire‐tin‐tagged seeds, respectively, and showed great difference. Despite most being eaten in situ or after removal, 41% of seeds were cached for wire‐plastic‐tagged seeds, much more than for wire‐tin‐tagged seeds. A total of 71 primary caches (123 seeds) were found for wire‐plastic‐tagged seeds, with the average and maximum cache sizes being 1.73 and 6, respectively. However, only three caches were found, and cache size was equal to one for wire‐tin‐tagged seeds. The above data suggests there is some uncertainty in different tagging methods to used track seed fates. Despite their effectiveness in helping to trace seed dispersal or movement by seed‐dispersing rodents, different tagging methods—including size, color, and mass—need to be fully understand in enclosure experiments.

Sex‐biased dispersal in western lowland gorillas (Gorilla gorilla gorilla)

We explored two hypotheses related to potential differences between sexes in dispersal behaviour in western lowland gorillas (Gorilla gorilla gorilla). Direct observations suggest that immature females have more opportunities to move between breeding groups than immature males. The distribution of kin dyadic relationships within and between groups does not, however, support this hypothesis. At larger geographical scales, dispersal is likely to be easier for males than females because of the solitary phase most blackbacks experience before founding their own breeding group. However, previous work indicates that males settle preferentially close to male kin. By specifically tracing female and male lineages with mitochondrial and Y-chromosomal genetic markers, we found that male gorillas in the 6000 km2 area we surveyed form a single population whereas females are restricted to the individual sites we sampled and do not freely move around this area. These differences are more correctly described as differences in dispersal distances, rather than differences in dispersal rates between sexes (both sexes emigrate from their natal group in this species). Differences in resource competition and dispersal costs between female and male gorillas are compatible with the observed pattern, but more work is needed to understand if these ultimate causes are responsible for sex-biased dispersal distances in western lowland gorillas.

Dispersal and climate change: a case study of the Arctic ternSterna paradisaea

AbstractDispersal is an important evolutionary process that can affect admixture of populations and cause rapid responses to changing climatic conditions due to gene flow from populations at different altitudes or latitudes already experiencing these conditions. We investigated long‐term patterns of natal and breeding dispersal in a coastal seabird, the Arctic ternSterna paradisaea, that experiences specific climatic conditions in the northern temperate and Arctic climate zones during breeding and different climatic conditions in the Antarctic during winter. Long natal and breeding dispersal distances were costly as shown by their effects on delayed breeding. Dispersal distances varied significantly among years, with natal dispersal showing a strong temporal increase during the last 70 years. Annual differences in dispersal distance could be accounted for by climate conditions in the breeding grounds and the winter quarters. Natal dispersal was related to climate conditions in both the year of hatching and the year of breeding, whereas breeding dispersal was only related to climate conditions in the second year of the dispersal event. Only the north Atlantic oscillation (NAO) index for winter showed a consistent temporal trend, suggesting that the temporal trend in natal dispersal distance must be caused by changes in the NAO (or associated phenomena). These findings indicate that dispersal can change rapidly in response to changing climate conditions.

Using seed-tagging methods for assessing post-dispersal seed fate in rodent-dispersed trees

Seed tagging is widely used for tracking seeds during dispersal by seed-caching animals. No studies, however, have fully examined the effects of seed tagging on post-dispersal seed fate. We studied how two seed tagging techniques – thread-marking and wire tin-tagging – affected seed fate by placing tagged and untagged seeds in simulated seed sources and caches and comparing removal rates and fates, and by comparing seedling establishment between tagged and untagged seeds. Tagging had little effect on whether seeds were eaten or dispersed, though both marking methods significantly delayed seed removal by rodents. Both marking methods proved effective for retrieving removed seeds and their fates, but because rodents bit off thread not wire, wire tin-tagging yielded a much higher recovery rate and more accurate estimation of seed fate. We found little difference in dispersal distance between the tagging methods. Piercing of the cotyledons negatively affected seedling emergence in one of two seed species tested. Wire tin tags are a suitable alternative for tracking seeds where seed-caching rodents tend to cut or detach thread marks and yield results comparable to thread-marking. However, both seed tagging methods may underestimate seed dispersal and survival due to delayed removal and damage of the cotyledons by piercing.

FOREST COVER INFLUENCES DISPERSAL DISTANCE OF WHITE-TAILED DEER

Animal dispersal patterns influence gene flow, disease spread, population dynamics, spread of invasive species, and establishment of rare or endangered species. Although differences in dispersal distances among taxa have been reported, few studies have described plasticity of dispersal distance among populations of a single species. In 2002‐2003, we radiomarked 308 juvenile (7- to 10-month-old), male white-tailed deer (Odocoileus virginianus) in 2 study areas in Pennsylvania. By using a meta-analysis approach, we compared dispersal rates and distances from these populations together with published reports of 10 other nonmigratory populations of white-tailed deer. Population density did not influence dispersal rate or dispersal distance, nor did forest cover influence dispersal rate. However, average (r 2 ¼ 0.94, P , 0.001, d.f. ¼ 9) and maximum (r 2 ¼ 0.86, P ¼ 0.001, d.f. ¼ 7) dispersal distances of juvenile male deer were greater in habitats with less forest cover. Hence, dispersal behavior of this habitat generalist varies, and use of landscape data to predict population-specific dispersal distances may aid efforts to model population spread, gene flow, or disease transmission.

Natal Dispersal Patterns of a Subsocial Spider Anelosimus cf. jucundus (Theridiidae)

AbstractSpecies that alternate periods of solitary and social living may provide clues to the conditions that favor sociality. Social spiders probably originated from subsocial‐like ancestors, species in which siblings remain together for part of their life cycle but disperse prior to mating. Exploring the factors that lead to dispersal in subsocial species, but allow the development of large multigenerational colonies in social species, may provide insight into this transition. We studied the natal dispersal patterns of a subsocial spider, Anelosimus cf. jucundus, in Southeastern Arizona. In this population, spiders disperse from their natal nests in their penultimate and antepenultimate instars over a 3‐mo period. We tracked the natal dispersal of marked spiders at sites with clustered vs. isolated nests. We found that most spiders initially dispersed less than 5 m from their natal nests. Males and females, and spiders in patches with different densities of nests, dispersed similar distances. The fact that both sexes in a group dispersed, the lack of a sex difference in dispersal distance, and the relatively short distances dispersed are consistent with the hypothesis that natal dispersal results from resource competition within the natal nest, rather than inbreeding avoidance in competition for mates. Additionally, an increase in the average distance dispersed with time and with the number of spiders leaving a nest suggests that competition for nest sites in the vicinity of the natal nest may affect dispersal distances. The similar distances dispersed in patches with isolated vs. clustered nests, in contrast, suggest that competition among dispersers from different nests may not affect dispersal distances.

Dispersal of Tournament-caught Black Bass

Relocation and concentration of fish at fishing-tournament release-sites is a concern for many fishery management agencies. I compiled published and unpublished estimates of dispersal distances by black basses (Micropterus spp.) captured and released alive in fishing tournaments. Only 14% of tournament-caught largemouth bass (M. salmoides) and 32% of smallmouth bass (M. dolomieu) returned to their sites of capture. Fifty-one percent of largemouth bass and 26% of smallmouth bass dispersed less than 1.6 km from their release sites. On average, smallmouth bass dispersed a greater distance (7.3 km) from their release sites than did largemouth bass (3.5 km). There was no difference in dispersal distances for fish captured and released in rivers versus those released in lakes and reservoirs. Twenty-two percent of largemouth bass and 15% of smallmouth bass caught and released in fishing tournaments were subsequently recaptured by anglers. Previous studies recommended modifications to tournament release practices. These recommendations generally have been disregarded because of a lack of regulatory or other incentives.

Field experiments on seed dispersal by wind in ten umbelliferous species (Apiaceae)

This report presents data from experiments on seed dispersal by wind for ten species of the family Apiaceae. Seed shadows were obtained in the field under natural conditions, using wind speeds between four and ten m/s. The flight of individual seeds was followed by eye, and seed shadows were acquired, with median distances varying from 0.7 to 3.1 m between species. Multiple regression models of wind speed and seed weight on dispersal distance were significant for six out of ten species; wind speed had significant effects in seven cases, but seed weight only once. A good correlation between mean terminal falling velocity of the seeds of a species and median dispersal distance, indicates the promising explanatory power that individual terminal velocity data might have on dispersal distance, together with wind speed and turbulence. The theory that seeds that seem to be adapted to wind dispersal travel much longer distances than seeds that have no adaptation was tested. Flattened and winged seeds were indeed found to be transported further by wind, but not much further. Moreover, the species with wind-adapted seeds were also taller, being an alternative explanation since their seeds experienced higher wind speeds at these greater heights. Furthermore, flattened and winged seeds were disseminated from ripe umbels at lower wind speeds in the laboratory. This means that the observed difference in dispersal distance would have been smaller when species specific thresholds for wind speed were incorporated in the field experiments. We argue therefore, that seed morphology is not always the best predictor in classifying species in groups with distinctly different dispersal ability.

Long-Term Movement Patterns for Seven Species of Wading Birds

-We obtained banding and recovery records from 1914 through 1994 for seven species of wading birds from the Bird Banding Laboratory, United States Geological Survey, Patuxent Wildlife Research Center. We analyzed these data to evaluate differences in dispersal distance and frequency of dispersal movement among species. All records were from birds banded as juveniles and recovered at least five months later between March and July, which is the breeding season in most regions of North America. Focusing on recoveries during the breeding season reduced the chance that movements were related to migration rather than dispersal. When an individual was banded and recovered in the same ten-minute block of latitude and longitude, a movement distance of zero km was recorded. The frequency of zero-distance records provides an indication of breeding site fidelity for each species at a spatial resolution of ten minutes. Our results showed that mean dispersal distance was greatest for the Little Blue Heron (Egretta caerulea; 1148 km) followed by Glossy Ibis (Plegadis falcinellus; 1142 km), Tricolored Heron (Egretta tricolor 1019 km), Great Egret (Casmerodius albus; 909 km), Snowy Egret (Egretta thula; 837 km), Great Blue Heron (Ardea herodias; 758 km), and White Ibis (Eudocimus albus; 545 km). Species which dispersed large distances also exhibited fewer zero-distance records, indicating greater movement frequency. The White Ibis has been classified as a nomad, at one end of a continuum defined by low breeding site-fidelity and several life history traits associated with unpredictable foraging habitat. We found that White Ibises were indeed recovered at new locations the majority (76%) of the time but that the other six species of wading birds we examined were even more likely to move to different sites during subsequent breeding seasons. Movement distance and site fidelity will both likely affect whether a response to habitat restoration is due to immigration or local reproduction. Although an increase in total birds using a restored habitat may be an indication of increased habitat quality, caution should be used in inferring population changes without understanding reproduction, mortality, and movement of individuals using restored habitats. Received 20July 1999, accepted 8 September 1999.