Onset Of Dispersal Research Articles

Ambrosia beetles adjust dispersal preferences to their degree of exhaustion

Abstract Delayed dispersal of sexually mature offspring is a fundamental component of cooperative breeding in fungus farming ambrosia beetles. These beetles dwell in logs of recently deceased trees, where female offspring postpone reproduction and invest in alloparental care before dispersing to found a new nest. The wood quality affects investment of adult offspring in alloparental care and hence the breeder's reproductive success. This raises the question of whether dispersing breeders choose habitats strategically to optimise breeding prospects and modulate their offspring's helping propensity. To answer this question, here we tested experimentally whether during dispersal, Xyleborinus saxesenii Ratzeburg (Coleoptera: Scolytinae) uses olfactory cues emitted by mutualistic or pathogenic fungi as an information source on prospective habitat quality. As the mutualistic relationship between the fungi and beetles is obligate, fungus scent should provide a reliable source of information on habitat quality, indicating prior successful colonisation by conspecifics. We found no evidence for direct pathogen avoidance. However, the beetles clearly responded to scent of their mutualistic fungi, dependent on dispersal state. At the onset of dispersal, females avoided the scent of fungus mutualists, whereas they were attracted to them after being exhausted by an experimentally prolonged dispersal time. The observed change of preference during dispersal suggests that beetles freshly emerging from their home gallery may choose pristine habitat by avoiding mutualist scent. This might help to avoid competition with conspecifics and potential pathogen and parasite cross contamination. Exhausted beetles, however, may accept these risks and choose successfully colonised habitat to avoid starvation. State‐dependent adjustment of habitat preferences may be exhibited also in other economically impactful bark and ambrosia beetles, which prompts further study of the olfactory cues used by these beetles during dispersal.

Juvenile survival curves in a solitary ground squirrel with a prolonged hibernation: effects of individual characteristics, environment, and maternal investment.

Juvenile survival is a key life-history influence on population dynamics and adaptive evolution. We analyzed the effects of individual characteristics, early environment, and maternal investment on juvenile survival in a large solitary hibernating rodent-yellow ground squirrel Spermophilus fulvus using Cox mixed-effects models. Only 48% of weaned pups survived to dispersal and 17% survived to hibernation. Early life expectancy was primarily determined by individual characteristics and, to a lesser extent, by the early environment. The strongest and positive predictor of juvenile survival was body mass which crucially affected mortality immediately after weaning. Males suffered higher mortality than females after the onset of dispersal; however, the overall difference between sexes was partly masked by high rates of mortality in the first days after emergence in both sexes. Later emerged juveniles had lower life expectancy than the earliest pups. The overall effect of local juvenile density was positive. Prolonged lactation did not enhance juvenile survival: Pups nursed longer survived shorter than the young nursed for a shorter period. Our findings support the hypothesis that females of S. fulvus cannot effectively regulate maternal expenditures to mitigate the effects of unfavorable conditions on their offspring. The strategy to deal with seasonal time constraints on life history in female S. fulvus suggests an early termination of maternal care at the cost of juvenile quality and survival. This female reproductive strategy corresponds to a "fast-solitary" life of folivorous desert-dwelling S. fulvus and other solitary ground squirrels with prolonged hibernation.

Coexistence patterns and diversity in a trait-based metacommunity on an environmental gradient

The dynamics of trait-based metacommunities have attracted much attention, but not much is known about how dispersal and spatial environmental variability mutually interact with each other to drive coexistence patterns and diversity. Here, we present a spatially explicit model of competition for two essential resources in a metacommunity on a one-dimensional environmental gradient. We find that both the strength of dispersal and the range of spatial environmental variability affect coexistence patterns, spatial structure, trait distribution, and local and regional diversity. Without dispersal, species are sorted according to their optimal growth conditions on the gradient. With the onset of dispersal, source-sink effects are initiated, which increases the effects of environmental filtering and interspecific competition and generates trait lumping, so that only a few species from an environment-defined trait range can survive. Interestingly, for very large dispersal rates, species distributions become spatially homogeneous, but nevertheless two species at the extreme ends of the trade-off curve can coexist for large environmental variability. Local species richness follows a classic hump-shaped dependence on dispersal rate, while local and regional diversity exhibit a pronounced peak for intermediate values of the environmental variability. Our findings provide important insights into the factors that shape the structure of trait-based metacommunities.

When and why do sit-and-wait social spiders disperse?

Abstract Dispersal is inherent to all living organisms. Sit-and-wait predators such as social spiders, with their sedentary lifestyles, present an intriguing and underexplored case to examine the proximate and ultimate reasons for dispersal. Though a reduction in dispersal tendencies must accompany the evolution of sociality in spiders, a fraction of the colony may disperse in groups or individually in many species. Such group or solitary dispersal by female social spiders in specific life stages, can lead to colony fission or colony foundation. Males move between colonies, however, there are no direct estimations of male dispersal distances for any species. The structured populations and high inbreeding within colonies suggest that dispersal events occur over limited spatial scales and may be mediated by extrinsic and intrinsic factors. Future studies exploring complex relationships between environmental variables, phenotypes of individuals, colony state and dispersal are advocated. Another area of interest is probing the dispersal process itself to understand the mechanisms of information transfer between individuals at the onset of dispersal. This involves designing studies to examine how break-away groups reach a consensus on when to disperse and where to go.

Detecting dispersal: A spatial dynamic occupancy model to reliably quantify connectivity across heterogeneous conservation landscapes

Connectivity shapes species distribution, spatial population dynamics and genetic structure, and is critical for conservation. It is imperative to reliably identify factors that limit connectivity across heterogeneous, fragmented landscapes. Viewing connectivity as the persistence of movement in space from source to destination—along potential corridors simulated from correlated random walks—we adapt the dynamic occupancy modeling framework to present an approach to reliably quantify connectivity. This approach allowed us to estimate the probability of spatial persistence of movement along potential corridors, while accounting for imperfect detection of animal use of the matrix. We use simulations to test our model, and data from sign surveys of Asian elephant Elephas maximus space use in Garo Hills, Northeast India, as a practical application of the method. Distance to forests and ruggedness predominantly shaped elephant connectivity patterns. Negative effects of distance to forests were intensified at the onset of dispersal, and in the more disturbed part of our landscape. We mapped locations critical to maintaining connectivity in our study landscape. We demonstrate that the widely used occupancy modeling approach, when combined with appropriate field data collection, permits explicit assessment of matrix impacts on connectivity while accounting for imperfect detection of animal movement. In so doing, we highlight the value of the approach in enabling inference on where animals move, as well as why. Obtaining a reliable understanding of factors shaping connectivity is central to understanding and predicting species responses to environmental change, thereby facilitating effective long-term conservation in fragmented landscapes.

Social intolerance is a consequence, not a cause, of dispersal in spiders.

From invertebrates to vertebrates, a wealth of species display transient sociality during their life cycle. Investigating the causes of dispersal in temporary associations is important to better understand population dynamics. It is also essential to identify possible mechanisms involved in the evolutionary transition from transient to stable sociality, which has been documented repeatedly across taxa and typically requires the suppression of dispersal. In many animals, the onset of dispersal during ontogeny coincides with a sharp decline in social tolerance, but the causal relationship still remains poorly understood. Spiders offer relevant models to explore this question, because the adults of the vast majority of species (>48,000) are solitary and aggressive, but juveniles of most (if not all) species are gregarious and display amicable behaviors. We deployed a combination of behavioral, chemical, and modelling approaches in spiderlings of a solitary species to investigate the mechanisms controlling the developmental switch leading to the decline of social cohesion and the loss of tolerance. We show that maturation causes an increase in mobility that is sufficient to elicit dispersal without requiring any change in social behaviors. Our results further demonstrate that social isolation following dispersal triggers aggressiveness in altering the processing of conspecifics’ cues. We thus provide strong evidence that aggression is a consequence, not a cause, of dispersal in spiderlings. Overall, this study highlights the need of extended social interactions to preserve tolerance, which opens new perspectives for understanding the routes to permanent sociality.

Evidence of long-distance dispersal of a gray wolf from the Chernobyl Exclusion Zone

The Chernobyl Exclusion Zone (CEZ) is a ~ 4300 km2 area in Belarus and Ukraine that remains heavily contaminated with radiation from the nuclear accident of 1986. Long standing controversy persists on the fate of wildlife within the CEZ following human abandonment of the area. Human residency remains extremely sparse, and the CEZ has become a refuge for some populations of wildlife, including gray wolves (Canis lupus). Using GPS telemetry, we documented the first long-distance movements of a young (1–2 years) male wolf from the CEZ into the surrounding landscape. The wolf traveled 369 km from its home range center over a 21-day period in February 2015. In the 95 days prior to dispersal, the wolf maintained a home range of ~ 28 km2, with daily displacements rarely exceeding 5 km. With the onset of dispersal, daily displacement increased to a mean of 16.8 km. The dispersal of a young wolf is an important observation because it suggests that the CEZ may serve as a source for some wildlife populations outside of the CEZ, and raises questions about the potential spread of radiation-induced genetic mutations to populations in uncontaminated areas.

First-Year Dispersal of Golden Eagles from Natal Areas in the Southwestern United States and Implications for Second-year Settling

Knowledge of dispersal from natal areas by pre-breeding-age Golden Eagles (Aquila chrysaetos) in North America is sparse, though crucial for conservation planning. During 2010–2015, we used satellite telemetry to document movement behavior of pre-breeding-age Golden Eagles from the Colorado Plateau and Southern Rocky Mountains of the southwestern U.S.A. Here we report on (1) 1st-yr dispersal timing, distances, strategies, and survival; (2) influences of age, sex, nest-mates, and area of origin; and (3) progressive distancing from natal nests and coinciding space use, including overlap between individuals' home ranges at the end of their 1st and 2nd yr. Our dataset included 293,960 GPS fixes from 66 Golden Eagles monitored through at least the onset of dispersal. All dispersed at age <1 yr. Most (66.7%) initiated dispersal during 16 September–21 November (median = 22 October, 191 d after median hatch date). We could assign each of 60 eagles to one of four 1st-yr dispersal categories based on maximum distance traveled from natal nests: short-distance (SD), generally <120 km (66.7% of eagles); moderate-distance (MD), 120–500 km (16.7%); long-distance (LD) >500 km (13.3%); and Other (3.3%). LDs dispersed at younger ages than SDs and were more likely to be from the arid half of our study area. First-year survival was significantly lower for LDs. Overlap of 95% kernel density home ranges at ages 12 and 24 mo was 42.2% (±6.4 SE) for 26 SDs and 26.5% (±9.5) for eight MDs. Our data indicate that, during at least their 1st and 2nd yr of life, most Golden Eagles from the Colorado Plateau and Southern Rocky Mountains remain within 120 km of their nests, where they experience high survival and are relatively settled by the end of their 1st yr. As such, these landscapes are key habitat for at least 1st- and 2nd-yr eagles as well as breeding pairs.

A photoevaporative gap in the closest planet-forming disc

Abstract The dispersal of the circum-stellar discs of dust and gas surrounding young low-mass stars has important implications for the formation of planetary systems. Photoevaporation from energetic radiation from the central object is thought to drive the dispersal in the majority of discs, by creating a gap which disconnects the outer from the inner regions of the disc and then disperses the outer disc from the inside-out, while the inner disc keeps draining viscously on to the star. In this Letter, we show that the disc around TW Hya, the closest protoplanetary disc to Earth, may be the first object where a photoevaporative gap has been imaged around the time at which it is being created. Indeed, the detected gap in the Atacama large millimeter/submillimeter array images is consistent with the expectations of X-ray photoevaporation models, thus not requiring the presence of a planet. The photoevaporation model is also consistent with a broad range of properties of the TW Hya system, e.g. accretion rate and the location of the gap at the onset of dispersal. We show that the central, unresolved 870 μm continuum source might be produced by free–free emission from the gas and/or residual dust inside the gap.

Independence and juvenile dispersal distances in wild and reintroduced Spanish imperial eagles

Reintroductions have been increasingly used for species restoration and it seems that this conservation tool is going to be more used in the future. Consequently a better knowledge of consequences of this kind of management is needed. Several authors have found differences in dispersal distances among wild and reintroduced individuals; although no common explanation for this general trend (i.e. released animals moving farther than wild ones) has been proposed. Here we compared the dates of dispersal and the distribution of maximum distances during juvenile dispersal between a natural high density population and an alternative situation where young Spanish imperial eagles (Aquila adalberti) were reintroduced in a new area with a very low intra-specific density, and ad libitum feeding until the onset of dispersal. Results showed that maximum dispersal distances were longer in translocated (mean=205km) than in control juvenile eagles (mean=119.70km), and the shape of the distribution changed from leptokurtic right-skewed to quasi-normal. According to our results, for reintroduced young fed ad libitum, we can predict that effective dispersal distances will be longer in reintroduced young during juvenile dispersal than in natural populations. But dispersal distances might also depend on the distance from the release area to the nearest breeding population of the species. For reintroductions close to other existing populations, immigration of released young into existing populations would be greater than expected.

Intersexual difference in early natal dispersal: abrupt departure by females and gradual emigration by males in Tengmalm’s Owl Aegolius funereus

The decision to emigrate from the natal area can influence future fitness prospects, yet detailed data on sex-specific juvenile dispersal behaviour is still lacking for most bird species. We tracked 13 radio-tagged Tengmalm’s Owl Aegolius funereus juveniles from 13 different nests from fledging to independence and onwards. Six out of the seven female juveniles departed abruptly and disappeared from the natal area. In contrast, only one male juvenile departed abruptly, whereas the other five males and one female remained in the study area until tracking was terminated. We propose two alternative interpretations: (1) females initiated natal dispersal earlier than males, or (2) the manner of dispersal differed between the sexes, with females departing abruptly, and males moving gradually out of the natal area. We found no statistically significant influence of body condition or date of independence on dispersal behaviour. We suggest that early onset of dispersal and fast movements out of the natal area may increase a juvenile female’s chances of successful breeding in the following spring. In contrast to females, male Tengmalm’s Owls rarely breed as 1-year-olds, and the benefits of early/abrupt dispersal may be lower for juvenile males. We suggest that female-biased natal dispersal in Tengmalm’s Owl may come about through relatively higher lifetime reproductive success of early dispersing in females than in males.

Post-Weaning Social behaviour within Mother—Offspring Groups of the Bushveld Gerbil,Gerbilliscus leucogaster: Implications for Dispersal

Social behaviour has been implicated in the natal dispersal of several small mammal species. We studied social interactions within groups of bushveld gerbil Gerbillhcus leucogaster mothers and their weaned offspring in captivity. We examined groups (n = 8) over several weeks to assess whether mothers and juveniles tolerate one another beyond weaning, and to investigate behavioural influences surrounding the onset of dispersal. Each group was placed in a series of interconnecting tanks, allowing juveniles free movement between tanks but restricting the movement of the mother. In two of the eight groups the mother produced a second litter during the study; mothers in these two groups appeared to be less tolerant of their first litter compared to mothers in the remaining groups. The remaining groups showed very high levels of tolerance throughout the study, both between mothers and their offspring, and between siblings. Juveniles began showing independence from the mother around weaning, but although indepen...

Post-weaning social behaviour within mother–offspring groups of the bushveld gerbil, Gerbilliscus leucogaster: implications for dispersal

Social behaviour has been implicated in the natal dispersal of several small mammal species. We studied social interactions within groups of bushveld gerbil Gerbilliscus leucogaster mothers and their weaned offspring in captivity. We examined groups (n = 8) over several weeks to assess whether mothers and juveniles tolerate one another beyond weaning, and to investigate behavioural influences surrounding the onset of dispersal. Each group was placed in a series of interconnecting tanks, allowing juveniles free movement between tanks but restricting the movement of the mother. In two of the eight groups the mother produced a second litter during the study; mothers in these two groups appeared to be less tolerant of their first litter compared to mothers in the remaining groups. The remaining groups showed very high levels of tolerance throughout the study, both between mothers and their offspring, and between siblings. Juveniles began showing independence from the mother around weaning, but although independent behaviour increased with juvenile age, there was no clear breakdown of the mother–offspring bond. In nature, offspring probably disperse passively at around five to six weeks old if no subsequent litter is born. However, the high tolerance within these groups suggests that dispersal could be delayed under particular circumstances.

Personality-dependent dispersal: characterization, ontogeny and consequences for spatially structured populations.

Dispersal is one of the most fundamental components of ecology, and affects processes as diverse as population growth, metapopulation dynamics, gene flow and adaptation. Although the act of moving from one habitat to another entails major costs to the disperser, empirical and theoretical studies suggest that these costs can be reduced by having morphological, physiological or behavioural specializations for dispersal. A few recent studies on different systems showed that individuals exhibit personality-dependent dispersal, meaning that dispersal tendency is associated with boldness, sociability or aggressiveness. Indeed, in several species, dispersers not only develop behavioural differences at the onset of dispersal, but display these behavioural characteristics through their life cycle. While personality-dependent dispersal has been demonstrated in only a few species, we believe that it is a widespread phenomenon with important ecological consequences. Here, we review the evidence for behavioural differences between dispersers and residents, to what extent they constitute personalities. We also examine how a link between personality traits and dispersal behaviours can be produced and how personality-dependent dispersal affects the dynamics of metapopulations and biological invasions. Finally, we suggest future research directions for population biologists, behavioural ecologists and conservation biologists such as how the direction and the strength of the relationship between personality traits and dispersal vary with ecological contexts.

Young flying squirrels (Pteromys volans) dispersing in fragmented forests

Dispersal is a key determinant of the population dynamics of species. Thus, a better understanding of how dispersal is affected by the landscape structure and how animals make decisions about moving across different landscapes is needed. We studied the dispersal of 60 radio-collared juvenile Siberian flying squirrels (Pteromys volans) in southern Finland. The effect of landscape structure on selected dispersal direction, dispersal distance, and straightness of dispersal path was studied. Flying squirrels were capable of dispersing over long distances in fragmented forest landscapes. The patches used as temporary roosting sites during dispersal were of a lower quality than were those used as finally occupied patches. The patches used were larger than were patches on average in the study areas. There was a very clear directional bias in the dispersal path (i.e., it was nearly a straight line), which remained over a large scale, but wide-open areas obstructed the straightness of the path. As the distances between crossed patches increased, short-distance dispersers were found further away from their natal home range. However, there were no differences in the landscape that could explain the differences between individuals in decisions to remain philopatric or to become short- or long-distance dispersers. In addition, whereas short-distance dispersers dispersed in random directions, longdistance dispersers started to disperse in directions dominated by preferred habitat. Thus, there were behavioral differences between dispersers. Our results supported the hypotheses stating that individuals decide to disperse long or short distances before the onset of dispersal. Key words: dispersal path, dispersal direction, fragmentation, landscape structure, Pteromys volans, radio tracking, short- and long-distance. [Behav Ecol 15:564–571 (2004)]

Effects of experimental food supplementation on movements of juvenile northern goshawks (Accipiter gentilis atricapillus).

Food availability is thought to strongly influence the leaving phase of natal dispersal in animals with condition-dependent dispersal. We conducted a food supplementation experiment to determine the influence of extra food on the onset of dispersal and early dispersal movement patterns of 42 radio-tagged northern goshawks (Accipiter gentilis atricapillus) from 28 broods in north-central New Mexico during 1992 and 1993. We randomly assigned half of the broods each year as treatments and the other half as controls. Treatment broods were given supplemental food from hatching (late April) until mid-October. Control broods received the same visitation rate but no food. Birds were located approximately every 2 days from fledging until mid-October in 1992 and 1993. Timing of fledging and independence were not affected by the treatment. However, extra food significantly influenced post-fledging movements of juvenile goshawks. During the late fledgling-dependency period (>65 days of age until independence) control birds were located in the natal area (<2 km from nest tree) more frequently than supplemented birds. This pattern reversed after independence (approximately 82 days of age) when supplemented birds were located more frequently in the natal area than controls. After independence the control birds were never located in the natal area and by the end of September in both years the controls had all left the study area (study area boundaries were approximately 25 km from nest tree). Supplemented birds were never located outside of the study area for the duration of the experiment. We conclude that the control birds dispersed out of the study area and the supplemented birds remained. Since the experimentally fed juveniles remained near a known food source and the controls did not, our study demonstrates that food availability influences at least the first 4 months of post-fledging movement patterns in this population. These results also suggest individuals base dispersal decisions on knowledge of their environment at a local scale, which can influence juvenile recruitment.

Community-wide germination strategies in a temperate rainforest of Southern Chile: ecological and evolutionary correlates

Delayed seed germination (‘dispersal in time’), as a component of a plant’s germination strategy, was studied in dicotyledoneous species of a temperate rainforest flora in Chiloé Island (42°30′S), southern Chile. The objective of this investigation was to assess, for this temperate rainforest flora, what proportion of interspecific variation in the time of seed germination—measured in days since the onset of seed dispersal in space—could be attributed to the plants’ historical and phylogenetic background and what proportion was associated with life history and ecological attributes such as seed mass, life form, dispersal syndromes and dispersal periods. To characterise germination times for 44 species from Chiloé forests (n = 150 seeds sowed per species in laboratory assays), we computed the mean germination time (GT), in days since sowing, for all seeds germinated of each species. Seeds were taken from the plants at the onset of dispersal and germinated in Petri dishes at 10/20°C. Considering all species, GTs varied between 3 and 385 days and presented an L-shaped frequency distribution. One-way ANOVAs measured the effects of each factor across all other variables. Two-way ANOVAs were used to assess significant interactions between factors. Multifactorial ANOVAs were used to evaluate the independent effects of each of six historical, phylogenetic and ecological factors on GT and to detect associations between factors. In one-way ANOVAs, phylogenetic grouping (at or above order) explained 12% of the variance in GT; dispersal period (summer v. mainly autumn dissemination of ripe seeds), biogeographic element (endemic, austral, neotropical or cosmopolitan) and dispersal syndrome (fleshy v. dry propagules) explained 7, 6 and 5% of the variance in GT, respectively. The factors life form (trees, shrub and woody vines combined, herbs and non-woody epiphytes) and seed mass (light v. heavy) explained the 4 and 2% of the variance in GT, respectively. Taxa related to Ranunculales presented the longest mean GT (148 days). Endozoochorous species had a more delayed germination than species with other dispersal syndromes. Herbs and non-woody epiphyte species showed mean GT (41 days) significantly shorter than trees and shrubs plus woody vines combined (86 and 85 days, respectively). All interactions in two-way ANOVAs were significant. Multifactorial ANOVAs revealed that the three major factors contributing to differences in GT in this temperate rainforest flora were phylogenetic relatedness, dispersal syndromes and life form (7, 6 and 6% of the interspecific variation, respectively). In this analysis, biogeographic element, dispersal period and seed mass were not significantly related to GT. For the factors examined, failure-time analysis, which takes into account all viable seeds not germinating in laboratory assays, confirmed results from multifactorial ANOVAs.

Predispersal Movements of Coyote (Canis latrans) Pups in Eastern Maine

We documented the progression of movements from den and rendezvous sites, and the monthly changes in predispersal movement rates and home-range areas for coyote ( Canis latrans ) pups in eastern Maine during 1981–1984. Pups began to move short distances from dens at 6–8 weeks of age. The radius and rate of pup movements increased linearly with age. Large increases from September to October in sizes of home ranges and movement rates of pups were associated with the disbanding of the family group and onset of dispersal. Home-range areas and movement rates of late-dispersing juveniles were similar to those of their parents, and likely resulted from interfamily territoriality. Exploratory movements outside of the natal home range were uncommon before dispersal. Further, no sex-specific differences in predispersal-movement patterns were observed. Recent data refuting the hypothesis of sex-specific dispersal in coyotes are consistent with the predispersal-movement patterns presented herein.