Habitat exploration and use in dispersing juvenile flying squirrels

1. Variation in behaviours involved in habitat selection is important for several evolutionary and ecological processes. For example, habitat use during dispersal may differ from breeding habitat use, and for dispersers the scale of habitat familiarity is determined by exploratory behaviour. We studied habitat use and exploration of 56 radio-collared juvenile flying squirrels Pteromys volans L. within natal home range and during dispersal, and compared habitat use between juveniles and 37 adults within breeding home range. 2. Before dispersal, young flying squirrels actively moved around the natal site. Surprisingly, long-distance dispersers explored less than short-distance dispersers, but philopatric individuals explored similar distances as dispersers. Females explored less than males, although females are the more dispersive sex in flying squirrels. 3. For most of the individuals the settlement area was unfamiliar due to long dispersal distance. Consequently, direction and distance of exploration were not very strong predictors of settlement location. However, individuals familiar with the settlement area concentrated exploration to that area. Exploration did not correlate with short-term survival. 4. Dispersers preferred breeding habitat while dispersing, but were found more often in matrix habitat than juveniles within natal, or adults within breeding, home ranges. 5. We conclude that familiarity does not determine settlement as much as, for example, availability of the habitat for flying squirrels. Based on our results, it also seems clear that data on adult habitat use are not enough to predict habitat use of dispersing individuals. In addition, our results support the recent view that short- and long-distance dispersers may need to be analysed separately in ecological and evolutionary analyses.     

Metacommunity structuring in stream networks: roles of dispersal mode,distance type,and regional environmental context

Within a metacommunity, both environmental and spatial processes regulate variation in local community structure. The strength of these processes may vary depending on species traits (e.g., dispersal mode) or the characteristics of the regions studied (e.g., spatial extent, environmental heterogeneity). We studied the metacommunity structuring of three groups of stream macroinvertebrates differing in their overland dispersal mode (passive dispersers with aquatic adults; passive dispersers with terrestrial adults; active dispersers with terrestrial adults). We predicted that environmental structuring should be more important for active dispersers, because of their better ability to track environmental variability, and that spatial structuring should be more important for species with aquatic adults, because of stronger dispersal limitation. We sampled a total of 70 stream riffle sites in three drainage basins. Environmental heterogeneity was unrelated to spatial extent among our study regions, allowing us to examine the effects of these two factors on metacommunity structuring. We used partial redundancy analysis and Moran's eigenvector maps based on overland and watercourse distances to study the relative importance of environmental control and spatial structuring. We found that, compared with environmental control, spatial structuring was generally negligible, and it did not vary according to our predictions. In general, active dispersers with terrestrial adults showed stronger environmental control than the two passively dispersing groups, suggesting that the species dispersing actively are better able to track environmental variability. There were no clear differences in the results based on watercourse and overland distances. The variability in metacommunity structuring among basins was not related to the differences in the environmental heterogeneity and spatial extent. Our study emphasized that (1) environmental control is prevailing in stream metacommunities, (2) dispersal mode may have an important effect on metacommunity structuring, and (3) some factors other than spatial extent or environmental heterogeneity contributed to the differences among the basins.     

Social personalities influence natal dispersal in a lizard

Animal personalities are common across taxa and have important evolutionary and ecological implications. Such consistent individual differences correlate with important life-history traits such as dispersal. Indeed, some environmental conditions are supposed to determine dispersers with a specific personality. For example, an increased density should promote the departure of individuals with less social tolerance. Therefore, we hypothesized that dispersers from high-density populations should primarily be asocial individuals, whereas dispersers from low-density populations should be social individuals. In the common lizard (Lacerta vivipara), we measured attraction towards the odour of conspecifics on juveniles at birth as a metric of social tolerance. We then released these juveniles into populations of different densities and measured dispersal and settlement behaviours with regard to social tolerance. One year later, we again measured the social tolerance of surviving individuals. The social tolerance is constant across time and strongly reflects the individual's dispersal and settlement patterns with respect to population density. These results strongly suggest that social personalities exist and influence dispersal decisions. Further studies will help to elucidate the proximate and ultimate determinants of social personalities.     

Social constraints limit dispersal and settlement decisions in a group-living bird species

Dispersal is a fundamental process affecting the genetic structureof populations, speciation, and extinction. Nevertheless, ourunderstanding of the evolution of dispersal is limited by ourpaucity of knowledge on dispersal decisions at the individuallevel. We investigated the effect of interactions between residentsand juvenile dispersers on individual dispersal and settlementdecisions in Siberian jays (Perisoreus infaustus). In this group-livingbird species, some offspring remain on the parental territoryfor up to 3 years (retained juveniles) whereas other offspringdisperse within 2 months of fledging (dispersers). We foundthat retained juveniles constrained settlement decisions ofdispersers by aggressively chasing dispersers off their territory,resulting in dispersers continuing to disperse and settlingin groups without retained juveniles. Experimental removal ofmale breeders during the dispersal period also demonstratedthat dispersers were unable to settle in high-quality breedingopenings, which were instead filled by older nonbreeding residents.Rather, dispersers immigrated into groups without retained offspringwhere they became subordinate group members, queuing for a breedingopening. Also, they preferably settled in groups with shortqueues where no same-sex juveniles were present. Dispersal didnot inflict a cost to dispersers through increased mortality.However, the presence of immigrants was costly for breedersbecause it increased the rate of conflicts during the breedingseason which negatively affected nestling condition. These resultsdemonstrate that resident individuals constrain both dispersaland settlement decisions of dispersers. Social interactionsbetween residents and dispersers can thus be a key factor tounderstand the evolution of dispersal.     

Activity metabolism of the toad (Bufo americanus): Ecological consequences of ontogenetic change

Summary Following metamorphosis, juvenile toads form dense, heliothermic aggregations on the margins of the ponds from which they emerge. After a period of growth and development, during which body mass increases ten-fold, the juveniles disperse from the pond and assume the solitary, nocturnal habits that characterize adult toads.The dispersal of the toads coincides with the culmination of ontogenetic changes in activity metabolism. Unlike adults, juvenile toads exhaust rapidly when exercised and exhibit a low aerobic component of total metabolic scope. Values of aerobic scope for sustained activity ranged from 0.5 ml O₂/(g·h) for the smallest juveniles to 1.0 ml O₂/(g·h) for adults. The capacity of juveniles for oxygen consumption increases rapidly with growth, reaching the level of mature animals immediately prior to dispersal.In contrast to aerobic metabolism, anaerobic scope was independent of body size. Whole body lactate content after a 1 min bout of vigorous activity was elevated above the resting level by 0.14 mg lactate/g for both juvenile and adult animals.The elevated body temperatures that are achieved by basking juvenile toads probably hasten their physiological development and increase their capacity for aerobic metabolism.     

Dispersal, interpatch movements, and survival in a shrubland breeding bird community

ABSTRACT Dispersal events can affect the distribution, abundance, population structure, and gene flow of animal populations, but little is known about long‐distance movements due to the difficulty of tracking individuals across space. We documented the natal and breeding dispersal of shrubland birds among 13 study sites in a 1000 km² area in southeastern Ohio. In addition, we radio‐marked and tracked 37 adult males of one shrubland specialist, the Yellow‐breasted Chat (Icteria virens). We banded 1925 juveniles and 2112 adults of nine shrubland species from 2002 to 2005. Of these, 33 (1.7%) juveniles were encountered in subsequent years (2003–2006) as adults (natal dispersal) and 442 (20.9%) birds initially banded as breeding adults were re‐encountered in subsequent years (breeding dispersal). Apparent survival of juvenile shrubland birds on their natal patches was 0.024 (95% CI 0.016–0.036). After accounting for the probability of detection, we found that 21% of birds banded as juveniles and recaptured as adults returned to their natal patches, whereas 78% of adult birds showed fidelity to the patch where they were originally captured. Moreover, natal dispersers tended to move farther than breeding dispersers (corrected natal median = 1.7 km ± 0.37; corrected breeding median = 0.23 km ± 0.10). We used our estimates of natal dispersal and annual apparent survival to estimate true survival at 0.11 (95% CI 0.07–0.18) for juveniles in their first year. However, this estimate was only applicable for birds dispersing within 7 km of their natal patches. Interpatch movements of radio‐marked Yellow‐breasted Chats were not uncommon, with 13 of 37 males located in more than one habitat patch. Overall, we observed low natal philopatry, but high adult site fidelity for shrubland birds in our study area. Considering the frequency of short‐distance movements observed (median = 531 m, range = 88–1045 m), clustering of patches within 1 km might facilitate use of shrubland habitat.     

动物传播者对植物更新的促进与限制

在动物 植物的关系网络中,传播者对植物更新具有促进与限制两方面作用.本文从种群尺度总结了传播者取食、空间利用等行为对植物更新的影响;从群落尺度分析了多种传播者传播有效性对植物更新的促进与限制.传播者对食物的处理方式决定了种子的命运,且具有明显的种间差异;植物在传播者食谱中的地位亦决定其更新的成败,成为动物偏好的食物可助其摆脱森林破碎化等不利事件的影响.动物的空间行为可导致种子命运发生改变.传播者移动距离能否逃逸同种成树对种子的距离限制,影响种子的更新命运;动物偏好的适宜生境与适于植物萌发生境的空间一致性程度影响传播者传播的成效.有效传播者的非冗余性促使种子传播网络更稳定,利于植物更新;无效传播直接限制植物更新,但为其他植物定殖提供了可用空间.今后应将传播者行为融入植物种群更新研究,而从生态系统服务角度揭示传播者在植被恢复的作用应是未来恢复生态学研究的重点.     

Effects of individual condition and habitat quality on natal dispersal behaviour in a small rodent

1. Individuals should benefit from settling in high-quality habitats, but dispersers born under favourable conditions have a better physical condition and should therefore be more successful at settling in high-quality habitats. 2. We tested these predictions with root voles (Microtus oeconomus) by a manipulation of individual condition through litter-size enlargement and reduction during lactation combined with a manipulation of habitat quality through degradation of the vegetation cover. We accurately monitored movements of 149 juveniles during a settlement and breeding period of 3 months. 3. The litter size treatment had long-lasting effects on body size, life-history traits and home range size, but did not influence dispersal behaviour. 4. Different stages of dispersal were influenced by habitat quality. In low-quality patches, females dispersed earlier, spent more time prospecting their environment before settling, and settlers had a smaller adult body size than in high-quality patches. Preference and competition for high-quality patches is likely adaptive as it increased fitness both in terms of survival and reproduction. 5. We found no interactive effect of individual condition and habitat quality on natal dispersal and habitat selection. 6. These findings suggest that immediate conditions are more important determinants of dispersal decisions than conditions experienced early in life.     

Sex-biased dispersal: a result of a sex difference in breeding site availability

Sex-biased dispersal is often explained by assuming that the resource-defending sex pays greater costs of moving from a familiar area. We hypothesize that sex-biased dispersal may also be caused by a sex bias in breeding site availability. In avian resource-defense mating systems, site availability is often more constrained for females: males can choose from all vacant sites, whereas females are restricted to sites defended by males. Using data on breeding dispersal of a migratory passerine, we show that average number of available breeding options and availability of the previous year's territory was greater for males than females. The female bias in site unavailability may explain the female bias in probability of breeding dispersal because there was no sex bias in dispersal among birds with their previous year's territory available. We suggest that sex biases in the availability of breeding options may be an important factor contributing to observed variation in sex-biased dispersal patterns.     

Genetic evidence for female-biased dispersal and gene flow in a polygynous primate

Many models of sex-biased dispersal predict that the direction of sex-bias depends upon a species' mating system. In agreement with this, almost all polygynous mammals show male-biased dispersal whereas largely monogamous birds show female-biased dispersal (FBD). The hamadryas baboon (Papio hamadryas hamadryas) is polygynous and so dispersal is predicted to be male biased, as is found in all other baboon subspecies, but there are conflicting field data showing both female and male dispersal. Using 19 autosomal genetic markers genotyped in baboons from four Saudi Arabian populations, we found strong evidence for FBD in post-dispersal adults but not, as expected, in pre-dispersal infants and young juveniles, when we compared male and female: population structure (F(st)), inbreeding (F(is)), relatedness (r), and the mean assignment index (mAIc). Furthermore, we found evidence for female-biased gene flow as population genetic structure (F(st)), was about four times higher for the paternally inherited Y, than for either autosomal markers or for maternally inherited mtDNA. These results contradict the direction of sex-bias predicted by the mating system and show that FBD has evolved recently from an ancestral state of male-biased dispersal. We suggest that the cost-benefit balance of dispersal to males and females is tightly linked to the unique hierarchical social structure of hamadryas baboons and that dispersal and social organization have coevolved.     

Sex ratio evolution when fitness and dispersal vary

In a heterogeneous environment, when the fitness of males and females are differently influenced by habitat quality, habitat-dependent sex ratios may evolve to favor the production of the sex that benefits more (or loses less) from the local habitat. Similarly, sex-biased dispersal favors the evolution of habitat-dependent sex ratios. The present study documents the convergence stable sex ratios expected in the presence of sex-specific fitness gains when dispersal is partial, sex-biased or costly, using a simple model with patches of two qualities. Results show that partial dispersal reduces the sex ratio bias expected with sex-specific fitness gains. The direction of the sex ratio bias can be reversed by sex-biased dispersal or the existence of sex-specific dispersal costs, provided that fitness gains for the two sexes are not too different. The reversal of the sex ratio bias is more readily observed when sex-specific dispersal rates are opposite and extreme. Both dispersal and fitness gains, especially when they are sex-specific, should thus be considered when making predictions about sex ratio evolution in a heterogeneous environment.     

Seed dispersal distances by ant partners reflect preferential recruitment patterns in two ant-dispersed sedges

An important feature of seed dispersal mutualism is the differentiation of dispersal-related seed traits (dispersal syndrome), which potentially contribute to partitioning of both seed dispersers and regeneration sites among sympatric plants. Yet, the selective factors underlying the diversity in dispersal syndromes are largely unknown. The differential requirements for seed dispersal distances are often proposed as a main factor in plant adaptations to disperser animals. Focusing on two sympatric ant-dispersed sedges Carex lanceolata and Carex tristachya (Cyperaceae), we tested the association of the adaptation to different dispersers with requirements for seed dispersal distances. We found that C. lanceolata was more frequently dispersed by the large ant Formica japonica (which had relatively long dispersal distances compared with other smaller ants) than by C. tristachya, and this was caused by the higher seed attractiveness of C. lanceolata to F. japonica. Pot experiments manipulating adult-to-seedling distances showed that isolation from conspecific adults only benefited C. lanceolata seedlings, and C. tristachya seedlings were not affected. These results support the importance of differential requirements for seed dispersal distances as a factor underlying the diversity in dispersal syndromes among animal-dispersed plants.     

Dispersal traits may reflect dispersal distances,but dispersers may not connect populations demographically

Ecological traits that reflect movement potential are often used as proxies for measured dispersal distances. Whether such traits reflect actual dispersal is often untested. Such tests are important because maximum dispersal distances may not be achieved and many dispersal events may be unsuccessful (without reproduction). For insects, many habitat patches harbour ‘resident’ species that are present as larvae (sedentary) and adults (winged and dispersing), and ‘itinerant’ species present only as adults that have dispersed from elsewhere and fail to reproduce. We tested whether itinerancy patterns were temporally consistent, and whether itinerant and resident species differed in wing morphology, a strong correlate of flight capability. Over 3 years and at multiple locations in a 22 km stream length, we sampled larvae and adults of caddisflies in the genus Ecnomus to categorize species as residents or itinerants. Flight capacity was measured using wing size (length and area) and shape parameters (aspect ratio and the second moment of wing area). Three species of Ecnomus were residents and three species were itinerants, and patterns were consistent over 3 years. On average, itinerant species had larger wings, suggesting a greater capacity to fly long distances. Wing shape differed between species, but did not differ systematically between residents and itinerants. Wing morphology was associated with actual but not effective dispersal of some species of Ecnomus. Morphological traits may have weak explanatory power for hypotheses regarding the demographic connectedness of populations, unless accompanied by data demonstrating which dispersers contribute new individuals to populations.     

Social Mating System and Sex-Biased Dispersal in Mammals and Birds: A Phylogenetic Analysis

The hypothesis that patterns of sex-biased dispersal are related to social mating system in mammals and birds has gained widespread acceptance over the past 30 years. However, two major complications have obscured the relationship between these two behaviors: 1) dispersal frequency and dispersal distance, which measure different aspects of the dispersal process, have often been confounded, and 2) the relationship between mating system and sex-biased dispersal in these vertebrate groups has not been examined using modern phylogenetic comparative methods. Here, we present a phylogenetic analysis of the relationship between mating system and sex-biased dispersal in mammals and birds. Results indicate that the evolution of female-biased dispersal in mammals may be more likely on monogamous branches of the phylogeny, and that females may disperse farther than males in socially monogamous mammalian species. However, we found no support for a relationship between social mating system and sex-biased dispersal in birds when the effects of phylogeny are taken into consideration. We caution that although there are larger-scale behavioral differences in mating system and sex-biased dispersal between mammals and birds, mating system and sex-biased dispersal are far from perfectly associated within these taxa.     

Tests for sex-biased dispersal using bi-parentally inherited genetic markers

Understanding why dispersal is sex-biased in many taxa is still a major concern in evolutionary ecology. Dispersal tends to be male-biased in mammals and female-biased in birds, but counter-examples exist and little is known about sex bias in other taxa. Obtaining accurate measures of dispersal in the field remains a problem. Here we describe and compare several methods for detecting sex-biased dispersal using bi-parentally inherited, codominant genetic markers. If gene flow is restricted among populations, then the genotype of an individual tells something about its origin. Provided that dispersal occurs at the juvenile stage and that sampling is carried out on adults, genotypes sampled from the dispersing sex should on average be less likely (compared to genotypes from the philopatric sex) in the population in which they were sampled. The dispersing sex should be less genetically structured and should present a larger heterozygote deficit. In this study we use computer simulations and a permutation test on four statistics to investigate the conditions under which sex-biased dispersal can be detected. Two tests emerge as fairly powerful. We present results concerning the optimal sampling strategy (varying number of samples, individuals, loci per individual and level of polymorphism) under different amounts of dispersal for each sex. These tests for biases in dispersal are also appropriate for any attribute (e.g. size, colour, status) suspected to influence the probability of dispersal. A windows program carrying out these tests can be freely downloaded from http://www.unil.ch/izea/softwares/fstat.html     

Spatial sorting drives morphological variation in the invasive bird, Acridotheris tristis

The speed of range expansion in many invasive species is often accelerating because individuals with stronger dispersal abilities are more likely to be found at the range front. This 'spatial sorting' of strong dispersers will drive the acceleration of range expansion. In this study, we test whether the process of spatial sorting is at work in an invasive bird population (Common myna, Acridotheris tristis) in South Africa. Specifically, we sampled individuals across its invasive range and compared morphometric measurements relevant and non-relevant to the dispersal ability. Besides testing for signals of spatial sorting, we further examined the effect of environmental factors on morphological variations. Our results showed that dispersal-relevant traits are significantly correlated with distance from the range core, with strong sexual dimorphism, indicative of sex-biased dispersal. Morphological variations were significant in wing and head traits of females, suggesting females as the primary dispersing sex. In contrast, traits not related to dispersal such as those associated with foraging showed no signs of spatial sorting but were significantly affected by environmental variables such as the vegetation and the intensity of urbanisation. When taken together, our results support the role of spatial sorting in facilitating the expansion of Common myna in South Africa despite its low propensity to disperse in the native range.     

Personality-dependent dispersal cancelled under predation risk

Dispersal is a fundamental life-history trait for many ecological processes. Recent studies suggest that dispersers, in comparison to residents, display various phenotypic specializations increasing their dispersal inclination or success. Among them, dispersers are believed to be consistently more bold, exploratory, asocial or aggressive than residents. These links between behavioural types and dispersal should vary with the cause of dispersal. However, with the exception of one study, personality-dependent dispersal has not been studied in contrasting environments. Here, we used mosquitofish (Gambusia affinis) to test whether personality-dependent dispersal varies with predation risk, a factor that should induce boldness or sociability-dependent dispersal. Corroborating previous studies, we found that dispersing mosquitofish are less social than non-dispersing fish when there was no predation risk. However, personality-dependent dispersal is negated under predation risk, dispersers having similar personality types to residents. Our results suggest that adaptive dispersal decisions could commonly depend on interactions between phenotypes and ecological contexts.     

Advances in our understanding of mammalian sex-biased dispersal

Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns.     

Effects of seed dispersal by animals on the regeneration of Bursera graveolens (Burseraceae) on Santa Fe Island,Galápagos

Summary The importance of animals as seed dispersers for Bursera graveolens (Burseraceae) was assessed by analysis of juvenileadult interplant distances on Santa Fe Island, Galápagos. The Santa Fe Bursera population consists of two non-overlapping classes old, large adults, and juveniles recruited since the exermination of feral goats in 1971. Juveniles occurred on a variety of substrate types, as well as under and away from woody vegetation. Most juveniles arise from seeds dispersed by animals; 86% of the juveniles were 3 m away from the crown of the nearest adult, and half were 7 m away. Although all juveniles occurred within 35 m of an adult Bursera, seed dispersal by animals is an important factor in the regeneration of B. graveolens on Santa Fe.     

Fine-scale genetic structure of a long-lived reptile reflects recent habitat modification

Anthropogenic habitat fragmentation — ubiquitous in modern ecosystems — has strong impacts on gene flow and genetic population structure. Reptiles may be particularly susceptible to the effects of fragmentation because of their extreme sensitivity to environmental conditions and limited dispersal. We investigate fine-scale spatial genetic structure, individual relatedness, and sex-biased dispersal in a large population of a long-lived reptile (tuatara, Sphenodon punctatus) on a recently fragmented island. We genotyped individuals from remnant forest, regenerating forest, and grassland pasture sites at seven microsatellite loci and found significant genetic structuring (R_ST = 0.012) across small distances (< 500 m). Isolation by distance was not evident, but rather, genetic distance was weakly correlated with habitat similarity. Only individuals in forest fragments were correctly assignable to their site of origin, and individual pairwise relatedness in one fragment was significantly higher than expected. We did not detect sex-biased dispersal, but natural dispersal patterns may be confounded by fragmentation. Assignment tests showed that reforestation appears to have provided refuges for tuatara from disturbed areas. Our results suggest that fine-scale genetic structuring is driven by recent habitat modification and compounded by the sedentary lifestyle of these long-lived reptiles. Extreme longevity, large population size, simple social structure and random dispersal are not strong enough to counteract the genetic structure caused by a sedentary lifestyle. We suspect that fine-scale spatial genetic structuring could occur in any sedentary species with limited dispersal, making them more susceptible to the effects of fragmentation.