Dispersers

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Dispersers

  • active disperser
  • poor disperser
  • seed disperser


  • Selected Abstracts


    CONFLICTING SELECTION FROM AN ANTAGONIST AND A MUTUALIST ENHANCES PHENOTYPIC VARIATION IN A PLANT

    EVOLUTION, Issue 4 2010
    Adam M. Siepielski
    The raw material for evolution is variation. Consequently, identifying the factors that generate, maintain, and erode phenotypic and genetic variation in ecologically important traits within and among populations is important. Although persistent directional or stabilizing selection can deplete variation, spatial variation in conflicting directional selection can enhance variation. Here, we present evidence that phenotypic variation in limber pine (Pinus flexilis) cone structure is enhanced by conflicting selection pressures exerted by its mutualistic seed disperser (Clark's nutcracker Nucifraga columbiana) and an antagonistic seed predator (pine squirrel Tamiasciurus spp.). Phenotypic variation in cone structure was bimodal and about two times greater where both agents of selection co-occurred than where one (the seed predator) was absent. Within the region where both agents of selection co-occurred, bimodality in cone structure was pronounced where there appears to be a mosaic of habitats with some persistent habitats supporting only the seed disperser. These results indicate that conflicting selection stemming from spatial variation in community diversity can enhance phenotypic variation in ecologically important traits. [source]


    Neritid and thiarid gastropods from French Polynesian streams: how reproduction (sexual, parthenogenetic) and dispersal (active, passive) affect population structure

    FRESHWATER BIOLOGY, Issue 3 2000
    Marilyn J. Myers
    Summary 1The streams of French Polynesia contain several species of Neritidae and Thiaridae (Mollusca: Gastropoda). The neritids are dioecious and amphidromous with a freshwater adult stage and a poorly known, marine larval stage. The thiarids are parthenogenetic and viviparous, and rely on passive dispersal for colonisation of new habitats. 2Populations of the neritid Clithon spinosus and the thiarids Melanoides tuberculata and Thiara granifera were analysed using mitochondrial DNA sequences from COI to compare the population structure of the snails at three different scales: between streams (N = 9), between islands (N = 4), and between age and distance of paired islands. 3The amphidromous C. spinosus showed no evidence of genetic isolation at any of the scales tested (Fst values 0.02). Parsimony analyses resulted in two haplotype clusters separated by a three-step segment, which were not linked to geographic isolation. The larval phase of C. spinosus is most likely a long-lived planktotroph and a very effective disperser. 4Two haplotypes of M. tuberculata, separated by 16 base pairs, were found. Both haplotypes were found in snails on all islands, and individuals representing both were often collected in the same habitat. One haplotype of T. granifera was found. M. tuberculata has the characteristics of the ,general-purpose genotype' of clonal population structure and although it relies on passive dispersal, it has colonised nearly all freshwater habitats on the islands. [source]


    Small and large anemonefishes can coexist using the same patchy resources on a coral reef, before habitat destruction

    JOURNAL OF ANIMAL ECOLOGY, Issue 5 2002
    Akihisa Hattori
    Summary 1According to meta-population models, a superior competitor and a superior disperser can coexist in a patchy environment. The two anemonefishes, a large aggressive Amphiprion clarkii Bennett and a small less-aggressive A. perideraion Bleeker, use the same host anemone Heteractis crispa Ehrenberg on a coral reef, Okinawa, Japan, where most of the hosts disappeared after the coral bleaching in 1998. Their microhabitat (host) use and coexistence, and the quality and quantity of microhabitats were investigated in 1988, 1989, 1999 and 2000 on the coral reef. Their interspecific interaction was also examined. 2Before the habitat destruction, the two species coexisted. Although A. clarkii was behaviourally dominant over A. perideraion in a cohabiting group, A. perideraion was a superior competitor in terms of site displacement, because A. perideraion could displace a microhabitat. Adult A. clarkii emigrated from a cohabiting group probably due to the high cost of interactions with adult A. perideraion . Although it is easier to defend a small area for a larger species, sharing a host with adult A. perideraion may not pay for A. clarkii because A. clarkii needs a larger area. 3A. clarkii was not only a superior disperser, which was able to find a vacated host, but also a pioneer species that was able to use newly settled small hosts. Larval A. clarkii settled on such a small host because they were able to move to larger hosts for future reproduction, while A. perideraion did not settle on a small host because of low mobility after settlement. Microhabitat (host) with various sizes might have promoted their coexistence. 4After the habitat destruction, the superior competitor A. perideraion went extinct locally due probably to lack of small host utilization ability. The present study implies that the difference in body size between the two competitors plays an important role in their coexistence, because species with different body sizes can have different mobility and require different amounts of resources. [source]


    Using GIS to relate small mammal abundance and landscape structure at multiple spatial extents: the northern flying squirrel in Alberta, Canada

    JOURNAL OF APPLIED ECOLOGY, Issue 3 2005
    MATTHEW WHEATLEY
    Summary 1It is common practice to evaluate the potential effects of management scenarios on animal populations using geographical information systems (GIS) that relate proximate landscape structure or general habitat types to indices of animal abundance. Implicit in this approach is that the animal population responds to landscape features at the spatial grain and extent represented in available digital map inventories. 2The northern flying squirrel Glaucomys sabrinus is of particular interest in North American forest management because it is known from the Pacific North-West as a habitat specialist, a keystone species of old-growth coniferous forest and an important disperser of hypogeous, mycorrhizal fungal spores. Using a GIS approach we tested whether the relative abundance of flying squirrel in northern Alberta, Canada, is related to old forest, conifer forest and relevant landscape features as quantified from management-based digital forest inventories. 3We related squirrel abundance, estimated through live trapping, to habitat type (forest composition: conifer, mixed-wood and deciduous) and landscape structure (stand height, stand age, stand heterogeneity and anthropogenic disturbance) at three spatial extents (50 m, 150 m and 300 m) around each site. 4Relative abundances of northern flying squirrel populations in northern and western Alberta were similar to those previously reported from other regions of North America. Capture rates were variable among sites, but showed no trends with respect to year or provincial natural region (foothills vs. boreal). 5Average flying squirrel abundance was similar in all habitats, with increased values within mixed-wood stands at large spatial extents (300 m) and within deciduous-dominated stands at smaller spatial extents (50 m). No relationship was found between squirrel abundance and conifer composition or stand age at any spatial extent. 6None of the landscape variables calculated from GIS forest inventories predicted squirrel abundance at the 50-m or 150-m spatial extents. However, at the 300-m spatial extent we found a negative, significant relationship between average stand height and squirrel abundance. 7Synthesis and applications. Boreal and foothill populations of northern flying squirrel in Canada appear unrelated to landscape composition at the relatively large spatial resolutions characteristic of resource inventory data commonly used for management and planning in these regions. Flying squirrel populations do not appear clearly associated with old-aged or conifer forests; rather, they appear as habitat generalists. This study suggests that northern, interior populations of northern flying squirrel are probably more related to stand-level components of forest structure, such as food, microclimate (e.g. moisture) and understorey complexity, variables not commonly available in large-scale digital map inventories. We conclude that the available digital habitat data potentially exclude relevant, spatially dependent information and could be used inappropriately for predicting the abundance of some species in management decision making. [source]


    Dispersal characteristics and management of a rare damselfly

    JOURNAL OF APPLIED ECOLOGY, Issue 4 2003
    Bethan V. Purse
    Summary 1Coenagrion mercuriale is a rare damselfly in Britain and mainland Europe and has been declining in the last 30 years. It has specialized habitat requirements and has been viewed, traditionally, as a poor disperser. Knowledge of its dispersal ability was considered in its Biodiversity Species Action Plan as essential for the formulation of appropriate conservation management strategies. 2Mark,release,recapture (MRR) studies of C. mercuriale in two large UK heathland populations were undertaken. Mature adults had a low rate of movement within continuous areas of habitat (average < 25 m movement), low emigration rates (1·3,11·4%) and low colonization distances (maximum 1 km), all comparable to similarly sized coenagrionids. 3Movements were more likely within than between patches of suitable habitat over short to medium distances (50,300 m). Between-patch movements were more likely between patches that were close together. Scrub barriers reduced dispersal. 4The probability of dispersal between two recaptures depended on the length of the time interval between them. Coenagrion mercuriale performed considerable between-patch movements within a small fraction (1,2 days) of its mean mature adult life span (7,8 days). 5Qualitative comparison of field colonization distances measured here and distances between UK sites occupied by C. mercuriale revealed that empty sites within large clusters of sites would probably be recolonized rapidly and dispersal events would be frequent. However, such events would occur rarely within small isolated sites or clusters of sites, leaving local populations prone to extinction. 6Synthesis and applications. These data show that management effort should be directed towards maximizing the likelihood of C. mercuriale recolonizing sites naturally within 1,3 km of other populations (particularly within large clusters). Scrub boundaries should be removed between existing populations and empty, but suitable, sites to facilitate stepping-stone dispersal movements. [source]


    Seasonal inventory and status of flying insects, in Kihansi Gorge, Tanzania

    AFRICAN JOURNAL OF ECOLOGY, Issue 3 2009
    Edward K. Msyani
    Abstract Sampling of flying insects in Kihansi Gorge was conducted in six micro-habitats namely Lower, Upper, Main, Mid-Gorge and Mhalala Spray Wetlands and adjacent forest. The four traps used were, malaise, pitfall, light and artificial substrate sampler, besides sweep netting and beating. In the wet season, 65,549 flying insects (65.13%) were recorded when compared to 35,633 flying insects (34.87%) in dry season. At its peak, 29,783 flying insects (29.15%) were recorded at the start of wet season (December 2004). The abundance value was significant (,2 = 1794.98, d.f. = 5, P , 0.001). The favourable weather condition at the beginning of the wet season might have triggered emergence of high numbers of winged insects like ants, to facilitate migration through dispersal and reproduction, and some aquatic insects (Plecoptera, Odonata and Trichoptera) moulted and entered into terrestrial life to raise terrestrial abundance. No association was recorded between abundance of flying insects and amphibians (Kihansi Spray Toad; Nectophynoides asperginis), for Mid-Gorge and Main Spray Wetlands (r = ,0.71, n = 4, P = 0.147 and r = ,0.69, n = 5, P = 0.201) respectively. Résumé On a récolté des échantillons d'insectes volants dans la Kihansi Gorge, dans six micro-habitats à savoir les Lower, Upper, Main, et Mid-Gorge et les Mhalala Spray Wetlands ainsi que dans les forêts voisines. Les quatre pièges utilisés étaient le piège malaise, le piège-fosse ou Barber, le piège lumineux et l'échantillonnage sur substrat artificiel, auxquels s'ajoutaient le filet et la frappe. En saison des pluies, 65.549 insectes volants (65,13%) ont été rapportés, comparéà 35.633 (34,87%) en saison sèche. Le maximum a été atteint avec 29.783 insectes volants (29,15%) capturés au début de la saison des pluies, en décembre 2004. L'abondance avait une valeur significative (,2 = 1 794,98, d.f. = 5, P , 0.001). Les conditions climatiques favorables au début de la saison des pluies peuvent avoir suscité l'émergence d'insectes ailés qui devaient se reproduire et se disperser, comme les fourmis, et de certains insectes aquatiques (Plécoptères, Odonates et Trichoptères) qui entament leur vie terrestre pour augmenter l'abondance des espèces. On n'a rapporté aucune association entre l'abondance des insectes ailés et les amphibiens (crapaud de Kihansi Spray, Nectophynoides asperginis) pour la Mid-gorge ni pour les Main Spray Wetlands (r = ,0,71, n = 4, P = 0.147; et r = ,0,69, n = 5, P = 0.201) respectivement. [source]


    Turnover in flightless invertebrate species composition over different spatial scales in Afrotemperate forest in the Drakensberg, South Africa

    AFRICAN JOURNAL OF ECOLOGY, Issue 3 2009
    Charmaine Uys
    Abstract An understanding of species turnover at different spatial scales and the influence of environmental variables including distance are important for conservation planning and management. Ground dwelling, flightless invertebrates have poor dispersal abilities and other taxa may not be effective as surrogates. This is an important consideration for biodiversity conservation in Afrotemperate forests of the Drakensberg Mountains, South Africa, where flightless invertebrates are geographically isolated by the naturally fragmented state of forests. Seventeen Afrotemperate forests in four reserves across the Drakensberg were sampled using soil and leaf litter sampling, pitfall traps, active search quadrats and tree beats. Seventy-two species were recorded, comprising 31 mollusc, nine earthworm, one onychophoran, six centipede, twelve millipede and thirteen ant species. Canonical correspondence analysis indicated that latitude (distance); fire history (disturbance) and mean annual precipitation were the most important factors governing invertebrate assemblage composition. ,sim measurements detected change in species at all spatial scales investigated, but no clear trends were evident. Distance or spatial scale alone does not explain species turnover and community composition. Effective selection of target areas, therefore, requires species level information to identify species of special concern. Résumé Une bonne compréhension de la rotation des espèces à différentes échelles spatiales et de l'influence des variables environnementales, y compris de la distance, est importante pour la planification et la gestion de la conservation. Les invertébrés qui vivent dans le sol, ceux qui ne volent pas, n'ont que de faibles capacités de se disperser, et d'autres taxons peuvent ne pas être des substituts efficaces. Ceci pourrait être une réflexion importante pour la conservation de la biodiversité dans les forêts afro-tempérées des monts Drakensberg, en Afrique du Sud, où des invertébrés qui ne volent pas sont isolés géographiquement par l'état naturellement fragmenté des forêts. On a prélevé des échantillons dans 17 forêts afro-tempérées, dans quatre réserves du Drakensberg, en utilisant des échantillons de sols et de litière de feuilles, des pièges, la recherche active dans des quadrats et le battage d'arbres. On a enregistré 72 espèces comprenant 31 mollusques, neuf vers de terre, un onychophore, six centipèdes, 12 mille-pattes et 13 fourmis. L'analyse canonique des correspondances a indiqué que la latitude (distance), l'historique des feux (perturbations) et les précipitations annuelles moyennes étaient les facteurs les plus importants pour la composition des assemblages d'invertébrés. Des mesures de ,sim ont détecté des changements d'espèces dans toutes les échelles spatiales étudiées, mais aucune tendance nette n'était visible. L'échelle de distance ou d'espace n'explique pas seule la rotation des espèces et la composition de la communauté. La sélection effective de zones cibles requiert donc des informations au niveau des espèces pour pouvoir identifier les espèces dont le statut est particulièrement inquiétant. [source]


    Optimization of dispersive liquid,liquid microextraction of Co(II) and Fe(III) as their oxinate chelates and analysis by HPLC: Application for the simultaneous determination of Co(II) and Fe(III) in water samples

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 23-24 2009
    Mir Ali Farajzadeh
    Abstract In this study, dispersive liquid,liquid microextraction method was used for the preconcentration and simultaneous determination of Co(II) and Fe(III) in water samples as their oxinate chelates. In dispersive liquid,liquid microextraction process, methanol and chloroform were used as disperser and extracting solvents, respectively, and the ligand 8-hydroxy quinoline was used as a chelating agent for the extraction of Co(II) and Fe(III). HPLC was applied for the quantitation of the analytes after preconcentration. An experimental design, central composite design, coupled with response surface methodology was used for the optimization of the involved experimental parameters. In addition, the effect of various experimental parameters in the extraction was investigated using one variable at a time method. The calibration graphs were linear in the range of 20,4000,,g/L with the LODs of 3,,g/L for both analytes. The RSDs for six replicate measurements of 500,,g/L of Co2+ and Fe3+ were 3.3 and 4.1%, respectively. [source]


    Context-dependency of a complex fruit,frugivore mutualism: temporal variation in crop size and neighborhood effects

    OIKOS, Issue 3 2010
    Soumya Prasad
    The quantity of fruit consumed by dispersers is highly variable among individuals within plant populations. The outcome of such selection operated by frugivores has been examined mostly with respect to changing spatial contexts. The influence of varying temporal contexts on frugivore choice, and their possible demographic and evolutionary consequences is poorly understood. We examined if temporal variation in fruit availability across a hierarchy of nested temporal levels (interannual, intraseasonal, 120 h, 24 h) altered frugivore choice for a complex seed dispersal system in dry tropical forests of southern India. The interactions between Phyllanthus emblica and its primary disperser (ruminants) was mediated by another frugivore (a primate), which made large quantities of fruit available on the ground to ruminants. The direction and strength of crop size and neighborhood effects on this interaction varied with changing temporal contexts. Fruit availability was higher in the first of the two study years, and at the start of the season in both years. Fruit persistence on trees, determined by primate foraging, was influenced by crop size and conspecific neighborhood densities only in the high fruit availability year. Fruit removal by ruminants was influenced by crop size in both years and neighborhood densities only in the high availability year. In both years, these effects were stronger at the start of the season. Intraseasonal reduction in fruit availability diminished inequalities in fruit removal by ruminants and the influence of crop size and fruiting neighborhoods. All trees were not equally attractive to frugivores in a P. emblica population at all points of time. Temporal asymmetry in frugivore-mediated selection could reduce potential for co-evolution between frugivores and plants by diluting selective pressures. Inter-dependencies formed between disparate animal consumers can add additional levels of complexity to plant,frugivore mutualistic networks and have potential reproductive consequences for specific individuals within populations. [source]


    Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique,

    PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2002
    Dieter Petrak
    Abstract The objective of this study was to compare the measuring results of a fiber-optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber-optical spatial filtering velocimetry was modified by fiber-optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber-optical probe system can be used as an in-line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow-sized glass beads in the range 30,100,,m and irregularly shaped test particles were limestone particles in the range 10,600,,m. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle-laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle-probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity. [source]


    Dispersal ability determines the genetic effects of habitat fragmentation in three species of aquatic insect

    AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010
    Kozo Watanabe
    Abstract 1.The dispersal ability of species and the geographic scale of habitat fragmentation both may influence the extent of gene flow between fragments, but their interactions have rarely been tested, particularly among co-occurring species. 2.Population genetic structures of three species of aquatic insect were compared in streams fragmented by reservoirs and in unfragmented streams in north-eastern Japan, using 52, 37, and 58 RAPD markers. The three species studied included a strong disperser Cincticostella elongatula (Ephemeroptera: Ephemerellidae), an intermediate disperser Stenopsyche marmorata (Trichoptera: Stenopsychidae), and a weak disperser Hydropsyche orientalis (Trichoptera: Hydropsychidae). 3.The patterns of genetic isolation by distance (IBD) supported a priori hypotheses of dispersal ability. The strong disperser (C. elongatula) exhibited significant IBD only at the largest spatial scale studied (among drainages, r=0.50, P<0.01). The intermediate disperser (S. marmorata) showed IBD both within (r=0.22, P<0.01) and among (r=0.45, P<0.01) drainages. The weak disperser (H. orientalis) did not exhibit significant IBD at any scale. 4.Pairwise genetic differentiation (,) indicated that neither the weak disperser nor the strong disperser were genetically differentiated above and below reservoirs when compared with reference sites. This was in contrast to previous results for S. marmorata, for which subpopulations were genetically fragmented across larger (>4.1,km), but not smaller (<2.9,km) reservoirs. 5.We suggest that intermediate dispersers, i.e. those at equilibrium between migration and genetic drift within drainages, are more likely to be affected by fragmentation than either strong or weak dispersers. Intermediate dispersers could therefore be used as indicator species in studies aimed at detecting the effects of distance between habitat fragments (e.g. reservoir size) for conservation planning. Copyright © 2010 John Wiley & Sons, Ltd. [source]


    Frugivory and seed dispersal by foxes in relation to mammalian prey abundance in a semiarid thornscrub

    AUSTRAL ECOLOGY, Issue 7 2005
    SERGIO I. SILVA
    Abstract We examine the role of the native fox, Pseudalopex culpaeus, as a frugivore and seed disperser in a semiarid thornscrub of Chile. We quantified the fruit and animal components in its diet versus the availability of fruits and small mammals in the field over a 2-year period (January 1998 through February 2000). We tested the legitimacy and effectiveness of foxes as dispersers by quantifying the percentages of seed viability and of germination of seeds that passed through fox gut versus those picked from plants. We also studied their efficiency as dispersers, monitoring the fate of seeds in faeces placed in the field. The highest frequencies of fruit consumption by foxes were observed when abundances of small mammal prey were <6 individuals per hectare, regardless of fruit abundance in the field. Thus, foxes consumed fruits as a supplementary food resource. Based on 326 faeces, the total number of fruits consumed was about 34 000 over the 2-year study period, and fruits from the alien shrub Schinus molle represented 98% of that total, with the native Porlieria chilensis a distant second. Germination and viability of defecated seeds of P. chilensis were reduced by 66% and 48%, respectively, in comparison to controls. In contrast, germination of seeds of S. molle increased by 50% and no effect on viability was observed. With regard to P. chilensis, foxes were legitimate (they defecated viable seeds), but ineffective (seeds in faeces had lower germination than those taken directly from parental plants and there was no seedling establishment in the field) and inefficient dispersers (seeds in faeces were deposited on microhabitats hostile to seed germination and seedling establishment). However, with regard to S. molle, foxes were legitimate, effective (seeds in faeces had higher germination than those taken directly from parental plants; there was germination but no establishment in the field), and efficient dispersers (over 41% of seeds were deposited on safe microsites). Thus, a native fox may be contributing to the spread of an alien shrub, co-opting existing community processes. [source]


    Frugivory and Seed Dispersal by the Lowland Tapir Tapirus terrestris in the Peruvian Amazon

    BIOTROPICA, Issue 2 2010
    Mathias W. Tobler
    ABSTRACT The lowland tapir Tapirus terrestris is the largest herbivore in the Neotropics and feeds on a large quantity of fruits, often ingesting the seeds and defecating them intact. Seed dispersal by the lowland tapir in the southwestern Amazon was studied by examining seeds from 135 dung samples collected between 2005 and 2007. Seeds of a total of 122 plant species were identified, representing 68 genera and 33 families. The species accumulation curve showed that more species can be expected with further sampling. Many species (45%) were only encountered once, and only 10 percent of all species were found in >10 samples, indicating that the lowland tapir is an opportunistic forager. Seed diversity showed a clear seasonal pattern and was highly correlated with fruit availability. Seed diameter ranged from <1 to 25 mm with 81 percent <10 mm diam. The size distribution of seeds found in lowland tapir dung generally followed that of seeds found in the forest, but had a lower proportion of seeds in the smallest size class (<2.5 mm) and a larger proportion found in the largest size class (20,25 mm). The diversity of seeds encountered in dung of the lowland tapir in this study was much higher than in previous studies. We conclude that the lowland tapir is a potential disperser for a large number of plant species, including many that previously have been thought to be dispersed only by large primates. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp. [source]


    Seed Dispersal of the Palm Syagrus romanzoffiana by Tapirs in the Semi-deciduous Atlantic Forest of Argentina

    BIOTROPICA, Issue 4 2009
    Mariano I. Giombini
    ABSTRACT Vertebrates play a fundamental role in the dispersal of Neotropical trees, generating different seed shadows according to their physical and behavioral features. Tapirs are capable of consuming great quantities of large fruits, and they defecate seeds far from parent trees. For instance, intact seeds of the palm Syagrus romanzoffiana have been found in tapir dung piles in the Atlantic Forest of southeastern Brazil, suggesting that tapirs effectively disperse this species. However, recruitment was not examined therein. We studied tapir endozoochory of large and medium seeds in the semi-deciduous Atlantic Forest of Argentina by examining dung piles found within Iguazu National Park. We recorded dung-pile positions to evaluate the spatial distribution. We also counted the number of juveniles in 2 × 2 m quadrats placed on old dung piles in latrines, beneath adults and in random sites to estimate recruitment levels. Syagrus romanzoffiana seeds were present in 98 percent of dung piles, averaging >200 seeds/dung pile, indicating that this species constitutes the main fruit component in the tapir's diet. Dung piles showed a clumped deposition pattern reflecting the use of latrines. Juvenile recruitment in latrines was 21 times higher than that of under-adult sites and 500 times greater than in random sites, and correlated with the frequency of use of the areas. We concluded that the lowland tapir is a major disperser of S. romanzoffiana. Given that this palm can be considered a keystone species, a disruption of this interaction might affect the entire community of frugivores in the long term. [source]


    Distribution of myrmecochorous species over the landscape and their potential long-distance dispersal by emus and kangaroos

    DIVERSITY AND DISTRIBUTIONS, Issue 1 2008
    María Calviño-Cancela
    ABSTRACT Topographical heterogeneity can create a mosaic of substrate types leading to the formation of isolated plant populations. Seed dispersal then becomes crucial for the colonization of such suitable but remote substrate types. We surveyed the distribution of seven elaiosome-bearing species (myrmecochores) over 5 km2 of natural heathland in southwestern Australia. Ants are the standard means of dispersal of these species, which provide limited dispersal (usually of a few metres). Six species were associated with particular substrate types (dune or swale) and all occurred as discrete populations, on average 270,500 m apart, with closest dune edges 280 m apart. We evaluated the possible roles of emus and kangaroos as alternative agents of long-distance seed dispersal between substrate types. Their droppings contained viable seeds of three of the target species, as well as other myrmecochores, and were evenly distributed over the substrate types. While migration of these plant species between preferred substrate types seems unlikely when considering only their standard dispersal agents (ants), it is highly likely in the presence of emus (in particular) and kangaroos that act as non-standard dispersers. This may have important consequences for plant species conservation by increasing habitat connectivity and favouring regional persistence. [source]


    Spatial pattern of adult trees and the mammal-generated seed rain in the Iberian pear

    ECOGRAPHY, Issue 3 2010
    Jose M. Fedriani
    The degree to which plant individuals are aggregated or dispersed co-determines how a species uses resources, how it is used as a resource, and how it reproduces. Quantifying such spatial patterns, however, presents several methodological issues that can be overcome by using spatial point pattern analyses (SPPA). We used SPPA to assess the distribution of P. bourgaeana adult trees and their seeds (within fecal samples) dispersed by three mammals (badger, fox, and wild boar) within a 72-ha plot across a range of spatial scales. Pyrus bourgaeana trees in our study plot (n=75) were clearly aggregated with a critical spatial scale of ca 25,m, and approximately nine randomly distributed tree clusters were identified. As expected from their marking behaviors, the spatial patterns of fecal deposition varied widely among mammal species. Whereas badger feces and dispersed seeds were clearly clustered at small spatial scales (<10,m), boar and fox feces were relatively scattered across the plot. A toroidal shift null model testing for independence indicated that boars tended to deliver seeds to the vicinity of adult trees and thus could contribute to the maintenance and enlargement of existing tree clusters. Badgers delivered feces and seeds in a highly clumped pattern but unlike boars, away from P. bourgaeana neighborhoods; thus, they are more likely to create new tree clusters than boars. The strong tree aggregation is likely to be the result of one or several non-exclusive processes, such as the spatial patterning of seed delivery by dispersers and seedling establishment beneath mother trees. In turn, the distinctive distribution of P. bourgaeana in Doñana appeared to interact with the foraging behavior of its mammalian seed dispersers, leading to neighbourhood-specific dispersal patterns and fruit-removal rates. Our study exemplifies how a detailed description of patterns generates testable hypotheses concerning the ecology of zoochorous. Pyrus bourgaeana dispersers were unique and complementary in their spatial patterning of seed delivery, which likely confers resilience to their overall service and suggests lack of redundancy and expendability of any one species. [source]


    Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

    ECOGRAPHY, Issue 1 2010
    Juan P. González-Varo
    Human-induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant-frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit-rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non-predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit-poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation-tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area. [source]


    Sex, isolation and fidelity: unbiased long-distance dispersal in a terrestrial amphibian

    ECOGRAPHY, Issue 5 2006
    M. Alex Smith
    Amphibians in general are considered poor dispersers and thus their dispersal curve should be dominated by short movements. Additionally, as male toads do not compete for females and sexual selection is by female choice, dispersal should be male-biased. Furthermore, since adults are site-loyal and polygynous, juveniles should move farther and faster than adults. We tested the hypotheses that dispersal would be limited and both sex- and age-biased in a population of Fowler's toads Bufo fowleri at Lake Erie, Ontario, Canada. Based on a mark-recapture study of 2816 toads, 1326 recaptured at least once, we found that although the toads did show high site fidelity, the dispersal curve was highly skewed with a significant "tail" where the maximum distance moved by an adult was 34 km. Dispersal was neither sex-biased nor age-biased despite clear theoretical predictions that dispersal should be biased towards males and juveniles. We conclude that the resource competition hypothesis of sex-biased dispersal does not predict dispersal tendencies as readily for amphibians as for mammals and birds. Toad dispersal only appears to be juvenile-biased because the juveniles are more abundant than the adults, not because they are the more active dispersers. [source]


    The effects of dispersal and recruitment limitation on community structure of odonates in artificial ponds

    ECOGRAPHY, Issue 4 2006
    Shannon J. McCauley
    I examined the effects of isolation on the structure of both adult and larval dragonfly (Odonata: Anisoptera) communities forming at physically identical artificial ponds over two years. Isolation, whether measured by distance to the nearest source habitat or by connectivity to multiple sources, was significantly negatively related to the species richness of dragonflies observed at and collected in these ponds. These results indicate that dispersal and recruitment limitation acted as filters on the richness of communities at these artificial ponds. The richness of larval recruits in artificial ponds was lower than the richness of adult dispersers observed at ponds, and distance from a source habitat explained a greater fraction of the variation in larval than adult richness (83 and 50%, respectively). These results and a male biased sex-ratio in adults observed at artificial ponds suggest that isolated habitats may be more recruitment limited than observations of dispersers would suggest. A Mantel test indicated there was a spatial component to the composition of communities forming in tanks, and that distance between tanks and community dissimilarity (1-Jaccard's) were significantly positively related (r=0.52). This pattern suggests that their position with respect to alternative source environments influenced the composition of the communities that recruited into these ponds. These results provide further evidence of recruitment limitation in this system. Results from this study highlight the importance behaviorally limited dispersal may have in taxa morphologically capable of broad dispersal and suggest that the role of dispersal and recruitment limitation may be critical in shaping community structure across habitat gradients that include variation in habitat duration. [source]


    Variation in mistletoe seed deposition: effects of intra- and interspecific host characteristics

    ECOGRAPHY, Issue 2 2002
    Juliann Eve Aukema
    We investigated differences in host infection by a desert mistletoe, Phoradendron californicum, and examined one of the processes that contributes to these differences: variation in seed deposition among host individuals and species. In the Sonoran Desert, P. californicum parasitizes the sympatric leguminous trees Olneya tesota, Cercidium microphyllum, Prosopis velutina, Acacia constricta, and Acacia greggii. We hypothesized that seed deposition depends on host height and crown architecture. At a site in Arizona, frequency of infection did not reflect host relative abundance. Olneya tesota was parasitized at a higher frequency than expected from its abundance and maintained the highest mistletoe loads per individual host. In contrast, P. velutina was infected less frequently than expected. Infection frequency increased with host tree height for all hosts. Mistletoe seed deposition by avian dispersers differed among host species and was disproportionately high in O. tesota and P. velutina. Seed deposition was higher in infected than in non-infected host trees, and increased with tree height in O. tesota but not in C. microphyllum. We suspect that increased seed deposition with height in O. tesota may be due to the preference of seed-dispersing birds for higher perches. Some host tree species, such as C. microphyllum and A. constricta, probably received fewer mistletoe seeds because birds avoid hosts with dense and spiny crowns. Mistletoe populations are plant metapopulations in which host trees are patches and the frequency of infection in each host species/patch type is the result of interspecific differences in the balance between mistletoe colonization and extinction. From this perspective, our study of host use and seed dispersal is a metapopulation study of patch occupancy and propagule distribution among available patch types. Our seed-dispersal study demonstrates that the mechanisms that create pattern in patchy plant populations can be investigated in mistletoe systems. [source]


    Dung beetles in a Central Amazonian rainforest and their ecological role as secondary seed dispersers

    ECOLOGICAL ENTOMOLOGY, Issue 3 2002
    Ellen Andresen
    Abstract 1. The role of several factors that affect the composition of the dung beetle assemblages in an Amazonian rainforest was quantified, together with the effect of these factors on the role that dung beetles play as secondary seed dispersers. 2. A total of 61 dung beetle species was captured during 3360 h of trapping. During nocturnal trapping periods, more dung beetles, of larger mean size, and more species were captured per trap than during diurnal trapping periods. 3. During the rainy season, more dung beetle species were captured per trap than during the dry season, but the number of individuals and their mean size did not vary between seasons. 4. Bait size had a significant effect on the mean number of beetles and mean number of species but not on mean beetle size. As bait size increased from 5, 10, 25, to 50 g, more beetles and more species were captured per trap. 5. Between 6 and 73% of plastic beads, used as seed mimics, were buried by dung beetles at depths that ranged from 0.5 to 7 cm. Both the proportion of beads buried and burial depth decreased with increasing bead size, and increased with increasing amounts of dung surrounding each bead (5, 10, and 25 g). 6. The proportion of buried seeds for three species varying in size between 5 and 27 mm, increased with increasing dung beetle size, using beetles of seven sizes, varying between 10 and 25 mm. 7. Seeds surrounded by dung were buried more often and more deeply when placed on the forest floor during the late afternoon than when placed during the early morning. Seeds were also buried more often when placed on the forest floor during the rainy season than when placed during the dry season, but season had no effect on burial depth. 8. Forests in Central Amazonia hold a rich dung beetle community that plays an active role in secondary seed dispersal, and consequently in plant regeneration. The interaction between seeds and beetles is complex because it is affected by many factors. [source]


    Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations

    ECOLOGY LETTERS, Issue 3 2009
    Jean Clobert
    Abstract There is accumulating evidence that individuals leave their natal area and select a breeding habitat non-randomly by relying upon information about their natal and future breeding environments. This variation in dispersal is not only based on external information (condition dependence) but also depends upon the internal state of individuals (phenotype dependence). As a consequence, not all dispersers are of the same quality or search for the same habitats. In addition, the individual's state is characterized by morphological, physiological or behavioural attributes that might themselves serve as a cue altering the habitat choice of conspecifics. These combined effects of internal and external information have the potential to generate complex movement patterns and could influence population dynamics and colonization processes. Here, we highlight three particular processes that link condition-dependent dispersal, phenotype-dependent dispersal and habitat choice strategies: (1) the relationship between the cause of departure and the dispersers' phenotype; (2) the relationship between the cause of departure and the settlement behaviour and (3) the concept of informed dispersal, where individuals gather and transfer information before and during their movements through the landscape. We review the empirical evidence for these processes with a special emphasis on vertebrate and arthropod model systems, and present case studies that have quantified the impacts of these processes on spatially structured population dynamics. We also discuss recent literature providing strong evidence that individual variation in dispersal has an important impact on both reinforcement and colonization success and therefore must be taken into account when predicting ecological responses to global warming and habitat fragmentation. [source]


    The silver spoon effect and habitat selection by natal dispersers

    ECOLOGY LETTERS, Issue 11 2006
    Judy A. Stamps
    Abstract The silver spoon effect in the context of habitat selection occurs when dispersers in good condition are more likely to settle in high-quality habitats than dispersers in poor condition. Positive relationships between disperser condition and the quality of post-dispersal habitats are predicted by at least two non-exclusive ultimate hypotheses. The competition hypothesis assumes that a disperser's condition affects its chances of competing for space or joining an established group after arriving at a high-quality habitat, while the search hypothesis assumes that a disperser's condition affects its selectivity, and hence its chances of accepting a lower-quality habitat when it is searching for a new habitat. Thus far, silver spoon effects in the context of habitat selection have been reported in only a handful of species (several birds and marine invertebrates), but this study suggests that they may be relatively common in particular species and situations. [source]


    Population genetics of the European trout (Salmo trutta L.) migration system in the river Rhine: recolonisation by sea trout

    ECOLOGY OF FRESHWATER FISH, Issue 1 2005
    A. Schreiber
    Abstract , Allozyme genetics (34 loci) is studied in up to 1010 European trout (Salmo trutta) from the Rhine, Meuse, Weser, Elbe and Danube river systems in Central Europe. Population samples from single collection sites, chiefly small streams (GCG = 0.2126), rather than the divergence of the trout from Atlantic and Danubian drainages (GSG = 0.0711), contributed to the overall gene diversity of GST = 0.2824. Sea trout (n = 164) and brown trout (n = 767) in Atlantic rivers adhere to the same biogeographical stock, but anadromous trout from the Rhine and the Elbe display more genetic cohesion than resident brown trout from the Rhine system alone. Strayers from the Elbe could have founded the recently re-established sea trout population of the Rhine, after a few decades of absence or precarious rarity. Migrants may even connect the Rhine and Elbe stocks by ongoing gene flow. A release,recapture study confirms that all trout in the Rhine belong to one partly migratory population network: Six of 2400 juvenile sea trout released into a tributary of the Rhine were later recorded as emigrants to the Rhine delta, against three of 1600 released brown trout. One migrant had entered the open North Sea, but the other dispersers were recorded in fresh waters of the Rhine delta (Ijsselmeer, Amstelmeer). Stocking presumably elevated both heterozygosity and fixation indices of brown trout, but this effect is subtle within the range of the Atlantic population group. Improved sea trout management in the Rhine, and modifications to brown trout stocking in the upper Danubian area are recommended. [source]


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

    ETHOLOGY, Issue 9 2003
    Kimberly S. Powers
    Species 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. [source]


    HETEROSIS AND OUTBREEDING DEPRESSION IN DESCENDANTS OF NATURAL IMMIGRANTS TO AN INBRED POPULATION OF SONG SPARROWS (MELOSPIZA MELODIA)

    EVOLUTION, Issue 1 2002
    Amy B. Marr
    Abstract We studied heterosis and outbreeding depression among immigrants and their descendants in a population of song sparrows on Mandarte Island, Canada. Using data spanning 19 generations, we compared survival, seasonal reproductive success, and lifetime reproductive success of immigrants, natives (birds with resident-hatched parents and grandparents), and their offspring (F1s, birds with an immigrant and a native parent, and F2s, birds with an immigrant grandparent and resident-hatched grandparent in each of their maternal and paternal lines). Lifetime reproductive success of immigrants was no worse than that of natives, but other measures of performance differed in several ways. Immigrant females laid later and showed a tendency to lay fewer clutches, but had relatively high success raising offspring per egg produced. The few immigrant males survived well but were less likely to breed than native males of the same age that were alive in the same year. Female F1s laid earlier than expected based on the average for immigrant and native females, and adult male F1s were more likely to breed than expected based on the average for immigrant and native males. The performance differences between immigrant and native females and between F1s and the average of immigrants and natives are consistent with the hypothesis that immigrants were disadvantaged by a lack of site experience and that immigrant offspring benefited from heterosis. However, we could not exclude the possibility that immigrants had a different strategy for optimizing reproductive success or that they experienced ecological compensation for life-history parameters. For example, the offspring of immigrants may have survived well because immigrants laid later and produced fewer clutches, thereby raising offspring during a period of milder climatic conditions. Although sample sizes were small, we found large performance differences between F1s and F2s, which suggested that either heterosis was associated with epistasis in F1s, that F2s experienced outbreeding depression, or that both phenomena occurred. These findings indicate that the performance of dispersers may be affected more by fine-scale genetic differentiation than previously assumed in this and comparable systems. [source]


    A comparative study of the dispersal of 10 species of stream invertebrates

    FRESHWATER BIOLOGY, Issue 9 2003
    J. M. Elliott
    Summary 1. Apart from downstream dispersal through invertebrate drift, few quantitative data are available to model the dispersal of stream invertebrates, i.e. the outward spreading of animals from their point of origin or release. The present study provides comparative data for 10 species, using two independent methods: unmarked animals in six stream channels built over a stony stream and marked animals in the natural stream. Experiments were performed in April and June 1973 and 1974, with initial numbers of each species varying from 20 to 80 in the stream channels and 20 to 60 for marked animals. 2. Results were the same for marked invertebrates and those in the channels. Dispersal was not density-dependent; the number of dispersing animals was a constant proportion of the initial number for each species. The relationship between upstream or downstream dispersal distance and the number of animals travelling that distance was well described by an inverse power function for all species (exponential and log models were poorer fits). Results varied between species but were similar within species for the 4 months, and therefore were unaffected by variations in mean water velocity (range 0.04,0.35 m s,1) or water temperature (range 6.7,8.9 °C in April, 12.1,14.8 °C in June). 3. Species were arranged in order, according to their dispersal abilities. Three carnivores (Perlodes, Rhyacophila, Isoperla) dispersed most rapidly (70,91% in 24 h, maximum distances 9.5,13.5 m per day), followed by two species (Protonemura, Rhithrogena) in which about half their initial numbers dispersed (50,51% in 24 h, 7.5,8 m per day), and four species (Ecdyonurus, Hydropsyche, Gammarus, Baetis) in which less than half dispersed (33,40% in 24 h, 5.5,7 m per day). Dispersal was predominantly upstream for all nine species. Few larvae (20%) of Potamophylax dispersed, with similar maximum upstream and downstream distances of 3.5 m per day. The mean time spent drifting downstream was known for seven species from previous studies, and correlated positively with their dispersal distances. Therefore, the species formed a continuum from rapid to very slow dispersers. These interspecific differences should be considered when evaluating the role of dispersal in the maintenance of genetic diversity in stream invertebrates, and in their ability to colonise or re-colonise habitats. [source]


    Studies in Urban Ecology: the First Wave of Biological Invasion by Pistacia chinensis in Armidale, New South Wales, Australia

    GEOGRAPHICAL RESEARCH, Issue 3 2000
    J. M. B. Smith
    Biological invasions by deliberately introduced organisms seriously compromise the integrity of ecosystems, but their early stages have seldom been documented, especially in urban contexts. Since the 1940s, the small Asian tree Pistacia chinensis has been widely planted in streets and gardens in Armidale, New South Wales, Australia, where it makes a major contribution to the autumn colours that are exploited to promote the city. Numerous wild plants are now becoming established in and near Armidale. This ongoing biological invasion may have been accelerated by the large size of the initial (planted) population, and by the presence of efficient avian seed dispersers. It is now at the stage of the first wild generation reaching reproductive maturity. While it is probably still possible to halt the invasion, various human factors appear to make this an unlikely prospect. [source]


    Does size matter for dispersal distance?

    GLOBAL ECOLOGY, Issue 4 2007
    David G. Jenkins
    ABSTRACT Aim, The aim of this study is to answer the questions: (1) do small organisms disperse farther than large, or vice versa; and (2) does the observed pattern differ for passive and active dispersers? These questions are central to several themes in biogeography (including microbial biogeography), macroecology, metacommunity ecology and conservation biology. Location, The meta-analysis was conducted using published data collected worldwide. Methods, We collected and analysed 795 data values in the peer-reviewed literature for direct observations of both maximal dispersal distance and mass of the dispersing organisms (e.g. seeds, not trees). Analysed taxa ranged in size from bacteria to whales. We applied macroecology analyses based on null models (using Monte Carlo randomizations) to test patterns relative to specific hypotheses. Results, Collected dispersal distance and mass data spanned 9 and 21 orders of magnitude, respectively. Active dispersers dispersed significantly farther (P < 0.001) and were significantly greater in mass (P < 0.001) than passive dispersers. Overall, size matters: larger active dispersers attained greater maximum observed dispersal distances than smaller active dispersers. In contrast, passive-disperser distances were random with respect to propagule mass, but not uniformly random, in part due to sparse data available for tiny propagules. Conclusions, Size is important to maximal dispersal distance for active dispersers, but not for passive dispersers. Claims that microbes disperse widely cannot be tested by current data based on direct observations of dispersal: indirect approaches will need to be applied. Distance,mass relationships should contribute to a resolution of neutral and niche-based metacommunity theories by helping scale expectations for dispersal limitation. Also, distance,mass relationships should inform analyses of latitudinal species richness and conservation biology topics such as fragmentation, umbrella species and taxonomic homogenization. [source]


    Barn Swallows Hirundo rustica disperse seeds of Rooikrans Acacia cyclops, an invasive alien plant in the Fynbos Biome

    IBIS, Issue 3 2007
    LES G. UNDERHILL
    Rooikrans Acacia cyclops is an invasive plant species in the coastal region of South Africa, especially the Fynbos Biome. It is endemic to southwestern Australia. Seeds are bird-dispersed, mostly by frugivores and granivores. We report that at one locality in South Africa, Barn Swallows Hirundo rustica, normally regarded as obligate foragers of aerial arthropods, also consumed the seeds and associated arils of Rooikrans shrubs and trees. The seeds were voided and the arils digested. Three thousand Barn Swallows in the region where this was observed conceivably consumed and voided two million Rooikrans seeds during the 5-month non-breeding period. Barn Swallows are therefore dispersers of Rooikrans seeds. Many of the bird species known to consume Rooikrans seeds are territorial, so that seeds are not dispersed far beyond existing acacia stands. Barn Swallows cover large distances between feeding areas and roosts, and could therefore disperse seeds far from existing stands. This development adds urgency to the need to eradicate Rooikrans from the Fynbos Biome. [source]