Effective Long-distance Dispersal Research Articles

Off-host survival of Eriophyoidea and remarks on their dispersal modes.

Dispersal of eriophyoid mites is crucial for the successful colonization of new plants. Literature suggests that their long-distance dispersal is through aerial transfer. During dispersal, eriophyoids might be captured in vapor or fine drops of water (perhaps most likely in clouds) where they might be protected against water loss and desiccation, but where they would have no food and be exposed to low temperatures and oxygen concentrations. Considerable resistance of these mites to these stressful environmental conditions is expected and has only partly been confirmed experimentally. The aim of the bioassays conducted here was to assess the survival of five eriophyoid species off their host plants, with poor oxygen availability under two temperature regimes. The bioassays were carried out on live mites dipped into two media used as microenvironments: (1) vaseline oil (used also as control treatment), and (2) water solution of Tween 80 (0.2%) and cycloheximide (50mg/l). The bioassays were performed at 5 ± 1and 25 ± 1°C. The survival of mites was assessed weekly (5°C) or daily (25°C) by counting live and active specimens. The following species were subjected to the bioassays: Aceria caulobia (a stem gall mite), Aceria ficus (a vagrant mite), Cecidophyopsis hendersoni (a vagrant mite), Colomerus vitis (protogyne/male population and deutogyne morphs; a leaf gall mite) and Phytoptus avellanae (a bud gall mite). The survival rate of the mites was higher at 5°C than at 25°C under both experimental conditions. At 5°C, the survival of almost all species was higher in the water solution (up to 6-7weeks) than in vaseline oil (3-5weeks). Longer survival was found for A. caulobia and P. avellanae (gall-making species) than for C. hendersoni and A. ficus (vagrant species). As expected, the deutogynes of C. vitis survived longer than its protogynes. The current results suggest that individuals of some of the tested species are well suited for withstanding cold, starvation and low oxygen rates, which could be found at higher atmospheric layers, within the clouds, allowing them an effective long-distance dispersal.

Global grass (Poaceae) success underpinned by traits facilitating colonization, persistence and habitat transformation.

Poaceae (the grasses) is arguably the most successful plant family, in terms of its global occurrence in (almost) all ecosystems with angiosperms, its ecological dominance in many ecosystems, and high species richness. We suggest that the success of grasses is best understood in context of their capacity to colonize, persist, and transform environments (the "Viking syndrome"). This results from combining effective long-distance dispersal, efficacious establishment biology, ecological flexibility, resilience to disturbance and the capacity to modify environments by changing the nature of fire and mammalian herbivory. We identify a diverse set of functional traits linked to dispersal, establishment and competitive abilities. Enhanced long-distance dispersal is determined by anemochory, epizoochory and endozoochory and is facilitated via the spikelet (and especially the awned lemma) which functions as the dispersal unit. Establishment success could be a consequence of the precocious embryo and large starch reserves, which may underpin the extremely short generation times in grasses. Post-establishment genetic bottlenecks may be mitigated by wind pollination and the widespread occurrence of polyploidy, in combination with gametic self-incompatibility. The ecological competitiveness of grasses is corroborated by their dominance across the range of environmental extremes tolerated by angiosperms, facilitated by both C3 and C4 photosynthesis, well-developed frost tolerance in several clades, and a sympodial growth form that enabled the evolution of both annual and long-lived life forms. Finally, absence of investment in wood (except in bamboos), and the presence of persistent buds at or below ground level, provides tolerance of repeated defoliation (whether by fire, frost, drought or herbivores). Biotic modification of environments via feedbacks with herbivory or fire reinforce grass dominance leading to open ecosystems. Grasses can be both palatable and productive, fostering high biomass and diversity of mammalian herbivores. Many grasses have a suite of architectural and functional traits that facilitate frequent fire, including a tufted growth form, and tannin-like substances in leaves which slow decomposition. We mapped these traits over the phylogeny of the Poales, spanning the grasses and their relatives, and demonstrated the accumulation of traits since monocots originated in the mid-Cretaceous. Although the sympodial growth form is a monocot trait, tillering resulting in the tufted growth form most likely evolved within the grasses. Similarly, although an ovary apparently constructed of a single carpel evolved in the most recent grass ancestor, spikelets and the awned lemma dispersal units evolved within the grasses. Frost tolerance and C4 photosynthesis evolved relatively late (late Palaeogene), and the last significant trait to evolve was probably the production of tannins, associated with pyrophytic savannas. This fits palaeobotanical data, suggesting several phases in the grass success story: from a late Cretaceous origin, to occasional tropical grassland patches in the later Palaeogene, to extensive C3 grassy woodlands in the early-middle Miocene, to the dramatic expansion of the tropical C4 grass savannas and grasslands in the Pliocene, and the C3 steppe grasslands during the Pleistocene glacial periods. Modern grasslands depend heavily on strongly seasonal climates, making them sensitive to climate change.

Relatedness and other finescale population genetic analyses in the threatened eastern box turtle (Terrapene c. carolina) suggest unexpectedly high vagility with important conservation implications

Genetic analyses of populations are essential to the conservation of threatened and cryptic taxa such as Chelonians. Turtles and tortoises are among the most imperiled vertebrate taxa worldwide, yet many of the natural history traits remain unknown leaving management decisions ill- or improperly informed. The eastern box turtle Terrapene c. carolina is no exception, with many gaps in our knowledge about traits such as juvenile dispersal and patterns of relatedness across the landscape, especially as it is a species not particularly tied to water and vulnerable to human disturbance. In addition, all long-term studies of this species have documented demographic population declines, even in protected habitats. In this study we explore finescale population structuring, gene flow, dispersal, and relatedness at four sites across the species range. These sites vary in habitat fragmentation and surrounding habitat quality. Many radiotelemtery and mark-recapture studies suggest that Terrapene spp. have a sedentary natural history, with small and temporally conserved home ranges and little propensity for dispersal. Based on these data we predicted that populations would be highly structured at fine geographic scales, closely related individuals (1st- and 2nd-degree relatives) would coexist in close proximity, and individuals exhibiting transient behavior would be true transients. All sites had low levels of population structuring, mean pairwise relatedness values were statistically zero, over 90 % of pairs of individuals were unrelated, 4.4–8.7 % were half-siblings, and fewer than 1.0 % were full siblings or parent-offspring pairs. These patterns were consistent across all four sites, regardless of habitat fragmentation. Furthermore, while some related pairs were found within a few meters of each other, others ranged up to 33 km apart. We found that one of two individuals with transient behavior was indeed a true genetic transient. These findings suggest that box turtles may be much more vagile than current management practices recognize. As most turtle species are strongly affected by anthropogenic disturbance, many may require much larger contiguous blocks of intact habitat for species persistence as the box turtle likely does. Management plans may therefore need to be updated to allow for safe and effective long-distance dispersal at the appropriate spatial scales in order to maintain genetic health of these species.

High levels of effective long-distance dispersal may blur ecotypic divergence in a rare terrestrial orchid.

BackgroundGene flow and adaptive divergence are key aspects of metapopulation dynamics and ecological speciation. Long-distance dispersal is hard to detect and few studies estimate dispersal in combination with adaptive divergence. The aim of this study was to investigate effective long-distance dispersal and adaptive divergence in the fen orchid (Liparis loeselii (L.) Rich.). We used amplified fragment length polymorphism (AFLP)-based assignment tests to quantify effective long-distance dispersal at two different regions in Northwest Europe. In addition, genomic divergence between fen orchid populations occupying two distinguishable habitats, wet dune slacks and alkaline fens, was investigated by a genome scan approach at different spatial scales (continental, landscape and regional) and based on 451 AFLP loci.ResultsWe expected that different habitats would contribute to strong divergence and restricted gene flow resulting in isolation-by-adaptation. Instead, we found remarkably high levels of effective long-distance seed dispersal and low levels of adaptive divergence. At least 15% of the assigned individuals likely originated from among-population dispersal events with dispersal distances up to 220 km. Six (1.3%) ‘outlier’ loci, potentially reflecting local adaptation to habitat-type, were identified with high statistical support. Of these, only one (0.22%) was a replicated outlier in multiple independent dune-fen population comparisons and thus possibly reflecting truly parallel divergence. Signals of adaptation in response to habitat type were most evident at the scale of individual populations.ConclusionsThe findings of this study suggest that the homogenizing effect of effective long-distance seed dispersal may overwhelm divergent selection associated to habitat type in fen orchids in Northwest Europe.

Alpine flora may depend on declining frugivorous parrot for seed dispersal

Globally, bird numbers are declining, with potentially serious flow-on effects on ecosystem processes, such as seed dispersal mutualisms. However, management to maintain seed dispersal may be inappropriate if unexpected animals are the most important dispersers. Numbers of the world’s only alpine parrot, the New Zealand kea (Nestor notabilis), have declined drastically over the last 120years after an intense period of official persecution. Today <5000kea remain in the wild. Previously it has been assumed that like other parrots, kea would destroy most of the seeds they eat, thereby contributing little to seed dispersal. The New Zealand alpine flora is rich in fleshy-fruited species yet has a limited disperser fauna. Consequently, we investigated the relevance of kea as a seed disperser in New Zealand’s alpine ecosystems. Field-based foraging observations coupled with faecal analyses showed kea were by far the most important extant alpine avian frugivore. Kea selected more fruiting species (21 vs. 17species), consumed more fruit, and dispersed more seeds (8137 vs. 795) than all other birds combined. Rates of seed predation by kea were extremely low, and evident in only 25% of species eaten. Kea are the only species that make frequent long-distance flights within and between mountain ranges. Hence, much of the effective long-distance dispersal of the alpine flora may be currently performed by kea. Conservation of kea is therefore important both for ensuring the survival of the species and for their role in seed-dispersal mutualisms for which there are few extant substitutes.

Genetic Structure of Two Protist Species (Myxogastria, Amoebozoa) Suggests Asexual Reproduction in Sexual Amoebae

Plasmodial slime molds (Myxogastria or Myxomycetes) are common and widespread unicellular organisms that are commonly assumed to have a sexual life cycle culminating with the formation of often macroscopic fruiting bodies that efficiently disseminate spores. However, laboratory studies based on mating compatibility revealed the coexistence of asexual as well as sexual strains. To test this hypothesis in natural populations, we investigated the genetic variability of two species of the genus Lamproderma. Detailed ecological relevés were carried out in 2007 and 2009 in several deep ravines in the Elbsandsteingebirge (Saxony, south-eastern Germany). Morphological characters of 93 specimens of Lamproderma were recorded and genetic analyses, based on the small subunit ribosomal gene, the internal transcribed spacer 1 and partial elongation factor 1α sequences were carried out for 52 specimens. Genetic analyses showed the existence of two major clades, each composed of several discrete lineages. Most of these lineages were composed of several identical sequences (SSU, ITS 1 and EF-1α) which is explained best by an asexual mode of reproduction. Detrended Correspondence Analysis of morphological characters revealed two morphospecies that corresponded to the two major clades, except for one genotype (Lc6), thus challenging the morphospecies concept. Genetic patterns were not related to the geographical distribution: specimens belonging to the same genotype were found in distinct ravines, suggesting effective long-distance dispersal via spores, except for the Lc6 genotype which was found only in one ravine. Implications for the morphological and biological species concept are discussed.

Migration potential as a new predictor of long-distance dispersal rate for plants

AbstractHow biotic and abiotic factors interact to shape the overall pattern of dispersal of propagules is critical in understanding the evolution of dispersal mechanisms as well as predicting dispersal rates between patchily-distributed habitats. But which plant traits, demographic and/or habitat factors best predict the capacity for dispersal? We introduce the concept of migration potential (v), a readily interpretable parameter that combines recruitment efficiency (recruits per adult / seeds per adult per dispersal cycle) with level of habitat occupancy for predicting effective long-distance dispersal (LDD) of seeds. Using our empirical (genotype assignment) estimates of LDD and statistics on life-history traits and demographic features for contrasting co-occurring shrub species as a test case, and comparing alternative plant traits, we demonstrate that rate of LDD is best described as a simple function of v. As the direct consequence of life-history and demographic traits in a specific environmental context, v has the potential to predict LDD rates in both stable and changing ecosystems

Dynamic expansion in recently introduced populations of fire ant parasitoids (Diptera: Phoridae)

Combating invasive species requires a detailed, mechanistic understanding of the manner and speed with which organisms expand their ranges. Biological control efforts provide an opportunity to study the process of species invasions and range expansions under known initial conditions. This study examines the rate, pattern and mechanisms of spread for two populations of the biological control agent Pseudacteon tricuspis, phorid-fly parasitoids of imported fire ants. We employ a trap-based survey method that detects phorid flies in low-density populations, and provides data on abundance. This technique allows us to differentiate between continuous population spread and effective long-distance dispersal and to examine density gradients of phorid flies across the expanding population front. We find that occupied sites in front of the leading edge of continuous populations were common; forming small populations we refer to as satellite populations. Satellite populations are tens of kilometers from the nearest possible source. Wind governs the dynamics of spread in these two central Texas populations. Population edges expanding with the wind exhibited a higher frequency of effective long-distance dispersal than did populations expanding into the wind. This enhanced effective long-distance dispersal rate translated into a five times faster rate of spread for population edges traveling with the wind. This planned invasion shares many characteristics in common with unplanned species invasions including: protracted establishment phase during which densities were below detection thresholds, and slow initial spread immediately after establishment followed by rapid, accelerating spread rates as population sizes grew.

An Attempt to Predict Which Amazonian Tree Species May be Threatened by Logging Activities

The impacts of logging on Amazonian ecosystems has been the focus of considerable attention both within and outside of Amazonia. However, the impacts of logging on individual timber species has not been at all adequately investigated. Logging affects timber species by: (1) removing mature individuals that are important sources of seeds; (2) damaging seedlings and saplings (i.e future generations of canopy adults); and (3) creating conditions that favour fire by opening the canopy and leaving slash as fuel on the forest floor.In this study we summarize information on the ecological characteristics of 305 timber species in Brazilian Amazonia. We identify seven ecological parameters that are useful in evaluating a species' ability to resist the negative impacts of logging. These characteristics are: (1) effective long-distance dispersal ability; (2) abundance of saplings in forest regeneration; (3) rapid growth; (4) ability to resprout; (5) capacity to withstand fire; (6) broad geographic distribution; and (7) high density of adults. We hypothesize thai species with characteristics opposed to these parameters and subjected to intense logging pressure will have difficulty in maintaining their populations in logging regions.We use a simple scoring system to rank species with regard to their hypothesized ability to withstand logging impacts. Among the species that are potentially susceptible to logging impacts are Euxylophora paraensis (‘Pau Amarelo’) and Swietenia macrophylla (American Mahogany). The sawn lumber from these two species goes principally to European and North American buyers, revealing a direct link between First World consumption and possible biodiversity impoverishment in the Brazilian rain-forest. These two species, and others that might experience population reductions as a result of logging, merit special study.