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Dispersal Corridors (dispersal + corridor)
Selected AbstractsFish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basinsJOURNAL OF BIOGEOGRAPHY, Issue 9 2008Kirk O. Winemiller Abstract Aim, The aim of this study was to determine whether the Casiquiare River functions as a free dispersal corridor or as a partial barrier (i.e. filter) for the interchange of fish species of the Orinoco and Negro/Amazon basins using species assemblage patterns according to geographical location and environmental features. Location, The Casiquiare, Upper Orinoco and Upper Negro rivers in southern Venezuela, South America. Methods, Our study was based on an analysis of species presence/absence data and environmental information (11 habitat characteristics) collected by the authors and colleagues between the years 1984 and 1999. The data set consisted of 269 sampled sites and 452 fish species (> 50,000 specimens). A wide range of habitat types was included in the samples, and the collection sites were located at various points along the entire length of the Casiquiare main channel, at multiple sites on its tributary streams, as well as at various nearby sites outside the Casiquiare drainage, within the Upper Orinoco and Upper Rio Negro river systems. Most specimens and field data used in this analysis are archived in the Museo de Ciencias Naturales in Guanare, Venezuela. We performed canonical correspondence analysis (CCA) based on species presence/absence using two versions of the data set: one that eliminated sites having < 5 species and species occurring at < 5 sites; and another that eliminated sites having < 10 species and species occurring at < 10 sites. Cluster analysis was performed on sites based on species assemblage similarity, and a separate analysis was performed on species based on CCA loadings. Results, The CCA results for the two versions of the data set were qualitatively the same. The dominant environmental axis contrasted assemblages and sites associated with blackwater vs. clearwater conditions. Longitudinal position on the Casiquiare River was correlated (r2 = 0.33) with CCA axis-1 scores, reflecting clearwater conditions nearer to its origin (bifurcation of the Orinoco) and blackwater conditions nearer to its mouth (junction with the Rio Negro). The second CCA axis was most strongly associated with habitat size and structural complexity. Species associations derived from the unweighted pair-group average clustering method and pair-wise squared Euclidean distances calculated from species loadings on CCA axes 1 and 2 showed seven ecological groupings. Cluster analysis of species assemblages according to watershed revealed a stronger influence of local environmental conditions than of geographical proximity. Main conclusions, Fish assemblage composition is more consistently associated with local environmental conditions than with geographical position within the river drainages. Nonetheless, the results support the hypothesis that the mainstem Casiquiare represents a hydrochemical gradient between clearwaters at its origin and blackwaters at its mouth, and as such appears to function as a semi-permeable barrier (environmental filter) to dispersal and faunal exchanges between the partially vicariant fish faunas of the Upper Orinoco and Upper Negro rivers. [source] On the occurrence of the Asiatic cyprinid Pseudorasbora parva in the NetherlandsJOURNAL OF FISH BIOLOGY, Issue 5 2006B. J. A. Pollux A large scale inventory along the Meuse River (the Netherlands), showed that floodplain lakes function as spawning, nursery and adult habitats, while the main river channel merely serves as a dispersal corridor for adult Pseudorasbora parva, one of the most successful invasive fish species that have colonized Europe. [source] The dispersal and deposition of hydrochorous plant seeds in drainage ditchesFRESHWATER BIOLOGY, Issue 10 2010HESTER SOOMERS Summary 1. Surface water is an important dispersal vector for wetland plant species. However, most previous studies on hydrochory (i.e. water dispersal) have focused on ecosystems with relatively rapid water flow. Therefore, there is a need to study such dispersal in slow-flowing or stagnant waterbodies, such as drainage ditches, which might act as dispersal corridors between habitat patches. 2. To gain insight into the mechanisms by which seeds are transported in drainage ditches, the effect of the velocity of wind and water on the rate of transport of floating seeds of three wetland species (Carex pseudocyperus L., Iris pseudacorus L. and Sparganium erectum L.) was investigated. Furthermore, in release and retrace experiments with painted C. pseudocyperus seeds, a number of factors potentially determining the probability of seed deposition were investigated. 3. Net wind speed was found to be the main factor determining the rate at which seeds are transported in drainage ditches. No relation between water flow at middepth in the ditches and seed transport was found. Wind speed and flow at the water surface were positively related. The effect of wind speed on the rate of transport of floating seeds was greater for S. erectum seeds, because a greater ratio of their volume protrudes from the water, than for C. pseudocyperus and I. pseudacorus seeds. 4. The principal factors that determine seed deposition were aquatic plant cover, ditch slope and indentations in the ditch bank. Seeds changed direction if the wind direction changed, or if there was a bend in the ditch. The final pattern of deposition was related to mean net wind speed. Mean transport distance after 2 days varied between 34 and 451 m. 5. Unlike in rivers, seed transport in ditches was determined by wind speed and direction, enabling multidirectional seed dispersal. We conclude that in slow-flowing waters, wind is a more important driver for hydrochorous seed transport than the flow of water. This sheds a new light on hydrochory and has important consequences for the management of otherwise fragmented wetland remnants. [source] Optimizing dispersal and corridor models using landscape geneticsJOURNAL OF APPLIED ECOLOGY, Issue 4 2007CLINTON W. EPPS Summary 1Better tools are needed to predict population connectivity in complex landscapes. ,Least-cost modelling' is one commonly employed approach in which dispersal costs are assigned to distinct habitat types and the least-costly dispersal paths among habitat patches are calculated using a geographical information system (GIS). Because adequate data on dispersal are usually lacking, dispersal costs are often assigned solely from expert opinion. Spatially explicit, high-resolution genetic data may be used to infer variation in animal movements. We employ such an approach to estimate habitat-specific migration rates and to develop least-cost connectivity models for desert bighorn sheep Ovis canadensis nelsoni. 2Bighorn sheep dispersal is thought to be affected by distance and topography. We incorporated both factors into least-cost GIS models with different parameter values and estimated effective geographical distances among 26 populations. We assessed which model was correlated most strongly with gene flow estimates among those populations, while controlling for the effect of anthropogenic barriers. We used the best-fitting model to (i) determine whether migration rates are higher over sloped terrain than flat terrain; (ii) predict probable movement corridors; (iii) predict which populations are connected by migration; and (iv) investigate how anthropogenic barriers and translocated populations have affected landscape connectivity. 3Migration models were correlated most strongly with migration when areas of at least 10% slope had 1/10th the cost of areas of lower slope; thus, gene flow occurred over longer distances when ,escape terrain' was available. Optimal parameter values were consistent across two measures of gene flow and three methods for defining population polygons. 4Anthropogenic barriers disrupted numerous corridors predicted to be high-use dispersal routes, indicating priority areas for mitigation. However, population translocations have restored high-use dispersal routes in several other areas. Known intermountain movements of bighorn sheep were largely consistent with predicted corridors. 5Synthesis and applications. Population genetic data provided sufficient resolution to infer how landscape features influenced the behaviour of dispersing desert bighorn sheep. Anthropogenic barriers that block high-use dispersal corridors should be mitigated, but population translocations may help maintain connectivity. We conclude that developing least-cost models from similar empirical data could significantly improve the utility of these tools. [source] Phylogeography of sexual Heteronotia binoei (Gekkonidae) in the Australian arid zone: climatic cycling and repetitive hybridizationMOLECULAR ECOLOGY, Issue 9 2005JARED L. STRASBURG Abstract The biota of much of continental Australia have evolved within the context of gradual aridification of the region over several million years, and more recently of climatic cycling between relatively dry and humid conditions. We performed a phylogeographical study of three sexual chromosome races of the Heteronotia binoei complex of geckos found throughout the Australian arid zone. Two of these three races were involved in two separate hybridization events leading to parthenogenetic lineages (also H. binoei), and the third is widespread and broadly sympatric with the parthenogens. Based on our analyses, the three sexual races diversified approximately 6 million years ago in eastern Australia, during a period of aridification, then each moved west through northern, southern, and central dispersal corridors to occupy their current ranges. In each case, the timing of major phylogeographical inferences corresponds to inferred palaeoclimatic changes in continental Australia. This scenario provides a simple explanation for diversification, secondary contact, and hybridization between the races. However, data presented elsewhere indicate that formation of the parthenogens was considerably more recent than the westward expansion of the hybridizing races, and that multiple hybridization events were geographically and temporally distinct. We suggest that cyclical climate changes may have led to regional range changes that facilitated hybridization between the races, which are not currently known to be in sympatry. [source] | ||||||||||