Gene flow of common ash (<em>Fraxinus excelsior</em> L.) in a fragmented landscape

Gene flow dynamics of common ash (Fraxinus excelsior L.) is affected by several human activities in Central Europe, including habitat fragmentation, agroforestry expansion, controlled and uncontrolled transfer of reproductive material, and a recently introduced emerging infectious disease, ash dieback, caused by Hymenoscyphus fraxineus. Habitat fragmentation may alter genetic connectivity and effective population size, leading to loss of genetic diversity and increased inbreeding in ash populations. Gene flow from cultivated trees in landscapes close to their native counterparts may also influence the adaptability of future generations. The devastating effects of ash dieback have already been observed in both natural and managed populations in continental Europe. However, potential long-term effects of genetic bottlenecks depend on gene flow across fragmented landscapes. For this reason, we studied the genetic connectivity of ash trees in an isolated forest patch of a fragmented landscape in Rösenbeck, Germany. We applied two approaches to parentage analysis to estimate gene flow patterns at the study site. We specifically investigated the presence of background pollination at the landscape level and the degree of genetic isolation between native and cultivated trees. Local meteorological data was utilized to understand the effect of wind on the pollen and seed dispersal patterns. Gender information of the adult trees was considered for calculating the dispersal distances. We found that the majority of the studied seeds (55-64%) and seedlings (75-98%) in the forest patch were fathered and mothered by the trees within the same patch. However, we determined a considerable amount of pollen flow (26-45%) from outside of the study site, representing background pollination at the landscape level. Limited pollen flow was observed from neighbouring cultivated trees (2%). Both pollen and seeds were dispersed in all directions in accordance with the local wind directions. Whereas there was no positive correlation between pollen dispersal distance and wind speed, the correlation between seed dispersal distance and wind speed was significant (0.71, p < 0.001), indicating that strong wind favours long-distance dispersal of ash seeds. Finally, we discussed the implications of establishing gene conservation stands and the use of enrichment planting in the face of ash dieback

Modeling the ecology and evolution of biodiversity: Biogeographical cradles, museums, and graves

Individual processes shaping geographical patterns of biodiversity are increasingly understood, but their complex interactions on broad spatial and temporal scales remain beyond the reach of analytical models and traditional experiments. To meet this challenge, we built a spatially explicit, mechanistic simulation model implementing adaptation, range shifts, fragmentation, speciation, dispersal, competition, and extinction, driven by modeled climates of the past 800,000 years in South America. Experimental topographic smoothing confirmed the impact of climate heterogeneity on diversification. The simulations identified regions and episodes of speciation (cradles), persistence (museums), and extinction (graves). Although the simulations had no target pattern and were not parameterized with empirical data, emerging richness maps closely resembled contemporary maps for major taxa, confirming powerful roles for evolution and diversification driven by topography and climate

Spatial genetic pattern in an economically beneficial insect, the cyclical African wild silk moth (Gonometa postica)

The African wild silk moth (Gonometa postica) exhibits large inter-annual population size fluctuations in the Kalahari region of southern Africa. Spent cocoons from this species are currently being utilized in a local silk industry. An understanding of the recolonization dynamics of a particular harvested site, and of the population genetic effects of such dispersal, are crucial for designing a scientifically-based harvesting strategy. I link morphological estimates of flying ability to microsatellite genotyping in the determination of dispersal ability of this species. Morphological results suggest that the moth is a poor disperser with high wing loadings and males are better fliers than females. There is a significant effect of isolation-by-distance. Spatial population genetic analyses of microsatellite data further indicate lower and upper bounds on dispersal of 90 m and 50 km. The combined evidence suggests male-biased dispersal over several dozen kilometers with females that do not disperse over large distances. I discuss the potential influences of large population size fluctuations on patterns of genetic diversity and the implications for the inference of dispersal in my study species.The Mellon Foundation Grant to the Ph.D. project of W. Delport, and by a National Research Foundation grant.http://africanzoology.journals.ac.za/2015-04-30am2014ab201

Spatial association between a spider wasp and its host in fragmented dune habitats

Volume: 33Start Page: 222End Page: 22

Multi-scale processes in metapopulations : Contributions of stage structure, rescue effect, and correlated extinctions

Peer reviewedPublisher PD

Eco-evolutionary dynamics in fragmented landscapes

Peer reviewedPostprin

A complex speciation-richness relationship in a simple neutral model

Speciation is the "elephant in the room" of community ecology. As the ultimate source of biodiversity, its integration in ecology's theoretical corpus is necessary to understand community assembly. Yet, speciation is often completely ignored or stripped of its spatial dimension. Recent approaches based on network theory have allowed ecologists to effectively model complex landscapes. In this study, we use this framework to model allopatric and parapatric speciation in networks of communities and focus on the relationship between speciation, richness, and the spatial structure of communities. We find a strong opposition between speciation and local richness, with speciation being more common in isolated communities and local richness being higher in more connected communities. Unlike previous models, we also find a transition to a positive relationship between speciation and local richness when dispersal is low and the number of communities is small. Also, we use several measures of centrality to characterize the effect of network structure on diversity. The degree, the simplest measure of centrality, is found to be the best predictor of local richness and speciation, although it loses some of its predictive power as connectivity grows. Our framework shows how a simple neutral model can be combined with network theory to reveal complex relationships between speciation, richness, and the spatial organization of populations.Comment: 9 pages, 5 figures, 1 table, 50 reference

Gene-flow between populations of cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) is highly variable between years

Both large and small scale migrations of Helicoverpa armigera Hübner in Australia were investigated using AMOVA analysis and genetic assignment tests. Five microsatellite loci were screened across 3142 individuals from 16 localities in eight major cotton and grain growing regions within Australia, over a 38-month period (November 1999 to January 2003). From November 1999 to March 2001 relatively low levels of migration were characterized between growing regions. Substantially higher than average gene-flow rates and limited differentiation between cropping regions characterized the period from April 2001 to March 2002. A reduced migration rate in the year from April 2002 to March 2003 resulted in significant genetic structuring between cropping regions. This differentiation was established within two or three generations. Genetic drift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Helicoverpa armigera in Australia demonstrated isolation by distance, so immigration into cropping regions is more likely to come from nearby regions than from afar. This effect was most pronounced in years with limited migration. However, there is evidence of long distance dispersal events in periods of high migration (April 2001–March 2002). The implications of highly variable migration patterns for resistance management are considered.K.D. Scott, K.S. Wilkinson, N. Lawrence, C.L. Lange, L.J. Scott, M.A. Merritt, A.J. Lowe and G.C Graha

Community dynamics of insular biotas in space and time

The various features determining species distributions remain enigmatic in ecology. This thesis deals with the spatial and temporal dynamics of land birds on the islands of the Dahlak archipelago, the Red Sea, and of mammals, birds and reptiles among the forest fragments of the archipelago-like east African coastal forest. The bird species richness on the islands of the Dahlak archipelago depended on area, isolation and extent of habitat. Similarly, species richness of the east African forest fragments was related to area, habitat diversity and isolation but the importance of each factor varied among taxa as well as among generalists and specialists. For example, area influenced species richness of most categories except specialist mammals and reptiles, habitat diversity was more important for forest specialists than generalists, and isolation was important only for birds. In both study areas, similarity in bird species composition decreased with increasing distances among isolates suggesting that dispersal from source pools and among isolates facilitate re-colonization. The nested community structure, i.e. species composition of species−poor communities are a subset of species−rich communities, of birds in the Dahlak archipelago depended on area and the distribution of a few habitats. Similarities in community patterns and cooccurrence patterns, at both community and species levels, were mainly related to habitat preferences and corresponding distributions of habitats as well as inter-island distances. Also, the distributional patterns suggest that predator-prey interactions can be a determinant of the spatial distribution of, at least, the prey. There was no evidence of competitive exclusion. The nested structure on the islands of the Dahlak archipelago remained fairly stable over a period of 35 years even in this arid region. The turnover dynamics were broadly predictable from the nested pattern but not always consistent with other expectations from nested community structure. Taken together my results show that mechanisms on varying spatial and temporal scales act on species distributions, and that the influence may vary among taxa mainly depending on dispersal ability. In the case of conservation, comprehensive strategies accounting for these variations are needed