Large-scale Geographic Patterns Research Articles

Effects of pollination distance on reproduction and offspring performance in Hypochoeris radicata: Experiments with plants from three European regions

Fragmentation of habitats has resulted in increased inbreeding for many plant species, while the introduction of foreign seed material for ecological restoration has resulted in crosses between plants from distant populations. Both processes may reduce plant fitness and increase the risk of extinction. Variation in the expression of inbreeding and outbreeding depression has been found among different genotypes and among populations, but little is known about large scale geographical patterns within species. We studied the effects of cross-proximity on seed production and offspring performance in the perennial meadow plant Hypochoeris radicata (Asteraceae) from five populations in each of three European regions (Bohemia in northwest Czechia, Northern Hesse in central Germany, and Salland in the central Netherlands). Five artificial cross types were conducted with varying proximity of mates: selfing (self), within family crosses (WF), within population crosses (WP), between population crosses (BP), and between region crosses (BR), and the offspring were grown in a common garden. Independent of the region of origin of the maternal plant, selfing, WF and BP crosses resulted in lower seed set and germination than WP crosses, indicating partial self-incompatibility, inbreeding depression and reduced performance in the F1 progeny resulting from outbreeding. However, crosses between regions resulted in similar seed set and germination as within population crosses. For late traits, the effects of inbreeding and interpopulation crosses differed among regions. WP crosses exhibited the highest survival, flowering and multiplicative fitness only in progeny from Czech maternal plants. Our results suggest that the sensitivity of populations to introgression may vary among regions and that outbreeding depression does not necessarily increase with interpopulation distance. However, the current study investigated only effects in the F1 in a common garden and outbreeding depression may be stronger in the F2 and in field populations.

Small- to large-scale geographical patterns within the macrobenthic Abra alba community

The Abra alba community is widely spread in the coastal zone of the English Channel and the Southern Bight of the North Sea. The community is located on shallow, fine muddy sands. Its spatial distribution can be broken up into a number of isolated patches (Atlantic French, British and German coast) and one large continuous distribution area (northern France up to the Netherlands). The aim of this study is to investigate the geographical patterns within the macrobenthic A. alba community at different scales: the community's full distribution range (i.e. large scale) and a selected area with a continuous distribution of the A. alba community (i.e. small scale) in relation to structuring environmental variables. Therefore, an analysis of newly collected samples along the Belgian coastal zone was combined with available information on the A. alba community throughout its distribution range. Although the community structure shows a high similarity across the full distribution range of the A. alba community, large- as well as small-scale changes in community composition were observed: the Belgian Continental Shelf (BCS) should be considered as a major transition from the rich southern to the relatively poorer northern distribution area of the A. alba community. At a large scale (i.e. full distribution range), the differences in community structure are expected to result from (1) the specific hydrodynamic conditions in the English Channel (Atlantic ocean waters) and the Southern Bight of the North Sea, with a consequent differential connectivity between the different areas and (2) the climatological and related faunal shift from temperate (English Channel) to boreal conditions (German Bight). At a small scale (i.e. within the continuous distribution area), structural and functional community aspects may result from geographic differences in (1) detrital food availability, related to riverine input and pelagic productivity, along and across the coastline and (2) the amount of suspended matter, impoverishing the A. alba community when excessively available.

Large-scale geographic patterns of genetic variation in Melica nutans , a widespread Eurasian woodland grass

The geographic distribution of allozyme variation within the Eurasian boreo-nemoreal woodland grass Melica nutans L. has been investigated together with a minor subset of other Melica species. Twenty alleles were found at nine polymorphic loci in M. nutans. Allelic richness was highest in areas central in the species' European distribution, i.e. in southern Fennoscandia. High population densities, reducing the effects of genetic drift, as well as accumulation of variation through long-distance gene-flow from different marginal populations, is proposed to explain high allelic richness in this area. Several alleles showed geographic patterns in distribution and frequency variation. However, these patterns were not congruent, e.g. some alleles appear to have migrated to northern Europe from the south-west whereas others may have spread from the east. Genetic distances between geographic regions, each consisting of 2–6 populations, were generally low between all Fennoscandian, Russian and Siberian regions, but much higher between western and continental European regions. On the population level, cluster analysis grouped populations from Siberia, Russia, coastal and lowland areas in Fennoscandia and British Cumbria into one subcluster whereas other subclusters contained mainly south-west European populations or populations from almost throughout the distribution range. A scenario with several independent glacial refugia in central Europe, south-western Siberia and possibly western Norway, and subsequent colonisation of Fennoscandia mainly from the east, but with some long-distance gene-flow from central Europe, is proposed.

Canal construction destroys the barrier between major European invasion lineages of the zebra mussel.

Since the mid-1980s the zebra mussel, Dreissena polymorpha, Pallas 1771, has become the protagonist of a spectacular freshwater invasion in North America due to its large economic and biological impact. Several genetic studies on American populations have failed to detect any large-scale geographical patterns. In western Europe, where D. polymorpha has been a classical invader from the Pontocaspian since the early 19th century, the situation is strikingly different. Here, we show with genetic markers that two major western European invasion lineages with lowered genetic variability within and among populations can be discriminated. These two invasion lineages correspond with two separate navigable waterways to western Europe. We found a rapid and asymmetrical genetic interchange of the two invasion lines after the construction of the Main-Danube canal in 1992, which interconnected the two waterways across the main watershed.

Variation in Growth of Nestling Tree Swallows Across Multiple Temporal and Spatial Scales

AbstractDifferences within a species in rates of growth of nestlings can be used as indicators of the quality of parental care, environmental conditions, and future success of offspring, whereas comparisons among different species may reflect a history of different ecological conditions or life-history strategies. The presesnt study examines the patterns of variation in growth in nestling Tree Swallows (Tachycineta bicolor) from across the species' range and compares Tree Swallows to other species. Growth of Tree Swallows was typical of other species in the family Hirundinidae. As a family, the Hirundinidae have slower growth than typical for passerines. Growth rate of species of Hirundinidae was not correlated with adult body mass or average brood size. Contrary to predictions, species that are double-brooded did not have higher growth rates, but swallow species living at higher latitudes did have higher growth rates than tropical species. Substantial variation in growth rates was observed among populations of Tree Swallows, yet the amount of variation observed between breeding colonies only a few kilometers apart, or from the same colony in different years, was as great as that seen in populations separated by hundreds of kilometers. Within a population, differences in growth among years were correlated with temperature and food supply when nestlings were being raised. No correlation between climate and growth was seen when comparing different populations. Differences between populations were not explained by local habitat, nor were large-scale geographic patterns evident. I used both experimental and observational evidence to evaluate the implications of short-term reduction in growth for subsequent growth and survival. Nestlings were slow to recover from even very short periods of delayed growth that occur early in the nestling phase. Return of nestlings with experimentally or naturally induced delayed growth was reduced, which suggests that short interruptions in growth may have long term effects on postfledging survival, even though mass at fledging is not affected.

Spatial patterns of diversity in the sea: bryozoan species richness in the North Atlantic.

1. We have examined large-scale geographical patterns in species richness for continental shelf bryozoan assemblages in the North Atlantic. Bryozoans are common and often abundant benthic organisms, but they have not previously been examined at this scale of resolution. 2. Assemblage species richness was estimated by sample species richness. This was highest at intermediate depths (10-75 m) at all latitudes where there were sufficient data, but there was no statistically significant variation with depth for the overall data set (all latitudes pooled). Mean assemblage species richness showed no significant variation with latitude, although the highest individual values were generally from lower latitudes. There is thus as yet no convincing evidence for a latitudinal cline in the alpha diversity of North Atlantic bryozoans. 3. Pooling of data into bins of 10 degrees of latitude, or into biogeographic provinces, to estimate regional species richness revealed significant undersampling. Two independent techniques to correct for this undersampling revealed a latitudinal cline in the regional species richness of North Atlantic bryozoans, with a peak around 10-30°N, and a steady decrease in richness north to 80°N. 4. Two measures of beta diversity (Whittaker and Jaccard) revealed relatively high turnover, presumably related to habitat heterogeneity within regional bins or to significant environmental variation across bins. There was a tendency for beta diversity to be higher at lower latitudes, as would be expected from a combination of a latitudinal cline in regional diversity with a mean assemblage species richness invariant with latitude. Null models were used to clarify the expected relationship between the two measures of beta diversity, and these indicated a strong influence of species-abundance structure in the North Atlantic bryozoan data.

The relationship between electrical conductivity and selected macroinvertebrate communities in four river systems of south-west Victoria, Australia

In order to relate macroinvertebrate fauna to electrical conductivity (EC), a survey of selected orders of macroinvertebrates was conducted in the Glenelg, Hopkins, Merri and Barwon River Catchments in south-west Victoria, Australia. The survey consisted of sampling 21 paired sites at confluences of streams. There was little difference between the in-stream habitat but there was a range of differences in EC between each of the paired sites. The dissim- ilarity of macroinvertebrate fauna between the paired sites was compared to the proportional difference in EC and other water quality variables (dissolved oxygen, water temperature, pH, NO2-N, NO3-N, PO4 and turbidity). This allowed the elimination of EC being confounded with geographical scale parameters and took into account other water quality parameters that may be confounded with EC. A positive relationship was found between the dissimilarity of the fauna at each of the two paired sites and the proportional difference in EC. No such relationship was found for any other measured water quality variable. The results of this survey show that macroinvertebrate community structure is associated with EC of the river systems investigated after eliminating large scale geographical patterns, in-stream habitat and the measured water quality parameters.

Mark-release-recapture experiments with Anopheles gambiae s.l. in Banambani Village, Mali, to determine population size and structure.

Mark-release-recapture experiments with Anopheles gambiae s.l. were performed during the wet seasons of 1993 and 1994 in Banambani, Mali. All recaptured mosquitoes were identified to species by PCR analysis and, when possible, by chromosomal analysis to chromosomal form. Two species of the An. gambiae complex were present: An. gambiae s.s. and An. arabiensis; their ratio differed greatly from one year to the next. Three chromosomal forms of An. gambiae s.s. were found--Bamako, Savanna and Mopti. The drier 1993 was characterized by a high frequency of An. arabiensis and of the Mopti chromosomal forms of An. gambiae s.s. These trends were consistent with large-scale geographical patterns of abundance along a precipitation gradient. We observed no difference in dispersal between the two species, nor among the chromosomal forms of An. gambiae s.s. Therefore, in this situation at least, it is reasonable to group such data on the An. gambiae complex as a whole for analysis. Population size of An. gambiae s.l. females in the village was estimated to be 9000-11,000 in 1993 and 28,000 in 1994. The corresponding numbers were somewhat higher when independently-derived values of daily survival were used. These were consistent with estimates of effective population size obtained from patterns of gene frequency change.

Spatial Autocorrelation and Assessment of Habitat–Abundance Relationships in Littoral Zone Fish

Spatial autocorrelation, wherein intersite similarity is correlated with distance between sites, is a characteristic of most ecological studies spanning a large environmental range. If data are spatially autocorrelated, classical statistical techniques provide biased estimates of relationships between species attributes and environmental variables. We examined abundances of seven littoral fishes in 25 lakes that varied substantially in morphometry, chemistry, and elevation across central Ontario. Weak correlations were observed between abundances of particular species and environmental variables before correcting for spatial autocorrelation, and we hypothesized that correlations reflected species' habitat preferences. However, spatial autocorrelation existed in the abiotic and fish abundance datasets. Once large-scale geographic patterns (spatial autocorrelation) were removed using partial Mantel tests, correlations changed within and between datasets. A strong relationship emerged between abundances and lake elevation. By comparing patterns within geographically corrected data with those without correction, we identified particular species that exhibited spatially autocorrelated abundances. The geographic direction of spatial autocorrelation provided additional insights into environmental factors also correlating with species abundance. We recommend that ecologists examine both geographically corrected and noncorrected data when developing hypotheses to explain regional variation in species abundance.