Nearby Source Populations Research Articles

A Rose Is a Rose Is a Rose... Or Is It? Ecotypes versus Locally Sourced Plants for Aquatic Habitat Restoration and Enhancement Projects

Horticulturists and agronomists have a long history of using selective breeding to take advantage of intraspecific (within-species) variation with the goal of developing novel varieties of plant species. These efforts are responsible for the availability of countless improved food, forage, and ornamental varieties that are valued by farmers, landscapers, and home gardeners. In contrast, little attention has been paid to the idea of evaluating intraspecific variation to identify plants derived from a specific ecosystem (ecotypes) of native species that could improve the success rate of habitat restoration and enhancement projects, especially in aquatic systems. These projects often specify that plant material used for restoration be collected from local donor sites to preserve the area’s gene pool, but nearby source populations may be nonexistent or may not be well-adapted to conditions at the recipient (transplant) site. This paper, which summarizes information presented at the American Society for Horticultural Science Invasive Plants Research Professional Interest Group workshop in 2022, provides evidence that unimproved, wild-type species can be useful in aquatic habitat restoration and enhancement projects, particularly when conditions at sites targeted for restoration differ from those in nearby systems, or when sites are expected to undergo shifts in conditions because of factors such as climate change.

Patterns of Aquatic Insect Biodiversity in the Highly Urbanized Bronx River, NY

Aquatic insects are important components of stream food webs and are greatly impacted by anthropogenic disturbances, including urbanization. Successful restoration of urban rivers is contingent on the growth of aquatic insect populations from colonizers from local, less-disturbed streams. However, rivers in highly urbanized watersheds may not have nearby source populations, and therefore must rely only on individuals already surviving in the river. At the regional level, urbanization is a homogenizing process, but the impacts could be heterogeneous at the local level. Therefore, some sites within highly urban rivers might support higher local biodiversity and provide source populations for restoration projects focused on other sites in the river. In this study, we collected aquatic insects from sites within the Bronx River, a highly urbanized river in the New York City metropolitan area, NY, in the summers of 2021 and 2022. We found that while taxonomic richness was similar among sites, insect abundance and dominant taxa, particularly members of Hydropsychidae (Trichoptera), varied significantly among sites. These findings suggest sites within the Bronx River are not homogenous and that some sites within the river harbor larger populations of aquatic insects and may be integral to the success of future conservation projects. This pattern of within-river heterogeneity may exist in other urban rivers and deserves consideration in determining conservation goals and the planning of stream-restoration projects.

Population genetics and plant growth experiments as prerequisite for conservation measures of the rare European aquatic plant Luronium natans (Alismataceae).

Information provided by population genetic studies is often necessary to effectively protect endangered species. In general, such data is scarce for aquatic plants and this holds also for Luronium natans, an aquatic macrophyte endemic to northwestern and western Europe. It is threatened across its whole distribution range due to human influences, in particular due to eutrophication and intensive fish farming. In spite of habitat protection populations continue to decline and re-introductions are one possibility to prevent the species' extinction. Therefore, insights in genetic diversity and relatedness of source populations is warranted. Thus, we performed Amplified Fragment-Length Polymorphism (AFLP) on two large populations in Saxony, Germany (Großenhainer Pflege and Niederspree), complemented with numerous additional occurrences from Europe. In addition, we conducted experiments on plant growth to assess optimal conditions for ex-situ cultivation taking water temperature, water level and substrate into account. We revealed considerably high levels of genetic diversity within populations (Shannon Indices ranged from 0.367 to 0.416) implying that populations are not restricted to clonal growth only but reproduce also by open-pollinated flowers. Remarkably, the two geographically close Saxon populations were genetically distant to each other but subpopulations within a locality were completely intermingled. Concerning optimal cultivation conditions, longest roots were obtained at temperatures >14°C and saturated, but not submerging water levels. Thus, our findings advocate for a re-introduction scheme from nearby source populations and provide detailed information on successful ex-situ cultivation.

Sensitivity of the combined fit of energy spectrum, shower depth distributions, and arrival directions at the Pierre Auger Observatory

The Pierre Auger Observatory measures several characteristics of ultra-high-energy cosmic rays (UHECRs), most importantly the energy spectrum, the distribution of maximum shower depths and the arrival directions. We use all three observables for a combined fit, in which parameters of possible UHECR sources can be constrained. The astrophy sical model used in the fit consists of homogeneo usly distributed background sources as well as an adaptable contribution from a nearby source population . For this, the catalogs of starburst galaxies and active galactic nuclei are used which show an indication for a correlation with the UHECR arrival directions . The signal fraction, as well as the size of a rigidity-dependent magn etic field blurring, are part of the fit parameters, along with the parameters describing the source emission. Tn this work, we present an astro-physical simulation containing an energy-dependent contribution from starburst galaxies, which simultaneously describes the energy spectrum, shower depth distributions, and arrival directions measured by the Pierre Auger Observatory. On this simulation, the discrimination power of the method regarding the differentiation of source catalogs is demonstrated, and the expected statistical significance of the result is investigated.

Present in the western European Alps but absent in the eastern part: Can habitat availability explain the differences in red‐billed chough occurrence?

The absence of a species in apparently suitable regions is often attributed to habitat deterioration, which, according to the IUCN‐guidelines, would preclude reintroduction unless the habitat is sufficiently restored. The crux is therefore to determine species' key habitat requisites and to localize potentially restorable sites based on the habitat selection of thriving populations in similar environments. The distribution of the red‐billed chough Pyrrhocorax pyrrhocorax in the Alpine arch is currently restricted to its western side. The eastern Alps have only been occupied sporadically during past centuries, which triggered a discussion around reintroduction. The fact that the last confirmed pairs bred at middle elevation, in derelict buildings instead of alpine cliffs, suggested a lack of habitat suitability in the uplands. To test this hypothesis, we modelled seasonal foraging habitat (during winter, breeding and dispersal) and nest site‐selection in the western Swiss Alps using long‐term observation data together with a wide palette of environmental predictors. The models were extrapolated to eastern Switzerland to estimate the quality and extent of the available habitat. Both foraging and nesting habitats were predicted with a high level of accuracy (AUC > 0.8). Despite variation between seasons, south‐exposed dry meadows and extensively‐grazed pastures were always preferred as foraging habitat, while forested and snow‐covered areas were avoided. Availability of, and distance to suitable foraging habitats were the main determinants of nest‐site selection, probably reflecting strong energetic constraints during reproduction. However, the extrapolation to eastern Switzerland revealed an even higher overall amount and relative percentage of all habitat types. One explanation could be that our predictors were too coarse to encapsulate qualitative, structural or compositional differences of the grasslands. However, the results could also point to an alternative hypothesis, namely that post‐glacial recolonization patterns, in particular the absence of nearby source populations, precluded the occupation of the eastern Alps.

Population genomics of invasive rodents on islands: Genetic consequences of colonization and prospects for localized synthetic gene drive.

Introduced rodent populations pose significant threats worldwide, with particularly severe impacts on islands. Advancements in genome editing have motivated interest in synthetic gene drives that could potentially provide efficient and localized suppression of invasive rodent populations. Application of such technologies will require rigorous population genomic surveys to evaluate population connectivity, taxonomic identification, and to inform design of gene drive localization mechanisms. One proposed approach leverages the predicted shifts in genetic variation that accompany island colonization, wherein founder effects, genetic drift, and island‐specific selection are expected to result in locally fixed alleles (LFA) that are variable in neighboring nontarget populations. Engineering of guide RNAs that target LFA may thus yield gene drives that spread within invasive island populations, but would have limited impacts on nontarget populations in the event of an escape. Here we used pooled whole‐genome sequencing of invasive mouse (Mus musculus) populations on four islands along with paired putative source populations to test genetic predictions of island colonization and characterize locally fixed Cas9 genomic targets. Patterns of variation across the genome reflected marked reductions in allelic diversity in island populations and moderate to high degrees of differentiation from nearby source populations despite relatively recent colonization. Locally fixed Cas9 sites in female fertility genes were observed in all island populations, including a small number with multiplexing potential. In practice, rigorous sampling of presumptive LFA will be essential to fully assess risk of resistance alleles. These results should serve to guide development of improved, spatially limited gene drive design in future applications.

Aquatic and riparian ecosystem recovery from debris flows in two western Washington streams, USA.

An exceptionally powerful storm struck southwestern Washington in December 2007 causing large debris flows in two adjacent streams. The two affected streams had been studied prior to the storm, providing a rare opportunity to examine ecosystem recovery. We monitored the streams and their riparian zones for six years after the disturbances to determine whether recovery rates of biota, physical habitat, and water temperature differed, and if so, what factors affected resilience. Along both streams, the debris flows removed wide swaths of soil, rock, and coniferous riparian forests, widening the active channel and increasing solar exposure and summer water temperatures. Initially depauperate of vegetation, after four years red alder trees dominated the riparian plant communities. The warmer water, greater solar radiation, and unstable substrates likely contributed to variable benthic insect and tailed frog tadpole densities over time, although benthic insect communities became more similar after three years. The debris flows also decreased channel slopes and removed channel step barriers such that cutthroat trout were able to rapidly occupy habitats far upstream, but sculpins were slower to recolonize and both fish species exhibited some differences in recovery between the two streams. Crayfish were severely impacted by the debris flows; this may be due to attributes of their life history and the timing of the flows. Overall, we found that recolonizing aquatic species exhibited varying levels of resilience and recovery after the disturbances being related to the influence of physical habitat conditions, species dispersal ability, and the presence of nearby source populations.

Seasonal abundance of cotton thrips (Thysanoptera: Thripidae) across crop and non-crop vegetation in an Australian cotton producing region

The spatio-temporal relationships of thrips populations across weeds and cotton (Gossypium hirsutum L. (Malvales: Malvaceae) crops were studied across the agricultural landscape of the Namoi Valley, New South Wales, Australia. In a structured sampling program, the seasonal patterns of host plant use by Thrips tabaci Lindeman, Frankliniella occidentalis Pergrande and F. schultzei Trybom (Thysanoptera: Thripidae) were quantified in relation to their invasion of cotton crops. Plants of 69 species (in 20 families) were sampled; T. tabaci was the most numerous thrips species and was recorded from 31 plant species, F. occidentalis was less numerous but recorded from 35 plant species, and F. schultzei was present at very low densities on 25 plant species. Both T. tabaci and F. occidentalis were mostly collected from weeds flowering in spring and summer, when these plants were most abundant. The seasonal composition of thrips populations on cotton changed from predominately T. tabaci on seedling cotton to F. schultzei and F. occidentalis on mature flowering cotton later in the season. High T. tabaci abundance on early season cotton was attributed to the abundance of T. tabaci on the surrounding weed species, because the weed hosts on which it was recorded were plentiful then. In contrast, the patterns of F. occidentalis and F. schultzei abundance on cotton were not correlated with their abundance on weeds, but rather with the emergence of cotton flowers. The genetic relationships and cryptic species identity of thrips on cotton relative to those on the other host plant species sampled was investigated through the analysis of mitochondrial CO1 gene sequences. Thrips tabaci and F. occidentalis collected from cotton were genetically identical to conspecifics collected from weeds. This is consistent with these insects moving onto cotton plants from nearby source populations on weeds. Frankliniella schultzei is a species complex in Australia, two members of which are present in this region, but only the black species was found in these surveys. This study demonstrates that (i) weeds play an important role in the population ecology of thrips, particularly in T. tabaci infesting early season cotton crops, (ii) the role of weeds warrants consideration in relation to pest management strategies, and (iii) without considering the surrounding landscape (which needs definition relative to each pest species) invasions cannot be readily understood mechanistically.

Disentangling the effects of habitat suitability, dispersal, and fragmentation on the distribution of river fishes.

Habitat suitability, dispersal potential, and fragmentation influence the distribution of stream fishes; however, their relative influence and interacting effects on species distributions are poorly understood, which may result in uncertain outcomes of river rehabilitation and conservation. Using empirical data describing 17 relatively common stream fishes, we combine (1) species habitat suitability models (MaxEnt) with a (2) species dispersal model (FIDIMO) and a (3) worst-case scenario of the influence of river fragmentation on dispersal. Using generalized linear mixed models, we aimed to uncover the role of these factors in explaining the probability of presence. Simulations over nine years allowed for assessing the relative importance of dispersal over time for structuring species occurrences vs. the importance of habitat suitability. Models combining all three structuring factors performed consistently better in predicting the spatial occurrence patterns than models including only single factors. Our results confirmed that distribution patterns of stream fishes are jointly controlled by species dispersal and habitat suitability. An increase of 0.1 habitat suitability probability more than doubled the odds of species occurrence; an increase of 0.1 dispersal probability yielded a 14-fold increase of the odds of species occurrence. Temporal simulations revealed that over short time frames (1-2 years) dispersal from nearby source populations is four times more important than habitat suitability for species presence. However, over longer time periods, the importance of habitat suitability increases relative to the importance of dispersal. Surprisingly, fragmentation by migration barriers did not appear as a significant driver of occurrence patterns. Concluding, these findings demonstrate the importance of the spatial arrangement of suitable habitats and potential source populations, as well as their relative position in relation to barriers. We emphasize considering the direction of connections within river networks and the dispersal abilities of fishes, as well as providing (access to) new, suitable habitat for successful river rehabilitation.

One method does not suit all: variable settlement responses of three procellariid species to vocalisation playbacks

Attempts to establish seabird colonies at restoration sites using artificial visual and auditory social cues have had varying success rates, differing between sites and species. The biological mechanisms responsible for this variation are poorly understood. We used experimental call playback to test the attraction of three sympatric procellariid species to auditory social cues in northern New Zealand. To test whether the size of nearby breeding colonies affected the level of response to call playback, audio recordings were broadcast from three similar locations with varying densities of breeding conspecifics within 1 km. Grey-faced Petrel (Pterodroma gouldi) were attracted to conspecific vocalisation playbacks at all three sites and also to playbacks of other species. Fluttering Shearwater (Puffinus gavia) were attracted to playback at only two locations. Flesh-footed Shearwater (Puffinus carneipes) were not attracted to playbacks, broadcast from only one location. For Grey-faced Petrels and Fluttering Shearwaters, response to call playback increased with increasing densities of nearby breeding conspecifics, suggesting there may be a relationship between attraction and the size of nearby potential source populations. For some procellariid species call playback represents a cost-effective alternative to other active restoration approaches, such as translocation. However, we caution that its effectiveness for individual species at different sites should be assessed at the outset of restoration initiatives.

Inferring invasion patterns of Lonicera maackii (Rupr) Herder (Caprifoliaceae) from the genetic structure of 41 naturalized populations in a recently invaded area

We studied the genetic structure of populations of the invasive shrub Amur honeysuckle (Lonicera maackii) in 41 woodlots in an agricultural landscape in a recently invaded area in southwest Ohio. Using six polymorphic microsatellite loci, we found high allelic diversity and high heterozygosity in all populations and low to moderate levels of genetic differentiation among populations. We also found significant positive correlations between geographic distance and (1) Nei’s genetic distance and (2) the coefficient of genetic differentiation (FST/(1 − FST) among all possible pairs of populations. These relationships were stronger when we tested the correlations of each of five putative source populations against the remaining non-source populations; and were especially strong when only the populations located within 30 km of each putative source were included in the analyses. Genetic analysis also revealed the existence of four distinct clusters that were not equally distributed across the study area, with high levels of admixture within populations. In particular, our findings indicate that the individuals present in six newly established populations in Darke county are made up of individuals belonging to multiple clusters, suggesting that these new populations were colonized from multiple nearby source populations. From these findings, we infer that the genetic structure of these L. maackii populations is determined by a combination of long-distance dispersal events and shorter distance diffusion from neighboring uninvaded woodlots, as well a history of multiple introductions into Ohio, and a predominantly outcrossing mating system.

Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?

Brown bears are recorded from Ireland during both the Late Pleistocene and early–mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British–Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear–polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions.

Rapid Buildup of Genetic Diversity in Founder Populations of the Gynodioecious Plant Species Origanum vulgare after Semi-Natural Grassland Restoration

In most landscapes the success of habitat restoration is largely dependent on spontaneous colonization of plant species. This colonization process, and the outcome of restoration practices, can only be considered successful if the genetic makeup of founding populations is not eroded through founder effects and subsequent genetic drift. Here we used 10 microsatellite markers to investigate the genetic effects of recent colonization of the long-lived gynodioecious species Origanum vulgare in restored semi-natural grassland patches. We compared the genetic diversity and differentiation of fourteen recent populations with that of thirteen old, putative source populations, and we evaluated the effects of spatial configuration of the populations on colonization patterns. We did not observe decreased genetic diversity in recent populations, or inflated genetic differentiation among them. Nevertheless, a significantly higher inbreeding coefficient was observed in recent populations, although this was not associated with negative fitness effects. Overall population genetic differentiation was low (FST = 0.040). Individuals of restored populations were assigned to on average 6.1 different source populations (likely following the ‘migrant pool’ model). Gene flow was, however, affected by the spatial configuration of the grasslands, with gene flow into the recent populations mainly originating from nearby source populations. This study demonstrates how spontaneous colonization after habitat restoration can lead to viable populations in a relatively short time, overcoming pronounced founder effects, when several source populations are nearby. Restored populations can therefore rapidly act as stepping stones and sources of genetic diversity, likely increasing overall metapopulation viability of the study species.

Experimental Summary: Very High Energy Cosmic Rays and their Interactions

The XVII International Symposium on Very High Energy Cosmic Ray Interactions, held in August of 2012 in Berlin, was the first one in the history of the Symposium, where a plethora of high precision LHC data with relevance for cosmic ray physics was presented. This report aims at giving a brief summary of those measurements and it discusses their relevance for observations of high energy cosmic rays. Enormous progress has been made also in air shower observations and in direct measurements of cosmic rays, exhibiting many more structure in the cosmic ray energy spectrum than just a simple power law with a knee and an ankle. At the highest energy, the flux suppression may not be dominated by the GZK-effect but by the limiting energy of a nearby source or source population. New projects and application of new technologies promise further advances also in the near future. We shall discuss the experimental and theoretical progress in the field and its prospects for coming years.

Phenotypic selection to increase floral scent emission, but not flower size or colour in bee‐pollinated Penstemon digitalis

Fragrance is a putatively important character in the evolution of flowering plants, but natural selection on scent is rarely studied and thus poorly understood. We characterized floral scent composition and emission in a common garden of Penstemon digitalis from three nearby source populations. We measured phenotypic selection on scent as well as floral traits more frequently examined, such as floral phenology, display size, corolla pigment, and inflorescence height. Scent differed among populations in a common garden, underscoring the potential for scent to be shaped by differential selection pressures. Phenotypic selection on flower number and display size was strong. However, selection favoured scent rather than flower size or colour, suggesting that smelling stronger benefits reproductive success in P. digitalis. Linalool was a direct target of selection and its high frequency in floral-scent bouquets suggests that further studies of both pollinator- and antagonist-mediated selection on this compound would further our understanding of scent evolution. Our results indicate that chemical dimensions of floral display are just as likely as other components to experience selective pressure in a nonspecialized flowering herb. Therefore, studies that integrate visual and chemical floral traits should better reflect the true nature of floral evolutionary ecology.

Carnivore Translocations and Conservation: Insights from Population Models and Field Data for Fishers (Martes pennanti)

Translocations are frequently used to restore extirpated carnivore populations. Understanding the factors that influence translocation success is important because carnivore translocations can be time consuming, expensive, and controversial. Using population viability software, we modeled reintroductions of the fisher, a candidate for endangered or threatened status in the Pacific states of the US. Our model predicts that the most important factor influencing successful re-establishment of a fisher population is the number of adult females reintroduced (provided some males are also released). Data from 38 translocations of fishers in North America, including 30 reintroductions, 5 augmentations and 3 introductions, show that the number of females released was, indeed, a good predictor of success but that the number of males released, geographic region and proximity of the source population to the release site were also important predictors. The contradiction between model and data regarding males may relate to the assumption in the model that all males are equally good breeders. We hypothesize that many males may need to be released to insure a sufficient number of good breeders are included, probably large males. Seventy-seven percent of reintroductions with known outcomes (success or failure) succeeded; all 5 augmentations succeeded; but none of the 3 introductions succeeded. Reintroductions were instrumental in reestablishing fisher populations within their historical range and expanding the range from its most-contracted state (43% of the historical range) to its current state (68% of the historical range). To increase the likelihood of translocation success, we recommend that managers: 1) release as many fishers as possible, 2) release more females than males (55–60% females) when possible, 3) release as many adults as possible, especially large males, 4) release fishers from a nearby source population, 5) conduct a formal feasibility assessment, and 6) develop a comprehensive implementation plan that includes an active monitoring program.

Nine years of vegetation development in a postmining site: effects of spontaneous and assisted site recovery

Summary1. Highly disturbed areas such as surface‐mined land provide a great challenge for ecological restoration. The goal is to identify appropriate restoration approaches in a continuum between technical reclamation and spontaneous succession. In particular, on slopes endangered by erosion, appropriate methods are needed that quickly establish vegetation cover but also take into account the natural potentials of the site.2. In the mined area Roßbach (Saxony‐Anhalt, Germany), we evaluated the effects of spontaneous succession and assisted site recovery (species introduction through hay transfer and sowing) during a 9‐year experiment. We asked how rates and pathways of vegetation development differ between treatments and whether species composition converges over time owing to species exchange.3. The application of green hay as well as the sowing of regional seed mixtures clearly accelerated vegetation development and led to the rapid establishment of species‐rich grasslands. Hay transfer was most successful owing to the high amount of transferable target species. Moreover, both treatments facilitated the establishment of cryptogams and provided effective erosion control. Also, hay transfer and sowing clearly affected the pathway of succession.Calamagrostis epigejosmigrated from nearby source populations and became increasingly dominant at sites with spontaneous succession. In contrast, the species‐rich grasslands established after hay transfer and sowing were highly resistant to invasion ofCalamagrostisand other ruderals.4. Species exchange between treatments led to increasing similarity in vegetation composition over time. Nine years after implementation of the experiment, we did not find any significant differences between treatments in terms of total vegetation cover, species richness and the number of target species. However, the dominance ratio between target and nontarget species differed significantly. Species introduction through hay transfer and sowing led to a permanently higher abundance of grassland species and a lower coverage of ruderals compared with spontaneously developed sites. Hence, our results highlight the importance of initial floristic composition and the order of species arrivals for long‐term vegetation development.5. Synthesis and applications. Hay transfer and sowing of regional seed mixtures are appropriate restoration tools to achieve rapid revegetation when no potential seed sources of target species are available nearby or there are undesirable species that need to be suppressed. Our results show that introduced grassland species are able to grow under postmining site conditions and can migrate into adjacent spontaneously developing sites. A combination of spontaneous and assisted site recovery can promote the development of species‐rich grasslands in postmining landscapes.

Dispersal as a limiting factor in the colonization of restored mountain streams by plants and macroinvertebrates

Summary1. Over the past centuries, European streams have been heavily influenced by humans through pollution and regulation. As a result, the quality and diversity of freshwater riparian habitats have declined strongly, and the diversity of riparian flora and fauna has decreased. Recent restoration measures have resulted in stream habitat improvements, but biodiversity improvements have failed to follow in fragmented streams. It has been suggested that dispersal limitation could play an important role in the lack of biodiversity improvement in restored streams, but to date, there is no conclusive evidence for this assumption.2. In this study, we investigated whether colonization of restored streams by plants and macroinvertebrates is limited by dispersal. We hypothesized that colonization success increases with increasing availability of (nearby) source populations and with increasing ability of species to disperse over long distances. We related species composition in seven restored stream sections to species’ abundances in the surroundings and to species’ dispersal abilities.3. For both plants and macroinvertebrates, colonization success is strongly related to the abundance of species in the local and regional species pools.4. For plants, dispersal strategy has an additional influence on colonization success: short‐lived plants with high production of small, well‐dispersed seeds colonized best within the 3‐ to 5‐year period after restoration.5. The existence of dispersal strategy constraints could not be confirmed in macroinvertebrates, possibly because these are limited by a lack of connectivity on larger spatial scales. On the landscape scale, beneficial effects of increased plant diversity might further improve habitat suitability for macroinvertebrates.6. Synthesis and applications. Dispersal appears to be a limiting factor for successful (re)colonization of restored streams in fragmented landscapes. In plants, this is attributed to limitations in seed dispersal abilities and likely to a lack of nearby source populations as well. In macroinvertebrates, lack of nearby source populations may also be a limiting factor. Hence, we suggest restoring landscape connectivity at larger spatial scales and optimizing the availability of near‐natural ‘source’ areas in the vicinity of restoration projects, at least for plants, to improve the success of biodiversity restoration in fragmented habitats.

Patterns of genetic diversity in colonizing plant species:Nassauvia lagascaevar.lanata(Asteraceae: Mutisieae) on Volcán Lonquimay, Chile

The effect of colonization on the distribution of genetic diversity within and among populations in relation to species characteristics remains an open empirical question. The objective of this study was to contrast genetic diversity within and among established and colonizing populations of Nassauvia lagascae var. lanata on Volcán Lonquimay (Araucanía Region, Chile), which erupted on 25 December 1988, and relate genetic diversity to biological characteristics of the populations. We analyzed a total of 240 individuals from 15 populations distributed along the Andes Cordillera using AFLP and obtained a total of 307 AFLP bands, of which 97.7% are polymorphic. Values of population differentiation (F(ST)) did not differ significantly among established and colonizing populations, but colonizing populations did have reduced levels of genetic divergence (as indicated by private and rare bands) and genetic variation (e.g., Shannon index). We conclude that a founder effect through limited numbers of founding propagules derived from nearby source populations has not yet been compensated for by subsequent population growth and migration. Low rates of secondary dispersal via running water, kin-structure within populations, and slow population growth seem to contribute to the slow recovery of genetic diversity.

Changes in fish communities following recolonization of the Cedar River, WA, USA by Pacific salmon after 103 years of local extirpation

AbstractMigration barriers are a major reason for species loss and population decline of freshwater organisms. Significant efforts have been made to remove or provide passage around these barriers; however, our understanding of the ecological effects of these efforts is minimal. Installation of a fish passage facility at the Landsburg Dam, WA, USA provided migratory fish access to habitat from which they had been excluded for over 100 years. Relying on voluntary recruitment, we examined the effectiveness of this facility in restoring coho (Oncorhynchus kisutch) salmon populations above the diversion, and whether reintroduction of native anadromous species affected the distribution and abundance of resident trout (O. mykiss and O. clarki). Before the ladder, late summer total salmonid (trout only) density increased with distance from the dam. This pattern was reversed after the ladder was opened, as total salmonid density (salmon + trout) approximately doubled in the three reaches closest to the dam. These changes were primarily due to the addition of coho, but small trout density also increased in lower reaches and decreased in upper reaches. A nearby source population, dispersal by adults and juveniles, low density of resident trout and high quality habitat above the barrier likely promoted rapid colonization of targeted species. Our results suggest that barrier removal creates an opportunity for migratory species to re‐establish populations leading to range expansion and potentially to increased population size. Copyright © 2008 John Wiley & Sons, Ltd.