The population genetics of nonmigratory Allen’s Hummingbird (Selasphorus sasin sedentarius) following a recent mainland colonization

Allen''s Hummingbird comprises two subspecies, one migratory (Selasphorus sasin sasin) and one nonmigratory (S. s. sedentarius). The nonmigratory subspecies, previously endemic to the California Channel Islands, apparently colonized the California mainland on the Palos Verdes Peninsula some time before 1970 and now breeds throughout coastal southern California. We sequenced and compared populations of mainland nonmigratory Allen''s Hummingbird to Channel Island populations from Santa Catalina, San Clemente, and Santa Cruz Island. We found no evidence of founder effects on the mainland population. Values of nucleotide diversity on the mainland were higher than on the Channel Islands. There were low levels of divergence between the Channel Islands and the mainland, and Santa Cruz Island was the most genetically distinct. Ecological niche models showed that rainfall and temperature variables on the Channel Islands are similar in the Los Angeles basin and predicted continued expansion of nonmigratory Allen''s Hummingbird north along the coast and inland. We also reviewed previous genetic studies of vertebrate species found on the Channel Islands and mainland and showed that broad conclusions regarding island–mainland patterns remain elusive. Challenges include the idiosyncratic nature of colonization itself as well as the lack of a comprehensive approach that incorporates similar markers and sampling strategies across taxa, which, within the context of a comparative study of island–mainland relationships, may lead to inconsistent results.     

Island–mainland difference in <Emphasis Type="Italic">Nicotiana glauca</Emphasis> (Solanaceae) corolla length: a product of pollinator-mediated selection?

A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist. I first determined differences in floral morphology and pollinator composition between island and mainland populations of N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites. I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift.     

Evolutionary effects of geographic and climatic isolation between Rhododendron tsusiophyllum populations on the Izu Islands and mainland Honshu of Japan

Geographic and environmental isolations of islands and the mainland offer excellent opportunity to investigate colonization and survival dynamics of island populations. We inferred and compared evolutionary processes and the demographic history of Rhododendron tsusiophyllum, in the Izu Islands and the much larger island Honshu, treated here as the mainland, using thousands of nuclear SNPs obtained by ddRAD-seq from eight populations of R. tsusiophyllum and three populations of R. tschonoskii as an outgroup. Phylogenetic relationships and their habitats suggest that R. tsusiophyllum had evolved and migrated from cold north to warm south regions. We detected clear genetic divergence among populations in three regions of Honshu and the Izu Islands, suggesting restricted migration between them due to isolated habitats on mountains even in the mainland. The three regions have different changes in effective population size, especially, genetic diversity and population size of the Izu Islands are small compared to the others. Further, habitats of populations in the Izu Islands are warmer than those in Honshu, suggesting that they have undergone adaptive evolution. Our study provides evidences of montane rather than insular isolation on genetic divergence, survival of populations and significance of adaptive evolution for island populations with small population size and low genetic diversity, despite close proximity to mainland populations.Subject terms: Genetic variation, Plant evolution, Conservation biology     

Microsatellite variation and microevolution in the critically endangered San Clemente Island loggerhead shrike (Lanius ludovicianus mearnsi)

Polymorphic nuclear microsatellite loci were used to characterize genetic variation in contemporary and historic populations of the San Clemente Island loggerhead shrike (Lanius ludovicianus mearnsi), an endangered bird with a current population of 30 individuals that is endemic to to one of the California Channel Islands. We also compared the population of the shrike with two contemporary populations of the still abundant subspecies, L. l. gambeli, which live 120 km away on the adjacent mainland. The current population of L. l. mearnsi has 60 per cent of the genetic variation of the mainland shrike populations and is strongly differentiated from them. Comparison of living birds with 19 birds collected in 1915 shows that most of the variation within the island population was lost before the recent 90 per cent decline in population size, and the 20 per cent decrease in variation this century is probably attributable to genetic drift. Mitochondrial DNA control region sequence data from 80 year old specimens show that there may have been limited introgression to L. l. mearnsi, this century, from another island subspecies, L. l. anthonyi, found in the northern Channel Islands. Today, gene flow between L. l. mearnsi and mainland L. l. gambel is very low, even though a few mainland birds visit the island annually. The island subspecies population has evolved sufficient genetic independence to justify ongoing conservation efforts to counter demographic collapse and genetic erosion; the course of genetic erosion can now be monitored non-invasively, as demonstrated by this study, based on DNA amplified from feathers.     

Random Amplified Polymorphic DNA (RAPD) Variation among Populations of the Insular Endemic Plant Campanula microdonta(Campanulaceae)

RAPD variation was examined in nine populations of Campanulamicrodonta Koidz., endemic to the Izu Islands, Japan. Ninety-eightbands were obtained for all populations, 94% of which were polymorphicat least within a population. Shannon's H values were calculated;these have frequently been used in RAPD studies to estimategenetic diversity. The values within populations did not correlatewith the allozyme gene diversity estimated by a previous studyor with distance from the Japanese mainland. The possible reasonsfor this discrepancy are different selection regimes betweenthe two markers, higher RAPD mutation rates, and each marker'sdifferent coverage of genomes. Cluster analysis of genetic similaritiessuggested that colonization of each island probably occurredonce, except for Miyake Island, where immigration has occurredat least twice. Copyright 2001 Annals of Botany Company AMOVA, Campanula microdonta Koidz., insular endemic plant, genetic diversity, population genetic structure, RAPD     

Evolutionary assembly of island faunas reverses the classic island–mainland richness difference in Anolis lizards

Aim Islands are widely considered to be species depauperate relative to mainlands but, somewhat paradoxically, are also host to many striking adaptive radiations. Here, focusing on Anolis lizards, we investigate if cladogenetic processes can reconcile these observations by determining if in situ speciation can reduce, or even reverse, the classical island–mainland richness discrepancy. Location Caribbean islands and the Neotropical mainland. Methods We constructed range maps for 203 mainland anoles from museum records and evaluated whether geographical area could account for differences in species richness between island and mainland anole faunas. We compared the island species–area relationship with total mainland anole diversity and with the richness of island‐sized mainland areas. We evaluated the role of climate in the observed differences by using Bayesian model averaging to predict island richness based on the mainland climate–richness relationship. Lastly, we used a published phylogeny and stochastic mapping of ancestral states to determine if speciation rate was greater on islands, after accounting for differences in geographical area. Results Islands dominated by in situ speciation had, on average, significantly more species than similarly sized mainland regions, but islands where in situ speciation has not occurred were species depauperate relative to mainland areas. Results were similar at the scale of the entire mainland, although marginally non‐significant. These findings held even after accounting for climate. Speciation has not been faster on islands; instead, when extinction was assumed to be low, speciation rate varied consistently with geographical area. When extinction was high, there was some evidence that mainland speciation was faster than expected based on area. Main conclusions Our results indicate that evolutionary assembly of island faunas can reverse the general pattern of reduced species richness on islands relative to mainlands.     

ANALYSIS OF MITOCHONDRIAL DNA POLYMORPHISMS AMONG CHANNEL ISLAND DEER MICE

Mitochondrial DNA (mtDNA) from 131 deer mice, Peromyscus maniculatus, collected on the eight California Channel Islands and from seven southern California mainland locations, was isolated and analyzed for restriction endonuclease fragment polymorphisms. A total of 26 mtDNA genotypes were distinguishable among the deer mice sampled. All of the island samples had mtDNA restriction-fragment patterns not found among the mainland samples. Distributions of specific restriction-fragment patterns provide evidence for at least four separate colonization events to the Channel Islands. The estimated percentage of sequence divergence between all mtDNA's in this study was less than 1%, suggesting that colonization of the islands occurred fairly recently, probably within the last 500,000 years. Levels of mtDNA heterogeneity were much lower within island populations than within mainland populations.     

THE INHERITANCE OF DIVERGENT MITOCHONDRIA IN THE LAND SNAIL, CEPAEA NEMORALIS

The mitochondrial genomes of Cepaea nemoralis can differ widelybetween individuals in the same population. Various hypothesishave been proposed to account for this diversity, includingunusually fast evolution and the retention of deep lineagesin sub-divided populations. Another possibility is that pulmonatemitochondria are inherited in the doubly uniparental mode, asin Mytilus, allowing separate maternal and paternal lineagesto coexist. In Mytilus, separate lineages may differ by as muchas 20% and may pre-date the origin of the species carrying them. Until now, mitochondrial inheritance has not been studied inany molluscan group except the bivalves. I have investigatedit in C. nemoralis through a series of matings, and assayedindividuals for evidence of heteroplasmy. In five matings, mitochondrialinheritance was maternal, and no heteroplasmic individuals weredetected. The maintenance of the divergent haplotypes can notbe explained by doubly uniparental inheritance. (Received 30 April 1999; accepted 6 July 1999)     

Are islands more susceptible to plant invasion than continents? A test using Oxalis pes‐caprae L. in the western Mediterranean

Aim We tested the relative vulnerability of islands to Oxalis pes‐caprae L. invasion compared to mainland regions. Oxalis pes‐caprae is a South African annual geophyte that reproduces via bulbils, and has spread in many Mediterranean and temperate regions of the world where introduced. Our study is one of the first detailed regional analyses of the occurrence and local abundance of a non‐native plant. Methods We conducted an extensive survey (2000 sampling points) to examine local and coarse‐scale patterns in both the occurrence and abundance of O. pes‐caprae on islands and in neighbouring mainland regions of Spain. Location We analysed occurrence (number of samples where present) and abundance (percentage cover) on two Balearic Islands (Menorca and Mallorca) and in two mainland administrative provinces of Spain (Murcia and València). Results Oxalis pes‐caprae occurrence was consistently higher on islands. Occurrence varied among habitats, being the highest in tree groves and the lowest in forests and shrublands. It was never found in these two habitats on the mainland. Mean O. pes‐caprae abundance was greatest in tree groves on the mainland, and in field margins and old fields on the islands. However, in general there were not significant differences in local abundances between island and mainland locations. Main conclusions These findings suggest that local processes (such as the biotic resistance of plant communities) are less important than coarse‐scale phenomena (such as environmental driving forces) in explaining differences in the invasion patterns observed between islands and adjacent mainland regions. We suggest that O. pes‐caprae has occupied a larger proportion of available habitats on islands due to: (1) its strong dependence on domestic animal and human‐mediated dispersal which are probably greater on the islands than in mainland areas, and (2) the smaller area encompassed by islands that, over a comparable period of time, enables a greater proportion of available habitats to be colonized (and hence higher occurrence) than equivalent larger mainland areas.     

Genetic Divergence of an Avian Endemic on the Californian Channel Islands

The Californian Channel Islands are near–shore islands with high levels of endemism, but extensive habitat loss has contributed to the decline or extinction of several endemic taxa. A key parameter for understanding patterns of endemism and demography in island populations is the magnitude of inter–island dispersal. This paper estimates the extent of migration and genetic differentiation in three extant and two extinct populations of Channel Island song sparrows (Melospiza melodia graminea). Inter–island differentiation was substantial (G''''_ST: 0.14–0.37), with San Miguel Island having the highest genetic divergence and lowest migration rates. Santa Rosa and Santa Cruz Island populations were less diverged with higher migration rates. Genetic signals of past population declines were detected in all of the extant populations. The Channel Island populations were significantly diverged from mainland populations of M. m. heermanni (G''''_ST: 0.30–0.64). Ten mtDNA haplotypes were recovered across the extant and extinct Channel Island population samples. Two of the ten haplotypes were shared between the Northern and Southern Channel Islands, with one of these haplotypes being detected on the Californian mainland. Our results suggest that there is little contemporary migration between islands, consistent with early explanations of avian biogeography in the Channel Islands, and that song sparrow populations on the northern Channel Islands are demographically independent.     

Rapid evolution in unstable habitats: a success story of the polymorphic land snail Cepaea nemoralis (Gastropoda: Pulmonata)

The present study reports on a natural experiment with twelve replicates in which rapid, predictable and consistent divergence of Cepaea nemoralis populations occurred in response to repeated selection gradient of adjacent open and shaded habitats. Because the frequencies of various genetically‐based phenotypes varied widely among surveyed populations, and there was a large overlap between habitat types, no overall association with habitat was apparent. In paired comparisons, however, significant changes were consistently towards higher frequencies of light morphs in the open than corresponding shaded habitats, and this result is attributable to natural selection. This shows that the knowledge of the genetic composition of reference populations is often essential for discerning selection from random processes. At each site, a different morph combination contributed to the divergence of populations, indicating that there are many genetic solutions to similar ecological problems; this likely enhances the maintenance of high levels of polymorphism. Adaptation of populations occurred in contemporary time and was fast. In one case where it was possible to follow changes, significant shifts in morph frequencies occurred within just two snail generations (selection coefficients of 0.404 and 0.518). High evolvability may be one of the factors contributing to the ecological success of Cepaea nemoralis. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 251–262.     

Conservation genetics of an island-endemic lizard: low Ne and the critical role of intermediate temperatures for genetic connectivity

Island populations are at higher risk of extinction than mainland populations. Therefore, understanding the factors that facilitate connectivity is particularly pressing for the conservation of island taxa. Sceloporus occidentalis becki, the Island Fence Lizard, is an endemic taxon restricted to the Northern Channel Islands, part of a nearshore archipelago in Southern California, USA. Since the Last Glacial Maximum, fence lizard habitat on the Northern Channel Islands has decreased with rising sea levels and increasing temperatures that have reduced the availability of woody vegetation. More recently, the introduction (and subsequent removal) of invasive ungulates over the last 170 years and recovery of vegetation has resulted in further dramatic habitat modification. Given the potential for genetic bottlenecks, the history of habitat alteration, and topographic and landscape complexity, we used landscape and population genetic approaches to characterize patterns of genetic diversity and structure of Island Fence Lizards on Santa Cruz Island, the largest of the Northern Channel Islands. Our analyses revealed shallow population structure across the island, low effective population size (N_e?=??~?200), and evidence for a recent genetic bottleneck. Landscape genetic analyses showed that connectivity is facilitated by tree canopy cover and shrubland, as well as by intermediate temperatures, emphasizing the importance of woody vegetation and habitats with variable thermal regimes as the climate warms. Combined, these population and landscape genetic analyses suggest that the Island Fence Lizard is of greater conservation concern than currently appreciated, and increased conservation management focus is warranted for this island endemic.

     

Pilchard (Sardina pilchardus, Walbaum) egg distribution in the English Channel from plankton surveys in 1978, 1981, 1988 and 1991

The distribution, abundance and production of pilchard (Sardinapilchardus, Walbaum) eggs are described from a series of planktonsurveys in the English Channel. These are discussed in relationto surface temperature and compared with the results from previouslypublished surveys. The surveys confirm that spawning beginsin the western English Channel during the second half of March,progresses eastwards and is 2–3 weeks later in the easternEnglish Channel. Some spawning still occurs in the southernNorth Sea and at a similar level to that found on surveys in1950 and 1967. Pilchard eggs were found developing in surfacetemperatures down to 8.5C. Concentrations as high as 1500 m^–2were found in the Bay of the Seine at 10–10.5C. Thesesurveys suggest that increasing egg production is linked toincreasing sea temperature and that the major production occursin the western English Channel at surface temperatures >14.5C.     

Complementary Association of an Endophytic Red Alga and a Shell-encrusting Green Alga

Endophytic filaments of a red alga in the shell-encrusting greenalga Pseudulvella consociata S. & G. collected from subtidaland intertidal habitats in the San Juan Islands, WashingtonState, U.S.A., have been identified as Audouinella sparsa (Harvey)Dixon. The association appears to be complementary. Pseudulvella consociata, Audouinella sparsa, alage, Rhodophyta, Chlorophyta, endophyte     

Review Oribatid mites of the Galápagos Islands – faunistics, ecology and speciation

The results from investigations on oribatid mites of the Galápagos archipelago during 10 years are presented. Samples were taken on all larger and most smaller islands of the archipelago, as well as in all vegetation zones and some special habitats such as grass or cactus litter and fumaroles. A total of 202 oribatid species belonging to 64 families were encountered; among them 81 species are new to science. The Oribatida occur from the littoral zone to the summit of the volcanoes. Diversity and abundance increases from the arid to the moister zones at higher elevations. Most species prefer moist habitats at medium to higher elevations of the islands, in some parts reaching remarkably high abundances (in the Scalesia zone of Santa Cruz approximately 18 000 individuals m–2). The species richness of an island depends on the altitude and number of available habitats rather than the area of the island. Many oribatid species on the Galápagos Islands have a wide biogeographical distribution. The majority originate from the Central and South American mainland, but several Pacific and even Holarctic elements were also found. In comparison with the species composition of the adjacent mainland, the oribatid mite fauna of the Galápagos Islands can be regarded as disharmonic. Sea surface transportation has been proved at least between the islands, which also applies to oribatid species living at higher elevations. Long distance dispersal can be assumed to be mainly hydrochorous. The oribatid fauna of the littoral and arid vegetation zones is presented in detail. Some species even inhabit such extreme habitats as warm fern litter in fumaroles or hot volcanic soils. Others were mainly found in or near agricultural areas, suggesting human introduction. Striking distribution patterns within the archipelago are discussed. The distribution of endemic forms in the genera Aeroppia, Scapheremaeus, Scheloribates and Cultrobates indicates both speciation on different islands, as well as speciation on the same island by occupying different habitats.     

Island biogeography extends to small-scale habitats: low competitor density and richness on islands may drive trait variation in nonnative plants

Previous island biogeography studies have quantified species richness on the scale of entire islands rather than smaller scales relevant to plant-to-plant competitive interactions. Further, they have not accounted for density compensation. Using mainland and island sites along the New England coast, we asked two questions. First, are both richness and density lower in small-scale habitats within islands than in similar mainland habitats? Second, do differences in competitor richness and density drive post-establishment trait variation in nonnative plant species? We used field surveys and individual-based rarefaction to estimate richness and density in 100-m² plots and demonstrated that island sites have significantly fewer species and individuals per unit area than mainland sites. We then conducted a field study in which we removed competing neighbors from nonnative plant individuals and found that when competitors were removed, individuals in low-competition environments demonstrated a lesser increase in vegetative growth but a greater increase in reproductive effort and herbivore tolerance relative to mainland individuals whose neighbors were also removed. We found that the central concept of island biogeography, i.e., that islands host fewer species than comparable mainland habitats, can be extended to smaller-scale habitats and that this difference in competitive pressure between mainland and island habitats can act as a driver of trait variation in nonnative plants.     

Selection and disequilibrium in Cepaea nemoralis

The snail Cepaea nemoralis (L.) is usually polymorphic for linked loci conferring pink or yellow shell ground colour and banding or lack of bands. An unlinked locus, mid‐banded, modifies the appearance of banded shells. These characters have a very wide range of frequencies across the species range and even within limited areas. In Britain, frequencies differ between populations from shaded woodland habitats and those from closely adjacent open habitats. Using data from the Evolution MegaLab Project, it is shown that the greater frequency of pink unbanded in shaded habitats is associated with a greater excess of the favoured allele combinations, measured as linkage disequilibrium. Examination of the relationship of disequilibrium to allele frequency in samples from the full geographical range and all habitats and climates shows that, in general, the allele combinations at high frequencies are in gametic excess. This suggests that selection tends to diversify rather than move frequencies towards stable equilibria. The result is important in relation to the as yet unresolved question how the polymorphism is maintained. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

GROWTH, MORTALITY, AND FEEDING RATES OF THE SNAIL HELIX ASPERSA AT DIFFERENT POPULATION DENSITIES IN THE LABORATORY, AND THE DEPRESSION OF ACTIVITY OF HELICID SNAILS BY OTHER INDIVIDUALS, OR THEIR MUCUS

When reared at high densities, young Helix aspersa show lessshell growth, even if waste products are removed. They alsofeed less, and show increased mortality. It is suggested thatthese effects are linked to reduced activity. Juveniles showreduced activity in the presence of adults or their mucus. Mucusof adult Cepaca nemoralis also depresses the activity of bothadult and young Helix and Cepaea. ^* Present Address: Unit Zoologi, Universiti Kebangsaan Malaysia,Jalan Pantai Baru, Kuala Lumpur, West Malaysia. (Received 12 May 1981;     

Stable nitrogen and carbon isotope ratios in bone collagen as indices of prehistoric dietary dependence on marine and terrestrial resources in southern California

The ratios of 15N to 14N and 13C to 12C tend to be higher in marine than in terrestrial organisms. The concentrations of these isotopes in human bone collagen consequently can be used to make inferences about the contribution of marine and terrestrial resources to prehistoric diets. The utility of studying 15N/14N and 13C/12C ratios in conjunction with each other is illustrated by our analysis of 40 human burials from archaeological sites in the Santa Barbara Channel area of southern California. The mean delta 13C and delta 15N values (in per mil) of collagen from these skeletons decrease progressively from the Channel Islands (delta 13C = -14.0, delta 15N = +16.3) to the mainland coast (delta 13C = -14.5, delta 15N = +14.9) to the interior (delta 13C = -17.2, delta 15N = +10.9). These data suggest that Indians living on the Channel Islands during the late prehistoric period were heavily dependent on marine resources. The inhabitants of the mainland interior, in contrast, had a diet composed largely of terrestrial foods. From their isotope ratios, it appears that the Indians who lived on the mainland coast consumed a mixed diet containing substantial quantities of both marine and terrestrial resources. Differences in 15N/14N and 13C/12C ratios of individuals from mainland sites dating from the early and late prehistoric periods show that the marine component of the diet increased substantially through time. These isotopic data are consistent with pathological, faunal, and artifactual evidence of increased marine resource exploitation during the late prehistoric period.     

Potential Nitrification as an Indicator of Preferential Uptake of Ammonium or Nitrate by Plants in an Oak Woodland Understorey

The preferences of some woodland understorey species for ammoniumand nitrate were investigated by measuring the potential nitrification(conversion of ammonium to nitrate) in the rhizosphere comparedwith the bulk soil. Less acid-tolerant species, which usuallyprefer nitrate or a mixture of ammonium and nitrate in hydroponicculture, should have a higher potential nitrification in therhizosphere compared to the bulk soil due to a low uptake ofammonium (since ammonium is relatively immobile). Acid-tolerantspecies should have a high uptake of ammonium and thereby loweror equal potential nitrification in the rhizosphere comparedto the bulk soil. The hypothesis was tested in a field investigationof five understorey herb species, Deschampsia flexuosa, Convallariamajalis, Poa nemoralis, Geum urbanum andAegopodium podagrariaperformed in oak forests in southern Sweden. Overall, the twoless acid-tolerant species, Geum urbanum and Aegopodium podagraria,had high potential nitrification in the rhizosphere comparedto the bulk soil (indicating a relatively low uptake of ammonium),whilst the acid tolerant species, Deschampsia flexuosa andConvallariamajalis , had approximately equal potential nitrification inthe rhizosphere compared to the bulk soil (indicating a relativelyhigh uptake of ammonium). In the case of Poa nemoralis, a specieswhich grows in both acid and less acid soils, we found the potentialnitrification in the rhizosphere and in the bulk soil to besimilar at low inorganic nitrogen concentrations, but the difference(rhizosphere > bulk) increased when nitrification in thebulk soil was enhanced (i.e. when the nitrogen availabilityincreased). The potential nitrification in the bulk soil variedbetween 0 and 16 nmol g^-1h^-1and was positively correlated withpH. When species occurred at the same site, the potential nitrificationin the bulk soil tended to be lower for the acid tolerant species.Despite a large variation in potential nitrification, the methodoffers a possibility of measuring the preference of plants forammonium/nitrate in a soil system, under natural conditions.Copyright 2000 Annals of Botany Company Ammonium uptake, nitrate uptake, nitrogen preference, potential nitrification, rhizosphere, Deschampsia flexuosa, Convallaria majalis, Poa nemoralis, Geum urbanum, Aegopodium podagraria