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The altitudinal vegetation distribution in the northern Andes during glacial time differed from the present-day conditions as a result of temperature and precipitation change. New evidence indicate that as a response to a reduced atmospheric partial CO(2) pressure (pCO(2)), the competitive balance between C(3) and C(4) plants have changed. Effects may have remained virtually undetected in pollen records, but can be observed using a stable carbon isotope analysis. Vegetation dominated by C(4) taxa, belonging to the families Cyperaceae (e.g. Bulbostylis and Cyperus) and Poaceae (e.g. Muhlenbergia, Paspalum and Sporobolus), may have been able to replace for a significant part the modern type C(3) taxa (e.g. species belonging to Carex, Rhynchospora, Aciachne, Agrostis, Calamagrostis, and Chusquea). Impact of reduced glacial atmospheric pCO(2) levels and lower glacial temperatures on the composition and the elevational distribution of the vegetation types is discussed. The present high Andean vegetation communities may differ from the glacial equivalents (non-modern analogue situation). We identified dry Sporobolus lasiophyllus tussock grassland and Arcytophyllum nitidum dwarfshrub paramo as the possible relict communities from glacial time. The effect on previous estimates of paleo-temperatures is estimated to be small.

The pollen record of a 65cm long core Laguna Carimagua-Bosque (4 degrees 04'N, 70 degrees 13'W) shows the late Holocene environmental history from a lake located within the gallery forest of the savannas of the Llanos Orientales of Colombia. Nine AMS radiocarbon dates of the organic deposits show that the core represents the period from ca. 1300(14)CyrBP to the present. The lake evolved from an active drainage system.During the period from ca. 1300 to 875(14)CyrBP (zone CMB-Ia), Mauritia-dominated swamp and gallery forest was present, dominated by Cecropia, and later also Acalypha and Alchornea. From 875 to 700(14)CyrBP (zone CMB-Ib), the lake was completely surrounded by gallery forest. Mauritiella and Cecropia occurred around the lake. Cecropia pioneer forest reached its greatest abundance and became gradually replaced by a more species-rich gallery forest, including Acalypha, Alchornea, Euterpe/Geonoma, Moraceae/Urticaceae, Piperaceae, and Virola. From 700 to 125(14)CyrBP (zone CMB-II), Cecropia lost its dominant role, and Mauritiella palms became more frequent. The main vegetation categories were swamp forest, gallery forest, understory elements, savanna shrubs and trees, and grass savanna. From 125(14)CyrBP to recent (zone CMB-III), the plant diversity in the gallery forest became highest, Mauritiella became very abundant, and among the savanna elements, woody Didymopanax increased.Comparison of four pollen records from savanna sites shows that pollen of savanna vegetation is markedly underrepresented in lake sediments when the lake lies within the gallery forest. As most of the drainage system of a savanna is hidden by gallery forest, we also expect a significant underrepresentation of the savanna ecosystem in river-transported pollen assemblages.

A pollen record from Timbio, located at an elevation of 1750m on the high plain of Popayán (2 degrees 24'N, 76 degrees 36'W) is presented. This forms the basis for reconstructing the vegetation and climate history for the periods from 27000 to 9200 radiocarbon years before the present (14Cyr BP) and 2100 14Cyr BP to sub-recent. The 5m sediment core has time control based on seven AMS radiocarbon dates. Four pollen assemblage zones (TIM-1 to TIM-4) are recognized. During the period of 27200 to 26000 14Cyr BP, an Andean forest was near the site. The vegetation consisted of forest and open herb-rich vegetation, climatic conditions were moist and temperatures some 6 degrees C lower than compared to those of today. During the period of 26000 to 16000 14Cyr BP forest was less open. The observed succession from a Podocarpus-Weinmannia dominated forest to a Hedyosmum dominated forest, and finally to a forest with Ilex, Myrica and ferns indicates a progressive decrease of temperature during this period, with a maximum temperature depression of ca. 5-7.5 degrees C compared to present-day conditions. During the period of 16000 to 9200 14Cyr BP, temperature decrease is estimated at ca. 7.5 degrees C and the climate was the driest. During the period of 2100 to 600 14C2600m altitude (ca. 8 degrees C) and those at sea-level (2.5-6 degrees C) and supports the observation that glacial lapse rates were higher than in modern times.

To determine the origin of the tetraploid annuals Microseris campestris and M. acuminata, chloroplast RFLP, RAPD and ITS sequence variability among nine populations of the two polyploids and 14 populations of the diploid annuals M. elegans and M. douglasii have been surveyed. Previously described variable chloroplast restriction sites infer M. douglasii as the possible maternal parent of both tetraploid species. However, the chloroplast genome typical for M. douglasii has now also been found in some plants of M. elegans. RAPD analysis revealed 172 polymorphic DNA markers that defined all four species as genetically distinct groups, but demonstrated closer associations between M. douglasii and M. acuminata, and between M. elegans and M. campestris. Sequencing of the ITS-1 and ITS-2 region yielded 73 phylogenetically informative sites. Thirty basepair mutations separated the annual Microseris species from the outgroup, Uropappus lindleyi. The putative interspecific allotetraploid M. campestris contained only one type ITS sequence that, on the basis of eight synapomorphic substitutions was derived from M. elegans. The single ITS of M. acuminata shares six common sites with M. douglasii. Surprisingly, six sites were synapomorphic for the two tetraploids, M. campestris and M. acuminata, suggesting recombination within the ITS of both species with that of a common, now extinct, parental taxon, possibly the donor of the M. douglasii type chloroplasts found in both tetraploids. These results confirm the interpretation of M. campestris as derived from M. douglasii (extinct population) and M. elegans, and resolve the unknown origin of M. acuminata as an intraspecific hybrid between two very distinct populations of M. douglasii, one of them the same extinct M. douglasii form that contributes to M. campestris.

A comparative litter fall study was made in five rain forest stands along a gradient of humus form development and soils in the Amazon lowlands of eastern Colombia. The total fine litter fall was highest in a plot on a well drained soil of the flood plain of the Caquetá River (1.07 kg · m -2 · y -1 ), lower in three plots on well drained upland soils (0.86, 0.69, and 0.68 kg · m -2 · y -1 ), and lowest in a plot on a poorly drained, upland podzolised soil (0.62 kg · m -2 · y -1 ). In the four upland plots, leaf litter fall patterns were highly associated, which points at climatic regulation. Litter resource quality, as represented by nutrient concentrations and area/weight ratio of the leaf litter fall, was comparatively high in the flood plain plot. In the upland plots, concentrations and fluxes of Ca, Mg, K, and P were as low as in oligotrophic central Amazonian upland forests. This questions generalisations that the western peripheral region of the Amazon basin should be less oligotrophic than central Amazonia. The upland plot on the podzolised soil showed the lowest concentrations and fluxes of N. Mean residence times of organic matter and nutrients in the L horizons hardly differed between the five plots, suggesting that edaphic properties and litter resource quality are of little importance in the first step of decomposition. Mean residence time of organic matter in all ectorganic horizons combined (estimated on the basis of litter input and necromass on the forest floor, and uncorrected for dead fine root input) varied from 1.0 y in the flood plain forest, 1.1-3.3 y in the well drained upland forests, and 10.2 y in the forest on the podzolised soil.

Levels and distribution of genetic variation were studied in central and western European populations of Taraxacum section Ruderalia containing differing mixtures of sexual diploid and asexual triploid plants. All sexual populations were panmictic with their variation partitioned mainly among populations. Genotypic diversity in triploid samples was very high with few clones widespread and many clones restricted to one or a few populations. Extensive amounts of gene (pollen) flow between the diploid and triploid components of a population were inferred from the following data: (1) the two ploidy levels share all major allozyme polymorphisms; (2) the intrapopulational homogeneity in genic variation between diploids and triploids contrasts strongly with the geographic differentiation at each ploidy level separately; (3) population-unique alleles simultaneously occur at the two ploidy levels; (4) not only sexuals but also asexuals generally simulate Hardy-Weinberg expectations. Most likely, intrapopulational gene exchange occurs bidirectionally by mechanisms such as reductional pollen meiosis in apomictic plants, facultative apomixis, and formation of unreduced gametes in sexuals. Thus, diploid and triploid Taraxacum section Ruderalia are less genetically isolated than has previously been supposed and probably form a cohesive evolutionary unit with the level at which gene pools are shared differing by population., (© 1995 The Society for the Study of Evolution.)

Segregation for 289 random amplified polymorphic DNA markers (RAPDs) has been determined in 106 F2 plants of an interspecific hybrid (H27) between Microseris douglasii (strain B14) and M. bigelovii (C94). Multicelluar trichomes ("type D", specific for Microseris) occur on the leaf teeth of early vegetative rosettes of the B14 parent and on the leaf blades of later rosettes in both parents. Trichomes on the leaf blades appear earlier and eventually more densely in B14. Segregation for trichome appearance is quantitative and strongly transgressive in the F2 hybrid. Cosegregation between RAPDs and trichome phenotypes combined with linkage data have revealed a main gene ("quantitative trait locus A", QTL-A) with a pleiotropic effect on all trichome characters and two unlinked additive modifiers (QTL-B, QTL-C). Alleles of both modifiers reduce the main gene effect in each parent. Their recombination explains the occurrence of plants with transgressive phenotypes in the hybrid offspring. Additional QTLs affecting trichomes are at and below the level of statistical significance.

The reproductive behaviour of Gentiana pneumonanthe L., a rare plant species in The Netherlands, was studied in a relatively large wet heathland population during summer 1989. The species co-occurred with the grass Molinia caerulea and co-flowered with Erica tetralix and Calluna vulgaris. The flowering period lasted from July to October, peaking in late August to late September. Flowers are protandrous. The species appeared to be self-compatible, but spontaneous self-pollination was strongly limited. Hand-crossing and hand-selfing resulted in the same amount of seed set as in natural pollination. Reproductive success was dramatically reduced late in the season. Pollination was achieved sternotribically by the species Bombus pascuorum, which visited the flowers for nectar. In the study area, three patch types were distinguished: co-dominated by Erica, by Calluna and Erica, and by Molinia, respectively. Frequency of visits to Gentiana was highest in the Erica-patch. However, this did not result in a higher seed set. In the Molinia-patch seed set was reduced. However, in the Molinia-patch the mean number of ovules was greater than in the others (as high as in plants raised indoors and in cross-pollinated plants). Fruits from the Calluna-patch had less ovules than those from the Erica-patch. We conclude that, in this remnant population, Gentiana is not pollination-limited. However, it is likely that in the Molinia-patch geitonogamy is frequent, which may lead to inbreeding depression. The greater number of ovules observed in Molinia-patches may reflect an excess of nutrients available there, relative to the Calluna-patch where there may be reduced water availability.

Seeds were sampled from 19 populations of the rare Gentiana pneumonanthe, ranging in size from 5 to more than 50,000 flowering plants. An analysis was made of variation in a number of life-history characters in relation to population size and offspring heterozygosity (based on seven polymorphic isozyme loci). Life-his-tory characters included seed weight, germination rate, proportion of seeds germinating, seedling mortality, seedling weight, adult weight, flower production per plant and proportion of plants flowering per family. Principal component analysis (PCA) reduced the dataset to three main fitness components. The first component was highly correlated with adult weight and flowering performance, the second with germination performance and the third component with seed and seedling weight and seedling mortality. The latter two components were considered as being maternally influenced, since these comprised life-history traits that were significantly correlated with seed weight. Multiple regression analysis showed that variation in the first fitness component was mainly associated with heterozygosity and not with population size, while the third fitness component was only correlated with population size and not with heterozygosity. The latter relationship appeared to be non-linear, which suggests a stronger loss of fitness in the smallest populations. The second (germination) component was neither correlated with population size nor with genetic variation. There was only a weak association between population size, heterozygosity and the population coefficients of variation for each life history character. Most correlation coefficients were negative, however, which suggests that there is more variation among progeny from smaller populations. We conclude that progeny from small populations of Gentiana pneumonanthe show reduced fitness and may be phenotypically more variable. One of the possible causes of the loss of fitness is a combination of unfavourable environmental circumstances for maternal plants in small populations and increased inbreeding. The higher phenotypic variation in small populations may also be a result of inbreeding, which can lead to deviation of individuals from the average phenotype through a loss of developmental stability.

Various methods from molecular biology reveal sequence polymorphisms in organelle and nuclear DNA that can be used as highly informative markers for the structure and dynamics of genomes at the level of populations and individuals. Molecular markers that can be determined without regard to the phenotype permit an unbiased comparison of the adaptation of organisms to their environment, its genetic basis and its effect on evolution. Several marker types used in ecological research and their uses and limitations arc briefly discussed. PCR-based methods, especially arnitrary-primer-based RAPDs, are likely to be most widely used and receive most attention. The limited use of DNA markers for overall quantitative (phenetic) comparisons of 'genetic variability' and 'generic distance' is stressed and fheir power as qualitative markers for any and all relevant regions in the genome is emphasized. Specific applications relevant to plant ecology are illustrated. These are: identification of organism and genotype even where morphology is of little help, as in mycorrhiza; identification of clones in asexually-reproducing species, even when they are widespread and intermingled; determining if genetic variation in elonal populations comes from mutations within elonal lines or from independent origins of clonal lines; reconstructing the genotype phylogeny and fruit dispersal of elonal (apomicuc) and inbred selling organisms, measuring the degree of outcrossing by offspring exclusion analysis; detecting and analyzing introgression and characterizing reeombinant genotypes in hybrid zones relative to differential adaptive responses: tracing the phylogenetic origin and extent of ecologically differentiated races or species; characterizing the genetic basis, mapping and isolating the genes responsible for special adaptive responses. In a final outlook, 1 speculate about unconventional sources of genetic variation affecting the ecological characteristics of plants that will become accessible to experimental analysis with the new molecular methods. Contents Summary 403 I. Introduction 404 II. Most ecological applications concern markers in the nuclear geonome 404 III. DNA polymorphisms differ from allozyme pohmorphisms 404 IV. Types of molecular marker 405 V. The application of markers in ecology 409 VI. From marker to character 413 VII. Outlook 414 References 414.

The allotetraploid lactucean Microseris scapigera of Australia and New Zealand has presumably arisen in western North America by hybridization between an annual and a perennial diploid species followed by polyploidization and long-distance dispersal. A phylogenetic tree of various North American diploids, based on RFLPs in the nuclear DNA, confirmed the division of the genus into a clade containing the diploid annuals and a clade containing the diploid perennials. Four RFLP markers were shared among all accessions of M. scapigera and all the diploid accessions. Twelve markers found in the outgroup (Uropappus lindleyi) were absent in all Microseris. A cladogram of plants from six populations of M. scapigera based on eight RFLP markers shows a progressive specialization of three clades of two populations each. Two populations without any markers differentiating them from the North American diploids form the basic clade. These consist of plants with an apparently derived morphology that are self-compatible (or agamospermic) and thereby differ from most M. scapigera. Few markers in M. scapigera could be attributed to one or the other parental genome. As yet, we have found only one ITS 1 sequence of the nuclear ribosomal cistrons in M. scapigera. This sequence has features of both parental sequences.

In order to investigate crossability between the European section Ruderalia Kirschner, H. Øllgaard & Štěpánek and the Asian section Mongolica Dahlst. of the genus Taraxacum Wigg., artificial hybridization experiments were carried out. After inter-sectional crosses on the diploid level, Mongolica plants showed high fruit-set, not strikingly different from either the control (within-populational crosses) or inter-specific crosses within the same section. However, a substantial decrease of fruit-set was detected when Ruderalia plants were the seed parents. Electrophoretic analysis revealed that Ruderalia seed parents in inter-sectional crosses showed relatively low out-crossing rates with low fruit-set, whereas Mongolica plants as seed parents showed high out-crossing rates, mostly 100%. These results indicate that the crossing-barrier is stronger in the direction from Mongolica to Ruderalia than vice versa. Crosses between diploid Mongolica (♀) and triploid Ruderalia (♂) were also successful, although fruit-set was far lower than in 2x-2x crosses, a result which confirms previous reports. Contrary to published accounts, it was found by means of electrophoretic analyses that some 87.5 % of the progeny in 2x-3x crosses were not true hybrids but sexual diploids originating from self-fertilization. Only approximately 12.5 % of the progeny were found to be true agamospermous triploid or tetraploid hybrids. A strong doubt is raised concerning reports in the literature which assume that diploid hybrids originate in 2x-3x crosses. The possible reasons why self-incompatibility was broken down by triploid pollen are discussed.

Seed dispersal by ants in Polygala vulgaris, Luzula campestris and Viola curtisii was studied in a primary dune valley on the island of Terschelling, The Netherlands. Normally developed seeds of all three species are taken by the ants into their nests. The ants show a distinct preference for the seeds of the specialized myrmecochore Polygala vulgaris, as compared with the two diplochorous species. It could be demonstrated that the elaiosome is the attractive part of the seed. Mapping studies demonstrate that the dispersal of the seeds by ants has a marked effect on the distribution pattern of the standing population of Polygala and Viola. Adult plants are often found on or close to the active nest mounds of all ant species present, while the growing sites of juvenile individuals and seedlings are practically restricted to the nest environment. The nests of two of the seed-dispersing ant species, viz., those of Lasius niger and Tetramorium caespitum, show differences in soil chemistry with the surroundings. The ant nests are significantly richer in some essential plant macronutrients, such as phosphate, potassium and nitrate. The advantage of myrmecochory in the dune area of Terschelling is discussed.

A study is presented of the possibilities and limitations of semi-automated karyotype analysis on the basis of chromosome length and centromere index. A number of computer programs have been developed for 1) quick and precise measurements of chromosome arm length with the help of a graphics tablet, 2) computing (relative) length and centromere index and statistical analyses of the data, and 3) representation of these chromosomal parameters in two-dimensional scattergrams. An ellipse representing 95% of the probability mass is drawn around the bivariate mean of each chromosome. The size and orientation of the axes are calculated from repeated measurements of the chromosomes of one metaphase plate. If there is a correlation between length and centromere index, which is often the case, the axes of the ellipse are tilted. Incorporation of such a covariance analysis proved to be of great importance for an accurate karyotype analysis. The "Computer Aided Karyotyping" package does not contain routines for an automated classification of the chromosomes. The main reason is that the variation in length and centromere index of a given chromosome in different cells is often much larger than the variation between nonhomologous chromosomes. In addition, it was our aim to develop universal karyotyping aids which can be used regardless of the species studied.

Condition in the understory of aBetula-carr appeared to be favourable for the growth ofSphagnum recurvum. The estimates of annual productivity and nutrient accumulations forS. recurvum obtained in this wetland forest are in the high range of those reported for peatmosses. On an annual basis, the organic matter production, vegetative reproduction (forking), and accumulation of N, P and K were very much the same for a relatively dry and for a relatively wet year. Periodicity in growth and length increase of the plants, however, differed remarkably between these years, and fruiting was observed in the dry year only.S. recurvum was characterized by a distinct variation in nutrient concentrations both with time and with distance from the capitulum. Organic weight loss during breakdown ofS. recurvum in the wetland forest was low. Release of N, P and particularly K was larger than that of organic matter in decomposingS. recurvum. Nevertheless, a relatively large proportion of the original N and P stock remained associated with the peatmoss material after a 12 month decay period. Observations with the scanning electron microscope revealed that after a year the cells of deadS. recurvum were hardly damaged and only poorly colonized by microorganisms. The characteristics ofS. recurvum described here indicate its potency in directing succession in peatland forests.