František Krahulec

Small-scale spatial dynamics of plant species in a grassland community over six years

. In a species-rich mountain grassland in the Krkonosse Mts., Czechoslovakia, data from four permanent plots of 50 cm x 50 cm were recorded annually from 1985 to 1990 to study the spatial dynamics of the species. Plots were divided into 15 x 15 subplots and the number of vegetative units of all plants within each subplot was determined. There was not much net change at the plot level, but the subplots were very dynamic. Two aspects of the spatial dynamics of the species were followed: (1) persistence, i.e. the tendency of the species to remain in the same subplot, and (2) long-distance spreading, i.e. movement to subplots beyond the immediate neighbourhood. Species differed widely in their persistence and longdistance spreading and were classified into mobility types: long-range guerrilla, short-range guerrilla, phalanx and sitting’. The mobility types were, to a certain extent, correlated with the growth form of plants, but some species of one growth form showed different types of small-scale dynamics and some species with different growth forms had the same spatial dynamics.

Small‐scale variability as a mechanism for large‐scale stability in mountain grasslands

. Data from a 7-yr permanent plot study of grassland dynamics were used to address the relationship between processes at two levels of resolution (3.3 cm x 3.3 cm, 50 cm x 50 cm). Grasslands mown and manured in the traditional way in the Krkonose Mts. (Riesengebirge) were used as a model system. Spatial dynamics at the finest scale were very high, as demonstrated by turnover of individual species in 3.3 cm x 3.3 cm subplots and year-to-year transition matrices of the same subplots. The direction of these dynamics was not correlated with grassland treatment, although there was some correlation within years. An extrapolation of such year-to-year dynamics to larger time scales would result in big large-scale changes on the community level, and large shifts in species composition of the whole sward. However, dynamics at larger spatial or temporal scales were generally small. Some directional change occurred in manured plots, whereas little change occurred in unmanured plots. Large-scale dynamics were not correlated with small-scale dynamics in plots without manuring, but some correlation was detectable in manured plots. There are probably several processes that drive small-scale dynamics, such as non-linear interactions and environmental fluctuations. We argue that within certain limits these forces act on species composition so as to make small-scale dynamics non-directional. This results in both large-scale species diversity and apparent large-scale stability of these grasslands. However, if these forces are beyond these limits, the small-scale dynamics may become directional, resulting in rapid changes at larger spatial scales.

Within population genetic differentiation in traits affecting clonal growth: Festuca rubra in a mountain grassland

Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within‐population variation in these parameters. Clones were sampled in a mountain grassland (The Krkonoše Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber.

Complex distribution patterns, ecology and coexistence of ploidy levels of Allium oleraceum (Alliaceae) in the Czech Republic

BACKGROUND AND AIMS Despite extensive study of polyploidy, its origin, and ecogeographical differences between polyploids and their diploid progenitors, few studies have addressed ploidy-level structure and patterns of ecogeographical differentiation at various spatial scales using detailed sampling procedures. The pattern of coexistence of polyploids in the geophyte Allium oleraceum at the landscape and locality scale and their ecology were studied. METHODS Flow cytometry and root-tip squashes were used to identify the ploidy level of 4347 plants from 325 populations sampled from the Czech Republic using a stratified random sampling procedure. Ecological differentiation among ploidy levels was tested by comparing sets of environmental variables recorded at each locality. KEY RESULTS Across the entire sampling area, pentaploids (2n = 5x = 40) predominated, while hexaploids (2n = 6x = 48) and tetraploids (2n = 4x = 32) were less frequent. The distribution of tetra- and hexaploids was partially sympatric (in the eastern part) to parapatric (in the western part of the Czech Republic) whereas pentaploids were sympatric with other cytotypes. Plants of different ploidy levels were found to be ecologically differentiated and the ruderal character of cytotypes increased in the direction 4x --> 5x --> 6x with the largest realized niche differences between tetra- and hexaploids. Most populations contained only one ploidy level (77 %), 22 % had two (all possible combinations) and 1 % were composed of three ploidy levels. The majority of 4x + 5x and 5x + 6x mixed populations occurred in sympatry with uniform populations of the participating cytotypes in sites with ecologically heterogeneous or marginal environment, suggesting secondary contact between cytotypes. Some mixed 4x + 6x populations dominated by tetraploids being sympatric and intermixed with uniform 4x populations might represent primary zones of cytotype contact. Almost no mixed accessions were observed on the fine spatial scale in mixed populations. CONCLUSIONS The results provide evidence for adaptive differences among ploidy levels, which may contribute to their complex distribution pattern. The prevalence of asexual reproduction, limited dispersal and equilibrium-disrupting processes may support local coexistence of cytotypes.

SPATIOTEMPORAL DYNAMICS IN MOUNTAIN GRASSLANDS: SPECIES AUTOCORRELATIONS IN SPACE AND TIME

Permanent plots with a fine scale recording system were used to trace the spatiotemporal process within two mountain grasslands in the Krkonoše Mts., Czech Republic. The analysis used autocorrelation over increasing lags in space and/or time. MoransI was used to measure the autocorrelation. There was a lot of variation between species both in spatial and temporal correlograms. The spatiotemporal pattern of species correlated well with the growth form of the species and the degree of its clonality. Clonally-growing species tended to have high clumping at distances of a few cells, whereas rosette species often did not show any clumping. The type of clonal growth (compact vs. long spacers) is well corrlated, with the temporal correlogram (species mobility). There is a relation between low mobility and high clumping at low distances. Attempts to explain the mechanisms of species coexistence in these grasslands should take into account the particular structure of the fine-scale dynamics of these communities of predominantly clonal plants. *** DIRECT SUPPORT *** A02DO006 00007

Variation inHieracium subgen.Pilosella (Asteraceae): What do we know about its sources?

The present paper reviews mechanisms producing complicated patterns of variation withinHieracium subgen.Pilosella. The taxonomic complexity of this subgenus is due to highly variable basic species and intermediate (hybridogenous) species. The most important sources of variation are polyploidy, hybridization and (mostly) facultative apomixis of the aposporous type. The combination of hybridization, apomixis and clonal growth leads to the maintenance of various hybrids having originated from backcrossing and hybridization among more than two species, which is possible because of the fertile pollen of apomictic hybrids. Ever since Mendel’s experiments, some of F1 hybrids have been found to be highly variable, probably reflecting the high heterozygosity of some of the basic species. Variable progeny can also result from unreduced gametes, or the rare parthenogenetic development of reduced gametes. While these processes were detected in experiments, their role within field populations remains unknown. However, multiple origins of intermediate species, and introgression within basic species are highly likely to result in high levels of variation. While few population level studies have been undertaken in Europe, several such studies have been carried out on adventive populations in New Zealand, and these show a different pattern. Aneuploid plants, rare in Europe, are common in New Zealand, and there is frequently more than one ploidy level within a population.

Genome size discriminates between closely related taxaElytrigia repens andE. intermedia (Poaceae: Triticeae) and their hybrid

Flow cytometric and karyological investigations were performed on the closely related taxaElytrigia repens andE. intermedia (Poaceae: Triticeae) from the Czech Republic. DNA-hexaploids clearly prevailed among 238 examined plants and amounted to 96.2% of all samples. 2C-values ± s.d. for hexaploidElytrigia repens andE. intermedia were estimated at 23.27 ± 0.20 pg and 27.04 ± 0.24 pg respectively. Genome size thus allowed reliable separation of the two species (difference ca. 16%) as well as the identification of hybrid individuals. Natural hybridization inE. repens — E. intermedia alliance seems to be quite a common phenomenon as indicated from a large proportion (one sixth) of hexaploid samples with intermediate 2C-values. Previously, the crosses were most probably overlooked or misidentified due to their weak morphological differentiation. New nonaploid cytotypes (2n=9x=63) were revealed for both species as well as for the hybrid (determined on the basis of morphological characters only), representing the first records from the field. Fusion of unreduced and reduced gametes of the hexaploids is the most plausible mode of nonaploid origin.

Anthoxanthum odoratum andA. alpinum: Life history parameters at two different altitudes

The closely related species, diploidAnthoxanthum alpinumÁ. Löve etD. Löve and tetraploidAnthoxanthum odoratum L., have distinct distributions:A. alpinum is an arctic-alpine species, whileA. odoratum is a species of lower altitudes and more southerly latitudes. However, some authors suggest that both species are potentially able to maintain their populations in the distribution area of the other species.Reciprocal transplant experiments in two mountain localities (one withA. alpinum, the other withA. odoratum) were carried out to study the survival and vegetative and generative reproduction of tussocks of both species in the area of distribution of the other species. The mortality of tussocks ofA. alpinum was higher in the “alien” locality, the life span of tillers was greatly reduced and the size of tussocks decreased considerably during the experiment compared to its “native” locality. These results suggest that there was a lack of favourable microsites forA. alpinum in the “alien” locality probably caused by the presence of strong competitors.A. odoratum flowered far less in the “alien” locality (both on tussocks and tillers) compared to the “native” one. These results suggest that environmental conditions are not suitable for the flowering ofA. odoratum in the “alien” locality.We conclude thatA. alpinum could have been limited in extending its distribution into the area ofA. odoratum by the presence of strong competitors, whileA. odoratum could have been limited by its ability to reproduce by seed.

Introgressive hybridization between a native and an introduced species:Viola lutea subsp.Sudetica versusV. Tricolor

A hybrid swarm betweenViola lutea subsp.sudetica (2n=50, native species) andViola tricolor (2n=26, introduced species) originated in the 1970’s in the Krkonoše Mts. Analyses of chromosome numbers, reproductive biology, morphology, and ecology gave the following results: (1) Compared to the plants found in the 1970’s, the number of colour morphs have decreased and the types now prevailing in the field are morphologically closer toV. lutea subsp.sudetica, forming a continuum. (2) In the field, hybrids having approximately the same chromosome number as the primary hybrids are most common. Some plants of the hybrid swarm have certain characters unknown to their parents. (3) In the field, autogamous types similar toV. tricolor were found. (4) A limited number of plants from the field and culture have higher somatic chromosome numbers thanV. lutea subsp.sudetica; there was a tendency towards increasing chromosome numbers in their progeny (up to 2n=62). These plants have some new morphological characters (a small proportion of hexacolpate pollen) not found in the parents (nor in the other hybrids with prevailing tetracolpate and pentacolpate pollen grains) and higher pollen fertility in comparison to the other hybrids. These plants also have the highest germination rate. (5) There is a tendency for chromosome numbers to decline in the progeny of open pollinated hybrid plants in the lowland experimental graden. (6) The phenology of the plants in the mountain grasslands and the lowland garden is different; the parents behave in a totally contrasting manner. (7) In the field at least some hybrids extend outside the geographical and ecological ranges of the parental species, invading new communities. (8) Seeds ofV. tricolor do not show any dormancy and germinate in the year of production; most of theV. lutea subsp.sudetica seeds germinate during the spring of the following year. Hybrids with intermediate chromosome numbers had both types of germination strategy. The germination rate of intermediates with high chromosome numbers was even higher than that ofV. tricolor.

Is a grassland community composed of coexisting species with low and high spatial mobility

Patterns of grasslands species mobility were compared between communities and within plant species. Data from high spatial resolution permanent plots with fine scale recording system, experiment with removal of the dominant recorded also at a fine scale were used. The permanent plots showed large variation within a community in the patterns of species mobility. The species mobility was partly dependent on the site and was higher in a more nutrient rich and climatically more favourable community. Mobility also varied within species. In some species (Nardus stricta, Anthoxanthum spp.) it differed between communities (it was higher in more nutrient rich and climatically more favourable community) and did not respond to removal of the dominant species. In another species,Festuca rubra, mobility also differed between plots; in contrast, it did not show consistent variation attributable to community type and showed strongly increased spatial persistence in plots with the dominant species removed. In this species the mobility seems to be dependent on the competitive pressure of the coexisting species.