Mária Höhn

Worldwide evidence of a unimodal relationship between productivity and plant species richness

Grassland diversity and ecosystem productivity The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity. Science, this issue p. 302 The humped-back model of plant species diversity is confirmed by a global grassland survey. The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.

Genetic structure of peripheral, island-like populations: a case study of Saponaria bellidifolia Sm. (Caryophyllaceae) from the Southeastern Carpathians

Geographically peripheral populations often experience a reduction of genetic diversity and divergence from the core populations. Habitat geometry and quality can induce a local genetic diversity pattern, which overlies the regional variability issued from the range-wide phylogeography. We evaluated the genetic variation and genetic divergence of Saponaria bellidifolia Sm. on limestone outcrops within peripheral island-like populations from the Southeastern Carpathians, using RAPD markers. We also determined the degree of isolation related to other European populations, using AFLP. The Romanian populations had a decreased overall genetic diversity shared among populations, with lower level in small populations. Potential habitat size had a positive effect on genetic diversity estimates. Fisher’s exact tests of genetic differentiation revealed significant divergences only between the geographically most distant populations. Romanian populations were genetically pauperised as compared to Bulgarian and Italian populations and our results suggest that they might have originated from a recent range expansion from southern glacial refugia.

Genetic structure in Pinus cembra from the Carpathian Mountains inferred from nuclear and chloroplast microsatellites confirms post-glacial range contraction and identifies introduced individuals

Genetic differentiation of scattered populations at neutral loci is characterized by genetic drift counteracted by the remaining gene flow. Populations of Pinus cembra in the Carpathian Mountains are isolated and restricted to island-like stands at high-elevation mountain ranges. In contrast, paleobotanical data suggest an extended early Holocene distribution of P. cembra in the Carpathians and its surrounding areas, which has contracted to the currently disjunct occurrences. We analyzed the genetic variation of 11 Carpathian populations of P. cembra at chloroplast and, in part newly developed, nuclear microsatellites. Both marker types revealed low levels of genetic differentiation and a lack of isolation by distance, reflecting the post-glacial retraction of the species to its current distribution. Stronger effects of genetic drift were implied by the higher genetic differentiation found for haploid chloroplast than for diploid nuclear markers. Moreover, we found no association between the values of population genetic differentiation for the two marker types. Several populations indicated recent genetic bottlenecks and inbreeding as a consequence of decline in population sizes. Moreover, we found individuals in two populations from the Rodnei Mountains that strikingly differed in assignment probabilities from the remaining specimens, suggesting that they had been introduced from a provenance outside the studied populations. Comparison with Eastern Alpine P. cembra and individuals of the closely related Pinus sibirica suggests that these individuals presumably are P. sibirica. Our study highlights the importance of the maintenance of sufficiently large local population sizes for conservation due to low connectivity between local occurrences.

Current range characteristics of Swiss stone pine (Pinus cembra L.) along the Carpathians revealed by chloroplast SSR markers.

We investigated the diversity pattern of nine Swiss stone pine (Pinus cembra L.) populations along the Carpathian range including the High Tatras, by using six chloroplast DNA microsatellites (cpSSR). Our aim was to detect genetically distinct regions by clustering of populations, and to tackle possible historical colonization routes. Our analysis referred to an investigated geographical range with the two most distant populations situated at about 500 air km. We found that the most diverse populations are situated at the two edges of the investigated part, in the Retezat Mts. (South Carpathians) and the High Tatras, and diversity decreases towards the populations of the Eastern Carpathians. Hierarchical clustering and NMDS revealed that the populations of the South Carpathians with the Tatras form a distinct cluster, significantly separated from those of the Eastern Carpathians. Moreover, based on the most variable chloroplast microsatellites, the four populations of the two range edges are not significantly different. Our results, supported also by palynological and late glacial macrofossil evidences, indicate refugial territories within the Retezat Mts. that conserved rich haplotype composition. From this refugial territory Pinus cembra might have colonized the Eastern Carpathians, and this was accompanied by a gradual decrease in population diversity. Populations of the High Tatras might have had the same role in the colonizing events of the Carpathians, as positive correlation was detected among populations lying from each other at a distance of 280 km, the maximum distance between neighbouring populations.

Competitive replacement of the native Vitis and Hedera taxa by invasive aliens: morphological, cytological and molecular evidences

We describe here case studies of two woody climber species native to the broadleaf forests of the Carpathian basin. Wild grape ( Vitis sylvestris C.C.Gmel.), considered to be one of the ancestors of the domesticated grapevine ( Vitis vinifera L.) became a highly threatened species since the introduction of the American grape species as rootstocks for grapevine. Among these, especially, Riparian grape ( Vitis riparia Minchx.) escaped from the wine yards and by invading the natural habitats replaced the autochthonous wild grape. In consequence of the competitive exclusion Vitis sylvestris suffered a strong withdrawal along its native habitats. 20 morphological traits, including leaf shape and trichome structure were studied to tackle evidence of the introgressive hybridization among the alien and native taxa. Most of the studied Hungarian habitats were already dominated by hybrid specimens of Vitis taxa. Molecular analysis based on 8 nuclear microsatellites markers supported the morphological results.

Spatial genetic structure in Swiss stone pine suggests a region-specific population history of the species along the Carpathian range

Recently reported evidence supports the existence of ancient populations of cold-tolerant boreal forest species in the upper ranges of the Carpathians. Studies on allele length polymorphism designated several glacial refugia for Norway spruce (Picea abies) in the South Carpathians. Former molecular studies performed on live remnant populations of Swiss stone pine (Pinus cembra) and Scots pine (Pinus sylvestris) suggest that the Carpathians are important in terms of accumulation of genetic diversity