Department of Population Ecology

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Population biology of critically endangered and invasive species in central European flora

In our department we study population dynamics of many different species. We stress studying the entire life cycle because only these kinds of studies enable us to identify which stages of the life cycle are important, what environmental factors they depend on and how it is possible to influence them. The studies typically use modeling with transition matrices, which is simple enough for data collection and provides a versatile enough tool for modeling. This knowledge can then be applied in a study of a species that deserves attention for various reasons. These tend to be species of rare and threatened species (Dracocephalum austriacum, Ligularia sibirica, Aster amellus, Gladiolus imbricatus and G. palustris, Thesium linophyllon, Minuartia verna, Linum flavum and many others), where knowledge of population biology can be used to support their populations, and where, therefore, population biology represents a substantial extension of existing approaches based mainly on long-term monitoring without sufficient knowledge about real mechanisms in the populations. For rare species we also study the relationship between population dynamics and genetic diversity of populations. We are also interested in invasive species (Rumex alpinus, Pinus strobus, Heracleum mantegazzianum), where we use knowledge of population biology to propose targeted actions to limit the growth of their populations. As a consequence of studies of grassland communities we also study the population dynamics (at the level of genets and ramets as well) of selected grassland species, particularly Festuca rubra and Anthoxanthum odoratum agg.

Biology of seed dispersal

In the department, we also focus on another important part of species population biology (especially at the landscape level) – species dispersal mechanisms. We investigate experimentally the processes related to seed dispersal, especially using information on terminal velocity of seeds and their ability to attach to animal fur. We also use observations such as seed trap experiments and we count individuals occurring depending on distances from the parental plant. Target species are the species selected for the description of population and landscape dynamics. We also use techniques of approximation of dispersal curves by simple formulas (e.g. hyperbolic, exponetial) with subsequent testing of obtained dispersal curves. This information is then used for modeling of species population dynamics at the landscape level.

Populations dynamics at the landscape level

We research species dynamics at the landscape level (especially in fragmented agricultural landscape) using a spatially explicit model and information on population biology of species. This approach enables us to evaluate the knowledge of population biology, seed biology and dispersal, and landscape/vegetation structure (including its suitability for individual populations). We also use the information on historical maps. It enables us to test hypotheses about past species distribution and to determine whether the species distribution and current landscape structure are in equilibrium, or the species is in extinction debt. Target species are species from fragmented habitats in agricultural landscapes: e.g. Succisa pratensis, Jasione montana, Scorzonera hispanica, as well as invasive species: e.g. Rumex alpinus or Pinus strobus. Another system under study for species dynamics and distribution is that of meadow anthills (of Lasius flavus) hosting annual plant species. The species survival depends here on its ability to colonize recently created habitats (and overcome unsuitable places in meadows) and to survive the disturbance caused ant building activity. 

Dynamics of invasive tree species, Pinus strobus

Pinus strobus L. (eastern white pine), a conifer tree native to eastern North America, has been cultivated in central Europe since the end of the 18th century. It has been introduced into mixed conifer forests to improve species composition and to prevent pest development in species-poor forests. The species' ability to regenerate in the new area was noticed during the early days of cultivation and its massive spread into the surrounding forests was first recorded in the 1990s, when the species entered predominantly acidophilus pine (Dicrano-Pinetum) and oak-pine (Vaccinio vitis-idaeae-Quercetum) forests. In sandstone areas, P. strobus is now a component of not only cultivated mixed forests, but also of natural forests and sparse vegetation on the rocks. However, the sandstones are nature-protected areas because of their unique environment. That means the large-scale regeneration of an alien tree has become a major ecological problem and hence a major conservation issue. Pinus strobus suppress the native tree growth, tree regeneration and the undergrowth herb, moss and lichen composition. The aim of our research is to examine the role of landscape structure and different dispersal parameters for the P. strobus invasion spread using a realistic spatially-explicit invasion model. The invasion is modeled in the sandstone landscape of the Bohemian Switzerland, the area with highly varying degree of connectivity and density of suitable habitats. Data on the population biology of the species, vegetation and a digital model of the terrain are used in the model. 

Do non-indigenous species benefit from enemy release? A field comparison with native congeners

One of the hypotheses explaining the success of non-indigenous species (NIS) in a new range is release from enemies (Enemy Release Hypothesis, ERH). Lowering enemy pressure may provide NIS an advantage over native species when competing for resources. To test this hypothesis, we are carrying out field comparison of enemy impact on 12 exotic species and the same number of native congeners. We are focusing on the impact of four enemy guilds – seed and soil pathogens, herbivores and frugivores. In the search for potential impact of specialized enemies we also are evaluating the link between the phylogenetic composition of the colonized community and the impact of enemies on exotics.

Dynamics of grassland communities

Grassland communities are a classical example of plant species coexistence at a fine scale. We study mechanisms involved (niche requirements, resource competition, growth forms of the plants involved, within-species variation), primarily in the model region (Krkonoše Mts.). In particular, we address dynamics running at a small scale (ramet-level). Our recordings of fine-scale dynamics over long time intervals (now more than 20 years are used to disentangle interactions between individual species. We also address between-year variation. A series of different manipulative experiments (fertilization, removal, implants) has been used to address interactions of individual species pairs and interactions within and between functionally defined guilds.

Belowground structures and processes in grasslands

Grasslands typically have a high root/shoot ratio, and many important processes run below the ground. Most of the work has concentrated on three main topics: (i) rhizome structure and growth of matrix species. This enabled the detection of the presence of species-specific interactions between rhizome systems of the matrix species in the meadow; (ii) fine-scale root spatial structure and its links to spatial structure of aboveground organs using morphological tracing and /or tracer elements (Sr, Rb); (iii) fine-scale spatial and temporal heterogeneity of main soil resources (NO3-, NH4+ and PO43- ions) using analysis of soil water samples. We have been studying rhizome architecture under different levels of competition, tracer element transport horizontally and vertically, root spatial extension, fine-scale heterogeneity in root growth and associated heterogeneity in nutrient availability.

Spatially explicit models of communities of clonal plants 

Modelling spatio-temporal structure enables us to link the following kinds of data already available from grassland model systems (i) the spatio-temporal structure of species densities, (ii) data on species interactions, (iii) data on genet numbers and size of dominant species, (iv) data on rhizome architecture. The modeling framework used is based on a combination of an architectural model with an individual-based model of ramet competition and is calibrated using field data for these four species. Primary questions investigated are: (i) the link between architectural constraints, individual-based interactions and spatio-temporal structure in grasslands, and communities of clonal plants, (ii) determination of the frequency of seedling establishment that would be consistent with the observed numbers and sizes of genets of dominant plants, (iii) the processes involved in long-term coexistence of species. The same framework is used to assess the role of individual plant traits underlying plant performance and processes such as population growth, competition and community dynamics. Further, we use this framework to examine how effects of these traits differ (i) depending on the context of other traits (e.g., different identity of species), and (ii) depending on other species in the community.

Management of species-rich mountain grasslands

Species-rich mountain meadows are one of the prime targets of nature conservation, both for their high diversity and publicly appreciated value. As traditional management is largely economically unfeasible, alternative management schemes are being sought and studied.

Grazing as an alternative to traditional management.
Grazing leads to the suppression of species that dominate the degradation phases (Polygonum bistorta) and to an increase in grass species; with the increase being positively correlated with an increase in several herbs. No negative influence on rare and protected plants was observed. Sheep grazing, particularly when done on a rotating basis, seems to maintain most of the species of the species-rich grasslands. Grazing should therefore be combined with occasional mowing that is needed to suppress spreading of unpalatable species.

Mulching as an alternative to traditional management.
Mulching became a way of management of mountain meadows in the Czech Republic during the last decade. Unfortunately, there is no experience with it on longer time- scale. It is obvious that on a shorter time-scale (of years) it can substitute hay-making and that it is a better system than abandonment. There is a danger of long-term effects connected (i) with absence of export of biomass (and nutrients) from enriched part of meadows and (ii) with increase of undecomposed litter with a low decomposition rate in the meadow part. We therefore are running a long-term experiment to test the influence of mulching and manuring (to stimulate decomposition) on the species composition of mountain meadows. Further, dominance of one species may severely disrupt the whole system; understanding the conditions that lead to such dominance is important for meadow management and restoration of species-rich meadows.

Rare species in the Czech flora

This project aims to identify causes of rarity of a large part of our critically endangered species using methods of comparative population biology (i.e., phylogenetically fair comparison at an infrageneric level). At the level of species the project uses techniques and knowledge gained in the study of population biology of separate species but because of the large number of rare species it aspires to simplify the testing and use of techniques for estimation of their dynamics. It aims to identify and distinguish between types of rarity of each species. This enables us to answer general questions about general rarity patterns of species; as majority of all species in the flora are rare or relatively rare, this is essential for understanding overall biodiversitypatterns. At the same time it provides outputs useful for effective conservation of these species.

Ecology of polyploids 

In cooperation with the laboratory of plant flow cytometry we study the population biology of populations with more cytotypes. This is largely unexplored territory because such populations have been previously studied in the cytogenetic and phytogeographical way, but the studies were almost totally lacking knowledge about their possible diversity in terms of growth parameters, demography information in the field and interactions with herbivory or mycorrhiza interactions. The model species used is mainly Aster amellus, which occurs in the Czech Republic in two ecologically partially different and locally vicariant cytotypes.

The role of genetic diversity for the productivity and community stability 

It was recently shown that not only species diversity but also intraspecific genetic diversity is of great importance for the functioning of communities. That is why in this research we focus on the study of the importance of genetic diversity and the effect of spatial genet arrangement on the structure of the community and its stability (the model species used is Festuca rubra). We are interested in the effect of genetic diversity on productivity, stability and resistance to invasion. We also ask whether the resulting structure of the community is due more to "complementarity" or "sampling" effects (see Loreau and Hector, Nature, 2001) and what is the impact of spatial genet arrangement on the resulting parameters of communities. So that we can tell whether the resulting structure of communities reflects complementarity of individual genotypes  or a mere sampling effect, it is necessary to identify individuals in communities using genetic methods. In this field we cooperate with the Department of Genetic Ecology.

 International Projects

1. Realization of a part of an action plan for Gentiana verna subsp. verna

Project is supported by EEA and Norway Grants.
Gentiana verna ssp. verna is a critically endangered species of flora of Czech Republic. Currently, its lowland form occurs in one locality in reservation Rovná in Southern Bohemia and its mountain form at two localities in Jeseníky mts. Aim of the project is realization of part of an action plan. Specifically, monitoring of population in Rovná reservation, finding suitable localities for future reintroduction and assessing minimal size of viable population.

2. Preparation of an action plan for Gentianella praecox subsp. bohemica

Project is supported by EEA and Norway Grants.
At the beginning of the 20th century the Bohemian Early Gentian (Gentianella praecox bohemica) still occurred relatively abundantly in the entire Czech Republic except for western and north-western Bohemia and south-eastern and eastern Moravia. As a result of changes in the habitat management – abandonment of grazing and regular mowing, ploughing meadows and pastures, eutrophication of habitats, invasion of bushes etc. – the plant has been gradually disappearing in wild: currently its occurrence is limited to only 65 sites, most of them in Šumava (Bohemian Forest) and in the Šumava-Nové Hrady foothills. Aim of the project is to prepare an action plan for this species.