National Repository of Grey Literature 30 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Bird diversity and life-history patterns along gradients of productivity and its variation
Tószögyová, Anna ; Storch, David (advisor) ; Remeš, Vladimír (referee) ; Field, Richard (referee)
Geographical variability in species richness and life-history strategies shows remarkable and well-documented patterns generated by various processes that have not yet been fully revealed. However, the pronounced correlation between spatial patterns in species and trait diversity and spatial gradients in environmental conditions indicates that the environment may modulate these processes. The mechanisms related to environmental productivity (energy availability), as a strong predictor of biodiversity, have been hypothesized to explain the cause of these broad- scale biodiversity patterns. Still, there is no consensus in the explanation, as many of the environmental and biotic factors are strongly interrelated. We have derived testable predictions that allowed disentangling the mechanisms responsible for spatial distributions of life-histories and species richness. The patterns in spatial distribution of many avian traits across the striking productivity gradient in South Africa show a slow-fast continuum in life-history strategies. High environmental productivity in tropics may result in stable populations that favour slow life-history strategies; birds can utilize stable food resources - low food seasonality selects for small clutch sizes, long parental care and high juvenile survival. The...
Determinants of abundances in terrestrial vertebrates
Kundelová, Tereza ; Storch, David (advisor) ; Sedláček, Ondřej (referee)
The abundance of animals differs between species, however, they also vary in area and time. These differences relate to biotic and abiotic factors as well as to ecological characteristics of particular species. Studies focusing on these factors are aiming to answer the question; how and what influences the abundance of these species. Besides clarifying the dependence of abundance on particular factors, studies also try to ascertain which key factors are necessary for the determination of abundance. The most frequently studied factor is body size, but trophic level, specialization, net primary productivity, and competition also play a significant role in determination. However, all these factors explain only a small proportion of interspecific variability in abundances. This thesis focuses on terrestrial vertebrates; however, mainly on birds and mammals; since, these two taxa are the most studied. Key words: abundance, population density, terrestrial vertebrates, body size, competition, energy flux
Population trends of African mammals
Homová, Viktória ; Storch, David (advisor) ; Hulva, Pavel (referee)
The African continent is known for its rich species diversity (biodiversity). We can read about the decline in African mammal populations in various sources. The main reasons of decline include loss of habitats and animal hunting. In spite of the general idea of decline mammals, in some cases the population trend is stable or growing. The aim of my thesis is to explore and summarize what is really known about the changes in the populations of all known mammalian species over the past decades. The attention of public is mainly oriented towards large flagship species, which are very well studied and various measures are put in place to protect them, especially in protected areas. The most marked decline in the number of individuals occurs in the western part of Africa, which is probably caused by a combination of lack of financial and human resources in animal protection, a large range of biotope damage and growing bushmeat trade. Species with increasing population trends are predominantly in South Africa, where there is an improvement in the management and the protection of wildlife receives more attention. Considering small mammals, there is, in most cases, no relevant data available to help determine their population trend. The population trends of species residing in the tropical rainforests are...
Diversity dynamics across scales
Macháč, Antonín ; Storch, David (advisor) ; Remeš, Vladimír (referee) ; Ricklefs, Robert (referee)
Charles University, Prague Diversity dynamics across scales Antonin Machac 2018 Abstract Diversity dynamics remain controversial. It has been suggested that the dynamics are expansionary, such that the number of species across regions and clades increases constantly. However, the opposite has also been suggested, namely that species numbers are relatively stable, following equilibrial dynamics. Both views (expansionary and equilibrial) have been supported by compelling phylogenetic, biogeographic, and fossil evidence and, currently, it remains largely unclear how the two seemingly conflicting views could be reconciled. My dissertation addresses this question, based on the premise that diversity dynamics change systematically with scale. Specifically, I hypothesize that expansionary dynamics typify regionally distributed, small, and young clades whose diversity tends to expand, driven by a variety of regionally relevant factors (e.g. habitat-level adaptation, biotic interactions, or montane shifts leading to ecological divergence and speciation). Conversely, equilibrial dynamics typify large, ancient, and globally distributed clades, whose diversity is environmentally limited (e.g. by the total amount of resources that can sustain only a limited number of populations and species). Consequently, it seems...
Extinction risk and population size
Váňová, Lenka ; Storch, David (advisor) ; Reif, Jiří (referee)
There is generally accepted assumption that the probability of extinction risk increases with decreasing population size. But it's not sure at all, to what extent does this relation really work in real populations. The amount of studies dealing with this topic is on the increase, but still it's necessary to carry on researching. Previous results indicate that inspected connection is indeed true in many populations, in other words, preferential extinction of less abundant populations functions properly. Yet the dependence isn't as unambiguous and strong as expected. Many exceptions are known as well, which demonstrate that low number of individuals doesn't always have to be a disadvantage in terms of survival chance. Such deviations can be found both in paleontological papers and among current populations. For example, mass extinctions represent that kind of a special exception because each of them was probably driven by a different mechanism, so in one case the abundance could be an advantageous trait, whereas in another it was rather disadvantage. In my work, I briefly mention themes referring to extinction in general and subsequently I try to summarize findings about the phenomenon of population size and its connection to extinction risk. On the basis of explorers' ideas and by means of...
Dominance of different groups of animals in terrestrial ecosystems
Matysová, Barbora ; Storch, David (advisor) ; Tropek, Robert (referee)
There are some beliefs about the abundance and biomass of different animal groups, which persist in general awareness. At the same time, the ideas of the general public relate to the influence and importance of the animals for an ecosystem. The aim of this paper is to make sure that these assumed concepts of dominating entities are based on truth or if they are only mistaken rumors, and to answer the following questions: whether the biomass of large herbivores or termites is significant in the tropics, what is their influence on decomposition of vegetation matter; if the biomass of all ants actually exceeds the biomass of all people in the world; whether the abundance of prey and predators is stable across ecosystems; if there are more herbivores in tropical or cold ecosystems; or when predominant abundance of ants or termites is present in tropical ecosystems. Responses are gained through the extensive collection of abundance and animal biomass data from expert articles and publications. In order to be verifiable as well as the stability of the given ratios over the years,there were used data from the oldest traceable materials about 80 years old to the current data from current works. In addition to biomass and abundance values, attention is also paid to the methods used by scientists to collate...
Influence of landscape fragmentation on characteristics of pollination networks in meadows
Filip, Jan ; Tropek, Robert (advisor) ; Storch, David (referee)
Traditionally managed semi-natural grasslands are unique for their high plant species richness. Pollinators are crucial for maintaining this plant biodiversity. Plant-pollinator interactions of these grasslands are influenced by habitat fragmentation since the 20th century. Main drivers of this landspace disturbance are abandonment and agricultural usage. Network analysis of structural characteristics changes in plant-pollinator interactions can facilitate understanding of habitat fragmentation and its impacts on pollination interactions.
Dichromatism in Passerine Males and other aspects of sexual selection
Schwarzová, Lucie ; Fuchs, Roman (advisor) ; Grim, Tomáš (referee) ; Storch, David (referee)
Dichromatism in Passerine Males and Other Aspects of Sexual Selection Lucie Schwarzová 1. Summary of PhD Thesis Themaingoalof thepresentedlhesiswasto testsomeof thepredictionsof lrypotheses conoerningdolayedplumagemefurstion(DPM) in ťreBlack Frodsbrrt(Phoenicurus ochraros),a speoiossuitablefor suoha studydueto itshighbreodingdensityin urban hebitats.I studiedarrival pattorrl size, quality anddishibutional pattemoftemitories and aggressivebehaviourofsubadultandadultmalegandhormonaloorrelatosofplumage colourationin Black Redstart. ThebirdsinhabitingSoulhMoravianvillagesdid notshowdifferentialtimingof anivals betweenyearlings andolder birds in thoresource-richenvironment. On theotheÍ hand,undersuboptimaloonditionsin Praguetheyoarlingsworedelayedofthroedayson averagecomparedtotheadultmales.Thoreis thepossibiliý for theyoungbirdsofthis speciesb samplethesituationona potentialbroedingsite during autumnalsinging periď andflexibly fit its migratingbehaviouraccordingto tro circumstances.In suoha casethorďuction investnenthypothosisis thobestexplanationfor diÍferentarrival timingof yearlingandadultmalosin Black Redstart. To testp,redictionsof statussignallrypothesigwhich olaimsthattheadultsless frequently attrokdull colourď subadultmales,andconsoquerrtlyDPM facilitatessurvivalofsubadults...
Habitat as a determinant of abundance and distribution of birds in space and time
Reif, Jiří ; Storch, David (advisor) ; Fuchs, Roman (referee) ; Konvička, Martin (referee)
of the thesis The thesis focuses on various aspects of bird-habitat relationships. We found that the positive correlation between local abundance and regional distribution of birds is not a universal pattern. Its strength and direction depends on the similarity of habitat cover at the locality where the species abundances are measured and habitat cover of the wider region where the species distribution is assessed. In the case of the Cameroon Mountains, many locally abundant species had relatively small ranges in subsaharan Africa. They were probably well-adapted to specific conditions of montane environment, and such tight habitat association precluded their occurrence in regions covered by savannah or humid lowland forest. At the same time, isolation and unusual environmental conditions of the montane forest in the Cameroon Mountains reduced possibilities of their colonization by species widespread within Africa. Such species were confined to deforested areas in the Cameroon Mountains. The strongest gradient in bird community structure was between birds of montane forest and birds of non-forest habitats, and this gradient is probably one of the most important bird-habitat gradients worldwide. Endemic species and species confined to afrotropical mountains had the highest association with montane...
Universality in biodiversity trends
Bohdalková, Eliška ; Storch, David (advisor) ; Keil, Petr (referee)
Biodiversity trends (such as the relationship between species richness and temperature or productivity) are always defined for a particular taxon at a specific area (the entire range of the taxon or often just a region arbitrarily chosen by researchers). The form of these trends varies between taxa and regions. The weak relationship between richness and temperature or productivity is sometimes interpreted as a counterevidence for the hypothesis explaining diversity patterns by these variables. However, the delimitation of taxa or region may play a crucial role for the form of the trends. The aim of this thesis is to determine whether some taxon properties (its size) or region properties (its area, range of explanatory variables, the temperature-productivity relationship or average temperature) affect the strength and slope of the richness-temperature and richness-productivity relationships. 46 data sets of species richness for a wide range of plants, invertebrates and ectothermic vertebrates within different regions of the world were used for the analysis. While the taxon size is likely to affect the strength and slope of the relationship when comparing individual (nested) subclades within larger clade, the comparison of different taxa in different regions of the world shows only the effect of the region...

National Repository of Grey Literature : 30 records found   1 - 10nextend  jump to record:
Interested in being notified about new results for this query?
Subscribe to the RSS feed.