David Hořák

David Hořák
Charles University in Prague | CUNI · Department of Ecology (PF)

PhD

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81
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Publications

Publications (81)
Article
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The parasite island syndrome denotes shifts in parasite life histories on islands, which affect parasite diversity, prevalence and specificity. However, current evidence of parasite island syndromes mainly stems from oceanic islands, while sky islands (i.e. mountains isolated by surrounding low-elevation habitats) have received limited attention. T...
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Biodiversity plays a vital role in ecosystem functioning, so understanding how species coexist is a cornerstone of ecology. However, despite decades of research, our current knowledge is incomplete due to methodological limitations and sampling bias, particularly in the species‐rich tropics. In this study, we combined bill and body morphological tr...
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Two distinct diversity patterns are observed along tropical elevations: (a) decreasing number of species toward high elevations and (b) a hump‐shaped pattern with the peak at mid‐elevations. As diversity is likely supported by ecological capacity of the environment, decomposition of the overall richness into ecological facets and considering number...
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Environmental productivity, i.e., the amount of biomass produced by primary producers, belongs among the key factors for the biodiversity patterns. Although the relationship of diversity to environmental productivity differs among studied taxa, detailed data are largely missing for most groups, including insects. Here, we present a study of moth di...
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Species' geographical distributions and abundances are a central focus of current ecological research. Although multiple studies have been conducted on their elucidation, some important information is still missing. One of them is the knowledge of ecological traits of species responsible for the population density variations across geographical (i....
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Tropical bird species are characterized by a comparatively slow pace of life, being predictably different from their temperate zone counterparts in their investments in growth, survival and reproduction. In birds, the development of functional plumage is often considered energetically demanding investment, with consequences on individual fitness an...
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Many natural ecosystems in tropical regions are under immense anthropogenic pressure, mostly connected with forest logging. However, several other factors may play important roles. From a conservation perspective, it is important to assess the impacts of these changes in biodiversity hotspots, but adequate data are scarce. We repeated point-count b...
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Tropical forests store 40-50% of terrestrial vegetation carbon. Spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests. Because of climatic and soil changes with increasing elevation, AGC stocks are lower in tropical montane compared to lowland forests. Here we ass...
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Tropical forests store 40–50 per cent of terrestrial vegetation carbon1. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests2. Owing to climatic and soil changes with increasing elevation3, AGC stocks are lower in tropical montane forests compared with...
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While birds are known to show preferences for distinct vertical strata in forests, detailed studies on the vertical distribution of whole communities are still scarce. Furthermore, of those conducted, most have used ground‐based methods, including in both tropical and temperate forest. Here, we utilised ground‐to‐canopy mist nets to explore the ver...
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Trait matching—a correlation between the morphology of plants and their pollinators—has been frequently observed in pollination interactions. Different intensities of natural selection in individual regions should cause such correlations to be observable across different local assemblages. In this study, we focused on matching between spur lengths...
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Sperm cells vary tremendously in size and shape across the animal kingdom. In songbirds (Aves: Passeri), sperm have a characteristic helical form but vary considerably in size. Most of our knowledge about sperm morphology in this group stems from studies of species in the Northern temperate zone, while little is known about the numerous species in...
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Aim Temporal dynamics of biodiversity along tropical elevational gradients are unknown. We studied seasonal changes of Lepidoptera biodiversity along the only complete forest elevational gradient in the Afrotropics. We focused on shifts of species richness patterns, seasonal turnover of communities and seasonal shifts of species’ elevational ranges...
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The original online version of this article contained an error in Figure 2b. The scale in the figure published contained a second incidence of 0.3 where 0.2 should have appeared. The scale has now been corrected to accurately display a range from 0.0–0.6 at the correct 0.1 intervals.
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Recently, there has been an increased effort to unravel selective factors behind female song evolution in songbirds. Female birds which produce songs may sing either solo or in duets; although the 2 vocal performances likely evolved through different selection forces and mechanisms, the majority of large-scale studies to date have focused only on d...
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The level of habitat specialization is informative in terms of animals’ population status and conservation concern. Therefore, identifying the areas where specialist species are aggregated and understanding the ecological constrains that might shape their distribution has become an important issue. In this sense, we tested whether specialist commun...
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Aim To test if tree species richness and forest structure drive spatial variation in avian communities along a tropical elevation gradient and to present information about the role of detailed forest parameters. Location A 2,000‐m long elevational gradient of tropical forest on Mt. Cameroon, west‐central Africa. Taxon Birds and trees. Methods We...
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Although birds have genetically determined sex, the sex ratio has been reported to deviate from parity in several studies. Temperature-dependent sex determination, which is common in reptiles, is absent in birds. However, females are able to adjust their investment into eggs according to the sex of the embryo, which may cause sex-specific embryonic...
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Environmental change has reshuffled communities often causing taxonomic homogenization rather than differentiation. Some studies suggest that this increasing similarity of species composition between communities is accompanied by an increase in similarity of trait composition—functional homogenization—although different methodologies have failed to...
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Positive selection acting on Toll‐like receptors (TLRs) has been recently investigated to reveal evolutionary mechanisms of host‐pathogen molecular co‐adaptation. Much of this research, however, has focused mainly on the identification of sites predicted to be under positive selection, bringing little insight into the functional differences and sim...
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Urban bird communities are homogenized across large spatial scales, suggesting that the urban environment acts as an environmental filter. We hypothesize that large scale commonness is a better predictor of urban affinity of birds than any particular species trait. We estimated the relative importance of taxonomy, reproductive, ecological and morph...
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Motivation Birds are an extremely diverse group in terms of adaptations to environmental conditions, which is reflected in their life histories and ecological traits. Recently, functional aspects of avian diversity have been used frequently in comparative analyses as well as in community ecology studies; thus, open access to complete datasets of tr...
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Recent observations from the tropics indicate seasonal peaks in breeding and vocal activity of some bird species. However, information about seasonality in vocal activity at the community level is still lacking in the tropics. We examined seasonal variation in the diurnal vocal activity of lowland rain forest birds on Mount Cameroon, using weekly a...
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Maximizing the area under biodiversity-related conservation measures is a main target of the European Union (EU) Biodiversity Strategy to 2020. We analyzed whether agri-environmental schemes (AES) within EU common agricultural policy (CAP), special protected areas for birds (SPAs) and Annex I designation within EU Birds Directive had an effect on b...
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Aim: Among the world’s three major nectar-feeding bird taxa, hummingbirds are the most phenotypically specialized for nectarivory, followed by sunbirds, while the honeyeaters are the least phenotypically specialized taxa. We tested whether this phenotypic specialization gradient is also found in the interaction patterns with their floral resources....
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Reproductive traits provide information about the ways by which available resources are allocated during breeding. We tested for environmental drivers of large scale geographical patterns in assemblage mean clutch size, number of broods and overall reproductive investment per breeding season in European birds. We combined data about geographical di...
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The usual positive inter-specific relationship between range size and abundance of local populations can have notable exceptions in Afrotropical montane areas, where range-restricted bird species are unusually abundant. We tested how the area occupied locally by passerines and their geographic range size relate to local abundances along a tropical...
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Conspecific brood parasites lay eggs in nests of other females of the same species. A variety of methods have been developed and used to detect conspecific brood parasitism (CBP). Traditional methods may be inaccurate in detecting CBP and in revealing its true frequency. On the other hand more accurate molecular methods are expensive and time consu...
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Birds show considerable variation in sperm morphology. Closely related species and subspecies can show diagnostic differences in sperm size. There is also variation in sperm size among males within a population, and recent evidence from passerine birds suggests that the coefficient of inter-male variation in sperm length is negatively associated wi...
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Sperm morphology is highly diversified across the animal kingdom and recent comparative evidence from passerine birds suggests that postcopulatory sexual selection is a significant driver of sperm evolution. In the present study, we describe sperm size variation among 20 species of African greenbuls and one bulbul (Passeriformes: Pycnonotidae) and...
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Nest predation is assumed to be an important factor driving avian life histories. Altitudinal gradients offer valuable study systems to investigate how avian nest predation risk varies between bird populations. In this study, a hypothesis postulating an increase in avian nest survival rate with elevation as a result of decreasing predation pressure...
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Acoustic signals are frequently used for estimating avian species richness, abundance and community composition. However, sampling by traditional methods of bird surveys is often limited by availability of experienced researchers in the field, especially in the tropics. New bioacoustic approaches offer some solutions to such limitations and provide...
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Ecological specialization provides information about adaptations of species to their environment. However, identification of traits representing the relevant dimensions of ecological space remains challenging. Here we endeavoured to explain how complex habitat specializations relate to various ecological traits of European birds. We employed phylog...
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Abstract The reproductive success of precocial birds depends on investments in clutch formation and incubation. Egg quality strongly affects the phenotypic traits correlated with survival of the hatchling, but parental ability to maintain incubation temperature can also influence hatchling outcomes. The effect of incubation temperature on hatchling...
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Habitat loss and fragmentation in tropical areas have long been presumed to reduce avian nesting success due to increased predation rates. Nevertheless, this prediction remains largely untested in tropical areas, because empirical data on the impacts of forest fragmentation on nest predation at both the landscape and patch scales in the tropics are...
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AimTo separate the effect of overall resource level from the effect of seasonality on avian clutch size to test Ashmole's hypothesis that birds have larger clutch sizes in seasonal environments due to high per capita food availability during the breeding season.LocationSouth Africa and Lesotho.Methods We used a large-scale environmental gradient to...
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Climatically induced shifts of species' geographic ranges can provide important information about the potential future assembly of ecological communities. Surprisingly, interspecific variability in the magnitude and direction of these range shifts in birds has been the subject of few scientific studies, and a more detailed examination of species' e...
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The western mountain greenbul, Andropadus tephrolaemus, is a poorly-known monomorphic forest greenbul. We investigated whether morphological measurements could be used to discriminate between sexes of this species, with a sample of birds captured in two forest types on Mt Cameroon. We used discriminant function analysis based on a combination of tr...
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The western mountain greenbul, Andropadus tephrolaemus, is a poorly-known monomorphic forest greenbul. We investigated whether morphological measurements could be used to discriminate between sexes of this species, with a sample of birds captured in two forest types on Mt Cameroon. We used discriminant function analysis based on a combination of tr...
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Closely related bird species can coexist in areas of range overlap due to differentiation of their ecological niches. If coexisting species have similar habitat requirements, separation of food niches presumably plays a crucial role. Theoretically, two possible food niche separation scenarios are possible: (1) use of different food resources or (2)...
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Nest predation is the leading cause of reproductive failure in birds and thus it shapes their life history strategies. Intensities of nest predation appear to differ among nest locations and types in both temperate and tropical regions. However, there is limited knowledge of factors influencing susceptibility of avian nests to predation in Africa....
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The Cameroon volcanic line montane forests host specific avian assemblages with many endemic species. Such unique bird assemblages deserve adequate description for proper protection. For this purpose, we sampled birds in the upper montane forests of Mts Cameroon and Oku situated at 2,250 m. We combined point counts and continuous observations to de...
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Conspecific brood parasitism is an alternative reproductive tactic in which parasitic females lay eggs into the nests of other females of the same species who carry out the subsequent parental care. Conspecific brood parasitism is reported to be common among birds, however detailed information about rates of parasitism based on molecular identifica...
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Sperm competition represents an important component of post-copulatory sexual selection. It has been argued that the level of sperm competition declines in birds towards the equator. However, to date, sperm competition estimates have been available mainly for avian species inhabiting the northern temperate zone. Here we apply a novel approach, usin...
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Community-level studies have shown that plantpollinator interactions are much more generalized than previously expected. Consequently, many authors have questioned the significance of phenotypic complementarity between plants and pollinators and abundance effects in pollination interactions. Here, we compare the behaviour of three sunbird species f...
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Capsule A higher animal component in the diet and a greater amount of food result in better condition.Aims To investigate the relative importance of different food types to nestling House Sparrows.Methods Faecal sac samples (n = 206) from 106 nestlings of 31 broods were analyzed in 2 breeding seasons (2008, 2009). The nests were in a nestbox colony...
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Community-level studies have shown that plant–pollinator interactions are much more generalized than previously expected. Consequently, many authors have questioned the significance of phenotypic complementarity between plants and pollinators and abundance effects in pollination interactions. Here, we compare the behaviour of three sunbird species...
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Geographic variation in avian clutch size is thought to be related to the variation in nest predation rate and food availability. We studied predation on artificial ground nests along a large-scale geographic gradient in South Africa characterised by increasing productivity from the deserts in the west to humid savannas in the east, and calculated...
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Vigilance is a behavioural tactic that allows individuals to control their surroundings and to assess predation risk. In contrast, sleep is unique behavioural state with widely hypothesized restorative and energy-saving functions, but reducing attentiveness and increasing susceptibility to predation. Sleeping birds resolve this conflict by interrup...
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(hereafter cisticola), representing frugivorous, nectarivo-rous, granivorous and insectivorous species, respectively. Since the isotopic composition of keratinous tissues, such as feathers, reflects the diet of the organism during the period when these structures were synthesised (Hobson 1999), we expected feather δ
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Waterfowl management on breeding grounds focuses on improving nest success, but few studies have compared waterfowl nest success and factors affecting nest survival along a wetland gradient and simultaneously identified nest predators. We monitored nests (n = 195) of common pochards (Aythya ferina) in Trebon Basin Biosphere Reserve, Czech Republic,...
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Incorporation of unrelated eggs into a clutch by incubating females (egg retrieval), which has an obvious adaptive value when female retrieves her own egg, seems to be also a part of the reproductive tactics related to brood parasitism. In open nesting waterfowl, the parasitic egg remains frequently outside the nest bowl after the parasitic event....
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Večlová B. & Hořák D. 2009: Příčiny proměnlivosti ve zbarvení ptačích vajec. Sylvia 45: 51–72. Zbarvení skořápky ptačích vajec, jakož i velikost a tvar skvrn jsou velmi proměnlivé. Velké odlišnosti existují převážně mezi druhy, ale variabilitu můžeme najít i v rámci jednoho druhu, či dokonce v rámci jedné snůšky. Pestrá škála barev je způsobena pří...
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Trade-off between offspring size and number belongs to the most discussed concepts in the life history theory. Although it has been frequently described at interspecific level as a negative correlation between egg size and number, it is usually difficult to provide similar evidence at a population level. In congruence with most of previous studies,...
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2008: An observation on conspecific egg Ladoption during a parasitic event in the Tufted Duck (Aythya fuligula). Sylvia 44: 63–66. We describe behavioural interaction between a brood parasite and a host we observed during a conspecific parasitic event in the Tufted Duck (Aythya fuligula). The parasite came to the host nest during morning hours whil...
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Investigators studying the relationship between egg size and young size often face difficulties in assigning particular young to particular eggs. We present a new method based on the use of separate net sacks for each egg that allowed us to study this phenomenon in Common Pochards (Aythya ferina) without excessive disturbance of breeding birds. We...
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Offspring survival and subsequent fitness are assumed to increase with offspring size. Although the relationship between egg size and young size in birds has attracted considerable scientific attention, to our knowledge no study so far has investigated differences among nests with respect to this relationship. The aim of this study was to find out...
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Two woody Hypericum species (H. roeparianum and H. revolutum) often coexist in forest edge and stream mantle communities in the Bamenda-Banoso Highlands, Cameroon. Morphologically nonspecialized flowers of both species are visited by specific eye-catching visitors. Nectarless flowers of H. roeparianum are visited by a large carpenter bee Xylocopa s...
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Although the high species richness and endemism of birds in the Bamenda Highlands has attracted ornithological research for decades, most studies have been restricted to bird communities of continuous montane forests. Instead, we focused on a mosaic landscape with montane forest remnants, where the habitat preferences of birds remain unknown. We pe...
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We surveyed a non-protected montane forest mosaic in Bamenda Highlands, Cameroon, in the periods 11 Nov to 17 Dec 2003 and 22 Nov to 7 Dec 2005. We summarise information on abundance, habitat use, vocalisation and breeding activity of 109 bird species. Despite considerable forest fragmentation, species confined to montane forest constituted a subst...
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Aim To show that the frequently reported positive trend in the abundance–range-size relationship does not hold true within a montane bird community of Afrotropical highlands; to test possible explanations of the extraordinary shape of this relationship; and to discuss the influence of island effects on patterns of bird abundance in the Cameroon Mou...
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Hořák D. 2006: Egg mass and egg components allometry in the Common Pochard (Aythya ferina). Sylvia 42: 104–111. Egg size is considered a reliable predictor of young size at hatching. Larger young have an advantage over conspecifics especially because they should have higher amount of nutrients available. The aim of this study was to examine the rel...
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From 11 to 15 January 2004, we visited Bakingili village (4°3´N, 9°3´E), in the SW foothills of Mt Cameroon. During two short trips to the lowland rainforest interior (13 and 14 January 2004), we found a new locality for Grey-necked Picathartes, c. 1 km north-west of the village, at an altitude of c. 100 m. The nearest known population, discovered...
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The aim of this paper is to analyse the effect of drying up of a wetland on qualitative and quantitative composition of a passerine bird assemblage. Between 2000 and 2003 the mist netting of birds was carried out in the Vypálenky marsh near Moravský Písek (48°59'N 17°02'E, Czech Republic). Netting efficiency was standardised and the effect of water...
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A total of 360 ringing recoveries of Bearded Tits (Panurus biarmicus) ringed or recovered on the territory of the Czech Republic and Slovakia during 1934–2001 were analysed with respect to their natal philopatry, site fidelity, movements, age and mate fidelity. Migration system of the Bearded Tit has a complicated pattern, some individuals are sede...
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A total of 360 ringing recoveries of Bearded Tits (Panurus biarmicus) ringed or recovered on the territory of the Czech Republic and Slovakia during 1934–2001 were analysed with respect to their natal philopatry, site fidelity, movements, age and mate fidelity. Migration system of the Bearded Tit has a complicated pattern, some individuals are sede...
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2004: Poznámky k výskytu palearktických migrantů v Kamerunu. Sylvia 40: 63–78. V práci jsou shrnuty výsledky našich pozorování palearktických migrantů v subsaharské Africe. Údaje byly získány během dvou expedic do Kamerunu, které se konaly od listopadu do ledna v letech 2000/2001, resp. 2003/2004. Navštívili jsme široké spektrum biotopů od pobře-ží...