Historically, P. praelongus occurred in many localities, which is confirmed by analyses of macrofossils in lake sediments, e.g. the lake Šúr in Slovakia, Jezioro Lake in south Poland and lakes in Greenland. Changes in species distribution are connected to climatic changes affecting water ecosystems, vegetation cover, trophic level of habitats and thus competition among species. Extinction of the species from the lake in the central part of east Greenland was probably due to summer temperatures decline and high increase of temperature differences after the early and mid-Holocene, which caused changes in water chemistry. Occurrence of P. praelongus in Greenland was enabled by birds migrating from northwest Europe after the glacial period (7000 years ago).
Changes of physical and chemical water character and flow rate, and floods in river floodplains are related to climatic changes, especially rising air temperatures. Fluctuating precipitation distribution during the year causes a significant fluctuation of water column in floodplains. A high water level can cause washing away of P. praelongus stems and disturbance of its populations by the waterflow. This was observed in Lithuanian rivers and during flood events in the ČR in 1997.
Heated water column is favourable for many organisms. Their expansion affects the water transparency, biomass accumulation and trophic level of the water environment. Eutrophication of water is caused by nutrient runoff from nearby landscape and surface water pollution. This trend is known from different parts of the species distribution area, and is most striking in small ponds and streams in intensively urbanised and utilised areas. Studies from north Europe prove aquatic macrophytes´ decline related to rising eutrophication. P. praelongus has a higher tolerance range (ecological amplitude) and can grow in oligomesotrophic, mesotrophic and eutrophicwater; therefore, it is able to disappear from highly eutrophic water and spread to localities which were once oligotrophic.
In this succession induced by trophic level changes, P. praelongus replaces Isoëtessp.,
Chara sp., and Nitella sp. vegetation and is being replaced by broadleaved pondweed vegetation(Potamogeton lucens, P. natans, P. pusillus agg., P. pectinatus etc.) and other macrophytes (Nuphar lutea, Persicaria amphibia). Studies from Finland, Estonia, Lithuania, Poland, the Czech Republic and the USA show disappearance of P. praelongus from particular localities due to eutrophication.
Other organisms inhabiting the localities have a significant influence on P. praelongus populations. They often spread due to spontaneous succession connected to eutrophication, shading and significant changes of water parameters. A negative competition effect was observed with filamentous algae; mainly the genera of Cladophora, Vaucheria and Oedogonium are strong competitors of P. praelongus. Algae cover the leaf surface, decrease the gas exchange and increase the pH on the leaf surface. Parts of stems covered with algae necrotize and a smelly muddy black substrate is formed of organic material on the bottom.
Moss Caliergonella cuspidata overgrows especially small, shallow pools. It grows from the bottom through the whole water column, displaces other aquatic macrophytes and completely prevails after only several growing seasons.
Decrease of P. praelongus populations connected to spread of littoral species and their communities (reeds) was observed not only in small and shallow pools in the CR and Poland, but also in bigger lakes in Finland, Estonia and Lithuania. Spreading reeds decrease the open water surface, cause shading of P. praelongus and clogging of the pools. Reeds composed of Schoenoplectus lacustris are more favourable for aquatic macrophytes then covers of Phragmites australis and Typha sp.
Also invasive organisms which uncontrollably spread in new localities considerably influence P. praelongus populations. There was a spread and negative influence of European species Myriophyllum spicatum on populations of aquatic species including P. praelongus in Bearlake in Manistee region in Michigan recorded.
Another factor limiting growth of P. praelongus and other aquatic macrophytes is the influence of animals, especially inconveniently introduced carp, that digs the bottom and causes bad water transparency, and other herbivorous fish (especially Ctenopharyngodonidella) that disturb populations of aquatic macrophytesby intensive grazing. A negative influence of Ondatra zibethica in the American lake ClearLake was recorded. In the Czech Republic a negative influence of semi-wild ducks (hybrids of artificially introduced and native Anas platyrhynchos populations) is known.
Concerning landscape changes, P. praelongus populations are mainly endangered by regulation of streams and their floodplains, inappropriate management off shore and riparian zone, fishing in areas with P. praelongus occurrence and duck breeding. In recent years in the Czech Republic, irresponsible approach to terrain work in localities with P. praelongus has become a serious problem.
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