Two localities for Huperzia selago subsp. arctica are recorded from Lithuania, to the south of its known distribution area. The habitats of this subspecies are cutover peatlands whose natural vegetation was disturbed 6-8 years ago during peat exploitation. One of the dominant species of latest vegetation cover is the invasive bryophyte Campylopus introflexus. Characteristics of the habitats of H. selago subsp. arctica and the frequency of this taxon in populations were analysed.
The influence of episode of density-independent mortality on the time-space variability of phytoplankton distribution in the near surface layer of a stratified sea is the aim of this paper. The mortality of phytoplankton in unpredictable conditions, like a spill of crude oil or other chemicals is considered. The numerical simulations were carried out using a biological model of upper layer with a developed primary production and regeneration mechanisms and of daily migration of zooplankton. In such cases an increase in the mortality rate intensifies the decrease in phytoplankton biomass. Such a situation can on occasion lead to phytoplankton extinction, and hence to irreversible changes in its distribution area.
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