Tardigrade diversity and community composition across Norwegian boreal forests

Abstract

Tardigrades are common in many terrestrial environments and habitats. Although little is known on their ecological preferences, previous studies found diversity and community composition significantly affected by various variables. This study associated tardigrade species’ records with climatic variables, forest type, and substrate categories exploring tardigrade diversity and species communities to find associations with ecological characteristics of Norwegian forests. A total of 17 473 specimens were identified, encompassing 131 species (including putatively new species) from 305 samples of different substrates (leaf litter, bryophytes, and lichens). Bryophytes and lichens of samples were classified according to the main species, and growth form, and associated with tardigrade species and sample metadata. Tardigrade species’ richness was related to climatic variables and forest type, increased with precipitation, decreased with summer temperature, and not varied with precipitation seasonality. Although there was an unbalanced representation of substrate categories in the different forest types, some tendencies were detectable. Mixed oak and birch forests reached the highest species’ richness. Tardigrade community composition varied between substrate categories and, to a lesser degree, between forest types, but not with climatic variables. Our study highlights the importance of large-scale variables on tardigrade diversity, and substrate categories for tardigrade community composition.

A first look into moss living tardigrades in boreal peatlands

“…As in some previous studies (Guidetti et al., 2024 ; Jönsson, 2003 ; Mäenpää et al., 2023 ), we found (Table 1 ) the highest tardigrade densities in the moss group Hypnales (the feather mosses Pleurozium schreberi and Hylocomnium splendens ), which are commonly found in the hummocks of more wooded peatland types. Over 80% of the identified specimens in Hypnales mosses were omnivorous, of which most belonged to the family Macrobiotidae (Figures 2 and 3 ).…”

“…In contrast, a recent study by Guidetti et al. ( 2024 ) found a positive correlation between species richness of tardigrades and increased rainfall in mosses in a study across boreal forests in different regions of Norway. Altogether, studies have shown contrasting results of the connection between moisture and tardigrade occurrence, and it is likely to affect species differently depending on, for example, their anhydrobiosis ability.…”

“…It has been discussed whether the spatial variation in occurrence and population densities is a consequence of passive distribution, carried out by wind, rain, and floodwaters or more determined by habitat conditions. However, many studies have concluded that favorable conditions for the population growth of tardigrades arise from combinations of macro‐, meso‐, and microscale environmental factors (Guidetti et al., 2024 ; Guil et al., 2009 ).…”

Terrestrial Tardigrada (Water Bears) of the Słowiński National Park (Northern Poland)

“…Similar to our result, studies in Costa Rica [82] and in Great Smoky Mountains National Park (USA) [83] also showed no significant differences in estimates of tardigrade diversity between mosses and lichens, including species richness and the Shannon index. Moreover, in a study by Guidetti et al [84], similar to our study, most species were recorded in mosses and lichens, with only a comparatively small number found in cryptogams (mosses mixed with lichens). However, they also concluded that there was a considerable heterogeneity in species richness for some of the habitats, as well as noted the poor effects of habitat categories on species richness in the multiple regression, where other environmental variables were controlled [84].…”

“…Moreover, in a study by Guidetti et al [84], similar to our study, most species were recorded in mosses and lichens, with only a comparatively small number found in cryptogams (mosses mixed with lichens). However, they also concluded that there was a considerable heterogeneity in species richness for some of the habitats, as well as noted the poor effects of habitat categories on species richness in the multiple regression, where other environmental variables were controlled [84]. When comparing species diversity across different sampling substrates (i.e., concrete walls, ground surface, trees and dead wood), we have found there to be in general no significant differences between different substrates.…”