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Springtails spreading
Springtails spreading
We've seen how springtails have been springing around for around 100 million years, following the bacteria. They would be following developments in the soil surface. The earlier litter players provided some structure for development, but as soil went wider and deeper, imagine the weight on creatures the greater distance from oxygen. Some springtails and mites would have kept moving out along the surface, while others in their groups could follow the roots down, adapting to the new conditions. This would have been a new world to select new creatures, adapted to the pressures and darkness, and capable of spending a long time away from air, yet also being capable of living in damp conditions while also capable of withstanding periodic droughts. It appears the springtails diversified more than the mites, especially the Entomobryomorphs and Tomoceroids, both still springing. What does that tell us about the prevailing conditions?
Deadwood
Deadwood
The deadwood would also have created new habitats. Springtails had been around for a hundred million years, but new forms would have emerged in the new circumstances. Collembola have been shown to have on the important indirect contribution to stump-decay and Vertagopusalpa, Hymenaphoruracocklei, and Folsomia stella are found in old-growth forests, and Anurophorusseptentrionalis and Ballistura libra in regenerating areas.
“Understanding the importance of dead wood-associated biodiversity and related ecological functions has become increasingly important in forest ecosystem management. Yet, studies on dead wood diversity frequently focus on conspicuous organisms such as birds or ‘saproxylic’ beetles”, as we will see soon. “Here, we investigated the potential role of deadwood as a habitat for springtails, an understudied group of invertebrates generally associated with soils” (Setala et al 1995)
We are learning to use today’s habitats to work out what may have gone on then. “Our results indicated that dead wood was used as a habitat by 74 springtail species. A clear latitudinal diversity gradient was observed, with southern communities being on average two times richer and over 13 times more abundant than the northern ones per log. The most abundant species and morphospecies in the entire dataset were Sminthurinusquadrimaculatus (17% of all individuals sampled), Lepidocyrtus gr. 1 (11%), Ptenothrixdelongi (8%), Entomobrya sp. 4 (7%) and Hypogastruranivicola (4%).” It is no surprise that the surface dwelling little globular Sminthurids would dominate in these circumstances.(Setala et al 1995)
“The numbers of Collembola species and specimens increase with deadwood decomposition rates, as severely decayed deadwood attracts not only saproxylic species but also those residing in the soil and litter as well. When compared to decomposition stage II, densities of Collembola were considerably decreased in wood at the stages I(early) and III–V (later-last), whereas densities of mite were relatively lower only at the stage I of deadwood decomposition” (Skarżyński et al 2016)
Oncopodura
Oncopodura
"According to the fossil-calibrated evolutionary time frame, the first transition from aboveground to belowground habitat (the divergence between Oncopodura and the stem Tomoceroidea) occurred during the Carboniferous–Permian, (Yu et al 2022)
Oncopodura
I think there was an earlier 'transition' in Early Carboniferous times, with Poduromorphs, like Onychiurids - as seen in this graphic above.
Tomocerus
Followed by a second transition (the divergence between Harlomillsia and Tomoceridae) during the Permian–Triassic and multiple later transitions (within Entomobryoidea and Isotomoidea) during the Mesozoic. (Yu et al 2022), as we will see later.
Ancestral entomobryomorphs were reconstructed as surface-living, whereas soil-living groups evolved several times independently across the Palaeozoic–Mesozoic, suggesting ancient evolutionary interaction between aboveground and belowground ecosystems since ∼300 Ma" (Yu et al 2022). We will meet these soil dwelling developments later.
Signal deeper soils?
Signal deeper soils?
We saw earlier (360-300mya) how Poduromorphs, like Onychiurids, appeared in Early Carboniferous period, indicating there was some soil to live in. Does does this transition from aboveground to belowground habitat signal deeper soils in Permian times?
We must be able to read something about the condition of the soil , from the development of Onychuirids to Oncopodura. They sound similar, but emerged 50 million years apart - with different characters well spelt out. It is well past my knowledge, but there will be people who know what these characters can tell us about the surrounding soil.
"More than one insect extinction events, accompanied by significant diversity drop and turnovers of faunal compositional, occurred in the Permian and Triassic". Gui et al 2023
Stratification
Stratification
"The results suggest that the stratification structure of terrestrial ecosystem, consisting of aboveground–interface–belowground subsystems, had already formed by the Late Paleozoic (300-250mya), and the independent transitions may reflect multiple ecological successions in the geological history. Our finding partially resembles that about oribatid mites, also inferring a Palaeozoic establishment of aboveground–belowground ecological interactions (Schaefer and Caruso 2019). Interestingly, the estimated times (CIs) of the ecological divergences of Entomobryomorpha roughly overlap several key palaeoenvironmental changes, notably the Late Pennsylvanian–Permian global aridification (Gulbranson et al. 2015), the end-Permian extinction and subsequent “Coal Gap” (Retallack et al. 1996), and the Cretaceous diversification of angiosperms (Herendeen et al. 2017)" (Yu et al 2022). As we shall see...
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