Abstract
Despite the major role of Collembola in forest soil animal food webs, ecological and evolutionary determinants of their community composition are not well understood. We investigated abundance, community structure, life forms, and reproductive mode of Collembola in four different forest types (coniferous, young managed beech, old managed beech, and unmanaged beech forests) representing different management intensities. Forest types were replicated within three regions across Germany: the Schorfheide‐Chorin, the Hainich, and the Swabian Alb, differing in geology, altitude, and climate. To account for temporal variation, samples were taken twice with an interval of 3 years. To identify driving factors of Collembola community structure, we applied structural equation modeling, including an index of forest management intensity, abiotic and biotic factors such as pH, C‐to‐N ratio of leaf litter, microbial biomass, and fungal‐to‐bacterial ratio. Collembola abundance, biomass, and community composition differed markedly between years, with most pronounced differences in the Schorfheide, the region with the harshest climatic conditions. There, temporal fluctuations of parthenogenetic Collembola were significantly higher than in the other regions. In the year with the more favorable conditions, parthenogenetic species flourished, with their abundance depending mainly on abiotic, density‐independent factors. This is in line with the “Structured Resource Theory of Sexual Reproduction,” stating that parthenogenetic species are favored if density‐independent factors, such as desiccation, frost or flooding, prevail. In contrast, sexual species in the same year were mainly influenced by resource quality‐related factors such as the fungal‐to‐bacterial ratio and the C‐to‐N ratio of leaf litter. The influence of forest management intensity on abundances was low, indicating that disturbance through forest management plays a minor role. Accordingly, differences in community composition were more pronounced between regions than between different forest types, pointing to the importance of regional factors.
Highlights
Understanding the structure and functioning of soil animal communities has been one of the long-standing challenges for soil ecologists
To identify the driving factors determining Collembola abundance, we considered environmental drivers including soil pH, soil microbial biomass, mass of leaf litter, fungal-to-bacterial ratio in leaf litter, leaf litter microbial biomass, and C-to-N ratio of leaf litter
Collembola abundance, biomass, and community composition differed between years, presumably due to varying weather conditions, resulting in a shift in structuring forces of Collembola communities
Summary
Understanding the structure and functioning of soil animal communities has been one of the long-standing challenges for soil ecologists. Collembola are among the most abundant and species-rich taxa in forest soil animal food webs, reaching similar high biomasses as Oribatida and Enchytraeidae in beech and spruce forests (Schaefer, 1990; Scheu et al, 2003). Detritus as the main resource is abundant and this may favor parthenogenetic species as it is never exploited fully (Scheu & Drossel, 2007) Biotic factors such as resource quality and availability may be superimposed by abiotic factors, for example, when environmental conditions are harsh. To investigate major determinants of Collembola community composition, we sampled and identified Collembola species from four different forest types (coniferous, young and old managed beech, and unmanaged beech) across three regions in Germany, the Swabian Alb in the southwest, the Hainich in the center, and the Schorfheide in the northeast. We expected temporal fluctuations to favor parthenogenetic rather than sexual species as the latter reproduce more quickly
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