Shifts in trophic interactions with forest type in soil generalist predators as indicated by complementary analyses of fatty acids and stable isotopes

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Anthropogenic land use shapes the dynamics and composition of central European forests and changes the quality and availability of resources of the decomposer system. Th ese changes likely alter the structure and functioning of soil animal food webs. Using stable isotope analysis ( 13 C, 15 N) we investigated the trophic position and resource use of soil animal species in each of four forest types (coniferous, young managed beech, old managed beech and unmanaged beech forests) across three regions in Germany. Twenty-eight species of soil invertebrates were analyzed covering three consumer levels and a representative spectrum of feeding types and morphologies. Data on stable isotope signatures of leaf litter, fi ne roots and soil were included to evaluate to which extent signatures of soil animals vary with those of local resources. Soil animal δ 15 N and δ 13 C signatures varied with the respective signatures of leaf litter and fi ne roots. After calibration to leaf litter signatures, soil animal stable isotope signatures of the diff erent beech forests did not diff er signifi cantly. However, thick leaf litter layers, such as those in coniferous forests, were associated with low animal stable isotope signatures presumably due to reduced access of decomposer animals to root-derived resources, suggesting that the decomposer food web is shifted towards leaf litter based energy pathways with the shift aff ecting all consumer levels. Variation in stable isotope signatures of soil animal species with litter quality parameters suggests that nutrition of third level but not fi rst and second level consumers is related to litter quality, potentially due to microorganisms locking up litter resources thereby hampering their propagation to higher trophic levels.

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 68%

Trophic shift of soil animal species with forest type as indicated by stable isotope analysis

Klarner

Ehnes

Erdmann

et al. 2014

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“…Moreover, the absence of larger (lithobiid) predators, which can compete for same prey or even interact as intraguild predators, allows a better exploitation of its prey resources (Finke and Denno ). Fatty acid analysis of L. crassipes from the same lithobiid predators corroborate our findings, showing small L. crassipes being more effective in exploiting prey in deeper organic layers than the large L. mutabilis (Ferlian and Scheu ).…”

Section: Discussionsupporting

confidence: 87%

Variations in prey consumption of centipede predators in forest soils as indicated by molecular gut content analysis

Günther

Rall

Ferlian

et al. 2013

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Predation is an important ecological factor driving animal population structures, community assemblages and consequently ecosystem stability and biodiversity. Many environmental factors influence direction and intensity of predation, suggesting that trophic linkages between animals vary between different habitats. This in consequence has particular relevance in anthropogenically altered habitats such as managed forests, where disturbance regime, tree composition and stand age may change the natural food web structure. We investigated how prey consumption of three common centipede predators (Lithobius spp., Chilopoda), representing two body sizes varies between four differently managed forest types in two regions across Germany. We hypothesized that prey preference of these generalist predators is independent of forest type but rather driven by habitat structure, prey abundance and predator body size. Applying specific PCR assays to test for DNA of three abundant prey groups, i.e. Collembola, Diptera and Lumbricidae, in the predators’ guts, we tracked trophic interactions. The results showed that management type indeed has no influence on centipede prey consumption but depth of litter layer and soil pH. Trophic interactions varied between the two sampled forests regions mainly due to changes in the detection of Lumbricidae and Diptera. Also, effect of litter layer and prey abundance significantly differed between the smaller L. crassipes and the larger L. mutabilis, indicating a body size effect. The results complement food web analyses using fatty acids and stable isotopes by elucidating trophic interactions in soil in unprecedented detail.

“…Overall, we found only few effects of the land‐use types on food‐web topology. Most of these effects could readily be assigned to the dominant tree species that cause different litter types (needles vs leaf litter) and habitat structures (Ferlian and Scheu , Günther et al ). This suggests that the structure of soil food webs is relatively robust against variation in forest types.…”

Section: Discussionmentioning

confidence: 99%

Unravelling the complex structure of forest soil food webs: higher omnivory and more trophic levels

Digel¹,

Curtsdotter

Riede

et al. 2014

153

168

Food web topologies depict the community structure as distributions of feeding interactions across populations. Although the soil ecosystem provides important functions for aboveground ecosystems, data on complex soil food webs is notoriously scarce, most likely due to the difficulty of sampling and characterizing the system. To fill this gap we assembled the complex food webs of 48 forest soil communities. The food webs comprise 89 to 168 taxa and 729 to 3344 feeding interactions. The feeding links were established by combining several molecular methods (stable isotope, fatty acid and molecular gut content analyses) with feeding trials and literature data. First, we addressed whether soil food webs (n = 48) differ significantly from those of other ecosystem types (aquatic and terrestrial aboveground, n = 77) by comparing 22 food web parameters. We found that our soil food webs are characterized by many omnivorous and cannibalistic species, more trophic chains and intraguild‐predation motifs than other food webs and high average and maximum trophic levels. Despite this, we also found that soil food webs have a similar connectance as other ecosystems, but interestingly a higher link density and clustering coefficient. These differences in network structure to other ecosystem types may be a result of ecosystem specific constraints on hunting and feeding characteristics of the species that emerge as network parameters at the food‐web level. In a second analysis of land‐use effects, we found significant but only small differences of soil food web structure between different beech and coniferous forest types, which may be explained by generally strong selection effects of the soil that are independent of human land use. Overall, our study has unravelled some systematic structures of soil food‐webs, which extends our mechanistic understanding how environmental characteristics of the soil ecosystem determine patterns at the community level.