Detrital Food Webs Research Articles

Aquatic invertebrate production in moist-soil managed wetlands on Richland Creek Wildlife Management Area, east-central Texas

Abstract Aquatic invertebrates have significant value to wetland-dependent species as well as to wetlands themselves. They process organic matter through producer and detritus food webs, modify wetland habitats, and provide a food resource to wetland-dependent species such as waterfowl and shorebirds. Timely flooding and drawdown of water within moist-soil managed wetlands will increase invertebrate diversity and abundance, allowing wetland managers to maximize the production of such areas. We examined how flood timing and duration influenced aquatic invertebrate density, diversity, richness, and production within four moist-soil managed wetlands on Richland Creek Wildlife Management Area, east-central Texas from January 2004 through December 2006. A total of 12,089 aquatic invertebrates from 41 aquatic invertebrate families were collected. Overall, diversity indices were 0.76 (Simpson's Index) and 2.47 (Shannon-Wiener Index). Most common aquatic invertebrates were Crustacea (n = 3,568) and Ephemeroptera ...

How the litter‐feeding bioturbator Orchestia gammarellus promotes late‐successional saltmarsh vegetation

Summary Traditionally, studies on vegetation succession have focused either on plant–plant interactions or on interactions between plants and their physical environment, for example through organic matter build‐up and increased nutrient cycling. These interactions can change conditions for macrodetritivores that feed on plant litter, but their role in vegetation succession is rarely studied. In this paper, we explore whether the bioturbating crustacean macrodetritivore Orchestia gammarellus alters soil conditions in a saltmarsh ecosystem in such a way that it promotes late‐successional, less stress‐tolerant plant species at the expense of early successional species. To answer this, we performed a field and a laboratory experiment in which we manipulated abundances of O. gammarellus, and studied the consequences for soil physical and chemical parameters and for vegetation community composition. Our field experiment showed that O. gammarellus stimulated nitrogen mineralization, likely resulting from the positive effect of this macrodetritivore on soil aeration and litter decomposition. Moreover, results from the laboratory experiment showed that O. gammarellus negatively affected dicot seedling survival of mainly early successional plant species, likely through grazing, thus affecting plant community composition. The experiments together provided evidence that O. gammarellus promotes late‐successional plant species in multiple ways: by alleviation of anoxic conditions, by promoting nutrient cycling and by selective herbivory on early successional species. Synthesis. By demonstrating that a species traditionally considered as part of the detrital (‘brown’) food web is thus an important accelerator of vegetation succession, this study documents an important but often overlooked link in food web and ecosystem ecology.

Effects of experimental warming, litter species, and presence of macroinvertebrates on litter decomposition and associated decomposers in a temperate mountain stream

Small woodland streams make the majority of water courses in most watersheds. Litter decomposition is a key ecosystem process in these shaded streams, and its response to warming can have profound consequences for food webs and the carbon (C) cycle. However, these responses can be modulated by litter identity and the structure of the detrital food web. Here we report on a manipulative study aiming at evaluating the effects of warming (+2.8 °C), litter identity (chestnut (Castanea sativa) or oak (Quercus robur) litter), and the structure of the detrital food web (presence or absence of macroinvertebrates) on litter decomposition and decomposers in a small, temperate woodland stream. Warming significantly stimulated overall (microbial- + macroinvertebrate-driven) decomposition of oak and microbial-driven decomposition of chestnut. The similar shredder densities at elevated and ambient temperatures suggest that stimulated overall decomposition of oak resulted from increased activity of macroinvertebrate individuals. Stimulated microbial-driven decomposition of chestnut resulted from higher fungal activity with warming. Stimulation of litter decomposition by warming can lead to increases in the amount of C returned to the atmosphere and to a faster disappearance of litter from the benthos, with consequences to the C cycle and aquatic food webs.

Dynamics of natural populations of the dertitivorous mudsnail Potamopyrgus antipodarum (Gray) (Hydrobiidae) in two interconnected Lakes differing in trophic state.

Here we investigate the allocation of resources between growth and reproduction by surveying the dynamics of natural populations of the aquatic detritivorous mudsnail Potamopyrgus antipodarum from two interconnected lakes that differ in trophic state. The size distributions and reproductive output of the snail populations was analyzed monthly by field surveys spanning 3 years, and in a controlled microcosm experiment to evaluate the reproductive potential under laboratory conditions. Snails in the meso-oligotrophic lake showed reduced growth and a smaller size compared to snails in the eutrophic lake. However, the numbers of eggs and nearly-neonates per adult snail did not differ significantly between the two populations. It is speculated that P. antipodarum populations living under meso-oligotrophic conditions may consistently invest more internal energy in reproduction at the expense of growth and that food quantity may be an important driver for macro-invertebrate resource allocation in detrital food webs.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-736) contains supplementary material, which is available to authorized users.

Trophic cascade of a web-building spider decreases litter decomposition in a tropical forest floor

Trophic cascade effects on detritus-based food webs of forest floor have the potential to alter ecosystem functioning, but due to the complexity of detrital food web no general pattern of cascading effects has emerged. The goal of this study was to evaluate trophic cascade effects of a dominant funnel-web building spider on leaf-litter decomposition rate and microbial biomass in a tropical forest floor. We manipulated the density of a dominant funnel-web building spider Macrothele yunnanica in permanent plots (1 m2) for one year. Three spider treatments were applied: 0 spider, 6 spiders (natural density) and 10 spiders (high density). We found that the high density of M. yunnanica led to significant negative cascading effects on litter decomposition rate, which is probably due to decreased density of one dominant collembolan, Entomobrya, in the litter layer. We detected no cascading effects from the natural density of M. yunnanica, and changes in spider densities had no cascading effects on microbial biomass. Modifying spider densities can generate a trophic cascade effect and alter leaf litter decomposition, with a potential to influence ecosystem function in tropical forest floors. This study suggests that trophic interactions in detritus-based food webs should be considered to better understand soil organic matter dynamics in tropical forests.

Role of detritus in a spatial food web model with diffusion.

One of the central themes in modern ecology is the enduring debate on whether there is a relationship between the complexity of a biological community and its stability. In this paper, we focus on the role of detritus and spatial dispersion on the stability of ecosystems. Using Monte Carlo simulations we analyze two three-level models of food webs: a grazing one with the basal species (i.e., primary producers) having unlimited food resources and a detrital one in which the basal species uses detritus as a food resource. While the vast majority of theoretical studies neglects detritus, from our results it follows that the detrital food web is more stable than its grazing counterpart, because the interactions mediated by detritus damp out fluctuations in species' densities. Since the detritus model is the more complex one in terms of interaction patterns, our results provide evidence for the advocates of the complexity as one of the factors enhancing stability of ecosystems.

Spatial variations in the trophic structure of soil animal communities in boreal forests of Pechora-Ilych Nature Reserve

Soil animal communities and detrital food webs are spatially compartmentalized. In old-growth boreal forests the dynamics of dominating plant species forms a considerable heterogeneity of edaphic conditions in the soil layer. We demonstrate a strong difference in total and relative abundance of main trophic groups of soil macrofauna in four microsites, i.e. under tree crowns, in gaps, in mounds and in pits created by fallen spruce trees. The variation in the functional structure of soil animal communities is likely related to different availability of key energy resources (leaf litter, roots and root deposits) in the microsites studied. However, results of the stable isotope analysis suggest that mobile litter-dwelling predators occupy very similar trophic positions in different microsites. The compartmentalization of soil invertebrate communities caused by the vegetation-induced mosaic of edaphic conditions seemingly does not lead to spatial isolation of local food webs that are integrated at the top trophic levels.

Non-trophic effects of earthworms on enchytraeids: An experimental investigation

Lumbricids and enchytraeids are two keystone fauna groups strongly responsible for the functioning of detrital food webs in temperate soils but acting at contrasting spatial scales. The relationships between both groups are poorly understood: considering their close kinship and trophic habits as generally microbi-/saprovores, competitive interactions are expected. However, due to engineering activities, various non-trophic earthworm impacts on enchytraeids also play a role, which has never been evaluated. We experimentally simulated and quantitatively estimated the effects of major non-trophic earthworm activities (burrowing, cast deposition, mucus release) and, in addition, of earthworm mortmass decay on the abundance of enchytraeids. Effects of two earthworm species belonging to epigeic (Lumbricus rubellus) and endogeic (Aporrectodea caliginosa) ecological groups were tested.Non-trophic earthworm effects strongly varied (a) between the types of activity (burrowing, casts, mucus), (b) across the soil profile, (c) between the earthworm species. In general, enchytraeids responded positively to earthworm non-trophic activities. Mucus release and burrowing showed usually stronger impacts than cast deposition. The participation of different non-trophic effects in the resulting joint effect (burrowing + casts + mucus) varied with earthworm species and soil horizon. Decomposition of dead earthworms stimulated enchytraeid abundance at lower, but inhibited it at higher mortmass amount.A comparison between enchytraeid responses to live earthworm (integrated trophic and non-trophic activities) and joint non-trophic (burrowing + casts + mucus) impacts allowed an approximate separation of both activity types. Rates of trophic and non-trophic impacts were quantitatively comparable and earthworm species-specific. In particular, L. rubellus and A. caliginosa earthworms rendered adverse (negative and positive, respectively) influence on enchytraeid abundance. It was concluded that the negative effects of live L. rubellus on enchytraeids were primarily related to its trophic activity, whereas the positive effects of live A. caliginosa were strongly connected with its non-trophic activities.

Cascading effects of predator–detritivore interactions depend on environmental context in a Tibetan alpine meadow

Studies of grazing food webs show that species traits can interact with environmental factors to determine the strength of trophic cascades, but analogous context dependencies in detrital food webs remain poorly understood. In predator-detritivore-plant interaction chains, predators are expected to indirectly suppress plant biomass by reducing the density of plant-facilitating detritivores. However, this outcome can be reversed where above-ground predators drive burrowing detritivores to lower soil levels, strengthening their plant-facilitating effects. Here, we show that these trait-mediated indirect interactions further depend on environmental context in a Tibetan alpine meadow. In our study system, undulating topography generates higher (dry soil) patches interspersed with lower (wet soil) patches. Because the ability of detritivores to form deep burrows is likely to be limited by oxygen availability in low patches (wet soil), we hypothesized that (i) burrowing detritivores would undergo a vertical habitat shift, allowing them to more effectively avoid predation, in high - but not low - patches, and (ii) this shift would transmit positive effects of predators to plants in high patches by improving conditions in the lower soil layer. We tested these hypotheses using complementary field and glasshouse experiments examining whether the cascading effects of above-ground predatory beetles (presence/absence) on the density and behaviour of tunnel-forming detritivorous beetles, soil properties, and plant growth varied with patch type (low/high). Results revealed that predatory beetles did not reduce the density of detritivores in either patch type but had context-dependent trait-mediated effects, increasing the tunnelling depth of detritivores, improving soil conditions and ultimately increasing plant biomass in the high but not low patches. This study adds to an emerging predictive framework linking predators to plants in detritus food webs, demonstrating that these indirect interactions depend not just on the relative habitat domains of predators and prey, but also on environmental conditions that can predictably constrain the behavioural response of detritivores to predation risk.

Large13C/12C and small15N/14N isotope fractionation in an experimental detrital foodweb (litter–fungi–collembolans)

AbstractCorrectly estimating the trophic fractionation factors (Δ15N and Δ13C) in controlled laboratory conditions is essential for the application of stable isotope analysis in studies on the trophic structure of soil communities. Laboratory experiments usually suggest large15N/14N and small13C/12C trophic fractionation, but in field studies litter‐dwelling microarthropods and other invertebrates are consistently enriched in13C relative to plant litter. In the present study, we report data from two laboratory experiments investigating both fungi–collembolans and litter–fungi–collembolans systems. In the fungi–collembolans system, Δ15N and Δ13C averaged 1.4 ± 0.1 and 1.0 ± 0.2 ‰, respectively. In microcosms with fungi‐inoculated litter, the difference in δ15N between collembolans and plant litter averaged 1.5 ± 0.2 ‰, confirming the relatively small15N/14N trophic fractionation at the basal level of detrital foodwebs reported in numerous field studies. In full agreement with field observations, the difference in δ13C between bulk litter and collembolans in laboratory microcosms averaged 3.6 ± 0.1 ‰ and only little depended on collembolan species identities or the presence of water‐soluble compounds in the litter. We conclude that increased δ13C values typical of litter‐dwelling decomposers are largely determined by an increased13C content in saprotrophic microorganisms.

Chronic nitrogen deposition alters the structure and function of detrital food webs in a northern hardwood ecosystem

During the next century, atmospheric nitrogen (N) deposition is projected to more than double, potentially slowing litter decomposition by altering microbial community composition and function. If the flow of energy though detrital food webs is diminished by the slowing of decay under higher rates of atmospheric N deposition, this agent of global change could also negatively impact the abundance and composition of soil fauna. To test this hypothesis, we studied soil faunal communities in four sugar-maple-dominated forests that comprise a long-term N deposition experiment. To examine whether changes in soil faunal communities could then feed back to influence litter decay, litterbags with 13C-enriched aspen litter were placed in the forest floor in one study site. The microbial community within the litterbags was characterized using PLFA analysis. Overall, long-term experimental N deposition reduced the abundance of microarthropods (ambient vs. experimental N deposition: 7844 vs. 4357 individuals/m2, respectively; P = 0.004). We attribute this overall decline partly to the reduced energy flow entering the detrital food web, which has been documented in previous work in our system. Although there was no difference in microarthropod species richness between N deposition treatments, there was a shift in community composition within the most abundant group (Oribatida), indicating species-specific responses to N deposition. Experimental N deposition reduced the number of microarthropods colonizing litterbags by 41% (P = 0.014). This was associated with a reduction in 13C mobilization from leaf litter into microbial biomass. Overall, this study demonstrates that chronic N deposition has a detrimental effect on the soil detritus food web, and that the negative effect may feed back to influence litter decay and ecosystem functioning.

Temporal changes of Collembola population and alterations of life history parameters and acetylcholinesterase and superoxide dismutase activities in Cyphoderus javanus (Collembola) as biomarkers of fly ash pollution in lateritic soil

Fly ash is applied in agricultural fields to improve soil quality and crop yield; however, there are concerns regarding environmental hazards and toxicity to ecologically important soil organisms. The soil microarthropod fauna is a vital component of detritus food web, and major groups like Collembola are sensitive indicators of soil quality; however, information is scanty on their biomarker potentials against xenobiotics in tropical soils. The present study was aimed to evaluate temporal changes of Collembola population in fly ash amended field plots, and assess the biomarker potentials of life history parameters and biochemical responses such as acetylcholinesterase (AChE) and superoxide dismutase (SOD) activities in Cyphoderus javanus Borner (Collembola, Insecta), exposed to fly ash treated soil in microcosms. The field study using 5% (50 t ha−1) and 20% (200 t ha−1) doses of fly ash revealed dose-dependent and persistent decline in the density and relative abundance of Collembola population in sandy loam lateritic soil. The microcosm experiments showed negligible lethal effect of fly ash on C. javanus, but major life history parameters namely survival success, fecundity, and molting were significantly inhibited by fly ash treatments. The activity of AChE was downregulated, whereas activity of SOD was upregulated within 7 days of exposure of C. javanus to fly ash treated soil. These biological and biochemical parameters in Collembola are potential biomarkers, and therefore, the effects of fly ash are significant in C. javanus, an ecologically relevant species in the tropical soils of India.

Nutrient enrichment of a heterotrophic stream alters leaf litter nutritional quality and shredder physiological condition via the microbial pathway

Streams receiving agricultural runoff are typically enriched with nutrients, which variously impact stream communities. We examined the effects of phosphate and nitrate enrichment on leaf litter breakdown, microbial biomass and the nutrition of an invertebrate shredder to determine how nutrients are transferred through the stream detrital food web. Using artificial streams, individuals of Anisocentropus kirramus (Trichoptera: Calamoceratidae) were fed leaves of Apodytes brachystylus (Icacinaceae) under different nutrient regimes. We measured the amount of leaf material consumed or decomposed and the microbial biomass colonising the leaves. The dry mass, and protein, lipid and carbohydrate composition of A. kirramus larvae were determined after 28-day feeding on the leaves. Supplements of phosphorus, but not nitrogen, enhanced leaf breakdown, microbial growth and growth of larvae. Microbial biomass and dry mass of larvae increased with nutrient enrichment and they were significantly correlated. Thus, the phosphorus supplement was transmitted through the detrital food web via the microbial pathway, resulting in higher nutritional quality of leaves and enhanced physiological condition of the shredder. Understanding such subtle relationships is important in determining the impacts of anthropogenic contaminants on freshwater ecosystems.

Temperature and nutrient availability interact to mediate growth and body stoichiometry in a detritivorous stream insect

Summary Regimes of temperature and nutrient availability are undergoing rapid modification at global scales. Both temperature and nutrients can influence consumer physiology and growth via several mechanisms. We examined how temperature and the nutrient content of food interact to affect consumption, growth and body stoichiometry of a detritivorous consumer (the caddisfly Pycnopsyche gentilis). In a 7‐week growth study, P. gentilis larvae were reared at two different temperatures (5 and 10 °C) while fed conditioned red maple (Acer rubrum) litter at one of two stoichiometric qualities (manipulated by raising phosphorus supply in one litter conditioning treatment; Amb: mean litter P = 0.03%, mean litter N = 0.79%; Hi‐P: mean litter P = 0.14%, mean litter N = 1.2%). Temperature and litter quality had differential effects on bulk consumption, element‐specific (N and P) consumption, growth and elemental body content of P. gentilis larvae. Temperature was the only factor affecting bulk feeding rates. Larvae in the Warm/Hi‐P treatment had by far the highest growth rates; the negligible growth in the Cold/Amb treatment was increased by either higher temperature (Warm/Amb) or higher food quality (Cold/Hi‐P). Higher temperature had no effect on body P content in Hi‐P treatments, but decreased body P content in the Amb treatments. Shifts in temperature and resource quality are both important components of global change and our results show that these factors can have interactive effects on detrital food webs, through which most primary production flows.

Do non-native Platanus hybrida riparian plantations affect leaf litter decomposition in streams?

In forest headwater streams where the riparian canopy limits autochthonous primary production, leaf litter decomposition is a key process controlling nutrient and carbon cycling. Any alteration of the riparian vegetation may influence litter decomposition and detrital food webs. We evaluated the effect of non-native Platanus hybrida riparian plantations on leaf litter decomposition in Mediterranean streams. The experiment was conducted in six headwater streams; three lined by native riparian vegetation and three crossing P. hybrida plantations. We have characterized the processing rates of alder leaves and the assemblages of shredder macroinvertebrates and fungi. Litter decomposition was significantly faster in the P. hybrida than in the reference streams. Although the dissolved inorganic nitrogen concentration was higher in P. hybrida, no significant effect was observed in decomposition rates. Differences in decomposition rates reflected the macroinvertebrate and shredder colonization in alder litter, with higher abundance and richness in the P. hybrida streams. However, aquatic hyphomycete sporulation rate was higher in reference streams, suggesting that the variation in decomposition rates is a direct consequence of shredder abundance. Our findings support part of the substrate quality-matrix quality (SMI) hypothesis, which expects that high-quality litter will show increased decomposition rates in a low-quality litter matrix.

Soil–litter nitrogen transfer and changes in δ13C and δ15N values in decomposing leaf litter during laboratory incubation

Abtract Leaf litter is the main source of nutrient and energy input into the soil. Therefore, detailed knowledge on the short-term variations in the isotopic composition of plant litter is needed for correctly estimating the “isotopic baseline” in stable isotope-based studies on detrital foodwebs. In a laboratory experiment, standardized fragments of freshly fallen leaves of Quercus robur, Ulmus glabra, and Populus tremula were incubated on the surface of natural or 15N-labeled soil during 260 days. At the end of the experiment, the remaining mass represented 62, 53 and 50% of the initial mass for oak, elm and aspen litter, respectively. There was a small decrease in the mean δ13C values during the initial stages of decomposition, although it was inconsistent among the three litter species tested and did not exceed 1.0‰ during the decomposition period. Calculations based on the total N content, as well as the isotope mixing model suggested that up to 50% of the total litter N was incorporated from the underlying soil. The rates of N transfer from the soil to litter were not affected by the disruption of mycelial connections between the soil and litter. As indicated by δ15N values of filter paper placed on the soil surface, labile soil N was depleted by 6–8‰ in 15N relative to bulk soil organic matter. However, in the given experimental settings the input of 15N-depleted labile N from mineral soil was likely counterbalanced by an increase in the 15N-enriched microbial biomass and bulk litter δ15N values changed little.

Predatory beetles facilitate plant growth by driving earthworms to lower soil layers

Theory suggests that predators of soil-improving, plant-facilitating detritivores (e.g. earthworms) should suppress plant growth via a negative tri-trophic cascade, but the empirical evidence is still largely lacking. We tested this prediction in an alpine meadow on the Tibetan Plateau by manipulating predatory beetles (presence/absence) and quantifying (i) direct effects on the density and behaviour of earthworms; and (ii) indirect effects on soil properties and above-ground plant biomass. In the absence of predators, earthworms improved soil properties, but did not significantly affect plant biomass. Surprisingly, the presence of predators strengthened the positive effect of earthworms on soil properties leading to the emergence of a positive indirect effect of predators on plant biomass. We attribute this counterintuitive result to: (i) the inability of predators to suppress overall earthworm density; and (ii) the predator-induced earthworm habitat shift from the upper to lower soil layer that enhanced their soil-modifying, plant-facilitating, effects. Our results reveal that plant-level consequences of predators as transmitted through detritivores can hinge on behaviour-mediated indirect interactions that have the potential to overturn predictions based solely on trophic interactions. This work calls for a closer examination of the effects of predators in detritus food webs and the development of spatially explicit theory capable of predicting the occurrence and consequences of predator-induced detritivore behavioural shifts.

Inter-relationship between Physico-chemical Variables and Litter Production in Mangroves of Indian Sundarbans

Litter production in mangrove has immense ecological importance, as it sustains both the planktonic and detritus food webs in the aquatic phase and intertidal mudflats, respectively. The present study was undertaken in the western and central sectors of Indian Sundarbans that are different in terms of physico-chemical variables (particularly salinity). Litter production was higher in the western sector owing to higher diversity of mangrove species in the selected plots. High salinity and wind action also accelerated the process of litter fall (both leaf litter and miscellaneous litter), and hence, the peak values of total litter, leaf litter and miscellaneous litter fall (except Sagar Island) was observed in premonsoon season, in both the western and central sectors of the study area.

Ecoenzymatic Stoichiometry and Ecological Theory

The net primary production of the biosphere is consumed largely by microorganisms, whose metabolism creates the trophic base for detrital foodwebs, drives element cycles, and mediates atmospheric composition. Biogeochemical constraints on microbial catabolism, relative to primary production, create reserves of detrital organic carbon in soils and sediments that exceed the carbon content of the atmosphere and biomass. The production of organic matter is an intracellular process that generates thousands of compounds from a small number of precursors drawn from intermediary metabolism. Osmotrophs generate growth substrates from the products of biosynthesis and diagenesis by enzyme-catalyzed reactions that occur largely outside cells. These enzymes, which we define as ecoenzymes, enter the environment by secretion and lysis. Enzyme expression is regulated by environmental signals, but once released from the cell, ecoenzymatic activity is determined by environmental interactions, represented as a kinetic cascade, that lead to multiphasic kinetics and large spatiotemporal variation. At the ecosystem level, these interactions can be viewed as an energy landscape that directs the availability and flow of resources. Ecoenzymatic activity and microbial metabolism are integrated on the basis of resource demand relative to environmental availability. Macroecological studies show that the most widely measured ecoenzymatic activities have a similar stoichiometry for all microbial communities. Ecoenzymatic stoichiometry connects the elemental stoichiometry of microbial biomass and detrital organic matter to microbial nutrient assimilation and growth. We present a model that combines the kinetics of enzyme activity and community growth under conditions of multiple resource limitation with elements of metabolic and ecological stoichiometry theory. This biogeochemical equilibrium model provides a framework for comparative studies of microbial community metabolism, the principal driver of biogeochemical cycles.

Contributions of detrital subsidies to aboveground spiders during secondary succession, revealed by radiocarbon and stable isotope signatures

Prey subsidies originating from detritus add nutrients and energy to arboreal communities. Measurement of this subsidy is required in the understanding of how food web dynamics respond to changes in surrounding environments. Shrub spiders are one of the key predators involved in food web coupling. We evaluate the effects of potential changes in prey availabilities during secondary succession on the contribution of subsidy from detrital food webs to shrub spiders and how different spider feeding guilds used the subsidy of prey from detrital food webs. We measured the relative importance of the subsidy for the spider feeding guilds, using the ratios of stable isotopes of C (δ(13)C), and N (δ(15)N) and C isotope discrimination (Δ(14)C). Diet age was calculated from Δ(14)C values, because old diet ages of spiders indicate that the spiders consume prey from detrital food sources. Dominant aerial prey (Diptera) had a distinctively old diet age compared with arboreal prey, which indicates that aerial prey were subsidized from detrital food webs. Sit-and-wait spiders tended to have an older diet age than active hunting spiders, which indicates that sit-and-wait spiders depended more on subsidies. Diet age varied only slightly for spiders in stands of different ages, indicating that rates at which spiders use grazing and detrital prey are probably determined more by foraging strategies and not by stand age. A dominance of sit-and-wait predators will lead to higher detrital subsidy inputs in shrub habitats. This study highlights the effect of shrub spider community structure (feeding guild composition) on the volume of the subsidy received from the detrital food web.