Litter Arthropod Communities Research Articles

Litter arthropod communities in a Northeastern Cerrado area of Maranhão state, Brazil

Litter arthropod communities in a Northeastern Cerrado area of Maranhão state, Brazil

Trechus (Coleoptera: Carabidae) of Appalachia: A Phylogenetic Insight into the History of High Elevation Leaf Litter Communities

Elevation gradients provide a wealth of habitats for a wide variety of organisms. The southern Appalachian Mountains in eastern United States are known for their high biodiversity and rates of endemism in arthropods, including in high-elevation leaf-litter taxa that are often found nowhere else on earth. Trechus Clairville (Coleoptera: Carabidae) is a genus of litter inhabitants with a near-global distribution and over 50 Appalachian species. These span two subgenera, Trechus s. str. and Microtrechus Jeannel, largely restricted to north and south of the Asheville basin, respectively. Understanding the diversification of these 3–5 mm flightless beetles through geological time can provide insights into how the litter-arthropod community has responded to historical environments, and how they may react to current and future climate change. We identified beetles morphologically and sequenced six genes to reconstruct a phylogeny of the Appalachian Trechus. We confirmed the Asheville Basin as a biogeographical barrier with a split between the north and south occurring towards the end of the Pliocene. Finer scale biogeography, including mountain-range occupancy, was not a reliable indication of relatedness, with group ranges overlapping and many instances of species-, species group-, and subgeneric sympatry. This may be because of the recent divergence between modern species and species groups. Extensive taxonomic revision of the group is required for Trechus to be useful as a bioindicator, but their high population density and speciose nature make them worth additional time and resources.

Alteration of a temperate forest invertebrate community by invasive Japanese barberry (Berberis thunbergii) has limited influence on the diet composition of territorial ovenbirds (Seiurus aurocapilla)

Invasive species are widely implicated in the decline of songbird populations, potentially via indirect effects such as the restructuring of ecological communities by non-native plants. We used stable isotope analysis to investigate whether ground-foraging, generalist insectivore ovenbirds ( Seiurus aurocapilla (Linnaeus, 1766)) shifted diets following invasion by a non-native shrub, Japanese barberry ( Berberis thunbergii DC.), in a temperate woodland system in New York, USA where barberry was previously linked to trophic downgrading in the leaf litter arthropod community. Assimilated ovenbird diets were primarily composed of predatory invertebrates followed by sucking herbivores, chewing herbivores, and detritivores. The only notable changes in assimilated ovenbird diets were a modest 14.7% decrease in chewing herbivore contributions and a minor 7.0% increase in sucking herbivore contributions in forest patches with high barberry densities. Our results indicate that the effects of non-native plants on connections between higher trophic levels are context-dependent, and comparisons with other studies suggest that community complexity and time since introduction are key contextual differences that affect the outcome of an invasion. Our results may reflect compensatory shifts in individual foraging effort by ovenbirds, but, in combination with our previous research, provide little evidence that barberry affects ovenbird condition and therefore downstream outcomes.

Leaf litter arthropods show little response to structural retention in a Central European forest

Decomposition of leaf litter is a central process of energy and nutrient cycling in forests, in which arthropods hold important roles. Thus, safeguarding the diversity of organisms including arthropods is increasingly being considered in contemporary forestry, not least to facilitate continued ecosystem functioning. Retention forestry tries to achieve biodiversity conservation by preservation of tree structural elements such as deadwood and tree microhabitats to provide more heterogeneous habitat. Leaf litter arthropods are, however, only indirectly connected with tree structure, which raises the question if and how the currently practised retention forestry influences the leaf litter arthropod community. As the leaf litter arthropod community includes a very diverse range of taxa that is challenging to identify morphologically, we sampled environmental DNA from leaf litter on 66 plots in the Black Forest in southern Germany that were distributed over gradients of forest and landscape features and differed in forest management intensity. We found that the richness of operational taxonomic units, a surrogate for species, was not related to forest structure but tended to increase with recent harvest intensity (which did not exceed a medium harvest intensity on our plots). Community composition was related to the share of coniferous trees present on a plot, and to a lesser extend to elevation and leaf litter coverage. Our results indicate that the leaf litter arthropod community is not responsive towards different degrees of forest structural changes introduced by management as long as the forest type is retained.

Shrub facilitative effects on the plant litter arthropod community shifts with decreasing precipitation in desertified ecosystems in northwestern China

Understanding shrub effects on plant litter arthropod community structure in contrasting semiarid and arid grassland ecosystems could lead to the promotion of biodiversity conservation and sustainable management in afforested plantations. An investigation of litter arthropod abundance and diversity beneath the shrub canopy and in open spaces between shrubs was conducted via a litterbag field experiment during two consecutive years in a semiarid and an arid grassland ecosystem. Litter arthropod diversity and abundance were significantly higher in the shrub understory than in open spaces in the arid grassland. Furthermore, a similar abundance of both total mites and predatory mites was found in the shrub understory. However contrasting trends were found in the semiarid grassland. Significantly higher detritivorous mite abundance was found in the open areas between shrubs with no clear facilitation effects on the detritivore community. In conclusion, shrub facilitation could expand biodiversity conservation towards open spaces in extreme arid grasslands. The increasing drought expected for the region under climate change scenarios strengthens the importance of conserving shrub cover in these ecosystems to sustain biodiversity and ecosystem functioning.

Litter arthropods community in multifunctional landscapes: Spatial and temporal complementarity of Brazilian ecosystems

In view of the heterogeneity of ecosystems that make up the Cerrado biome, frequent replacement of native vegetation by exotic components and typically seasonal climate, the present study aimed to investigate: (1) How litter arthropods communities are distributed in time and space in a multifunctional landscape in Cerrado biome, and (2) the importance of natural and anthropized ecosystems for the litter arthropod community in the dry and rainy seasons. The research was carried out in 12 sites in the Triângulo Mineiro region, state of Minas Gerais, Brazil. The study area is part the Cerrado biome and, of the 12 sites, three were composed of fragments of cerrado sensu stricto (s.s.), three by abandoned pastures, three by veredas and three by eucalypt plantation. The collection of litter arthropods occurred through pitfall traps in the dry and rainy seasons. The individuals collected were identified at the family level and categorized according to the trophic function and body size. Although the different ecosystems in isolation did not influence the quantitative parameters of arthropod communities, an important interaction between ecosystems and seasonality was observed. During the rainy season the litter arthropod communities in cerrado s.s. and veredas presented similar richness with slightly greater Simpson diversity in the cerrado s.s., but the veredas were much richer and diverse than other ecosystems in the dry season. A high diversity was also observed in the eucalypt plantations in the rainy season, but with a low functional richness. The functional and taxonomic compositions of the litter arthropod communities differed among ecosystems. In addition, even with a high richness in anthropized ecosystems, the communities present in the savannas were not similar to those present in anthropized ecosystems. Therefore, it was observed that the litter arthropod communities formed spatial and temporal mosaics that play complementary roles in supporting litter arthropod biodiversity.

Influence of edaphic factors along an altitudinal gradient on a litter arthropod community in an Abies-Quercus forest in Mexico

Elevational gradients can serve as natural experiments to study how species are restricted spatially according to environmental conditions. The variation in resources and conditions that habitats experience in relation to the seasons can be useful for understanding why the abundance and distribution of the species change temporarily. In this study, we evaluated the influence of an altitudinal gradient and seasonality on the composition, richness (S), diversity (Hʹ), and density of arthropod community associated with litter in a conserved Abies-Quercus forest in Central Mexico. We defined five altitudinal ranges in an altitudinal gradient that oscillated between 2570 and 2770 m, in which edaphic factors [pH, organic matter (OM), carbon (C), total nitrogen (N), total phosphorous (P), C/N, C/P, N/P ratios] and environmental temperature were characterized. Litter arthropods were collected through this vertical gradient in dry and rainy season. We identified 163 species belonging to 22 orders. Arthropods composition on each elevation zone is significantly different from one another in both seasons. The highest abundance and S values through altitudinal gradient were registered in the rainy season; in contrast, H’ values were higher during the dry season. We detected a significant negative effect related to the altitude on S, Hʹ and abundance of litter arthropods during the dry season and total data. An exception was the rainy season in which we did not detect any pattern. The community similarity reduces as altitude increases. Surprisingly, the intermediate altitudinal range showed the higher density values in the rainy season. On the other hand, OM, C/N and C/P ratios had a negative influence on litter community parameters analyzed in the rainy season and total data. In contrast, P shows a positive influence on S of litter arthropods in the same period. Edaphic characteristics recorded along the altitudinal gradient can explain differences in litter arthropod communities.

Who gives a flux? Synchronous flowering ofCoffea arabicaaccelerates leaf litter decomposition

AbstractCoffee (Coffea arabica) flowers synchronously and flowers are only open for a few days before senescing. Flower petals often decompose easily, containing higher concentrations of nutrients relative to other plant tissues. Thus, a pulse of petals into the detrital pool could be beneficial for the decomposer community and accelerate decomposition processes. Our research assessed the magnitude of the pulse of petals within a shaded coffee farm, and the impact of petals on the litter arthropod community and on the rate of leaf litter decomposition. Three plots of 12 coffee plants were monitored throughout the flowering period to estimate the magnitude of the bloom. Pitfall traps were used to assess the litter arthropod community before and after flowering. Finally, litterbags withC. arabicaleaves alone andC. arabicaleaves with flower petals were used to compare the effect of petals on decomposition rates. The average number of flowers open per plant at the peak of the bloom was 792 flowers. When scaling to obtain an estimate per hectare in a year, our results indicate flower petals could contribute 26.27 kg of nitrogen, 2.03 kg of phosphorus, and 26.7 kg of potassium. The leaf litter community did not change during our sampling, suggesting that any community effects may be acting on a longer time scale or smaller spatial scale. Leaf litter decomposed nearly three times as quickly in litterbags that included flower petals, relative to litterbags with onlyC. arabicaleaf litter in the first month and twice as fast in the second month. The rate of decomposition with petals exceeded the rate of decomposition without petals and was highest after one month, though the benefit continued after two months. Our results demonstrate that the presence of flower petals can accelerate short‐term decomposition processes.

Effects of Chinese privet (Ligustrum sinense) invasion on decomposition and litter-dwelling invertebrates in Southeastern U.S. floodplain forests

Chinese privet (Ligustrum sinense) is one of the most problematic invasive plants in many parts of the world where it often dominates the shrub layer in riparian forests. We aimed to evaluate the role of privet invasion on litter inputs, rates of litter decomposition and litter-dwelling arthropods in the Southeastern United States. To do this we: (1) evaluated the relative contribution of privet to total litter-fall, (2) compared breakdown of artificial leaves (filter paper) in plots which had or had not been subjected to experimental privet removal, and (3) compared litter breakdown and arthropod communities among the following litter types: (a) native sweetgum, (b) invasive Chinese privet, and (c) a mixed sweetgum–privet litter treatment. Privet accounted for 10% of annual litter-fall at our study sites and leaf fall phenology differed from native species. Filter paper decomposed about twice as quickly in reference compared to removal plots but there were no differences between plot types in litter decomposition. This difference may relate to flooding during the litter bag experiment. In both plot types, privet litter decomposed faster than sweetgum or mixed litter but there were no differences in decay rates between the latter two litter types, suggesting that sweet gum may slow the rate of decomposition in mixed bags. There were no differences among litter or plot types in invertebrate community composition or overall abundances, but detritivores were marginally more abundant in the reference plots. Our findings suggest that flooding may affect the impact of privet invasion on litter decay rates and associated invertebrate communities.

Impacts of rainfall extremes predicted by climate-change models on major trophic groups in the leaf litter arthropod community.

Arthropods in the leaf litter layer of forest soils influence ecosystem processes such as decomposition. Climate-change models predict both increases and decreases in average rainfall. Increased drought may have greater impacts on the litter arthropod community. In addition to affecting survival or behaviour of desiccation-sensitive species, lower rainfall may indirectly lower abundances of consumers that graze drought-stressed fungi, with repercussions for higher trophic levels. We tested the hypothesis that trophic structure will differ between the two rainfall scenarios. In particular, we hypothesized that densities of several broadly defined trophic groupings of arthropods would be lower under reduced rainfall. To test this hypothesis, we used sprinklers to impose two rainfall treatments during three growing seasons in roofed, fenced 14-m2 plots and documented changes in abundance from initial, pre-treatment densities of 39 arthropod taxa. Experimental plots were subjected to either LOW (fortnightly) or HIGH (weekly) average rainfall based upon climate models and the previous 100years of regional weekly averages. Unroofed open plots, our reference treatment (REF), experienced higher than average rainfall during the experiment. The two rainfall extremes produced clear negative effects of lowered rainfall on major trophic groups. Broad categories of fungivores, detritivores and predators were more abundant in HIGH than LOW plots by the final year. Springtails (Collembola), which graze fungal hyphae, were 3× more abundant in the HIGH rainfall treatment. Taxa of larger-bodied fungivores and detritivores, spiders (Araneae), and non-spider predators were 2× more abundant under HIGH rainfall. Densities of mites (Acari), which include fungivores, detritivores and predators, were 1.5× greater in HIGH rainfall plots. Abundances and community structure of arthropods were similar in REF and experimental plots, showing that effects of rainfall uncovered in the experiment are applicable to nature. This pattern suggests that changes in rainfall will alter bottom-up control processes in a critical detritus-based food web of deciduous forests. Our results, in conjunction with other findings on the impact of desiccation on arthropods and fungal growth, suggest that drier conditions will depress densities of fungal consumers, causing declines in higher trophic levels, with possible impacts on soil processes and the larger forest food web.

Managed Fire Frequency Significantly Influences the Litter Arthropod Community in Longleaf Pine Flatwoods.

Frequent prescribed burns are essential to pine forest restoration and management. Research studies have assessed effects of prescribed fire and burn frequency on plants and vertebrates, but impacts of fire on terrestrial invertebrate communities are still poorly understood. This case study investigated effects of burning frequency on species richness and community composition of social insects (ants, Hymenoptera: Formicidae and termites, Blattodea: Isoptera) in fire-managed Southern longleaf pine flatwoods in central Florida. Community response to different fire frequencies was assessed: burned annually, every 2 yr, or every 3 yr, 30 yr unburned and 75 yr unburned. Richness was similar across all treatments, but ant community composition and species density significantly differed between frequently burned (1, 2, and 3 yr) and long-unburned (30 and 75 yr) treatments. Long-unburned treatments had higher ant abundance, but the species present were less characteristic of open canopy longleaf pine habitat than ants in frequently burned treatments. The annual burn treatment differed from 2-yr burn in species density, but to a lesser degree. Exotic species abundance was highest in frequently burned sites; only native species were detected in the 75-yr unburned plot. The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), was detected in all regularly burned plots but not in long-unburned sites. Frequent burning at this site increased habitat suitability for ant species adapted to the sunny, open canopy, and diverse niches characteristic of longleaf pine forest; however, regular fire disturbance also increased the likelihood of exotic ant species establishment.

Behavioral interactions between terrestrial salamanders and spiders: competition or intraguild predation?

Several studies suggest that small terrestrial salamanders are important regulators of leaf litter arthropod communities, and likely contribute to ecosystem processes such as decomposition and nutrient cycling. Despite the recognition that salamanders have the potential to strongly affect ecosystem function through both direct and indirect pathways, little is known regarding the nature of interactions between small vertebrates and the large, predatory arthropods with which they share both microhabitat and prey. Our study was designed to explore interactions between Eastern Red-backed Salamanders, Plethodon cinereus, and spiders in the genus Wadotes in an eastern North American temperate forest ecosystem. We were particularly interested in teasing apart behaviors such as territoriality and intraguild predation in an attempt to determine specifically which interaction is most likely responsible for the observed negative relationship between salamander and spider abundance at our field site. Field data indicate that P. cinereus and large syntopic spiders exhibit negative spatial associations in the microhabitat beneath cover objects, a possible indication of interspecific territoriality. In our laboratory experiments, resident salamanders displayed agonistic postures similarly toward both intruding conspecifics and spiders, suggesting that salamanders may perceive large intruding spiders as competitors. Finally, we observed no injuries to individual P. cinereus or adult spiders even though occasional chases and bites by both were recorded during the behavioral trials. We found no evidence that adults or juveniles of P. cinereus were envenomated by adult Wadotes spp., and there were no instances of intraguild predation in this study. Multiple lines of evidence from this study, and others, suggest that the primary interaction between individuals of P. cinereus and large spiders is competitive in nature rather than predatory. We suggest that the cost associated with intraguild predation on salamanders with noxious skin secretions may preclude them from being preyed upon by spiders.

Tree functional diversity affects litter decomposition and arthropod community composition in a tropical forest

AbstractDisturbance can alter tree species and functional diversity in tropical forests, which in turn could affect carbon and nutrient cycling via the decomposition of plant litter. However, the influence of tropical tree diversity on forest floor organisms and the processes they mediate are far from clear. We investigated the influence of different litter mixtures on arthropod communities and decomposition processes in a 60‐year‐old lowland tropical forest in Panama, Central America. We used litter mixtures representing pioneer and old growth tree species in experimental mesocosms to assess the links between litter types, decomposition rates, and litter arthropod communities. Overall, pioneer species litter decomposed most rapidly and old growth species litter decomposed the slowest but there were clear non‐additive effects of litter mixtures containing both functional groups. We observed distinct arthropod communities in different litter mixtures at 6 mo, with greater arthropod diversity and abundance in litter from old growth forest species. By comparing the decay of different litter mixtures in mesocosms and conventional litterbags, we demonstrated that our mesocosms represent an effective approach to link studies of litter decomposition and arthropod communities. Our results indicate that changes in the functional diversity of litter could have wider implications for arthropod communities and ecosystem functioning in tropical forests.

Warming magnifies predation and reduces prey coexistence in a model litter arthropod system.

Climate warming can destabilize interactions between competitors as smaller organisms gain advantages in warmer environments. Whether and how warming-induced effects on competitive interactions are modified by predation remains unknown. We hypothesized that predation will offset the competitive advantage of smaller prey species in warmer environments because of their greater vulnerability to predation. To test this, we assembled a litter arthropod community with two Collembola species (Folsomia candida and Proisotoma minuta) of different body sizes across a temperature gradient (three thermal environments) and in the presence and absence of predatory mites. Predatory mites reduced Collembola coexistence with increasing temperatures. Contradicting our hypothesis, the larger prey species always outperformed the smaller prey species in warmer environments with predators. Larger prey probably benefited as they expressed a greater trait (body length) plasticity to warming. Warming can thus magnify predation effects and reduce the probability of prey coexistence.

Effects of Fire Intensity on Litter Arthropod Communities in Ozark Oak Forests, Arkansas, U.S.A

Fires are a significant source of landscape scale disturbance in forested ecosystems, but fire effects also vary on small spatial scales due to differences in fuel loads and local environmental conditions. We tested the hypothesis that such variation influences post fire arthropod communities and faunal recovery rates on a 1 m2 scale. We measured the abundance and species richness of selected arthropod taxa pre- and post-fire in patches of leaf litter experimentally burned at different intensities. Arthropod abundance declined sharply immediately after a burn and decreased with increasing fire intensity. Consistent with other studies of this system, the effects of fire on arthropod communities were still apparent >4 w post burn. The abundance of epigeic beetles recovered more quickly than the abundance of ants or springtails in some treatments. Recovery rates also differed among treatments but did not consistently support the prediction that recovery would be faster in plots subject to low intensity burns. We conclude that small scale differences in intensity within prescribed fires have measurable effects on litter arthropod communities in Ozark forests; however, these differences appear to be overshadowed by the more general effects of fire on arthropods.

Litter manipulation and the soil arthropod community in a lowland tropical rainforest

Tropical soil arthropod communities are highly diverse and provide a number of important ecosystem services, including the maintenance of soil structure, regulation of hydrological processes, nutrient cycling and decomposition. Experiments in temperate regions suggest that litter dynamics are important in determining the abundance, richness and community composition of soil fauna, but there is little information for lowland tropical forests. We used a long-term litter manipulation experiment (removing, doubling and control) in a neotropical forest to investigate the consequences of changing litter dynamics on the soil arthropod community. The abundance and biomass of arthropods were reduced significantly by the removal of litter, but not affected by litter addition. Litter manipulation had no effect on simple measures of taxonomic richness or diversity, but multivariate ordination techniques revealed a significant shift in arthropod community composition with the removal, but not addition, of litter. This suggests the overall importance of top-down controls on the arthropod community in this ecosystem, with bottom-up influences only important following the removal of large quantities of litter. Of the parameters measured, the faunal composition of experimental plots was best predicted by litter depth and the concentrations of total carbon and readily-exchangeable phosphorus (in order of importance), highlighting the influential role of soil chemical properties, in addition to the physical properties of litter, in shaping soil arthropod communities. Comparison with the results of a previous study of litter-dwelling fauna in the same litter manipulation experiment suggested that the soil and litter arthropod communities are influenced by different parameters: total carbon and litter depth for the soil community, but sodium and calcium for the litter community, although phosphorus was important in both environments. We conclude that arthropod community composition is controlled by different factors in the soil than in the litter and is affected by decreasing, but not increasing, depth of litter.

Community-level effects in edaphic fauna from an abandoned mining area: Integration with chemical and toxicological lines of evidence

As a part of the Ecological Risk Assessment of a deactivated uranium mining area (Cunha Baixa), the aim of this study was to assess the drivers of litter arthropod community (ecological line of evidence) inhabiting soils with different degrees of contamination. Litter arthropods were collected in the mining area using a total of 70 pitfall traps, in the spring and autumn of 2004. Unlike information previously collected in the chemical and ecotoxicological lines of evidence, we found no clear evidence of impacts of soil contamination on the edaphic arthropod assemblage. Multivariate analyses were unable to extract relevant environmental gradients related to contamination, as most of the sites shared the same taxa overall. Given the consistency of the chemical and ecotoxicological lines of evidence, we must conclude that the litter arthropod assemblage underestimated the impacts of contamination in this abandoned mining area. In part, this could be due to the uncertainty caused by confounding factors that affect the litter arthropod community in the area. Nevertheless, despite the overall lack of responsiveness of the epigeic arthropod community data, a few taxa were negatively correlated with metal concentrations (Clubionidae and Staphylinidae), while Pseudoscorpionida were associated with the toxicological profile of the sites. These evidences suggest that community-level approaches with other animal and plant assemblages are necessary to reduce uncertainty relatively to the assessment of risks in higher evaluation tiers in the Cunha Baixa mine area.

Associations between invasive eucalyptus psyllids and arthropod litter communities under tree canopies in southern California

AbstractHoneydew‐producing psyllids are an important pest of eucalyptus (Myrtaceae) in California, USA, and may influence surrounding litter arthropod communities. In particular, the introduced Australian psyllids Glycaspis brimblecombei Moore and Eucalyptolyma maideni Froggatt (both Hemiptera: Psyllidae) may facilitate the prevalence of invasive ant species. We examined ground‐dwelling arthropod communities under eucalyptus trees infested by psyllids. We used a model comparison approach to examine the association of psyllid infestation, ant abundance, and environmental factors with ground arthropod abundance and richness. We found a significant positive association between ant activity on eucalyptus trees and psyllid abundance. Higher psyllid abundance and higher Argentine ant abundance were associated with increased arthropod richness. Irrigation was also associated with increased arthropod richness and abundance. Regardless of location collected, arthropod communities collected in pitfall traps under trees with high psyllid abundance had high similarity to arthropod communities under trees with high ant activity. Abundance of isopods was positively associated with both ant and psyllid abundance. Other arthropod groups differed in their association with ants and psyllids. Argentine ants may exacerbate pest impacts and may also decrease the effectiveness of biological control programs for eucalyptus lerp psyllids.

Influence of fallen coarse woody debris on the diversity and community structure of forest-floor spiders (Arachnida: Araneae)

Purely observational studies have documented differences in the abundance and diversity of several litter-dwelling arthropods between sites adjacent to, and far from, CWD, which suggests that reduction of fallen coarse woody debris (CWD) in temperate forests by traditional forestry practices may affect the litter arthropod community. As few field experiments have directly tested the impact of CWD on arthropods inhabiting the litter at different distances from CWD, we removed CWD from replicated open plots on the floor of a second-growth deciduous forest in order to reveal the causal connection between CWD and litter-dwelling spiders, often the most diverse and abundant predators among the litter macrofauna of temperate forests. We also documented the impact of the CWD manipulation on spider prey and several other major macroarthropod groups. Before removing CWD (∅ = 14.3 ± 0.7 cm), we measured response variables as a function of distance (0.5–1.5 m) from CWD in both removal and control plots. In agreement with results of previous research that solely utilized this observational approach in temperate forests, volume and dry mass of litter, spider diversity, overall spider density, and densities of 8 of 16 major spider genera were higher adjacent to CWD before experimental manipulations. Removing CWD reduced the amount of litter and the density of spiders in litter close to where the CWD had been. Removing CWD also altered spider community structure, which had differed between litter sites adjacent to, and far from, CWD prior to the experimental removal of CWD. The patterns, though, were not completely congruent, as some of the taxa affected by the manipulation had not differed between sites prior to the removal of CWD, and vice-versa. Our findings suggest that complex interactions among structural, biotic and microclimatic factors underlie the observed responses to CWD removal by spiders and other arthropods in the litter layer. We also conclude that drawing inferences solely from observational studies is not a reliable approach for predicting the impact of changes in the amount of CWD on arthropods of forest-floor leaf litter. Further field experiments manipulating different volumes of CWD are needed in order to determine the minimum amount of CWD that should be kept on the forest floor of managed forests in order to maintain densities and diversities of major leaf-litter arthropods.

Dynamics of the Leaf-Litter Arthropod Fauna Following Fire in a Neotropical Woodland Savanna

Fire is an important agent of disturbance in tropical savannas, but relatively few studies have analyzed how soil-and-litter dwelling arthropods respond to fire disturbance despite the critical role these organisms play in nutrient cycling and other biogeochemical processes. Following the incursion of a fire into a woodland savanna ecological reserve in Central Brazil, we monitored the dynamics of litter-arthropod populations for nearly two years in one burned and one unburned area of the reserve. We also performed a reciprocal transplant experiment to determine the effects of fire and litter type on the dynamics of litter colonization by arthropods. Overall arthropod abundance, the abundance of individual taxa, the richness of taxonomic groups, and the species richness of individual taxa (Formiciade) were lower in the burned site. However, both the ordinal-level composition of the litter arthropod fauna and the species-level composition of the litter ant fauna were not dramatically different in the burned and unburned sites. There is evidence that seasonality of rainfall interacts with fire, as differences in arthropod abundance and diversity were more pronounced in the dry than in the wet season. For many taxa the differences in abundance between burned and unburned sites were maintained even when controlling for litter availability and quality. In contrast, differences in abundance for Collembola, Formicidae, and Thysanoptera were only detected in the unmanipulated samples, which had a lower amount of litter in the burned than in the unburned site throughout most of our study period. Together these results suggest that arthropod density declines in fire-disturbed areas as a result of direct mortality, diminished resources (i.e., reduced litter cover) and less favorable microclimate (i.e., increased litter desiccation due to reduction in tree cover). Although these effects were transitory, there is evidence that the increasingly prevalent fire return interval of only 1–2 years may jeopardize the long-term conservation of litter arthropod communities.