Transport and particle size distribution of suspended and benthic organic matter in three headwater streams

The breakdown and decomposition of two species of deciduous leaf litter, Fagus sylvatica L. and Salix viminalis L. and two species of aquatic macrophyte Isoetes lacustris L. and Potamogeton perfoliatus L. were examined in an oligotrophic lake. In all cases plant litter in coarse mesh litter bags lost significantly more material than the fine mesh after 1 years submergence in the lake. This however was considered to be the result of physical environmental factors and microbial activity rather than animal processing. The litter was ranked in order of fastest to slowest rates of decay as follows — Isoetes, Potamogeton, Salix and Fagus. Decomposition processes proceeded at a relatively slow rate as a result of low temperatures and low phosphate and mineral ion concentration. The results suggested that there was an accumulation of organic material in the lake.     

Decomposition of cellulose,soil organic matter and plant litter in a temperate grassland soil

The formation of mor humus in an experimental grassland plot, which has been acidified by long-term fertiliser treatment, has been studied by comparing the rates of cellulose, soil organic matter and plant litter decay with those in an adjacent plot with near-neutral pH and mull humus. The decomposition of cellulose filter paper in litter bags of 5 mm, 1-mm and 45-μm mesh size buried at 3 to 4 cm depth the plots was followed by measuring the weight loss and changes in glucose content over a 6 month period. Soil pH was either 5.3 or 4.3. Decomposition of native soil organic matter and plant litter in soil from the same plots were followed using CO₂ evolution in laboratory microcosms. Cellulose weight loss at pH 5.3 was greatest from the 5-mm mesh bags and least from the 45-um mesh bags. At pH 4.3 there was little weight loss from bags and no significant differences in weight loss between bags with different sized mesh. There was, however, a reduction in the glucose content of the hydrolysed and derivatised filter paper with time. The decomposition rate of native soil organic matter in the low pH soil was increased to that observed in the less acid soil when the pH of the former was increased from 4.3 to 5.3. The increase in decomposition rate of added plant litter in the more acid soil as a result of CA(OH)₂ addition was only 60% of that observed in the soil with pH 5.3. These data support the hypothesis that the absence of soil animals and the restricted microbial decomposition in the acidic soil was responsible for mor humus formation.     

Differential Effects of Typha Litter and Plants on Invasive Lythrum Salicaria Seedling Survival and Growth

Invasive species are a problem because of their detrimental ecological and economic effects. Increased disturbance caused by human impacts is hypothesized as a primary factor promoting the spread of invaders. Plants and plant litter can have important effects on plant colonization and community composition by affecting seedling survival and growth. I examined the hypothesis that invasion of non-native Lythrum salicaria in Typha-dominated marshes is disturbance-dependent. If so, the removal of Typha plants or litter would increase the survival and growth of L. salicaria seedlings. Additionally, the removal of both plants and litter could result in an additive or synergistic effect on the establishment of L. salicaria. Alternatively, L. salicaria may be a successful invader because it has a high capacity to establish and grow regardless of neighbours. In this case, L. salicaria would be expected to perform well even in plants and litter. Strategies for managing L. salicaria will depend on which factors promote invasion. I measured the differential effects of plants and litter, alone and in combination, on the survival and growth of L. salicaria seedlings transplanted into marshes. The presence of plants and litter did not affect seedling survival in relatively dry wetland sites, indicating that L. salicaria seedlings have the capacity to persist in the presence of neighbouring Typha spp. competitors. However, removal of both plants and litter allowed increased growth of L. salicaria seedlings in drier wetlands. Therefore, growth was facilitated by disturbance that removed all vegetation. Small disturbances (0.6 m²) decreased competitive suppression by native Typha spp. neighbours and resulted in significant increases in growth. Disturbance of wetlands at risk of invasion by L. salicaria should be avoided.     

A modified litter bag design for use in lentic habitats

A modified litter bag design and handling procedure were tested to establish whether these reduced the exaggerated fragmentation losses that occur with standard litter bags. The modified design was compared with standard coarse (5 mm) and fine (0.25 mm) mesh litter bags using Phragmitesleaf litter. All were positioned in a section of a reedbed subject to water level management but negligible water flow. Breakdown rates were significantly reduced with the modified design but these were still significantly greater than those in the fine mesh bags. Owing to the extended period, results were influenced by invertebrates colonising the fine mesh bags. The significance of bag design and invertebrate colonisation are discussed.     

The influence of invertebrates on the breakdown ofPotamogeton pectinatus L. in a coastal marina (Zandvlei,South Africa)

The influence of invertebrates upon the decomposition ofPotamogeton pectinatus L. in a coastal Marina system was examined over 112 days using litter bags. Invertebrate inclusion bags (2 mm mesh, 5 mm holes) registered a dry mass loss of 1% d^–1, while exclusion litter bags (80 µm mesh) produced a 0.4% mass loss d^–1 (a 2.5 fold difference). Losses of ash and N from inclusion bags were greater than those from exclusion bags (p < 0.05). There was a three fold difference between the two treatments in the time taken for litter to breakdown to half the initial stock: T_1/2 for inclusion bags = 43 d, exclusion bags = 130 d. In both treatments, minerals showed an expected rapid loss, due to leaching, with a subsequent slow increase relative to the dry material remaining. A total of nine invertebrate taxa was recorded from inclusion bags, with a peak biomass of 64 mg g^–1 dry massPotamogeton bag^–1 reached at 64 days after immersion. Grazing amphipods,Melita zeylanica Stebbing andAustrochiltonia subtenuis (Barnard), numerically dominated the litter bag fauna, whileM. zeylanica and nymphs of the zygopteran predatorIschnura senegalensis (Rambur) formed most of the biomass. Scanning Electron Microscopy indicated heavy grazing of micro-organisms by invertebrates, with major qualitative differences occurring 112 days after immersion. Invertebrates significantly accelerated the rate of litter breakdown through their feeding activities, assisting fragmentation and thus contributing to plant losses and also by increasing the surface area for microbial colonisation and attack.     

Diet and dietary selectivity of Cane Toads (Rhinella marina) in restoration sites: a case study in Far North Queensland,Australia

Cane Toads (Rhinella marina, formerly Bufo marinus) in restoration sites on the Atherton Tableland in NE Australia consumed invertebrates belonging to 11 different taxa with ants being the most abundant prey item. Principal component analyses showed that the composition of invertebrates in Cane Toad diet is largely a reflection of invertebrates found in pitfall and leaf litter samples suggesting that the species is an indiscriminant feeder. However, pitfall samples contained more Collembola and Isopoda than were found in Cane Toad stomachs. The Cane Toad may benefit from restoration management practices by utilizing food resources enhanced by mulching and providing microhabitats (e.g. rock piles, logs) as shelter. While further studies would be needed to test this practitioners working in areas where the Cane Toad is problematic may consider trade‐offs between attracting invertebrates and Cane Toads by monitoring provided microhabitat features.     

On body size and habitat selection in rotifers in a macrophye-dominated lake Budzyńskie,Poland

Lake Budzyńskie is shallow, freshwater lake with a well-developed and differentiated macrophytic vegetation. Zooplankton samples were collected from five stations: two of them in submerged macrophytes (Chara and Myriophyllum), one in the zone of floating leaves (Potamogeton), a rush station (Typha) and one in the open water surrounding the vegetation beds. The mean Rotifera densities differed significantly between the lake parts. Furthermore, different habitats were characterised by differences in body size with the exception of the middle body size group (Keratella cochlearis, Polyarthra vulgaris and Trichocerca similis), which was dominated by limnetic representatives. However, in all the other size-dependent groups both stands of submerged macrophytes were characterised by much higher densities than other zones. Additionally, body size within the examined habitats significantly differed. Thus, the size structure of Rotifera communities was directly related to morphological and spatial structures of the substrata. Two groups of habitats were distinguished: the first one consisting of open water and two vegetated zones of less complicated structure (Potamogeton and Typha), and the second of more complex submerged macrophyte species (Chara and Myriophyllum). The differentiation of the architecture of macrophytes affected the nutritional conditions and refuge effectiveness of these habitats.     

Mixed leaf litter effects on decomposition rates and soil microarthropod communities in an oak–pine stand in Japan

Rates of decomposition, and soil faunal abundance and diversity associated with single-species and mixed-species litters were studied in a litter bag experiment in an oak–pine forest. We used two canopy species of leaf litter, pine and oak, and one shrub species, Sasa, and compared decomposition rates, and soil microarthropod abundance and community structure of oribatid mites in the litter bags. Mass loss of single species decreased in the order: oak > pine > Sasa. While the total mass loss rates of mixed litter were intermediate between those of the constituent species, enhancement of mass loss from the three-species mixture and from mixed slow-decomposing litters (pine and Sasa) was observed. Faunal abundance in litter bags was higher in mixed-species litter than in those with single-species litter, and species richness of oribatid mites was also higher in the three-species mixed litter. Faunal abundance in single-species litter bags was not correlated with mass loss, although enhancement of mass loss in mixed litter bags corresponded with higher microarthropod abundance. Habitat heterogeneity in mixed litter bags seemed to be responsible for the more abundant soil microarthropod community.     

鄱阳湖湿地优势植物枯落物的分解速率及碳、氮、磷释放动态特征

植物枯落物分解对生态系统碳通量和养分循环有至关重要的作用,这一过程主要由3个相互作用的因素决定,即化学（枯落物理化特性）、物理（气候和环境）以及生物（参与枯落物分解的微生物和无脊椎动物）因素。在气候和立地环境条件相同的情况下,枯落物质量是制约分解的内在因素。在鄱阳湖湿地开展了野外定位观测实验,采用分解袋技术研究了鄱阳湖湿地优势植物芦苇（Phragmite）、南荻（Triarrhena lutarioriparia）和薹草（Carex.cinerascens Kükenth）枯落物分解速率及碳（C）、氮（N）、磷（P）元素释放动态特的征差异性。结果表明,在0-150 d内三种植物枯落物的干物质分解速率和残留率以及碳相对归还指数（CRRI）、氮相对归还指数（NRRI）、磷相对归还指数（PRRI）差异性都极其显著。在0-150 d内分解速率都是芦苇的最大,薹草的次之,南荻最小。分解进行150 d后,芦苇、南荻和薹草枯落物干物质残留率依次约为56.57%、67.99%和60.88%,CRRI依次约为57.44%、34.58%和41.75%,NRRI依次约为50.71%、-22.66%、和23.18%,PRRI依次约为88.91%、79.27%和85.63%。用Olson负指数衰减模型拟合方程预测芦苇、南荻、薹草枯落物分解完成50%所需的时间大约依次为184 d、249 d和210 d,分解完成95%所需的时间依次为795 d、1078 d和908 d。芦苇和薹草枯落物碳、氮和磷在分解过程中都表现出净释放模式,而南荻枯落物的碳和磷也一直表现为净释放模式,但是氮一直表现为净积累模式。芦苇分解过程中的营养释放作用最强,而南荻群落对氮的吸收和富集效应最强。研究表明植物种类及基质物质量对枯落物分解及其养分释放有很强的调控作用。今后的研究应考虑不同物种枯落物混合时的分解过程以及分解过程中的微生物因素,以便能揭示植物群落物种多样性及微生物活动在湿地生物地球化学循环中的调控作用机制,以期为鄱阳湖湿地碳、氮和磷的生物地球化学循环提供更新的认识,为鄱阳湖湿地的科学管理、保护与恢复提供科学依据。     

Episodic acidification affects the breakdown and invertebrate colonisation of oak litter

1. Although European streams are now recovering chemically from acidification, biological recovery is limited. One hypothesis is that continuing acid episodes restrict acid‐sensitive species in recovering locations either through direct toxicity or by affecting ecological processes. Here, we test this hypothesis by assessing the effects of episodic acid exposure on the breakdown and macroinvertebrate colonisation of oak (Quercus robur) litter. 2. Over 83 days, acid episodes of 4 days’ duration were simulated by repeatedly transplanting litter bags of contrasting mesh size between replicate acidic and circumneutral streams around Llyn Brianne (Wales, U.K.). Results were compared against controls from circumneutral streams and circumneutral transplants, while invertebrates colonising litter were compared with adjacent assemblages. 3. Breakdown was retarded significantly by repeated acid exposure in comparison with circumneutral transplants, but only in litter to which invertebrates had access. Overall breakdown was also significantly slower in fine‐mesh than in coarse‐mesh bags. 4. Plecopteran shredders were the major invertebrate colonists of litter, along with smaller numbers of grazers and predators. However, acid exposure eliminated or suppressed acid‐sensitive families, resulting in an overall composition converging on that in acid streams. 5. The rapid loss of sensitive invertebrates from acid‐exposed litter supports the hypothesis that acid episodes suppress biological recovery from acidification through direct physiological effects. However, our litter breakdown data indicate that (i) some effects of acid episodes could be mediated through litter processing; and (ii) episodic acidification could disrupt litter breakdown through effects on invertebrate composition or activity. These data suggest that delayed biological recovery from acidification can reflect a combination of direct toxic and indirect ecological effects.     

Cave invertebrate assemblages differ between native and exotic leaf litter

Abstract Allochtonous leaf litter is an important source of energy and nutrients for invertebrates in cave ecosystems. A change to the quality or quantity of litter entering caves has the potential to disrupt the structure and function of cave communities. In this study, we adopted an experimental approach to examine rates of leaf litter decomposition and the invertebrate assemblages colonizing native and exotic leaf litter in limestone caves in the Jenolan Caves Karst Conservation Reserve, New South Wales, Australia. We deployed traps containing leaf litter from exotic sycamore (Acer pseudoplatanus) and radiata pine (Pinus radiata) trees and native eucalypts (Eucalyptus spp.) in twilight zones (near the cave entrance) and areas deep within the caves for 3 months. Thirty‐two invertebrate morphospecies were recorded from the litter traps, with greater richness and abundance evident in the samples from the twilight zone compared with areas deep within the cave. Sycamore litter had significantly greater richness and abundance of invertebrates compared with eucalypt and pine litter in samples from the twilight zone, but there was no difference in richness or abundance among litter samples placed deep within the cave. Relative rates of decay of the three litters were sycamore > eucalypt > pine. We discuss the potential for the higher decomposition rates and specific leaf area in sycamores to explain their higher invertebrate diversity and abundance. Our findings have important implications for the management of exotic plants and the contribution of their leaf litter to subterranean ecosystems.     

Elevated UV-B radiation has no effect on litter quality and decomposition of two dune grassland species: evidence from a long-term field experiment

From studies on living plant tissues it has been inferred that elevated UV‐B radiation could negatively affect litter quality and subsequent decomposition. However, in general, the effects of UV‐B radiation on litter chemistry and decomposition reported in the literature are variable and are often only marginally (if at all) significant. This might be due to the ecologically unrealistic conditions under which these experiments were performed. We investigated the effects of elevated UV‐B radiation on litter quality and subsequent decomposition on initial litter chemistry and long‐term (2 years) decomposition of freshly senesced Carex arenaria and Calamagrostis epigejos leaf litter under ecologically realistic conditions. This material was collected from a dune grassland that had received UV‐B radiation treatments for three growing seasons. It was then used in a 2‐year decomposition study using litter bags. We found no significant effects of elevated UV‐B radiation on any of the litter chemistry parameters in either of the two species, nor did we find significant effects on litter decomposition. However, we did find significant differences in litter decomposition between the species. These differences were related to the interspecific differences in litter chemistry, particularly the litter phenolics concentration. These results show that litter quality and decomposition in dune grasslands are, also under ecologically realistic conditions, not affected by UV‐B radiation. Instead, litter decomposition is determined by constitutive interspecific differences in litter chemistry. In conclusion, with our results added to the already existing literature, the preponderance of evidence now clearly suggests that elevated UV‐B radiation has very little, if any, impact on litter quality and subsequent decomposition in real ecosystems.     

Breakdown of four leaf litter species and associated fauna in a Basque Country forested stream

Leaves of 4 species (Quercus robur, Castanea sativa, Corylus avellana and Pinus pinaster) were incubated in a forested headwater stream using bags (1 mm and 5 mm net size) and trays (5 mm net size). The type of treatment influenced litter breakdown rates. Differences in loss rates were noted between Pinus and the deciduous species, and between Quercus and Corylus. Numbers of invertebrates per sample and per gram leaf AFDW generally increased with exposure time. The taxa colonizing the four leaf species were largely identical but colonization was greatly dependent on type of treatment. Taxa richness (Hmax) increased with time. Differences between Hmax and specific diversity (H) were high, due to the importance of Chironomids. Collectors and scrapers, among other functional groups, exhibited the highest densities. Differences in loss rates between fine and coarse treatments were related to differences in shredder biomass, corroborating the importance of this functional group in litter processing.     

Plant palatability to leaf‐cutter ants (Atta laevigata) and litter decomposability in a Neotropical woodland savanna

Although leaf‐cutter ants have been recognized as the dominant herbivore in many Neotropical ecosystems, their role in nutrient cycling remains poorly understood. Here we evaluated the relationship between plant palatability to leaf‐cutter ants and litter decomposability. Our rationale was that if preference and decomposability are related, and if ant consumption changes the abundance of litter with different quality, then ant herbivory could affect litter decomposition by affecting the quality of litter entering the soil. The study was conducted in a woodland savanna (cerrado denso) area in Minas Gerais, Brazil. We compared the decomposition rate of litter produced by trees whose fresh leaves have different degrees of palatability to the leaf‐cutter ant Atta laevigata. Our experiments did not indicate the existence of a significant relationship between leaf palatability to A. laevigata and leaf‐litter decomposability. Although the litter mixture composed of highly palatable plant species showed, initially, a faster decay rate than the mixture of poorly palatable species, this difference was no longer visible after about 6 months. Results were consistent regardless of whether litter invertebrates were excluded or not from litter bags. Similarly, experiments comparing the decomposition rate of litter from pairs of related plant species also showed no association between plant palatability and decomposition. Decomposition rate of the more palatable species was faster, slower or similar to that of the less palatable species depending upon the particular pair of species being compared. We suggest that the traits that mostly influence the decomposition rate of litter produced by cerrado trees may not be the same as those that influence plant palatability to leaf‐cutter ants. Atta laevigata select leaves of different species based – at least in part – on their nitrogen content, but N content was a poor predictor of the decomposition rates of the species we studied.     

Variation in the decomposition of Phragmites australis litter in a monomictic lake: the role of gammarids

A decomposition study has been carried out in Lake Geestmerambacht, a moderately deep (max. ca. 22 m), monomictic slightly brackish lake in The Netherlands. To assess the relative importance of biotic (benthos) and physico-chemical factors, the mass loss rate (K) of reed leaf litter was measured at 10 sites, both in winter and in summer, in the absence (`protected' litter bags) and the presence (`unprotected' litter bags) of invertebrates. The aim was to investigate the variation in mass loss rate within the habitat and between seasons, and the role of the litter-associated invertebrate community. The experiments showed high spatial variation in decomposition rates. The spatial pattern changed with season. In summer, decomposition rates were higher than in winter: 4.4 times in the presence of invertebrates, and 2.6 times in their absence. The exclusion of invertebrates (`protected' litter bags versus `unprotected' litter bags) led to significantly lower decomposition rates. In particular, the decomposition rate was strongly correlated with the number of gammarids, the dominant taxon in the litter bags, which are well known for their ability to feed on leaf litter. The abundance of gammarids was directly correlated to the level of dissolved oxygen and inversely correlated to the effective fetch in summer, when the spatial structure of the decomposition process was evident. Therefore, the results of this study indicate that there are seasonal and spatial differences in the rate of detritus decomposition, most likely due to changes in habitat characteristics that influence the distribution of gammarids, key-species responsible for the first steps of the leaf breakdown in Lake Geestmerambacht. The spatial dependency of the process leads to formation of heterogeneous ecological patches in which the probability of disturbance propagation may vary.     

Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shredders

1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions. 2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day⁻¹ and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046–0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 μg g⁻¹, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 μg g⁻¹ (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g⁻¹). 3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves. 4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L⁻¹), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source.     

Role of transported particulate organic matter in the macroinvertebrate colonization of litter bags in streams

1. The exposure of mesh litter bags has been widely used to investigate the role of benthic macroinvertebrates in leaf processing in freshwaters. In this sense, several studies have related litter bag breakdown rates to the presence of colonizing invertebrates. A possible confounding factor in such experiments is that the litter bags trap suspended particulate organic matter that can itself attract invertebrate colonists, irrespective of the intended experimental treatment.
2. We attempted to quantify the accumulation of particulate organic matter (POM) within litter bags and to investigate its possible impact on macroinvertebrate density and richness. In seven headwater forested streams we exposed mesh bags filled either with beech leaves ( Fagus sylvatica ) or with plastic strips of an equal surface area.
3. Principal component analysis (PCA) showed that bag type and stream were the main explanatory variables for invertebrate colonization and POM accumulation within the bags. In contrast, there was little variation among sampling dates (6.4% of the total inertia).
4. The accumulated POM within the bags was substantial (up to 8.83 g ash-free dry mass (AFDM)) but highly variable among sites (mean from 0.32 to 4.58 g AFDM). At each of the seven sites, both richness and abundance of invertebrates were positively correlated with the mass of accumulated POM in bags. Macroinvertebrate colonization (notably taxon richness) was directly linked with the quantity of POM accumulated.
5. Our findings provide evidence of a potential pitfall in linking invertebrates to litter processing in mesh bags, particularly when large amounts of POM, entrained in stream flow, accumulate within the bags. An evaluation of the POM mass trapped in litter bags could account for the erratic patterns sometimes observed in their colonization by invertebrates.     

Riparian plant species loss alters trophic dynamics in detritus-based stream ecosystems

Riparian vegetation is closely connected to stream food webs through input of leaf detritus as a primary energy supply, and therefore, any alteration of plant diversity may influence aquatic ecosystem functioning. We measured leaf litter breakdown rate and associated biological parameters in mesh bags in eight headwater streams bordered either with mixed deciduous forest or with beech forest. The variety of leaf litter types in mixed forest results in higher food quality for large-particle invertebrate detritivores (‘shredders’) than in beech forest, which is dominated by a single leaf species of low quality. Breakdown rate of low quality (oak) leaf litter in coarse mesh bags was lower in beech forest streams than in mixed forest streams, a consequence of lower shredder biomass. In contrast, high quality (alder) leaf litter broke down at similar rates in both stream categories as a result of similar shredder biomass in coarse mesh bags. Microbial breakdown rate of oak and alder leaves, determined in fine mesh bags, did not differ between the stream categories. We found however aquatic hyphomycete species richness on leaf litter to positively co-vary with riparian plant species richness. Fungal species richness may enhance leaf litter breakdown rate through positive effects on resource quality for shredders. A feeding experiment established a positive relationship between fungal species richness per se and leaf litter consumption rate by an amphipod shredder (Gammarus fossarum). Our results show therefore that plant species richness may indirectly govern ecosystem functioning through complex trophic interactions. Integrating microbial diversity and trophic dynamics would considerably improve the prediction of the consequences of species loss.     

Invasive litter, not an invasive insectivore, determines invertebrate communities in Hawaiian forests

In Hawaii, invasive plants have the ability to alter litter-based food chains because they often have litter traits that differ from native species. Additionally, abundant invasive predators, especially those representing new trophic levels, can reduce prey. The relative importance of these two processes on the litter invertebrate community in Hawaii is important, because they could affect the large number of endemic and endangered invertebrates. We determined the relative importance of litter resources, represented by leaf litter of two trees, an invasive nitrogen-fixer, Falcataria moluccana, and a native tree, Metrosideros polymorpha, and predation of an invasive terrestrial frog, Eleutherodactylus coqui, on leaf litter invertebrate abundance and composition. Principle component analysis revealed that F. moluccana litter creates an invertebrate community that greatly differs from that found in M. polymorpha litter. We found that F. moluccana increased the abundance of non-native fragmenters (Amphipoda and Isopoda) by 400% and non-native predaceous ants (Hymenoptera: Formicidae) by 200%. E. coqui had less effect on the litter invertebrate community; it reduced microbivores by 40% in F. moluccana and non-native ants by 30% across litter types. E. coqui stomach contents were similar in abundance and composition in both litter treatments, despite dramatic differences in the invertebrate community. Additionally, our results suggest that invertebrate community differences between litter types did not cascade to influence E. coqui growth or survivorship. In conclusion, it appears that an invasive nitrogen-fixing tree species has a greater influence on litter invertebrate community abundance and composition than the invasive predator, E. coqui.     

Mechanisms of dominance by the invasive hybrid cattail Typha?×?glauca

The mechanisms by which invasive plants displace native species are often not well elucidated, limiting knowledge of invasion dynamics and the scientific basis for management responses. Typha × glauca Godr. invades wetlands throughout much of North America. Like other problematic wetland invaders, Typha is large, grows densely, and leaves behind copious litter. It thus has the potential to impact wetlands both in life and after death. We assessed patterns in field settings and used simulated wetland-plant communities to experimentally test abiotic and community responses to live Typha, Typha litter, and water-level differences (confounded in the field) using a full-factorial design. In general, litter was a stronger driver of change than live Typha. The greatest impacts were seen where, as in nature, live and dead Typha co-occurred. Live-Typha treatments did not differ from controls in light or temperature conditions but did reduce community biomass and alter community composition. Litter strongly affected light, temperature and its variability, community and species-level plant biomass, and community composition. Interactions between live Typha and litter affected aspects of plant-community composition. Advantageously for Typha, interspecific litter effects were not mirrored by intraspecific suppression of live Typha. These findings clarify how Typha is such an effective invader. Similar mechanisms are likely involved in invasions by other plant species, particularly in wetlands. Managers should respond quickly to new Typha invasions and, when dealing with established stands, remove litter in addition to eradicating live plants.