Decomposition of Eucalyptus globulus leaves and three native leaf species (Alnus glutinosa, Castanea sativa and Quercus faginea) in a Portuguese low order stream

Leaf decomposition of the exotic evergreen Eucalyptus globulus (eucalyptus), and three native deciduous tree species, Alnus glutinosa (alder), Castanea sativa (chestnut) and Quercus faginea (oak), was compared in a second order stream in Central Portugal. Changes in dry weight, nitrogen and polyphenolic compounds and microbial colonization were periodically assessed for three months.Negative exponential curves fit the leaf weight loss with time for all leaf species. Mass loss rate was in the order alder (K = 0.0161) > chestnut (K = 0.0079) > eucalyptus (K = 0.0068) > oak (K = 0.0037). Microbial colonization followed the same pattern as breakdown rates. Evidence of fungal colonization was observed in alder after 3 days in the stream, whereas it took 21 days in oak leaves to have fungal colonization. Fungal diversity was leaf species-dependent and increased with time. In all cases, percent nitrogen per unit leaf weight increased, at least, at the initial stages of decay while soluble polyphenolics (expressed as percentage per unit leaf weight) decreased rapidly in the first month of leaves immersion.Intrinsic factors such as nitrogen and polyphenolic content may explain differences in leaf decomposition. The possible incorporation of eucalyptus litter into secondary production in a reasonable time span is suggested, although community balance and structure might be affected by differences in allochthonous patterns determined by eucalyptus monocultures.     

Leaf‐Litter Mixtures Affect Breakdown and Macroinvertebrate Colonization Rates in a Stream Ecosystem

Previous work in terrestrial and aquatic ecosystems has suggested that the relationship between breakdown rates of leaf litter and plant species richness may change unpredictability due to non‐additive effects mediated by the presence of key‐species. By using single‐ and mixed‐species leaf bags (7 possible combinations of three litter species differing in toughness; common alder [Alnus glutinosa ], sweet chestnut [Castanea sativa ], and Spanish oak [Quercus ilex ilex ]), I tested whether leaf species diversity, measured as richness and composition, affects breakdown dynamics and macroinvertebrate colonization (abundance, richness and composition) during 90 days incubation in a stream. Decomposition rates were additive, i.e., observed decomposition rates were not different from expected ones. However, decomposition rates of individual leaf species were affected by the mixture, i.e., there were species‐specific responses to mixing litter. The invertebrate communities colonizing the mixtures were not richer and more diverse in mixtures than in single‐species leaf bags. On the opposite, mixing leaf species had a negative, non‐additive effect on rates of shredder and taxa colonization and on macroinvertebrate diversity. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Leaf Litter Decomposition of Three Riparian Tree Species and Associated Macroinvertebrates of Eswathu Oya,a Low Order Tropical Stream in Sri Lanka

Leaf decomposition, an important component of the organic matter dynamics in streams, has been widely examined in temperate regions but much less documented in tropical regions. We report here the first study of leaf decomposition in a Sri Lankan stream. The litterbag technique was used. Coarse (8 mm) and fine (100 µm) litterbags, that included or excluded macroinvertebrates respectively, were used to enclose leaves of three dominant riparian tree species: native Ochlandra stridula (bamboo), and the introduced Alstonia macrophylla and Hevea brasiliensis (rubber). A fourth set of litterbags contained a mixture of these three species. Leaf colonization by macroinvertebrates was highest in the early stages of the decomposition process on Hevea leaves but invertebrate densities declined later. The opposite colonization effect was observed on the native Ochlandra leaves: slow colonization with continuing low densities from the beginning to the end of the process. Decomposition of all three species was significantly faster in the coarse than in the fine mesh bags. Alstonia, which has the softest leaf tissue, was most rapidly decomposed while Ochlandra, with its tough structure, was the slowest. Among the invertebrates, insects were the most important leaf colonizing animals, with Diptera, Coleoptera and Trichoptera the most dominant. The invertebrate variety in the mixed bags was higher than in the single‐species leaf bags, where Chironomidae dominated the colonizing assemblages. This study has shown that toughness, indicated by the ‘specific weight of leaf tissue’, and the quality of the leaves was more important in determining breakdown rates than their origin. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Colonization of decomposing deciduous leaf litter by Testacea (Protozoa,Rhizopoda): Species succession,abundance, and biomass

Summary The colonization of leaf litter by testate amoebae in a cool temperate deciduous forest was studied over the first 60 months of decomposition. No colonization of fresh leaf litter by Testacea was recorded before the first spring thaw period. Colonization of aspen and balsam leaves was similar in terms of species and numbers of species, with the balsam litter being colonized by slightly fewer species. In the aspen litter bags, all the L-layer species were present after 18 months, and all the species recorded in all soil layers were found after 60 months. The proportion of species which constructed their tests from platelets rather than sediment was 70% of the total number of species for the first 36 months of colonization of both litter types. After 60 months, seven species comprised 70% of the total numbers of Testacea but only 33–38% of the total biomass. Significant, positive correlation existed between the dry weight loss of leaf litter and the total number of active Testacea, the total number of living Testacea, and the total number of species present. The prime limitations to testacean colonization of decomposing leaf litter appeared to be substrate quality, food supply and/or availability of test-building materials.     

Evaluation of macrofaunal effects on leaf litter breakdown rates in aquatic and terrestrial habitats

Abstract Decomposition of the organic matter is a key process in the functioning of aquatic and terrestrial ecosystems, although different factors influence processing rates between and within these habitats. Most patterns were described for temperate regions, with fewer studies in tropical, warmer sites. In this study, we carried out a factorial experiment to compare processing rates of mixed species of leaf litter between terrestrial and aquatic habitats at a tropical site, using ?ne and coarse mesh cages to allow or prevent colonization by macroinvertebrates. The experiment was followed for 10 weeks, and loss of leaf litter mass through time was evaluated using exponential models. We found no interaction between habitat and mesh size and leaf litter breakdown rates did not differ between ?ne and coarse mesh cages, suggesting that macroinvertebrates do not influence leaf litter decomposition in either habitat at our studied site. Leaf breakdown rates were faster in aquatic than in terrestrial habitats and the magnitude of these differences were comparable to studies in temperate regions, suggesting that equivalent factors can influence between‐habitat differences detected in our study.     

Oribatid mite (Acari: Oribatida) contribution to decomposition dynamic of leaf litter in primary forest, second growth, and polyculture in the Central Amazon.

We studied the contribution of oribatid mites in the dynamics of litter decomposition in an experiment using litterbags of three different mesh sizes (20 microns, 250 microns, and 1 cm). The experiment was carried out at a primary forest (FLO), a secondary forest (SEC), and at two polyculture systems (POA and POC). We compared the weight loss of the leaves of Vismia guianensis and the changes of the oribatid mite species community. We processed the samples after 26, 58, 111, 174, 278, and 350 days from the beginning of the experiment by using the Berlese-Tullgren to extract the animals. We hypothesized that: 1. the abundance and diversity of oribatid mites would exert an influence in the decomposition process; 2. there would be a successional changing of the species during decomposition; and 3. there would be differences in the colonization of species in relation to the mesh size of the litterbags. A total of 95 species of oribatid mites was found. The biomass data was the first registered for the Amazon region. The great dominance of oribatid mites did not exert an influence in the decomposition process. There was not a successional changing of the species during the course of the decomposition process, unlike those shown by results obtained in the temperate forest, because we found neither early colonizers nor species that prefer advanced decomposition stages. The oribatid mite community, which developed in the litterbags under tropical conditions, was atypical of the normal stages of leaf litter breakdown and decomposition. There were differences in the colonization of species in relation to the mesh size of the litterbags. These differences were very closely related to the specific habits and habitat of the dominant species.     

Do secondary compounds inhibit microbial- and insect-mediated leaf breakdown in a tropical rainforest stream, Costa Rica?

We examined the hypothesis that high concentrations of secondary compounds in leaf litter of some tropical riparian tree species decrease leaf breakdown by inhibiting microbial and insect colonization. We measured leaf breakdown rates, chemical changes, bacterial, fungal, and insect biomass on litterbags of eight species of common riparian trees incubated in a lowland stream in Costa Rica. The eight species spanned a wide range of litter quality due to varying concentrations of nutrients, structural and secondary compounds. Leaf breakdown rates were fast, ranging from 0.198 d⁻¹ (Trema integerrima) to 0.011 d⁻¹ (Zygia longifolia). Processing of individual chemical constituents was also rapid: cellulose was processed threefold faster and hemicellulose was processed fourfold faster compared to similar studies in temperate streams. Leaf toughness (r = −0.86, P = 0.01) and cellulose (r = −0.78, P = 0.02) were the physicochemical parameters most strongly correlated with breakdown rate. Contrary to our initial hypothesis, secondary compounds were rapidly leached (threefold faster than in temperate studies), with all species losing all secondary compounds within the first week of incubation. Cellulose was more important than secondary compounds in inhibiting breakdown. Levels of fungal and bacterial biomass were strongly correlated with breakdown rate (fungi r = 0.64, P = 0.05; bacteria r = 0.93, P < 0.001) and changes in structural compounds (lignin r = −0.55, P = 0.01). Collector−gatherers were the dominant functional group of insects colonizing litterbags, in contrast to temperate studies where insect shredders dominate. Insect biomass was negatively correlated with breakdown rate (r = −0.70, P = 0.02), suggesting that insects did not play an important role in breakdown. Despite a wide range of initial concentrations of secondary compounds among the eight species used, we found that secondary compounds were rapidly leached and were less important than structural compounds in determining breakdown rates. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impact of plant architecture versus leaf quality on attack by leaf-tying caterpillars on five oak species

Because shelter-building herbivorous insect species often consider structural features of their host plants in selecting construction sites, their probability of attack is likely to be a function of some combination of plant architectural traits and leaf quality factors. We tested the hypothesis that plant architecture, in the form of the number of touching leaves, influences interspecific variation in attack by leaf-tying caterpillars in five species of sympatric Missouri oaks (Quercus). We compared colonization on control branches, in which both architecture and leaf quality were potentially important, with colonization on experimental branches for which we controlled for the effects of architecture by creating equal numbers of artificial ties. Colonization of artificial ties was highly correlated with natural colonization on neighboring control branches, suggesting that leaf quality factors and not architecture influenced interspecific variation in attack by leaf-tying caterpillars. Of the leaf quality factors measured (water, protein-binding capacity, nitrogen, specific leaf area, pubescence, and toughness), nitrogen was the most explanatory. With the exception of white oak, natural leaf tie colonization was positively correlated with nitrogen availability (ratio of nitrogen to protein-binding capacity), and negatively correlated with protein-binding capacity of leaf extracts. Both host plant species and subgenus oak influenced the community composition of leaf-tying caterpillars and the non-tying symbionts colonizing the ties. Host plant differences in leaf nitrogen content were positively correlated with pupal weight of one of two caterpillar species reared on all five host plant species. Thus, interspecific differences in nitrogen, nitrogen availability, and protein-binding capacity of leaf extracts are the best predictors at this time of interspecific differences in attack by leaf-tying caterpillars, in turn affecting their success on individual host plants in the laboratory.     

Shredder colonization and decomposition of green and senescent leaves during summer in a headwater stream in northern Japan

We conducted a decomposition experiment using green and senescent maple and alder leaves in a coastal headwater stream in Hokkaido, northern Japan, during June and July 2000. We estimated whether shredder colonization on the leaves and leaf breakdown differed between green and senescent leaves during the experimental period. Late-instar Lepidostoma complicatum (Trichoptera) and Sternomoera rhyaca (Amphipoda) were the predominant shredder taxa among the macroinvertebrates that colonized litterbags. There was no significant difference in shredder colonization between green and senescent leaves although we found a significant difference between maple and alder leaves. The colonization patterns of large individuals of L. complicatum and S. rhyaca differed from those of small individuals. All decomposition coefficients of green and senescent leaves were high. During the experiment, decomposition was significantly faster in maple than in alder leaves, although no significant difference was found between green and senescent leaves. However, the fragmented nitrogen portion was higher in green leaves than in senescent leaves during the experiment. Higher nitrogen release (2–2.5 times more) as particulate organic matter in green than in senescent leaves indicates that green leaves may be a potentially valuable food resource for other macroinvertebrate collector–gatherer species.     

Leaf breakdown in an Atlantic Rain Forest stream

The hypothesis of this study was that colonizers in decaying leaf litter prefer native species (Erythrina verna) to exotic ones (Eucalyptus camaldulensis and Protium heptaphyllum). Therefore, native species are expected to show higher breakdown rates, increased biomass, richness and density of invertebrate species, and increased biomass of decomposer fungi. Breakdown of leaf litter from these three species was assessed in an Atlantic Rain Forest stream. Four samples were collected during a period of 90 days and washed on a sieve to separate the invertebrates. Then, a series of leaf disks were cut to determine ash‐free dry mass and fungal biomass, and the remaining material was oven‐dried to determine the dry weight. Eucalyptus camaldulensis and E. verna showed higher breakdown rates than P. heptaphyllum, due to differences in leaf physical and chemical characteristics. The harder detritus (P. heptaphyllum) broke down more slowly than detritus with high concentrations of labile compounds (E. camaldulensis). The density of the invertebrates associated with detritus increased with time. There were no differences in density, taxonomic richness or biomass of invertebrates among the leaf types, which indicated that the invertebrates did not distinguish between exotic and native detritus. Fungal colonization varied among samples; E. camaldulensis showed the lowest ergosterol concentrations, mainly due to a high concentration of total phenolics. The detritus with the highest hardness value was colonized most slowly by fungi. These results showed that leaf breakdown in Atlantic Rain Forest streams could be affected either by changes in riparian vegetation, or by becoming more savanna‐like process due to climate change.     

A Study of the Decomposition of Reed (Phragmites australis ) as a Possible Source of Aquatic Humic Substances by Measuring the Natural Abundance of Stable Carbon Isotopes

The decomposition of leaf and steam litter of reed (P. australis) was measured both in the field and in the laboratory. The breakdown rates, the total carbon and the stable carbon isotope dynamics of reed litter were determined. The stable carbon isotope ratios of isolated humic substances (fulvic and humic acids) were also analysed. The δ¹³C value in reed remains increased from –26‰ to –24‰ for stems and from –27‰ to –26‰ for leaves. The dissolved fulvic and humic acids isolated from the experimental bottles (mean δ¹³C was –27.6‰) and the reservoir water were depleted in ¹³C (mean δ¹³C was –28.6‰) relative to the reed remains. The results show that reed litter is an important source of coloured aquatic humic substances. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Habitat Use of Juvenile Fish in the Lower Danube and the Danube Delta: Implications for Ecotone Connectivity

Functional processes in freshwater ecosystems are highly influenced by acidic conditions. Foodwebs are affected and macroinvertebrate species diversity is decreased. This study aims to investigate leaf decomposition at very low pH in the acidic Banyupahit–Banyuputih river originating from the acidic crater lake Kawah Ijen in Indonesia. Leaf decomposition experiments were carried out for 200 days in the acidic river at pHs of approximately 0.7, 2.3 and 3.0 and in the neutral Kali Sengon river, using leaves from teak, Tectona grandis, and bamboo, Bambusa sp. Two different types of leaf packs were used: fine mesh size packs were used to exclude macroinvertebrates and coarse mesh size packs allowed macroinvertebrate colonization. Clear differences in decomposition rate were observed between the neutral Kali Sengon and the acidic Banyupahit–Banyuputih river with decomposition in the Kali Sengon river proceeding significantly faster for both leaf types. In the Kali Sengon k values (d⁻¹) over 46 days were 0.0202 for fine teak, 0.0236 for coarse teak, 0.0114 for fine bamboo and 0.0151 for coarse bamboo. No significant differences were observed between the three sites in the acidic Banyupahit–Banyuputih river with k values of 0.0034–0.0066 for fine teak, 0.0002–0.0057 for coarse teak, 0.0029–0.0054 for fine bamboo and 0.0000–0.0068 for coarse bamboo. Moreover, no clear adaptation of macroinvertebrates or microbes to low pH conditions could be detected. The coarse mesh leaf packs in the neutral Kali Sengon river revealed that macroinvertebrates are important in the breakdown process. Fine mesh packs revealed that microbial activity is depressed under acidic conditions. Based on this evidence, we conclude that the toxicity at low pH conditions, and probably also the precipitation of metals on the leaf material, seriously affects leaf decomposition.     

Effect of legume understorey on decomposition and nutrient content of eucalypt forest litter

Summary In Jarrah (Eucalyptus marginata Donn ex Sm.) forest of south-western Australia dense germination and regeneration of the native legumeAcacia Pulchella R. Br. can occur following moderate to high intensity fire. The effect of this legume understorey on rate of decomposition and change in nutrient content ofE. marginata litter was investigated using the mesh bag techniques and by examining four components of forest floor litter representing increasing stages of decomposition. E. marginata leaf litter confined in mesh bags lost 37% of its initial dry weight in the first 8 months on the forest floor and 44% of its initial dry weight after 20 months. During this period weight loss was similar for leaf litter located in forest without legume understorey and for leaf litter placed under dense stands ofA. pulchella. MixingA. pulchella litter withE. marginata litter had no significant effect on rate ofE. marginata litter breakdown. The presence of understorey vegetation had a marked effect on chemical composition of decomposingE. marginata leaves. After 8 and 20 months exposure on the forest floor, leaf litter in mesh bags placed underA. pulchella understorey had significantly (P<0.001) higher concentration and contained significantly (P<0.001) greater amounts of N, P, K, S, Ca and Mg than leaf litter placed in areas without legume understorey. This effect was particularly marked for N and P. In forest without legume understorey the amounts of these two nutrients inE. marginata leaf litter changed little during the first 20 months of decomposition, but forE. marginata leaf litter in mesh bags underA. pulchella there were absolute gains of up to 68% in the amount of N and 109% in the amount of P during this period. This represents accumulation of N and P from sources outside the litter bags. The concentration of N, P, S, Ca and Mg were higher at each of the four stages of decomposition in eucalypt leaf litter collected from the forest floor beneathA. pulchella compared to eucalypt leaf litter collected in forest without understorey. Concentrations of N, P and S increased with stage of decomposition. Levels of these three nutrients in eucalypt litter from under the legume were 1.5 to 2.9 fold higher than in the same component of litter from forest without understorey. The effect of legume understorey on nutrient concentrations in the forest floor and on Cielement ratios in decomposing litter is discussed in relation to long term rates of litter breakdown and net mineralisation of litter nutrients.     

针阔凋落叶混合分解过程中可溶性有机碳释放的动态特征

为了调整低效马尾松(Pinus massoniana, P)人工纯林的林分结构,探明其与乡土阔叶树种凋落叶混合分解过程中的可溶性有机碳(DOC)释放规律,该研究以马尾松、香樟(Cinnamomum camphora, C)和香椿(Toona sinensis, T)的凋落叶为研究对象,将其按照不同树种和质量比例组合为15个处理(3个单一树种处理 + 12个混合处理)后进行野外凋落叶分解实验,并探讨DOC释放最佳的凋落叶树种组合以及混合比例。结果表明:(1)马尾松和大部分混合处理凋落叶(除了PT64)在分解初期(0～6个月)的DOC含量均显著升高,出现富集现象,之后随着分解时间的延长而降低,在分解中后期(12～18个月)或分解末期(18～24个月)再次出现小幅度的碳富集现象。阔叶所占比例越高,其后期DOC含量越低。(2)分解前期(0～6个月)凋落叶DOC释放的拮抗效应较强(58.33%),仅有8.33%(1/12)的混合处理表现出协同效应。之后(6～18个月)其协同效应逐渐增强(91.67%),分解末期(18～24个月)凋落叶的协同效应有所减弱(66.67%)。在所有混合处理中,PT64在整个分解期间均出现协同效应,其次为PT73、PCT622和PCT613在大部分分解时期(3/4)出现协同效应。(3)偏最小二乘法(PLS)回归分析表明,凋落叶初始质量因子中N含量、P含量、木质素含量、缩合单宁含量、C/N、C/P、木质素/N以及木质素/P是影响该研究区域中凋落物DOC释放的重要因素。总体而言,马尾松与阔叶凋落叶混合后的DOC释放受到树种、混合比例及分解时间的共同影响。相对于其他混合处理,阔叶占比大于等于30.00%且含有香椿(T)的凋落叶混合处理(PT64、PT73、PCT622和PCT613)更能促进DOC的释放。     

Suitability of Eucalyptus and Corymbia for Mnesampela privata (Guenée) (Lepidoptera: Geometridae) larvae

Abstract 1 Mnesampela privata (Guenée) has a host list of 40 Eucalyptus and at least one Corymbia species. Larval survival and performance was studied on 19 species to investigate how certain leaf traits influence the suitability of different species. 2 After 7 days, survival on Eucalyptus aggregata and Eucalyptus camphora is greater than 70% even though the toughness of leaves is 0.15–0.19 mg/mm². However, after the same time, survival on genotypes of Eucalyptus melliodora and Eucalyptus sideroxylon was less than 60%, or even 0%, even though the toughness of some leaves was as low as 0.11 mg/mm². An unmeasured allelochemical, rather than toughness, may reduce survival on these species. 3 Dry weights of first‐instar larvae were negatively correlated with leaf toughness for 13 of the species studied. Species that produced the heaviest first‐instar larvae were not the same hosts that produced the heaviest second‐instar larvae. 4 Dry weights of female pupae were negatively correlated with total oil content for five of the species studied. 5 Larvae exhibit age‐related changes in feeding behaviour. Neonates skeletonize leaves (avoid leaf veins and oil glands) and post‐third‐instar larvae ingest whole leaf fragments (consume small leaf veins and oil glands). These findings suggest that neonates are sensitive to high leaf toughness and non‐oil plant secondary metabolites whereas older larvae are less sensitive to high leaf toughness and are likely to become larger adults on hosts with lower oil contents.     

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.     

Over-winter decomposition and associated macroinvertebrate communities of three deciduous leaf species in forest streams on the Canadian Boreal Shield

The decomposition of deciduous leaf material provides a critical source of energy to aquatic food webs. Changes to riparian forests through harvesting practices may alter the species composition of deciduous leaf material entering streams. We compared over-winter decomposition of three different riparian leaf species (speckled alder (Alnus incana ssp. rugosa (Du Roi) J. Clausen), white birch (Betula papyrifera Marsh.), and trembling aspen (Populus tremuloides Michx.)) to determine their importance as a food resource for macroinvertebrate communities within Boreal Shield streams in northeastern Ontario, Canada. Leaf pack decomposition of the three leaf species formed a processing continuum throughout winter, where alder and birch leaf packs decomposed at a medium rate (k = 0.0065/day and 0.0053/day, respectively) and aspen leaf packs decomposed more slowly (k = 0.0035/day). Macroinvertebrate community colonization on leaf packs changed through time regardless of leaf species. Alder leaf packs supported higher abundances of macroinvertebrates in the fall while aspen leaf packs supported greater shredder abundances in the following spring. The study shows that leaf diversity may be important for providing a sustained food resource for aquatic macroinvertebrates throughout the relatively long over-winter period in Canadian Boreal Shield streams. Riparian forest management strategies should ensure that deciduous plant species richness is sustained in riparian areas.     

The role of leaf defensive traits in oaks on the preference and performance of a polyphagous herbivore,Orgyia vetusta

1. Leaves possess traits that mediate the preference and performance of herbivores. Most evidence for the importance of leaf traits as defences against herbivory comes from studies of few model plant species. 2. In a phylogenetically explicit comparison, I explain the differences in preference and performance of tussock moth (Orgyia vetusta Boisduval) larvae on leaves of 27 oak (Quercus) species using nine putative leaf defences. 3. The preference for an oak species correlated positively with the survival of caterpillars. The correlation between preference and performance did not differ between oak species native to the range of tussock moth versus those from outside the herbivore's range. 4. The first principal component of leaf traits predicted survival of caterpillars on oak leaves but only marginally predicted their preference between oak species. A multiple regression model showed that evergreenness, toughness, and condensed tannin content were the best predictors of caterpillar survival, and leaf toughness was the best predictor of host preference. 5. Generalist caterpillars may accurately assess the value of novel food sources. Moreover, many leaf traits that have been found to affect herbivory within a plant species can also be used to predict the fitness of a generalist herbivore between species.     

Litter quality, stream characteristics and litter diversity influence decomposition rates and macroinvertebrates

1. We examined the relative importance of litter quality and stream characteristics in determining decomposition rate and the macroinvertebrate assemblage living on autumn‐shed leaves. 2. We compared the decomposition rates of five native riparian tree species (Populus fremontii, Alnus oblongifolia, Platanus wrightii, Fraxinus velutina and Quercus gambelii) across three south‐western streams in the Verde River catchment (Arizona, U.S.A.). We also compared the decomposition of three‐ and five‐species mixtures to that of single species to test whether plant species diversity affects rate. 3. Decomposition rate was affected by both litter quality and stream. However, litter quality accounted for most of the variation in decomposition rates. The relative importance of litter quality decreased through time, explaining 97% of the variation in the first week but only 45% by week 8. We also found that leaf mixtures decomposed more quickly than expected, when all the species included were highly labile or when the stream environment led to relatively fast decomposition. 4. In contrast to decomposition rate, differences in the invertebrate assemblage were more pronounced across streams than across leaf litter species within a stream. We also found significant differences between the invertebrate assemblage colonising leaf mixtures compared with that colonising pure species litter, indicating non‐additive properties of litter diversity on stream invertebrates. 5. This study shows that leaf litter diversity has the capacity to affect in‐stream decomposition rates and stream invertebrates, but that these effects depend on both litter quality and stream characteristics.     

Canopy cover and leaf age affect colonization by tropical fungal endophytes: Ecological pattern and process in Theobroma cacao (Malvaceae)

Fungal endophytes inhabit healthy tissues of all terrestrial plant taxa studied to date and are diverse and abundant in leaves of tropical woody angiosperms. Studies have demonstrated that plant location and leaf age influence density of endophyte infection in leaves of tropical forest trees. However, ecological factors underlying these observations have not been explored in detail. Here, we establish that foliar endophytes of a tropical tree (Theobroma cacao, Malvaceae) are transmitted horizontally and that endophyte-free seedlings can be produced for experimental manipulation by protecting aerial tissues from surface wetting. At Barro Colorado Island, Panama, we used transects of endophyte-free seedlings to determine the importance of several factors (canopy cover, abundance of aerial and epiphytic propagules, leaf age, leaf chemistry, leaf toughness and duration of exposure to viable air spora) in shaping colonization by endophytic fungi. Endophytes colonized leaves of T. cacao more rapidly beneath the forest canopy than in cleared sites, reflecting local abundance of aerial and epiphytic propagules. The duration of exposure, rather than absolute leaf age, influenced endophyte infection, whereas leaf toughness and chemistry had no observed effect. Endophytes isolated from mature T. cacao grew more rapidly on media containing leaf extracts of T. cacao than on media containing extracts from other co-occurring tree species, suggesting that interspecific differences in leaf chemistry influence endophyte assemblages. Together, these data allow us to identify factors underlying patterns of endophyte colonization within healthy leaves of this tropical tree.