Community structure of canopy arthropods associated to Quercus crassifolia×Quercus crassipes complex

Quercus crassifolia and Q. crassipes are dominant species in temperate forests of central Mexico and hybridize between each other when they occur in sympatry. Oak canopies contain a considerable portion of arthropod diversity and the hybrid zones can provide new habitats to epiphyte fauna. We tested if the establishment of hybrids in contact zones with their parental hosts increases the species diversity of canopy arthropods assuming that hybrid trees constitute new genotypes of potential new habitats to small organisms. We examined the effect of hybridization on some community structure parameters (diversity, composition, similarity and density of arthropod fauna) of canopy arthropods compared to their parental species in a hybrid zone located in central Mexico. We employed 17 leaf morphological traits and six diagnostic RAPD primers to identify parental and hybrid plants. The RAPDs marker showed unidirectional introgression towards Q. crassifolia, and were detected hybrid (F₁), backcrosses and introgression individual trees. In total, 30 oak canopies were fogged during rainy and dry season. We recognized 532 taxa of arthropods belonging to 22 orders associated with tree canopies. The taxonomic status of host‐trees may be an important factor in the arthropod community structure and that seasonality (dry and rainy) is not a factor that could modify their organization. Trees of Q. crassipes registered the highest densities of arthropod fauna followed by hybrid hosts (F₁); trees originated by backcrosses towards Q. crassifolia registered a significant less arthropod density than F₁ hybrids; and trees of Q. crassifolia had the lowest density. Hybrid plants and Q. crassipes individuals had higher diversity (H′) of arthropods than Q. crassifolia plants. Hybrid plants had also more rare species in both seasons in comparison with parental species. This study suggests that hybrid oaks act as a center of biodiversity by accumulating arthropods of both parental and different species including a considerable number of rare species.     

Differential effects of host plant hybridization on herbivore community structure and grazing pressure on forest canopies

Interspecific hybridization in plants is known to have ecological effects on associated organisms. We examined the differences in insect herbivore community structure and grazing pressure on tree canopy leaves among natural hybrids and their parental oak species. We measured leaf traits, herbivore community structure, and grazing pressure on leaves of two oak species, Quercus crispula and Q. dentata, and their hybrids. The concentration of nitrogen in canopy leaves was greater in hybrids and in Q. dentata than in Q. crispula. The concentration of total phenolics was lower in hybrids than in Q. crispula. The concentration of condensed tannin was greater in hybrids than in Q. crispula. Relative herbivore abundance and species richness were greater on oak hybrids than on either parental species; herbivore species diversity and composition on hybrids were close to those on Q. crispula. Herbivore grazing pressure was lower on hybrids and Q. dentata than on Q. crispula. There was a negative correlation between herbivore grazing pressure and leaf nitrogen, suggesting that interspecific variation among oak taxa in herbivore pressure may be explained by leaf nitrogen; variation in herbivore community structure among oak taxa is likely to be controlled by polygenic leaf traits. Differing responses of (1) herbivore community structure and (2) herbivore grazing pressure to host plant hybridization may play important roles in regulating herbivore biodiversity in cool‐temperate forest canopies.     

The effects of seed size, cotyledon reserves, and herbivory on seedling survival and growth in Quercus rugosa and Q. laurina (Fagaceae)

In a greenhouse experiment, seedling survival of two oak species (Quercus rugosa and Q. laurina) was greatly affected by the excision of cotyledons 1 mo after germination, with a greater impact on Q. laurina. The effect of seed size was also significant for both species, with a positive correlation between seed mass and survival and growth. The effect of cotyledon excision on seedling growth persisted throughout the first growing season in Q. rugosa and was not analyzed for Q. laurina due to the low number of seedlings that survived cotyledon excision. Seed size significantly affected seedling height, diameter, leaf area, and biomass at 6 mo. Seed size and cotyledon retention affected the ability of Q. rugosa to recover from herbivory, as both factors had a significant effect on relative growth rates after aerial biomass removal. The results show that seedlings originating from large seeds can better endure loss of cotyledons and aerial biomass and thus are better equipped to confront stress early in their lives.     

Insect diversity: facts,fiction and speculation*

Biologists are still trying to grasp the global dimensions of the phylum Arthropoda and its major class the Insecta, in spite of the fact that over a million species of arthropods have been described. The canopy of rain forest trees is believed by many to hold the key to the immense diversity of insects. In recent years the use of knock-down insecticides to sample insects from rain forest canopy has revealed information on the canopy's arthropod inhabitants and community structure. The sampling techniques involved are outlined and data reviewed on taxonomic and guild structure, species abundance, body size and biomass of insects, and the faunal similarity of trees. Calculations by Erwin (1982), based on knock-down insecticide studies of the beetle fauna of one species of Central American tree, suggest there may be 30 million species of tropical forest arthropods. Reanalysis of these calculations, using additional data, produces a range of possible estimates from about 10 to 80 million. The unknown range of plant host-specificities of tropical insects is the main weakness of this method of calculation. Assessment of the faunal importance of the canopy in relation to that of other rain forest biotopes requires comparative quantitative studies. The preliminary results of one such simple study suggest that over 42 million arthropods may be found in a hectare of Seram rain forest (at the time of study), and that 70% occur in the soil and leaf litter and 14% in the canopy. They also suggest that Collembola and Acarina are the dominant groups in this hectare, and that there are as many ants as all the other insects (excluding Collembola).     

Hybridization increases canopy arthropod diversity in the <Emphasis Type="Italic">Quercus affinis</Emphasis> × <Emphasis Type="Italic">Quercus laurina</Emphasis> complex

Understanding the factors that influence the diversity and composition of arthropod communities is a major topic in ecology. Canopy arthropod communities are a major constituent of biodiversity and show great variation in time and space according to different factors. Recently, genetic variation within tree species has attracted attention as a significant factor determining the diversity and composition of canopy arthropod communities. A major source of genetic and phenotypic novelty in plant species is interspecific hybridization, and therefore it is of interest to evaluate how this process affects the communities of associated organisms. In this study, we used microsatellite markers and geometric morphometry of leaf shape to analyze genetic and morphological variation in 45 individuals in a local hybrid zone between the oaks Quercus affinis and Q. laurina in Mexico. Individual trees were assigned to one of the parental species or to the hybrid category. The percentage of leaf area removed by herbivores was quantified in each individual and the canopies of five individuals of each categeory (two parental species and hybrids) was fogged with insecticide to assess the diversity and composition of arthropod communities. Results indicated that hybrid trees experience higher levels of herbivory than parental species and also sustain a higher abundance and richness of canopy arthropods. In general, our study supports the “hybrid susceptibility hypothesis” that predicts a higher incidence of associated arthropods on hybrid plants than in their parental species as result of the disruption of co-adapted gene complexes associated to resistance traits.     

Reactions of the fauna on the bark of trees to the frequency of fires in a North American savanna

Summary The arthropod communities living on the bark of the oak species Quercus macrocarpa and Q. ellipsoidalis were investigated in a North American oak savanna. Differences were found in the community structure of the arthropods living on the bark of these two tree species, although they have the same fissured bark type. In the North American oak savanna ecosystem the most important disturbance factor is fire, which maintains species richness. Highest numbers of species and specimens were found at moderately disturbed sites. Three main ecological groups of arthropods living on the bark of trees can be distinguished in relation to the degree of disturbance: (1) Inhabitants of bark of trees restricted to undisturbed sites: they do not occur in fire-disturbed areas; (2) Inhabitants of bark of trees adapted to a moderate degree of disturbance: many species occur in high numbers only in moderately disturbed areas; and (3) Specialist inhabitants of bark of trees in heavily disturbed areas. The number of specimens of these species increases per trunk with the frequency of disturbance.     

A survey method for assessing the richness of epiphytic lichens using growth forms

The species richness of epiphytic lichens is continuously decreasing by degradation and loss of habitat. Considering that taxonomic identification of all species is time and resource consuming, rapid assessment methods to extrapolate the total number of species are needed for practical conservation. This paper describes an alternative method using the correlation between lichens growth forms and species richness. The study was conducted in 406 forest stands located in Central Spain, covering a wide range of mediterranean-climate ecosystem regions, management intensity levels, canopy cover conditions, and tree sizes. The presence/absence of epiphytic lichens was determined in 6090 trees, which were dominated by oak species (Quercus ilex, Q. faginea, and Q. pyrenaica). In all type of forests, the diversity of growth forms was positively correlated with the total epiphytic lichen richness. In all cases, species richness increased in non-managed forest stands with dense canopies. Thus, we propose the use of lichen growth forms as a helpful surrogate of species richness to detect potentially conservation priority areas in the Mediterranean region.     

LiDAR‐derived canopy structure supports the more‐individuals hypothesis for arthropod diversity in temperate forests

Despite considerable progress in the ability to measure the complex 3‐D structure of forests with the improvement of remote‐sensing techniques, our mechanistic understanding of how biodiversity is linked to canopy structure is still limited. Here we tested whether the increase in arthropod abundance and richness in beech forest canopies with increasing canopy complexity supports the more‐individuals hypothesis or the habitat‐heterogeneity hypothesis. We used fogging to collect arthropod samples from 80 standardized plots from canopies of single‐ to multi‐layered mature montane European beech stands. Tree height and an independent measure of vertical heterogeneity – the vertical distribution ratio – on each arthropod sampling plot were derived from high‐resolution full‐waveform airborne laser scanning data. Mixed‐model path analysis based on almost 20 000 specimens of 762 species from 11 orders provided support for the more‐individuals hypothesis, with higher arthropod abundance but not higher species richness in stands with a more equal vertical distribution of plant biomass. By contrast, we found no support for the habitat‐heterogeneity hypothesis. The increase in the number of individuals with increasing vertical distribution of biomass might be caused either by increasing leaf area, as indicated by higher space filling and productivity in multi‐layered stands, or by higher persistence of arthropod populations owing to better shelter, reduced competition and more refuges under harsh conditions, or by both. High‐resolution airborne laser scanning, with its ability to penetrate dense canopies under leaf‐on conditions, has proved suitable for measuring vertical structures as a predictor for canopy diversity. Expanding combinations of remote‐sensing and canopy‐biodiversity data opens many avenues for improving our understanding of the link between diversity and forest structures.     

Assessment of the biocontrol effects of three aromatic plants on multiple trophic levels of the arthropod community in an agroforestry ecosystem

1. Studies have shown that plant diversity plays a major role in influencing arthropod community composition. However, the effects of increasing plant species diversity on arthropod abundance at multiple trophic levels in the presence of aromatic plants have not been well documented. 2. To explore the potential of using aromatic plants to biocontrol arthropods at multiple trophic levels, three aromatic plant species – French marigold (Tagetes patula L.), Ageratum (Ageratum houstonianum Mill.) and Catnip (Nepeta cataria L.) – were introduced into an apple orchard to increase ground plant species composition. 3. The aromatic plants influenced the structure of arthropod communities at multiple trophic levels, particularly the herbivores in the tree canopy and predators in ground covers. Aromatic plants negatively influenced total arthropod community abundance. Compared with the control treatment, the total arthropod community abundance in the treated areas declined 24.99–33.84% and 14.35–24.65% in the tree canopy and ground covers, respectively. 4. Aromatic plants negatively influenced herbivore abundance, both overall and relative to the total community. By contrast, aromatic plants positively influenced predator abundance, both overall and relative to the total community, in the treatments containing both ageratum and catnip. However, aromatic plants had no effect on species richness at each trophic level or on parasitoid abundance. 5. These results suggest that increasing ground plant species diversity by introducing aromatic plants into apple orchards may considerably affect arthropod community composition, and that aromatic plants are potentially effective for the biocontrol of herbivore pests in agroforestry ecosystems.     

Long‐term nutrient addition alters arthropod community composition but does not increase total biomass or abundance

A simple bottom–up hypothesis predicts that plant responses to nutrient addition should determine the response of consumers: more productive and less diverse plant communities, the usual result of long‐term nutrient addition, should support greater consumer abundances and biomass and less consumer diversity. We tested this hypothesis for the response of an aboveground arthropod community to an uncommonly long‐term (24‐year) nutrient addition experiment in moist acidic tundra in arctic Alaska. This experiment altered plant community composition, decreased plant diversity and increased plant production and biomass as a deciduous shrub, Betula nana, became dominant. Consistent with strong effects on the plant community, nutrient addition altered arthropod community composition, primarily through changes to herbivore taxa in the canopy‐dwelling arthropod assemblage and detritivore taxa in the ground assemblage. Surprisingly, however, the loss of more than half of plant species was accompanied by negligible changes to diversity (rarefied richness) of arthropod taxa (which were primarily identified to family). Similarly, although long‐term nutrient addition in this system roughly doubles plant production and biomass, arthropod abundance was either unchanged or decreased by nutrient addition, and total arthropod biomass was unaffected. Our findings differ markedly from the handful of terrestrial studies that have found bottom‐up diversity cascades and productivity responses by consumers to nutrient addition. This is probably because unlike grasslands and salt marshes (where such studies have historically been conducted), this arctic tundra community becomes less palatable, rather than more so, after many years of nutrient addition due to increased dominance of B. nana. Additionally, by displacing insulating mosses and increasing the cover of shrubs that cool and shade the canopy microenvironment, fertilization may displace arthropods keenly attuned to microclimate. These results indicate that terrestrial arthropod assemblages may be more constrained by producer traits (i.e. palatability, structure) than they are by total primary production or producer diversity.     

Importance of habitat structure to the arthropod food-web in Douglas-fir canopies

This study tested the hypothesis that habitat structure dictates the distribution and community composition of arboreal arthropods. A diverse arthropod assemblage of Douglas-fir canopies, which included Araneae, Psocoptera, Collembola and Homoptera, was chosen as a model system. Habitat structural diversity, defined as needle density and branching complexity of Douglas-fir branches, was manipulated in a four-month experiment by needle removal, thinning and tying of branches. Abundance of canopy spiders declined significantly following needle density reduction and branch thinning, branch tying significantly increased spider abundance. Distinct habitat utilization patterns were found among individual spider guilds. Orb weavers (Araneidae) dominated spider assemblages in structurally simple habitats, whereas tied branches were colonized primarily by sheet-web weavers (Linyphiidae) and nocturnal hunting spiders (Anyphaenidae and Clubionidae). Spider species richness and average body size of several spider species increased in structurally more complex habitats. Arboreal spiders appeared to be limited by strong bottom-up effects in the form of habitat quality and, to a lesser degree, prey availability. Habitat manipulations did not affect densities or biomass of flying arthropod colonists in the branch vicinity. Needle removal and branch thinning led to a significant decline in the abundance of Psocoptera and Collembola. Tying of branches resulted in an eight-fold increase in Collembola numbers, organisms most sensitive to habitat alterations. Canopy habitat structure modified vertical dispersal of Collembola from forest litter, which may have significant implications for arboreal consumers. Our results lend strong support to the importance of habitat structural diversity in explaining general patterns of arthropod abundance and diversity on plants.     

Comparisons of arthropod assemblages on an invasive and native trees: abundance,diversity and damage

The success of exotic plants may be due to lower herbivore loads than those on native plants (Enemies Release Hypothesis). Predictions of this hypothesis include lower herbivore abundances, diversity, and damage on introduced plant species compared to native ones. Greater density or diversity of predators and parasitoids on exotic versus native plants may also reduce regulation of exotic plants by herbivores. To test these predictions, we measured arthropod abundance, arthropod diversity, and foliar damage on invasive Chinese tallow tree (Triadica sebifera) and three native tree species: silver maple (Acer saccharinum), sycamore (Platanus occidentalis), and sweetgum (Liquidambar styraciflua). Arthropod samples were collected with canopy sweep nets from six 20 year old monoculture plots of each species at a southeast Texas site. A total of 2,700 individuals and 285 species of arthropods were caught. Overall, the species richness and abundance of arthropods on tallow tree were similar to the natives. But, ordination (NMS) showed community composition differed on tallow tree compared to all three native trees. It supported an arthropod community that had relatively lower herbivore abundance but relatively more predator species compared to the native species examined. Leaves were collected to determine damage. Tallow tree experienced less mining damage than native trees. The results of this study supported the Enemies Release Hypothesis predictions that tallow tree would have low herbivore loads which may contribute to its invasive success. Moreover, a shift in the arthropod community to fewer herbivores without a reduction in predators may further limit regulation of this exotic species by herbivores in its introduced range.     

Best host‐plant attribute for species–area relationship,and effects of shade,conspecific distance and plant phenophase in an arthropod community within the grass Muhlenbergia robusta

Increased understanding of the species–area relationship (SAR) can improve its usefulness as a tool for prediction of species loss for biodiversity conservation targets. This study was conducted: (i) to determine the best plant attribute for the SAR in the community of arthropods living within the grass Muhlenbergia robusta; (ii) to determine the contribution of phenophases of plant foliage (dry and fresh), shade and conspecific distance to the variation in arthropod richness within the plant; (iii) to determine the best functional model of changes in the abundance, diversity and biomass in communities of arthropods in response to increases in plant size; (iv) to determine the best host‐plant attribute for prediction of these community attributes; and (v) to determine the effect of the plant phenophase, shade and M. robusta isolation on the abundance, diversity and biomass of the arthropod community. The above‐ground dry weight of grass was found to be the best host‐plant attribute for the SAR, while the light environment explained the arthropod richness within the grass, with higher richness observed in shaded environments. This study also showed that the best functional mathematical models for estimation of changes in the abundance, dry weight and diversity of arthropods in response to increases in grass size (dry weight) are the power model, exponential model and logarithmic model, respectively. Furthermore, the host‐plant foliage phenophase, shade and the isolation of M. robusta with other conspecifics had no effect on the abundance, biomass or diversity per basal area of the grass.     

Metabarcoding as a tool for investigating arthropod diversity in Nepenthes pitcher plants

The biodiversity of tropical forests consists primarily of small organisms that are difficult to detect and characterize. Next‐generation sequencing (NGS) methods can facilitate analyses of these arthropod and microbial communities, leading to a better understanding of existing diversity and factors influencing community assembly. The pitchers of carnivorous pitcher plants often house surprisingly discrete communities and provide ideal systems for analysis using an NGS approach. The plants digest insects in order to access essential nutrients while growing in poor soils; however, the pitchers are also home to communities of living organisms, called inquilines. Certain arthropods appear to have coevolved with their pitcher plant hosts and are not found in other environments. We used Illumina amplicon sequencing of 18S rDNA to characterize the eukaryotes in three species of Nepenthes (Nepenthaceae) pitcher plants – N. gracilis, N. rafflesiana and N. ampullaria – in each of three different parks in Singapore. The data reveal an unexpected diversity of eukaryotes, significant differences in community diversity among host species, variation in host specificity of inquilines and the presence of gregarine parasites. Counts of whole inquiline arthropods from the first collection year were roughly correlated with scaled 18S sequence abundances, indicating that amplicon sequencing is an effective means of gauging community structure. We barcoded a subset of the dipteran larvae using COI primers, and the resulting phylogenetic tree is mostly congruent with that found using the 18S locus, with the exception of one of five morphospecies. For many 18S and COI sequences, the best BLASTn matches showed low sequence identity, illustrating the need for better databases of Southeast Asian dipterans. Finally, networks of core arthropods and their host species were used to investigate degree of host specificity across multiple hosts, and this revealed significant specialization of certain arthropod fauna.     

Fire frequency and tree canopy structure influence plant species diversity in a forest-grassland ecotone

Disturbances and environmental heterogeneity are two factors thought to influence plant species diversity, but their effects are still poorly understood in many ecosystems. We surveyed understory vegetation and measured tree canopy cover on permanent plots spanning an experimental fire frequency gradient to test fire frequency and tree canopy effects on plant species richness and community heterogeneity within a mosaic of grassland, oak savanna, oak woodland, and forest communities. Species richness was assessed for all vascular plant species and for three plant functional groups: grasses, forbs, and woody plants. Understory species richness and community heterogeneity were maximized at biennial fire frequencies, consistent with predictions of the intermediate disturbance hypothesis. However, overstory tree species richness was highest in unburned units and declined with increasing fire frequency. Maximum species richness was observed in unburned units for woody species, with biennial fires for forbs, and with near-annual fires for grasses. Savannas and woodlands with intermediate and spatially variable tree canopy cover had greater species richness and community heterogeneity than old-field grasslands or closed-canopy forests. Functional group species richness was positively correlated with functional group cover. Our results suggest that annual to biennial fire frequencies prevent shrubs and trees from competitively excluding grasses and prairie forbs, while spatially variable shading from overstory trees reduces grass dominance and provides a wider range of habitat conditions. Hence, high species richness in savannas is due to both high sample point species richness and high community heterogeneity among sample points, which are maintained by intermediate fire frequencies and variable tree canopy cover.     

Temporal dynamics in non-additive responses of arthropods to host-plant genotypic diversity

Genotypic diversity within host‐plant populations has been linked to the diversity of associated arthropod communities, but the temporal dynamics of this relationship, along with the underlying mechanisms, are not well understood. In this study, we employed a common garden experiment that manipulated the number of genotypes within patches of Solidago altissima, tall goldenrod, to contain 1, 3, 6 or 12 genotypes m^?2 and measured both host‐plant and arthropod responses to genotypic diversity throughout an entire growing season. Despite substantial phenological changes in host plants and in the composition of the arthropod community, we detected consistent positive responses of arthropod diversity to host‐plant genotypic diversity throughout all but the end of the growing season. Arthropod richness and abundance increased with genotypic diversity by up to～65%. Furthermore, arthropod responses were non‐additive for most of the growing season, with up to 52% more species occurring in mixtures than the number predicted by summing the number of arthropods associated with component genotypes in monoculture. Non‐additive arthropod responses were likely driven by concurrent non‐additive increases in host‐plant aboveground biomass. Qualitative differences among host‐plant genotypes were also important early in the season, when specialist herbivores dominated the arthropod community. Neither arthropod diversity nor flower number was associated with genotypic diversity at the end of the growing season, when generalist floral‐associated herbivores dominated. Taken together, these results show that focusing on the temporal dynamics in the quantity and quality of co‐occurring host‐plant genotypes and associated community composition can help uncover the mechanisms that link intraspecific host‐plant diversity to the structure of arthropod communities. Furthermore, consistent non‐additive effects in genotypically diverse plots may limit the predictability of the arthropod community based solely on the genetic make‐up of a host‐plant patch.     

Arthropod community associated with the canopy of Attalea phalerata Mart. (Arecaceae) during the flood period of the Pantanal of Poconé, Mato Grosso, Brazil

Six trees of the palm species Attalea phalerata Mart. were sampled during high water (aquatic phase) of the Pantanal of Mato Grosso (February 2001), by canopy fogging. The composition, structure, and biomass of the arthropod community associated with their canopies were analysed, as well as the influence the flood pulse renders on it. Each tree was fogged once, followed by three consecutive collections. A total of 63,657 arthropods (643.0 +/-; 259.87 ind./m(2)) were collected, representing 25 orders in the classes Insecta, Arachnida, Diplopoda and Crustacea. The dominant groups were Acari (40.0%; 257.2 +/- 116.50 ind./m(2)), Coleoptera (12.0%; 77.5 +/- 64.93 ind./m(2)), Psocoptera (9.2%; 59.0 +/- 38.00 ind./m(2)), Diptera (8.4%; 54.1 +/- 18.72 ind./m(2)), Collembola (8.3%; 53.4 +/- 26.24 ind./m(2)) and Hymenoptera (7.9%; 50.6 +/- 21.40 ind./m(2)), the latter mostly represented by Formicidae (49.2%). Arthropod biomass amounted to 8.86 g dry weight and 0.18 mg/m(2). Coleoptera, Blattodea, Orthoptera, Araneae and Hymenoptera were the most representative taxa. The hydrological regime (flood pulse), as well as seasonality, appear to strongly affect the composition and structure of this canopy community.     

Cascading ecological effects of landscape moderated arthropod diversity

Understanding the mechanisms regulating the diversity and distribution of arthropods is essential to understanding food web interactions and ecosystem functioning. Local arthropod diversity is known to be linked to features of surrounding landscapes, including the area of human‐developed land. Yet, how such landscape moderation of diversity affects processes within local sites remains understudied. We report on a study that 1) measured the impacts of human development surrounding old‐field habitats of arthropods on arthropod food web structure within those habitats and 2) determined if these shifts were associated with cascading impacts on the plant community. We sampled the arthropod community in 16 old‐fields that span an urban‐rural gradient throughout southern New England, USA. In each field, we also established paired mesocosms enclosing vegetation, one of which allowed arthropod herbivory while the other excluded such interactions, to isolate impacts of arthropod herbivory on three functional groups of plants: grasses, goldenrod and non‐goldenrod forbs. Biomass of both herbivorous and predatory arthropods were positively related to the proportion of natural area surrounding a field early in the growing season (June). This relationship persisted later into the season for predatory arthropods (through July), but not for herbivorous arthropods. We found no evidence that the biomass of predators was related to the abundance of herbivorous arthropods in a field; or that biomass of herbivores was correlated to change in plant biomass between the two types of mesocosms. We did, however, find that in fields with low predator abundance there was greater herbivory on grasses (nutritious host), but that in high predator fields goldenrod was increasingly impacted (safe host), as is predicted by past work in old‐field ecosystems. The findings support the generalizability of landscape moderated biodiversity to non‐agricultural systems and suggests that observed shifts in food webs have implications for community and ecosystem dynamics.     

Testing the effects of an introduced palm on a riparian invertebrate community in southern california

Despite the iconic association of palms with semi-arid regions, most are introduced and can invade natural areas. Along the San Diego River (San Diego, California, USA), the introduced Canary Island date palm (Phoenix canariensis) forms dense patches among native riparian shrubs like arroyo willow (Salix lasiolepis). The structural differences between the palm and native shrubs are visually obvious, but little is known about palm's effects on the ecosystem. We tested for the effects of the palm on a riparian invertebrate community in June 2011 by comparing the faunal and environmental variables associated with palm and willow canopies, trunks and ground beneath each species. The palm invertebrate community had lower abundance and diversity, fewer taxa feeding on the host (e.g., specialized hemipterans), and more taxa likely using only the plant's physical structure (e.g., web-builders, oak moths, willow hemipterans). There were no observed effects on the ground-dwelling fauna. Faunal differences were due to the physical and trophic changes associated with palm presence, namely increased canopy density, unpalatable leaves, trunk rugosity, and litter accumulations. Palm presence and resulting community shifts may have further ecosystem-level effects through alteration of physical properties, food, and structural resources. These results were consistent with a recent study of invasive palm effects on desert spring arthropods, illustrating that effects may be relatively generalizable. Since spread of the palm is largely localized, but effects are dramatic where it does occur, we recommend combining our results with several further investigations in order to prioritize management decisions.