Influence of leaf traits on the spatial distribution of arboreal arthropods within an overstorey rainforest tree

Abstract.

• 1 Several attributes of foliage were measured from the Australian rainforest tree Argyrodendron actinophyllum Edlin (Sterculiaceae). These were related to estimates of abundance per leaf area of the most common arthropod guilds and families sampled with restricted canopy fogging.
• 2 When all these arthropod groups were considered, much of the overall variance in arthropod spatial distribution could be attributed to leaf age characteristics, arthropod aggregation patterns, arthropod activity and distance to tree trunk.
• 3 The fraction of variance which could be specifically explained by foliage attributes such as nitrogen-, water- and fibre-content, specific leaf weight, and epiphyll load was small for most arthropod groups (usually <30%). However, an index of food quality explained a higher proportion of variance (50%) in the abundance of phloem-feeders. Leaf size and foliage compactness did not influence significantly the abundance of any arthropod group.
• 4 Most herbivores were more abundant on young foliage than on mature leaves. With the exception of Corylophidae and Chrysomelidae, which were more abundant in the lower and upper canopy respectively, arthropod stratification was not conspicuous within the inner core of tree crowns.
• 5 The results firstly emphasize the distribution of young foliage as a key factor affecting the abundance of many herbivores and, secondly, the importance of the local illumination regime for host leaf production and its indirect effects on the spatial distribution of arboreal arthropods.

     

Communities of insect herbivores foraging on saplings versus mature trees of Pourouma bicolor (Cecropiaceae) in Panama

The arthropod fauna of 25 saplings and of three conspecific mature trees of Pourouma bicolor (Cecropiaceae) was surveyed for 12 months in a tropical wet forest in Panama, with particular reference to insect herbivores. A construction crane erected at the study site provided access to tree foliage in the upper canopy. A similar area of foliage (ca. 370 m²) was surveyed from both saplings and trees, but samples obtained from the latter included 3 times as much young foliage as from the former. Arthropods, including herbivores and leaf-chewing insects with a proven ability to feed on the foliage of P. bicolor were 1.6, 2.5 and 2.9 times as abundant on the foliage of trees as on that of saplings. The species richness of herbivores and proven chewers were 1.5 (n=145 species) and 3.5 (n=21) times higher on trees than on saplings, respectively. Many herbivore species preferred or were restricted to one or other of the host stages. Host stage and young foliage area in the samples explained 52% of the explained variance in the spatial distribution of herbivore species. Pseudo-replication in the two sampling universes, the saplings and trees studied, most likely decreased the magnitude of differences apparent between host stages in this forest. The higher availability of food resources, such as young foliage, in the canopy than in the understorey, perhaps combined with other factors such as resource quality and enemy-free space, may generate complex gradients of abundance and species richness of insect herbivores in wet closed tropical forests.     

Abundance of white lace lerp psyllids on understorey and canopy river red gums and relationships with foliar sugars and tannins

1. Trees present herbivorous insects with the greatest diversity of resources of any plant growth form. Both ontogeny and shading can alter suitability for arboreal insect herbivores. 2. We conducted a longitudinal study of tagged ‘mature’ (>12 months old) Eucalyptus camaldulensis leaves to compare the suitability of understorey and canopy trees for the leaf senescence-inducing psyllid, Cardiaspina albitextura. We quantified sugars and tannins as possible predictors of nymphal abundance. 3. Canopy leaves hosted double the number of nymphs as understorey leaves. Variation among individual trees (understorey and canopy) was the most important source of heterogeneity explaining psyllid abundance, although relative leaf age significantly influenced oviposition on canopy leaves. The diversity of foliar sugars was higher among canopy leaves than among understorey leaves. There was significant between-tree diversity in total hydrolysable tannins (HTs) and total condensed tannins (CTs) among understorey trees but not among canopy trees. Heterogeneity among understorey and canopy trees was explained by greater diversity of ellagitannins (HTs) than of CTs. 4. Shading is detrimental to the survival of nymphs on both host types, but sugars are unlikely to explain variation in suitability. Vescalagin (an ellagitannin) was negatively correlated with the abundance of nymphs on both host types.     

Convergence in Arthropod Assemblages with Various Restoration Approaches for Canadian Deciduous Forests

Silvicultural practices are traditionally aimed at increasing forest profits; however, recent approaches to forest conservation have broadened to include nature-based silviculture for regenerating forests. In southern Ontario (Canada), originally dominated by deciduous forests, conifer plantations were established on abandoned agricultural sites. Currently, there is an increasing interest to convert these conifer stands to a state that mimics the original deciduous forest. We investigated arthropod abundance, species richness of carabid beetles, and abundance of arthropod assemblages (trophic and prey groups) under five silvicultural treatments conducted to regenerate deciduous forests (the natural forest type) from the old conifer plantations. The treatments included: (1) uniform canopy removal; (2) uniform canopy removal and understory removal; (3) group canopy removal; (4) group canopy removal and understory removal; and (5) untreated control plots (relatively pure red pine). Insects were sampled annually using sweepnets and pitfall traps. Results revealed treatment effects on the abundance of Coleoptera, Heteroptera, herbivores, and small arthropods (<3 mm) caught in sweepnet samples, where plots subjected to group shelterwood removal and understory removal supported higher abundances than the control plots. There was no treatment effect on the abundance of other arthropod groups or on the species richness and abundance of carabid beetles. The silvicultural treatments used to encourage natural regeneration did not seem to affect arthropod food availability for insectivorous vertebrates. Thus, the type of silvicultural strategy used to convert pine plantations to a stage that mimics the natural deciduous forests had little overall impact on arthropods.     

Interplant variation in creosotebush foliage characteristics and canopy arthropods

Summary We conducted a field study to test the hypothesis that creosotebush (Larrea tridentata) shrubs growing in naturally nutrient-rich sites had better quality foliage and supported greater populations of foliage arthropods than shrubs growing in nutrient-poor sites. Nutrient-rich sites had significantly higher concentrations of soil nitrogen than nutrient-poor sites. Multivariate analysis of variance revealed significant differences between high nutrient and low nutrient shrubs based on a number of structural and chemical characteristics measured. High nutrient shrubs were larger, had denser foliage, greater foliage production, higher concentrations of foliar nitrogen and water, and lower concentrations of foliar resin than low nutrient shurbs. Numbers of foliage arthropods, particularly herbivores and predators, were significantly higher on high nutrient shrubs. Shrub characteristics and foliage arthropod abundances varied considerably from shrub to shrub. Shrub characteristics representing shrub size, foliage density, foliage growth, and foliar nitrogen and water concentrations were positively correlated with arthropod abundances. Foliar resin concentrations were negatively correlated with foliage arthropod abundances. The positive relationship between creosotebush productivity and foliage arthropods is contradictory to the tenet that physiologically stressed plants provide better quality foliage to insect herbivores.     

The seasonality of arboreal arthropods foraging within an Australian rainforest tree

Abstract.

• 1 The seasonality of arboreal arthropods foraging within the crown of the canopy tree Argyrodendron actinophyllum. Edlin (Sterculiaceae) was studied in a subtropical rain forest near Brisbane, Australia, during 2 years with interception traps and restricted canopy fogging.
• 2 Minimal air temperatures explained most of the seasonal variance in arthropod‘density activity'. However, the host phenology was important for several phytophagous groups. Rainfall, relative humidity and lunar phase influenced arthropod activity slightly.
• 3 Seasonal ranges were significantly different among arboreal guilds and were related to food resource availability in time, associated with both the host and the rainforest environment. Seasonal peaks of herbivores were more marked than in tropical rain forests, but less sharp than in temperate woodlands.'
• 4 Quantitative changes in arthropod density activity and abundance were important for most groups, with a marked trough during cool and dry months. The numerical contribution of most arthropod guilds to the arboreal community was not constant throughout the year.
• 5 Seasonal changes in the species composition of the arboreal community appeared not as a succession of well-defined subcommunities throughout the year, but as a continuum of species of extended seasonal ranges.
• 6 This subtropical insect-plant system presented several phenological features which were classified under tropical and temperate characteristics. This partition is open to discussion.

     

Additive and interactive effects of plant genotypic diversity on arthropod communities and plant fitness

Recent research suggests that genetic diversity in plant populations can shape the diversity and abundance of consumer communities. We tested this hypothesis in a field experiment by manipulating patches of Evening Primrose ( Oenothera biennis ) to contain one, four or eight plant genotypes. We then surveyed 92 species of naturally colonizing arthropods. Genetically diverse plant patches had 18% more arthropod species, and a greater abundance of omnivorous and predacious arthropods, but not herbivores, compared with monocultures. The effects of genotypic diversity on arthropod communities were due to a combination of interactive and additive effects among genotypes within genetically diverse patches. Greater genetic diversity also led to a selective feedback, as mean genotype fitness was 27% higher in diverse patches than in monocultures. A comparison between our results and the literature reveals that genetic diversity and species diversity can have similar qualitative and quantitative effects on arthropod communities. Our findings also illustrate the benefit of preserving genetic variation to conserve species diversity and interactions within multitrophic communities.     

Structural complexity of arthropod guilds is affected by the agricultural landscape heterogeneity generated by fencerows

Intensive farming imposes harsh conditions impeding the persistence of most arthropod species within crop fields. Hence, arthropods surviving the unfavourable conditions prevailing within crop fields may disperse towards nearby uncropped margins, such as fencerows. Here, we evaluate the influence of landscape heterogeneity on the abundance of different guilds, particularly herbivores and their natural enemies. Said heterogeneity mostly derives from fencerow network density. Hence, we developed an approach based on fitting linear‐mixed models to elucidate the effects of landscape heterogeneity and field position (fencerows and crop interiors) on arthropod diversity. Mixed models were fitted to arthropod data obtained by pitfall trap samplings in 36 crop fields. Arthropod communities were structurally and functionally more complex along fencerows than within nearby crop interiors. Arthropods abundance was modulated by landscape heterogeneity, increasing the abundance of natural enemies as the landscape heterogeneity increased. On the contrary, herbivores abundance decreased as landscape heterogeneity increased. Consequently, the ratio between herbivores and natural enemies also decreased as landscapes became more heterogeneous. Natural enemies with larger body sizes, mostly carabid beetles, were more sensitive to landscape homogenisation. Our study reveals that, despite the coarse‐grained landscapes in the Rolling Pampa, fencerow density appears as a key factor for structuring complex arthropod guilds in intensively farmed agricultural mosaics. In landscapes with higher density of fencerows, arthropods tend to concentrate along them, thus increasing the community structural complexity as well as the predation pressure over herbivores. This structural complexity of upper trophic levels enhances the ‘top‐down’ regulation of herbivore populations, consequently decreasing the probability of pest outbreaks within crop fields.     

Feeny revisited: condensed tannins as anti-herbivore defences in leaf-chewing herbivore communities of Quercus

Abstract. 1. Community level oak–tannin–insect patterns have been largely unexplored since Paul Feeny's ground‐breaking research. Two hypotheses were tested for Quercus velutina and Q. alba in the Missouri Ozarks: abundance and richness of leaf‐chewing herbivores are negatively correlated with foliar condensed tannin concentrations and variation in condensed tannin concentrations explains variation in herbivore community structure. 2. In 2001, foliar condensed tannins in the understorey and canopy of these two oak species were quantified simultaneously with censuses of herbivores in May, during leaf expansion, and in June and August, when leaves were fully expanded. Thirty‐eight of the 134 species encountered had densities sufficient to be analysed individually (n = 10). Of those, Acronicta increta (Noctuidae) and Attelabus sp. (Curculionidae), both oak specialists, were negatively correlated with condensed tannins in the canopy of Q. alba. One additional specialist, Chionodes pereyra (Gelechiidae), was marginally negatively correlated with condensed tannins in the understorey of Q. velutina. Understorey species richness of May Q. velutina herbivores was negatively correlated with condensed tannins, as were total canopy insect density and species richness of August herbivores on Q. alba. 3. Principal component analysis (PCA) of insect abundances indicated that understorey and canopy Q. velutina and Q. alba had different communities of leaf‐chewing insects. Furthermore, condensed tannin levels contributed significantly to variation in PCA scores for Q. velutina, explaining 25% of the total variation. 4. Overall, these results indicate that specialists were more likely than generalists both to correlate negatively with condensed tannins and to occur in lower tannin habitats; abundance and richness of both early and late season fauna correlated negatively with tannins; and species were more likely to correlate negatively with condensed tannins when feeding on Q. alba than on Q. velutina and when feeding in the canopy than in the understorey. Future studies of tannin–insect interactions should manipulate leaf quality in combination with manipulations of other factors that likely influence community structure.     

Genetic variation in functional traits influences arthropod community composition in aspen (Populus tremula L.)

We conducted a study of natural variation in functional leaf traits and herbivory in 116 clones of European aspen, Populus tremula L., the Swedish Aspen (SwAsp) collection, originating from ten degrees of latitude across Sweden and grown in a common garden. In surveys of phytophagous arthropods over two years, we found the aspen canopy supports nearly 100 morphospecies. We identified significant broad-sense heritability of plant functional traits, basic plant defence chemistry, and arthropod community traits. The majority of arthropods were specialists, those coevolved with P. tremula to tolerate and even utilize leaf defence compounds. Arthropod abundance and richness were more closely related to plant growth rates than general chemical defences and relationships were identified between the arthropod community and stem growth, leaf and petiole morphology, anthocyanins, and condensed tannins. Heritable genetic variation in plant traits in young aspen was found to structure arthropod community; however no single trait drives the preferences of arthropod folivores among young aspen genotypes. The influence of natural variation in plant traits on the arthropod community indicates the importance of maintaining genetic variation in wild trees as keystone species for biodiversity. It further suggests that aspen can be a resource for the study of mechanisms of natural resistance to herbivores.     

Fine-scale temporal dynamics of flower visitors sheds light on insect-assemblage overlap between sexes in a dioecious Ecuadorian palm

Dioecious plants generally display sexual dimorphism in male and female floral traits, potentially attracting slightly different pollinator communities. The sharing of common floral visitors between male and female flowers and their timing of visits to both sexes is of critical importance to ensure plant's reproductive success. Palm inflorescences are visited by abundant and diverse insect communities, yet the temporal patterns of insect visits on both sexes remain poorly known. We characterized the composition of a community of flower-visiting arthropods associated with the dioecious ivory palm (Phytelephas aequatorialis, Spruce) in a pre-montane forest of Ecuador. We monitored the temporal variations in insect visits along the flowering of 12 inflorescences (eight female and four male) using interception traps recovered every 4 h. We report 59 morphospecies in the arthropod community, dominated by three beetle families: Staphylinidae, Nitidulidae, and Curculionidae. Male inflorescences were more abundantly visited than female, but visitors of the later were taxonomically more diverse. Among the 16 pollinator candidates identified, nine visited both inflorescence sexes synchronously at dusk /night whereas the others did so asynchronously during the day. Our study provides new insights into the pollination mechanism of P. aequatorialis. We found evidence of differential pollinator attraction between floral sexes, which may be explained by the sexual dimorphism of both flowers. Synchronicity in dusk/night visits of both inflorescence sexes suggests a sexual synchronization of the signal used to attract pollinators.     

Arthropod Distribution in a Tropical Rainforest: Tackling a Four Dimensional Puzzle

Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods.     

Intercropping in high input agriculture supports arthropod diversity without risking significant yield losses

Arthropod diversity of different taxonomic groups and ecosystem services are declining, yet current measures to counteract losses are often restricted to small areas of land or field margins, particularly in agricultural systems. At the same time, large areas of land will be required to feed a growing global population. Intercropping has been proposed as a potential solution to maximize both biodiversity and yield at large scale, but experimental evidence is scarce.In a three-year field experiment, we manipulated crop diversity and management intensity in a cereal-legume intercropping experiment in Germany, where 50% of wheat was replaced by faba beans. We measured arthropod abundance and diversity of different functional groups (pollinators, natural enemies, herbivores) and crop yield.We found that increasing crop diversity increased abundance and diversity of arthropods. Notably, pollinator and natural enemy abundances increased in intercropped systems. Low management intensity generally had positive effects on arthropod abundance and especially on pollinator diversity, indicating benefits of reduced inputs of fertilizers and herbicides. While wheat yield was higher in monocultures and for high management intensity, total grain yield of the intercrop (indicated by land equivalent ratio) was higher in mixtures. We found that trade-offs were stronger between arthropod diversity and wheat yield than between arthropod abundance and wheat yield. Specialist wheat herbivores and generalist herbivores were more abundant at higher wheat yields. Conversely, pollinator and natural enemy diversity were negatively associated with wheat yield.Our results show that diversification can promote both higher yields and greater diversity of arthropods. Intercropping can thus be an opportunity to support biodiversity without risking significant yield losses.     

Arthropod assemblages in a focal tree species (Eucalyptus microcarpa) depends on the species mix in restoration plantings

The composition of arthropods in trees has long been a topic of interest, with many studies exploring ways in which arthropod communities differ among tree species or entire forests. Few studies, however, have examined arthropods from trees in restoration plantings, and little is known about how different tree plantings might lead to different biodiversity outcomes. The aim of our study was to determine if a focal tree species hosted a different arthropod fauna depending on its context. We examined arthropod assemblages from the foliage of Eucalyptus microcarpa (Grey Box) trees present in two kinds of plantings: (i) simple plantings with only Eucalyptus trees, and (ii) mixed plantings with both Eucalyptus and Acacia trees. We examined the composition of the assemblages, and looked for associations between ant and psyllid (Hemiptera) diversity across each kind of planting. We found more species of psyllids, beetles and ants in E. microcarpa trees when they were grown in simple plantings compared with the mixed species plantings. We also found that psyllid richness and abundance was positively correlated with ant richness and abundance across all plantings. Our study shows that a more diverse context (i.e. a mixed planting) is not necessarily associated with a more diverse fauna within a focal tree species, and that simple Eucalyptus-only plantings may encourage higher numbers of insect herbivores. The apparent association between psyllids and ants suggests a complex interaction that may drive patterns in tree arthropod assemblages.     

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.     

Patterns in the use of rainforest vertical space by Neotropical aerial insectivorous bats: all the action is up in the canopy

In tropical rainforests environmental conditions vary dramatically from the ground to the canopy, resulting in a marked stratification in the way vertical space is used by organisms, but research work is often limited to the understorey layer. Aerial insectivorous bats are a highly diverse group that plays key roles in the ecology of rainforests, but their use of vertical space remains elusive. Using automatic ultrasound recording stations placed in the canopy, subcanopy and understorey we tested if bat activity and species diversity are vertically stratified, both in the forest interior and near the edges of water bodies. These patterns were tested separately for individual species, and for two functional groups – open space and edge space bats. Insectivorous bat activity increased by roughly seven fold, and species diversity doubled, from the understorey to the canopy. Both edge space and open space bats were more active in the upper strata, but this tendency was much more accentuated in the latter. Myotis riparius was the only species with greater activity near the understorey. These patterns were altered at the edges of water bodies, where vertical stratification was much less marked. The observed patterns are parsimoniously explained by constraints imposed by vegetation clutter that change across strata, which affect bat species differently. Only bats better adapted to closed spaces are usually capable of foraging within the understorey, whereas the majority of species can exploit the free spaces immediately below the canopy; open space bats seem to concentrate their activity above the canopy. This importance of the inter strata open spaces for bat foraging highlights the need to preserve pristine stratified rainforests, as even selective logging usually disrupts vertical stratification. Moreover, the concentration of insectivorous bats at the upper strata of rainforests underlines the need to include canopy level sampling in ecological studies.     

Assessment of higher insect taxa as bioindicators for different logging-disturbance regimes in lowland tropical rain forest in Sabah, Malaysia

One of the serious environmental problems since the 1980s has been the conflict between the high rate of deforestation and maintenance of healthy ecosystem services and biological values in tropical forests. There is an urgent demand for setting up an appropriate environmental assessment to keep healthy ecosystem functions and biodiversity along with sustainable forest use based on ecology. In this study, we tried to assess logging-disturbance effects on the abundances of several flying insect groups (higher-taxon approach) in lowland tropical rain forest (Deramakot Forest Reserve, Sabah, Malaysia), while considering seasonal changes and vertical forest stratification. The season was the most important factor affecting the abundances of all the insect groups. Effects of logging disturbance were prominent in the understorey but obscure in the canopy. Changes in physical conditions caused by logging—possibly an increased evaporation due to solar radiation—may have decreased the abundance of desiccation-sensitive insects, especially in the understorey. There are also two probable reasons for the difference between events in the understorey and those in the canopy: (1) noise effects of various physical, environmental factors may have obscured insect responses to logging disturbance in the canopy; (2) higher spatio-temporal variation in quality and quantity of living food resources—such as leaves, flowers and fruits—provided in the canopy may have affected the abundance of their consumer insects independently of logging disturbance. Thus, this study suggests that the abundance of some insect groups at higher-taxon level, especially in the understorey, can be used as bioindicators for assessing effects of logging disturbance on the forest ecosystem.     

Influence of native ants on arthropod communities in a vineyard

• 1 Ants can have a range of effects on arthropods in crops, including suppressing herbivores such as caterpillars. However, ants can also increase hemipteran densities while reducing natural enemy numbers. In vineyard ecosystem, the effects of native ants and their interactions with other arthropods are poorly understood.
• 2 An ant‐exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism of light brown apple moth (LBAM) eggs, a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were counted after a season of ant‐exclusion.
• 3 Among 23 ground ant species collected, six were found to forage in the canopy, with two Iridomyrmex species being the most commonly encountered.
• 4 There was no difference in the abundance of most arthropod orders and feeding groups between ant‐excluded and control vines, although ground spiders were more abundant under ant‐excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs.
• 5 In conclusion, native ants did not consistently suppress arthropod assemblages, including natural enemies, and they did not promote the survival of scale insects. Interactions among native ant species within a vineyard might minimize their effects on other arthropods, although this needs further study.

     

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.     

Arthropod community structure along a latitudinal gradient: Implications for future impacts of climate change

Abstract The structure of free‐living arthropod communities on the foliage of Acacia falcata was assessed along an extensive latitudinal gradient in eastern Australia. We hypothesized that abundance and biomass of arthropods within feeding groups would increase from temperate latitudes towards the tropics. We also hypothesized that the ratio of carnivores to herbivores would be consistent along the latitudinal gradient. Three sites at each of four latitudes, spanning 9° and 1150 km (Batemans Bay, Sydney, Grafton, Gympie in Australia), were sampled every season for 2 years, using pyrethrum knockdown. Abundance and biomass (based on dry weight) of arthropods within eight feeding groups were measured. The relative size of the feeding groups, and the ratio of carnivores to herbivores were then compared among latitudes and seasons. We found no consistent north to south (tropical to temperate) change in feeding group structure in terms of abundance. A weak latitudinal trend was evident for predator biomass, consisting of a reduction from north to south, but no significant trends in biomass for other feeding groups were found. Relative abundance and relative biomass of both carnivores and herbivores, as well as the ratio of carnivores to herbivores were consistent among latitudes. Finally, we compared a subset of these data to arthropod communities found on congeneric host species at individual sites along the latitudinal gradient. Overall, 68% of comparisons showed no significant differences in abundance or biomass within different feeding groups between host plants and among latitudes. We conclude that arthropod communities show consistencies among latitudes and between congeneric host species, in terms of feeding group and trophic structure. These results have implications for predicting the impacts of future climate change on arthropod communities.