Multi‐trophic guilds respond differently to changing elevation in a subtropical forest

Negative relationships between species richness and elevation are common and attributed to changes in single environmental properties associated to elevation, such as temperature and habitat area. However, research has lacked taxonomic breadth and comprehensive elevation studies that consider multiple groups from different trophic levels are rare. We thus analysed 24 groups of plants, arthropods, and microorganisms grouped into six trophic guilds (predators, detritivores, herbivores, plants, bacteria and fungi) along a relatively short elevational gradient (~600 m) in a subtropical forest in south‐east China. The total species richness of all organisms was not related to elevation, nor was the richness of plants, herbivores or microorganisms. However, species richness and abundance in two major trophic guilds of arthropods changed with elevation, which was mediated by changes in elevation‐associated habitat properties. Specifically, deadwood mass increased with elevation, which increased detritivore richness indirectly via detritivore abundance, thus supporting the ‘more individuals hypothesis’. In contrast, lower predator richness at higher elevations was directly related to lower mean temperatures, which had no effect on abundance. Our study demonstrates that even along relatively short gradients, elevation can have strong direct and abundance‐mediated effects on species richness, but with effects varying from positive to negative signs depending on local resource availability and the characteristics of groups or trophic guilds. If elevation positively influences local environmental properties that benefit a given group, richness can increase towards higher elevations. Thus, the effect of global change in mountainous regions should be evaluated within the local environmental context using multi‐taxon approaches.     

The effect of an invasive alien vine, <Emphasis Type="Italic">Vincetoxicum rossicum</Emphasis> (Asclepiadaceae), on arthropod populations in Ontario old fields

Vincetoxicum rossicum is an invasive alien vine introduced from Europe in the late 1800s that is now an emerging pest in upstate New York and eastern Ontario. The plant can form dense, monotypic stands in woodlots and old fields, and may be displacing native vegetation. As a consequence, V. rossicum may be displacing arthropod fauna associated with native vegetation. In June and August 2002, we sampled V. rossicum and three other old field plants (Asclepias syriaca, Solidago altissima, and mixed graminoids) for arthropods using pitfall traps and by sampling individual plants. A total of 7868 arthropods were counted on plants and 18,195 individuals were trapped; these were sorted by feeding guild. Overall, stands of V. rossicum supported the lowest abundance of both stem- and ground-dwelling individuals, as well as the lowest number of arthropods in most phytophagous guilds. Some feeding guilds are entirely absent: V. rossicum stands are completely devoid of gall-makers and miners, and support few pollinators. This study suggests that arthropod diversity will decline if V. rossicum displaces native old-field plants.     

Ants and plant size shape the structure of the arthropod community of Hirtella myrmecophila, an Amazonian ant-plant

Abstract.  1. To investigate the influence of plant size and the presence of resident ants on the arthropod community associated with the ant-plant Hirtella myrmecophila , ants ( Allomerus octoarticulatus ) were experimentally removed from plants of various sizes, with a second group of similar-sized plants remaining as controls. The abundance and diversity of arthropods on these plants were determined at 45-day intervals for 7 months. Collected arthropods were assigned into one of three predetermined groups: herbivores, spiders (mostly web-building spiders), or 'tourists' (mostly non-resident ants, hemipterans, dipterans, or scarabeid beetles).
2. Ant removal had a positive influence on the abundance and diversity of herbivores, but no measurable effects on the abundance and diversity of 'tourists', while the effect on spider abundance was significant only when data from Dipoena sp. nov. were removed from the analysis. While A. octoarticulatus had a negative effect on most spiders, it favoured Dipoena sp. nov., which was found to be a specialist predator of A. octoarticulatus .
3. Plant size positively affected the abundance and diversity of 'tourists' in plants with and without ants, but for herbivores and spiders this effect was dependent on ant treatment. In ant-maintained plants the per-plant abundance of herbivores and spiders was independent of plant size, whereas in ant-removed plants it was not.
4. These results suggest that A. octoarticulatus affects all arthropods found on its host plant, except those presenting an occasional and temporary association with the plant, and that the magnitude of ant effects on the susceptible guilds increases as plant size increases.     

Effect of biomass on assemblages of large mammals in a seasonally dry forest in the Brazilian Amazonia

Aiming to understand the relationship between body mass and abundance, a community of middle-sized and larger mammals was studied in a seasonally dry forest in the far north of the Brazilian Amazonia. Diurnal and nocturnal surveys were carried out by the line-transect method along a 10-km transect. Data were collected on density, biomass, use of forest types, forest strata, diet and feeding strategies by the mammals. Biomass explained animal abundance better than did body mass across the two forest types: Terra Firme forest and mixed forest. There was a statistically significant positive relationship between the biomass of all the 33 mammals studied and group density, as well as between biomass and group size, in both forests. When terrestrial and arboreal mammals, and also different feeding guilds were considered separately, they exhibited very similar results, where biomass alone was positively associated with group density and group size. The slope of the relationships between body mass and group density, body mass and group size, biomass and group density, and biomass and group size varied considerably, with significant scatter around the regression line. Food and food competition shaped the relationship between animal mass and abundance, and this relationship can even vary widely between assemblages. As a result of competition for the available resources, group density increased with increasing biomass.     

Restoration of Arthropod Assemblages in a Spartina Salt Marsh following Removal of the Invasive Plant Phragmites australis

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plant Phragmites australis and if the restoration of the native vegetation in brackish Spartina alterniflora marshes results in the reestablishment of the arthropod community. The invasion of Phragmites into a coastal Spartina marsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free‐living specialists (e.g., planthoppers) in Spartina to concealed feeders in Phragmites (stem‐feeding cecidomyiids). Moreover, free‐living arthropods in Phragmites became dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web‐building linyphiids, were significantly reduced in Phragmites habitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages in Phragmites, as seen in the large shifts in feeding guilds, was significantly different from that in Spartina. Removal of Phragmites with the herbicide glyphosate resulted in the rapid return of Spartina (≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated with Spartina also quickly returned to its preinvasion state and was not distinguishable from that in uninvaded Spartina reference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat.     

Caterpillar assemblages on Chusquea bamboos in southern Ecuador: abundance,guild structure,and the influence of host plant quality

1. Information on the guild structure of foliage‐associated tropical insects is scarce, especially as caterpillars are mostly considered only as herbivores feeding on living leaves. However, many caterpillar species display alternative trophic associations, feeding on dead or withered leaves or epiphylls (‘non‐herbivores’). 2. To determine the contribution of these non‐herbivores, caterpillar communities associated with Chusquea Kunth (Poaceae) in the Andes of southern Ecuador were investigated. Caterpillars were collected at two elevation levels (montane rainforest ～2000 m and elfin forest at ～3000 m a.s.l.) and assigned to three feeding guilds (strict herbivores, non‐herbivores, and switchers) based on feeding trials. Foliage quality and leaf area were recorded to test for their influence on guild composition and caterpillar density. 3. Three hundred and eighty‐nine individuals belonging to 175 Lepidoptera species associated with Chusquea bamboos were found. The species richness of caterpillars was similarly high at both elevation levels but varied between feeding guilds. Approximately half (46.5%) displayed an alternative feeding association, i.e. were non‐herbivores (31.1%) or switchers (15.4%). 4. Caterpillar density was nearly two‐fold higher in the elfin forest, but only strict herbivores and switchers increased significantly with elevation. Leaf area positively influenced the density of strict herbivores and switchers; foliage quality only affected strict herbivores. The density of non‐herbivores did not differ significantly between the forest types and was not related to leaf area or foliage quality. 5. The present study underpins that non‐herbivores make up a considerable fraction of caterpillar communities in tropical mountain ecosystems and demonstrates that elevation, foliage quality and available plant biomass further shape feeding guild composition.     

Impacts of large herbivorous mammals on bird diversity and abundance in an African savanna

Large native mammals are declining dramatically in abundance across Africa, with strong impacts on both plant and animal community dynamics. However, the net effects of this large-scale loss in megafauna are poorly understood because responses by several ecologically important groups have not been assessed. We used a large-scale, replicated exclusion experiment in Kenya to investigate the impacts of different guilds of native and domestic large herbivores on the diversity and abundance of birds over a 2-year period. The exclusion of large herbivorous native mammals, including zebras (Equus burchelli), giraffes (Giraffa camelopardalis), elephants (Loxodonta africana), and buffalos (Syncerus caffer), increased the diversity of birds by 30%. Most of this effect was attributable to the absence of elephants and giraffes; these megaherbivores reduced both the canopy area of subdominant woody vegetation and the biomass of ground-dwelling arthropods, and both of these factors were good predictors of the diversity of birds. The canopy area of subdominant trees was positively correlated with the diversity of granivorous birds. The biomass of ground-dwelling arthropods was positively correlated with the diversity of insectivorous birds. Our results suggest that most native large herbivores are compatible with an abundant and diverse bird fauna, as are cattle if they are at a relatively low stocking rate. Future research should focus on determining the spatial arrangements and densities of megaherbivores that will optimize both megaherbivore abundance and bird diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The Amazonas‐trap: a new method for sampling plant‐inhabiting arthropod communities in tropical forest understory

Methods to quantify plant‐insect interactions in tropical forests may miss many important arthropods and can be time consuming and uneven in capture efficiency. We describe the Amazonas‐trap, a new method that rapidly envelops the target plant for sampling arthropods. We evaluated the efficiency of the Amazonas‐trap by comparing it with two commonly used sampling methods to collect arthropods from plants: the beating tray and manual collection. Samples were collected in 10 permanent plots, in the Ducke forest reserve, Manaus (Amazonas, Brazil). In each plot we sampled 18 plant individuals of Protium sp. (Burseraceae): six by a beating tray, six by manual collection, and six using the Amazonas‐trap. All insects were identified to the family level and those belonging to the order Hymenoptera were identified to the species and morphospecies level. The new method sampled more insect families and more Hymenoptera species than tree beating and manual collection. Of the 75 total families collected, 20 were sampled exclusively by the Amazonas‐trap, seven were only collected with a beating tray, and seven were sampled exclusively with manual collecting. A similar pattern was found for abundance: Amazonas‐trap sampled more individuals, followed by the beating tray and manual collection. Small and winged arthropods were more abundant in Amazonas‐trap, explaining the highest richness of Hymenoptera and insect families sampled with this method. The new method sampled more spiders, wood‐fungi feeders, sap suckers, omnivorous, parasitoids, and insect predators than the other methods, but was equally effective in sampling leaf‐feeders and ants. Amazonas‐trap was more time consuming in the field, but for all diversity parameters evaluated, the new method showed better performance for collecting invertebrates on plants.     

How do herbivorous insects respond to drought stress in trees?

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant–insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon‐based and nitrogen‐based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap‐sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought‐induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO₂ levels. There is a need for larger, temperate and tropical forest‐scale drought experiments to look at herbivorous insect responses and their role in tree death.     

Effect of prey availability on the abundance of White‐breasted Wood‐Wrens,insectivorous birds of tropical lowland forests

Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White‐breasted Wood‐Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100‐m radius) in two old‐growth forests, two second‐growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood‐wren abundance (wi = 0.75). Wood‐wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood‐wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood‐wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood‐wrens in a fragmented tropical landscape.     

Variation in the species composition and mean body size of an avian foliage-gleaning guild along an elevational gradient: correlation with arthropod body size

The composition of an avian foliage-gleaning guild was analyzed with respect to body size at nine sites along an elevational gradient in the Oregon Cascades. Mean body size decreased from 20.5 g near the lower forest boundary where it meets the grassland at about 775 m to 9.3 g near timberline at about 1720 m. Both the loss of larger species and the gain of smaller species contributed to the change. Mean volume of the foliage-dwelling arthropods also decreased with increasing elevation by two orders of magnitude along the same gradient. A significant decrease in body size occurred in three arthropod groups, larval Lepidoptera, Homoptera, and spiders, and of these, larval Lepidoptera dominated the overall size trend among arthropods. Both developmental differences (higher elevation sites are delayed seasonally on the same calendar date) and taxonomic differences contributed to the change in mean arthropod size. Mean bird size was positively correlated (r=0.93) with the body size of foliage-dwelling arthropods. A similar pattern was suggested for other avian guilds dependent directly or indirectly upon foliage-dwelling arthropods, but not for guilds independent of foliage-dwelling arthropods.     

The Multiple Impacts of Tropical Forest Fragmentation on Arthropod Biodiversity and on their Patterns of Interactions with Host Plants

Tropical rain forest fragmentation affects biotic interactions in distinct ways. Little is known, however, about how fragmentation affects animal trophic guilds and their patterns of interactions with host plants. In this study, we analyzed changes in biotic interactions in forest fragments by using a multitrophic approach. For this, we classified arthropods associated with Heliconia aurantiaca herbs into broad trophic guilds (omnivores, herbivores and predators) and assessed the topological structure of intrapopulation plant-arthropod networks in fragments and continuous forests. Habitat type influenced arthropod species abundance, diversity and composition with greater abundance in fragments but greater diversity in continuous forest. According to trophic guilds, coleopteran herbivores were more abundant in continuous forest and overall omnivores in fragments. Continuous forest showed a greater diversity of interactions than fragments. Only in fragments, however, did the arthropod community associated with H aurantiaca show a nested structure, suggesting novel and/or opportunistic host-arthropod associations. Plants, omnivores and predators contributed more to nestedness than herbivores. Therefore, Heliconia-arthropod network properties do not appear to be maintained in fragments mainly caused by the decrease of herbivores. Our study contributes to the understanding of the impact of fragmentation on the structure and dynamics of multitrophic arthropod communities associated with a particular plant species of the highly biodiverse tropical forests. Nevertheless, further replication of study sites is needed to strengthen the conclusion that forest fragmentation negatively affects arthropod assemblages.     

Arthropod communities in a Japanese cedar (Cryptomeria japonica D. Don) plantation: Abundance,biomass and some properties

Arboreal arthropod communities were censused by insecticidal knockdown in a plantation of Japanese cedar,Cryptomeria japonica, in central Japan from April 1983 to February 1985 at intervals of two months. All arthropods sampled were allocated to higher taxonomic groups or guilds and the composition of the communities was analyzed with respect to abundance, biomass and their seasonal trends. The total densities fluctuated seasonally from 200 to 3500 m⁻²; corresponding biomass values ranged from 7 to 600 mg fresh weight m⁻². Maximum density and biomass generally occurred in summer and were minimum in winter. The consistently dominant guild in terms of abundance were the detritivores, mostly comprising Collembola and oribatid mites, accounting for 36–93% of all arthropods; phytophages, predators and detritivores were major guilds in terms of biomass, showing average proportions of 27%, 23% and 20%, respectively. Biomass ratios of predators to prey were generally high in some canopy communities, suggesting the importance of predation pressure in regulating the population levels of arthropods in forests. Average individual size of predators was approximately proportional to that of prey, irrespective of tree locality. Soil arthropod communities maintained densities approximately 10²–10³ times as large as the corresponding canopy communities throughout the year. The seasonal variations in abundance were much greater in canopy than in soil communities.     

Activity and ranging patterns of Colombian woolly monkeys in north-western Amazonia

In this study, I revise three aspects of the socioecology of woolly monkeys (genus Lagothrix) that might give us a better understanding of the patterns found in this species: (1) the association between temporal variation in fruit abundance and diet, activity, and ranging patterns; (2) the individual trade-offs associated with living in small or large groups, and (3) the relationship between social dominance and foraging success. Using behavioral and ecological data collected during 3 years in Tinigua Park, Colombia, I found that woolly monkeys tend to avoid open-degraded forests, where fruit production is generally lower than it is in mature forests. Diet and activity budgets were highly associated with temporal patterns of fruit production. Daily path length was positively correlated with group size and monthly fruit abundance, and negatively correlated with habitat quality. I found differences in activity budgets and the diet preferences of different age/sex classes. For example, adult males rest more and juveniles play more than other classes. Juveniles and adult females without infants look for arthropods more often than adult males and females with young infants, who showed the highest frequencies of fruit feeding. Dominant adult males were not consistently the most efficient foragers on fruits according to two different indexes. Most of these results are consistent with the expectations from strong intra-group competition for resources. However, females with infants received benefits during feeding similar to those of dominant adult males, which may be mediated by differential aggression from males to other group members (juveniles and females without infants).     

Short-term Effects of Harvest Technique and Mechanical Site Preparation on Arthropod Communities in Jack Pine Plantations

Arthropods play a key role in the functioning of forest ecosystems and contribute to biological diversity. However, the influence of current silvicultural practices on arthropod communities is little known in jack pine (Pinus banksiana) forests, a forest type comprising a major portion of the Canadian boreal forest. In this study, the effects of silvicultural treatments on arthropod communities were compared to identify those treatments that minimize ecological impacts on arthropods. The influence of harvesting techniques and mechanical site preparations on insect family richness and abundance of arthropods (total, by orders and by trophic groups) was examined in young (three-year-old) jack pine plantations of northern Ontario. Each of the following treatments were conducted in three plots: (1) tree length harvest and trenching; (2) full tree harvest and trenching; (3) full tree harvest and blading; and (4) full tree harvest and no site preparation. Arthropods were collected using sweepnets and pitfall traps over two years. Blading significantly reduced insect family richness, the total abundance of arthropods, abundance of Orthoptera, Heteroptera, Hymenoptera, Diptera, insect larvae, and plant feeders when compared to the other treatments. The use of either full tree or tree length harvesting had similar short-term effects on family richness and the abundance of arthropods. Arthropod diversity declined with increasing post-harvest site disturbance. These results suggest that arthropod communities in the understory and on the ground are reduced most on sites mechanically prepared by blading, but are similar under conditions immediately following either full tree or tree length harvesting. The implications for regenerating jack pine in the boreal forest are discussed.     

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.     

Context-dependent responses of terrestrial invertebrates to anthropogenic nitrogen enrichment: A meta-analysis

Anthropogenic increases in nitrogen (N) concentrations in the environment are affecting plant diversity and ecosystems worldwide, but relatively little is known about N impacts on terrestrial invertebrate communities. Here, we performed an exploratory meta-analysis of 4365 observations from 126 publications reporting on the richness (number of taxa) or abundance (number of individuals per taxon) of terrestrial arthropods or nematodes in relation to N addition. We found that the response of invertebrates to N enrichment is highly dependent on both species' traits and local climate. The abundance of arthropods with incomplete metamorphosis, including agricultural pest species, increased in response to N enrichment. In contrast, arthropods exhibiting complete or no metamorphosis, including pollinators and detritivores, showed a declining abundance trend with increasing N enrichment, particularly in warmer climates. These contrasting and context-dependent responses may explain why we detected no overall response of arthropod richness. For nematodes, the abundance response to N enrichment was dependent on mean annual precipitation and varied between feeding guilds. We found a declining trend in abundance with N enrichment in dry areas and an increasing trend in wet areas, with slopes differing between feeding guilds. For example, at mean levels of precipitation, bacterivore abundance showed a positive trend in response to N addition while fungivore abundance declined. We further observed an overall decline in nematode richness with N addition. These N-induced changes in invertebrate communities could have negative consequences for various ecosystem functions and services, including those contributing to human food production.     

Impacts of an invasive willow (Salix × rubens) on riparian bird assemblages in south‐eastern Australia

We explored how a woody plant invader affected riparian bird assemblages. We surveyed 15 200‐m‐long transects in riparian zones in a much‐changed landscape of eastern Victoria, Australia. Abundance, species‐richness, foraging‐guild richness and composition of birds were compared in transects in three habitat types: (i) riparian zones dominated by the invasive willow Salix × rubens; (ii) riparian zones lined with native woody species; and (iii) riparian zones cleared of almost all woody vegetation. We also measured abundance and richness of arthropods and habitat structure to explore further the effects of food resources and habitat on the avifauna. We observed 67 bird species from 14 foraging guilds. Native riparian transects had more birds, bird species and foraging guilds than willow‐invaded or cleared transects. Habitat complexity increased from cleared to willow‐invaded to native riparian transects, as did abundance of native and woodland‐dependent birds. Native shrub and trees species had more foliage and branch‐associated arthropods than did willows, consistent with a greater abundance and variety of foraging guilds of birds dependent on this resource. Willow spread into cleared areas is unlikely to facilitate greatly native bird abundance and diversity even though habitat complexity is increased. Willow invasion into the native riparian zone, by decreasing food resources and altering habitat, is likely to reduce native bird biodiversity and further disrupt connectivity of the riparian zone.     

Egg size, first instar behaviour and the ecology of Lepidoptera

There is striking variation in egg size among Lepidoptera. Part of the explanation could be a link between egg size and larval feeding ecology.
The relationship between absolute egg size and aspects of feeding ecology for different Lepidoptera families from different temperate regions is examined. Species that overwinter in the egg stage have larger eggs. There are significant differences in egg size with respect to feeding specificity but different families show different patterns. Woody plant feeders have larger eggs than herb feeders. There is little effect of proximity of the egg to the plant part that is eaten.
Patterns in the behaviour and survival of newly hatched larvae of 42 spp. of British Lepidoptera and their relationship to egg and larval size and to food plant characteristics are examined. Patterns in egg size with respect to feeding ecology are similar to those described above. There is a strong correlation between egg size and the size of newly hatched larvae. Newly hatched larvae survived for a mean of 1–20 days without food. Survival is not correlated with larval weight. Grass feeders survive longer than herb and woody plant feeders; the species surviving the longest feeds on lichens. Newly hatched larvae moved at a mean speed of 0.7-267.8 cm h^-1. Speed is not correlated with larval weight or survival time. Grass feeders move faster than woody plant feeders which, in turn, move faster than herb feeders. Woody plant feeders tend to move upwards, grass feeders downwards and herb feeders both upwards and downwards. The proportion of larvae silking is negatively correlated with larval weight.
The strong links between egg size and larval feeding ecology and between feeding ecology and larval behaviour are discussed. It is surprising that larval body size does not appear to constrain the speed of movement, nor tolerance to starvation.     

Agroecological transition increases arthropod diversity and decreases herbivore abundance on field margins

1. In peri-urban areas, many farmers are transitioning from conventional agriculture to agroecological practices to reduce pesticide input and preserving ecosystem services such as natural pest control. Field margins represent a stable habitat for arthropods, but community structure depends on many factors, including management type and vegetation features.
2. We studied the effects of agroecological transitions and vegetation features on arthropods of horticultural field margins, focusing on three feeding guilds (herbivores, predators and parasitoids). We sampled arthropods using the beat-sheet method in five conventional fields and five under agroecological transition. We also measured vegetation height, richness, flower abundance and plant cover.
3. Our results showed that arthropod diversity was higher in agroecological fields whereas herbivore abundance was lower, with a consistent pattern across most taxonomic orders. Vegetation features displayed multiple effects among functional and taxonomic groups. Herbivores did not respond to most vegetation variables whereas predators correlated with several, with similar trends among orders.
4. We conclude that agroecological transitions and field margins with high vegetation richness and floral resources influence arthropod communities with potential benefits regarding pest regulation. These practices might be more effective if considered alongside other methods that enhance biodiversity and if they are consistent at a landscape scale.