Contrasting impacts of highly invasive plant species on flower-visiting insect communities

Invasive alien plants threaten biodiversity, ecosystems and service provision worldwide. They can have positive and negative direct and indirect effects on herbivorous insects, including those that provide pollination services. Here, we quantify how three highly invasive plant species (Heracleum mantegazzianum, Impatiens glandulifera and Fallopia japonica) influence the availability of floral resources and flower-visiting insect communities. We compared invaded with comparable uninvaded areas to assess floral resources and used pan-trapping to quantify insect communities. Only F. japonica influenced floral resource availability: sites invaded by this species had a higher flowering plant species richness and abundance of open floral units than uninvaded sites, probably due to its late flowering and the paucity of other flowering species at this time of year. Fallopia japonica was also associated with higher abundances of bumblebees, higher overall insect diversity and higher hoverfly diversity than uninvaded areas. Differences in pollinator communities were also associated with I. glandulifera and H. mantegazzianum, despite there being no detectable differences in floral resources at these sites. Specifically, there were more bumblebees and solitary bees in I. glandulifera sites, and a higher overall diversity of insects, particularly hoverflies. By contrast, H. mantegazzianum sites had a lower abundance of solitary bees and hoverflies. These findings confirm that invasive plant species have a range of species-specific effects on ecological communities. This supports the emerging view that control of invasive species, as required under international obligations, is not simple and that potential losses and gains for biodiversity must be carefully evaluated on a case-by-case basis.     

The changing nature of plant–microbe interactions during a biological invasion

Invasive plant species can alter belowground microbial communities. Simultaneously, the composition of soil microbial communities and the abundance of key microbes can influence invasive plant success. Such reciprocal effects may cause plant–microbe interactions to change rapidly during the course of biological invasions in ways that either inhibit or promote invasive species growth. Here we use a space-for-time substitution to illustrate how effects of soil microbial communities on the exotic legume Vicia villosa vary across uninvaded sites, recently invaded sites, and sites invaded by V. villosa for over a decade. We find that soil microorganisms from invaded areas increase V. villosa growth compared to sterilized soil or live soils collected from uninvaded sites, likely because mutualistic nitrogen-fixing rhizobia are not abundant in uninvaded areas. Notably, the benefits resulting from inoculation with live soils were higher for soils from recently invaded sites compared to older invasions, potentially indicating that over longer time scales, soil microbial communities change in ways that may reduce the success of exotic species. These findings suggest that short-term changes to soil microbial communities following invasion may facilitate exotic legume growth likely because of increases in the abundance of mutualistic rhizobia, but also indicate that longer term changes to soil microbial communities may reduce the growth benefits belowground microbial communities provide to exotic species. Our results highlight the changing nature of plant–microbe interactions during biological invasions and illustrate how altered biotic interactions could contribute to both the initial success and subsequent naturalization of invasive legume species.     

Effect of Argentine ant invasions on ground-dwelling arthropods in northern California riparian woodlands

Although the Argentine ant (Linepithema humile) is a widespread invasive species that displaces native ants throughout its introduced range, the effects of these invasions on arthropods other than ants remain poorly known. This study documents the consequences of Argentine ant invasions on ants and other ground-dwelling arthropods in northern California riparian woodlands. Baits and unbaited pitfall traps were used to sample different components of the arthropod communities at five pairs of uninvaded and invaded sites. Sites occupied by Argentine ants supported almost no native epigeic ants except for the winter-active Prenolepis imparis. Sites with Argentine ants averaged four to ten times more ant workers than did sites with native ants, but ant worker biomass did not differ between uninvaded and invaded sites. Argentine ants recruited to baits in invaded areas, on average, in less than half the time of native ants in uninvaded areas. Despite the loss of epigeic native ants, higher Argentine ant worker abundance, and faster recruitment by Argentine ants at invaded sites, pitfall trap samples from uninvaded and invaded areas contained similar abundances and diversities of non-ant arthropods. These findings suggest that Argentine ants and the native ants they displace interact with the ground-dwelling arthropods of these habitats in a similar manner. Received: 24 February 1997 / Accepted: 9 November 1997     

Impacts of the invader giant reed (<Emphasis Type="Italic">Arundo donax</Emphasis>) on riparian habitats and ground arthropod communities

Riparian areas have experienced long-term anthropogenic impacts including the effects of plant introductions. In this study, 27 plots were surveyed across three Mediterranean rivers in north-eastern Spain to explore the effects of the invader giant reed (Arundo donax) on riparian habitat features and the diversity, trophic structure, body size, and abundances of epigeal and hypogeal arthropods in riparian areas. Using pitfall traps and Berlese funnels, this study detected a significant increase in collembola abundance and a decrease in the abundance, body size and diversity of macro-arthropods at order and family levels in invaded plots compared to native stands. Invaded and un-invaded areas also differed in the taxonomical structure of arthropod assemblies but not in trophic guild proportions. However, the fact that arthropods were smaller in A. donax soils, together with the absence of particular taxa within each trophic guild or even an entire trophic group (parasitoids), suggests that food-web alterations in invaded areas cannot be discarded. Habitat features also differed between invaded and un-invaded areas with the poorest herbaceous understory and the largest leaf litter deposition and soil carbon stock observed in A. donax plots. The type of vegetation in riparian areas followed by the total native plant species richness were identified as major causal factors to changes in the abundance, diversity and composition of macro-arthropods. However, our analyses also showed that some alterations related to A. donax invasion were inconsistent across rivers, suggesting that A. donax effects may be context dependent. In conclusion, this study highlights an impoverishment of native flora and arthropod fauna in A. donax soils, and suggests major changes in riparian food webs if A. donax displaces native riparian vegetation.     

Flowering banker plants for the delivery of multiple agroecosystem services

Ecosystem services provided by agricultural ecosystems include natural pest control and pollination, and these are important to ensure crop productivity. This study investigates the use of the banker plant Calendula officinalis L. to provide multiple ecosystem services by increasing the abundance of natural enemies for biological control of tomato pests, providing forage resources to wild bees, and improving crop yield. C. officinalis was selected for this experiment as it is used as a banker plant for Dicyphini (Hemiptera: Miridae) predators. Strips of flowering C. officinalis were established in the field edges of tomato fields and arthropod visitation to C. officinalis strips and tomato was measured. Crop damage from multiple pests of tomato was assessed in fields with C. officinalis strips and control sites. The contribution of pollination to crop yield was assessed through a pollinator exclusion experiment. The inclusion of C. officinalis in tomato fields was associated with increased abundance of Dicyphini, parasitoids, bees and other arthropod groups within these strips. A reduction in the total leaf crop damage from Lepidoptera pests was recorded in fields with C. officinalis strips. Increased fruit set and biomass were recorded in open-pollinated tomato but this was not significantly different between control and C. officinalis fields. Results presented here demonstrate that the inclusion of a companion plant can improve the conservation of beneficial arthropods and the delivery of agroecosystem services but efficacy is likely to be improved with the addition of plants, with different functional traits, and with improved attractiveness to crop pollinators.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

An invasive plant provides refuge to native plant species in an intensely grazed ecosystem

Invasion by exotic plant species and herbivory can individually alter native plant species diversity, but their interactive effects in structuring native plant communities remain little studied. Many exotic plant species escape from their co-evolved specialized herbivores in their native range (in accordance with the enemy release hypothesis). When these invasive plants are relatively unpalatable, they may act as nurse plants by reducing herbivore damage on co-occurring native plants, thereby structuring native plant communities. However, the potential for unpalatable invasive plants to structure native plant communities has been little investigated. Here, we tested whether presence of an unpalatable exotic invader Opuntia ficus-indica was associated with the structure of native plant communities in an ecosystem with a long history of grazing by ungulate herbivores. Along 17 transects (each 1000 m long), we conducted a native vegetation survey in paired invaded and uninvaded plots. Plots that harboured O. ficus-indica had higher native plant species richness and Shannon–Wiener diversity H′ than uninvaded plots. However, mean species evenness J was similar between invaded and uninvaded plots. There was no significant correlation between native plant diversity and percentage plot cover by O. ficus-indica. Presence of O. ficus-indica was associated with a compositional change in native community assemblages between paired invaded and uninvaded plots. Although these results are only correlative, they suggest that unpalatable exotic plants may play an important ecological role as refugia for maintenance of native plant diversity in intensely grazed ecosystems.     

Non-native plants affect generalist pollinator diet overlap and foraging behavior indirectly,via impacts on native plant abundance

Flowering invasive plants can have dramatic effects on the resource landscape available to pollinators. Because many pollinators exhibit behavioral plasticity in response to competitor or resource density, this in turn can result in impacts on ecological processes such as pollination and plant reproduction. We examine how interactions between five common generalist eusocial bees change across an invasion gradient by examining how bee abundance and diet overlap changed with variation in both invasive plant abundance and competitor abundance in a temperate oak-savannah ecosystem. Specifically we focus on the bumblebees Bombus bifarius, B. mixtus, B. melanopygus and B. vosnesenskii, as well as the non-native honeybee Apis mellifera, and their interactions with the native flowering plants Camassia quamash, Camassia liechtlinii, and the invasive shrub Cytisus scoparius. We further examine whether changes in pollinator visits to the invasive and two common native plants can explain changes in diet overlap. Abundance of the invasive plant and other common floral resources had strong impacts on focal bee abundance, with certain species more likely to be present at highly invaded sites. This may be because highly invaded sites tended to be embedded in forested landscapes where those bees are common. Diet overlap was most affected by abundance of a common native plant, rather than the invasive plant, with diet overlap increasing non-linearly with abundance of the native plant. Furthermore, Apis mellifera, did not appear to have direct competitive effects on native bumblebees in this habitat. However, visit patterns suggest that bees most abundant at highly invaded sites may compete for access to native resources. Thus the impacts of this invasive plant on our focal bee species may be primarily indirect, via its’ competitive effects on native plants.     

Invasive herb <Emphasis Type="Italic">Impatiens glandulifera</Emphasis> has minimal impact on multiple components of temperate forest ecosystem function

Forests understories in Europe are known to generally resist invasion, though some alien plants do invade woodland communities. Here we focused on the impact of the widespread invasive annual Impatiens glandulifera, common along watercourses, but recently spreading in forests up to timberline. We investigated its impact on plant–soil feedback and ecosystem functioning. We recorded >40 variables focusing on: soil characteristics, including micro- and macro-nutrients; characteristics of litter layer and enzyme activity in litter; and richness and species composition of the forest understory. Three treatments were followed for 3 years: plots invaded by I. glandulifera; adjacent invader removal plots within the invaded area; and spatially separated uninvaded plots outside the invaded area. The effect of year-to-year variation was generally greater than that of the treatments, especially in soil and litter characteristics. Copper and boron were higher in invaded than invader removal and uninvaded plots, though in quantities that are unlikely to harm other plants. We found no effect of I. glandulifera on litter characteristics or enzyme activity. Despite almost 80% cover of I. glandulifera, we did not detect any difference in species richness and total vegetation cover between invaded and uninvaded plots. The floristic composition differed among the uninvaded, invader removal and invaded plots across 3 years. Our results indicate that the effect of I. glandulifera on the forest community studied was minor, and largely resulted from its increased shading to other plant species. In conclusion, we show how misleading the evaluation of impacts can be if based on a single season.     

Interaction between a threatened endemic plant (<Emphasis Type="Italic">Anchusa crispa</Emphasis>) and the invasive Argentine ant (<Emphasis Type="Italic">Linepithema humile</Emphasis>)

Seed dispersal mutualisms are essential to ensure the survival of diverse plant species and communities worldwide. Here, we investigated whether the invasive Argentine ant can replace native ants by fulfilling their functional role in the seed dispersal of the rare and threatened endemic myrmecochorous plant, Anchusa crispa, in Corsica (France). Our study addressed the potential of Linepithema humile to disperse elaiosome-bearing seeds of A. crispa, examining L. humile’s effects on (1) the composition of communities of ants removing seeds, (2) the number of seed removals, (3) seed preference, (4) the distance of seed dispersion, and (5) seed germination. We caught seven native species at the control site, but only the Argentine ant at invaded sites. L humile removed A. crispa seeds in greater numbers than did native ants, respectively 66 and 23%, probably due to their higher worker density. The invader was similar to native ants with respect to distance of seed transport. Finally, rates of seed germination were not significantly different between seeds previously in contact with either Argentine ants or not. Taken all together, these results suggest that the Argentine ant is unlikely to pose a threat to A. crispa population. These results have important implications for the management of this rare and threatened endemic plant and provide an example of non-negative interactions between invasive and native species.     

Native predators living in invaded areas: responses of terrestrial amphibian species to an Argentine ant invasion

Predator–prey interactions play a key role in the success and impacts of invasive species. However, the effects of invasive preys on native predators have been poorly studied. Here, we first reviewed hypotheses describing potential relationships between native predators and invasive preys. Second, we examined how an invasive prey, the Argentine ant (Linepithema humile), affected a native terrestrial amphibian community. In the field, we looked at the structure of the amphibian community in invaded versus uninvaded areas and characterized amphibian trophic ecology. The amphibian community sampled seemed to show a species-dependent response in abundance to invasion: adults of the natterjack toad (Bufo calamita), the species demonstrating the highest degree of ant specialization, were less abundant in invaded areas. Although available ant biomass was significantly greater in invaded than in uninvaded areas (only Argentine ants occurred in the former), amphibians consumed relatively fewer ants in invaded areas. In the lab, we quantified amphibian consumption of Argentine ants versus native ants and assessed whether consumption patterns could have been influenced by prior exposure to the invader. The lab experiments corroborated the field results: amphibians preferred native ants over Argentine ants, and prior exposure did not influence consumption. Differences in preference explained why amphibians consumed fewer Argentine ants in spite of their greater relative availability; they might also explain why the most ant-specialized amphibians seemed to avoid invaded areas. Our results suggest the importance to account for predator feeding capacities and dietary ranges to understand the effects of invasive species at higher trophic levels.     

Low interspecific pollen transfer between invasive aquatic <Emphasis Type="Italic">Ludwigia grandiflora</Emphasis> and native co-flowering plants

Showy invasive alien plants are often integrated in the diet of generalist pollinators and because of the lack of co-evolvement with the native plant community, a high amount of interspecific pollen transfer (IPT) can be expected. We investigated pollinator switching and magnitude plus distance of IPT between the alien aquatic Ludwigia grandiflora and the native Lythrum salicaria in both directions in uninvaded and invaded sites with a different relative abundance of L. grandiflora (% cover of the alien plant: no cover; low cover: <5%; high cover: 50–75%). A field experiment was conducted to include both pollinator interspecific movements and tracking of IPT, using fluorescent dye as a pollen analogue. Despite a substantial overlap in pollinators between L. grandiflora and the native L. salicaria, less than 10% of the observed flights were interspecific. Similar results were found in dye transfer patterns. The proportions of stigmas with conspecific dye were always higher than the proportions of stigmas with heterospecific dye for L grandiflora and L. salicaria. There were no differences in conspecific dye loads for L. salicaria between uninvaded and invaded sites. Conspecific pollen loss (native CPL) and heterospecific pollen deposition (alien HPD) were in general low and species-specific. The distance of HPD ranged respectively from 1.7 to 39 m and from 0.3 to 54.8 m in the low cover and high cover sites while CPL ranged respectively from 6.40 to 68.02 m and from 0.60 to 40.18 m in the low cover and high cover sites. We can conclude that, in this system, CPL and HPD will play a minor role in pollinator-mediated interaction. Furthermore, interspecific competition for pollinators will cover a larger distance than just neighboring individuals. Our results suggest the necessity to consider the combined effect of insect visitation, pollen deposition, relative alien abundance, distance and seed set when investigating pollinator-mediated interactions of invasive plants.     

Do biological invasions by <Emphasis Type="Italic">Eupatorium adenophorum</Emphasis> increase forest fire severity?

The invasive species Eupatorium adenophorum is known to influence stand structure and wildfire the hazard in forests. In the current work, we quantitatively examined fire effects in invaded and uninvaded plots in southwestern Sichuan Province, China, with five different forest sites that had different types of dominant species: Pinus yunnanensis, P. yunnanensis–Quercus spp., Keteleeria fortunei, K. fortunei–Quercus spp., and Eucalyptus robusta. We compared the fuel chemistry (moisture, ash, heat value, and ignition point) and fire severity (flame length, fire intensity) under three burning conditions between the invaded and uninvaded plots in each forest sites, and then analyzed the results using multivariate response permutation procedures (MRPP). The burning conditions included: low (fine fuel moisture of 15 % and 5 km/h windspeed), moderate (fine fuel moisture of 10 % and 15 km/h windspeed), and extreme (fine fuel moisture of 5 % and 30 km/h windspeed). With all five sites, the fire severity and fuel loads were clearly significantly higher at the invaded sites. Fire severity was also intensified in the invaded coniferous sites compared to their mixed forest sites. These results indicate that biological invasions may increase the surface fire severity, perhaps through an increase in the heat value, and fuel loads, while reducing the moisture, ash, and ignition point of the understory herbaceous.     

Nonnative plant shifts functional groups of arthropods following drought

Nonnative plants alter the composition of native plant communities, with concomitant effects on arthropods. However, plant invasions may not be the only disturbance affecting native communities, and multiple disturbances can have compounding effects. We assessed the effects of invasion and drought on plant and arthropod communities by comparing grasslands dominated by nonnative Old World bluestem grasses (OWBs, Dichanthium annulatum) to grasslands dominated by native plants during a period of decreasing drought severity (2011–2013). Native plant communities had more species of plants and arthropods (/m²) than areas dominated by OWBs during extreme drought, but richness was comparable as drought severity decreased. Abundance of arthropods was greater in native plant communities than in OWB communities during extreme drought, but OWB communities had more arthropods during moderate and non-drought conditions. We observed a shift in the arthropod community from one dominated by detritivores to one dominated by herbivores following plant invasion; the magnitude of this shift increased as drought severity decreased. Both plant communities were dominated by nonnative arthropods. A nonnative leafhopper (Balclutha rubrostriata) and native mites (Mochlozetidae) dominated OWB communities as drought severity decreased, and OWBs may serve as refugia for both taxa. Nonnative woodlice (Armadillidium vulgare) dominated native plant communities during extreme and non-drought conditions and abundance of this species may be associated with an increase in plant litter and available nutrients. Given the importance of arthropods for ecosystem services, incorporating arthropod data into conservation studies may demonstrate how changes in arthropod diversity alter ecosystem function where nonnative plants are dominant.     

Differences in Aggressive Behaviors between Two Ant Species Determine the Ecological Consequences of a Facultative Food-for-Protection Mutualism

Ant-hemipteran mutualisms are widespread interactions in terrestrial food webs with far-reaching consequences for arthropod communities. Several hypotheses address the behavioral mechanisms driving the impacts of this mutualism, but relatively few studies have considered multiple ant species simultaneously as well as interspecific and intraspecific variation in ant behavior. In a series of field experiments that manipulated ant diet, this work examines the role of induced behaviors of forest ant species actively engaged in mutualism with Hemiptera. Based on other work in ant mutualisms, we predicted a higher frequency of aggressive behaviors towards prey and competitors by ants in the presence of honeydew-producing Hemiptera. We specifically compared Camponotus chromaoides and Formica neogagates (Formicidae), two abundant species in temperate forests of the northeastern U.S.A. After manipulating ant diet and interactions with sap-feeders experimentally, we observed 494 one-on-one interactions between ants and competitors, ladybird beetles and caterpillar prey. We found that C. chromaoides, exhibited behavioral dominance over F. neogagates, and C. chromaoides was more likely to attack ladybird beetles, competing ants, and caterpillar prey. However, contrary to other work in ant-Hemipteran mutualisms, we observed no evidence that food rewards provided by sap-feeders induced changes in ant behavior for either ant species examined. These results reveal the importance of considering interspecific differences in behavior as a mechanism underlying the ecological impacts of ant-Hemipteran protection mutualisms.     

Phenotypic and phylogenetic characterization of actinomycetes isolated from <Emphasis Type="Italic">Lasius niger</Emphasis> and <Emphasis Type="Italic">Formica cunicularia</Emphasis> ants

Multiple actinomycete strains were isolated from two ant species, Lasius niger and Formica cunicularia, and their phenotypic properties and phylogenetic position were studied. Partial sequencing of 16S rRNA assigned the greater part of them to the genus Streptomyces, but only one belonged to Nocardia. However, some isolates had significant color and morphological differences from their closest phylogenetic relatives. The abundance and biodiversity of actinomycete communities isolated from L. niger ants greatly exceeded those found for F. cunicularia. All of the actinomycetes associated with F. cunicularia ants demonstrated cellulolytic activity, but only one had such ability among the strains associated with black ants.     

Low-head dams facilitate Round Goby <Emphasis Type="Italic">Neogobius melanostomus</Emphasis> invasion

Round Goby Neogobius melanostomus invasion of the Grand River (Ontario, Canada) presents an opportunity to assess the role of abiotic gradients in mediating the establishment and impact of nonnative benthic fishes in rivers. In this system, sequential low-head dams delineate uninvaded and invaded river reaches and create upstream gradients of increasing water velocity. We hypothesized that flow refugia created by impounded reservoirs above low-head dams enhance local Round Goby abundance. Round Goby influence on the native fish community was determined by variance partitioning, and we used generalized additive models to identify small-bodied benthic fish species most likely to be impacted by Round Goby invasion. Round Goby abundance declined as the degree of reservoir effect decreased upstream. The distributions of four species (including the endangered Eastern Sand Darter Ammocrypta pellucida) in invaded reaches were best explained by inclusion of both reservoir-associated abiotic variables and Round Goby abundance as model terms. To determine establishment potential of the uninvaded reach immediately upstream, four environmental habitat characteristics were used in discriminant function analysis (DFA) to predict three potential outcomes of introduction: non-invaded and either lower or higher Round Goby abundance (low and high invasion status, respectively) than the median number of Round Goby at invaded sites. Our DFA function correctly classified non-invaded and high-abundance invasion status sites > 85% of the time, with lower (73%) success in classifying low-abundance invasion status sites, and the spatial pattern of our results suggest that likelihood of establishment is greatest in impounded habitat.     

Effect of habitat structure on reproduction and prey capture of a rare carnivorous plant, <Emphasis Type="Italic">Pinguicula lutea</Emphasis>

Habitat degradation is one of the greatest threats to biodiversity worldwide and the main contributor to the decline of many carnivorous plant species. For carnivorous plants in the southeastern United States, including many Pinguicula species (butterwort, Lentibulariaceae), degradation via altered fire regime has been implicated in their decline. Despite this decline, limited empirical research has been conducted examining the influence of habitat structural changes (through natural succession or human management) on reproduction and prey capture by carnivorous plants. The objectives of our study were to compare reproduction and prey capture for Pinguicula lutea (yellow butterwort) in habitats with different vegetation structures in the Florida Panhandle, where differences were largely due to management history. Pinguicula lutea is a self-compatible carnivorous plant that inhabits fire-dependent longleaf pine savannas of the southeastern United States and is threatened in the state of Florida. In 2014 and 2015, 13 sites were identified occupying three different habitat structures: maintained (intermittently mowed), grassy (dominated by Aristida stricta var. beyrichiana), and woody (encroachment by Hypericum and Ilex). Reproductive output was determined by assessing fruit set and ovule fertilization rate at each site. Additionally, prey availability and prey capture were assessed at each habitat site. In general, there were no differences in either measure of reproduction across habitat structure types. There were differences in prey abundance of Collembola, Diptera, and total arthropods both in terms of availability and capture. Total arthropod availability and prey capture were lowest in grassy sites compared to maintained habitat sites and woody habitat sites. Microclimatic conditions associated with each habitat structure and leaf morphology or physiology could explain the observed arthropod abundance and prey capture patterns. This study is the first ecological assessment of plant–insect interactions for Pinguicula species of the southeastern US and highlights the importance of habitat quality and management for this understudied group of carnivorous plants.     

Seasonal and altitude effects on the structure of arthropod communities associated with <Emphasis Type="Italic">Tillandsia violacea</Emphasis> Baker (Bromeliaceae) in a temperate forest of Mexico

The canopy of forests has been considered “the last biotic frontier,” and study of its elements is very important in explaining the global functionality in ecosystems. Epiphytic plants and arthropods are essential elements in canopy habitats, and their relationships have been studied in order to understand the high diversity in tropical forests. Nevertheless, there are few studies on this development in temperate forests. The arthropod community was studied during the rainy and dry seasons at two altitudes, and a total of 240 T. violacea plants of three sizes were collected from Abies religiosa and Quercus spp. host trees. A total of 163,043 arthropods were collected and about 200 morphospecies identified. The highest abundance was obtained during the dry season, while high diversity was found during the rainy season. There was a significant effect of plant size, host trees and collecting season on abundance and diversity, and there were seasonal variations in community composition. The community hosted on A. religiosa epiphytes showed higher abundance and density than that of Quercus.     

Influences of the invasive tamarisk leaf beetle (<Emphasis Type="Italic">Diorhabda carinulata</Emphasis>) on avian diets along the Dolores River in Southwestern Colorado USA

The tamarisk leaf beetle (Diorhabda carinulata), introduced from Eurasia in 2001 as a biological control agent for the invasive plant Tamarix ramosissima, has spread widely throughout the western USA. With D. carinulata now very abundant, scientists and restoration managers have questioned what influence this introduced arthropod might have upon the avian component of riparian ecosystems. From 2009 through 2012 we studied the consequences of biological invasions of the introduced tamarisk shrub and tamarisk leaf beetles on the diets of native birds along the Dolores River in southwestern Colorado, USA. We examined avian foraging behavior, sampled the arthropod community, documented bird diets and the use of invasive tamarisk shrubs and tamarisk leaf beetles by birds. We documented D. carinulata abundance, on what plants the beetles occurred, and to what degree they were consumed by birds as compared to other arthropods. We hypothesized that if D. carinulata is an important new avian food source, birds should consume beetles at least in proportion to their abundance. We also hypothesized that birds should forage more in tamarisk in the late summer when tamarisk leaf beetle larvae are more abundant than in early summer, and that birds should select beetle-damaged tamarisk shrubs. We found that D. carinulata composed 24.0 percent (±?19.9–27.4%) and 35.4% biomass of all collected arthropods. From the gut contents of 188 birds (25 passerine species), only four species (n?=?11 birds) contained tamarisk leaf beetle parts. Although D. carinulata comprised one-quarter of total insect abundance, frequency of occurrence in bird gut contents was only 2.1% by abundance and 3.4% biomass. Birds used tamarisk shrubs for foraging in proportion to their availability, but foraging frequency did not increase during the late summer when more tamarisk leaf beetles were present and birds avoided beetle-damaged tamarisk shrubs. Despite D. carinulata being the most abundant arthropod in the environment, these invasive beetles were not frequently consumed by birds and seem not to provide a significant contribution to avian diets.