Habitat complexity affects functional traits and diversity of ant assemblages in urban green spaces (Hymenoptera: Formicidae)

Habitat complexity conferred by vegetation characteristics mediates key processes that govern the assemblage of insect communities. Thus, species within the community should only persist if their functional traits are well-matched to the conditions of their environment. Here, we compared ant assemblages between habitats in terms of species richness and functional-trait distribution at the species and the assemblage level. Ants were collected from 36 sites representing different degrees of habitat complexity mediated by standing vegetation. We found fewer ant species in simpler habitats, supporting the "habitat-heterogeneity" hypothesis. We measured key functional traits of ants that reflect their foraging and dispersal strategies, such as body size, femur length, antenna scape length, and head length / width. Interactions of species traits with measured habitat complexity variables were assessed at the species and the assemblage level using a fourth-corner approach. Ant traits were closely related to environmental complexity. In wooded habitats, ants were larger and had broader heads, while ants with longer antenna scapes prevailed in habitats with a dense herb / grass layer. Our study suggests that vegetation structural complexity can act as an environmental filter, driving ant assemblages in terms of both species numbers and functional traits. Our results can be used to predict turnover patterns in ant assemblages due to changes in management practices

Atmospheric change causes declines in woodland arthropods and impacts specific trophic groups

1. Arthropod assemblages form a fundamental part of terrestrial ecosystems, underpinning ecosystem processes and services. Yet, little is known about how invertebrate communities, as a whole, respond to climatic and atmospheric changes, including predicted increases in carbon dioxide concentrations (CO2). 2. To date, woodland Free Air CO2 Enrichment (FACE) studies have focused entirely on northern hemisphere managed plantations. We manipulated atmospheric CO2 in a mature, native Eucalyptus woodland (0.15 ha, >32 000 m3) in Australia, using the Eucalyptus FACE (‘EucFACE’) facility. We used three complementary sampling methods (vacuum sampling, pitfall and sticky trapping) to record invertebrate abundances under ambient and elevated levels of CO2 (400 versus 550 ppm). 3. Based on the collection of over 83 000 invertebrates, we found significant declines in the overall abundance of ground-dwelling (14.7%) and aerial (12.9%) arthropods under elevated CO2, with significant decreases in herbivore, omnivore, scavenger and parasitoid functional groups. Even though several groups showed varying declines in abundance, elevated CO2 did not measurably affect community composition. 4. The results of the present study indicate that atmospheric CO2 levels predicted within the next 35 years may cause declines in arthropod abundances in Eucalyptus woodland. Declines found in several functional groups suggest that elevated atmospheric CO2 has the potential to affect ecosystem processes, possibly including nutrient cycling by herbivores and omnivores, as well as biocontrol by parasitoids

Crucial role of ultraviolet light for desert ants in determining direction from the terrestrial panorama

Ants use the panoramic skyline in part to determine a direction of travel. A theoretically elegant way to define where terrestrial objects meet the sky is to use an opponent-process channel contrasting green wavelengths of light with ultraviolet (UV) wavelengths. Compared with the sky, terrestrial objects reflect relatively more green wavelengths. Using such an opponent-process channel gains constancy in the face of changes in overall illumination level. We tested the use of UV wavelengths in desert ants by using a plastic that filtered out most of the energy below 400 nm. Ants, Melophorus bagoti, were trained to home with an artificial skyline provided by an arena (experiment 1) or with the natural panorama (experiment 2). On a test, a homing ant was captured just before she entered her nest, and then brought back to a replicate arena (experiment 1) or the starting point (the feeder, experiment 2) and released. Blocking UV light led to deteriorations in orientation in both experiments. When the artificial skyline was changed from opaque to transparent UV-blocking plastic (experiment 3) on the other hand, the ants were still oriented. We conclude that UV wavelengths play a crucial role in determining direction based on the terrestrial surround.10 page(s

Foraging patterns and strategies in an Australian desert ant

The Australian desert ant Melophorus bagoti (Formicidae) is a thermophilic, solitary foraging ant that inhabits the semi-arid regions of Australia. In recent years, it has become a model species for the study of navigation. However, its ecological traits are not well understood, especially on the level of the entire colony. Here, we investigated this species daily activity schedule and diet composition, and examined its foraging behaviour. Foraging activity is confined to a window of roughly 50-70°C soil surface temperature, and foragers reacted quickly to temperature changes. Consequently, the pattern of daily outbound traffic during summer is unimodal on warm days and bimodal on very hot days. Foragers are opportunistic scavengers; dead insects make up a large proportion of food items, but grass seeds are also occasionally brought back to the nest in large amounts. Diet composition changes with the seasonal availability of certain food groups. Melophorus bagoti foragers have the ability to recruit nestmates to profitable food sources. Recruitment seems to function without the use of pheromone trails, but the exact mechanism requires further investigation.10 page(s

Potential impacts of climate change on patterns of insect herbivory on understorey plant species : a transplant experiment

Species-specific responses to climate change will lead to changes in species interactions across multiple trophic levels. Interactions between plants and their insect herbivores, in particular, may become increasingly disrupted if mobile herbivores respond more rapidly to climatic change than their associated host plants. We present a multispecies transplant experiment aimed at assessing potential climatic impacts on patterns of leaf herbivory. Four shrubby understorey plant species were transplanted outside their native range into a climate 2.5°C warmer in annual mean temperature. After 12 months, we assessed the types and amount of herbivore leaf damage, compared with plants transplanted to a control site within their native range. The overall amount of foliage loss to herbivores ranged from approximately 3-10% across species and sites, a range consistent with most estimates of leaf loss in other studies. The most common types of leaf damage were sucking and chewing and this pattern was consistent for all four plant species at all sites. There were no significant differences in levels and patterns of herbivory between control and warm sites for three out of four plant species. This suggests that with moderate climate warming, most herbivory will continue to be dominated by chewers and suckers, and that the overall level of foliage loss will be similar to that experienced presently.9 page(s

The power of the transplant : direct assessment of climate change impacts

Understanding the factors that limit species distributions has become increasingly important in the face of rapid climate change. Many approaches have been used to predict responses of species and communities to new environmental challenges, including species distribution modelling, glasshouse and growth cabinet experiments, and small-scale field manipulations, all of which have both advantages and limitations. Here, we review the use of a powerful, direct method to predict how species and communities will respond to the changing climate: the field transplant experiment. We discuss how transplant experiments can elucidate the factors that limit species distributions; disentangle the role of genetic change vs. phenotypic plasticity in species’ responses; and improve understanding of the role of species interactions in driving community change. Several generalisations about potential species’ responses to climate change are emerging from these studies, including the critical role of specific life stages in response to warming trends, the role of natural enemies and new hosts in limiting or promoting adaptive capacity, and the role of niche saturation in conferring community stability at a functional guild level. Transplant experiments have also confirmed likely mechanisms of recent range shifts and highlighted the potential for some modelling exercises to overestimate future range changes. With the prospect that accelerating warming over the next few decades will increase extinction rates and accelerate ecosystem degradation, we urge researchers to utilise this powerful but underused method more widely

Patterns of insect herbivory on four Australian understory plant species

Australia harbours a very diverse phytophagous insect fauna, but little is known about the patterns of insect herbivory in dominant forest systems, especially in dry sclerophyll forests. Here, we assess variation in leaf herbivory in four species of narrow-ranged sclerophyllous shrubs across their geographical distribution. We assessed leaf herbivory as the percentage of missing leaf area, and estimated the proportion of damage types, such as chewing, sucking and mining.We found that the levels of leaf herbivory and the proportions of damage types were consistent among plant species but showed considerable variability within single plant species among sites and individual plants. This variability is most likely due to the patchy distribution of herbivorous insects in space and time. Leaf damage was dominated by chewing, but mining and sucking occurred on all plant four species. Sap sucking, although much less conspicuous, was found to be a major damage type, demonstrating that neglect of sap sucking damage in leaf herbivory assessments could lead to a considerable underestimation of the total herbivore damage inflicted on host plants

Transplant experiments : a powerful method to study climate change impacts

Transplant experiments are a direct test of whatmight happen in the future as species or entire communities are moved out of their current climate into a location with novel climate conditions. Here we assess our current understanding of climate change adaptation responses using transplant experiments. Firstly, we assess the current knowledge on species and community responses to climate change. We then identify the way climate change responses have been carried out to date with an emphasis on transplant experiments including: adaptation to a warmer climate; potential of range shifts; changes in phenology; shifts in species interactions; disentangling genotypic and phenotypic responses; and shifts in communities. Further, we assess transplant experiments that specifically assess invertebrate responses using network analyses and conclude with an assessment of what is missing in the current approaches and the way forward with future transplant experiments

Development of a new apparatus to partition ant body size reveals their respective functional role within ant communities

The rapid decline of biodiversity is directly threatening the maintenance of important ecosystem processes. Yet, biodiversity loss is not homogeneous, with species presenting specific traits being more prone to extinction. Ultimately this can lead to potential disruption of key ecosystem functions. Ants are ubiquitous and abundant in all terrestrial ecosystems. They provide a plethora of ecosystem functions and thus are well suited for studies assessing ecological processes. Within ant communities, body size of different species can vary by several orders of magnitude reflecting different ecologies. To this point, however, our understanding of the efficiency of ecological processes by different classes in function of their body size remains largely unexplored under field conditions. This is in part due to a lack of adequate methodology for an easy and accurate assessment of their respective contributions. Here, we describe a novel approach that separates ants into three size classes based on two parameters: height of the access point and size of the entrance; and evaluated the success of this method by assessing morphometric parameters of the size classes post-filtering and quantifying the scavenging efficiency as a key ecological process. This method successfully segregated individuals based on their body size, with the large-size treatment allowing access to ants 3 times larger than ants on the medium-size treatment and 5 times larger than those on the small-size treatment. The large-size treatment was the most efficient, removing 7 times more bait per hour than the medium-size treatment and 40 times more than the small-size treatment. This approach provides a new, adjustable method for differential exclusion in the field, highlighting the role that different size classes play within a community. This opens new opportunities to study the relative role of specific functional traits, and the importance of ecological interactions in shaping ecosystem functions

Coleoptera and Hemiptera feeding guild structure from eight plant species at three transplant sites.

<p><i>A. obtusata</i> (A), <i>A. parvipinnula</i> (B), <i>D.corymbosa</i> (C), <i>A. hispida</i> (D), <i>C. pinifolius</i> (E), <i>L. squarrosum</i> (F), <i>H. gibbosa</i> (G) and <i>T.speciosissima</i> (H) at control (C), warm 1 (W1) and warm 2 (W2), and congeneric plant species (conge) at the warm sites. Herbivore feeding guilds are ‘hatched’; mesophyll and phloem feeders combined are ‘sapsuckers’; numbers above bars show number of morphospecies.</p