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

Altered precipitation and root herbivory affect the productivity and composition of a mesic grassland

Background Climate change models predict changes in the amount, frequency and seasonality of precipitation events, all of which have the potential to affect the structure and function of grassland ecosystems. While previous studies have examined plant or herbivore responses to these perturbations, few have examined their interactions; even fewer have included belowground herbivores. Given the ecological, economic and biodiversity value of grasslands, and their importance globally for carbon storage and agriculture, this is an important knowledge gap. To address this, we conducted a precipitation manipulation experiment in a former mesic pasture grassland comprising a mixture of C-4 grasses and C-3 grasses and forbs, in southeast Australia. Rainfall treatments included a control [ambient], reduced amount [50% ambient] and reduced frequency [ambient rainfall withheld for three weeks, then applied as a single deluge event] manipulations, to simulate predicted changes in both the size and frequency of future rainfall events. In addition, half of all experimental plots were inoculated with adult root herbivores (Scarabaeidae beetles). Results We found strong seasonal dependence in plant community responses to both rainfall and root herbivore treatments. The largest effects were seen in the cool season with lower productivity, cover and diversity in rainfall-manipulated plots, while root herbivore inoculation increased the relative abundance of C-3, compared to C-4, plants. Conclusions This study highlights the importance of considering not only the seasonality of plant responses to altered rainfall, but also the important role of interactions between abiotic and biotic drivers of vegetation change when evaluating ecosystem-level responses to future shifts in climatic conditions.This work was partially supported by a Higher Degree Research Scholarship from the Hawkesbury Institute for the Environment at Western Sydney University. Additional funding came from a project grant to SAP and SNJ from the Hermon Slade Foundation (P00021516) and funding provided by Western Sydney University. The Western Sydney University Library provided financial assistance for open access publication fees. Documen

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

Resilience vs. decline : precipitation and atmospheric change drive contrasting responses in invertebrate communities

Invertebrates form the foundation of terrestrial ecosystems, far outnumbering their vertebrate counterparts in terms of abundance, biomass and diversity. As such, arthropod communities play vitally important roles in ecosystem processes ranging from pollination to soil fertility. Given the importance of invertebrates in ecosystems, predicting their responses – and those of the communities they form – to global change is one of the great challenges facing contemporary ecology. Our climate is changing as a result of the anthropogenic release of greenhouse gases, including carbon dioxide (CO2), produced from burning fossil fuels and land use change. The concentration of CO2 in the atmosphere now exceeds the range the Earth has seen in the last 800,000 years. Through the effect of such gases on radiative forcing, sustained greenhouse gas emissions will continue to drive increases in global average temperatures. Additionally, precipitation patterns are likely to change across the world, with increases in the occurrence of extreme weather events, such as droughts, as well as alterations in the magnitude and frequency of rainfall events. Climate change is already causing measurable changes in the Earth’s biotic environment. Past work has been heavily focused on the responses of plants to various climate change parameters, with most studies including invertebrates limited to highly controlled studies of pair-wise interactions between one arthropod species and its host plant. Relatively little work to date, however, has looked at the potential impacts of climatic and atmospheric change for invertebrate communities as a whole. The overarching goal of this project was to help remedy this research gap, specifically by investigating the effects of precipitation and atmospheric change on invertebrate communities in grassland and woodland habitat, respectively. Chapters 2 and 4 synthesised recent work on climate change-driven alterations in precipitation and atmospheric change impacts on invertebrates in grassland and woodland systems, respectively. These chapters both highlighted the need for more community-level studies looking at the effects of global change on invertebrates, coupled with greater geographical representation across ecosystems. Particularly for atmospheric change studies, there has been a strong bias toward Northern Hemisphere plantation systems in previous work. Empirical research chapters 3, 5 and 6 used two state-of-the-art field-scale experimental platforms to address the question of how climatic and atmospheric changes will impact invertebrate communities in two Southern Hemisphere systems. Specifically, chapter 3 investigated how a subtropical grassland invertebrate community will respond to five climate change precipitation scenarios, including alterations in the seasonality, frequency and magnitude of rainfall events. Chapters 5 and 6 determined the effects of elevated concentrations of CO2 gas on the overall invertebrate (chapter 5) and ant community (chapter 6) of a critically endangered Eucalyptus woodland. Altered precipitation regimes caused highly variable responses in the abundance of invertebrates across the community, which were strongly seasonal and only weakly related to changes in the underlying plant community. The short-term, transient nature of the observed responses suggests that the invertebrate community – which has evolved against a background of strong precipitation variability in Australia – will be resilient to changes in rainfall. Elevated CO2 on the other hand, caused widespread declines in the populations of various arthropods across the community, including herbivore (-48.3%) and parasitoid (-14.7%) functional groups, with overall declines in total arthropod abundance of up to 14.7%. Despite these reductions, elevated CO2 did not measurably affect overall invertebrate community composition; the widespread declines across the community resulted in compositionally-similar communities comprised of fewer total individuals, compared with those under ambient conditions. However, for the ant community, shifts in the dominant genus-level ant populations occurring under elevated CO2 drove changes in ant assemblage structure. This, coupled with the general declines witnessed in the ant and broader invertebrate community, supports the notion that elevated CO2 could lead to changes in the ecosystem processes these organisms support. Taken together, these results present contrasting evidence for invertebrate community-level responses to climatic and atmospheric change. On the one hand, communities may be able to cope with future increases in precipitation variability, suggesting that the ecosystem processes underpinned by invertebrates may remain stable in this system. On the other hand, exposure to levels of CO2 not recently experienced within evolutionary timescales, could result in declines in the abundance of organisms that could play important roles in ecological processes. Avenues for future research are discussed, as well as the limitations and challenges inherent in field-scale, community-level climate change research

Grasslands, Invertebrates, and Precipitation: A Review of the Effects of Climate Change

Invertebrates are the main components of faunal diversity in grasslands, playing substantial roles in ecosystem processes including nutrient cycling and pollination. Grassland invertebrate communities are heavily dependent on the plant diversity and production within a given system. Climate change models predict alterations in precipitation patterns, both in terms of the amount of total inputs and the frequency, seasonality and intensity with which these inputs occur, which will impact grassland productivity. Given the ecological, economic and biodiversity value of grasslands, and their importance globally as areas of carbon storage and agricultural development, it is in our interest to understand how predicted alterations in precipitation patterns will affect grasslands and the invertebrate communities they contain. Here we review the findings from manipulative and observational studies which have examined invertebrate responses to altered rainfall, with a particular focus on large-scale field experiments employing precipitation manipulations. Given the tight associations between invertebrate communities and their underlying plant communities, invertebrate responses to altered precipitation generally mirror those of the plants in the system. However, there is evidence that species responses to future precipitation changes will be idiosyncratic and context dependent across trophic levels, challenging our ability to make reliable predictions about how grassland communities will respond to future climatic changes, without further investigation. Thus, moving forward, we recommend increased consideration of invertebrate communities in current and future rainfall manipulation platforms, as well as the adoption of new technologies to aid such studies

Forest invertebrate communities and atmospheric change

Predicting the responses of invertebrate species, and the communities they form, to global change is one of the great challenges facing modern ecology. Invertebrates play vitally important roles in forests, underpinning fundamental ecosystem processes like nutrient cycling and pollination. Changes in the composition of our atmosphere, associated with increased levels of carbon dioxide (CO2) and ozone (O3), have the potential to affect the abundance, diversity and structure of invertebrate communities and the ecosystems they support. This chapter reviews the findings from the body of work looking at the responses of invertebrates to changes inCO2 and O3 concentrations with a special focus on the results from Free-Air Enrichment studies. The most consistent finding across the studies we review is the idiosyncratic nature of the responses of invertebrate species to the elevation of CO2 and/or O3. This finding can be explained to some extent by bottom-up and top-down processes. These include the species- and genotype-specific responses of host plant chemistry and differences in the abilities of individual insect species to physiologically and behaviourally overcome changes in resource quality. Although evidence is clearly mixed, certain general conclusions can be made regarding the influence of CO2 and/or O3 on invertebrates. Forest invertebrate herbivores tend to respond negatively to elevated concentrations of CO2. This response is likely due to diminished food-plant quality. Conversely, predators and parasitoids may benefit under enriched-CO2 conditions as prey susceptibility increases. Elevated O3 concentrations generally have opposing effects: herbivores show a tendency to consume more and develop faster while higher trophic levels experience declines in performance. Therefore, simultaneous elevation of both gases, such as is found in reality, may moderate the effects of either gas in isolation. There also appears to be some capacity for invertebrate communities to rebound over time, as evidenced by long-term studies. From the few community-level studies available, the current conclusion is that the structure of invertebrate communities will not be strongly disrupted by increases in CO2 and O3. This suggests that the ecosystem processes underpinned by these communities may be maintained under future atmospheres in these systems, though more work is needed. Looking forward, we emphasize the critical need for long-term studies of invertebrate responses at the population and community-level within natural systems. Such studies will be particularly important in tropical regions where no such information currently exists. Studies incorporating multiple climatic and atmospheric factors will also be of great value, such as those looking at the combined effects of atmospheric change and alterations in water availability. These studies will allow us to better predict the effects of future climates on these fundamental ecological systems

Upsetting the order: how climate and atmospheric change affects herbivore–enemy interactions

Gaining a better understanding of climate and atmospheric change effects on species interactions is one of the great challenges facing modern ecology.Here, we review the literature concerning the responses of insect herbivores and their natural enemies to atmospheric and climate change, focusing specifically on elevated concentrations of atmospheric CO2 and air temperatures.We recommend that future work on the responses of systems to climate change incorporates as far as possible the trophic complexity inherent in ecosystems, and where feasible, considers the effects of interrelated climate factors in tandem. Such studies will produce more realistic insights into how species interactions may respond under future climates

Upsetting the order : how climate and atmospheric change affects herbivore-enemy interactions

Gaining a better understanding of climate and atmospheric change effects on species interactions is one of the great challenges facing modern ecology. Here, we review the literature concerning the responses of insect herbivores and their natural enemies to atmospheric and climate change, focusing specifically on elevated concentrations of atmospheric CO2 and air temperatures. We recommend that future work on the responses of systems to climate change incorporates as far as possible the trophic complexity inherent in ecosystems, and where feasible, considers the effects of interrelated climate factors in tandem. Such studies will produce more realistic insights into how species interactions may respond under future climates

Raw data from experiment

Raw data from experimen

An insect ecosystem engineer alleviates drought stress in plants without increasing plant susceptibility to an aboveground herbivore

Climate change models predict more extreme rainfall patterns, ranging from droughts to deluges, which will inevitably affect primary productivity in many terrestrial ecosystems. Insects within the ecosystem, living above- and belowground, may modify plant responses to water stress. For example, some functional groups improve soil conditions via resource provision, potentially alleviating water stress. Enhanced resource provision may, however, render plants more susceptible to herbivores and negate beneficial effects. Using a model system, we tested how plants (Brassica oleracea) responded to drought, ambient and increased precipitation scenarios when interacting with both a soil conditioning ecosystem engineer (dung beetles; Bubas bison) and an aboveground herbivore, the major crop pest Diamond back moth (Plutella xylostella). Dung beetles enhanced soil water retention by 10% and promoted growth in plants subjected to drought by 280%, relieving the impacts of water stress on plants. Under drought conditions, plants grown with dung beetles had c. 30% more leaves and were over twice as tall as those without dung beetles. Dung beetles produced a 2.7 fold increase in nitrogen content and more than a threefold increase in carbon content of the shoots, though shoot concentrations of nitrogen and carbon were unchanged. Carbon concentrations in roots, however, were increased by dung beetles under both ambient and increased precipitation regimes. Increased precipitation reduced root and shoot nitrogen concentrations by 16% and 30%, relative to plants under ambient regimes, respectively, most likely due to dilution effects of increased plant growth under increased precipitation. Soil carbon and nitrogen concentrations were largely unaffected. While dung beetles enhanced plant growth and nitrogen content in plants experiencing drought, the anticipated increase in plant suitability to herbivores did not arise, possibly because shoot nitrogen concentrations and C:N ratio were unaffected. To our knowledge, this is the first report of an insect ecosystem engineer alleviating the effects of predicted drought events on plants via physical manipulation of the soil matrix. Moreover, their effects did not change plant suitability to an aboveground herbivore, pointing to potential beneficial role for insect ecosystem engineers in climate change adaptation and crop protection