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

Abstract

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.

Date of Award	2016
Original language	English