Experimental community and thermal ecology of rainforest Drosophila and their parasitoids

Thesis

Climate change is altering global biodiversity patterns and the ecological functions provided by nature. Species do not react to climate change independently: changes in one species’ distribution, abundance and performance influence, and sometimes reverse, the fundamental reaction of other species to climate change. Consequently, the observed shift in distribution and abundance of co-occurring species within a community vary widely. Understanding the causes of the varied responses is essential for predicting biodiversity changes and their ecological impact. Using a tropical Drosophila-parasitoid system in the lab, I investigated the determinants of species turnover on elevation-driven thermal gradients, as well as how species interactions alter responses of population and community to rising temperatures.

First, I compare the thermal traits and competitive ability of Drosophila species found along tropical elevational gradients. I demonstrate that reproduction limits imposed by high temperatures set the warmer boundaries, and that competitive exclusion explains the absence of lowland species at high elevations. Next, I study the impact of parasitism on the heat tolerance of host populations. I show that the interactive effects of parasitism and heatwaves on the mortality in host populations can be additive, antagonistic and synergistic, depending on the availability of protein resources and host identity. I then use mesocosms to investigate how different modes of rising temperatures (i.e. extremes vs. general warming) influence the range expansion of lowland Drosophila species, and their combined impact on the composition of the high-elevation Drosophila-parasitoid community. I show heatwaves but not general warming facilitate the establishment of the lowland species in the high-elevation community, which surprisingly increases the resident Drosophila abundance through its suppression of parasitoids. Finally, I focus on the contribution of parasitism to the coexistence of host species. This collaborative work highlights that the impact of a generalist parasitoid on host coexistence is idiosyncratic among different host pairs. Overall, this dissertation shows that rising temperatures, particularly through high-temperature extremes, have a significant impact on species range and community composition; and parasitism serves as a key species interaction that mediates the indirect impact of climate and novel species on populations and communities.

Authors: Chen, J

• DOI: 10.5287/ora-7e2q74dbb
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: host-parasitoid interaction; modern coexistence theory; parasitism; Drosophila; rainforest; nutrition; thermal performance curve; species coexistence; extreme heat event; novel biotic interaction; species distribution; range shift; top-down regulation; biotic competition; global warming; multiple stressors
• Subjects: Drosophila; Biotic communities; Zoology; Wet Tropics of Queensland World Heritage Area (Qld.); Ecology; Climatic changes; Parasitoids--hosts; Biodiversity