ProfessorDieter Hochuli

Project Opportunities

Title: Are ecological interactions in urban landscapes disrupted by shifts in biodiversity?

Summary of opportunity:

There are numerous opportunities for research projects pursuing questions driven by the main themes in our research.  My research group uses multi-species multi-scale approaches to give us a leaf to landscape understanding of insect-plant interactions. We’re currently examining herbivory, pollination and seed dispersal by insects in a number of contexts, looking at everything from the mechanistic underpinnings of these relationships to how landscape disturbances change the integrity of these interactions. 
The urban remnants of Sydney provide an excellent model system for studying ecological meltdown and the effects of urbanization. Remnant vegetation occurs in multiple urban contexts over several scales and can be compared with suitable spatially independent reference sites in areas managed for conservation. Using the model I will develop a globally significant case study integrating fundamental ecological principles within a dramatically altered environment to identify how ecological sustainability is compromised by urbanization Urban systems provide a distinctive context in which disruptions to ecological interactions through species shifts can be examined because the pervasive anthropogenic impacts in urban environments highlight dramatic shifts in biodiversity in urban habitats, driven by local extinctions and invasions by exotic species.
Multitrophic interactions are a vital tool for examining ecological meltdown. Increased levels of insect herbivory cause major functional changes to plant communities through localised dieback and regular outbreaks of insect pests in urban remnants have raised serious concerns over the long-term viability of these habitats. The well-known effects of urbanization on the physical landscape are potential mechanisms driving changes to rates of defoliation by herbivorous insects. Nutrient input heat island effects and increases of CO2 and O3 are all potential modifiers of leaf traits defining host plant quality. Urban sites may also be more productive than “natural” systems creating a haven for herbivores. The premise that predators and parasites suffer increased susceptibility to habitat fragmentation compared to herbivores and plants is consistent with the tenet that healthy systems support a rich diversity of parasites. 
The hypothesis that some predators and parasites are lost from urban sites is often supported although support across systems has been equivocal. Nevertheless, identifying parasite community responses to urbanization and subsequent functional consequences remain key unanswered questions in urban ecology. Tri-trophic plant-herbivore-parasite/predator systems provide ideal models for addressing these questions.

Opportunity synopsis:

Conserving remnant vegetation in cities is critical for two reasons: such vegetation is an important part of the quality of life for the 60% of the planet’s population who now live in cities; and in a rapidly urbanizing world, the remnants of urban vegetation are increasingly significant to total biodiversity. The long-term future of these habitats is ultimately dependent on the understanding of the broader ecological impacts of cities on remnant vegetation. In particular, the maintenance of ecological interactions is crucial to the ecological integrity and health of urban ecosystems.

Ecological meltdown is a consequence of fundamental and dramatic changes to ecological communities in fragmented habitats, driven by the disruption of ecological interactions through the losses of species with higher trophic roles.  The hyperabundance of herbivores in predator-free fragments is typically ascribed to shifts in the relative strength of top–down and bottom–up regulation of plant and animal communities. These biotic processes manifest as trophic cascades, where predators regulate the abundance of herbivores and subsequently affect plant biomass. Ecological meltdown may be a direct result of disruptions to important mutualisms vital to plant reproduction, such as pollination and seed dispersal.  In this context, plant–insect interactions provide compelling indicator systems for detecting structural and functional changes to the ecology of fragmented and disturbed landscapes.

This project will advance our understanding of how fragmented habitats remain viable by asking; Have shifts in species composition disrupted ecological interactions so severely that ecological integrity is compromised?  The project will provide the missing links between ecological patterns and process in urban systems, creating a framework for understanding the ecology of urban remnants that is relevant to all fragmented habitats, whether urban or otherwise.

The aim of this project is to understand how urbanization changes the composition of insect assemblages in remnant vegetation, and how these changes affect a crucial ecological interaction – herbivory, identifying how urbanization affects arthropod assemblages on dominant trees, and the associated levels of herbivory.