Research Themes

My research is focussed on trophic interactions as fundamental drivers of stability and coexistence in a changing world. Central themes include understanding the role of body size, temperature and physical habitat structure in driving the strength and form of trophic interactions, particularly in the context of biological invasions. The trajectory of my work is driven by the recognition that generalising trophic interactions from metabolic first-principles is parsimonious but provides only a partial picture. For example, the dimensionality and physical complexity of a consumers’ search space—along with factors such as fear—can have non-random effects on interaction strengths. Perhaps surprisingly, good data is hard to come by in this area of ecology, so I focus on efficient, high-turnover experimentation to produce the largest single-system datasets of their kind, in conjunction with experiments that represent the first attempts to understand the role of habitat structure in a non-confounded manner. My motivations are threefold: (i) to discover new and meaningful patterns of resource consumption; (ii) to build datasets capable of parameterising whole-system models, and; (iii) to use these data to develop tractable conservation applications.

Key Findings

CONTEXT-DEPENDENT SCALING (CDS): Metabolic Theory (MT) sets limits on feeding rates according to body size. But, beyond temperature, MT cannot make predictions that link feeding rates with a consumer’s physical environment. My work is the first experimental study—and the largest of its kind—that attempts to unpack the effects of the dimensionality and complexity of a consumer’s search space on the size-scaling of feeding rates. CDS suggests that changes in physical context drive non-random changes in the size scaling of feeding rates that are underpinned by changes in consumer detection regions and contact rates. Unifying MT and CDS into a single body of theory requires a new programme of work focussed on high turnover experiments that simultaneously quantify the effects of metabolic and physical factors on trophic interactions.

fig3

The size scaling of interactions is context-dependent. Interactions at optimal consumer-resource size ratios are disproportionately dampened by complex habitats, resulting in a collapse of the typical unimodal distribution. Barrios-O’Neill, D. et al. On the context-dependent scaling of consumer feeding rates. Ecol. Lett. 19, 668–678 (2016).

PREDATOR-FREE SPACE: Predator-free space is one of several poorly-characterised facets of physical habitat structure that can mediate trophic interactions. My work is the first to explore the effects of continuous changes in refuge space without confounding other facets—such as surface area and volume—and demonstrates that predator-free space has systematic effects on interaction shape and magnitude. This work highlights the limits of our understanding of vis-à-vis interactions and other quantifiable, continuously variable facets of habitat structure.

fig1

Artificial reefs (schematic circles: identical surface area and volume) with increasing predator-free space dampens trophic interactions. Barrios-O’Neill, D. et al. Predator-free space, functional responses and biological invasions. Funct. Ecol. 29, 377–384 (2015).

TRANSIENT KEYSTONE SPECIES: Keystone predators elicit strong consumptive and non-consumptive effects on lower trophic levels. However, my recent work has shown how these effects are contingent on the presence or absence of complex habitat structure, with keystone function disappearing where such structure is present. Where structure is itself provided by, for example, reef-forming species, feedbacks can downregulate keystone function—a pattern that characterises the concept of transience. Transience suggests that useful generalisations of top-down effects across systems cannot be made without incorporating the effects of habitat structure.

fig2

Apex predator effects on intermediate-basal interactions depend on habitat structure generated by basal reef-builders. Barrios-O’Neill, D., Bertolini, C. & Collins, P. C. Trophic cascades and the transient keystone concept. Biol. Conserv. 212, 191–195 (2017).