Dr Dirk Sanders
Environment and Sustainability Institute desk 40, 1.03
Environment and Sustainability Institute, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK
My research aims to link the structure of ecological communities to ecosystem processes, such as predation, pollination and ecosystem engineering, and the stability of these communities. In this context I am interested in the interplay of mutualistic and antagonistic, trophic and non-trophic interactions. A particular focus of my research is to reveal mechanisms of secondary extinctions and their consequences for ecological communities.
2008 PhD (University of Goettingen)
2013– Research Fellow, University of Exeter, Cornwall Campus
2011–2013 Assistant with independent research, University of Bern, Switzerland
2010–2011 Post-doctoral research fellow, University of Exeter, Cornwall Campus
2009–2010 Post-doctoral research fellow, Imperial College London, Silwood Park
Jumping spider Aelurillus v-insignitus. Photo credit: Dirk Sanders
The parasitoid Aphidius megourae attacking the aphid Megoura viciae. Photo credit: Dirk Sanders
Myrmica rubra. Photo credit: Dirk Sanders
My research explores the link between the structure of ecological communities and their stability. As carnivores appear especially vulnerable to global change and with their loss often causing disproportionate changes in community composition across trophic levels, there is a need to understand the implications of carnivore extinctions for ecosystem stability. My research aims to understand the ecological consequences of such losses and how they are transmitted through the network of interacting species. Experiments are a powerful tool to test this impact as they demonstrate the actual community response to species loss. I have manipulated predator presence and abundance, predator functional diversity, and the presence of predators that also act as mutualists or ecosystem engineers in various field experiments. As model systems I use (i) aphids, their parasitoids and hyperparasitoids, and (ii) soil bacteria as hosts for plasmids.
1. Vulnerability of ecological communities to extinction cascades (NERC)
Initial species losses are often followed by secondary extinctions of other species, for not always obvious reasons, with the danger that this leads to a cascade of further extinctions and ecosystem collapse. Predicting these cascades is challenging and requires a detailed understanding of how the interconnectedness of species in ecosystems affects the transmission of human impacts on one species to other species that are not directly linked to it. This is particularly important for species at higher trophic levels (carnivores) which are most vulnerable to extinction. The idea has long existed that species of carnivore that specialise on different prey have positive effects on each other by limiting their prey populations and thereby preventing one prey species from outcompeting the other. A consequence of this is that if a carnivore is lost from the community, its prey is released from control and may subsequently out-compete the other prey species leaving the other carnivore without food and facing extinction. This is potentially an important mechanism by which extinction cascades occur, however, it is difficult to obtain experimental evidence for such effects. We study these mechanisms in field experiments using aphid-parasitoid communities.
2. Integration of food webs and ecosystem engineering
Ecosystem engineering (the modification of the physical environment by organisms) is an important interaction in most ecosystems. When these engineers are trophically coupled to food webs as producers, consumers or decomposers, there is obviously the potential for trophic feedbacks to alter engineer density and engineering activity. This can then lead to a change in the degree to which the environment is modified, subsequent modification of trophic interactions affecting food webs dynamics and stability.
3. Interaction type drives network structure (NERC). Ecological communities exist as networks of interacting species, and the structure of these networks determine their stability and function. Observational studies suggest that network structure depends upon whether interactions between species are predominantly mutualistic or antagonistic, however the causality of this relationship remains unclear. Here, we will use communities of bacteria and their symbiotic plasmids to experimentally determine how interaction type (mutualistic versus antagonistic) affects community network structure. Our system is ideal to address these questions because bacteria-plasmid interactions can be switched from antagonistic to mutualistic through simple environmental manipulations (the addition of antibiotics to which the plasmids confer resistance), and changes in community network structure can be observed over a matter of weeks. The large-scale of this project is made possible by the application of a novel culture-free method, epicPCR, which allows high-throughput assessment of bacteria-plasmid associations. The predicted role of ecological stability, as well as novel eco-evolutionary mechanisms, underpinning the interaction type-network structure relationships will be assessed by a combination of phenotypic and genetic experiments complemented by theory.
Sanders, D., Frago, E., Kehoe, R. , Patterson, C., Gaston, K.J. (2021) A meta-analysis of biological impacts of artificial light at night. Nature Ecology Evolution 5, 74–81. https://www.nature.com/articles/s41559-020-01322-x
Sanders D., Kehoe, R., Cruse, D., van Veen F.J.F., Gaston, K.J. (2018) Low levels of artificial light at night strengthen top-down control in insect food web. Current Biology 28, Issue 15, 2474-2478. https://www.sciencedirect.com/science/article/pii/S0960982218307462
Sanders, D.,Thébault,E., Kehoe, R., van Veen, F.J.F. (2018) Trophic redundancy reduces vulnerability to extinction cascades. Proceedings of the National Academy of Sciences 115 (10) 2419-2424; https://www.pnas.org/content/115/10/2419.short
Sanders, D., Kehoe, R., van Veen, F.J.F., McLean, A., Godfray, H.C.J, Dicke, M., Gols, R., Frago, E. (2016) Protective insect symbiont leads to cascading extinctions and community collapse. Ecology Letters 19. http://onlinelibrary.wiley.com/doi/10.1111/ele.12616/full
Sanders D., Kehoe, R., van Veen F.J.F. (2015) Experimental evidence for the population-dynamic mechanisms underlying extinction cascades of carnivores. Current Biology 25, Issue 23, 3106–3109. http://www.sciencedirect.com/science/article/pii/S0960982215012452
Sanders D., Sutter, L., van Veen F.J.F. (2013) The loss of indirect interactions leads to cascading extinctions of carnivores. Ecology Letters, doi: 10.1111/ele.12096 http://onlinelibrary.wiley.com/doi/10.1111/ele.12096/full