A report by Sarah Perkins and Ali Dunn
The Parasites and Invasions Thematic Topic addressed the importance of enemy release in the context of parasites and pathogens, asking whether invaders really are bigger and better; what is the impact of introduced parasites; and how parasites modify native -invader interactions.
Mark Torchin, Helen Roy and Joe Ironside discussed the concept that invasive species have escaped the regulatory effects of parasites giving examples that included giant crabs, killer shrimps and un-harmonious ladybirds. But parasites are not always lost, as Ian Montgomery told us in his study of ectoparasites of an invasive vole in Ireland where he described the potential for pox mediated invasional meltdown in the native fauna, whilst Catherine Jones showed that invasive bumblebees have not lost their parasites, but instead may be showing adaptation towards reduced virulence.
Mark used biogeographical comparisons to show how loss of parasites in the invasive common shore crab can lead to dramatic increases in body size. He also illustrated the importance of parasites in estuarine ecosystems, with the biomass of trematodes outweighing that of the top (bird) predators. Given the role of parasites in foodweb dynamics, he ended by posing the intriguing question – what will be the impact of parasite loss in heavily invaded ecosystems?
Our speakers addressed whether the loss of parasites may translate into the evolution of increased competitive ability through reallocation of resources (Peter Kotanen, Line Ugelvig). Peter focuses on every hayfever sufferer’s worst nightmare- ragweed. His manipulation experiments showed how a small amount of isolation reduces enemies which translated into increased seed survival. The interesting question posed by Peter is will range expansion under climate change favour invasive over native species as a result of enemy loss? Line demonstrated decreased genetic diversity in invasive ants resulting in compromised behavioural immunity whilst Joe demonstrated a loss of genetic diversity and parasite fauna in invading shrimps.
A pervasive theme was the role of disease in mediating invasions through a range of trophic interactions. We saw how pox virus has speeded up competitive replacements of the red squirrel by the grey (Mike Boots). Mel Hatcher looked at the sublethal effects of parasitism on host behaviour; including the effect on intraguild predation; she showed that parasite-induced effects on host predation traits can potentially have as strong an impact on invasion dynamics and community structure as the more often considered effects of parasite-induced mortality.
The control of invasions in complex multispecies systems was discussed by Mike Boots and Lucy Gilbert. Lucy showed that removal of mountain hares may not prevent louping ill emergence given that even low densities of deer can lead to tick invasion across the landscape. Shelley Lachish reported an invading pathogen in the well studied Wytham wood great tits showing how the disease compromises fledging success. Mike highlighted how spatial spread of biological weapons could play a role in many systems and how refuges and buffers with limited connectivity can slow down epizootics. The importance of citizen science was clear in reporting the spread of invasive species (Helen & Catherine) as well as reporting the emergence of novel pathogens such as pox virus in great tits (Shelley).
Sarah and Ali had great fun working with our speakers and look forward to the special feature in Functional Ecology stimulated by this symposium.