Integrated ecological assessment and modelling of chytridiomycosis in support of sustainable farmland pond management

Abstract

Amphibians across the globe are experiencing alarming declines, with about half of all known species vulnerable to extinction. One of the drivers is the parasitic chytrid species Batrachochytrium dendrobatidis, which is a major causal agent of the virulent, infectious disease chytridiomycosis. To counteract population losses, it is important to create endemic situations in which the host-pathogen interaction constitutes a co-existence in the absence of mass mortality events. Investigating the chytrid infection requires an integrated view as it is in influenced by a variety of intertwining factors. Models are useful tools to help understand the epidemiological processes. However, the level of integration in current infection models is limited. In this PhD research, we aimed to provide integrated ecological insights in chytrid infection via models. Farmland ponds were the ecosystems of interest because they are likely to play a key role in infection mitigation. First, we investigated the habitat requirements of the alpine newt, a major chytrid host. Both fish absence and low levels of eutrophication and erosion ensured the presence of the alpine newt. Second, we developed a model which allowed to make a prediction of the infection probability based on several infection-steering ecological variables. Infection risk reduced with low host density, periodic drying and, to a lesser extent, low total phosphorous levels and low water temperatures. This model did not incorporate any non-host species interactions. However, biological control is a promising infection mitigation strategy as it involves the reduction in infectious motile zoospores in the water column through direct consumption by zooplankton. In the third research topic, we modelled the predation behaviour of two common water fleas in farmland ponds. The models revealed that water fleas mutually interfered with each other whilst feeding on zoospores and ingestion rate was positively related to body size. The results of this PhD research provide useful insights and tools for sustainable farmland pond management