The Conservation of Species Under Pathogen Pressure and Climate Change

Group Leader: Drew Harvell

Rapporteur (and public contact): Charles Mitchell

Other contributors: Bob Holt



Climate change models predict global-scale increases in mean temperature and moisture. Other large effects predicted are an increase in sea level and abrupt shifts in ocean currents. Climate change will cause changes in teh distribution and abundance of species, creating new conservation problems. Furthermore, the predicted climate changes should increase, perhaps substantialy, the probability of pathogen outbreaks in terrestrial and marine systems. Impacts will act with non-linear thresholds associated with changing host density adn temperature, both through changing species ranges and through direct changes in probability of transmission adn establishment of pathogens as well as degree of resistance and virulence. Therefore, considering the effects of climate change on disease will be essential to developing effective conservation measures.

We predict that increased warming and moisture wil cause increased pathogen outbreaks through the dual mechanisms of increased transmission of disease and compromised host resistance. Already small seasurface temperature changes are causing large impacts in the form of coral bleaching that could make corals more susceptible to disease and push pathogens closer to temperature optima. Through literature review, we will determine the relative importance of increased pathogen transmission versus decreased host resistance in facilitating the outbreak of new diseases in marine and terrestrial habitats. If the result of climate change is warmer and moister condistions in temperate regions, then we might expect tropical-like parasite distributions in temperate. We will review literature on latitudinal gradients to examine these predictions. Are parasites more prevalent and do they have a bigger impact in the tropics? Water plays a large role in the life cycle of most parasites, thus moister conditions would strongly favor increased parasite prevalence, particularly for vector borne and directly transmitted diseases.

The epidemiologically structured SIR model will be developed with basic parameters functions of temperature, to explore the non-linear effects of temperature on changing probability of outbreaks through effects on transmission and resistance. The model will be used to explore the conditions under which outbeaks will be favored by changes in disease transmission vs changes in host resistance.

Our objectives here are to review the prevalence and intensity of disease and consider how changing climate conditions projected by climate change models will affect these already intermittent, threshold phenomena. The particular focus here is also to understand how the combined pressures of climate change and disease will interact to threaten conservation efforts. Or rather, to develop particular recommendations to conserve species and intact comunities under the combined stress of disease and climate change.