When host populations move north, but disease moves south:
counter-intuitive impacts of climate warming on disease spread
Abstract
Empirical observations and mathematical models show that climate warming
can lead to the northern (or, more generally, poleward) spread of host
species ranges and their corresponding diseases. Here, we consider an
unexpected possibility whereby climate warming facilitates disease
spread in the opposite direction to the directional shift in the host
species range. To explore this possibility, we consider two host
species, both susceptible to a disease, but spatially isolated due to
distinct thermal niches, and where prior to climate warming the disease
is endemic in the northern species only. Previous theoretical results
show that species’ distributions can lag behind species’ thermal niches
when climate warming occurs. As such, we hypothesize that climate
warming may increase the overlap between northern and southern host
species ranges, due to the northern species lagging behind its thermal
tolerance limit. To test our hypothesis, we simulate climate warming as
a reaction-diffusion equation model with a Susceptible-Infected (SI)
epidemiological structure, for two competing species with distinct
temperature-dependent niches. We show that climate warming, by shifting
both species’ niches northwards, can facilitate the southward spread of
disease, due to increased range overlap between the two populations. As
our model is general, our findings may apply to viral, bacterial, and
prion diseases that do not have thermal tolerance limits and are
inextricably linked to their hosts’ distributions, such as the spread of
rabies from arctic to red foxes.