Heterogeneity in patch quality buffers metapopulations from pathogen impacts
Daniel J.
1
Becker
and Richard J.
1,2
Hall
1Odum
School of Ecology, University of Georgia
2Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia
Background
Modeling approach
Simulation results
Many wildlife persist as metapopulations on a network of
ephemerally occupied habitat connected by dispersal.
For metapopulations in decline (c < xL), metapopulation persistence always requires
some degree of resource improvement (extinction in black at low f and q).
A common conservation practice for rescuing declining
metapopulations is to increase habitat patch quality
through provisioning of food resources.
Along a gradient of increasing patch quality (q) and the fraction of high-quality
patches (f), resource improvement first promotes disease-free metapopulation
persistence (white), followed by pathogen invasion to an endemic (light blue) or
pandemic equilibrium in which all occupied patches are infected (dark blue).
Yet provisioning can also harm wildlife by facilitating the
local transmission and spatial spread of pathogens such
as Mycoplasma gallisepticum in house finches.
Under moderate local resource improvement (q = 2), occupancy is maximized for
mixtures of low- and high-quality patches, and pathogen invasion only occurs when
the majority of patches are provisioned.
A pressing need exists to understand how the effects of
local resource improvement influence landscape-level
infection dynamics and metapopulation persistence.
House finch © A. Davis
Study objectives
Our primary objective is to ask under which conditions
resource improvement can reduce or improve patch
occupancy in the presence of a virulent pathogen.
Here we develop a simple metapopulation model to
determine how equilibrium occupancy and pathogen
prevalence are related to two parameters describing
resource improvement across a landscape:
Yet with strong local provisioning (q = 4), the pathogen not only invades at a lower
fraction of improved habitat, but also can establish and infect all occupied patches.
(a) We use differential equations to model patch transitions
between three types: unoccupied (black), occupied by the
host but not the pathogen (white), and occupied by host and
pathogen (infected, blue).
(b) We consider two patch types: unmanaged (low quality,
square) and improved by resource provisioning (high
quality, circle). The parameter q is defined as the ratio of the
persistence times of high- versus low-quality patches.
(c) The metapopulation is configured by defining the fraction
of patches at which resource improvement occurs (f).
(d) A snapshot of metapopulation structure and (e) a time
series of total patch occupancy and pathogen prevalence.
1.  The increase in patch quality due to provisioning (q)
2.  The fraction of patches improved by management (f)
Daniel Becker
PhD Candidate
Email: [email protected]
Although improving habitat patch quality is necessary to prevent the extinction of
declining metapopulations, making resource conditions “too good” has
consequences for the invasion and spatial persistence of virulent pathogens.
Our finding of maximized occupancy at mixtures of low- and high-quality habitat
patches suggests that resource-poor patches may act as “sinks” for pathogens, as
infected low-quality patches undergo rapid local disease-induced extinction.
By varying these parameters, we derive the following:
1.  Conditions for metapopulation persistence
2.  Thresholds for pathogen invasion and persistence
3.  Equilibrium occupancy and infection prevalence
Conclusions
(e)
)
Therefore, heterogeneity in habitat patch quality may be an under-recognized
mechanism for buffering metapopulations from pathogen impacts.
Acknowledgements: We thank Sonia Altizer and members of the Altizer and Ezenwa Labs at the
University of Georgia for helpful comments and insight. Funding was provided by the National Science
Foundation, the Odum School of Ecology, and the ARCS Foundation.