| dc.description.abstract | Climate change has the potential to disrupt phenological synchronization between parasitic nematodes and their hosts, which may have implications for host regulation. Understanding the parasitic-climatic relations within ecosystems that are vulnerable to climate change is crucial for
disease management and conservation. Svalbard, an inherently simple ecosystem with a high
susceptibility to climate change, serves as an ideal site to study the dynamic between parasites
and hosts regarding climate. Historically the parasitic nematode Ostertagia gruehneri has regulated
Svalbard reindeer (Rangifer tarandus platyrhynchus) populations by reducing fat reserves, thereby
lowering fecundity, and limiting population growth. However, in the last two decades, reindeer
populations have more than doubled, raising questions about potential changes in the parasites’
life cycle. This study examines two potential factors that may explain the lack of regulatory
impact on host populations due to changes in infection risk. First, a dynamic simulation model
based on known parameters that govern nematode survival and developmental rates was used to
examine whether the potential negative effects of warmer temperatures outweigh the positive
effects of reindeer density, on seasonal abundance of the infective nematode stages in the
pasture. Historical (1997), present (2022), and potential future (2070-2100) temperature data
were examined alongside observed reindeer densities (1995-2021). Secondly, these simulated
seasonal curves were compared to empirical grazing height data throughout the growing season
(2022), to examine if a phenological mismatch may have occurred from reindeer feeding at
higher stratums during peaks in nematode availability, as feeding near moss levels may increase
infection rate. This study revealed that temperatures representing the warmest year (2022) had a
modest adverse impact on the availability of parasites in contrast to the coldest year (1997) when
the reindeer population was held stable in the model. However, when factoring in the observed
increase in reindeer densities from both cold (historic) and warm (recent) years, the large positive
effect of increased number of hosts outweighed the small negative impact of temperature.
Furthermore, infections that occur early in the season might be lessened due to potential shifts in
vegetation season and growth, further distancing the infection risk of feeding near soil levels
during predicted growth of nematode occurrence in the pasture, leading to a potential
phenological mismatch. This study underscores the challenges inherent in comprehending
parasitic-host relationships in the natural environment and emphasizes the need to adopt a
holistic approach that considers multiple factors that may impact complex multi-species systems. | |
