Arctic ecosystems are natural laboratories for climate change studies, because they are simple and undergo rapid warming. We have collected 25 years of ecological data from the simple terrestrial ecosystem of Svalbard, where reindeer is a keystone species. Data compose of vital rates of the reindeer as well as detailed data on the plant species composing their forage as well as their parasites. I our last project we also started collecting physiological data to investigate if Svalbard reindeer is ?trapped in a cold-adapted body?, results and methods we continue to build on in the current project. We focus our research around the paradox that the reindeer population has increased 2-3 fold in a time period with rapid climate change, by investigating if this change is due to changes in the diet plants, a relaxation of parasite load or ongoing behavioral and physiological adaptations. Our results will improve our understanding of adaptations to climate change in Arctic mammals.
In the botanical work package, PhD student Sam Dwinnell and master student Jacque Wanjiru have conducted one experiment and one observation study. The aim of both studies is to study how plant biomass buildup and phenology in summer impact on the diet quality and quantity in autumn and winter. In the experiment, Open Top Chambers (OTCs) in combination with heaters was used to heat plots to ca 2 and 6 degrees warmer than control plots. This is conservative treatments given that the worst climate predictions is up to 10 degrees warmer summers in Svalbard in a 100 year perspective. The experiment is just ended and we can visually see that some of the heated plots are greener than the controls, suggesting that warmer autumns delay plant ?brown down? and improve feeding conditions for reindeer in autumn. In the observation study we have investigated biomass and timing of senescence in three focal vegetation types. From GPS-collared reindeer, we have learned that individuals often select wetland in late autumn and we have asked the question if this is because of later plant senescence or simply access to high biomass dead residue. This work is still ongoing.
In the parasite work package, we asked the question if the reindeer population increase because regulation from gut nematodes has stopped. We got exiting preliminary results. Despite the 2-3 fold population increase, normally expected to increase parasite load, microscopy of reindeer feces relieved only half the number of parasite eggs as in our historic samples from the late 90?es. In October, 20 female reindeer will be culled and adult parasite count in the abomasum will provide the gold standard for assessing parasite load decline (samples of culled animals will be used for a multitude of other purposes, such as bacterial microbiome to answer questions related to the ?ecology within? under a different work package). We speculate if this is due to lower survival of the free-living parasite stage due to climate warming. We established a warming experiments (in the same plots as plants; see above) by deploying 100 larvae into small open-ended plastic tubes. Unfortunately, the current set up failed because we got recovery rates between 50 and 200%, where >100% indicate that parasitic larvae were already present in the soil in the plots. We are refining the protocol and make a new attempt next year. This work was done by PhD student Tirza Moerman and master student Harald Lislegaard.
In the physiology work package we investigate mechanism of individual variation in energy conservation. In our earlier project we found that individuals had large variation in their ability to conserve energy by reducing body temperature and heat loss to the environment. To investigate this mechanistically we sampled muscle and fat biopsies from 60 individuals this winter and at the same time deployed heart rate and temperature loggers. this work package is led by hibernation physiologist Walter Arnold. Interestingly, we se a large individual variation in omega-6 level in fat and also in what is termed SERCA activity. The latter is a quantification of how well cell walls function under cold muscle temperatures, a prerequisite for ability to reduce body temperatures without muscle malfunction. We will follow up this next summer by hunting for omega-6 rich plants that may be a crucial component in the reindeer diet as well as investigate feeding-ecology differences in the GPS-marked animals leading to the large individual variation in omega-6 fat content. This work will be led by Post Doc Monica Trondrud.
Terrestrial Arctic ecosystems are natural laboratories to study the effects of climate change, because of their simplicity and fast rate of warming. In Svalbard, reindeer are a keystone species directly affecting lower (plants and parasites) and indirectly higher trophic levels (carrion for Arctic fox), and therefore central to understanding ecosystem resilience. For more than 20 years we have studied tundra vegetation dynamics, reindeer impacts on habitat structure and ecosystem processes. At 4500 captures of 1000 individual reindeer we have the largest dataset for any Arctic herbivore. Two decades ago, we published what became a textbook study reporting that reindeer were strongly food limited and regulated by gut parasites, rendering the subsequent doubling of the population size an unsolved paradox. In our current RCN project, we discovered two phenotypes with contrasting thermoregulatory physiology; one drops subcutaneous body temperature to save energy, while the other keeps a stable high temperature throughout winter. The two phenotypes also differed in their diet, gut microbiome, body mass dynamics and reproduction, begging the question if one is better adapted to the ‘old’ and the other to the ‘new’ climate regime. We will develop innovative models of how the different phenotypes contribute to reindeer population growth, as the climate continues to warm. However, such models would not be realistic without considering trophic interactions, leading us to return to our unsolved population increase paradox, by investigating the role of higher plant productivity and the possible loss of parasite regulation. By looking at the issue of climate change in the Arctic through the prism of an ecosystem engineer, Svalbard reindeer, our work plan is both novel, because of its holistic scope, working across boundaries of sub-disciplines in biology, and ambitious, in moving empirical measurement out of traditional laboratory settings, into a rapidly warming world.