Resource Predictability and Movement Strategies in Ungulates: Does Temporal Uncertainty Lead to Nomadism?
The movements of all animals are affected by their need for resources such as food. Where and how quickly animals move often depends on where the best vegetation resources can be found and how predictable this food is from year to year. Some ungulate species with predictable environments migrate seasonally; caribou and wildebeest are examples of this. A few other species - gazelles, for example - appear to make large-scale, long-range movements that are seemingly unpredictable. This 'nomadism' likely occurs when the availability and location of resources varies considerably by season and by year. To make sense of these seasonal and annual movement strategies, researchers will combine: 1) theoretical computer models, 2) landscape-scale satellite images of vegetation, and 3) detailed movement data from individual gazelles in Mongolia (new field studies) and caribou in Alaska (historical data). By understanding long-distance animal movements, we will be in a much better position to know how environmental variability affects animal behavior. The conservation of these species and their habitats depends on understanding their large-scale movement patterns and ecology. Our research will help identify the mechanisms by which animals 'read' their environment to know when and where to move over complex landscapes.
Research in this project made significant findings with regard to gazelle movements in particular and also contributed more generally to the emerging field of movement ecology and to the conservation of the eastern steppes of Mongolia. From a scientific point of view, it has long been known that migratory animals move long distances between distinct summer and winter ranges, but our first major discovery was that that gazelles exhibit a fundamentally different kind of movement pattern. In common with more typical migratory animals, gazelles do move extremely long distances (hundreds to 1000+ kilometers total distances in a given year); however, they do not follow any kind of regular 'migratory' patterns between distinct summer and winter ranges. We labeled this new movement pattern that we observed 'nomadism'. We showed that these nomadic movements are likely driven by stochastic rainfall events and demonstrated that they have important conservation implications since individual fixed protected areas cannot be large enough to conserve gazelles. The importance of unpredictability in long distance animal movements has been brought to a general audience with a publication in Science Daily that highlights our work: www.sciencedaily.com/releases/2011/05/110511142138.htm Our research also showed significant effects of human settlements on gazelles and we used our findings to communicate to stakeholders that new and integrative conservation strategies are needed that will pertain to the entire steppe region. Our data were used in a report to the World Bank, and our study was instrumental for demonstrating the potential risks that fencing of new railroad projects may have on long distance movements and population viability of gazelles and other large herbivores such as khulan and goitered gazelle. The report provides many suggestions for policymakers how to best mitigate barrier effects of newly developed infrastructure projects. Beyond the specific findings about gazelle movements and our contribution to knowledge that will help conserve this remarkable species, our team also made several findings that are of general importance to the field of movement ecology. In particular, we developed methods to quantify movement patterns between individual animals: these new techniques allowed us to do a comparison between 4 different species and to show quantitatively that nomadism is distinct from other population level movement patterns such as range residency or migration. Using the field data that we collected in Mongolia, colleagues of ours were able to implement novel movement simulation techniques based on artificial intelligence methods that can detect the underlying navigational mechanisms of moving animals. We used these methods to demonstrate that animals who live in landscapes with unpredictable food resource tend to evolve a strategy of searching randomly for forage, while in more predictable seasonal landscapes, animals evolve to depend more heavily on spatial memory. We further demonstrated ways in which these behavioral mechanisms can have important consequences for animal populations when movement barriers (such as fences, roads or railway lines) are introduced to the landscape. Our final major scientific outcome was to demonstrate that a social transfer of spatial knowledge is critical for the survival of these animal populations, and we showed how a lack of leadership in animal populations can lead either to range residency or even to population collapse. Collecting animal tracking data like the gazelle movement data in this project can take a huge investment of time, effort, and funding. In order to maximize the value of the data we collected and to make it available to other researchers, we have archived the data at a widely-used online repository called movebank.org. In the past, after the scientific papers about a study like this one had been published, these data would usually have been privately stored and never used again. By archiving these data and making them publicly accessible, other people will now be able to address their own questions with our tracking data, and will be able to build upon the work we have done.
