Abstract
AbstractStudying nomadic animal movement across species and ecosystems is essential for better understanding variability in nomadism. In arid environments, unpredictable changes in water and forage resources are known drivers of nomadic movements. Water resources vary temporally but are often spatially stationary, whereas foraging resources are often both temporally and spatially variable. These differences may lead to different types of nomadic movements: forage‐ vs. water‐driven nomadism. Our study investigates these two different types of nomadism in relation to resource gradients from mesic steppe to xeric desert environments in Mongolia's Gobi‐Steppe Ecosystem. We hypothesized that in the desert, where water is a key resource, animals are more water‐dependent and may show water‐driven nomadism with frequent revisits to spatially fixed resources, while in the steppe, animals are less water‐dependent and may show forage‐driven nomadism, tracking high‐quality foraging patches with infrequent revisits to previously used resources. We utilized GPS movement data from 40 individuals of four ungulate species (Mongolian gazelle, goitered gazelle, saiga antelope, and Asiatic wild ass) in the Gobi‐Steppe Ecosystem. We calculated displacement distances and recursion metrics and subsequently performed a principal component analysis to quantify the variation in movement patterns. The satellite‐derived vegetation greenness served as a proxy for the resource gradient and was associated with variation in movement behaviors described by the first principal component, demonstrating that the variability in movements was closely related to the resource gradient from mesic to xeric habitats. We showed that ungulates in the resource‐rich steppe tended to move long distances with few revisits (forage‐driven nomadism), while ungulates in the resource‐poor desert tended to move shorter distances with more revisits (water‐driven nomadism). Our results suggest that xeric and mesic habitats promote different types of nomadic strategies. These results have important implications for conservation strategies: Forage‐driven nomads primarily require a high degree of landscape‐level permeability, and water‐driven nomads additionally require the protection of ephemeral water bodies and actions to maintain the functional connectivity between them.
Highlights
In resource-poor arid environments where precipitation is stochastic, nomadic movement is a common strategy employed by animals to cope with the unpredictable changes in resource availability (Dean 2004, Jonzen and Knudsen 2011)
Given our research interest in forage- vs. waterdriven nomadism, we focused on movement data collected in the warm, vegetation growing season and we excluded the cold non-growing season
❖ www.esajournals.org resource-poor arid environments, animals move longer distances than animals in resource-rich environments (Teitelbaum et al 2015, Tucker et al 2018). These macro-ecological studies, usually cover a broad gradient from forest to temperate grasslands, while our comparative study of nomadic ungulates focused on arid environments from herbaceous mesic steppes to shrubby xeric deserts. Along this resource gradient in arid environments, animals in deserts seem to reverse the general pattern found in the macroecological research, with animals moving longer distances in more mesic habitats (Fig. 2)
Summary
In resource-poor arid environments where precipitation is stochastic, nomadic movement is a common strategy employed by animals to cope with the unpredictable changes in resource availability (Dean 2004, Jonzen and Knudsen 2011). The most commonly observed driver of nomadic movement is unpredictable changes in ephemeral resources, such as water or forage, where animals tend to move long distances to track broadscale patchy resources (Fryxell et al 2004, Roshier et al 2008). Water availability at ephemeral oases and wetlands is temporally unpredictable, but their spatial location is often relatively static. These unpredictable changes in the water availability could lead to water-driven nomadism. The variability in nomadic movement patterns has not received much attention in the literature This is especially true for nomadic ungulates, where a lack of adequate movement data has made comparisons between species and ecosystems difficult. Such comparisons and research are essential to improve our understanding of variability in nomadism and its ecological consequences
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