Item

Abstract

Animals must contend with spatially heterogeneous and temporally varying environmental conditions. Animals move to selectively modify the set of environmental conditions to which they are exposed. These movements produce multidimensional and time-varying “individual niches” which are expected to covary with animals’ schedule of life history events such as breeding or migration. Here, we characterize individual niche variation for four species of migrant crane and find that temporal variation in environmental niche is linked to species-specific life history events and migratory movements. Our approach offers a tractable, data-driven framework for identifying dynamic and transitory niche associations which are important for understanding how animals survive in complex environments. Movement is a key means by which animals cope with variable environments. As they move, animals construct individual niches composed of the environmental conditions they experience. Niche axes may vary over time and covary with one another as animals make tradeoffs between competing needs. Seasonal migration is expected to produce substantial niche variation as animals move to keep pace with major life history phases and fluctuations in environmental conditions. Here, we apply a time-ordered principal component analysis to examine dynamic niche variance and covariance across the annual cycle for four species of migratory crane: common crane (Grus grus, n = 20), demoiselle crane (Anthropoides virgo, n = 66), black-necked crane (Grus nigricollis, n = 9), and white-naped crane (Grus vipio, n = 9). We consider four key niche components known to be important to aspects of crane natural history: enhanced vegetation index (resources availability), temperature (thermoregulation), crop proportion (preferred foraging habitat), and proximity to water (predator avoidance). All species showed a primary seasonal niche “rhythm” that dominated variance in niche components across the annual cycle. Secondary rhythms were linked to major species-specific life history phases (migration, breeding, and nonbreeding) as well as seasonal environmental patterns. Furthermore, we found that cranes’ experiences of the environment emerge from time-dynamic tradeoffs among niche components. We suggest that our approach to estimating the environmental niche as a multidimensional and time-dynamical system of tradeoffs improves mechanistic understanding of organism–environment interactions.