Revealing the Geospatial Responses of Animal Migratory Rhythm to Climatic Factors and Vegetation

Climate change affects all components of terrestrial ecosystems, including animal migration that is often ignored. Understanding how migratory rhythm responds to climate factors will provide new insights into the protection of the Earth’s ecosystem and environment. The Serengeti-Masai Mara Ecosystem is sustained by the world’s largest terrestrial large-herbivore migrations and is essential to the earth environment. While rainfall has long been recognized as its driver, the synergistic and multiple paths of precipitation-temperature-vegetation in synchronizing migration phenology remain poorly understood. The migration rhythm is being insufficiently explained why migratory animals track resources in specific regions, as the values of climate variables fluctuate greatly. The monitoring of the interior migratory path and absolute climatic values limits the explanations, and there still lack periodic models to monitor the migration rhythm. Here, we derive a novel geospatial model for periodic migration based on composite trigonometric functions, and implement a concave hull optimization to delineate migration corridors while minimizing spatial sampling errors. Interior-exterior contrasts of the migratory region are applied to explain the periodic rhythm. The statistical dependencies of migration on environmental factors are detected through multiple paths of influence, revealing the different roles by granger causality model, structural equation model and multivariate linear regression. The results showed that the migration features are well captured by the proposed periodic model, indicating two longitudinal migration cycles and one latitudinal cycle per year. The climatic factors directly affect migration with different roles of precipitation and temperature played in latitude and longitude directions, and also indirectly impact migration through vegetation. The interior-exterior contrasts of concave hulls are proven to be superior with higher correlations and lower error variances, presenting stronger causal relationship and influence, and can better explain why animals migrate during specific seasons, rather than absolute climatic values that fluctuate dramatically.

The illustrated abstract displays the theories, models, and results of how climatic factors impact animal migration. The top panel illustrates the research area and datasets including climate data (precipitation and temperature), vegetation data, and calculated centroid data of migratory animals from the Serengeti-Masai Mara Ecosystem in East Africa. The middle section outlines the methods for establishing periodic models and detecting multiple pathways and synergistic synchrony, including the conceptualization of interior-exterior contrasts through geographic concave hulls, theoretical construction of periodic models, and monitoring methods for correlations, causal relationships, and pathways for impacts detection. Finally, the main findings of the study are introduced at the bottom panel, including the novel geographic spatial models that reveal the migration rhythm and diverse influences. The geographic abstract not only provides a universal geographic model, but also reveals insights into deeper reasons for animal migration. This provides a basis for protecting migration and better understanding the geospatial responses of terrestrial ecosystem to climate.