Environmental seasonality and group size drive birth timing synchrony in wild odd-toed ungulates
A comparative analysis of 27 wild Perissodactyla populations across Africa and Asia identified key drivers of birth synchrony, including environmental seasonality, latitude, and group size. The study examined nine factors spanning ecology, life history, and predation pressure across a group of mammals of which 75% are currently threatened. The findings have direct implications for conservation and reintroduction strategies for endangered species such as rhinos and tapirs.
Researchers used a comparative analysis framework to investigate what drives the synchronization of births across 27 populations of wild Perissodactyla — the order of odd-toed ungulates including horses, rhinos, and tapirs — spanning Africa and Asia. The study confirmed that higher environmental seasonality and latitude are positively associated with birth synchrony, while greater environmental productivity reduces it; environmental unpredictability showed no significant effect. Life history traits played a limited role: neither the intensity of daily reproductive effort nor pace-of-life metrics reached significance, and migratory behavior showed an unexpected positive association with birth synchrony, complicating the assumption that migration simply relieves environmental constraints on reproduction. Group size had a positive effect on birth synchrony, consistent with the 'swamping hypothesis,' which holds that synchronized births dilute predation risk on vulnerable neonates. However, a qualitative predation exposure index combining species sensitivity and site-specific predator abundance did not yield strong support for a direct predation effect. The authors conclude that individuals appear to adjust reproductive cycles to local ecological and social conditions, and recommend that reintroduction programs account for differences between source and destination sites to improve juvenile survival and recruitment outcomes.
What's missing
The study relies on a qualitative index for predation exposure rather than quantitative predation rate data, which the authors acknowledge may limit detection of predation effects. The analysis is correlational and cannot establish causality between the identified factors and birth synchrony. The sample of 27 populations, while spanning two continents, may not capture the full ecological diversity within Perissodactyla, and captive population dynamics are not addressed. The mechanisms by which group size promotes synchrony — whether social cuing, shared environmental exposure, or other pathways — remain unresolved.
What different sources said
- bioRxivCenter
Effect of the environment, predation and life history on reproductive synchrony in Perissodactyla
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