Giraffe translocation population viability analysis

A giraffe reintroduction can look successful decades before its population collapses. Computer simulations produced populations that initially gained calves, then declined as their young founders aged and inbreeding accumulated. An encouraging first generation therefore need not establish that moving a small group has secured a lasting population.

Derek Lee and colleagues modelled 198 combinations of founding group size, sex ratio, population growth and the harmful effects of inbreeding. Each scenario ran 1,000 times over a simulated century, beginning with two-year-old giraffes. The researchers compared extinction risk and retained genetic diversity, asking how many founders would be needed if the new population remained isolated.

Under moderate growth and inbreeding assumptions, 30 females and three males kept estimated extinction risk below 1% over 100 years; retaining more than 95% of initial genetic diversity required 50 females and five males. Those numbers are conditional model results, not universal release instructions: actual sites can differ in habitat, mortality and genetic circumstances. Some simulated populations grew for roughly their first three decades before their weakness became apparent. Small introductions can still contribute to conservation when later movements bring in additional genes, but early breeding alone is too short a measure of success.