What If Gone

Species → Joshua Tree

Joshua Tree

Yucca brevifolia

More than 4.4 million acres occupied in California and Nevada today —…
Extinction risk Least Concern
Obligate mutualismDesert environmentClimate changePollinator
Joshua Tree (Yucca brevifolia)
Photo: Bernard Gagnon, Wikimedia Commons (CC BY-SA 3.0)

What if it disappeared?

Impact High
Ongoing

The Joshua tree can only reproduce through the yucca moth, its sole pollinator — but the moth also lays its eggs in the flowers it pollinates, and its larvae eat some of the seeds: the mutualism stays stable only because the plant itself limits how much of that predation it allows.

Documented
Detail

Addicott, J.F. et Bao, T. (1999). Limiting the costs of mutualism: multiple modes of interaction between yuccas and yucca moths. Proceedings of the Royal Society B, 266(1415), 197–202.

The authors show that the mechanism limiting the cost of seed predation varies across the yucca-moth systems studied: in some, the plant selectively aborts flowers that received too many eggs relative to the pollen delivered; in others, egg mortality within the fruit itself plays this limiting role — two distinct solutions to the same evolutionary constraint, rather than one universal mechanism.

Along the climate gradient

At the lowest, hottest elevations of its range, the Joshua tree still survives, but the yucca moth is no longer active there — the mutualism its reproduction depends on collapses locally even before the adult tree itself disappears.

Documented
Detail

Harrower, J. et Gilbert, G.S. (2018). Context-dependent mutualisms in the Joshua tree-yucca moth system shift along a climate gradient. Ecosphere, 9(9), e02439.

By comparing multiple sites along an elevation — and therefore climate — gradient, the authors show that the mutualism breaks down before any visible decline in the adult tree population — an early warning signal invisible if one tracks only tree numbers without measuring the pollinator's activity.

Within 60 to 90 years

A model combining six climate scenarios with fossil evidence of the species' past range shifts projects a 90% loss of its current range within 60 to 90 years — the rodents that disperse its seeds move them at only about 1.8 m a year, far too slow to keep pace with warming.

Documented
Detail

Cole, K.L., Ironside, K., Eischeid, J., Garfin, G., Duffy, P.B. et Toney, C. (2011). Past and ongoing shifts in Joshua tree distribution support future modeled range contraction. Ecological Applications, 21(1), 137–149.

The study combines climate modeling with the fossil record from Mojave Desert packrat middens, which allowed the authors to trace the species' past range shifts over tens of thousands of years — the migration observed in the past, like that projected by the current rodent-dispersal model, is judged too slow to keep pace with ongoing warming.

Documentation

Last verified: August 14, 2026