Sex allocation, pollen limitation and masting in whitebark pine
Article first published online: 10 JUN 2013
© 2013 The Authors. Journal of Ecology © 2013 British Ecological Society
Journal of Ecology
Volume 101, Issue 5, pages 1345–1352, September 2013
How to Cite
Rapp, J. M., McIntire, E. J. B., Crone, E. E. (2013), Sex allocation, pollen limitation and masting in whitebark pine. Journal of Ecology, 101: 1345–1352. doi: 10.1111/1365-2745.12115
- Issue published online: 30 AUG 2013
- Article first published online: 10 JUN 2013
- Manuscript Accepted: 30 APR 2013
- Manuscript Received: 9 OCT 2012
- NSF awards. Grant Number: DEB 05-15756
- Anna Sala. Grant Number: DEB 10-20889
- mast seeding;
- Pinus albicaulis ;
- pollen coupling;
- pollination efficiency;
- reproductive ecology;
- reproductive synchrony;
- seed production;
- sex ratio
- Masting, the synchronous and episodic production of seed crops, is thought to benefit plant reproductive success through positive density-dependent effects on pollination, dispersal and seed survival. Of these, only increased pollination efficiency in mast years can be a proximate mechanism for masting by synchronizing reproductive effort across individuals through pollen coupling.
- Increased pollination efficiency requires synchronous investment in male and female function during mast years. Sex allocation theory, however, predicts a trade-off in investment between male and female reproductive allocation dependent on total resources invested in reproduction.
- We describe patterns of sex allocation in Pinus albicaulis (whitebark pine), using data on pollen and seed cone counts over 5 years for 29 trees across 7 sites in Montana, U.S.A.
- Whitebark pine seed cone maturation increased with site pollen cone production, indicating pollen limitation, and pollen and seed cone production were positively correlated across years.
- Simulating mature seed cone production from these empirical relationships resulted in greater average mature seed cone production than alternative scenarios of (i) no synchrony between pollen cone production and pollen cone initiation, (ii) negative correlation (trade-off) between seed cone initiation and pollen cone production or (iii) no masting.
- Synthesis. Our data support a role for pollination efficiency in both increasing long-term seed production and as a proximate mechanism for synchronizing masting in Pinus albicaulis. Increased pollination efficiency joins greater seed dispersal and survival in mast years seen in other studies, as an additional positive density-dependent benefit of masting. Positive density-dependent fitness benefits may therefore influence patterns of sex allocation in relation to total resources invested in reproduction. The pollen limitation found here combined with stand isolation and reduced tree density due to mortality from forest pests and other environmental stressors may lead to reduced seed cone maturation and changes in masting patterns.