Predator satiation and recruitment in a mast fruiting monocarpic forest herb.
OBJECTIVE
Cross-pollination and satiation of seed predators are often invoked to explain synchronous mast reproduction in long-lived plants. However, explanations for the synchronous death of parent plants are elusive. The roles of synchronous seeding and post-reproductive mortality were investigated in a perennial monocarpic herb (Isoglossa woodii) in coastal dune forest in South Africa.


METHODS
Pre-dispersal seed predation and seed production were assessed by measuring fruit and seed set of inflorescences sprayed with insecticide or water and with no spray treatments. Seed predation was measured at different densities of I. woodii plants by monitoring removal rates of seed from the forest floor. The influence of adult plants on establishment of I. woodii seedlings was assessed by monitoring growth and survivorship of seedlings in caged and uncaged 1 × 1 m plots in understorey gaps and thickets.


RESULTS
Fruit and seed set were similar between spray treatments. An I. woodii stem produced 767·8 ± 160·8 seeds (mean ± s.e.) on dune crests and 1359·0 ± 234·4 seeds on the foredune. Seed rain was greater on the foredune than in other topographic locations. Seed predation rates were 32 and 54 % on dune crests and in dune slacks, respectively, and decreased with seed abundance, number of inflorescences per stem and plant height. Seedling recruitment was greater beneath synchronously dying adult plants than in natural understorey gaps (no I. woodii). However, seedling growth rate beneath I. woodii mid-way through its life-cycle was less than in gaps, although survivorship was similar.


CONCLUSIONS
The selective advantage of masting in I. woodii derives from satiation of both pre- and post-dispersal seed predators. In addition, post-seeding mortality of adult plants facilitates seedling establishment. Satiation of seed predators and the benefits of seedling establishment are strong drivers of the evolution of synchronous monocarpy in I. woodii.
Forest Biodiversity Research Unit, School of Biological and Conservation Sciences, University of KwaZulu-Natal, Scottsville 3209, South Africa.
Zivanai
Z
Tsvuura
Megan E
ME
Griffiths
Richard M
RM
Gunton
Michael J
MJ
Lawes
D027901:Acanthaceae / Q000502:physiology*; D000818:Animals; D020387:Food Chain; D007313:Insecta / Q000502:physiology*; D011157:Population Dynamics; D012098:Reproduction; D012639:Seeds; D013019:South Africa
Trends Ecol Evol. 1994 Dec;9(12):465-70
21236924
Trends Ecol Evol. 1990 May;5(5):135-40
21232341
Evolution. 1982 Jul;36(4):762-767
28568233
Am Nat. 1999 Sep;154(3):383-391
10506551
Plant Biol (Stuttg). 2010 May 1;12(3):495-502
20522186
Evolution. 1980 May;34(3):475-488
28568699
Oecologia. 2010 Dec;164(4):861-70
20628885