Flowering phenology of Ulex europaeus: ecological consequences of variation within and among populations

Abstract

Reproductive phenology of gorse (Ulex europaeus L., Genisteae, Fabaceae) is unusual in that the onset and duration of flowering vary greatly among individuals within populations: some plants initiate flowering in autumn or winter and continue flowering through spring, others initiate flowering in early spring. To understand the origin of this diversity and its ecological consequences, we investigated flowering phenology of randomly sampled individuals from five different natural populations in Brittany (France). Reproductive success was evaluated for individuals with contrasting flowering patterns, from 16 natural populations. Flower production, pod production, seed production and seed predation were estimated. Plants initiating flowering in spring produced larger numbers of flowers and pods over a shorter period than plants flowering from winter to spring, which produced few flowers and pods at a time but over a longer period. Pod production of longflowering plants did not differ significantly between winter and spring, but their pods were more intensively attacked by seed predators in spring than in winter. We discuss our results in relation to biotic and abiotic parameters. We postulate that long-flowering can be interpreted as a bet-hedging strategy, spreading the risk of pod failure (rotting or freezing) in winter and of seed predation in spring.

Time after time: flowering phenology and biotic interactions

“…Extended flowering duration might serve as a bet-hedging strategy to handle with tradeoffs both between pollinators and seed predators [37,56] and between pollinators and dispersers [53]. Interestingly, biotically pollinated plants flower for longer periods than do abiotically pollinated plants [20], as predicted if extended flowering evolves in response to tradeoffs between interactions with pollinators and other biotic agents.…”

“…Most field surveys compare temporal variation in the intensity of seed and flower predation and flowering phenology to infer the direction of selection acting on phenology. Most studies found that flowering off-peak (either early [23,[34][35][36][37], or late [11,[38][39][40][41]) is associated with reduced seed predation, probably because fewer herbivores are present at those times. Similar effects are highlighted by studies indicating highest seed predation during peak flowering [42][43][44], especially when peak flowering attracts more seed predators owing to a higher density of flowers and fruits ( [28], J.A.…”

“…Alternatively, stabilizing selection towards a peak flowering date might also occur if flowering synchronously during a short period satiates the herbivore [47]. In populations with higher densities of fruits, more fruits can escape predation [28,37] and this can also hold for changes in density over time. In dandelion Taraxacum officinale, for example, seeds produced during peak flowering are more likely to escape predation compared with seeds produced by early and late flowers [48].…”

Flowering phenology in Solidago altissima: adaptive strategies against temporal variation in temperature

“…For example, the spring wildflower Mertensia fusiformis bet-hedges by delaying the opening of some flowers to ensure pollination and seed development in years with late spring frosts (Forrest & Thomson 2010). Similarly, the timing and duration of flowering in Ulex europaeus has been suggested to follow a bet-hedging strategy to spread out the risk of freezing, rotting, and seed predation (Tarayre et al 2007). …”

Oviposition Decision of the Weevil Exapion ulicis on Ulex europaeus Depends on External and Internal Pod Cues

“…This system is particularly interesting because the relationship between U. europaeus and E. ulicis is very specific and very strong [19]. Indeed, the weevil undergoes its whole life-cycle on gorse, and gorse may suffer considerable damage from the weevils, which may infest up to 90% of the mature pods [19,20]. However, pod infestation rates are extremely variable in natural and experimental populations, and can vary from 20-98%, even among neighbouring individuals [19][20][21].…”