Staggered flowering times among ericad peatland plants increase likelihood of successful pollination by reducing competition for scarce pollinators.

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Peatland ecosystems are often characterized by having few pollinator species, as well as small pollinator population sizes. This affects plants by decreasing the rate of pollination, as fewer individuals are available to move pollen between plants, which decreases the number of plant offspring produced. In order to counteract the low numbers of both pollinator species and pollinator population sizes, plant species belonging to the ericad family have developed an interesting strategy. They stagger their flowering times, so they don’t overlap. This increases the rate of successful pollination, as there are fewer flowers to visit at any one time, thus reducing competition for pollinators, and ensuring that pollen is transferred to another member of the species. Differences in cold tolerance determine the sequential flowering times. The higher a plant’s cold tolerance, the sooner after a frost it can start to produce pollen. These differences result in different flowering times, reduced competition for pollinators, more targeted pollination, and ultimately increased rate of successful reproduction for the plants.

This summary was contributed by Thomas McAuley-Biasi.

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"Many plant species depend on insect pollinators, and such insects are often rare on peatlands. Bog dwarf shrubs have separated flowering times. For instance, in Ontario the flowering sequence is Chamaedaphne calyculata, Andromeda glaucophylla, Kalmia polifolia, Rhododendron groenlandicum, Vaccinium macrocarpon (with wide overlap in flowering time only between Andromeda and Kalmia). The pollinators (e.g. bees) are quite generalist and serve several species, so it may well be that the differentiation in flowering time has evolved to avoid competition for pollinators (Reader 1975)." (Rydin and Jeglum 2006:56)

“Studies by Bell and Burchill (1955), Judd (1958), and Pojar (1974) have shown that the
flowering times of ericaceous shrubs are staggered rather than coincident.” (Reader, 1975:1300)

“Because these plants are visited by the same hymenopteran pollinators, it would be most advantageous for their peak  flowering times to be non-overlapping. The probability of flower pollination would be maximized for each species by this temporal separation of peak flowering.” (Reader, 1975:1304-1305)

“Since indiscriminant transfer of pollen between species will not lead to the production of viable offspring and none of the five species is known to be an apomict, any mechanism that reduces interspecific visitation by a pollinator will be naturally selected for.” (Reader, 1975:1305)

“The diversification of flowering times in these ericaceous species is just as likely to have been the result of the inconstancy of their insect pollinators as the result of interspecific competition for a limited number of pollinators.” (Reader, 1975:1305)

“It is more reasonable to view sequential flowering of bog ericads as a consequence of competition for pollinators than of differential flower cold hardiness. The prime role of air temperature would be to determine the order in which ericads’ flowering peaks were reached by controlling how early in the year each species could flower with minimal frost damage” (Reader, 1979: 999)

The Biology of Peatlands, 2e (Biology of Habitats)September 15, 2013
Hakan Rydin

Journal article
Competitive relationships of some bog ericads for major insect pollinatorsCan. J. Bot.September 15, 2008
R. J. Reader

Journal article
Flower cold hardiness: a potential determinant of the flowering sequence exhibited by bog ericadsCan. J. Bot.November 22, 2007
R. J. Reader

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