How do orchids regulative their numbers?
2005
Kull, T. | Kull, K.
The reproductive biology of the entire orchid family has several features pertinent to orchid population dynamics. These features include: (a) a large number of very small seeds, (b) zoopollination, (c) a narrow range of suitable habitats, (d) perennial growth, (e) seedlings that are obligate mycotrophs, (f) dormancy of adult individuals in temperate regions, (g) sparse populations that include small numbers of individuals majority of species is rare. Pollination systems are specific and the fruit set of many non-rewarding deceivers is rather low, but considering the large number of seeds in single capsules, seed set is not limiting. In case of high number of seeds, it is generally difficult to explain how a population can have a low and stable population density. An orchid population can hardly be so high that any self-inhibition of further growth may be possible. Therefore, it is reasonable to assume that the population growth is generally not limited by seed production in orchids. The alternative limitation factors may be availability of: (1) microsites, (2) symbionts. There are seemingly three main factors which allow orchids to have a relatively high speed of evolution. These are, first, small populations, second, obligate communication with several symbionts (co-evolutionary enhancement), and third, complex specific mate recognition systems, the latter being possible due to the high morphogenetic potentials in orchid flower development. We also analyse the applicability of Zipf law and the importance of Allee effect in orchids.
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