Brief Notes on Competition for Pollination in Plants
Waser defines competition for pollination as “any interaction in which co-occurring plant species suffer reduced reproductive success because they harve pollinators”. He differentiates between two kinds of interaction, viz.,
(1) competition through pollinator preference, and
(2) competition through interspecific pollen transfer.
The latter type appears to be much more common than the former.
Floral mimicry is an important aspect of pollination biology in some taxa. It is based on the utilization of false sensory cues to attract animals to affect pollen transfer. Four categories can be distinguished (Wiens, 1978):
(1) food deception;
(2) territorial defence (pseudoantagonism);
(3) pseudocopulation; and
(4) brood site selection. Some concepts of floral mimicry based on food deception are tabulated below under three heads:
A. Basic Biological Conditions:
(1) Model and mimic must be sympatric
(2) Blooming times of model and mimic should overlap.
B. Pollination Biology:
(1) Mimic must require a pollinator to effect pollination.
(2) Floral rewards may be in small quantities or altogether lacking in mimic as compared to those in model.
(3) At least one pollinator must be constant to the model for a period of time.
(4) Mimic is pollinated on the same foraging flight as the model.
(5) Pollination rate and foraging times are greater for the model.
(6) Pollen from the model could be spatially separated from pollen of the mimic on the body of the pollinator.
(1) There is functional similarity between the morphologies of model and mimic.
(2) The habit of model is similar to that of mimic.
(3) The floral spectral patterns of model and mimic are similar, and
(4) if present, the floral odours in model and mimic are similar (Little, 1983).
The definition of mimicry has aroused considerable debate. Wickler (1968) described it as a 3-party interaction involving a model (signal-transmitter No. 1), a mimic (signal transmitter No. 2), and a deceived animal (signal-receiver). He further defined the mimic as “that one of the two signal transmitters to which the receiver directs a response which is not advantageous to the receiver itself’. The point to be noted is that the signal that the mimic sends to the signal receiver is a false one, i.e. deceptive.
Wickler’s view has been supported by Wiens (1978) who defined mimicry as the process whereby the sensory systems of one animal (operator) are unable to discriminate consistently a second organism or parts thereof (mimic) from either another organism or the physical environment (the models), thereby increasing the finess of the mimic.
A rather different meaning is attached to the term mimicry by Vane- Wright (1980) who defined it as involving an organism (the mimic) which stimulates signal properties of a second living organism (the model) which are perceived as signals of interest by a third living organism (the operator), such that the mimic gains in fitness as a result of the operator identifying it as an example of the model.