Evolutionary action of tropical animals on the reproduction of plants

Authors


Abstract

The value of structural characters should be assessed by their role in local reproductive processes. Just as in genetics the abstract species has been replaced by the population, the functional contacts between animals and plants should not be considered on the species level but in relation to the whole local ecosystem. Incidental cross-links therein are described as leading to ‘concurrent evolution’ as a corollary. Inside the rain forest homeostasis is provided in the vegetative sphere by pest-pressure, all-year germination and accidental replacement, but it is especially strong in the reproductive sphere, by mutual collaboration in time, this via a feedback by means of internal, permanent animal life. These circumstances explain the lack of vicariance and the polymorphy, maintaining nevertheless normal interspecific selection. A comparison with seeds, seedlings, flowers, etc., from temperate vegetation is illustrative. There, abiotic factors, edaphic and climatic, are dominant and the whole is more open to external influences. Their anemochory (wind dispersal) and autochory (self dispersal) prove to be not fundamental for plant-life.

In the tropics archaic dispersal methods (by fish and reptiles) of archaic, juicy, large seeds (sarcotesta) persist in a conservative, homeostatic environment alongside modern methods. Both lead to typically tropical traits and may serve to explain phylogenetic trends. These are discussed for Leguminosae. The aril is a compromise suited for dryer regions, but maintaining archaic attractivity of the seed–not yet the pericarp-fruit.

‘Bat-fruits’ provide a typical modern touch.

Archaic pollination-methods (for example by beetles and simple flies) are bound to the ecosystem as a whole, which provides subsistence. Deceptive cross-links (short-circuits) are here more important than food for such unadapted visitors. The flowers probe instincts chemically. Some flowers provide a brood-place, as in Ficus, which breeds its own wasps in an ancient relationship, allowing Ficus to escape from the forest. Monophily (deceptive or not) is not necessarily late.

The bond with other hymenopterans (wasps) arose also as an incidental cross-connection. Later this developed into a fixed relationship with flower-insects. Orchids as active ‘ecological parasites’ demonstrate the exploitation of pre-existing animal life.

The more modern impact of birds and bats is described in a synecological context, which makes some parts of syndromes understandable. Case-histories are given to illustrate the interaction between dispersal and pollination, between functions and structures in seed (fruit) and flowers. We see their clashes and the solution, always found, leading to permanently necessary changes. Dispersal may be anticipated in apparently functionless (or supposedly phylogenetical) floral characters.

Points from a pollination-syndrome may form preadaptations for a dispersal-syndrome and vice versa. The calyces of oriental Trifolium species illustrate monospermy, and their capitula the possible origin of these characters and the inferior ovary in the Compositae.

Ancillary