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1 The dispersal mode adopted by a plant species is frequently associated with other attributes of the plant and its habitat. In this paper we review these associations and present a set of hypotheses which, when considered together, make a probabilistic prediction of the dispersal mode adopted by a plant species. When applied to a species list, the hypotheses can be used to generate a prediction of its dispersal spectrum, i.e. the percentages of different dispersal modes that have been adopted. 2 The formulation of such a set of hypotheses has several purposes: (i) to summarize existing knowledge about dispersal adaptations and their interrelations with other attributes of plants and their habitats; (ii) to couch that knowledge in such a way that falsifiable predictions can be made; (iii) to arrive at provisional conclusions about which factors are the most important in shaping the evolution of dispersal mode in different plants or different environments. 3 The review of relationships between dispersal mode and other attributes of plants and their habitats lead to the following provisional conclusions; (i) seeds larger than 100 mg tend to be adapted for dispersal by vertebrates while those smaller than 0.1 mg tend to be unassisted; most seeds, however, are between 0.1 and 100 mg, and in this range all of the dispersal modes are feasible; (ii) plant growth form and stature (sometimes in relation to the canopy height of the vegetation) seem to exclude certain dispersal modes; (iii) the availability of specific dispersal vectors seems rarely to be an important determinant of dispersal mode; (iv) attributes of the physical environment also seem rarely to be important, except indirectly through their influence on plant stature and seed size.

Influences of ant behavior on short— and long—term fate of elaiosome—bearing seeds were investigated in fire—prone sclerophyll vegetation neary Sydney, New South Wales. The short—term fate of seeds was assessed by measuring dispersal distances, seed predation within ant nests, and seed burial. Most seeds were taken directly to ant nests. The mean dispersal distance was 1.1 m (range 0.06—11 m). Seed predation by three ant species was measured by feeding known quantities of seeds and inedible seed mimics, made from plastic beads, into nests. Nests were excavated 2, 7, and 30 d later to recover seeds and beads. The recovery rate of beads estimated the disappearance rate of seeds from nests due to factors other than predation. Pheidole sp. 1 appeared to eat most seeds soon after collection but also stored some seeds in small caches within the nest. Both Rhytidoponera "metallica" and Aphaenogaster longiceps removed most seeds for the nest intact (the elaiosome having been consumed) and discarded them on the surface, but left some within nests at depths <12 cm. Seeds discarded on the soil surface may undergo secondary dispersal by other ants. A transition matrix analysis was used to assess the importance of this secondary dispersal route and to estimate the probabilities that seeds initially taken by a particular ant species would be either eaten or finally buried within a nest. The analysis indicated firstly that a significant proportion of seeds initially removed by A. longiceps and R. "metallica" will eventually be eaten by Pheidole spp. Secondly, some seeds will be discarded in the nests of species other than the original seed remover. The analysis also indicated that seeds initially taken by A. longiceps and R. "metallica" would be more likely to survive than those taken by Pheidole sp. 1. As many Australian ant—dispersed seeds are stimulated to germinate by fire, long—term seed fate was investigated by monitoring seedling emergence after fire from ant nests that had been fed a known quantity of seeds. Overall emergence was °1% of seeds fed into nests. The greatest emergence was from nests of A. longiceps. This result is qualitatively consistent with those of the short—term experiments. However, the low overall emergence rate meant the power of this experiment to detect statistical differences between ant species was limited. The spatial pattern of emerging seedlings differed between nests of the different ant species. Seedlings from the nests of Pheidole sp. 1 were considerably more clumped than those from nests of the other three species. The seed fate experiments collectively indicated that seed—removing ants have different effects on seed fate, with A. longiceps and R. "metallica" being more beneficial than Pheidole.

We investigated the role of ant behavior as a selective influence on the presentation and morphology of elaiosome—bearing seeds in Australian sclerophyll vegetation by manipulating characteristics of natural and artificial diaspores. We compared the response to these diaspores of three seed—removing ant species, two of which (Rhytidoponera "metallica" and Aphaenogaster longiceps), produce more favorable seed fates than the third species (Pheidole sp. 1). We measured the effect on removal rate of diaspore arrangement (degree of clumping), elaiosome removal, diaspore size (i.e., mass), elaiosome/load ratio, and composition of both the elaiosome and seed. Clumped seeds were removed significantly faster than single seeds by Pheidole sp. 1, a group forager. A. longiceps, a solitary forager, removed single seeds faster while R. "metallica" removed single and clumped seeds at the same rate. The presence of elaiosomes on seeds increased removal rates, especially by A. longiceps and R. "metallica." Both A. longiceps and R. "metallica" responded positively to elaiosome/load ratio while Pheidole sp. 1 responded mainly to diaspore size. These species—specific responses were such that diaspores with high elaiosome/seed ratios are more likely to be removed by A. longiceps or R. "metallica" than by Pheidole sp. 1. Diaspore characteristics other than size had inconsistent effects on removal rates. The differential response of the ant species to such characteristics as seed arrangement and elaiosome/seed ratios demonstrates the way in which ant behavior may have been an important selective force in the evolution and maintenance of myrmecochory.

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