Seed Dispersal

'Principal dispersal agent (PDA); PDA subgroup; method by which PDA was determined; source reference; group(s) of animals that disperse the seeds; specific animals that disperse the seeds; notes relevant to the interpretation of the dispersal data'

The only compulsory fields are 'principal dispersal agent', 'method by which PDA was determined' and 'source reference'. The two fields detailing animal dispersal agents obviously only apply to species that are entered as having seeds that are animal dispersed.

Dispersal categories used and further information concerning the dispersal dataset:

Numerous systems for classifying the methods by which seeds are dispersed exist. The classification that we have adopted has been chosen to provide clarity and maximal information content, whilst remaining fully compatible with the major classification systems. Frequently, not all seeds of a given taxon are dispersed in exactly the same way. As examples, many seeds that have obvious adaptations for wind dispersal may also be transported by water, whilst some animal dispersed fruits also fall directly beneath the parent plant and are not further dispersed. To counter concerns such as the above we have classified species by their principal dispersal agent (PDA); i.e. the mechanism that accounts for the majority of seed dispersal. Six main classes of PDA are recognised, as detailed below. Names in brackets refer to other terms applied to these groups by different authors.

  • Animal (zoochory)
  • Wind (anemochory)
  • Water (hydrochory)
  • Methods originating from the parent plant or diaspore (autochory)
  • Unassisted (Barochory)
  • Dispersal prevented (atelochory, antitelochory)

Where no one dispersal agent predominates, or two or more methods are mentioned in a reference, but data are insufficient to decide which is the most important, various combinations of the above six classes are used (e.g. PDA=wind+water). Although not relating to seeds, an additional class 'vegetative growth' has also been included within the PDA field. Plants in this category primarily expand ('disperse') via vegetative growth as opposed to by seed. Each PDA is further divided into several descriptive sub-groups, and (where available) this information is also provided. In addition, dispersal of many seeds occurs in a multi-step fashion. For example, seeds of numerous species that are predominately animal dispersed initially fall beneath the parent plant (unassisted), before being dispersed further by animals. This is not always clear from the available data, but where authors have indicated that a a multi-step process occurs, it is indicated in the notes field. This field also contains information concerning the diaspore itself, including features that facilitate dispersal (e.g. wings, fleshy fruit etc).

Two care points are necessary when interpreting the dispersal data. Firstly, different authors have determined dispersal agents in different ways, with techniques ranging from direct or experimental observation to assumptions based upon diaspore morphology and even anecdotal evidence. To allow more confident interpretation of the data, the method by which the author(s) of the source reference determined the dispersal agent is stated. Secondly, the principal method by which a species is dispersed may vary according to the location in which it is growing. For example, dispersal by water may predominate in individual plants of a species that is usually wind dispersed if they are growing alongside a water course. For more complete information concerning how widely applicable individual data are likely to be, readers are referred back to the source references.

A read-across showing selected examples of how categories commonly used in other classification schemes (in addition to those already mentioned above) will appear in this database is given below. In some cases slightly different combinations are also possible, but are broadly similar to those given.

  • Ballistic dispersal — methods originating from parent plant or diaspore; explosive mechanism
  • Barochory — unassisted; seeds drop to the ground close to or beneath the parent plant
  • Chamaechory — wind; diaspore is rolled along ground surface by wind
  • Dyszoochory — animal; diaspore is eaten intentionally
  • Endozoochory — animal; diaspore is eaten intentionally/diaspore is eaten accidentally
  • Epizoochory/adhesive dispersal - animal; diaspore is carried accidentally
  • Geocarpy — dispersal prevented; seeds are produced below ground level
  • Meteoranemochory — wind; diaspore is blown by wind
  • Myrmecochory — animal; diaspore is carried intentionally; ants
  • Nautohydrochory — water; e.g. floating/submerged in fresh/saltwater currents
  • Ombrohydrochory — water; diaspore is propelled by action of rain on plant structure/wetting by rain or dew
  • Synzoochory — animal; diaspore is carried intentionally
  • Xerochasy/hygrochasy — water; wetting by rain or dew