MEANS OF SEED DISPERSAL A LECTURE BYMR. ALLAH DAD KHAN

BY SPLITTING SUDDENLY - EXPLOSIVE ACTION OF FRUITS

HYDROCHORY: Many aquatic (water) and some terrestrial (ground) plant species use hydrochory, or seed dispersal through water. Seeds can travel for extremely long distances, depending on the specific mode of water dispersal. The water lily is an example of such a plant. Water lilies' flowers make a fruit that floats in the water for a while and then drops down to the bottom to take root on the floor of the pond. The seeds of palm trees can also be dispersed by water. If they grow near oceans, the seeds can be transported by ocean currents over long distances, allowing the seeds to be dispersed as far as other continents. Mangrove trees live right in the water. Their seeds fall from the tree and grow roots as soon as they touch any kind of soil. During low tide, they might fall in soil instead of water and start growing right where they fell. If the water level is high, however, they can be carried far away from where they fell. Mangrove trees often make little islands as dirt and other things collect in their roots, making little bodies of land.

BY WATERThe fruits of most water plants have buoyant, waterproof coverings that allow them to float and disperse their seeds by water.

ALLOCHORY

Anemochory (wind dispersal) is one of the more primitive means of dispersal. Wind dispersal can take on one of two primary forms: seeds can float on the breeze or alternatively, they can flutter to the ground. The classic examples of these dispersal mechanisms include dandelions, which have a feathery pappus attached to their seeds and can be dispersed long distances, and maples, which have winged seeds (samara) and flutter to the ground

BY WINDSome seeds are enclosed in wing-like husks (with one or two

propeller blades) or fluffy coverings that help them drift some distance away from the parent plant.

DANDELION SEEDS FLOAT AWAY IN THE WIND. TO MAKE SURE AT LEAST SOME OF THE SEEDS LAND IN A SUITABLE GROWING PLACE, THE PLANT HAS TO PRODUCE LOTS OF SEEDS.

ZOOCHORY: DISPERSAL BY ANIMALS

EPIZOOCHORY: Seeds can be transported on the outside of vertebrate animals (mostly mammals), a process known as epizoochory. Plant species transported externally by animals can have a variety of adaptations for dispersal, including adhesive mucus, and a variety of hooks, spines and barbs. A typical example of an epizoochorous plant is Trifolium angustifolium, a species of Old World clover which adheres to animal fur by means of stiff hairs covering the seed. Epizoochorous plants tend to be herbaceous plants, with many representative species in the families Apiaceae and Asteraceae. However, epizoochory is a relatively rare dispersal syndrome for plants as a whole; the percentage of plant species with seeds adapted for transport on the outside of animals is estimated to be below 5%. Nevertheless, epizoochorous transport can be highly effective if seeds attach to wide-ranging animals. This form of seed dispersal has been implicated in rapid plant migration and the spread of invasive species

ENDOZOOCHORY: Seed dispersal via ingestion by vertebrate animals (mostly

birds and mammals), or endozoochory, is the dispersal mechanism for most tree species. Endozoochory is generally a coevolved mutualistic relationship in which a plant surrounds seeds with an edible, nutritious fruit as a good food for animals that consume it. Birds and mammals are the most important seed dispersers, but a wide variety of other animals, including turtles and fish, can transport viable seeds. The exact percentage of tree species dispersed by endozoochory varies between habitats, but can range to over 90% in some tropical rainforests

MYRMECOCHORY: Seed dispersal by ants is a dispersal mechanism of many

shrubs of the southern hemisphere or understorey herbs of the northern hemisphere. Seeds of myrmecochorous plants have a lipid-rich attachment called the elaiosome, which attracts ants. Ants carry such seeds into their colonies, feed the elaiosome to their larvae and discard the otherwise intact seed in an underground chamber. Myrmecochory is thus a coevolved mutualistic relationship between plants and seed-disperser ants. Myrmecochory has independently evolved at least 100 times in flowering plants and is estimated to be present in at least 11 000 species, but likely up to 23 000 or 9% of all species of flowering plants.

SEED PREDATORS, which include many rodents (such as squirrels) and some birds

(such as jays) may also disperse seeds by hoarding the seeds in hidden caches. The seeds in caches are usually well-protected from other seed predators and if left uneaten will grow into new plants. In addition, rodents may also disperse seeds via seed spitting due to the presence of secondary metabolites in ripe fruits.

SECONDARY ZOOCHORY: Secondary dispersal by animals: Seeds may be secondarily dispersed from seeds deposited by primary animal dispersers. For example, dung beetles are known to disperse seeds from clumps of feces in the process of collecting dung to feed their larvae.

ANTHROPOCHORY: DISPERSAL BY HUMANS

Dispersal by humans (anthropochory) used to be seen as a form of dispersal by animals. Recent research points out that human dispersers differ from animal dispersers by a much higher mobility based on the technical means of human transport. Dispersal by humans on the one hand may act on large geographical scales and lead to invasive species

BY ANIMALS / HUMANSAnimals often serve as seed carriers. Seeds (with sticky hairs,

bristles, hooks, or barbs) are transported by sticking to the fur of animals or on the clothing of human beings.

Birds and other animals eat the fleshy fruits and discard the seeds or they may eat both but the seeds are not digested and are passed out with their droppings, often far away from the parent plant.

THE KERERŪ IS IMPORTANT IN THE SEED DISPERSAL OF LARGE NATIVE BERRIES IN FOREST ECOSYSTEMS. TREES SUCH AS THE KAWAKAWA RELY ON NATIVE BIRDS FOR SEED DISPERSAL

BANKSIAS, EUCALYPTS AND OTHER AUSTRALIAN PLANTS RELY ON FIRE TO HELP SPREAD THEIR SEEDS.