Seed dispersal

 Introduction

Seeds are an essential component of plant reproduction by assisting in the distribution of seeds across the farming fields. Majority of the plant populations grow as a result of proper seed dispersal mechanism. If we take a casual walk across a farming field or a jungle, a variety of seeds, and the colourful pollen being stuck to our clothes. This is because many environmental agents have brought them from different plants. In order for the fertilization of flowering plants to occur, a medium is required. In this case, our clothes act as a medium of transfer of pollen and seeds.  Seeds exercises a number of vehicles to move from one area to another. Some of the common vehicles help in transferring the seeds are the wind, rainwater,  animal`s dung and insects. Seed dispersal can also happen through many other media. These vehicles help in the voluntary or involuntary picking up of seeds from one place to another. Imagine if seeds remain undistributed where all the seeds get accumulated in one area;  it leads to severe competition for the seeds to germinate and grow. Competition can occur for their survival needs such as sunlight, water, minerals, and space resulting in the destruction of weaker ones. Seed dispersal is actually a scientific process occur naturally or artificially. Seed dispersal is the process of spread of seeds to the distant locations away from their parent plant. As the plants have very limited mobility, they must rely on a variety of dispersal vectors to spread their propagules to reach the right place. Seed dispersal is carried out by both the abiotic and the biotic vectors. Abiotic factors include wind, water, and other natural forces, whereas biotic vectors are the living organisms such as birds and animals. A healthy and systematic dispersal of seeds helps the plants to grow and nurture properly. The growth and genetic composition of plants rely on the pattern of seed dispersal and the mechanism through which seeds get dispersed. There are 5 basic mediums of seed dispersal, they are, gravity, wind, water, animals and ballistic mode. 

Mechanism  of  Seed Dispersal

Seed dispersal differs between different types of seeds based on their size, weight, numbers etc. Lighter seeds disperse far away from the source plant, whereas the heavier ones might be settled near the parental plant. Different types of seeds are spread by different vehicles. Winged seeds like drumstick and maple are dispersed through some animals and insects. Light seeds of grasses or hairy seeds of Maida and sunflower are blown along with the wind.  Some seeds are dispersed by water. Spiny seeds having hooks are caught to the bodies of animals and are moved to remote places. Few of the seeds can be dispersed when the fruits burst with a sudden jerk, ultimately the seeds are scattered.

 

seed dispersal

Methods( vectors) of seed dispersal

1. Long-distance dispersal (LDD)  is the proportional distance to which the percentage of seeds (1% out of the total number of seeds produced)  travel the farthest distance. This is out of  99% probability distribution. There are 2 subtypes in LDD, the proportional type ( An average) and the absolute type(This is the actual or literal distance that the seeds spread ).

2. Autochory is an independent seed dispersal mechanism without any help from the outside vectors. This method is not highly favourable as autochory fails to spread the seeds to the farther distance. 

3. Barochory or Gravity based dispersal is the one in which the plant uses the gravity for dispersal. It occurs when a heavier fruits fall off from the plant once they are fully ripe. The seeds being burst out of the fruit to enter the soil. 

4. Ballistic dispersal or Ballochory is when the dispersal happens as a result of the seed being forcefully ejected by explosive dehiscence of the fruit.

5. Dispersal by allochory refers to the type of seed dispersal by using some secondary agent or vectors such as water, wind, animals, birds, insects etc. 

 

Further reading

1

Pollination                                   

2

Life cycle of angiosperms

3

Plant breeding

4          

Pollen grains                          

 

Questions

  1. Mention the vectors of seed dispersal.

  2. Which type of vector is used for dispersal if the seeds are very light?

  3. Distinguish between Ballochory and autochory.

  4. What is ballistic dispersal? Give an example.

  5. Explain the seed dispersal mechanism through animal with an example.

 



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