Exploitation and Interference Competition

There are two general mechanisms of competition. In 'exploitation competition', weeds (as with all plants) compete with one another by being better at exploiting the resources, i.e. obtaining more of them than others (Fig. 8.2). In 'interference competition', there can be a direct removal of a resource (taking it away from another who already captured it) or the occupation of a resource that may not be needed immediately, but denying it to others raises relative fitness (Murphy, 1999). In...

What Determines the Outcome of Competition

One of the reasons weeds are so successful is because they adapt rapidly to new environmental conditions, including the 'competitive neighbourhood' of other weeds, crops and plants in general. Weeds do not 'know' how competitive others are - if others are much better competitors, the weed simply dies without reproducing. If a weed is at a competitive disadvantage but still produces offspring, there should be selection for the offspring to develop better competitive abilities (as long as the...

Agamospermy

Images Agamospermy

Agamospermy is the production of seed without fertilization i.e. the fusion of gametes - sperm and ovum . There are three main types of agamospermy diplospory, apospory and adventitious embryony but there are numerous and often complex variations Fig. 5.2 . Normally, meiosis occurs and the gamete ovum contains one copy of all chromosomes, i.e. the ovum is 'haploid'. After being fertilized by sperm, the seed will have the normal number of copies of chromosomes i.e. it will be 'polyploid' . In...