An outwardly "purposeful" category of dispersal is accomplished by plants through myrmecochory, the employment of attractive seed appendages and chemicals that induce the ants to transport the seeds without harming the embryo or endosperm. Myrmecochory is an almost world wide phenomenon.
Some specialized plant-dwelling ants protect their myrmecophyte hosts not only from herbivores but also from other plants that crowd in too closely.
There are also worker ants that attack and destroy any foreign plant that sprouts within 40 centimeters of the trunk of the acacia in which they live, and they cut back vines and foliage of neighboring trees that touch the acacia crown.
This pruning action has the effect of promoting the growth and survival of the host plant, but it also removes bridges over which alien ants can attack the resident colony.