Seeds germinating on ant's nest
I took this picture on a morning hike with my family in the nearby town of Penela, in Portugal. In the picture, you can appreciate a worker ant (at 12), and several germinated seeds (at 3, 6, 9, and 11). Although I am not certain about the seed species, I am guessing they are European common gorse (http://en.wikipedia.org/wiki/Ulex_europaeus
Myrmecochorous plant species (like gorse) produce seeds with a protein-rich appendix called elaiosome (http://en.wikipedia.org/wiki/Myrmecochory
). Ants disperse the seeds and eat the elaiosome, in a win-win mutualistic interaction. Now, what happens to the seeds once the ants eat the elaiosome? Very often ants discard them at the entrance of their nests, which frequently happen to be nutrient rich, competition free, and with full light exposure. Ideal places for germinating and becoming an adult plant.
What happens when myrmecochorous plants are introduced into new non-native regions? Well, first off, usually they establish new mutualisms with ants in the non-native territory, then, they might become a terribly invasive weed, just as common gorse has become in the United States, Chile, and New Zealand!
Here is a link to a recent work I did about invasive myrmecochorous acacia trees from Australia which have established new mutualisms with Portuguese ants and subsequently became invasive here: http://www.web-ecol.net/12/33/2012/we-12-33-2012.html