A learner is like...

A learner is like a tree in an ecosystem.

Connectivism discusses a great deal of group more than individual knowledge. George Siemens (2005) describes connectivism as a cycle: "Personal knowledge is comprised of a network, which feeds into organizations and institutions, which in turn feed back into the network, and then continue to provide learning to individual." This cycle is entirely self sufficient in which the failure of one component of the cycle would ensure the destruction of the cycle as a whole. The cycle cannot exist without it's three key components: personal knowledge, a network, and institutions/organizations. This cycle is much like the ecosystem insofar as a tree is an component of an ecosystem dependent on other components in that system- all of which cannot survive on it's own. In basic terms a tree is dependent of water, sunlight, and  nutrients (soil comprised of decomposed matter). Beyond sunlight, the reason anything exists, a tree has it's part in providing and consuming the components of the cycle as a learner has their part in providing and consuming components in the connectivism cycle. 
In his video, "The Changing Nature of Knowledge," discussing connectivism George Siemens states that the networks that learners form become the primary point of learning, that "the network becomes the learning." This statement holds true to my earlier analogy of learners being a tree in an ecological environment. As a tree grows and develops within an ecological environment it grows its dependance on the environment in which it has formed. The environment acts as the tree's network in which it seeks and provides nourishment much like the network a learner forms, utilizes, and maintains.