Associations of reduced composition and simplified structure have arisen during physiographic or climatic change and migration through the elimination of some species and the loss of ecological status of others.
Associations
simplify or grow sparser
Should the terrain or the climate
Change for the harsher.
Some species move
Some disappear
Or their status drops.
That they have weakened
Is very clear:
They slip and sag
And they falter
And lag.