Natural Changes Mimic "Invaders"
Natural successional trajectories highly plastic, with pronounced stochastic component.
Natural outbreak-crash sequences (jackrabbits, lemmings, oak moths).
Natural changes in disturbance regimes and whiplashing of climate change community structure.
Natural pathogen outbreaks, cf. Tsuga. (Davis 1988)
Natural and frequent reciprocal "invasions". (Kellman 1980)
Natural & frequent translocations.
Natural "monocultures" (Typha, Phragmites, Sequoia, etc.)
Natural alterations of basic ecosystem properties by species (Pteridium, Spartina, etc.).
Natural wholesale changes in community composition and structure due to episodic recruitment or population variations of "keystone" species.
Episodic recruitment of highly visible species (Quercus, Macrozamia).