Biotic factors:

Predation has some effects on survival and behavior of some small mammal species.  However, these effects are relatively small and temporary.

--Predation neither prevents small mammal increases nor accelerates their declines

--Predators have greatest effects on principal prey (e.g., foxes on degus) when prey numbers are low or beginning to  increase (see graph at left)

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Abiotic factors:

Increased precipitation triggers dramatic changes in the plant community including higher ephemeral cover and seed densities (see graph at left)

 

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Abiotic factors:

Increased vegetation (and indirectly precipitation) leads to dramatic increases in small mammal populations among most species (see graph at left)

--Slower reproducing species such as O. degus  show cumulative increases whereas faster reproducing species such as P. darwini and A. olivaceus show about the same increases irrespective of rainfall duration

 

 

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Opportunistic species such as
O. longicaudatus show sporadic occurrence or long protracted increases (A. longipilis) with long periods of absence
--Thylamys elegans, a marsupial, has strong annual fluctuations in the thorn scrub (see graph at left)