Species interactions across trophic levels mediate rainfall effects on dryland vegetation dynamics

Arid ecosystems are strongly limited by water availability, and
precipitation plays a major role in the dynamics of all species in arid
regions, as well as the ecosystem processes that occur there. However,
understanding how biotic interactions mediate long-term responses of
dryland ecosystems to rainfall remains very fragmented. We report on a
unique large-scale field experiment spanning 25 years and three trophic
levels (plants, small mammal herbivores, predators) in a dryland ecosystem
in the northern Chilean Mediterranean Region where we assessed how biotic
interactions influence the long-term plant community responses to
precipitation. As the most persistent ecological changes in dryland
systems may result from changes in the structure, cover, and composition
of the perennial vegetation, we emphasized the interplay between bottom-up
and top-down controls of perennial plants in our analyses. Rainfall was
the primary factor affecting the dynamics of, and interactions among,
plants and small mammals. Ephemeral plant cover dynamics closely tracked
short-term annual rainfall, but seemed unaffected by top-down controls
(herbivory). In contrast, the response of the perennial plant cover to
precipitation was mediated by: (i) a complex interplay between subtle
top-down (herbivory) controls that become more apparent in the long-term,
(ii) competition with ephemeral plants during wet years, and (iii) an
indirect effect of predators on subdominant shrubs and perennial herbs.
This long-term field experiment highlights how climate-induced responses
of arid perennial vegetation are influenced by interactions across trophic
levels and temporal scales. In the face of global change, understanding
how multi-trophic controls mediate dryland vegetation responses to climate
is essential to properly managing the conservation of biodiversity in arid
systems.