Ecol Evol. 2015 Sep 4;5(18):4141-60. doi: 10.1002/ece3.1663. eCollection 2015.
Abstract
Mutually
enhancing organisms can become reciprocal determinants of their
distribution, abundance, and demography and thus influence ecosystem
structure and dynamics. In addition to the prevailing view of parrots
(Psittaciformes) as plant antagonists, we assessed whether they can act
as plant mutualists in the dry tropical forest of the Bolivian
inter-Andean valleys, an ecosystem particularly poor in vertebrate
frugivores other than parrots (nine species). We hypothesised that if interactions between parrots
and their food plants evolved as primarily or facultatively
mutualistic, selection should have acted to maximize the strength of
their interactions by increasing the amount and variety of resources and
services involved in particular pairwise and community-wide interaction
contexts. Food plants showed different growth habits across a wide
phylogenetic spectrum, implying that parrots
behave as super-generalists exploiting resources differing in
phenology, type, biomass, and rewards from a high diversity of plants
(113 species from 38 families). Through their feeding activities, parrots
provided multiple services acting as genetic linkers, seed facilitators
for secondary dispersers, and plant protectors, and therefore can be
considered key mutualists with a pervasive impact on plant assemblages.
The number of complementary and redundant mutualistic functions provided
by parrots to
each plant species was positively related to the number of different
kinds of food extracted from them. These mutually enhancing interactions
were reflected in species-level properties (e.g., biomass or dominance)
of both partners, as a likely consequence of the temporal convergence
of eco-(co)evolutionary dynamics shaping the ongoing structure and
organization of the ecosystem. A full assessment of the, thus far
largely overlooked, parrot-plant mutualisms and other ecological linkages could change the current perception of the role of parrots in the structure, organization, and functioning of ecosystems.
