12. The Importance of Plant-Bird Mutualisms in
the Temperate Rainforest of Southern South America
Juan J. Armesto, Cecilia Smith-Ramirez, and Carlos Sabag
In the Neotropics, numerous nectar- and fruit-eating birds engage in loose
mutualisms with plants that provide them with food (Feinsinger, 1983,
1987; Snow, 1981). While feeding on the fruit pulp or flower nectar, the
birds act as seed dispersers or pollinators. These relationships contribute
significantly to species diversity in many tropical forests (Gentry, 1982;
Stiles, 1985).
Most plant-disperser and plant-pollinator associations with birds can be
classified as "diffuse" mutualisms; that is, one species of frugivore or
nectarivore may feed on various plant species, while at the same time, the
pollen or seeds of a given plant species may be transported by several
bird species (Feinsinger, 1983; Herrera, 1982). Mutualistic relationships
are thus structured around guilds, or groups of interdependent plants and
birds (e.g., Herrera 1982, 1984; Jordano, 1987; Murray et al. , 1987),
rather than species pairs.
Howe (1984) has argued that in these diffuse mutualistic systems, plant
species that flower or fruit during periods of food scarcity or bird species
that are active during times of low pollinator or frugivore activity may
playa critical role in the maintenance of the entire assemblage. These are
called pivotal or keystone species (Gilbert, 1980; Howe, 1984). Knowledge
about these pivotal or keystone species is of critical importance for
understanding community dynamics and for evaluating the potential
248
the Temperate Rainforest of Southern South America
Juan J. Armesto, Cecilia Smith-Ramirez, and Carlos Sabag
In the Neotropics, numerous nectar- and fruit-eating birds engage in loose
mutualisms with plants that provide them with food (Feinsinger, 1983,
1987; Snow, 1981). While feeding on the fruit pulp or flower nectar, the
birds act as seed dispersers or pollinators. These relationships contribute
significantly to species diversity in many tropical forests (Gentry, 1982;
Stiles, 1985).
Most plant-disperser and plant-pollinator associations with birds can be
classified as "diffuse" mutualisms; that is, one species of frugivore or
nectarivore may feed on various plant species, while at the same time, the
pollen or seeds of a given plant species may be transported by several
bird species (Feinsinger, 1983; Herrera, 1982). Mutualistic relationships
are thus structured around guilds, or groups of interdependent plants and
birds (e.g., Herrera 1982, 1984; Jordano, 1987; Murray et al. , 1987),
rather than species pairs.
Howe (1984) has argued that in these diffuse mutualistic systems, plant
species that flower or fruit during periods of food scarcity or bird species
that are active during times of low pollinator or frugivore activity may
playa critical role in the maintenance of the entire assemblage. These are
called pivotal or keystone species (Gilbert, 1980; Howe, 1984). Knowledge
about these pivotal or keystone species is of critical importance for
understanding community dynamics and for evaluating the potential
248