258
1.1. Armesto et al.
We propose that Sephanoides and Elaenia are pivotal species for the
maintenance of regional diversity in the temperate rainforest of Chile and
that a reduction in their populations as consequence of increasing habitat
destruction (e.g., replacement of native forests by conifer plantations,
logging of native forest) could affect the regeneration and colonizing
ability of forest plants, resulting in a decline in these populations in other
areas of the temperate rainforest. This hypothesis is supported by two
lines of evidence: 1) the rich plant species assemblages that depend on
these two bird species for their reproduction; and 2) the apparent lack of
alternative species that could substitute Sephanoides and Elaenia in their
roles as major seed disperser and pollinator respectively.
From the point of view of the birds, another species that may also be
pivotal (sensu Howe, 1984) within the guild of hummingbird-pollinated
plants is the hemiparasite Tristerix corymbosus. This is the only species
providing a nectar source for hummingbirds during winter in Chiloe.
Although hummingbirds are reported to migrate locally (Vuilleumier,
1985), we do not know what fraction of the summer population comes
from immigrants versus overwinter residents. The survival of the latter
may depend of the extended flowering of Tristerix. For the resident fruiteating birds (e.g. , Turdus falcklandii), winter-fruiting species, such as
Pernettya mucronata , Luma apiculata, and Myrceugenia ovata, may be an
important food source yet to be documented .
Geographical Comparisons
In general, South American temperate forests are characterized by an
impoverished avifauna (Vuilleumier, 1985), which is reflected in the low
bird species richness as compared to other forests (Willson et aI., this
volume). This low species richness can be atrributed to avifaunal extinctions during glacial times and to a lack of postglacial recolonization
due to the extreme isolation of southern temperate forests from other
forested rigions in South America.
Only one species of hummingbird is found in the forest of Chiloe,
which feeds on at least 14 species of plants. This is one of the largest
assemblages of plant species dependent on a single hummingbird species
that we have found in a survey of guilds of hummingbird-pollinated plants
in various forest ecosystems, as shown in Table 12.4. Furthermore, unlike
in many tropical systems, there is no "interchangeable alternative"
hummingbird for Sephanoides were its population to decline. This
emphasizes the importance of Sephanoides for the guild of plants with
red, tubular flowers. Recently, we have identified other nectarivorus
birds, all passerines, feeding on flowers of Embothrium coccineum (Proteaceae). Although ' these species may have some role in pollination
(Smith-Ramirez & Armesto, unpublished manuscript), this does not
decrease the relevance of Sephanoides as the main pollinator in this
forest.
1.1. Armesto et al.
We propose that Sephanoides and Elaenia are pivotal species for the
maintenance of regional diversity in the temperate rainforest of Chile and
that a reduction in their populations as consequence of increasing habitat
destruction (e.g., replacement of native forests by conifer plantations,
logging of native forest) could affect the regeneration and colonizing
ability of forest plants, resulting in a decline in these populations in other
areas of the temperate rainforest. This hypothesis is supported by two
lines of evidence: 1) the rich plant species assemblages that depend on
these two bird species for their reproduction; and 2) the apparent lack of
alternative species that could substitute Sephanoides and Elaenia in their
roles as major seed disperser and pollinator respectively.
From the point of view of the birds, another species that may also be
pivotal (sensu Howe, 1984) within the guild of hummingbird-pollinated
plants is the hemiparasite Tristerix corymbosus. This is the only species
providing a nectar source for hummingbirds during winter in Chiloe.
Although hummingbirds are reported to migrate locally (Vuilleumier,
1985), we do not know what fraction of the summer population comes
from immigrants versus overwinter residents. The survival of the latter
may depend of the extended flowering of Tristerix. For the resident fruiteating birds (e.g. , Turdus falcklandii), winter-fruiting species, such as
Pernettya mucronata , Luma apiculata, and Myrceugenia ovata, may be an
important food source yet to be documented .
Geographical Comparisons
In general, South American temperate forests are characterized by an
impoverished avifauna (Vuilleumier, 1985), which is reflected in the low
bird species richness as compared to other forests (Willson et aI., this
volume). This low species richness can be atrributed to avifaunal extinctions during glacial times and to a lack of postglacial recolonization
due to the extreme isolation of southern temperate forests from other
forested rigions in South America.
Only one species of hummingbird is found in the forest of Chiloe,
which feeds on at least 14 species of plants. This is one of the largest
assemblages of plant species dependent on a single hummingbird species
that we have found in a survey of guilds of hummingbird-pollinated plants
in various forest ecosystems, as shown in Table 12.4. Furthermore, unlike
in many tropical systems, there is no "interchangeable alternative"
hummingbird for Sephanoides were its population to decline. This
emphasizes the importance of Sephanoides for the guild of plants with
red, tubular flowers. Recently, we have identified other nectarivorus
birds, all passerines, feeding on flowers of Embothrium coccineum (Proteaceae). Although ' these species may have some role in pollination
(Smith-Ramirez & Armesto, unpublished manuscript), this does not
decrease the relevance of Sephanoides as the main pollinator in this
forest.