Biology Reference
In-Depth Information
and large-seeded trees [15], [34]. In our study site, pioneer species represent over
80% of all tree species and individuals recorded in the fragments, whereas they
represent less 50% in core areas [19], [39]. Furthermore, recent surveys in this site
have documented an outstanding predominance of pioneer species in seed rain
[15] and seedling assemblages [34], [74] which suggests that pioneer dominance
may represent a more pervasive, long-term feature of old and severally fragmented
landscapes.
Assuming that pioneer plants are r-strategists and shade-tolerant (climax) ones
are K- strategists [21], it is reasonable to expect that these two species groups differ
in terms of reproductive traits, sexual systems, and reproductive systems. Some of
our findings, such as higher scores of pollination by DSI and flowers with easily
accessible resources (inconspicuous+open/dish flowers) in fragments, may simply
reflect the dominance of pioneer trees in this habitat as these traits appear to be
more frequent among pioneers (65% of the DSI-pollinated species and over 68%
of the species with inconspicuous/open/dish flowers are pioneers). On the other
hand, a trait such as pollination by bats that was significantly more frequent in
control plots (richness and abundance) is also positively associated with a sub-
set of shade-tolerant species-75% of the bat-pollinated species are shade-tolerant
(e.g. Bauhinia, Hymenaea-Fabaceae; Manilkara-Sapotaceae; Quararibea-Malva-
ceae sensu APG II [75]). Because the pioneer species recorded in the fragments
- including both short- and long-lived pioneers - belong to 16 orders and eight
superordinal clades (sensu APG II [75]), the patterns documented here cannot be
explained by phylogenetic clustering among pioneers. Even pioneer species that
were recorded exclusively in forest fragments belong to four families in four orders
and three superordinal clades. Unfortunately, because of the large number of cat-
egories for each reproductive trait and the low number of tree species within each
category, it was not possible to properly test trait-associated differences between
pioneer and shade-tolerant tree species.
In tropical forests, 98-99% of the flowering plant species (and 97.5% of the
trees) rely on biotic vectors such as insects and vertebrates for successful pollina-
tion [76], [77], and it has been broadly assumed that plant-pollinator interactions
are largely detrimentally affected by habitat loss and fragmentation [26]-[29],
[78]-[81]. Some of the changes we documented in our fragments are therefore
expected, particularly the lack or reduced occurrence of some pollination systems
[27], [28], [82]. For instance, fragmented habitats may support less pollinators
than continuous habitats due to limited resource availability for pollinators (area-
related effects on animal populations). In turn, plants can have a depressed repro-
ductive output as consequence of changes in pollinator diversity, composition, or
behavior [25], [28], i.e., reproductive impairment driven by pollination limita-
tion [sensu 29]. Studies on pollinator diversity carried out in our landscape have
