Abstract
Functional diversity has been postulated to be critical for the maintenance of ecosystem functioning, but the way it can be disrupted by human-related disturbances remains poorly investigated. Here we test the hypothesis that habitat fragmentation changes the relative contribution of tree species within categories of reproductive traits (frequency of traits) and reduces the functional diversity of tree assemblages. The study was carried out in an old and severely fragmented landscape of the Brazilian Atlantic forest. We used published information and field observations to obtain the frequency of tree species and individuals within 50 categories of reproductive traits (distributed in four major classes: pollination systems, floral biology, sexual systems, and reproductive systems) in 10 fragments and 10 tracts of forest interior (control plots). As hypothesized, populations in fragments and control plots differed substantially in the representation of the four major classes of reproductive traits (more than 50% of the categories investigated). The most conspicuous differences were the lack of three pollination systems in fragments-pollination by birds, flies and non-flying mammals-and that fragments had a higher frequency of both species and individuals pollinated by generalist vectors. Hermaphroditic species predominate in both habitats, although their relative abundances were higher in fragments. On the contrary, self-incompatible species were underrepresented in fragments. Moreover, fragments showed lower functional diversity (H' scores) for pollination systems (−30.3%), floral types (−23.6%), and floral sizes (−20.8%) in comparison to control plots. In contrast to the overwhelming effect of fragmentation, patch and landscape metrics such as patch size and forest cover played a minor role on the frequency of traits. Our results suggest that habitat fragmentation promotes a marked shift in the relative abundance of tree reproductive traits and greatly reduces the functional diversity of tree assemblages in fragmented landscapes.
Highlights
Functional diversity can be defined as a variety of life-history traits presented by an assemblage of organisms [1,2] and it has been postulated to be critical for the maintenance of ecosystem processes and properties [3]
Fragments had a 33% increase in the proportion of tree species pollinated by diverse small insects (DSI) in comparison to control plots (Table 2)
Fragments had proportionately more tree species pollinated by generalist vectors (66.43614.08%) than control plots (58.1867.87%; t = 1.616; d.f. = 18; P = 0.06); the relative abundance individuals pollinated by generalists was higher in fragments than control plots (71.71616.5% vs. 46.10615.53, U = 13.0; P = 0.0052)
Summary
Functional diversity can be defined as a variety of life-history traits presented by an assemblage of organisms [1,2] and it has been postulated to be critical for the maintenance of ecosystem processes and properties [3]. Previous empirical work has suggested that ecosystems with a high diversity of functional traits have greater efficiency of water, nutrient, and light use, as well as higher productivity [3,4]. They may be more resilient [5] and resistant to biological invasions and to biodiversity loss [6,7]. Fragments usually exhibit reduced species richness and diversity, near edges. Because tropical pioneer trees usually share a similar set of life-history traits irrespective of their taxonomic affinities [20,21,22], this biased ratio of pioneers to shade-tolerant plants may reduce the functional diversity of tree assemblages in fragments
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