Land-use and elevation interact to shape bird functional and phylogenetic diversity and structure: Implications for designing optimal agriculture landscapes

Conversion of rainforests into agriculture resulted in massive changes in
species diversity and community structure. Although the conservation of
the remaining rainforests is of utmost importance, identifying and
creating biodiversity-friendly agriculture landscape is vital for
preserving biodiversity and their functions. Biodiversity studies in
agriculture have often been conducted at low elevations. In this study, we
compared the functional diversity (FD), phylogenetic diversity (PD), and
community structure of birds along an interacting gradient of land-use
(protected rainforest, reserve buffer, and agriculture) and elevation
(low, middle and high) in Sri Lanka. Then, we measured compositional
change by identifying how ecological traits (dietary guild, vertical
strata, body mass, and dispersal ability) and conservation characteristics
(forest-dependence and threatened status) responded to land-use types.
Elevation and land-use interacted with each other to shape bird FD.
Depending on the elevation, FD in agriculture was either higher or similar
to forest. However, PD was similar across all elevation and land-use
types. Bird community structure in forest was functionally and
phylogenetically clustered in comparison to agriculture. Insectivorous
birds declined from forest to agriculture, and so did understorey and
middle-storey birds. But frugivorous and canopy birds did not change
across land-use types, while nectarivores, granivores and carnivores
proliferated in agriculture. Forests were dominated by birds with low
dispersal abilities, but birds in agriculture had more evenly distributed
dispersal abilities. About half of all the individuals in agriculture was
composed of forest species, several of which were threatened. Synthesis
and applications. Most farmers in Sri Lanka practice agriculture on small
farms (c. 2 ha) and rely on services (e.g., pest-control and pollination)
provided by biodiversity for their livelihoods. Our results underline the
important role of these heterogenous agriculture landscapes in maintaining
high functional diversity (FD) and harbouring several threatened species.
While FD in agriculture was comparatively high, conservation decisions
based on land-use alone cannot be reliable, because land-use effects were
elevation dependent. Thus, priority setting exercises aimed at designing
optimal agriculture landscapes should consider landscape features, in
combination with elevation, to benefit both people and wildlife outside
protected areas.