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| Aim
To understand cross-taxon spatial congruence patterns of bird and woody
plant species richness. In particular, to test the relative roles of functional relationships
between birds and woody plants, and the direct and indirect environmental
effects on broad-scale species richness of both groups.
Location
Kenya.
Methods
Based on comprehensive range maps of all birds and woody plants
(native species > 2.5 m in height) in Kenya, we mapped species richness of both
groups. We distinguished species richness of four different avian frugivore guilds
(obligate, partial, opportunistic and non-frugivores) and fleshy-fruited and nonfleshy-
fruited woody plants. We used structural equation modelling and spatial
regressions to test for effects of functional relationships (resource–consumer interactions
and vegetation structural complexity) and environment (climate and habitat
heterogeneity) on the richness patterns.
Results
Path analyses suggested that bird and woody plant species richness are
linked via functional relationships, probably driven by vegetation structural complexity
rather than trophic interactions. Bird species richness was determined in our
models by both environmental variables and the functional relationships with
woody plants. Direct environmental effects on woody plant richness differed from
those on bird richness, and different avian consumer guilds showed distinct
responses to climatic factors when woody plant species richness was included in path
models.
Main conclusions
Our results imply that bird and woody plant diversity are
linked at this scale via vegetation structural complexity, and that environmental
factors differ in their direct effects on plants and avian trophic guilds. We conclude
that climatic factors influence broad-scale tropical bird species richness in large
part indirectly, via effects on plants, rather than only directly as often assumed.
This could have important implications for future predictions of animal species
richness in response to climate change. | |
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