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| Ecological communities that experience stable climate conditions
have been speculated to preserve more specialized
interspecific associations and have higher proportions of
smaller ranged species (SRS). Thus, areas with disproportionally
large numbers of SRS are expected to coincide
geographically with a high degree of community-level ecological
specialization, but this suggestion remains poorly
supported with empirical evidence. Here, we analysed
data for hummingbird resource specialization, range size,
contemporary climate, and Late Quaternary climate stability
for 46 hummingbird–plant mutualistic networks
distributed across the Americas, representing 130 hummingbird
species (ca 40% of all hummingbird species).
We demonstrate a positive relationship between the proportion
of SRS of hummingbirds and community-level
specialization, i.e. the division of the floral niche among
coexisting hummingbird species. This relationship
remained strong even when accounting for climate, furthermore,
the effect of SRS on specialization was far stronger
than the effect of specialization on SRS, suggesting that climate
largely influences specialization through species’
range-size dynamics. Irrespective of the exact mechanism
involved, our results indicate that communities consisting
of higher proportions of SRS may be vulnerable to disturbance
not only because of their small geographical ranges,
but also because of their high degree of specialization. | |
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