Long-term demographic consequences of habitat fragmentation to a tropical understory bird community

By: , and 



Tropical deforestation continues to cause population declines and local extinctions in centers of avian diversity and endemism. Although local species extinctions stem from reductions in demographic rates, little is known about how habitat fragmentation influences survival of tropical bird populations or the relative importance of survival and fecundity in ultimately shaping communities. We analyzed 22 years of mark-recapture data to assess how fragmentation influenced apparent survival, recruitment, and realized population growth rate within 22 forest understory bird species in the Usambara Mountains, Tanzania. This represents the first such effort, in either tropical or temperate systems, to characterize the effect of deforestation on avian survival across such a broad suite of species. Long-term demographic analysis of this suite of species experiencing the same fragmented environment revealed considerable variability in species' responses to fragmentation, in addition to general patterns that emerged from comparison among species. Across the understory bird community as a whole, we found significantly lower apparent survival and realized population growth rate in small fragments relative to large, demonstrating fragmentation effects to demographic rates long after habitat loss. Demographic rates were depressed across five feeding guilds, suggesting that fragmentation sensitivity was not limited to insectivores. Seniority analyses, together with a positive effect of fragmentation on recruitment, indicated that depressed apparent survival was the primary driver of population declines and observed extinctions. We also found a landscape effect, with lower vital rates in one mountain range relative to another, suggesting that fragmentation effects may add to other large-scale drivers of population decline. Overall, realized population growth rate (λ) estimates were < 1 for most species, suggesting that future population persistence even within large forest fragments is uncertain in this biodiversity hotspot.
Publication type Article
Publication Subtype Journal Article
Title Long-term demographic consequences of habitat fragmentation to a tropical understory bird community
Series title Ecology
DOI 10.1890/11-1345.1
Volume 93
Issue 12
Year Published 2012
Language English
Publisher ESA
Publisher location Ithaca, NY
Contributing office(s) Wyoming Cooperative Fish and Wildlife Research Unit
Description 12 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Ecology
First page 2548
Last page 2559
Country Tanzania
Other Geospatial Usambara Mountains
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