Doctor of Philosophy (PhD)
Renewable Natural Resources
The Amazon rainforest is experiencing rapid deforestation due to ranching, agriculture, and urban development, which often leads to remnant patches serving as refugia for forest organisms. By mist-netting passerines in 11 forest fragments (1-, 10-, and 100-ha patches) and nearby continuous forest at the Biological Dynamics of Forest Fragmentation Project near Manaus, Brazil, I conducted a series of studies to identify mechanisms that drive population changes in fragmented landscapes. First, I examined the age structure of bird populations from six ecological guilds in fragments and continuous forest. Immatures are the dispersing age group in birds, and their relative abundance in fragments was often driven by the age of regenerating second growth surrounding fragments. The relative abundance of adults, the resident age group, in fragments was often driven by patch size. Differences in how guilds responded to fragmentation depended on their dispersal propensity, measured with mark–recapture techniques, with increasing dispersal propensity corresponding to increased relative abundance of immatures in fragments. Second, I quantified variation in the frequency of molting and breeding simultaneously (called molt–breeding overlap; MBO) among species. I propose that molting and breeding simultaneously requires a consistent or predictable environment, like a humid rainforest understory. Frequent molt–breeding overlap may preclude living in more seasonally fluctuating environments like rainforest fragments. Suboscines, particularly antbirds, had more frequent MBO and were more sensitive to fragmentation than oscine. Finally, I examined the consequences of fragmentation on host–ectoparasite dynamics. Feather mites, haematophagous mites, and chewing lice showed similar richness and abundance on hosts that occupied either interior forests or fragment edges. In Thamnophilidae and frugivores, ectoparasite removal caused an increase in body condition, but only for hosts occupying interior forests and not those on fragment edges. Feather mites were beneficial to hosts in interior forest, but became harmful along edges, suggesting that fragmentation can alter delicate host–parasite dynamics in complicated ways. Understanding these relationships may help explain host population declines in fragmented landscapes.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Johnson, Erik I., "Fragmentation sensitivity and its consequences on demography and host-ectoparasite dynamics in amazonian birds" (2011). LSU Doctoral Dissertations. 2618.
Stouffer, Philip C