population structure

Understanding survival and abundance of overwintering warblers: Does rainfall matter?

Dugger, KM, J. Faaborg, WJ Arendt, and KA Hobson. 2004. Understanding survival and abundance of overwintering warblers: Does rainfall matter? Condor 106 (4) (NOV): 744-60.

Abstract: 
We investigated relationships between warbler abundance and survival rates measured on a Puerto Rican wintering site and rainfall patterns measured on the wintering site and in regions where these warblers breed, as estimated using stable-isotope analysis (dD) of feathers collected from wintering birds. We banded birds using constant-effort mist netting from January 1989–2003 in the Gunica Forest of southwestern Puerto Rico. Blackand- white Warblers (Mniotilta varia), American Redstarts (Setophaga ruticilla), and Ovenbirds (Seiurus aurocapilla) dominated the Neotropical migrant capture totals each winter, with resulting sample sizes large enough to estimate survival rates. Estimates of capture probability from survival modeling allowed us to estimate abundance from mist-netting capture totals for Black-and-white Warblers and Ovenbirds. Stable-hydrogen isotopes showed that the three focal species came mostly from the eastern United States. Black-andwhite Warbler abundance was related to rainfall total deviations from normal in Gua´nica Forest, and Ovenbird abundance was related to total annual rainfall in the United States. Survival models with rainfall covariates were weakly supported overall, but apparent survival of Black-and-white Warblers and American Redstarts was negatively related to rain during the first 6 months of the year at Gua´nica, and Ovenbird survival was related to rainfall during the spring in the southeastern U.S. Abundance and apparent survival exhibited similar, species-specific patterns of association with rainfall for Black-and-white Warblers and Ovenbirds. Winter rainfall was important to demographic parameters of Blackand- white Warblers, and breeding-season rain was important to Ovenbirds.

Effects of Hurricane Hugo on Manilkara bidentata, a Primary Tree Species in the Luqillo Experimental Forest of Puerto Rico

Effects of Hurricane Hugo on Manilkara bidentata, a Primary Tree Species in the Luqillo Experimental Forest of Puerto Rico
Chengxia You and William H. Petty
Biotropica
Vol. 23, No. 4, Part A. Special Issue: Ecosystem, Plant, and Animal Responses to Hurricanes in the Caribbean (Dec., 1991), pp. 400-406

Abstract: 
Changes in the population structure and recruitment characteristics of Manilkara bidentata populations were investigated at two sites (El Verde & Bisley) in the Luquillo Experimental Forest (LEF), at one month and nine months after Hurricane Hugo. Fatal damage occurred to 4 percent of the trees at the El Verde site. Severe damage to mature trees disrupted seed production. Sixty percent of the young seedling population was destroyed, mainly as a result of burial by litter. For surviving seedlings, the posthurricane growth rate (in height) of old seedlings was 2 cm/mo, 17 times greater than that under prehurricane conditions. The prehurricane population of young seedlings had a large number of individuals and a long transition period (over 14 yr); whereas, the posthurricane population had fewer individuals and a shorter transition period (less than 2 yr). Increased growth rates of seedlings were related to increased light at the forest floor. The recruitment rate of the Manilkara population from the seedling size class into the sapling size class was greater than that under prehurricane conditions. Rapid adjustment to posthurricane conditions, high tree survival, and increased number of seedlings recruited into larger size classes may increase the abundance of Manilkara trees in the forest. These adaptations are especially significant in the LEF and other forests which experience frequent hurricane disturbances. Based upon the effects of Hurricane Hugo, it appears that hurricanes play an important role in releasing suppressed seedling growth of Manilkara populations and that hurricanes may contribute to the abundance of Manilkara trees in the LEF
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