Stable isotopes

Spatial and temporal patterns of water quality indicators in reef systems of southwestern Puerto Rico

Otero E.E. Spatial and temporal patterns of water quality indicators in reef systems of southwestern Puerto Rico. Carribbean journal of science, Vol 45, Is 2-3, 2009, pp. 168-180

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.

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.

Food Web Structure in Exotic and Native Mangroves: A Hawaii-Puerto Rico Comparison

Demopoulos, Amanda W. J., Brian Fry, and Craig R. Smith. 2007. Food web structure in exotic and native mangroves: A hawaii-puerto rico comparison. Oecologia 153 (3) (SEP): 675-86.

Plant invasions can fundamentally alter detrital inputs and the structure of detritus-based food webs. We examined the detrital pathways in mangrove food webs in native (Puerto Rican) and introduced (Hawaiian) Rhizophora mangle forests using a dual isotope approach and a mixing model. Based on trophic-level fractionation of 0- \%of or <513Can d 2-3%c for Sl5N, among the invertebrates, only nematodes, oligochaetes, and nereid polychaetes from native mangroves exhibited stable isotopes consistent with a mangrove-deriveddi et. Certainf auna,i n particulartu bificid oligochaetes, had Sl3C values consistent with the consumption of mangrove leaves, but they were depleted in 15N, suggesting their primary nitrogen source was low in 15N, and was possibly N2-fixing bacteria. In introduced mangroves, all feeding groups appeared to rely heavily on nonmangroves ources, especially phytoplanktonin puts.M ixing model results and discriminant analysis showed clear separation of introduced and native mangrove sites based on differential food source utilization within feeding groups, with stronger and more diverse use of benthic foods observed in native forests. Observed differences between native and invasive mangrove food webs may be due to Hawaiian detritivores being poorly adapted to utilizing the tannin-rich, nitrogen-poor mangrove detritus. In addition, differential utilization of mangrove detritus between native and introduced mangroves may be a consequence of forest age. We postulate that increasing mangrove forest age may promote diversification of bacterial food webs important in N and S cycling. Our results also suggest a potentially important role for sulfur bacteria in supporting the most abundantin faunalc onsumers,n ematodes,i n the most mature systems.

Differences in urbanization and degree of marine influence are reflected in d13C and d15N of producers and consumers in seagrass habitats of Puerto Rico

Olsen, Ylva S., Sophia E. Fox, Erin L. Kinney, Mirta Teichberg, and Ivan Valiela. 2010. Differences in urbanization and degree of marine influence are reflected in delta(13)C and delta(15)N of producers and consumers in seagrass habitats of puerto rico. Marine Environmental Research 69 (3) (APR): 198-206.

Couplings between land use and marine food webs in tropical systems are poorly understood. We compared land–sea coupling in seven sites around Puerto Rico, differing in the degree of precipitation and urbanization, by measuring d13C and d15N in producers and consumers. d15N values were influenced by human activity: the food web from sites near urbanized centers was on average 1‰ heavier in d15N compared to undeveloped sites. This is most likely due to wastewater inputs from septic systems relatively near the shoreline. Changes in d13C were best explained by differences in the degree of marine influence. Where terrestrial inputs from a major river dominated, d13C values were lighter, whereas sites further from land and in locations exposed to oceanic currents had heavier d13C values, characteristic of a marine source of dissolved organic carbon. We found no significant effect of precipitation on connectivity in spite of a twofold difference in annual average rainfall between the north and south coast. The results suggest there is some connectivity between land and sea in Puerto Rico, despite high rates of evaporation relative to precipitation.
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