food web

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.

Abstract: 
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.

Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp

Crowl, Todd A.; Welsh, Vanessa; Heartsill-Scalley, Tamara 2006. Effects of different types of conditioning on rates of leaf-litter shredding by Xiphocaris elongata, a Neotropical freshwater shrimp.. J. N. Am. Benthol. Soc., 25(1):198-208.

Abstract: 
Temperate headwater streams with closed canopies rely on inputs of terrestrially derived organic matter to provide the major energy basis for their food webs. Microbial colonization, or conditioning, makes leaf litter more nutritional and palatable to stream detritivores, but few studies have investigated the relative importance of litter source to macroshredders in tropical streams. We determined the source (terrestrial, aquatic, or aerial), quantity, and species composition of allochthonous inputs into the Quebrada Prieta, a tropical headwater stream in Puerto Rico, as a first step toward understanding the importance of conditioning history to rates of tropical leaf-litter processing by decapod consumers. Fresh leaves of 4 common species of leaves were treated by exposing them to different conditions for 2 wk. These exposure treatments (conditioning histories) represented routes by which leaves might enter streams and included submersion (aquatic input), incubation on the streambank soil (terrestrial input), and suspension above the ground (aerial input). Conditioned leaves were placed in small experimental microcosms with or without shrimp (Xiphocaris elongata) for 20 d. Shrimp significantly increased the rate of decomposition of all leaf species independent of conditioning history. Conditioning history had little effect on breakdown rates independent of the presence of shrimp. One species (Rourea surinamensis) had faster mass loss when the leaves were conditioned as aquatic inputs rather than as terrestrial or aerial inputs. Our results indicate that conditioning history has little effect on the ability of some macroconsumers to alter detrital foodweb dynamics in tropical streams. Tropical stream ecosystems may function differently from temperate ecosystems because of the dominance of large detritivores such as shrimps.

Experimental Removal of Insectivores from Rain Forest Canopy: Direct and Indirect Effects

Dial, Roman, and Jonathan Roughgarden. 1995. Experimental Removal of Insectivores from Rain Forest Canopy: Direct and Indirect Effects. Ecology 76:1821–1834

Abstract: 
This study considered the effects of insectivorous Anolis lizards on a large, complex food web of arthropods and associated herbivory in a tropical rain forest canopy. We excluded Anolis lizards for 6 mo from 20—30 m high tree crowns in Puerto Rican rain forest. Simultaneous with lizard exclusion, we sampled orb spiders, airborne arthropods, and leaf arthropods in lizard removal crowns and in controls. We also sampled herbivory at the end of the experiment. Lizard removal had strong, statistically significant, positive effects on arthropods >2 mm in length and weak negative effects on arthropods <2 mm. Parameters of arthropod body size distributions differed between removals and controls for leaf arthropods, but not for airborne arthropods. Among arthropod taxa >2 mm, both predatory, i.e., orb spiders and parasitic Hymenoptera, and nonpredatory forms, i.e. Diptera, Coleoptera, Orthoptera, and Blattaria, showed strong significant and positive responses to lizard removal. Large Psocoptera, Homoptera, leaf spiders, and ants did not show significant overall responses to lizard removal. Frequency of herbivore damage on new leaves was positively correlated with abundance of Orthoptera and Blattaria. This damage was significantly greater in lizard removal crowns than in controls, indicating an indirect effect of anoles on plants. The indirect effect of lizards on small arthropods through the predatory anthropod pathway appeared weak. Results of lizard removal shown by this study corroborate other lizard removal studies from more xeric, ground—level habitats with simpler food webs in the West Indies, particularly with respect to orb spiders and herbivory. Taken together with the results of similar experiments performed in trophically less complex systems, this experiment suggests that food web size is less important than body size in determining interaction strength between community members.
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