biological invasions

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.

Multi-scale analysis of species introductions: combining landscape and demographic models to improve management decisions about non-native species

Brown, K.A., Spector, S.& Wu, W. (2008)Multi-scale analysis of species introductions:
combining landscape and demographic models to improve management
decisions about non-native species. Journal of Applied Ecology, 45,

1. Non-native, invasive species can affect biological patterns and processes at multiple ecological scales. The multi-scalar effects of invasions can influence community structure, ecosystem processes and function, and the nature and intensity of ecological interactions. Consequently, efforts to assess the spread of invasive species may benefit from a multi-scale analytic approach. 2. We analysed results from landscape- and population-scale models for Syzygium jambos , a nonnative tree in the Luquillo Mountains of Puerto Rico, to demonstrate a multi-scale approach that can be used to inform management decisions about invasive plants. At the landscape-level, we used an Ecological Niche Modelling approach to predict environmentally suitable habitats for the target plant. At the population-level, we constructed matrix projection models to determine the finite rate of population increase ( λ ) for S. jambos . We then extrapolated λ values to the landscape-scale to obtain a distribution map of λ values for the Luquillo forest. 3. The landscape analyses suggested that the most environmentally suitable habitats were those most similar to where S. jambos had already been observed. The population-level analyses showed that four of the seven populations had λ values less than 1, indicating that they were projected to be below replacement. The λ distribution map showed that S. jambos growth was highest in areas where it was most common and lowest in areas where it was most rare. 4. Our analyses further suggested that the importance of different drivers of invasion and the environmental variables that mediate them appear to be strongly scale-dependent. Past disturbances seemed most important for controlling invasions at fine-spatial scales; while abiotic environmental variables modulated coarse-scale invasion dynamics. 5. Synthesis and applications. We have shown that a multi-scale analytic approach can be used to manage invasive species by simultaneously targeting susceptible life stages and rapidly growing populations in a landscape. The utility of this approach stems from an ability to: (i) map the distribution of habitats that can potentially sustain λ values above replacement; (ii) identify populations to manage or monitor during selected stages of an invasion; (iii) forecast the probability for a target species to increase above a critical threshold abundance; and (iv) set priorities for control and monitoring actions.

Non-Indigenous Bamboo along Headwater Streams of the Luquillo Mountains, Puerto Rico: Leaf Fall, Aquatic Leaf Decay and Patterns of Invasion

O'CONNOR, PAUL J.; COVICH, ALAN P.; SCATENA, F. N.; LOOPE, LLOYD L. 2000. Non-indigenous bamboo along headwater streams of the Luquillo Mountains, Puerto Rico: leaf fall, aquatic leaf decay and patterns of invasion. Journal of Tropical Ecology 16 :499-516.

The introduction of bamboo to montane rain forests of the Luquillo Mountains, Puerto Rico in the 1930s and 1940s has led to present-day bamboo monocultures in numerous riparian areas. When a non-native species invades a riparian ecosystem, in-stream detritivores can be affected. Bamboo dynamics expected to in¯uence stream communities in the Luquillo Experimental Forest (LEF) were examined. Based on current distributions, bamboo has spread downstream at a rate of 8 m y-1. Mean growth rate of bamboo culms was 15.3 cm d-1. Leaf fall from bamboo stands exceeded that of native mixed-species forest by c. 30% over a 10-mo study. Bamboo leaves (k = -0.021), and leaves from another abundant riparian exotic, Syzygium jambos (Myrtaceae) (k = -0.018), decayed at relatively slow rates when submerged in streams in ®ne-mesh bags which excluded macro-invertebrate leaf processors. In a second study, with leaf processors present, bamboo decay rates remained unchanged (k = -0.021), while decay rates of S. jambos increased (k = -0.037). Elemental losses from bamboo leaves in streams were rapid, further suggesting a change in riparian zone / stream dynamics following bamboo invasion. As non-indigenous bamboos spread along Puerto Rico streams, they are likely to alter aquatic communities dependent on leaf input.
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