Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of Puerto Rico

Lachnicht, SL, PF Hendrix, and X. Zou. 2002. Interactive effects of native and exotic earthworms on resource use and nutrient mineralization in a tropical wet forest soil of puerto rico. Biology and Fertility of Soils 36 (1) (AUG): 43-52.

Investigation of single or mixed assemblages of native Estherella sp. and exotic Pontoscolex corethrurus from a rain forest in Puerto Rico was undertaken to understand resource use patterns, and linkages with C and N mineralization in a 19-day incubation. Resource use was explored with addition of 15N-enriched leaf litter and 13Cenriched glucose to reconstructed organic and mineral soil horizons. Juvenile Estherella sp. became at least 6.06‰ more enriched in 13C than sub-adult Estherella sp. or adult P. corethrurus. Sub-adult Estherella sp. became >3.6‰ enriched in 13C over P. corethrurus. δ15N acquired by P. corethrurus was greater by 0.83–1.56‰ in the mixed-species than the single-species assemblages. δ15N of subadult Estherella sp. was enriched by 0.73–0.81‰ over juvenile Estherella sp. in the single-species assemblage. Net N immobilization occurred in the organic layer of all 15Nenriched treatments. Net N mineralization in mineral soil layers was significantly greater in microcosms with P. corethrurus than in those containing only Estherella sp.. Cumulative respiration was greatest in P. corethrurus assemblages, however, assemblages with only Estherella sp. released more 13C in respiration. P. corethrurus assimilated different N resources when incubated with, as compared to without, native Estherella sp.. δ13C and δ15N signatures acquired by assimilation of 13C and 15N differed by species, developmental stage, and competitive interactions. The results showed that alone, exotic P. corethrurus induced higher mineralization rates than native Estherella sp., but that the interaction of exotic and native species impinged on resource use by P. corethrurus, reducing the effect of the exotic species on C and N mineralization. Invasion of exotic P. corethrurus may change the mineralization potentials of C and N and their biogeochemical cycling in soils.

Early successional woody plants facilitate and ferns inhibit forest development on Puerto Rican landslides

Walker, L.R., Landau, F.H., Velázquez, E., Shiels,
A.B. and Sparrow, A.D. (2010). Early successional
woody plants facilitate and ferns inhibit forest
development on Puerto Rican landslides. Journal
of Ecology 98, 625-35.

1. The experimental removal of early successional species can explain how plant communities change over time. 2. During a 7.3-year period, early successional woody species, scrambling ferns and tree ferns were removed from a total of 10 landslides in the Luquillo Experimental Forest in north-eastern Puerto Rico. 3. Early successional woody plants in combination with tree ferns decreased species richness and cover of forbs and increased richness of late-successional woody plants compared to removals, facilitating long-term forest development. 4. Dense stands of scrambling ferns decreased both forb and woody plant richness compared to removals, inhibiting forest development. 5. Stands of monospecific tree ferns initially increased woody plant richness compared to removals, but overall decreased woody plant richness and cover, inhibiting forest development. 6. Synthesis. Early successional species both facilitate and inhibit succession on tropical landslides, but detailed predictions of successional trajectories remain elusive and are influenced by stochastic processes including arrival order, the life-form of colonizing species and their competitive interactions.

Plant responses to simulated hurricane impacts in a subtropical wet forest, Puerto Rico

Shiels, Aaron B.; Zimmerman, Jess K.; García-Montiel, Diana C.; Jonckheere, Inge; Holm, Jennifer; Horton, David; Brokaw, Nicholas. 2010. Plant responses to simulated hurricane impacts in a subtropical wet forest, Puerto Rico. Journal of Ecology. doi: 10.1111/j.1365-2745.2010.01646.x.

1. We simulated two key components of severe hurricane disturbance, canopy openness and detritus deposition, to determine the independent and interactive effects of these components on woody plant recruitment and forest structure. 2. We increased canopy openness by trimming branches and added or subtracted canopy detritus in a factorial design. Plant responses were measured during the 4-year study, which followed at least 1 year of pre-manipulation monitoring. 3. The physical conditions of canopy openness and detritus deposition in our experiment resembled the responses to Hurricane Hugo, a severe category 4 hurricane that struck this forest in 1989. 4. Canopy detritus deposition killed existing woody seedlings and provided a mechanical barrier that suppressed seedling recruitment. The increase in understorey light caused by canopy trimming stimulated germination from the seed bank and increased seedling recruitment and density of pioneer species several hundred-fold when hurricane debris was absent. Many significant interactions between trimming and detritus deposition were evident from the manner in which seedling density, recruitment and mortality changed over time, and subsequently influenced the composition of woody stems (individuals ‡ 1 cmd.b.h.). 5. When the canopy was trimmed, stem densities increased> 2-fold and rates of recruitment into the stem size class increased> 25-fold. Trimming had no significant effect on stem mortality. The two dominant species that flourished following canopy trimming were the pioneer species Cecropia schreberiana and Psychotria berteriana. Deposition of canopy detritus had little effect on stems, although basal area increased slightly when detritus was added. There were no evident effects of the interactions between canopy trimming and detritus deposition on stems. 6. Synthesis. The separate and interactive effects of canopy openness and detritus deposition result in variable short-term trajectories of forest recovery. However, the short interval of increased canopy openness due to hurricane impacts and its influence on the recruitment of pioneer trees is the dominant factor that drives short-termrecovery and may alter long-term structure and composition of the forest.

Thermal Biology of Anolis Lizards in a Complex Fauna: The Christatellus Group on Puerto Rico

Thermal Biology of Anolis Lizards in a Complex Fauna: The Christatellus Group on Puerto Rico
Raymond B. Huey and T. Preston Webster
Vol. 57, No. 5 (Late Summer, 1976), pp. 985-994

To describe the thermal biology of the three trunk-ground species of the Anolis cristatellus group on Puerto Rico, an island with 10 species of Anolis, we obtained samples of air and body temperatures of A. gundlachi (shady perches, montane forests), A. cristatellus (shady or sunny perches in open or closed forests, lowlands to mid-elevations), and A. cooki (sunny perches in open, xeric lowlands). Average body temperatures parallel altitudinal and habitat association (lowest for A gundlachi, highest for A. cooki). Within a species, body temperatures are strongly correlated with air temperatures and thus vary with altitude, time of day, habitat, and weather. Observed differences between sympatric species in body temperatures and habitat probably reflect physiological requirements, but may be magnified by competition. Relative thermal niche breadth of individuals of these species is approximated and compared with data on species from simple anole faunas to evaluate hypotheses on the evaluation of thermal niche breadth. Extent of basking behavior is inversely related to associated costs for these species. In closed forests where costs of raising body temperatures are high, A. gundlachi and A. cristatellus rarely bask and seemingly are routinely passive to ambient conditions. In open habitats where costs are low, A. cristatellus and A. cooki frequently bask.
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