Abstract: Termites represent one of the most abundant belowground animal taxa in tropical rainforests, where their species richness is much higher than in any other ecosystem. This high diversity in soil ecosystems is however difficult to explain by classical Hutchinsonian niche theory, as there is little evidence for spatial or temporal separation between species. Using delta C-13 and delta N-15 isotopic ratios, we tested if resource partitioning along the humification gradient occurs; in neotropical soldierless termites of the Anoplotermes-group. Two distinct sites were investigated to check if interspecific differences are transposable between sites. Significant differences in delta N-15 were found between species of the Anoplotermes-group. Although some species displayed higher intersite delta N-15 variation than others, species-average delta N-15 values for both sites were highly correlated, showing that sympatric soldierless soil-feeding termites feed on distinct components of the soil. Our data also suggest that some species are more likely to shift along this gradient than others, in response to overall habitat conditions or to the presence of competitors. Feeding niche differentiation can therefore account for the high species richness and diversity of soldierless soil-feeding termites in neotropical rainforests. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: Irradiance elicits a large plasticity in leaf traits, but little is known about the modulation of this plasticity by ontogeny. Interactive effects of relative irradiance and ontogeny were assessed on leaf traits for two tropical rainforest tree species: Dicorynia guianensis Amshoff and Tachigali melinonii (Harms) Barneby (Fabaceae, Caesalpinioideae). Eleven morphological and physiological leaf traits, relative to photosynthetic performance, were measured on saplings at three different architectural development stages (ASD 1, 2 and 3) and used to derive composite traits like photosynthetic N-use efficiency. Measurements were made along a natural irradiance gradient. The effect of ASD was very visible and differed between the two species. For Dicorynia guianensis, only leaf mass-per-area (LMA) significantly increased with ASDs whereas for Tachigali melinonii, almost all traits were affected by ASD: LMA, leaf N content and photosynthetic capacity increased from ASD 1 to ASD 3. Photosynthetic N-use-efficiency was not affected by ASD in any species. Leaf traits were severely modulated by irradiance, whereas the degree of plasticity was very similar among ASDs. Only few interactions were detected between irradiance and ASD, for leaf thickness, carbon content, and the ratio Chl/N in T. melinonii and for photosynthetic capacity in D. guianensis. We conclude that ontogenic development and irradiance-elicited plasticity modulated leaf traits, with almost no interaction, i.e., the degree of irradiance-elicited plasticity was stable across development stages and independent of ontogeny in these two species, at least in the early stages of development assessed here.

Abstract: Micrometeorological measurements of night time ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397-403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (F-C) and change in storage (F-S) of CO2 in the few hours after sundown. The sum of F-C and F-S reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration R-Rmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of F-c + F-s extrapolated to zero light, R-LRC, and (3) with a detailed process-based forest ecosystem model, R-cast. At most sites respiration rates estimated using the u*-filter, R-ust, were smaller than R-Rmax, and R-LRC. Agreement of our approach with independent measurements indicates that R-Rmax, provides an excellent estimate of nighttime ecosystem respiration. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Interspecific relationships among insects are often mediated by chemical cues, including non-volatile cuticular compounds. Most of these compounds are hydrocarbons that necessitate the use of solvents for their extraction, identification, and manipulation during behavioral assays. The toxicity of these solvents often precludes the removal and reapplication of hydrocarbons from and to live insects. As a consequence, dummies often are used in behavioral assays, but their passivity can bias the behavior of the responding insects. To overcome these limitations, we propose a method where cuticular compounds are extracted from live ants by placing them into glass vials half-filled with tepid water (ca. 34A degrees C) and vigorously shaking the vials to form an emulsion whose supernatant can be analyzed and/or reapplied to other ants. We demonstrate that cuticular compounds can be extracted from workers of the red fire ant, Solenopsis saevissima, and reapplied to the cuticle of workers from a sympatric species, Camponotus blandus (both Hymenoptera: Formicidae), while keeping the ants alive. Gas chromatographic-mass spectrometric analysis and behavioral assays were used to confirm the successful transfer of the behaviorally active compounds.

Abstract: Aechmea mertensii is a tank-bromeliad that roots on ant-gardens initiated by the ants Camponotus femoratus and Pachycondyla goeldii. Its leaves form compartments acting as phytotelmata that hold rainwater and provide habitats for invertebrates. In this article, we aimed to determine whether the association with either C. femoratus or P. goeldii influenced the vegetative traits of A. mertensii, invertebrate diversity and nutrient assimilation by the leaves. Transmitted light, vegetative traits and phytotelmata contents were compared between the two A. mertensii ant-gardens. Camponotus femoratus colonized partially shaded areas, whereas P. goeldii colonized exposed areas. The bromeliads' rosettes had a large canopy (C. femoratus ant-gardens), or were smaller and amphora shaped (P. goeldii ant-gardens). There were significant differences in leaf anatomy, as shaded leaves were thicker than exposed leaves. The mean volumes of water, fine particulate organic matter and detritus in C. femoratus-associated bromeliads were three to five times higher than in P. goeldii-associated bromeliads. Moreover, the highest invertebrate diversity and leaf delta N-15 values were found in C. femoratus-associated bromeliads. This study enhances our understanding of the dynamics of biodiversity, and shows how ant-plant interactions can have trophic consequences and thus influence the architecture of the interacting plant via a complex feedback loop.