Life history of the Mato Grosso Antbird Cercomacra melanaria in the Brazilian Pantanal

Here we describe the habitat use, reproductive biology, diet and details of the life history of the Mato Grosso Antbird Cercomacra melanaria , one of the least studied Cercomacra species. We located 30 nests, of which 22 became active and were monitored. The nest consists of a deep cup, placed among dense tangles of vegetation, almost always in forests of Vochysia divergens ( Cambarazal ). Eggs are pinkish-cream coloured, covered with reddish brown to purple spots and blotches that are concentrated around its centre and larger end. Average nest success was 32%. The Mayfield method indicated daily survival rates during egg and nestling periods of 0.94 and 0.96, respectively, and a success rate of 26%. Examination of 24 stomach contents revealed a diet based exclusively on arthropods.     

The generalism–specialism debate: the role of generalists in the life and death of species

Specialisms on resources and for niches, leading to specialization, have been construed to be tantamount to speciation and vice versa, while the occurrence of true generalism in nature has also been questioned. We argue that generalism in resource use, biotope occupancy, and niche breadth not only exists, but also forms a crucial part in the evolution of specialists, representing a vital force in speciation and a more effective insurance against extinction. We model the part played by generalism and specialism in speciation and illustrate how a balance may be maintained between the number of specialists and generalists within taxa. The balance occurs as an ongoing cycle arising from turnover in the production of specialists and generalists, speciation, and species extinction. The nature of the balance depends on the type of resources exploited, biotopes, and niche space occupied. These vary between different regions and create taxonomic biases towards generalists or specialists. We envisage that the process may be sympatric/parapatric, although it is more likely initiated by allopatry driven by abiotic forces. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 725–737.     

Seasonal hysteresis of net ecosystem exchange in response to temperature change: patterns and causes

Understanding how net ecosystem exchange (NEE) changes with temperature is central to the debate on climate change‐carbon cycle feedbacks, but still remains unclear. Here, we used eddy covariance measurements of NEE from 20 FLUXNET sites (203 site‐years of data) in mid‐ and high‐latitude forests to investigate the temperature response of NEE. Years were divided into two half thermal years (increasing temperature in spring and decreasing temperature in autumn) using the maximum daily mean temperature. We observed a parabolic‐like pattern of NEE in response to temperature change in both the spring and autumn half thermal years. However, at similar temperatures, NEE was considerably depressed during the decreasing temperature season as compared with the increasing temperature season, inducing a counter‐clockwise hysteresis pattern in the NEE–temperature relation at most sites. The magnitude of this hysteresis was attributable mostly (68%) to gross primary production (GPP) differences but little (8%) to ecosystem respiration (ER) differences between the two half thermal years. The main environmental factors contributing to the hysteresis responses of NEE and GPP were daily accumulated radiation. Soil water content (SWC) also contributed to the hysteresis response of GPP but only at some sites. Shorter day length, lower light intensity, lower SWC and reduced photosynthetic capacity may all have contributed to the depressed GPP and net carbon uptake during the decreasing temperature seasons. The resultant hysteresis loop is an important indicator of the existence of limiting factors. As such, the role of radiation, LAI and SWC should be considered when modeling the dynamics of carbon cycling in response to temperature change.     

Taxonomic separation of the genera Prosthechea and Encyclia (Laeliinae: Orchidaceae) using leaf and root anatomical features

Despite formal separation based on molecular and morphological evidence, the genera Prosthechea Knowles & Westc. and Encyclia Hook. have not been studied in terms of their vegetative anatomy. In this study we examine 16 Brazilian species of these genera. Additionally, one species of subtribe Laeliinae and another from subtribe Oncidiinae were studied in order to evaluate the taxonomic consistency of the anatomic characters observed. Except for Epidendrum crassifolium Lindl., all species possess a velamen differentiated into epivelamen and endovelamen. Endodermal cells with uniformly thickened walls, calcium oxalate raphides and cells with phi thickenings in the cortical region were observed in all species. Silica bodies, raphides and fibre bundles in the mesophyll were common in leaves of all species studied. By contrast, flavonoid crystals were observed in both roots and leaves of Prosthechea only. Encyclia is characterized by the presence of fibre bundles on the subepidermal layer, and a cuticle, which is clearly thicker than that of Prosthechea . These data strongly support the separation of Prosthechea and Encyclia .  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 293–303.     

Response properties of the prothoracic AN2 auditory interneurone to model calling songs in the cricket Gryllus bimaculatus

Sound processing properties for calling song (CS) models, as described for the prothoracic L3 auditory neurone in Acheta domesticus, are investigated for the homologous auditory neurone 2 (AN2) in female Gryllus bimaculatus De Geer. AN2 of G. bimaculatus responds selectively to the syllable period (SP) of models of a male CS. The selectiveness of this response parallels the selectivity of phonotaxis females perform in response to the same SPs. Both, the responses of AN2 and female behaviour show clear interindividual variability. The SP‐selective responses of AN2 result from an SP‐dependent reduction in the spiking to subsequent syllables of the model CSs, measured as the percentage decrement. This SP‐dependent response does not primarily result from inbuilt properties of the AN2 membrane. Rather, it is dependent on inhibitory input to the AN2. However, clear inhibitory postsynaptic potentials in dendritic recordings of the AN2 are not encountered. This immediate response of AN2 to CSs is followed by an increased rate of tonic firing between stimulus CSs, which is termed the prolonged response, and is dependent on the carrier frequencies that make up the male CSs. With stimulation on the contralateral side of the soma of AN2s, more than 50% of AN2s exhibit a prolonged response. However, with stimulation from the ipsilateral side of the soma, most AN2s exhibit a prolonged response. The prolonged response of AN2 at 5 kHz may be even more sensitive than the immediate response. Thus, the AN2 neurone could provide a basis for phonotaxis that is selective for both the SPs and the carrier frequencies of potentially attractive calling songs.     

Reproductive biology, variability of nectar features and pollination of Combretum fruticosum (Combretaceae) in Argentina

Flower morphology, nectary structure, nectar features (chemical composition, secretion pattern, standing crop, removal effects) and flower visitors are analysed in an Argentinian population of Combretum fruticosum. The variability of these data was examined throughout the flower lifetime. Nectar is hexose dominant. Its chemical composition and concentration are constant for all flowering stageS. Nectar volume varies as a function of flower age due to a combination of nectar secretion, cessation and resorption periods. The overall sugar production is decreased by nectar removal. The plant is self-incompatible and xenogamouS. Only 16.2% of the flowers set seedS. Inflorescences with green flowers were exclusively visited by two hummingbird and three perching bird species which transfer the pollen. A clear link was observed among nectar production pattern, standing crop of nectar, and visitors' behaviour.