Spatial eigenfunction analyses in stream networks: do watercourse and overland distances produce different results?

1. The use of spatial variables is a common procedure in ecological studies. The technique is based on the definition of a connectivity/distance matrix that conceptually defines the dispersal of organisms. The shortest distance between two points is a straight line. Despite the fact that a straight line may not represent the easiest dispersal path for many kinds of organisms, straight‐line distances are often used to detect patterns. We argue that other types of connectivity/distance matrices will better represent dispersal paths, such as the watercourse distance for aquatic organisms (e.g. fish, shrimps). 2. We used empirical and simulated community data to evaluate the usefulness of spatial variables generated from watercourse and overland (straight‐line) distances. 3. Spatial variables based on watercourse distances captured patterns that straight‐line distances did not, and provided better representations of the spatial patterns generated by dispersal along a dendritic network.     

Host‐plant dependent wing phenotypic variation in the neotropical butterfly Heliconius erato

Most phytophagous insects feed on a single plant during development, and this may influence not only performance‐linked traits, but also more subtle morphological differences. Insect–plant interactions are thus valuable for studying environmental influences on phenotypes. By using geometric morphometrics, we investigated the variation in forewing size and shape in the butterfly Heliconius erato phyllis reared on six species of passion vines (Passiflora spp.). We detected wing shape sexual dimorphism, for which the adaptive significance deserves further investigation. There was size as well as wing shape variation among individuals fed on different hosts. These subtle differences in shape were interpreted as environmental effects on development, which should be under weak natural selection for these traits, and therefore not strongly canalized. This result reinforces the role of plasticity on host‐plant use, as well as the corresponding consequences on developmental variability among phytophagous insects. We propose that this variation can be an important factor in resource specialization and partner recognition, possibly triggering reproductive isolation and sympatric speciation in phytophagous insects. This interaction also shows itself as a good model for studying the role of environmental and interaction diversity in evolution. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 765–774.     

Plant traits mediate effects of predators across pepper (Capsicum annuum) varieties

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Factors influencing egg parasitism in sub‐social insects: insights from the treehopper Alchisme grossa (Hemiptera,Auchenorrhyncha, Membracidae)

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Karyosystematic study of Potentilla L. subgen. Potentilla (Rosaceae) in the Iberian Peninsula

Chromosome numbers in 80 populations belonging to 18 species of Potentilla L. subgen. Potentilla from the Iberian Peninsula and two of P. maura, a North African endemic taxon, have been counted. The basic number of chromosomes is always x = 7 and these chromosomes are small (between 1 and 2 μm). For three species, the number of chromosomes is reported for the first time and, for another six, this number has been established in Iberian representatives. Moreover, new ploidy levels have been obtained for P. hispanica and P. crantzii with regard to their entire distribution area, and in P. cinerea and P. neumanniana for the Iberian Peninsula. Some taxonomic, phylogenetic and phytogeographic comments are made for several species or groups of species from the West Mediterranean region. In 13 species only one ploidy level has been found, but six species have several ploidy levels. Seven ploidy levels occur in the investigated taxa. The frequency of each ploidy level represented within Iberian Potentilla is analysed and the data are compared with those available for taxa from the rest of the distribution area of the genus.     

Behavioural flexibility does not prevent numerical declines of harvester ants under intense livestock grazing

1. Human‐induced rapid environmental change may decrease food resources and create unfavourable conditions for native species. Organisms showing a flexible foraging behaviour can exploit novel or alternative foods and are more likely to persist, whereas less flexible organisms might suffer starvation and numerical reductions. 2. This study assessed whether declines in the quality and availability of seeds prompted by grazing provoke behavioural and numerical responses in Pogonomyrmex mendozanus ants, and aimed to test whether behavioural flexibility buffers habitat degradation and prevents numerical declines. 3. Heavy grazing caused seed reductions, especially of the highly consumed and preferred grass seeds, and triggered two kinds of ant responses. Ants expanded their diet by incorporating a greater proportion of non‐seed items, and they reduced foraging activity. As a consequence, the rate of food intake per colony lessened, particularly that of carbohydrate‐rich seeds like grass seeds. Colony density under heavy grazing also fell. 4. Habitat degradation triggered a cascade of mechanisms that starts with a decrease in the seed resources and continues with changes in ant behaviour. However, behavioural responses were insufficient to prevent ant numerical declines. The results of this study suggest that the reduction in the colony density under habitat degradation was provoked by ant nutritional deficit and starvation, and predict a deterioration in body condition, colony performance and reproduction of ants, which deserve further assessment.     

Evaluation of Camera Trapping for Estimating Red Fox Abundance

ABSTRACT The nature reserve Serra da Malcata, Portugal, was recently considered a site for Iberian lynx (Lynx pardinus) reintroduction. Because of potential disease risk posed by red foxes (Vulpes vulpes) in the area, a reliable estimate of fox abundance was critical for a dependable reintroduction program. We adapted camera-trapping techniques for estimating red fox abundance in the reserve. From July 2005 to August 2007, we conducted 7 camera-trapping sessions, allowing for individual identification of foxes by physical characteristics. We estimated abundance using the heterogeneity (M_h) model of the software program CAPTURE. Estimated density ranged from 0.91 ± 0.12 foxes/km²to 0.74 ± 0.02 foxes/km². By estimating red fox density, it is possible to define the number of foxes that must be sampled to assess the presence of potential fox-transmitted diseases that may affect lynx reintroduction.     

Neuroendocrine Correlates of Circadian Rhythmicity in Crustaceans

The secretion of neurohormones from the crustacean X-organ –sinus gland system is controlled by environmental influences,light being the most conspicuous. Two sets of photoreceptorsappear to mediate the influence of light on neurosecretion basedon intracellular recordings from X-organ neurons and estimationsof hormone release. Extra-retinal photoreceptors can initiateneurohormonal release from the eyestalk. Neurosecretory activity is also influenced by putative neurotransmitters.GABA is found in high concentrations in the medulla temninalisof the eyestalk and is released by stimulation, in a calcium-dependentmanner. Diurnal variations occur in the amounts of eyestalk neurohormones,either those present in the eyestalk or released by electricalstimulation of the isolated sinus gland. Rhythm phases varyfrom one hormone to another. Neurohormones secreted in the eyestalkare also found in other regions of the central nervous system.Rhythms of neurosecretion are present both in the secretionin the isolated eyestalk and in eyestalkless animals, thus indicatingthat rhythmicity is a distributed property of the neurosecretorysystem.