Does foraging efficiency vary with colony size in the fairy martin Petrochelidon ariel?

Colonial breeding occurs in a wide range of taxa, however the advantages promoting its evolution and maintenance remain poorly understood. In many avian species, breeding colonies vary by several orders of magnitude and one approach to investigating the evolution of coloniality has been to examine how potential costs and benefits vary with colony size. Several hypotheses predict that foraging efficiency may improve with colony size, through benefits associated with social foraging and information exchange. However, it is argued that competition for limited food resources will also increase with colony size, potentially reducing foraging success. Here we use a number of measures (brood feeding rates, chick condition and survival, and adult condition) to estimate foraging efficiency in the fairy martin Petrochelidon ariel, across a range of colony sizes in a single season (17 colonies, size range 28–139 pairs). Brood provisioning rates were collected from multiple colonies simultaneously using an electronic monitoring system, controlling for temporal variation in environmental conditions. Provisioning rate was correlated with nestling condition, though we found no clear relationship between provisioning rate and colony size for either male or female parents. However, chicks were generally in worse condition and broods more likely to fail or experience partial loss in larger colonies. Moreover, the average condition of adults declined with colony size. Overall, these findings suggest that foraging efficiency declines with colony size in fairy martins, supporting the increased competition hypothesis. However, other factors, such as an increased ectoparasitise load in large colonies or change in the composition of phenotypes with colony size may have also contributed to these patterns.     

Does fruiting phenology vary with fruit syndrome? An investigation on animal-dispersed tree species in an evergreen forest in south-western Cameroon

Fruit syndrome found in zoochorous plants is regarded as a result of hypothetical coevolution with a seed disperser/predator. Fruiting phenology was compared among two representative syndromes, such as bird–monkey syndrome (BM) and ruminant–rodent–elephant syndrome (RRE), plus the gravity dispersal species for comparison, in south-western Cameroon in order to examine which biotic or abiotic factors educed syndrome variation. The individual size of selected plants (> 1.6 m in height) was recorded in a 16.95-ha area for recruitment estimation and their fruiting behaviour was checked for 9 months from June 1985 to February 1986. The BM species, a suggested successful group, fruited in a less synchronous manner within species and had fruiting peaks just before and during the rainy season. The RRE species, a suggested failing group, showed greater variation within syndrome in fruiting timing, duration and synchronization. Results obtained supported no clear phenological response to corresponding vertebrates except for the case of Sacoglottis gabonensis in the RRE. The reason for concealing potential responses is probably a result of conflicting requirements for seed dispersal and offspring survival. Periodical fruiting of the BM is likely to reflect ecological constraint, such as water stress on seedlings, caused from syndrome-specific morphological limitation. In this case, the animals have indirect effects on fruiting phenology through selecting syndrome-specific fruit morphology. The greater variation of the RRE suggests a broad spectrum of dispersal tactics from faithful zoochory to alternatives, with a trade off between agent restriction and seed size and another trade off between parental investment and seed-predation risk.     

Geographic patterns in fruit colour diversity: do leaves constrain the colour of fleshy fruits?

We tested for geographic patterns in fruit colour diversity. Fruit colours are thought to promote detection by seed dispersers. Because seed dispersers differ in their spectral sensitivities, we predicted that fruit colour diversity would be higher in regions with higher seed disperser diversity (i.e. the tropics). We collected reflectance data on 232 fruiting plant species and their natural backgrounds in seven localities in Europe, North and South America, and analysed fruit colour diversity according to the visual system of birds—the primary consumer types of these fruits. We found no evidence that fruit colours are either more conspicuous or more diverse in tropical areas characterised by higher seed disperser diversity. Instead, fruit colour diversity was lowest in central Brazil, suggesting that fruit colours may be more diverse in temperate regions. Although we found little evidence for geographic variation in fruit hues, the spectral properties of fruits were positively associated with the spectral properties of backgrounds. This result implies that fruit colours may be influenced by selection on the reflectance properties of leaves, thus constraining the evolution of fruit colour. Overall, the results suggest that fruit colours in the tropics are neither more diverse nor more conspicuous than temperate fruits, and that fruit colours may be influenced by correlated selection on leaf reflectance properties. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The first archaeobotanical evidence of Dasypyrum villosum in Hungary: an archaeophyte weed or a native grass?

Caryopsis and spikelet fork remains of Dasypyrum villosum (L.) Coss. & Durieu ex P. Candargy have been recovered from a Hallstatt period archaeobotanical assemblage (ca. 900/800–450 cal. bc) in western Hungary (Carpathian basin). The presence of D. villosum has not been reported previously from any Hungarian archaeological sites, however there are accounts of its possible occurrence from the Neolithic, the Bronze and Iron Age in northern Serbia. The exact identification of the species has been hindered by its morphological similarity to wild rye and wheat species, as well as to Secale cereale L. and Triticum timopheevii Zhuk. ssp. timopheevii. D. villosum has been found growing at seven locations in Hungary during the past 100 years. Most of these occurrences do not exist today, and the species is not considered indigenous to the present Hungarian flora. The new finds of this species from an Iron Age feature dated to 702–696 cal. bc in western Hungary leave doubts as to whether it is indigenous or not, and should encourage archaeobotanists to consider the possibility of the occurrence of this species on other sites.     

Does size matter?

For 40 years, the debate has raged. Do mammalian cells monitor cell size when deciding whether to divide? More recent models suggest an indirect solution, but the field is far from reaching a final verdict.     

Does insect folivory vary with latitude among temperate deciduous forests?

There is a widespread belief that warmer climate forests suffer more folivory, as a proportion of leaf area, than cooler climate forests. However, there is a need for closely standardized studies to test this assumption. In this study, we estimated total folivory as percentage area damaged in freshly fallen, undecayed autumn leaves from the forest floor during the lifetime of deciduous tree leaves, using scanner-linked software. Over a period of 2 years, 154 samples were taken at 96 forested localities in eastern North America, spanning 17° of latitude. In terms of percentage area damage per leaf, the results in both years sampled suggest that there is significantly more damage in warmer, lower latitude areas of eastern North America. The decreasing folivory rate is higher in northern than in southern regions. The observations of a latitudinal trend may suggest that ‘biotic’ interaction is indeed more important in warmer temperate climates compared to cool temperate climates.     

Does Chaffinch Fringilla coelebs song vary with the habitat in which it is sung?

The acoustic adaptation hypothesis suggests that song learning in birds is advantageous because it enables song to become adapted to the habitat in which it is sung. A comparison was made among song types recorded from male Chaffinches Fringilla coelebs at a variety of sites in open scrub and in coniferous plantations, as well as in mature pine forest. Although some significant differences were found among habitats, these were few and there was no systematic relationship with features of the environment. This study does not therefore support the acoustic adaptation hypothesis.     

Do phosphorus requirements for RNA limit genome size in crustacean zooplankton?

As for most other organisms, genome size in zooplankton differs widely. This may have a range of consequences for growth rate, development, and life history strategies, yet the causes of this pronounced variability are not settled. Here we propose that small genome size may be an evolutionary consequence of phosphorus (P) allocation from DNA to RNA under P deficiency. To test this hypothesis we have compared the two major groups of zooplankton, copepods and cladocerans, that have overlapping niches and body size. Relative to the cladocerans, copepods have a more complex life history and a lower mass-specific P content, while cladocerans tend to have higher P and RNA contents and higher specific growth rates and frequently experience P-limited growth, likely due to a shortage of P for ribosome synthesis. Cladocerans also generally have smaller genomes than copepods (1C = 0.17-0.63 pg DNA.cell-1 vs. 1C = 0.10-10 pg DNA.cell-1). Furthermore, cladocerans have a higher slope of the relationship of body size with DNA content (1.5 vs. 0.28 in copepods) and present almost 15-fold higher RNA:DNA ratios (24.8 in cladocerans vs. 1.6 in copepods). Hence, small genome size in cladocerans could reflect an evolutionary pressure towards "efficient" genomes to conserve a key element needed to maximize growth rate. We do not claim that this is a universal cause of genome size variability, but propose that streamlining of genomes could be related to P conservation rather than energy conservation. This could be relevant for a range of organisms that may suffer P-limited growth rates.     

Does size matter for hypoxia tolerance in fish?

Fish cover a large size range, from milligrams to tonnes, and many of them are regularly exposed to large variations in ambient oxygen levels. For more than half a century, there have been various, often divergent, claims regarding the effect of body size on hypoxia tolerance in fish. Here, we attempt to link old and new empirical data with the current understanding of the physiological mechanisms behind hypoxia tolerance. Three main conclusions are drawn: (1) body size per se has little or no impact on the ability to take up oxygen during hypoxic conditions, primarily because the respiratory surface area matches metabolic rate over a wide size range. If size-related differences are seen in the ability for oxygen uptake in a species, these are likely to reflect adaptation to different life-styles or habitat choice. (2) During severe hypoxia and anoxia, where fish have to rely on anaerobic ATP production (glycolysis) for survival, large individuals have a clear advantage over smaller ones, because small fish will run out of glycogen or reach lethal levels of anaerobic end-products (lactate and H(+)) much faster due to their higher mass-specific metabolic rate. (3) Those fish species that have evolved extreme adaptations to hypoxia, including haemoglobins with exceptionally high oxygen affinities and an alternative anaerobic end-product (ethanol), reveal that natural selection can be a much more powerful determinant of hypoxia tolerance than scaling of physiological functions.     

Does personality in small rodents vary depending on population density?

Personality means an individual's unique way of behaving and reacting to the environment. It is a stable and heritable trait, which is expressed consistently in different situations. The aim of our study was to develop novel tests to depict the personality structure of the bank vole Myodes glareolus, and to determine if the phase of the population cycle, i.e. population density, affects personality. We focused on some central aspects of bank vole behaviour: mobility, risk taking, exploratory behaviour, dominance, and aggressive behaviour towards pups. These behaviours were chosen because they directly affect bank vole survival or fitness or are classified as important factors of personality in other species. In total, 192 males from different populations went through four behavioural tests, in which 20 variables were measured. The tests were repeated after 3 weeks, which verified that all traits were stable, i.e. repeatable between trials. Three personality compounds emerged, named extroversion, novelty seeking and infanticide. Extroversion included dominance and mobility, while novelty seeking consisted of risk taking and exploration. Infanticide encompassed all indices measuring harmful behaviour towards pups. Mobility and dominance were connected, possibly because both seem to depend on condition. Time spent in captivity increased extroversion, which may be explained by good food, stable conditions and acclimation to strong social cues. Novelty seeking was connected to repeatability which could mean that novelty avoiding individuals adjust their behaviour to match new environments. Population density affected the infanticide trait but not novelty seeking or extroversion.     

Does carbon partitioning in ectomycorrhizal pine seedlings under elevated CO2 vary with fungal species?

Enhanced soil respiration in response to elevated atmospheric CO₂ has been demonstrated, and ectomycorrhizal (ECM) fungi are of particular interest since they partition host-derived photoassimilates belowground. Although a strong response of ECM fungi to elevated CO₂ has been shown, little is still known about the functional diversity among species. We studied carbon (C) partitioning in mycorrhizal Scots pine seedlings in response to short-term CO₂ enrichment, using seven ECM species with different ecological strategies. Mycorrhizal associations were synthesised and seedlings grown in large Petri dishes containing peat:vermiculite and nutrient solution for 10–15 weeks, after which half of the microcosms were exposed to elevated CO₂ treatment (710 ppm) for 15 days and the other half were kept in ambient CO₂ treatment. Partitioning of C was quantified by pulse labelling the seedlings with ¹⁴CO₂ and examining the distribution of labelled assimilates in shoot, root and extraradical mycelial compartments by destructive harvest and liquid scintillation counting. Fungal biomass was determined with PLFA analysis. The respiratory loss of ¹⁴CO₂ was on average greater in the elevated CO₂ treatment for most species compared to the ambient CO₂ treatment. More label was retrieved in the shoots in the ambient CO₂ treatment compared to elevated CO₂ (significant for P. involutus and P. fallax). Greater amounts of label were found in the extraradical mycelial compartment in all species (except P. involutus) in elevated CO₂ compared to ambient CO₂ (significant for L. bicolor, P. byssinum, P. fallax and R. roseolus). Fungal biomass production increased significantly with elevated CO₂ for two species (H. velutipes and A. muscaria); three species (P. fallax, P. involutus and R. roseolus) showed a similar but non-significant trend, whereas L. bicolor and P. byssinum produced less biomass in elevated CO₂ compared to ambient CO₂. When ¹⁴C in the mycelial compartment and respiration was expressed per unit fungal PLFA the difference between CO₂ treatments disappeared. We demonstrated that different ECM fungal isolates respond differently in C partitioning in response to CO₂ enrichment. These results suggest that under certain growth conditions, when nutrients are not limiting, ECM fungi respond rapidly to increasing C-availability through changed biomass production and respiration.     

Evolution of genome size in Drosophila. is the invader's genome being invaded by transposable elements?

Genome size varies considerably between species, and transposable elements (TEs) are known to play an important role in this variability. However, it is far from clear whether TEs are involved in genome size differences between populations within a given species. We show here that in Drosophila melanogaster and Drosophila simulans the size of the genome varies among populations and is correlated with the TE copy number on the chromosome arms. The TEs embedded within the heterochromatin do not seem to be involved directly in this phenomenon, although they may contribute to differences in genome size. Furthermore, genome size and TE content variations parallel the worldwide colonization of D. melanogaster species. No such relationship exists for the more recently dispersed D. simulans species, which indicates that a quantitative increase in the TEs in local populations and fly migration are sufficient to account for the increase in genome size, with no need for an adaptation hypothesis.     

Does leg-ring colour affect song tutor choice in zebra finches?

Young male zebra finches, Taeniopygia guttata, reared by their mothers alone showed no preference between males with red and with light-green colour rings in their choice of song tutor. Behavioural observations showed that the tutee associated more with the adult from which it was subsequently found to have learnt. In a second experiment, birds reared by both parents wearing either light-blue or light-green colour rings and then given a choice of tutors wearing these ring combinations also showed no preference between them. These young males did, however, more often approach the tutor ringed as their parents had been. This may explain why they did not show more interest in the tutor whose song they learnt. The majority of the tutors were used twice, with the ring colour swapped before they were used the second time. There was a strong tendency for the same male to be copied by the two young birds exposed to him. This could not be attributed to a difference in song rate between the two tutors. Further work will be required to discover the basis of that individual's greater attractiveness. Copyright 1999 The Association for the Study of Animal Behaviour.     

Does the strength of cross‐ecosystem trophic cascades vary with ecosystem size? A test using a natural microcosm

1. The cascading effect of predators on the functioning of adjacent ecosystems can occur when the life cycles of their prey include two ecosystems. However, there has been little consideration of which habitat attributes can modify the strength of these cross‐ecosystem trophic cascades. Habitat size can mediate the strength of predator–prey interactions, and thus affect within‐ecosystem trophic cascades. We hypothesise that similar effects of habitat size might affect cross‐ecosystem trophic cascades.
2. It has been shown that terrestrial predators (e.g. spiders) can capture terrestrial adult insects as they attempt to oviposit in the waters of bromeliads. Such terrestrial predators could therefore alter the trophic structure and functioning of the aquatic food web. If spiders affect an aquatic trophic level that is influenced by bromeliad size, then the strength of the cross‐ecosystem trophic cascade will also depend on bromeliad size.
3. To test this general hypothesis, we manipulated the presence of a funnel‐web spider (Aglaoctenus castaneus, Lycosidae), which builds a single web over water‐filled bromeliads, in bromeliads differing in size and examined effects on the aquatic invertebrate community and on ecosystem functions (decomposition, detrital nitrogen flux).
4. The effects of spiders were largely independent of bromeliad size. Spiders did initiate changes in the trophic structure of aquatic food webs, reducing the biomass of predators, especially damselflies and dytiscid beetles. Spiders also increased decomposition despite having no effect on detritivore biomass or composition.
5. These results are most parsimoniously explained by (i) a behaviourally mediated trophic cascade, whereby damselfly adults avoid bromeliads with spiders, and aquatic detritivores increase rates of detrital processing in the absence of damselfly larvae, and (ii) stimulation of decomposition through nutrients added from spider faeces and prey carcasses. We believe that this is the first study to show that terrestrial predators can affect decomposition by reducing the flux of keystone aquatic predators with complex life cycles.

     

Does rumen–reticulum capacity correlate with body size or age in black-tailed deer?

To accommodate an increased food intake with greater body size, rumen–reticulum capacity must become larger to allow heavier digesta loads. Recently, digesta load was found to correlate with age more strongly than body size. It was suggested that older animals had compromised mastication efficiency due to tooth wear and compensated for larger particles by increasing rumen–reticulum capacity to extend retention time. Herein, we constructed models and used Akaike Information Criteria corrected for small sample size to determine if digesta load was related with age or body weight in 80 female and 105 male black-tailed deer (Odocoileus hemionus columbianus). We also assessed if the presence of fetuses influenced relationships in females. Females were collected in spring, 1985–1988, and males were collected in autumn, 1980, 1982–1984, and 1988, from Hopland Research and Extension Center, Mendocino County, California. Digesta loads, fetuses, and carcasses were weighed, and animal ages were estimated. Digesta load was related to age in females and body weight in males. Our study shows that body size and age-related factors may both influence rumen–reticulum capacity.     

Does hippocampal size correlate with the degree of caching specialization?

A correlation between the degree of specialization for food hoarding and the volume of the hippocampal formation in passerine birds has been accepted for over a decade. The relationship was first demonstrated in family-level comparisons, and subsequently in species comparisons within two families containing a large number of hoarding species, the Corvidae and the Paridae. Recently, this approach has been criticized as invalid and excessively adaptationist. A recent test of the predicted trends with data pooled from previous studies found no evidence for such a correlation in either of these two families. This result has been interpreted as support for the critique. Here we reanalyse the original dataset and also include additional new data on several parid species. Our results show a surprising difference between continents, with North American species possessing significantly smaller hippocampi than Eurasian ones. Controlling for the continent effect makes the hoarding capacity/hippocampal formation correlation clearly significant in both families. We discuss possible reasons for the continent effect.     

Is genome size influenced by colonization of new environments in dipteran species?

Genome size differences are usually attributed to the amplification and deletion of various repeated DNA sequences, including transposable elements (TEs). Because environmental changes may promote modifications in the amount of these repeated sequences, it has been postulated that when a species colonizes new environments this could be followed by an increase in its genome size. We tested this hypothesis by estimating the genome size of geographically distinct populations of Drosophila ananassae, Drosophila malerkotliana, Drosophila melanogaster, Drosophila simulans, Drosophila subobscura, and Zaprionus indianus, all of which have known colonization capacities. There was no strong statistical differences between continents for most species. However, we found that populations of D. melanogaster from east Africa have smaller genomes than more recent populations. For species in which colonization is a recent event, the differences between genome sizes do not thus seem to be related to colonization history. These findings suggest either that genome size is seldom modified in a significant way during colonization or that it takes time for genome size of invading species to change significantly.