bluuebunny/crossref_metadata_2025 huggingface dataset:
Remarkable substrate‐specificity of CYP6AB3 in Depressaria pastinacella, a highly specialized caterpillar
Authors: Mao W. , Rupasinghe S. , Zangerl A. R. , Schuler M. A. , Berenbaum M. R.
Published: March 2006

The parsnip webworm, Depressaria pastinacella, a specialist on two genera in Apiaceae, feeds exclusively on the furanocoumarin‐containing reproductive structures of its host plants. This caterpillar relies principally on cytochrome P450‐mediated detoxification for coping with the high concentrations of furanocoumarins in its diet. A cDNA encoding the furanocoumarin‐inducible P450 CYP6AB3 from this species was coexpressed with house‐fly NADPH P450 reductase in baculovirus‐infected Sf9 cells and tested for binding and metabolism of the six furanocoumarins typically encountered in host plant tissues. Only imperatorin and bergapten bind in close proximity to the catalytic haem and only imperatorin is metabolized (Vmax and Km of 2.412 pmol/min per pmol P450 and 94.28 µm, respectively). Purification of the imperatorin metabolite by normal phase HPLC and characterization of its structure by MS–MS analysis indicate that CYP6AB3 initially epoxidizes the carbon–carbon pi‐bond on the isoprenyl side chain on imperatorin. An improved molecular model for the CYP6AB3 protein based on this biochemical characterization and the recently defined mammalian CYP3A4 crystal structure provides insight into the remarkable substrate specificity of this protein.
Isolation, endocrine regulation and mRNA distribution of the 3‐hydroxy‐3‐methylglutaryl coenzyme A synthase (HMG‐S) gene from the pine engraver, Ips pini (Coleoptera: Scolytidae)
Authors: Bearfield J. C. , Keeling C. I. , Young S. , Blomquist G. J. , Tittiger C.
Published: March 2006

We isolated a full‐length cDNA encoding 3‐hydroxy‐3‐methylglutaryl coenzyme A synthase (HMG‐S) from the pine engraver beetle, Ips pini (Say), and examined its genomic structure. The intron‐less gene has a predicted 460 amino acid cytosolic protein product with 73% identity to HMG‐S from Dendroctonus jeffreyi, and high identity (58–64%) with other insect HMG‐Ss. Topically applied juvenile hormone (JH) III induced HMG‐S mRNA levels up to 6.5‐fold in both sexes, mostly in the anterior midgut, though there were differences between males and females in the timing, sensitivity to JH III dose and tissue distribution of HMG‐S mRNA. These data further validate the coordinate regulation of mevalonate pathway genes for de novo isoprenoid pheromone production in bark beetles.
Co‐immunoprecipitation of putative proteins that interact with mosquito proliferating cell nuclear antigen
Authors: Ma L. , Gerenday A. , Coley K. M. , Fallon A. M.
Published: March 2006

We have sequenced cDNAs encoding proliferating cell nuclear antigen (PCNA) from Aedes albopictus cells and from Aedes aegypti mosquitoes. The mosquito cDNAs contained an open reading frame encoding a 260 amino acid protein with a calculated mass of 29.0 kDa and a pI of 4.46. There was a single amino acid difference between PCNA proteins from Ae. albopictus and Ae. aegypti. In An. gambiae, the PCNA homolog contained 260 residues, and the pcna gene was interrupted by a single 67 nucleotide intron in the βC2 region of the protein. A phylogenetic comparison grouped known Dipteran PCNA sequences into two clusters, representing the Nematocera and the Cyclorrhapha. PCNA transcripts measured 1.1 kb, and were stable, as was PCNA protein. Mosquito PCNA was efficiently recognized by a commercially available mouse anti‐PCNA monoclonal antibody, which coprecipitated 29 kDa and 35 kDa proteins from mosquito cells representing different growth states. These results support the feasibility of recovering mosquito cell cycle inhibitory proteins by virtue of their interaction with PCNA.
Effects of juvenile hormone on gene expression in the pheromone‐producing midgut of the pine engraver beetle, Ips pini
Authors: Keeling C. I. , Bearfield J. C. , Young S. , Blomquist G. J. , Tittiger C.
Published: March 2006

Juvenile hormone III (JH III) stimulates biosynthesis of the monoterpenoid aggregation pheromone component, ipsdienol, in the anterior midgut of the male pine engraver beetle, Ips pini (Say). To understand better the hormonal regulation of pheromone biosynthesis in this forest pest, and identify JH III‐responsive genes, microarrays were prepared and hybridized to cDNA from midguts of JH III‐treated beetles. Expression patterns were confirmed by quantitative real‐time RT–PCR. JH III co‐ordinately regulated mevalonate pathway genes and many other genes implicated in pheromone biosynthesis. Sex differences in basal levels of mevalonate pathway genes were consistent with their role in male‐specific pheromone biosynthesis. This is the first microarray‐based study of the developmental and hormonal regulation of insect pheromone biosynthesis.
The mitochondrial genome of the Korean hairstreak, Coreana raphaelis (Lepidoptera: Lycaenidae)
Authors: Kim I. , Lee E. M. , Seol K. Y. , Yun E. Y. , Lee Y. B. , Hwang J. S. , Jin B. R.
Published: March 2006

We determined the complete nucleotide sequences of the mitochondrial genome (mitogenome) of the Korean hairstreak, Coreana raphaelis (Lepidoptera: Lycaenidae). The entire mitochondrial DNA (mtDNA) molecule was 15 314 bp long. The C. raphaelis genes were in the same order and orientation as the completely sequenced mitogenomes of other lepidopteran species, except for the presence of an extra copy of tRNASer(AGN). High similarity in primary sequence and secondary structure between the two tandemly located copies of the tRNASer(AGN) suggest a recent duplication of an original single tRNASer(AGN). The DHU arm of the two copies of tRNASer(AGN) formed a simple loop as seen in many other metazoan mt tRNASer(AGN). The putative initiation codon for the C. raphaelis COI gene appears to be a tetranucleotide, TTAG, found commonly in the sequenced lepidopterans. ATPase8, ATPase6, ND4L and ND6 genes, which are next to another protein‐coding gene at their 3′ end all had the sequences potential to form a hairpin structure, suggesting the importance of such a structure for precise cleavage of the mature protein‐coding genes.
Caste‐specific cytochrome P450 in the damp‐wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae)
Authors: Cornette R. , Koshikawa S. , Hojo M. , Matsumoto T. , Miura T.
Published: March 2006

Termites are eusocial insects with a well‐defined caste system, which is an example of polyphenism. This polyphenism is based on hormonally controlled differential gene expression. In the damp‐wood termite Hodotermopsis sjostedti, we induced differentiation into the soldier caste by using juvenile hormone analogue treatment. We then investigated specific gene expression, which appeared during the hormonal response and triggered caste differentiation, using fluorescent differential display. A candidate cDNA sequence with similarity to cytochromes P450, CYP6AM1, was characterized and its transcript shown to be repressed between 1 and 3 days after hormone treatment. CYP6AM1 was specifically expressed in the fat body of pseudergates and soldiers. The putative function of this P450 is discussed with respect to the caste differentiation system.
Sex‐, stage‐ and tissue‐specific regulation by a mosquito hexamerin promoter
Authors: Jinwal U. K. , Zakharkin S. O. , Litvinova O. V. , Jain S. , Beneš Helen
Published: March 2006

A portion of the 5′‐flanking region of the female‐specific hexamerin gene, Hex‐1.2, from the mosquito Ochlerotatus atropalpus was used to drive expression of the luciferase reporter gene in Drosophila melanogaster. The proximal 0.7 kb of 5′‐flanking DNA were sufficient to partially repress reporter gene activity in males and to drive tissue‐ and stage‐specific expression comparable with that of the endogenous O. atropalpus Hex‐1.2 gene. The Drosophila doublesex transcription factor (DSX), expressed in Escherichia coli, bound putative DSX sites of the Hex‐1.2 gene differentially in vitro. Blocking expression of the female isoform of the Doublesex transcription factor in transgenic female flies resulted in reduction of luciferase expression to levels comparable with those in males, suggesting that Doublesex could contribute to regulation of female‐specific expression of the O. atropalpus Hex‐1.2 gene.
Factors affecting wafer sheet quality
Authors: Dogan Ismail S.
Published: March 2006

Wafers are low‐moisture‐baked foods. They are formed from a batter and baked between hot plates. The quality of wafer sheets is mainly controlled by flour property, water level and temperature, mixing action, baking time and temperature. The quality is judged by attributes of the batter such as the density, viscosity, holding time and temperature, and by properties of the wafer such as weight, surface colour, fragility and moisture content. In this study, the batter‐specific gravity of 1.11–1.19 was recorded. Water and gluten content did not affect density. Water level, but not gluten content, however affected viscosity. Batter holding time drastically changed viscosity. The temperature of plates did significantly affect bake time. For wafer sheets with a high quality, 155–165% water level, 170 °C baking temperature and 2 min of bake time were found to be adequate. Wafer sheets baked at the lower temperatures stuck to the plates and broke up to several pieces. At a lower water level (<145%) and baking temperature of 150 °C, tough and flinty sheets were obtained, whereas at a water level higher than 160% and a higher temperature (190 °C), fragile sheets were obtained.
Contrasting cascades: insectivorous birds increase pine but not parasitic mistletoe growth
Authors: MOONEY KAILEN A. , LINHART YAN B.
Published: March 2006

Intraguild predation occurs when top predators feed upon both intermediate predators and herbivores. Intraguild predators may thus have little net impact on herbivore abundance. Variation among communities in the strength of trophic cascades (the indirect effects of predators on plants) may be due to differing frequencies of intraguild predation. Less is known about the influence of variation within communities in predator–predator interactions upon trophic cascade strength.

We compared the effects of a single predator community between two sympatric plants and two herbivore guilds. We excluded insectivorous birds with cages from ponderosa pinePinus ponderosatrees parasitized by dwarf mistletoeArceuthobium vaginatum. For 3 years we monitored caged and control trees for predatory arthropods that moved between the two plants, foliage‐feeding caterpillars and sap‐feeding hemipterans that were host‐specific, and plant damage and growth.

Excluding birds increased the abundance of ant‐tended aphids on pine and resulted in an 11% reduction in pine woody growth. Mutualist ants protected pine‐feeding aphids from predatory arthropods, allowing aphid populations to burgeon in cages even though predatory arthropods also increased in cages. By protecting pine‐feeding aphids from predatory arthropods but not birds, mutualist ants created a three‐tiered linear food chain where bird effects cascaded to pine growth via aphids.

In contrast to the results for tended aphids on pine, bird exclusion had no net effects on untended pine herbivores, the proportion of pine foliage damaged by pine‐feeding caterpillars, or the proportion of mistletoe plants damaged by mistletoe‐feeding caterpillars. These results suggest that arthropod predators, which were more abundant in cages as compared with control trees, compensated for bird predation of untended pine and mistletoe herbivores.

These contrasting effects of bird exclusion support food web theory: where birds were connected to pine by a linear food chain, a trophic cascade occurred. Where birds fed as intraguild predators, the reticulate food webs linking birds to pine and mistletoe resulted in no net effects on herbivores or plant biomass. Our study shows that this variation in food web structure occurred between sympatric plants and within plants between differing herbivore guilds.
Ontogeny of diving behaviour in the Australian sea lion: trials of adolescence in a late bloomer
Authors: FOWLER SHANNON L. , COSTA DANIEL P. , ARNOULD JOHN P. Y. , GALES NICHOLAS J. , KUHN CAREY E.
Published: March 2006

Foraging behaviours of the Australian sea lion (Neophoca cinerea) reflect an animal working hard to exploit benthic habitats. Lactating females demonstrate almost continuous diving, maximize bottom time, exhibit elevated field metabolism and frequently exceed their calculated aerobic dive limit. Given that larger animals have disproportionately greater diving capabilities, we wanted to examine how pups and juveniles forage successfully.

Time/depth recorders were deployed on pups, juveniles and adult females at Seal Bay Conservation Park, Kangaroo Island, South Australia. Ten different mother/pup pairs were equipped at three stages of development (6, 15 and 23 months) to record the diving behaviours of 51 (nine instruments failed) animals.

Dive depth and duration increased with age. However, development was slow. At 6 months, pups demonstrated minimal diving activity and the mean depth for 23‐month‐old juveniles was only 44 ± 4 m, or 62% of adult mean depth.

Although pups and juveniles did not reach adult depths or durations, dive records for young sea lions indicate benthic diving with mean bottom times (2·0 ± 0·2 min) similar to those of females (2·1 ± 0·2 min). This was accomplished by spending higher proportions of each dive and total time at sea on or near the bottom than adults. Immature sea lions also spent a higher percentage of time at sea diving.

Juveniles may have to work harder because they are weaned before reaching full diving capability. For benthic foragers, reduced diving ability limits available foraging habitat. Furthermore, as juveniles appear to operate close to their physiological maximum, they would have a difficult time increasing foraging effort in response to reductions in prey. Although benthic prey are less influenced by seasonal fluctuations and oceanographic perturbations than epipelagic prey, demersal fishery trawls may impact juvenile survival by disrupting habitat and removing larger size classes of prey. These issues may be an important factor as to why the Australian sea lion population is currently at risk.
Abiotic factors control invasion by Argentine ants at the community scale
Authors: MENKE SEAN B. , HOLWAY DAVID A.
Published: March 2006

A prominent and unresolved question in ecology concerns why communities differ in their susceptibility to invasion. While studies often emphasize biotic resistance, it is less widely appreciated how the physical environment affects community vulnerability to invasion.

In this study we performed field experiments to test how abiotic variation directly and indirectly influences the extent to which Linepithema humile Mayr (Argentine ants) invade seasonally dry environments in southern California.

In controlled and replicated experiments involving drip irrigation, we demonstrate (i) that elevated levels of soil moisture increased both the abundance of Argentine ants and their ability to invade native ant communities and (ii) that cessation of irrigation caused declines in the abundance of Argentine ants and led to their withdrawal from previously occupied areas.

Because drip irrigation stimulated plant growth, in an additional experiment we manipulated both soil moisture and plant cover to assess the direct vs. indirect effects of added water on the abundance of L. humile.

Local abundance of Argentine ants increased in irrigated plots but was 38% higher in irrigated plots with plants compared to irrigated plots where plant growth was suppressed. The results of this experiment thus argue for a direct role of soil moisture in influencing Argentine ant abundance but suggest that that the indirect effects of added water may also be important.

Our study illustrates more generally that fine‐scale variation in the physical environment can control whether communities become invaded by non‐native species and suggests that an understanding of community susceptibility to invasion will be improved by a better appreciation of interactions between the biotic and abiotic environment.
Stomach temperature telemetry reveals temporal patterns of foraging success in a free‐ranging marine mammal
Authors: AUSTIN DEBORAH , BOWEN W. D. , MCMILLAN J. I. , BONESS D. J.
Published: March 2006

We studied feeding frequency in free‐ranging grey seals using stomach temperature telemetry to test if previously reported sex differences in the diving, movement and diet were reflected in the temporal pattern of foraging success.

Data were retrieved from 21 of 32 grey seals from 1999 to 2001, totalling 343 days and 555 feeding events, with individual record length varying from 2 to 40 days (mean: 16·33 ± 2·67 days/seal).

Seals fed on 57·8 ± 6·46% of days sampled and had an average of 1·7 ± 0·26 meals per day, but individual variability was apparent in the temporal distribution of feeding as evidenced by high coefficients of variation (coefficient of variation = 69·0%).

Bout analysis of non‐feeding intervals of six grey seals suggests that feeding intervals of individuals were varied and probably reflect differences in prey availability. Grey seals tended to have many single feeding events with long periods separating each event, as would be expected for a large carnivore with a batch‐reactor digestive system.

We found significant sex differences in the temporal distribution of feeding. The number of feeding events per day was greater in males (2·2 ± 0·4 vs. 1·0 ± 0·2), as was time associated with feeding per day (56·6 ± 5·8 min vs. 43·9 ± 9·4 min).

The number of feeding events varied with time of day with the least number occurring during dawn. Feeding event size differed significantly by time of day, with greater meal sizes during the dawn and the smallest meals during the night.

The length of time between meals increased with the size of the previous meal, and was significantly less in males (541·4 ± 63·5 min) than in females (1092·6 ± 169·9 min).

These results provide new insight into the basis of sex differences in diving and diet in this large size‐dimorphic marine predator.
Sequentially assembled food webs and extremum principles in ecosystem ecology
Authors: VIRGO NATHANIEL , LAW RICHARD , EMMERSON MARK
Published: March 2006

Successional changes during sequential assembly of food webs were examined. This was carried out by numerical methods, drawing one species at a time from a species pool and obtaining the permanent (persistent) community emerging at each step. Interactions among species were based on some simple rules about body sizes of consumers and their prey, and community dynamics were described in terms of flows of biomass density.

Sequential assembly acted as a sieve on the communities, assembled communities having many properties different on average from those of feasible, stable communities taken at random from the species pools.

Time‐series of community development were consistent with certain functions thought to go to an extremum (maximum or minimum) in ecosystem ecology, including a rapid early increase in net primary productivity and ascendency, although a clear trend in total biomass density was not evident and resilience decreased rather than increased.

In addition, more gradual changes in food web structure took place during succession to which the ecosystem goal functions were relatively insensitive. These changes included gradual increases in the number of species, invasion resistance, number of loops of length > 2 and number of prey species per consumer species.

We therefore argue that ecosystem and community dynamics can offer complementary insights into the process of ecological succession. The extremum principles of ecosystem ecology highlight some of the major properties of succession, whereas the community ecology sheds light on some more subtle changes taking place within the networks.
The distribution of eggs per host in a herbivorous insect − intersection of oviposition, dispersal and population dynamics
Authors: ZU DOHNA HEINRICH
Published: March 2006

The dynamics of parasitic organisms depend critically upon the frequency distribution of parasite individuals per host. However, the processes giving rise to this frequency distribution have rarely been modelled and tested for organisms with complex host selection behaviour.

In this study Microrhopala vittata, a chrysomelid beetle, was used to investigate how oviposition behaviour, movement and density of host plants interact in shaping the frequency distribution of egg clusters per host in the field.

Enclosures were stocked with two different host species and different beetle densities and various stochastic process models were fitted to egg cluster count data obtained from these enclosures. The different models were derived considering different scenarios, in particular whether or not plant density limits oviposition rate, whether or not ovipositing females actively seek out the most attractive plant within their perception radius and whether a female's oviposition rate is determined by plant intrinsic factors, the plant's egg cluster load or the surrounding beetle density.

The model parameters fitted to cage data were used to describe the frequency distribution of egg cluster counts obtained in a release experiment in the field. A total of 220 beetle pairs were released at five locations in a field where this beetle was not observed previously. Each release point was at a border between the two host species.

One model predicted for the preferred host species the egg cluster count frequencies in the field from parameters estimated in the cages. This model assumed that egg clusters present on a plant increased subsequent oviposition on this plant. All other models could not describe the distribution of egg cluster counts for either of the two host species.

The results suggest that females seek out attractive hosts actively and the attractiveness of a plant increases with its egg cluster load. This behaviour creates a frequency distribution of egg clusters per host that depends only on beetle density but not on plant density. This conclusion has important implications for modelling insect–plant interactions.
Pheromone component patterns of moth evolution revealed by computer analysis of the Pherolist
Authors: BYERS JOHN A.
Published: March 2006

The Pherolist internet site listing moth sex pheromone components reported in the literature was downloaded and processed by a basic program into a database with 2931 combinations of 377 unique chemical names of sex pheromone attractants used by 1572 moth species in 619 genera and 49 families. Names of pheromone compounds were analysed for aliphatic chain length, unsaturation position, geometric configuration, functional group (aldehyde, alcohol, acetate, epoxide, methyl‐branched and hydrocarbon) and number of instances such combinations are used by species and families.

The analyses revealed pheromone blends of species ranged from one to eight components (45% species with one component, 36% two, 12% three, 5% four, 1% five, ≤ 0·5% for ≥ six). The numbers of different components of various chain lengths and functional groups, the numbers of instances such compounds are used by species and the numbers of species using such compounds are presented.

The average number of pheromone components per species increased as the number of species in a family increased based on linear regression of components in the 10 largest families, with species numbers ranging from 19 to 461. Pooling the four largest families gave a mean of 1·96 components per species that was significantly greater than the mean of the next 14 smaller families (1·63). Because related species in a large family would need more communication channels, this suggests that these species on average evolved to produce and detect more components in their pheromone blends to achieve a unique communication channel than was needed by species in smaller families.

Speciation in moths would entail evolutionary changes in both pheromone biosynthetic and sensory systems that avoided competition for communication channels of existing species. Regression analysis indicated that the more species in a family the more unique pheromone components, but the increase diminishes progressively. This suggests that, as the number of components increases with species number in a family, new species are more likely to evolve a unique blend comprising a communication channel from among existing components of the family.
The role of trout in stream food webs: integrating evidence from field surveys and experiments
Authors: MEISSNER KRISTIAN , MUOTKA TIMO
Published: March 2006

We evaluated the effects of brown trout on boreal stream food webs using field surveys and enclosure/exclosure experiments. Experimental results were related to prey preference of uncaged trout in the same stream, as well as to a survey of macroinvertebrate densities in streams with vs. without trout. Finally, we assessed the generality of our findings by examining salmonid predation on three groups of macroinvertebrate prey (chironomid midges, epibenthic grazers, invertebrate predators) in a meta‐analysis.

In a preliminary experiment, invertebrate predators showed a strong negative response to trout, whereas chironomids benefited from trout presence. In the main experiment, trout impact increased with prey size. Trout had the strongest effect on invertebrate predators and cased caddis larvae, whereasBaetismayfly and chironomid larvae were unaffected. Trout impact on the largest prey seemed mainly consumptive, because prey emigration rates were low and independent of fish presence. Despite strong effects on macroinvertebrates, trout did not induce a trophic cascade on periphyton. Uncaged trout showed a strong preference for the largest prey items (predatory invertebrates and aerial prey), whereasBaetismayflies and chironomids were avoided by trout.

Densities of invertebrate predators were significantly higher in troutless streams.Baetismayflies also were less abundant in trout streams, whereas densities of chironomids were positively, although non‐significantly, related to trout presence. Meta‐analysis showed a strong negative impact of trout on invertebrate predators, a negative but variable impact on mobile grazers (mainly mayfly larvae) and a slightly positive impact on chironomid larvae.

Being size‐selective predators, salmonid fishes have a strong impact on the largest prey types available, and this effect spans several domains of scale. Discrepancies between our experimental findings and those from the field survey and meta‐analysis show, however, that for most lotic prey, small‐scale experiments do not reflect fish impact reliably at stream‐wide scales.

Our findings suggest that small‐scale experiments will be useful only if the experimental results are evaluated carefully against natural history information about the experimental system and interacting species across a wide array of spatial scales.
A truce with neutral theory: local deterministic factors, species traits and dispersal limitation together determine patterns of diversity in stream invertebrates
Authors: THOMPSON ROSS , TOWNSEND COLIN
Published: March 2006

Studies seeking to explain local patterns of diversity have typically relied on niche explanations, reflected in correlations with local environmental conditions, or neutral theory, invoking dispersal processes and speciation.

We used macroinvertebrate community data from 10 streams that varied independently in local ecological conditions and spatial proximity. Neutral theory predicts that similarity in communities will be negatively associated with distance between sites, while niche theory suggests that community similarity will be positively associated with similarity in local ecological conditions.

Similarity in total invertebrate, grazer and predator assemblages showed negative relationships with distance and, for grazers and predators, positive relationships with local ecological conditions. However, the best model predicting community similarity in all three cases included aspects of both local ecological conditions and distance between sites.

When assemblages were analysed according to dispersal ability, high‐dispersal species were shown to be freely accessing all sites and community similarity was not well predicted by either local ecology or spatial separation. Assemblages of species with low and moderate dispersal ability were best predicted by combined models, including distance between sites and local ecological factors.

The results suggest that the perceived dichotomy between neutral and local environmental processes in determining local patterns of diversity may not be useful. Neutral and niche processes structured these communities differentially depending on trophic level and species traits.

We emphasize the potential for both dispersal processes and local environmental conditions to explain local patterns of diversity.
Testing five hypotheses of sexual segregation in an arctic ungulate
Authors: LOE LEIF EGIL , IRVINE R. JUSTIN , BONENFANT CHRISTOPHE , STIEN AUDUN , LANGVATN ROLF , ALBON STEVE D. , MYSTERUD ATLE , STENSETH NILS CHR.
Published: March 2006

Sexual segregation occurs in most species of sexually dimorphic ungulates. At least five not mutually exclusive hypotheses have been formulated to explain patterns of social, habitat and spatial segregation; the indirect competition hypothesis (H1), the nutritional needs hypothesis (H2), the activity budget hypothesis (H3), the weather sensitivity hypothesis (H4), and the predation risk hypothesis (H5).

Each hypothesis has a unique set of predictions with respect to the occurrence of segregation, and how seasonality, density dependence and reproductive status affect sexual segregation.

We tested this set of predictions in order to separate the hypotheses H1–H5 for patterns of sexual segregation of the Svalbard reindeer based on 9 years data on seasonal estimates of spatial, habitat and social (i.e. grouping with their own sex) segregation in combination with resource selection functions.

Our results do not support that one single mechanism causes segregation. The activity budget hypothesis, the nutritional needs hypothesis and the weather sensitivity hypothesis were all partially supported, while the predation risk hypothesis was discarded for Svalbard reindeer because predators have been absent for at least 5000 years. Several mechanisms are thus interacting to explain the full‐year pattern of sexual segregation and the combination of mechanisms varies among species and populations.
Biodiversity as both a cause and consequence of resource availability: a study of reciprocal causality in a predator–prey system
Authors: CARDINALE BRADLEY J. , WEIS JEROME J. , FORBES ANDY E. , TILMON KELLEY J. , IVES ANTHONY R.
Published: March 2006

One of the oldest questions in ecology is how species diversity in any given trophic level is related to the availability of essential resources that limit biomass (e.g. water, nutrients, light or prey). Researchers have tried to understand this relationship by focusing either on how diversity is influenced by the availability of resources, or alternatively, how resource abundance is influenced by species diversity. These contrasting perspectives have led to a seeming paradox ‘… is species diversity the cause or the consequence of resources that limit community biomass?’

Here we present results of an experiment that show it is possible for species diversity and resource density to exhibit reciprocal causal relationships in the same ecological system. Using a guild of ladybeetle predators and their aphid prey, we manipulated the number of predator species in field enclosures to examine how predator diversity impacts prey population size. At the same time, we manipulated the abundance of aphid prey in discrete habitat patches within each enclosure to determine how smaller‐scale spatial variation in resource abundance affects the number of co‐occurring predator species.

We found that the number of ladybeetle species added to enclosures had a significant impact on aphid population dynamics because interference competition among the predators reduced per capita rates of predation and, in turn, the overall efficiency of the predator guild. At the same time, spatial variation in aphid abundance among smaller habitat patches generated variation in the observed richness of ladybeetles because more species occurred in patches where predators aggregated in response to high aphid density.

The results of our experiment demonstrate that it is possible for species diversity to simultaneously be a cause and a consequence of resource density in the same ecological system, and they shed light on how this might occur for groups of mobile consumers that exhibit rapid responses to spatial and temporal variation in their prey.
Ecological mechanisms favouring behavioural diversification in the absence of morphological diversification: a theoretical examination using brook charr (Salvelinus fontinalis)
Authors: DE KERCKHOVE DERRICK , MCLAUGHLIN ROBERT L. , NOAKES DAVID L. G.
Published: March 2006

Behavioural diversification is thought to be an important initial step in the origin of resource polymorphisms. We developed a model for young brook charr (Salvelinus fontinalisMitchill) to examine four mechanisms that could generate aU‐shaped relationship between growth rate (fitness) and the proportion of time spent moving that would favour alternative foraging tactics in the absence of obvious differences in body size and shape.

Recently emerged brook charr of similar size and shape inhabit still‐water pools along the sides of streams. Some individuals tend to sit and wait for crustacean prey at the pool substrate near the bank, while others tend to search actively for insect prey at the pool surface away from the bank.

The ecological mechanisms modelled were (i) the relationship between the rate of prey capture and the proportion of time spent moving is curvilinear, such that net rate of energy gain is maximized at two different levels of activity; (ii) switching between foraging locations and, hence, tactics involves lost opportunity and travel costs; (iii) switching between prey types and, hence, tactics involves a learning cost; and (iv) foraging success is status‐dependent with individuals switching between tactics having a lower status than those specializing at a tactic.

Singly, no mechanism predicted theU‐shaped relationship between growth rate and the proportion of time spent moving. Together, aU‐shaped relationship was obtained, indicating that the behavioural diversification and diversifying selection observed in the field may be a consequence of multiple, subtle mechanisms.
Climatic niche partitioning following successive invasions by fruit flies in La Réunion
Authors: DUYCK PIERRE‐FRANÇOIS , DAVID PATRICE , QUILICI SERGE
Published: March 2006

Biological invasions have profound effects on community structure. The community composition following invasions can be influenced by the habitat diversity and the species’ responses to abiotic factors.

We evaluated the tolerance to climatic factors and analysed the field distribution of four polyphagous fruit flies (Diptera: Tephritidae) of La Réunion Island (three exotic species that successively invaded the island and the endemic species Ceratitis catoirii) in order to evaluate the opportunities of coexistence by niche differentiation.

Atmospheric humidity and immersion in water in the laboratory greatly influence the survival of fruit fly pupae. While C. catoirii and C. rosa are very sensitive to desiccation, C. capitata and especially Bactrocera zonata are relatively tolerant. B. zonata also tolerated immersion in water much longer than did C. rosa and C. catoirii, that in turn were more resistant than C. capitata. Overall, field distributions agree with the predictions based on this study of humidity combined with previous data on the effects of temperature.

Climatic niche partitioning promotes coexistence between some but not all pairs of invasive species. Thus, C. rosa can coexist with both C. capitata and B. zonata at the regional scale, while climatic niches are not different enough to promote coexistence of the latter two species. The endemic species has no private climatic niche either and this now very rare species could be in the process of extinction.

By promoting coexistence or not, climatic diversity in invaded areas can directly affect the community composition following invasions.
Multiscale patterns of movement in fragmented landscapes and consequences on demography of the snail kite in Florida
Authors: MARTIN JULIEN , NICHOLS JAMES D. , KITCHENS WILEY M. , HINES JAMES E.
Published: March 2006

Habitat loss and fragmentation are major factors affecting vertebrate populations. A major effect of these habitat alterations is that they reduce movement of organisms. Despite the accepted importance of movement in driving the dynamics of many natural populations, movement of vertebrates in fragmented landscapes have seldom been estimated with robust statistical methods.

We estimated movement probabilities of snail kitesRosthramus sociabiliswithin the remaining wetlands in Florida. Using both radio‐telemetry and banding information, we used a multistate modelling approach to estimate transition probabilities at two temporal scales (month; year) and multiple spatial scales. We examined kite movement among wetlands altered by three different levels of fragmentation: among wetlands separated by small physical barriers (e.g. road); among wetlands separated by moderate amount of matrix (< 5 km); and among wetlands separated by extensive matrix areas (> 15 km).

Kites moved extensively among contiguous wetlands (movement probability 0·29 per month), but significantly less among isolated wetlands (movement probability 0·10 per month).

Kites showed high levels of annual site fidelity to most isolated wetlands (probability ranged from 0·72 to 0·95 per year).

We tested the effects of patch size and interpatch distance on movement. Our modelling indicated an effect of both distance and patch size on juveniles’ movement (but not adult) when examining movements among fragments.

Only a small proportion of kites escaped a regional drought by moving to refugia (wetlands less affected by drought). Many individuals died after the drought. During drought adult survival dropped by 16% while juvenile survival dropped by 86% (possibly because juveniles were less likely to reach refugia).

We hypothesize that fragmentation may decrease kite's resistance to drought by restricting exploratory behaviour.
Behavioural flexibility in the mating system buffers population extinction: lessons from the lesser spotted woodpecker Picoides minor
Authors: ROSSMANITH EVA , GRIMM VOLKER , BLAUM NIELS , JELTSCH FLORIAN
Published: March 2006

In most stochastic models addressing the persistence of small populations, environmental noise is included by imposing a synchronized effect of the environment on all individuals. However, buffer mechanisms are likely to exist that may counteract this synchronization to some degree.

We have studied whether the flexibility in the mating system, which has been observed in some bird species, is a potential mechanism counteracting the synchronization of environmental fluctuations. Our study organism is the lesser spotted woodpecker Picoides minor (Linnaeus), a generally monogamous species. However, facultative polyandry, where one female mates with two males with separate nests, was observed in years with male‐biased sex ratio.

We constructed an individual‐based model from data and observations of a population in Taunus, Germany. We tested the impact of three behavioural scenarios on population persistence: (1) strict monogamy; (2) polyandry without costs; and (3) polyandry assuming costs in terms of lower survival and reproductive success for secondary males. We assumed that polyandry occurs only in years with male‐biased sex ratio and only for females with favourable breeding conditions.

Even low rates of polyandry had a strong positive effect on population persistence. The increase of persistence with carrying capacity was slower in the monogamous scenario, indicating strong environmental noise. In the polyandrous scenarios, the increase of persistence was stronger, indicating a buffer mechanism. In the polyandrous scenarios, populations had a higher mean population size, a lower variation in number of individuals, and recovered faster after a population breakdown. Presuming a realistic polyandry rate and costs for polyandry, there was still a strong effect of polyandry on persistence.

The results show that polyandry and in general flexibility in mating systems is a buffer mechanism that can significantly reduce the impact of environmental and demographic noise in small populations. Consequently, we suggest that even behaviour that seems to be exceptional should be considered explicitly when predicting the persistence of populations.
Nutrient transfer from sea to land: the case of gulls and cormorants in the Gulf of Maine
Authors: ELLIS JULIE C. , FARIÑA JOSE MIGUEL , WITMAN JON D.
Published: March 2006

The structure of communities is influenced by the transport of resources across ecosystem boundaries. Seabirds are capable of introducing large amounts of marine‐derived nutrients to land, thereby modifying resource availability to terrestrial species.

In this study we investigated the hypothesis that variation in nesting densities of great black‐backed gulls Larus marinus and double‐crested cormorants Phalacrocorax auritus would modify the effect of these species on soil nutrients and plant species composition on offshore islands in the Gulf of Maine, USA.

Our results showed a significant positive correlation between nest density and concentrations of ammonia and nitrate in soils, but no significant relationship between nest density and phosphate. Ammonia and phosphate concentrations were good predictors of plant species composition; there were more annual forbs than perennial grasses in the abandoned cormorant colony compared with the gull colonies. Extremely high concentrations of ammonia in the highest density colony (active cormorant) may have been the main factor inhibiting plant germination at this site. All of the plant species in gull and cormorant colonies showed enriched δ15N signatures, indicating substantial input of marine‐derived nitrogen from seabirds.

Our study demonstrated that gulls and cormorants are effective vectors for the transport of marine nutrients to terrestrial ecosystems. However, transported nutrients occurred in particularly high concentrations in areas with nesting cormorants. Nesting densities and species‐specific variation in resource transport should be considered when predicting the effects of seabirds and other biogenic vectors of allochthonous resources.
Density effects on life‐history traits in a wild population of the great titParus major: analyses of long‐term data with GIS techniques
Authors: WILKIN TEDDY A. , GARANT DANY , GOSLER ANDREW G. , SHELDON BEN C.
Published: March 2006

Population density often has strong effects on the population dynamics and reproductive processes of territorial animals. However, most estimates of density‐dependent effects use the number of breeding pairs per unit area in a given season and look for correlations across seasons, a technique that assigns the same density score to each breeding pair, irrespective of local spatial variation.

In this study, we employed GIS techniques to estimate individual breeding densities for great tits breeding in Wytham Woods UK, between 1965 and 1996. We then used linear mixed modelling to analyse the effect of density on reproductive processes.

The areas of Thiessen polygons formed around occupied nestboxes were used to approximate territory size (necessarily inverse of breeding density). There were significant, independent and positive relationships between clutch size, fledging mass and the number of offspring recruited to the population, and territory size (allP < 0·001), but no effect of territory size on lay‐date or egg mass.

Thiessen polygons are contiguous and cover all of the available area. Therefore, at low nest densities territory polygons were excessively oversized. Using a novel procedure to address this limitation, territory sizes were systematically capped through a range of maxima, with the greatest effect in the models when territories were capped at 0·9–2·3 ha. This figure approximates to the maximum effective territory size in our population and is in close agreement with several field‐based studies. This capping refinement also revealed a significant negative relationship between lay‐date and territory size capped at 0·9 ha (P < 0·001).

These density‐dependent effects were also detected when analyses were restricted to changes within individual females, suggesting that density effects do not merely result from either increased proportions of low‐quality individuals, or increased occupation of poor sites, when population density is high.

Overall, these results suggest that, in the current population, great tits with territories smaller thanc.2 ha independently lay smaller and later clutches, have lighter fledglings, and recruit fewer offspring to the breeding population. These analyses thus suggest a pervasive and causal role of local population density in explaining individual reproductive processes.
Relationship between host abundance and parasite distribution: inferring regulating mechanisms from census data
Authors: STANKO MICHAL , KRASNOV BORIS R. , MORAND SERGE
Published: March 2006

We studied the effect of host abundance on parasite abundance and prevalence using data on 57 associations of fleas (Siphonaptera) and their mammalian hosts from Slovakia.

We assumed that flea‐induced host mortality could be inferred from the relationship between flea aggregation and flea abundance, whereas host‐induced flea mortality could be inferred from the relationship between flea abundance or aggregation and host abundance.

Relationships between flea abundance or prevalence and host abundance were either negative (in 23 flea–host associations) or absent (in 34 flea–host associations). Negative relationships between flea abundance and host abundance were always accompanied by negative relationships between flea prevalence and host abundance.

The link between flea abundance/prevalence and host abundance was evaluated as the coefficient of determination of the respective regressions. Across flea–host associations, this link decreased with an increase in the degree of flea aggregation (measured as a parameterbof Taylor's power law).

Mean crowding of fleas decreased with an increase of host abundance in eight flea–host associations, being asymptotic in four of them. On the other hand, mean crowding of fleas increased with an increase in flea abundance in 49 flea–host associations, being asymptotic in 15 of them.

Results of this study suggest that different flea–host associations are governed by different regulating mechanisms, but different regulation mechanisms may act simultaneously within the same flea–host associations.