bluuebunny/crossref_metadata_2025_split huggingface dataset:
The distribution of eggs per host in a herbivorous insect − intersection of oviposition, dispersal and population dynamics
Authors: ZU DOHNA HEINRICH 
Published: March 2006

Summary

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

Summary

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

SummaryWe 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

Summary

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

Summary

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

Summary

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

SummaryBehavioural 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

Summary

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

SummaryHabitat 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

Summary

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

Summary

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.