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1

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Changes in structure and composition of an assemblage of Hydroporus species (Coleoptera: Dytiscidae) along a pH gradient (1991)

JULIANO, STEVEN A.

Oxford, UK : Blackwell Publishing Ltd

Freshwater biology 25 (1991), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: SUMMARY. 1. Patterns of total abundance and species relative abundances in an assemblage of predatory dytiscid beetles of the genus Hydroporus were examined along a pH gradient within a ditch in north-cast England.2. During spring, total abundance of adult Hydroporus was greatest at the less acidic (pH 5.6–6.2) upstream sites, whereas total abundance of larval Hydroporus was greatest at the more acidic (pH 4.5) downstream sites. Both adults and larvae were more abundant in samples from the edge than from the middle of the ditch.3. Species number and evenness did not differ along the pH gradient.4. Species relative abundance patterns varied along the pH gradient, with particular species dominating at different sites. However, relative abundances of species changed discontinuously along the pH gradient.5. Comparison of species abundance patterns along this pH gradient with published patterns of presence/absence among bodies of water with different pH revealed that species relationships with pH are often not consistent. Possible sources of this inconsistency are: geographic variation in species' pH preferences; complex responses of individual species to many factors in addition to pH; or random variation among sites due to colonization and extinction history.6. The overall results suggest that pH is not the only, or even the most important, factor influencing Hydroporus populations and assemblage organization.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2427.1991.tb00499.x

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Extrinsic vs. intrinsic food shortage and the strength of feeding links: effects of density and food availability on feeding rate of Hyphydrus ovatus (1990)

Juliano, Steven A. ; Lawton, John H.

Springer

Oecologia 83 (1990), S. 535-540

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ISSN: 1432-1939

Keywords: Donor control ; Dytiscidae ; Food limitation ; Food webs ; Predator-prey interactions

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary We use field and laboratory experiments to determine whether Hyphydrus ovatus, a predatory aquatic beetle, is food limited, and whether any food shortage results from depletion of prey by these predators (intrinsic food shortage) or is independent of predation by these beetles (extrinsic food shortage). In the laboratory, differences in feeding rate influence body fat content, thus making fat content a useful index of recent feeding history. H. ovatus collected during the breeding season have fat contents significantly greater than those of H. ovatus starved for 25 days, but not significantly different from those of H. ovatus fed ad libitum for 25 days, indicating that natural feeding rates are near the maximum possible. H. ovatus confined at a density 60 times greater than natural show reduced fat content and feeding rate relative to natural, indicating that at very high densities H. ovatus is capable of depleting its prey. Addition of supplemental natural prey (primarily Cladocera) to experimental enclosures resulted in an order of magnitude increase in prey availability, and a significant increase in fat content and feeding rate of confined H. ovatus. Adults of this species do not appear to be food limited during the breeding season, and extraordinarily high densities of adults seem to be necessary to produce intrinsic food shortage. These results suggest that feeding links between H. ovatus an its principal prey do not have major effects on population dynamics under typical field conditions, and call into question the assumption that closely coupled predator-prey interactions are the sole explanation for observed food-web patterns.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317206

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Costs of reproduction and geographic variation in the reproductive tactics of the mosquito Aedes triseriatus (1999)

Frankino, W. Anthony ; Juliano, Steven A.

Springer

Oecologia 120 (1999), S. 59-68

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ISSN: 1432-1939

Keywords: Key words Life history evolution ; Treehole mosquito ; Mortality rate ; Predation ; Manipulation of reproductive investment

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The eastern treehole mosquito, Aedes triseriatus (Say), was used in two experiments testing assumptions and predictions of life history theory. Experiment 1 employed direct, phenotypic manipulations of reproductive investment (blood meal mass) to test for a physiological cost of reproduction expressed as reduced longevity with increasing reproductive investment. As predicted, A. triseriatus from Vero Beach, Fla., showed costs increasing with investment in reproduction, but mosquitoes from Ashland, Va., showed the opposite response. This difference in apparent costs of reproduction may influence patterns of reproductive investment documented in the second experiment. To test the hypothesis that different predator-induced expected mortality rates among juveniles result in different patterns of reproductive allocation, we compared the allocation tactics of A. triseriatus from eight geographic populations, four sympatric with and four allopatric to the predatory mosquito, Toxorhynchites rutilus (Coq). Path analysis identified a phenotypic trade-off between offspring size and number, supporting this fundamental assumption of life history theory. Analysis of covariance revealed significant variation among populations in replete blood meal mass, reproductive output per unit blood meal mass (both measures of reproductive investment), mean egg mass, and egg number, although intrapopulation variation greatly exceeded interpopulation variation for all traits. Despite this variation among populations, there were no consistent or significant differences between populations sympatric vs. allopatric to the predator T. rutilus. This experiment therefore fails to support the hypothesis that greater mortality of juveniles should be associated with greater offspring size, lower offspring number, and lower reproductive investment. Our results are interesting, however, because they suggest that reproductive investment, reproductive output, and the trade-off between offspring size and number may evolve independently in this system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050833

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Plasticity of insect reproduction: testing models of flexible and fixed development in response to different growth rates (1998)

Moehrlin, Gregory S. ; Juliano, Steven A.

Springer

Oecologia 115 (1998), S. 492-500

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ISSN: 1432-1939

Keywords: Key words Development rate ; Egg production ; Growth rate ; Reproductive tactics ; Romalea guttata

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We tested alternative developmental hypotheses describing when during an insect oviposition cycle reproductive tactics are determined. Newly eclosed adult females of the grasshopper Romalea guttata were raised on eight different feeding treatments consisting of a low food diet, a high food diet, and changes from high to low food, or low to high food, at different times during the first oviposition cycle. When initial food availability was high, a decline in food availability 〉7 days after adult eclosion produced no significant increase in time to oviposition compared to constant high food. In contrast, when initial food availability was low, an increase in food availability as late as day 14 produced a significant decrease in time to oviposition compared to constant low food. Thus, time to oviposition is determined by feeding rate early in the oviposition cycle, but the time of this determination is later when food availability is lower. Masses of individual eggs were unaffected by these treatments. When initial food availability was high, a decrease in food availability on day 21 produced no significant change in numbers of eggs in a clutch compared to constant high food. In contrast, when initial food availability was low, an increase in food availability after day 7 produced no significant change in number of eggs in a clutch compared to constant low food. Changes in egg production resulted from oocyte resorption, which appeared to become unresponsive to food availability between day 14 and day 21. Our results refute the hypothesis that reproductive tactics are continuously flexible. Development toward oviposition seems to be structured so that reproductive tactics become independent of feeding late during the first oviposition cycle. Reproductive tactics become unresponsive to food at different times for groups initially receiving low or high food, suggesting that a particular developmental state, rather than some absolute time, marks the shift to development that is unresponsive to␣food. Plasticity in reproductive tactics appears to be␣controlled by hormones in a manner similar to the hormonal control of plasticity of metamorphosis in other insects.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050546

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Negative effects of habitat drying and prior exploitation on the detritus resource in an ephemeral aquatic habitat (1998)

Aspbury, Andrea S. ; Juliano, Steven A.

Springer

Oecologia 115 (1998), S. 137-148

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ISSN: 1432-1939

Keywords: Key wordsAedes triseriatus ; Disturbance ; Ephemeral aquatic habitats ; Habitat drying ; Resources

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Ephemeral aquatic habitats are characterized by cycles of drying and subsequent inundation, and by production of sequential non-overlapping cohorts of organisms. Both processes may alter the quantity or quality of resources, and may therefore affect survival and development of cohorts that subsequently colonize ephemeral habitats. We examined these effects of habitat drying and non-overlapping cohorts on experimental cohorts of the tree hole mosquito Aedes triseriatus, testing specifically whether the value of leaf litter as a food resource is altered by cycles of inundation and drying, or by exploitation by a prior non-overlapping cohort. We created four treatments of leaf litter: (1) no prior cohort, continuously wet; (2) no prior cohort, one␣wet/dry cycle; (3) prior cohort, continuously wet, and (4) prior cohort, one wet/dry cycle, and tested for effects on individual fitness components (survivorship, mean dry mass at, and median days to eclosion) and on population growth (estimated finite rate of increase –λ′). Both resource drying and the presence of a prior cohort negatively affected individual fitness components in tires, increasing days to eclosion, and decreasing mean dry mass at eclosion for both sexes. Resource drying also negatively affected estimated rates of increase (λ′) in tree holes. A prior cohort had no significant effects on λ′. These results indicate that intraspecific interactions among mosquito larvae may include amensalistic effects of earlier, non-overlapping cohorts, and that resource drying reduces resource quality. The latter effect indicates that enhanced production of A. triseriatus from recently filled containers is not due to resource drying per se, and may result from more complex community-level effects of habitat drying. Extreme cycles of drying and inundation seem likely to increase intraspecific resource competition among drought-adapted species like A. triseriatus.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050500

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6

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Effects of growth rates on development to metamorphosis in the lubber grasshopper, Romalea microptera (2000)

Flanagin, Virginia L. ; Haase, Steven P. ; Juliano, Steven A.

Springer

Oecologia 125 (2000), S. 162-169

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ISSN: 1432-1939

Keywords: Development rate Complex life cycles Feeding efficiency Growth rate Plasticity Metamorphosis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract. We tested three developmental models postulating different effects of feeding and growth rates on nymphal development rate in female Romalea microptera (Beauvois). We also tested whether assimilation efficiency during the last stadium was affected by earlier feeding in ways that buffer effects of sub-optimal feeding. Hatchling R. microptera were raised in nine treatment groups consisting of high food, low food, and switches from low to high food, high to low food, and high to no food after molts to successive instars. High food during the middle three stadia (second through fourth) yielded significantly lower time to adulthood and larger adult size compared to low food during the middle three stadia. Feeding during the first and last stadia had no significant effect on mass at adulthood or total development time; however, some feeding and growth during the last stadium appeared to be required for successful metamorphosis. Feeding rate during one stadium usually had significant effects on durations of subsequent stadia. Assimilation efficiency in the fifth instar was significantly greater when food availability was low during early stadia, then high during the fifth stadium, compared to assimilation efficiency when food availability was high throughout development. Low food availability during the last stadium significantly lowered assimilation efficiency compared to high food availability during the last stadium, regardless of food availability during earlier stadia. Treatments did not significantly affect relative sizes of fore-, mid-, and hindguts. Our results suggest that development rate proceeds relatively independently of feeding during the last stadium. Our results support models that postulate loss of developmental plasticity late in nymphal life, and this constraint on plasticity may limit the ability of late-instar nymphs to respond to a variable environment.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420000441

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Specificity in host-fungus associations: Do mutualists differ from antagonists? (1991)

Borowicz, Victoria A. ; Juliano, Steven A.

Springer

Evolutionary ecology 5 (1991), S. 385-392

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ISSN: 1573-8477

Keywords: Specificity ; mutualists ; antagonists ; woody plants ; symbiosis

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Physically intimate interactions between organisms are assumed to be highly specific, yet intimate mutualisms exhibiting little specificity are common and important in many communities. We compare host records for ectomycorrhizal fungi (mutualists) to those for biotrophic shoot fungi and necrotrophic root fungi (both antagonists) in order to test two alternative predictions: (1) intimate physical associations (biotrophy) are more specific than less intimate ones (necrotrophy); (2) antagonisms are more specific than mutualisms. Specificity of fungi for hosts supports prediction (1): ectomycorrhizal fungi and shoot biotrophs are more host specific than root necrotrophs. Fungal symbiont ranges of hosts supports prediction (2): woody hosts are associated with a greater number of mutualistic fungi than antagonistic fungi. The numbers of fungi in the three groups infecting hosts are all significantly positively correlated. This result suggests that some hosts are resistant to fungal invasion and others are quite susceptible. Thus, plants may not be able to erect selective barriers to only antagonistic fungi. The marked asymmetry of specificity from the perspectives of hosts vs fungi suggests that evolutionary and ecological processes act differently on partners in symbioses.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02214155

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