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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 10 (1980), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Estimates of relative and absolute abundance in field populations of two Gerris species were compared using regression techniques. Separate equations for each gerrid size class allow prediction of population density from timed-catch sampling. Presence or absence of vegetation markedly affected capture rates, but capture rates were not affected by Gerris species or type of emergent vegetation. Availability for capture varied with gerrid leg length; this relationship can be used to estimate availability constants for other water-strider species.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1939
    Keywords: Prey use ; Dolomedes triton ; Gerridae ; Cannibalism ; Intraguild predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Prey of feeding juvenile and adult Dolomedes triton (Walckenaer 1837) were sampled over two seasons on three small ponds in central Alberta, Canada. Prey were mainly insects active at the water surface with truly aquatic species making up about 14% of the diet. Throughout the season aquatic and semi-aquatic Heteroptera represented about 30% of the prey. Diptera and adult Odonata were also important prey items but their abundance in the diet was more variable seasonally. Of the 625 prey items recorded nearly 50% were represented by taxa taken no more than once by spiders in one of the five size classes (adult females, adult males, large, intermediate and small juveniles). Large spiders did not take the smallest prey available, although small and intermediate-sized spiders fed on nearly the full size range taken by larger spiders. Cannibalism was common, accounting for 5% of the observations, with females and large juveniles as the most frequently observed cannibals. We hypothesize that intraguild predation (including cannibalism) could be an important coevolutionary force structuring phenology, population dynamics and microhabitat use of the predatory guild of the neuston community.
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  • 3
    ISSN: 1432-1939
    Keywords: Gerris ; Mortality factors ; Heteroptera ; Insecta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Impacts of predators, food levels and cannibalism on population growth of G. buenoi were studied in two experiments using field exclosures. In the first experiment, experiments using field exclosures. In the first experiment, impacts of (1) predation by freshwater invertebrates and (2) food limitation on gerrid populations were considered in a 2 x 2 factorial design, using food supplements and elimination of predators as the experimental treatments. In the second experiment, the possible contribution of intraspecific predation to fitness of gerrid cannibals was assessed. Presence of invertebrate predators decreased egg-adult survivorship 2–3 fold and decreased the range of juvenile development times. The main predators noted in this study were fishing spiders (Dolomedes), backswimmers (Notonecta), larvae of predaceous diving beetles (Dytiscus), and dragonfly naiads (Aeshna). Food supplements, at 50–200% (by weight) of average natural surface fall, did not significantly effect survivorship but were associated with decreases in mean development time and with increases in whole body dry mass of teneral adults. Increases were greater for females than for males, suggesting that females are more likely to be protein limited under field conditions. Absence of predators was associated with smaller body size among teneral adults of G. buenoi, suggesting that screening out aquatic predators also had significant impact on food available to semi-aquatic bugs. Results of the second experiment demonstrate that the ”food cache hypothesis” (Polis 1980) does not hold for G. buenoi. Neither survival to the adult stage nor dry mass of teneral males differed significantly between groups with or without access to early stages as potential prey. Dry mass of teneral females with access to younger stages during their own development was significantly less than for those without access to gerrid prey, suggesting that competition among stages for food was more important than cannibalism in, this experiment.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of insect behavior 6 (1993), S. 455-466 
    ISSN: 1572-8889
    Keywords: parasitoid search ; Scelionidae ; host location ; Gerridae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mechanisms used by a scelionid egg parasitoid to locate its gerrid host eggs were studied using field experiments. Parasitism by Tiphodytes gerriphaguswas higher in exclosures containing adults of Limnoporus dissortisthan in cages without gerrids. Higher densities of adult gerrids were associated with higher rates of parasitism, but dispersion of aquatic vegetation did not apparently affect rates of parasitism. T. gerriphagusmay use visual cues, chemical cues, or a combination of both to locate their hosts. We discuss the possible influence of T. gerriphaguson the reproductive behavior of its hosts.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biology and philosophy 15 (2000), S. 211-238 
    ISSN: 1572-8404
    Keywords: bottom-up pluralism ; competitive hierarchies ; contingency ; explanation ; generalization ; life-history ; many-to-one ; mating behavior ; multiple causation ; nested hierarchy ; one-to-many ; scale ; sex ; sex ratio ; triadic system ; truth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Philosophy
    Notes: Abstract We argue that broad, simplegeneralizations, not specifically linked tocontingencies, will rarely approach truth in ecologyand evolutionary biology. This is because mostinteresting phenomena have multiple, interactingcauses. Instead of looking for single universaltheories to explain the great diversity of naturalsystems, we suggest that it would be profitable todevelop general explanatory ‘frameworks’. A frameworkshould clearly specify focal levels. The process orpattern that we wish to study defines our level offocus. The set of potential and actual states at thefocal level interacts with conditions at thecontiguous lower and upper levels of organization,through sets of many-to-one and one-to-manyconnections. The number of initiating conditions andtheir permutations at the lower level define thepotential states at the focal level, whereas theactual state is constrained by the upper-levelboundary conditions. The most useful generalizationsare explanatory frameworks, which are road maps tosolutions, rather than solutions themselves. Suchframeworks outline what is understood about boundaryconditions and initiating conditions so that aninvestigator can pick and choose what is required toeffectively understand a specific event or situation. We discuss these relationships in terms of examplesinvolving sex ratio and mating behavior, competitivehierarchies, insect life-histories and the evolutionof sex.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 19 (1986), S. 87-95 
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We studied oviposition, feeding and mating behavior of the water striders Limnoporus dissortis and L. notabilis in sympatric and allopatric populations occurring on semi-permanent ponds in Alberta and British Columbia, Canada. Here we describe the mating system of the species and consider the evolution and maintenance of reproductive strategies employed by both sexes. Females of both species oviposited along edges of floating vegetation, either with a guarding, postcopulatory male in attendance, or alone and independent of copulation. Some females ovipositing alone were discovered by males, and when pressed for copulation, either (1) abandoned oviposition or (2) copulated and then resumed oviposition. Females that oviposited with a guarding male laid more eggs than those that completed oviposition alone. Most breeding females accepted prey offered experimentally, while a large proportion of males rejected prey but responded to model gerrids with aggressive displays and mating behavior. Males displayed three mating tactics: (1) territorial-signaling (TS), (2) patrol-signaling (PS), and (3) silent patrolling (SP). All territorial males produced surface waves from oviposition sites before attempting to mate. Some patrolling males signaled, while approaching potential mates as an aid in sex discrimination, but others did not signal and mounted both males and females. When presented with dead gerrid “models”, males of L. notabilis discriminated between sexes while those of L. dissortis mounted both male and female conspecifics. Collectively, males employing TS tactics fertilized more eggs than patrolling males and TS males of L. notabilis fertilized relatively more eggs than those of L. dissortis. Individual males switched frequently between territorial and patrolling behavior both under natural conditions and in field exclosures. TS males gave more signals per encounter than PS males suggesting that signaling varies with male dominance. Choice of tactic did not depend upon hunger level and was not associated with significant differences in body length in single-species populations. However, in a mixed population, the smaller males of L. dissortis were rarely territorial and signaled infrequently.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 19 (1986), S. 79-85 
    ISSN: 1432-0762
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In Alberta and British Columbia, breeding males of pond-dwelling Limnoporus dissortis and L. notabilis defend territories around floating leaves and produce ripple signals (repel signals) at intruders. Before and during mating and oviposition, males also produce courtship signals, and repel signals if intruders appear. Females do not maintain territories or produce repel signals. In the field, repel signals were recorded and analyzed by computer, then played back by oscillating a leaf tip with a magnet. Dead females (models) in natural position were guided with thread into territories, to entice males to signal. Models were guided so the forelegs were within 3 mm of a magnetbearing leaftip. Repel-signaling males approached models closely, then switched to courtship signals, wherepon playbacks of repel signals caused the males immediately to reply with repel signals and attack the model. Males thus distinguished sex by presence or absence of the repel signal. With a dead male L. notabilis pinned near a magnet on a territory leaf, playbacks were made to patrolling Limnoporus and Gerris buenoi males that skated by and showed interest in the model. After playbacks, Limnoporus notabilis (large) males skated away at the usual slow patrolling pace, but hybrid (medium) and L. dissortis (small) males skated away rapidly, indicating that repel signals repel at least smaller intruder males. Gerris buenoi males skated away slowly after playbacks, their relatively small size indicating that small size was not by itself a necessary reason for a strider to skate rapidly away. Coexistent Limnoporus dissortis and L. notabilis hybridize extensively in Alberta and British Columbia. Waveform and frequency comparisons of repel signals from pure and hybrid individuals showed no significant difference in these characteristics. Repel signals from both species resulted in similar playback responses from both species, indicating that in this area ripple signals are not involved effectively in species discrimination.
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  • 8
    Publication Date: 2004-01-01
    Description: Saproxylic beetles associated with Populus coarse woody material were sampled from two age classes of fire-origin aspen stands in north-central Alberta, Canada. A combination of rearings from wood bolts and window traps attached to snags yielded 9571 beetles representing 257 taxa over the 3-year period (19931995). We investigated faunal variation across regions, stand ages (mature, 6090 years; old, 〉100 years), decay classes, wood types, and years in terms of species richness, abundance, and trophic differences. Although trophic structure was similar, faunal composition differed between the two study regions. Species richness and abundance were similar across stand ages; however, many species were collected exclusively or in great majority from old stands and from snags of large diameter, which suggested that truncation of stand age structure through widespread industrial harvest could have serious consequences for saproxylic assemblages. Beetle species richness increased with the level of wood decay, whereas the total catch of beetles tended to be higher in early stages of decay. Wood borer abundance tended to be higher in snags; however, total species richness was higher in logs. Our analyses suggest that (i) many beetle species in the Canadian boreal forest depend directly upon standing and fallen large-diameter woody material from Populus trees, (ii) variation in stage of decay is critical to beetle diversity, and (iii) provision for retention of representative old stands is critical to conservation of saproxylic communities.
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 9
    Publication Date: 2018-12-01
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 10
    Publication Date: 2004-05-01
    Description: This study examines the short-term impact of forest soil compaction and organic matter removal on soil mesofauna, in general, and oribatid mite species, in particular. Both soil compaction and organic matter removal reduced the density of soil mesofauna. Stem-only harvesting reduced total mesofauna densities by 20% relative to uncut forest values. A combination of whole-tree harvest and forest floor removal with heavy soil compaction significantly reduced total soil mesofauna densities by 93% relative to the uncut forest control. Removal of the forest floor represents a substantial loss of habitat for most soil mesofauna. The forest floor apparently buffered the mineral soil by limiting both the impact of soil compaction and fluctuations in soil temperature and moisture. The relative abundance of Prostigmata and Mesostigmata increased with treatment severity, whereas that of Oribatida decreased. Species richness of the oribatid mite fauna was reduced as the severity of treatments increased. The number of rare oribatid species (those representing
    Print ISSN: 0045-5067
    Electronic ISSN: 1208-6037
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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