REGULAR ARTICLES / ARTICLES RÉGULIERSSize-related predation reduces intramorph competition in paedomorphic Alpine newts

2001 ◽  
Vol 79 (6) ◽  
pp. 943-948 ◽  
Author(s):  
Mathieu Denoël ◽  
Pierre Joly
Keyword(s):  
Resource Partitioning ◽  
Prey Size ◽  
Food Competition ◽  
Aquatic Habitats ◽  
Age At Maturity ◽  
Selective Predation ◽  
Facultative Paedomorphosis ◽  
Triturus Alpestris ◽  
Younger Age ◽  
Capture Range

Evolutionary theory assumes that facultative paedomorphosis in newts and salamanders is adaptive in allowing either a younger age at maturity or resource partitioning between the heterochronic morphs. In newt populations that only take the metamorphic ontogenetic pathway, juveniles are terrestrial and avoid food competition with larvae and breeding adults. In contrast, in populations where paedomorphosis occurs, branchiate newts of all sizes coexist in the aquatic habitats, posing the question of whether intramorph competition exists and its relationship with the evolution of paedomorphosis. We studied size-related predation in such a size-structured community of branchiate Alpine newts (Triturus alpestris) inhabiting a deep alpine lake. Although gape limitation may explain such size-related predation, individuals also exhibited selectivity according to prey size. Amongst small prey that were within the capture range of all newt size classes, smaller newts preyed on smaller items than did larger ones. We assume that such decisions favour the coexistence of different-sized individuals. It is suspected that such size-selective predation on items which are avoided by water-living metamorphs allows the maintenance of facultative paedomorphosis, in favouring resource partitioning between morphs.

scholarly journals Successful Predation of Filamentous Bacteria by a Nanoflagellate Challenges Current Models of Flagellate Bacterivory

2004 ◽  
Vol 70 (1) ◽  
pp. 332-339 ◽  
Author(s):  
Qinglong L. Wu ◽  
Jens Boenigk ◽  
Martin W. Hahn
Keyword(s):  
Prey Size ◽  
Ingestion Rate ◽  
Capture Rate ◽  
Food Concentration ◽  
Filamentous Bacteria ◽  
Selective Predation ◽  
Average Cell ◽  
Feeding Experiments ◽  
Contact Probability ◽  
Food Conditions

ABSTRACT Current models suggest that (i) filamentous bacteria are protected against predation by nanoflagellates, (ii) prey size is positively correlated with prey-predator contact probability, and (iii) contact probability is mainly responsible for size-selective predation by interception-feeding flagellates. We used five strains of filamentous bacteria and one bacterivorous nanoflagellate, Ochromonas sp. strain DS, to test these assumptions. The five strains, including one spirochete and four Betaproteobacteria strains, were isolated by the filtration-acclimatization method. All five strains possess flexible cells, but they differ in average cell length, which ranged from 4.5 to 13.7 μm. High-resolution video microscopy was used to measure contact, capture, and ingestion rates, as well as selectivity of the flagellate feeding. Growth and feeding experiments with satiating and nonsatiating food conditions, as well as experiments including alternative well-edible prey, were performed. In contrast to predictions by current models, the flagellate successfully consumed all the tested filamentous strains. The ingestion rate was negatively correlated with bacterial length. On the other hand, the lengths of the filamentous bacteria were not positively correlated to the contact rate and capture rate but were negatively correlated to ingestion efficiency. In experiments including alternative nonfilamentous prey, the flagellates showed negative selection for filamentous bacteria, which was independent of food concentration and is interpreted as a passive selection. Our observations indicate that (i) size alone is not sufficient to define a refuge for filamentous bacteria from nanoflagellate predation and (ii) for the investigated filamentous bacteria, prey-predator contact probability could be more influenced by factors other than the prey size.

Sexual size dimorphism in relation to resource partitioning in North American dabbling ducks

1984 ◽  
Vol 62 (10) ◽  
pp. 2009-2012 ◽  
Author(s):  
Thomas D. Nudds ◽  
Richard M. Kaminski
Keyword(s):  
North American ◽  
Resource Partitioning ◽  
Sexual Size Dimorphism ◽  
Prey Size ◽  
Dabbling Ducks ◽  
Male And Female ◽  
Size Dimorphism ◽  
Bill Morphology ◽  
Size Dimension ◽  
Bill Length

Data from museum specimens were used to examine patterns of sexual size dimorphism in bill morphology in relation to resource partitioning in seven species of North American dabbling ducks (Anas sp.). All species were dimorphic with respect to bill length. Male and female bill length distributions were skewed in opposite directions in five of seven species (P < 0.01). Four of seven species were dimorphic with respect to lamellar density, but male and female distributions were skewed in opposite directions in only two species. The four dimorphic species were positioned between other species along a prey size dimension; species which were not dimorphic had only one neighbour on the prey size dimension. These results are consistent with the hypothesis that intersexual competition for food promotes niche divergence between sexes and contributes to sexual size dimorphism in ducks.

scholarly journals Size-Selective Predation on Groundwater Bacteria by Nanoflagellates in an Organic-Contaminated Aquifer

1998 ◽  
Vol 64 (2) ◽  
pp. 618-625 ◽  
Author(s):  
N. E. Kinner ◽  
R. W. Harvey ◽  
K. Blakeslee ◽  
G. Novarino ◽  
L. D. Meeker
Keyword(s):  
Bacterial Degradation ◽  
Cape Cod ◽  
Aquatic Habitats ◽  
Selective Predation ◽  
Average Cell ◽  
Contaminated Aquifer ◽  
Groundwater Contaminants ◽  
Aquifer Sediments ◽  
Average Cell Volume ◽  
Protistan Grazing

ABSTRACT Time series incubations were conducted to provide estimates for the size selectivities and rates of protistan grazing that may be occurring in a sandy, contaminated aquifer. The experiments involved four size classes of fluorescently labeled groundwater bacteria (FLB) and 2- to 3-μm-long nanoflagellates, primarily Spumella guttula(Ehrenberg) Kent, that were isolated from contaminated aquifer sediments (Cape Cod, Mass.). The greatest uptake and clearance rates (0.77 bacteria · flagellate−1 · h−1 and 1.4 nl · flagellate−1 · h−1, respectively) were observed for 0.8- to 1.5-μm-long FLB (0.21-μm3 average cell volume), which represent the fastest growing bacteria within the pore fluids of the contaminated aquifer sediments. The 19:1 to 67:1 volume ratios of nanoflagellate predators to preferred bacterial prey were in the lower end of the range commonly reported for other aquatic habitats. The grazing data suggest that the aquifer nanoflagellates can consume as much as 12 to 74% of the unattached bacterial community in 1 day and are likely to have a substantive effect upon bacterial degradation of organic groundwater contaminants.

Effects of domestication on parr maturity, growth, and vulnerability to predation in Atlantic salmon

2014 ◽  
Vol 71 (9) ◽  
pp. 1371-1384 ◽  
Author(s):  
Paul V. Debes ◽  
Jeffrey A. Hutchings
Keyword(s):  
Atlantic Salmon ◽  
Prey Size ◽  
Wild Strain ◽  
Male Reproductive Success ◽  
Selective Predation ◽  
Predation Mortality ◽  
In The Wild ◽  
Related Stress ◽  
Induced Changes ◽  
Lower Size

Domestication can change fitness-related traits. We investigated domestication-induced changes in fitness-related traits in Atlantic salmon (Salmo salar) under naturally enriched laboratory conditions with and without threat of predation. Selection in two strains for rapid growth for three and five generations resulted in two and three times larger sizes of under-yearling parr relative to their wild ancestor. An initially larger size and ability to outgrow prey size more rapidly resulted in lower size-selective predation mortality for domesticated individuals. Growth under threat of predation was only reduced for wild individuals, suggesting that domestication co-selects for predator-related stress resistance. Size-adjusted male parr maturation probability was 34% in the wild strain, but significantly reduced to 10% and 7% after three and five generations of domestication, respectively. Together, freshwater-stage-specific survival for individuals with a domesticated background relative to individuals with a wild genetic background might be higher in the presence of gape-limited predators preferring small individuals, but male reproductive success might be lower for domesticated individuals as their reproduction potential during the freshwater phase is reduced.

Species Selective Predation on Juvenile Pink (Oncorhynchus gorbuscha) and Chum Salmon (O. keta) by Coho Salmon (O. kisutch)

1985 ◽  
Vol 42 (4) ◽  
pp. 659-668 ◽  
Author(s):  
N. Brent Hargreaves ◽  
Robin J. Lebrasseur
Keyword(s):  
Chum Salmon ◽  
Prey Species ◽  
Coho Salmon ◽  
Prey Size ◽  
Pink Salmon ◽  
Oncorhynchus Gorbuscha ◽  
Selective Predation ◽  
Pink Salmon Oncorhynchus Gorbuscha ◽  
Mixed Populations

Predation on juvenile pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta) by yearling coho (O. kisutch) was studied in marine enclosures in Masset Inlet, B.C. These experiments demonstrate that coho prey selectively upon pink salmon even when chums are both significantly smaller and more abundant than pink salmon. Reexamination of the results of similar experiments conducted in Burke Channel, B.C., also confirms that mortality was biased towards pink salmon. Prey species may be more important than prey size for coho that prey upon mixed populations of pink and chum salmon during early sea-life.

Resource partitioning in two heterochronic populations of Greek Alpine newts, Triturus alpestris veluchiensis

2003 ◽  
Vol 24 (1) ◽  
pp. 55-64 ◽  
Author(s):  
Mathieu Denoël ◽  
Robert Schabetsberger
Keyword(s):  
Resource Partitioning ◽  
Triturus Alpestris

scholarly journals Dietary partitioning in newly sympatric urban flying-foxes (Pteropus poliocephalus and Pteropus alecto)

2020 ◽  
Vol 42 (3) ◽  
pp. 361
Author(s):  
Phoebe Griffith ◽  
Kerryn Parry-Jones ◽  
Andrew A. Cunningham
Keyword(s):  
Resource Partitioning ◽  
New South ◽  
Microscopic Analysis ◽  
Food Competition ◽  
Flying Foxes ◽  
South Wales ◽  
Faecal Samples ◽  
Pteropus Poliocephalus ◽  
Competition For Food ◽  
Flying Fox

The black flying-fox (Pteropus alecto) is extending its range southward and is now sympatric with the grey-headed flying-fox (P. poliocephalus) in New South Wales. Competition for food between the two species has been suggested to be a contributor to declines of the vulnerable grey-headed flying-fox. During winter 2016 the diet of both species was investigated over one night at four sites of sympatry, by microscopic analysis of faecal samples. Resource partitioning between the two species was found, with the black flying-fox either preferentially choosing to eat more fruit than the grey-headed flying-fox or being an inferior competitor for pollen and nectar. These results, though limited, do not support the hypothesis that the black flying-fox threatens the grey-headed flying-fox through food competition.

Selective Predation by Drift-Feeding Brown Trout (Salmo trutta)

1979 ◽  
Vol 36 (4) ◽  
pp. 392-403 ◽  
Author(s):  
Neil H. Ringler
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Prey Size ◽  
Energy Content ◽  
Feeding Strategy ◽  
Invertebrate Drift ◽  
Selective Predation ◽  
Heterogeneous Distribution ◽  
Brown Trout Salmo Trutta ◽  
Dominant Characteristic

Consumption of three species of prey by brown trout (Salmo trutta) in a laboratory stream was studied during 7-d experiments. Two drift rates (5 and 10 organisms/min) and three ratios (1:1, 2:1, 5:1) of small:large alternative prey were employed. Responses to prey species stabilized after 4–6 d and 800–1200 prey captures, but no prey was completely excluded from the diet. Size-selective predation was a dominant characteristic of the response. The fish appeared to alter the area (depth) searched in response to prey density; electivity was greatest when prey densities were high. Disproportionate predation on abundant prey ("switching") was a temporary phenomenon, which may have been masked by prey size. Brown trout ultimately achieved 54–91% of a hypothetical diet in which prey are ranked in order of size (energy content). Deviations from an optimal diet may be explained in terms of a feeding strategy that deals with heterogeneous distribution of prey, as well as with the behavioral capabilities of the predator. Key words: behavior, fish, invertebrate drift, optimal foraging, predation, prey size and abundance, Salmonidae, search image, streams

Effects of Size-Selective Predation and Food Competition on High Altitude Zooplankton Communities

Ecology ◽  
1972 ◽  
Vol 53 (3) ◽  
pp. 375-386 ◽  
Author(s):  
W. Gary Sprules
Keyword(s):  
High Altitude ◽  
Food Competition ◽  
Selective Predation ◽  
Zooplankton Communities
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