Functional responses of the rotifers Brachionus calyciflorus and Brachionus rubens feeding on armore

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Functional responses of the rotifers Brachionus
calyciflorus and Brachionus rubens feeding on
armored and unarmored ciliatesexperiment an
notes by Silvia Mohr and Rita AdrianInstitue of
Freschwater Ecology and Inland Fischeries
BerlinPresentation by Kai Berends
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• Table of contens
• The experiment
• Literature review
• Results
• Conclusions

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The Experiment Brachionus calyciflorus Adult
length 250 - 300µm Preferenced prey diameter
10 µm Brachionus rubens Adult length 200-250
µm Preferenced prey diameter 5 µm Tetrahymena
Pyriformis Length 40-45 µm Width 10-15 µm Soft
body Coleps sp. Length 40-45 µm Width 10-15
µm Surface of calcereous plates with short spines
The 2 Ciliates are of similar size, shape,
mobility and swimming behavior but differ in
surface texture.
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• The Experiment
• - A series of prey solutions with densitys
  between 20 1300 ciliates/ml was established
• 10 rotifers were added to 1 ml of a prey solution
  for 4 hours at 20
• Samples were fixed with acid Lugols solutions
• Rotifers and Ciliates were counted under a
  stereoscope
• Clearence and ingestion rates were calculated
• For each model type, max. ingestion rate and
  ciliate density were calculated

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Rotifers are able to regulate their food uptake
by modification of their feeding behavior with
respect to prey density and type of prey. 3
Models to describe the density-depending feeding
strategies (Hollings Type 1, 2, 3) Type 1
handling time with prey items is negligible Type
2 typical for larger prey items and longer
handling time (also Ivlev Type 2 model) Type 3
reduced encounter rates at low prey densities
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• Literaturereview
• - Rotifers (in this case B. calycilflorus and B.
  rubens) change the type of functional response
  with increasing algae size
• Above an optimal prey size the feeding behavior
  changes from Type 1 to Type 2 ( Handling time
  increases with prey size)
• Many rotifers are herbivore, but it is also
  proven that they are able to feed on small prey
  such as bacteria or ciliates
• Untill the experiment the functionel response
  relationships between rotifers and ciliates were
  unknown
• Different shape, surface texture and mobility
  makes ciliates very different as compared to
  algae or bacteria

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The results
1. B.Calyciflorus Coleps
2. B.Calyciflorus T.pyriformis 3.
B.rubens T.pyriformis
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• Results
• B. calycifloris/Coleps sp.
• The Holling Type 2 model gave the best fit (Fig.
  1)
• Maximal clearance rate of 30.2 µl rotifer¹ h¹
  at density of 50 ciliates ml ¹
• Hyperbolic increase in ingestion rates with
  increasing Coleps densities
• B. calycifloris/T. pyriformis
• Type 1 model best fits (Fig. 2)
• At low prey densitys a range of constant maximal
  clearance rates was hard to define. Maximal
  clearance rates varied between 8.4 and 13.6 µl
  rotifers¹ h¹
• B. rubens/Coleps sp
• -B.rubens was not able to feed on armored Coleps
  sp.
• B.rubens/T. pyriformis

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• Results
• Width of both ciliate species (10-15µm) fell in
  the food size range of B. calyciflorus (about
  10µm) but lay above the preffered size of B.
  rubens (about 5µm)
• Expectation
• Type 1 model would be plausible for B.
  calyciflorus, Type 2 for B. rubens
• Results of the Experiment
• Type 1 best described feeding of B. calyciflorus
  on T. pyriformis
• Type 2 best described feeding of B. rubens on T.
  pyriformis
• Type 2 best described feeding of B. calyciflorus
  on Coleps sp.
• Rejection of Coleps sp. By B. rubens

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Conclusions(1) The change from Type
1(T.pyrirormis) to Type 2 (Coleps sp.) for B.
calyciflorus and the rejection of Coleps sp. By
B. rubens, shows that armored Ciliates are more
difficult to handle than the soft bodied. The
hard inflexible body of Coleps seems to be an
effektive defense against predation of B. rubens
The surface structures limites the upper prey
size for brachionids B. Calyciflorus is a more
eficient predator than B. rubens The 2 closely
related rotifers are both able to ingest large
soft ciliates, but B. rubens had lower ingestion
rates. B. Calyciflorus should have an higher
predatory impact on large cilates in natural
ciliate communitys than B. rubens.
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Conclusions(2) Contrary to expectation, B.
calyciflorus reached lower clearance rates and
ingestion rates for T. pyriformis than for Coleps
sp. An explanation may be a positive prey
selection A functional response Type 2 does not
necessarily lead to lower clearance rates for
rotifers