10.5061/DRYAD.17VF831
Karpestam, Einat
Linnaeus University
Merilaita, Sami
University of Turku
Forsman, Anders
Linnaeus University
Data from: Size variability effects on visual detection are influenced by
colour pattern and perceived size
Dryad
dataset
2019
visual stimuli
detection and perception
crypsis
Tetrix subulata
camouflage
colour pattern polymorphism
2019-08-09T00:00:00Z
2019-08-09T00:00:00Z
en
https://doi.org/10.1016/j.anbehav.2018.07.013
228797 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Most animals including humans use vision to detect, identify, evaluate and
respond to potential prey items in complex environments. Theories predict
that predators’ visual search performance is better when targets are
similar than when targets are dissimilar and require divided attention,
and this may contribute to colour pattern polymorphism in prey. Most prey
also vary in size, but how size variation influences detectability and
search performance of predators that utilize polymorphic prey has received
little attention. To evaluate the effect of size variability on prey
detection we asked human subjects to search for images of black, grey and
striped pygmy grasshoppers presented on computer screens in size-variable
(large, medium and small) or in size-invariable (all medium) sequences
(populations) against photographs of natural grasshopper habitat. Results
showed that size variability either increased or reduced detection of
medium-sized targets depending on colour morph. To evaluate whether bias
in perceived size varies depending on colour pattern, subjects were asked
to discriminate between two grasshopper images of identical size that were
presented in pairs against a monochromatic background. Subjects more often
incorrectly classified one of the two identical-sized targets as being
larger than the other in colour-dimorphic than in monomorphic
presentations. The distinctly patterned (striped) morph elicited stronger
size perception biases than the dorsally grey or black morphs, and striped
grasshoppers were incorrectly classified more often as smaller than grey
grasshoppers. The direction of the effect of size variability on detection
changed across colour patterns as the bias in perceived size increased.
Such joint effects of variation in size and colour pattern on detection
and perception can impact the outcome of behavioural and evolutionary
interactions between visually oriented predators and their camouflaged
prey. This may have consequences for population dynamics, evolution of
polymorphisms, community species composition and ecosystem functioning.
Effect of coloration on size perceptionData on response of 96 human
subjects each presented with four cards with two grasshopper images of
identical size and asked to indicate which if any of the images that was
largest. Grasshoppers were either black, grey or striped. One of the cards
showed one monomorphic pair (same colour) and three cards showed all three
dimorphic combinations with different-coloured grasshoppers. The file
includes information on participant (number only), and for each of the
four cards the colour morph combination and the response.Data experiment 2
effect of coloration on size perception.xlsxDetection of small, medium and
large grasshoppers in size-variable sequencesData on performance of 51
human subjects that were asked to search for images of either black, grey
or striped Tetrix subulata grasshoppers presented in size-variable
sequences (5 small, 5 medium and 5 large presented in random order) on
computer screens against photographs of natural grasshopper habitat. There
were 17 subjects for each grasshopper colour. Grasshoppers were of the
same colour within sequences but varied among sequences. The file includes
information on background image identity, grasshopper colour morph,
grasshopper image number, response time (time until response, either
detection of grasshopper or incorrect response) and response (detection of
grasshopper or incorrect response). Data for each subject/sequence is
included on a separate sheet.Data experiment 1 effect of size variability
on detection.xlsxDetection of medium sized grasshoppers in size-invariable
sequencesData on performance of 18 human subjects that searched for images
of medium sized Tetrix subulata grasshoppers presented in sequences (10
images in each sequence) on computer screens against photographs of
natural grasshopper habitat. The subjects were presented with three
size-invariable sequences each (one for each of the black, grey and
striped grasshopper colour morphs). The file includes information on
background image identity, grasshopper colour morph, grasshopper image
number, response time (time until response, either detection of
grasshopper or incorrect response) and response (detection of grasshopper
or incorrect response). Data for each sequence is included on a separate
sheet.Data experiment 1 detection of medium sized grasshoppers.xlsx
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