DOI: 10.5061/dryad.17vf831
title: Data from: Size variability effects on visual detection are influenced by colour pattern and perceived size

description: 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.
description: 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