How do animals assess their “fighting ability” (which influences the cost of fighting)?
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Transcript of How do animals assess their “fighting ability” (which influences the cost of fighting)?
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How do animals assess their “fighting How do animals assess their “fighting ability” (which influences the cost of ability” (which influences the cost of
fighting)?fighting)?
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Do animal assess each other's fighting ability
in contests?
Mutual Assessment HypothesisMutual Assessment Hypothesis
• Contestants assess each other
• EX. sequential assessment model (Enquist & Leimar 1983)
• a contest: a series of interactions during which individuals gradually assess each other’s fighting ability
• larger differences are more easily detected than smaller
• => contest durationsmaller > contest durationlarger
=> contest: less costly (display) -> more costly (escalation)
• observations: fighting ability => contest duration/intensity used as supporting evidences for mutual assessment in animal contests
• (e.g. Austad 1983; Crespi 1986; Robertson 1986; Crowley et al. 1988; Wells 1988; Englund & Olsson 1990; Rosenberg & Enquist 1991; Enquist et al. 1990; Olsson 1992; Stamps & Krishnan 1994; Hack 1997; Hack et al. 1997; Moya-Laraño & Wise 2000; Hofmann & Schildberger 2001; Pratt et al. 2003).
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Do animal assess each other's fighting ability
in contests?
Self Assessment HypothesisSelf Assessment Hypothesis
1. Energetic War of Attrition1. Energetic War of Attrition (Mesterton-Gibbons et al. 1996; Payne & Pagel 1997)
• persistence in contests: own ability (energy reserve)• size of opponents does NOT matter• size of smaller opponent => duration • But, how about the empirical data?• fighting ability => contest duration/intensity • Taylor & Elwood (2003): • random-pairing, self assessment can also generate the
pattern• small : any sized individuals vs. similar-sized opponents• large : smallest individuals vs. the biggest opponents • => negative relationship: "smaller size" vs. " fighting
ability "• smaller size => fighting ability => contest
duration/intensity
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Do animal assess each other's fighting ability
in contests?
Self Assessment HypothesisSelf Assessment Hypothesis
2. Cumulative Assessment2. Cumulative Assessment (Payne 1998)
• persistence in contests: own ability
• size of opponents does NOT matter
• a contestant gets into a contest with a preset cost threshold
• cost threshold: NOT influence by the ability of the opponent
• But, stronger opponent inflict more injury cost on the weaker
• => opponent ability => "cost threshold" reached faster
• => the ability of the opp. appears to have influence
• same predictions as the mutual assessment when interactions involve injury costs
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Self Assessment
Mutual Assessment
Cumulative Assessment
Energetic War of
Attrition
Random Size Pairings
Smaller size
Larger size
Size difference
Equal Size Pairings
Pair size
Predictions from the 3 Hypotheses
Contest Duration
† † †
†/N
†NN
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Which hypothesis do these data match?
General pattern of new findings...
Self Assessment
+ NS
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When the size of both contestants were considered...When the size of both contestants were considered...
Mutual AssessmentMutual Assessment
• Wasp (Hemipepsis ustulata; Kemp et al. 2006)• But did not test against the cumulative assessment
Self AssessmentSelf Assessment
1. Energetic War of Attrition
• Jumping spider (Plexippus paykulli; Taylor et al. 2001) • Fallow deer (Dama dama; Jennings et al. 2004)• Amphipod (Gammarus pulex; Prenter et al. 2006)• Cape dwarf chameleon (Bradypodion pumilum; Stuart-Fox
2006)
2. Cumulative Assessment
• Wellington tree weta (Hemideina crassidens; Kelly 2006)
• fiddler crabs (Uca mjoebergi; Morrell et al. 2005) • hermit crab (Briffa & Elwood 2000)