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How do animals assess their “fighting ability” (which influences the cost of fighting)?

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Presentation on theme: "How do animals assess their “fighting ability” (which influences the cost of fighting)?"— Presentation transcript:

1 How do animals assess their “fighting ability” (which influences the cost of fighting)?

2 Do animal assess each other's fighting ability in contests? Mutual 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 duration smaller  > contest duration larger  => 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).

3 Do animal assess each other's fighting ability in contests? Self Assessment Hypothesis 1. Energetic War of Attrition 1. 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 

4 Do animal assess each other's fighting ability in contests? Self Assessment Hypothesis 2. Cumulative Assessment 2. 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

5 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 — — — ——

6 Which hypothesis do these data match? General pattern of new findings... Self Assessment + NS

7 When the size of both contestants were considered... Mutual Assessment Wasp (Hemipepsis ustulata; Kemp et al. 2006) But did not test against the cumulative assessment Self 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)


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