1. Figure 10. 12. Fat reserves in male American rubyspot damselflies
Figure  Fat reserves in male American rubyspot damselflies. Mean (+ SE) fat reserves in grains (1 grain = 0.06 g). Territorial males had higher fat reserves than nonterritorial males (Source: Contreras-Garduño, Canales-Lazcano, & Córdoba-Aguilar 2006). Inset: territorial male.

2. Agonistic character displacement?
Figure  Male damselfly fat reserves after experimental challenge. Experimentally challenged males forced to defend their territory had lower mean (+ SE) fat reserves than did nonchallenged territorial males or nonterritorial males (units are grains) (Source: Contreras-Garduño, Canales-Lazcano, & Córdoba-Aguilar 2006).

3. Territorial dispute
Figure  White-tailed kite and vole. Kites (a) defend feeding territories that vary in size with environ­mental conditions. They feed on rodents, such as voles (b).

4. Figure 10. 15. Kite territory sizes
Figure  Kite territory sizes. Territory size correlates negatively with (a) the number of competitors and (b) the availability of food (number of voles per ha) (Source: Dunk & Cooper 1994).

5. Figure 10.16. Flies boxing. Fruit flies engage in contests over food.

6. Crab fight

8. Penguin fighting
Figure Magellanic penguin. These birds commonly use burrows as nests, a limited resource that males fight to obtain.

9. Figure 10. 18. Penguin fighting behavior
Figure  Penguin fighting behavior. (a) Bill duels are more common late in the season while (b) overt fights are more common early in the breeding season. The arrow indicates the cutoff date between early and late breeding dates (Source: Renison et al. 2006).

10. Figure 10. 19. Duration of penguin fights and injuries
Figure Duration of penguin fights and injuries. (a) The mean (+ SE) duration of fights and (b) mean (+ SE) total length of cuts during fights were lower before compared with after egg laying (Source: Renison et al. 2006).

11. Figure 10. 20. Red-spotted newts
Figure  Red-spotted newts. Males wrestle with rivals for access to mates.

12. Figure 10. 21. Duration of wrestling in male red-spotted newts
Figure Duration of wrestling in male red-spotted newts. The duration of wrestling increased with the size of the female that was amplexed (Source: Verrell 1986).

13. Figure  Aggression. (a) A cheetah chases a rival to defend its territory. (b) Wolves bare their teeth during threat displays.

14. Figure 10. 23. Testosterone variation in male song sparrows
Figure Testosterone variation in male song sparrows. Free-living males (blue circles) have high mean (± SE) plasma testosterone levels during territory formation and reproduction of the first brood. Captive males (orange circles) show similar patterns of variation over the spring, but with lower levels (Source: Wingfield, Lynn, & Soma 2001).

15. Figure 10. 24. Mouse contest results
Figure  Mouse contest results. Mice that won more previous contests in training had (a) a higher winning percentage against a larger rival in the final test and (b) a lower mean (+SE) latency to attack (Source: Oyegbile & Marler 2005). Inset: California mouse.

16. Figure 10. 25. Testosterone levels in mice
Figure Testosterone levels in mice. Mean (+SE) testosterone levels were higher in males that won fights compared to controls (Source: Oyegbile & Marler 2005).

17. Figure 10. 26. Testosterone variation in fish
Figure Testosterone variation in fish. Mean (+ SE) changes in testosterone levels for male bystanders that observed an aggressive interaction (orange) compared with changes in levels for controls (blue). Testosterone levels increased in bystanders that had observed a fight 30 minutes earlier compared to controls (Source: Oliveira, Lopos, & Carneiro 2001). Inset: Mozambique tilapia.

18. APPLYING THE CONCEPTS 10. 3 Figure 1
APPLYING THE CONCEPTS 10.3 Figure 1. Testosterone levels in male hockey players. Mean (+ SE) testosterone levels increased more in male hockey players after they watched a video of their team winning rather than watching either a video of their team (a) losing a prior contest or (b) a neutral video ( Source: Carré & Putnam 2010).