Análisis de SO 2 por estación

If there is general correspondence among ungulates that around a hundred males within a female’s range is critical for lekking to evolve, does that suggest that lekking has evolved for similar reasons in the different species?

A s predicted by the position model, but also many other models o f lek evolution, the most successful males have been found to occupy central territories in practically all studies on lekking ungulates (kob (Balmford et al., 1992a; Balmford and Turyaho, 1992; Buechner and Schloeth, 1965; Fryxell, 1987), fallow deer (Clutton-Brock et al., 1988; Thirgood et a l, 1999), blackbuck (Isvaran and Jhala, 2000), lechwe (Nefdt, 1992), topi (this study)). The exception is one study on fallow deer where the most successful territories were located at the focal point o f a funnel o f thick scrub; thus it was physically impossible to set up territories around the lek centre (Apollonio et a l, 1989; Apollonio et a l, 1990).

In support o f the position model, some studies have shown that the success o f individual males changes according to territorial position (kob (Balmford et al., 1992a), blackbuck (Isvaran and Jhala, 2000)). This suggests that it is centrality p e r se

rather than phenotypic or individually fixed behavioural traits that females go after. However, one study on fallow deer found that central males remained successful after being experimentally forced o ff their territory (Clutton-Brock et a l, 1989).

While territorial position generally seems to provide the critical cue, successful males are characterised by certain morphological traits. Larger body size o f central males has been found in all species where it has been investigated (kob (Balmford et a l, 1992a), fallow deer (hindfoot length) (Clutton-Brock et a l, 1988), topi (this study)), larger antlers were found in successful fallow bucks (Clutton-Brock et a l, 1988), and darker facemasks characterised topi males in more central lek positions (this study). Lek males were suspected to be relatively old in kob (Balmford et a l, 1992a) and topi (this study), but not in fallow deer (Apollonio et a l, 1992); in fallow deer, there was, however, evidence that mating success increased with age on lek (Apollonio et al., 1989; Apollonio et al., 1992).

Certain behavioural traits have been found to correlate with high mating success. As expected according to the position model, but again, several other models as w ell, defence o f successful lek territories seems generally to incur higher fighting

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costs (kob (Balmford et al., 1992a; Floody and Arnold, 1975; Fryxell, 1987), lechwe (Nefdt and Thirgood, 1997), blackbuck (Isvaran and Jhala, 2000), topi (Gosling and Petrie, 1990; Gosling et al., 1987, this study) and fallow deer (Apollonio et al., 1992; but see Apollonio et al., 1989; Festa-Bianchet et al., 1990)). In fallow deer, males with higher mating success were found to be more successful in fights in two studies (Clutton-Brock et al., 1988; Festa-Bianchet et al., 1990), but not in a third (Apollonio et al., 1989). Display rate has been positively correlated with mating success in kob (Balmford et al., 1992a) and fallow deer (Clutton-Brock et al., 1988); however, as the analyses did not control for female presence, it is unclear whether the higher display rate is a consequence rather than the cause o f higher mating success (Gibson and Bradbury, 1985). Male territorial attendance has been shown to correlate with mating success in fallow deer (Apollonio et al., 1989; Clutton-Brock et al., 1988) and kob (Floody and Arnold, 1975), a result expected by all models.

I know o f no strong evidence in favour o f the harassment-based models o f lek evolution. No study has to m y knowledge demonstrated markedly higher harassment levels on resource territories than on leks; on the contrary, this study identified higher levels o f harassment on lek in topi, and on a kob lek, females did not avoid males who vigorously chased them or whose courtship was more frequently disrupted (Balmford et al., 1992a).

Also, support in favour o f the hotspot models as sole explanations o f lek evolution is wanting. N o evidence exists to suggest that females obtain any kind o f resources on leks. Leks also do not form in areas o f exceptionally high density, and probably in all species, a disproportionate number o f oestrous females visit the lek, where the sex ratio is generally male-biased (Balmford et al., 1993, this study).

Contrary to the expectation o f the hotshot model, individual leks persisting for longer than the reproductive lifespan o f males have been reported in fallow deer (Apollonio et al., 1998), kob (Buechner and Roth, 1974; Leuthold, 1966) and topi (this study), and in topi, no significant difference was detected in mating success o f the two most successful males on any o f three leks (this study).

Where predation risk has been assessed, no overall support o f the antipredator models has been found. In kob (Balmford and Turyaho, 1992) and topi (this study), there was no evidence o f reduced predation risk on leks, although leks in these species are situated at sites o f good visibility (kob (Deutsch and Weeks, 1992), topi (Gosling and Petrie, 1990)).

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Not much is known about how the mating activities o f females are influenced by other females. In topi, females preferentially mate in the presence o f other oestrous females (this study). In all the lekking antelopes, olfactory cues on the ground are evaluated on lek (Deutsch and Nefdt, 1992; Isvaran and Jhala, 2000; Nefdt, 1992; this study), which could be a means o f identifying successful territories or monitoring the breeding activities o f others; however, the relative importance o f male and female odours is unresolved. Females have been found to copy each other's movements (aggregate?) on lek in kob (Balmford et al., 1992a; Deutsch, 1992), fallow deer (Clutton-Brock and McComb, 1993; McComb and Clutton-Brock, 1994), and lechwe (Nefdt, 1992). Although species that lek generally demonstrate a marked seasonality o f the rut, there is no clear difference in the degree o f synchronisation between lekking and non-lekking populations (Apollonio et al., 1989; Balmford, 1990; Clutton-Brock et al., 1989; Isvaran and Jhala, 2000; M cElligott et al., 2001; Moore et al., 1995; Nefdt, 1996; Schuster, 1980; Sinclair et al., 2000; W illiamson, 1991; this study).

This overview suggests that although species-specific traits undoubtedly modify the costs and benefits in individual species, there are general patterns characterising lekking ungulates. When in oestrus, females move to the lek where they identify the centre based on visual and olfactory cues. Their mating preference seems to be governed by centrality rather than specific morphological or behavioural cues. However, by mating preferentially in central locations, they end up with partners, who tend to be larger and possibly older. For males, lekking is associated with the benefit o f high mating success but costs include high fighting rates and low resource availability.

Based on these results, it is proposed that when more than approximately one hundred males are found within a female's range, leks may form in high density areas where high-quality males initially defend slightly clustered territories; extreme clustering is caused by a female preference for clustering, which has evolved due to the association between clustering and male quality. The leks subsequently become traditional sites and the close association with high density may disappear.

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