Abstract
The running speed of the North African monitor lizard, Varanus griseus is directly proportional to its body temperature of between 21 and 37°C. Above 37°C, sprint speed does not increase. However, below 21°C, the lizards are extremely sluggish. If pursued at this lowered body temperature the animal finds it difficult to escape and so stays behind and tries to fight the predator. The degree of aggressiveness increases as body temperature is further reduced. This monitor lives in the savanna regions of northern Nigeria where the vegetation is low and hiding places are rare. The lizard might have evolved this antipredatory mechanism at low body temperatures as its last resort to survive since there is no place to take refuge in a bare area when the predator emerges.
Highlights
Anti-predatory mechanisms in animals include aposematic colouration, rump patch signals, alarm calls mobbing of a predator, distraction displays, death feigns (Edmunds, 1974), flight (Kruuk, 1964), aggressive group defence (Mech, 1970) and so on
Very little or no work has been done on the behavioural ecology of African lizards; the paper attempts to determine precisely the influence of body temperature on antipredatory defence strategies of this North African monitor lizard, V. griseus
Maximum sprint speeds for V. griseus was directly correlated with body temperature with a Coefficient of linear correlation (r = 0.927524, P < 0.05) (Figure 1)
Summary
Anti-predatory mechanisms in animals include aposematic colouration (as in many insect species, Brower and Brower, 1964), rump patch signals (as in many mammalian species, Smythe, 1970), alarm calls (as in many birds and mammals, Charnov and Krebs, 1975; Dunford, 1977) mobbing of a predator (as in many vertebrate and invertebrate species Andrew, 1961), distraction displays (as in many birds, Armstrong, 1947), death feigns (Edmunds, 1974), flight (Kruuk, 1964), aggressive group defence (Mech, 1970) and so on. The behaviour of a lizard largely depends on the attainment of a certain range of temperature at which a type of activity can take place (Hardy, 1962) This means that there are threshold values for emergence from burrows, seeking food and so on (Hardy, 1962; Aranyosi and Freeman, 2004). Aggression and social dominance are usually observed at the peak of their daily body temperatures (Hardy, 1962; Fogel, 2003) Many workers such as Anderson (1963), Heatwole (1970) and Hertz et al (1982) have suggested the influence of physiological variables on defensive responses of poikilotherms. Very little or no work has been done on the behavioural ecology of African lizards; the paper attempts to determine precisely the influence of body temperature on antipredatory defence strategies of this North African monitor lizard, V. griseus
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