Grahame J. W. Webb

The nesting of crocodylus porosus in arnhem land northern australia

JAEGER, R. G. 1971. Competitive exclusion as a factor influencing the distributions of two species of terrestrial salamanders. Ecology 52:632-637. l e cannot explain the competi ive xP. n. shenandoah documented by ( 71, 1972). 1972. Food as a limited resource in competition between two species of terrestrial salamanders. Ecology 53:535-546. MILLER, R. S. 1967. Pattern and process in competition. Adv. Ecol. Res. 4:1-74. SIEGEL, S. 1956. Nonparametric statistics for the behavioral sciences. McGraw-Hill Book Co., N.Y.

Head-body temperature differences in turtles

Abstract 1. 1. When turtles are heated in water, either radiantly or with an immersion heater, there is little control of head temperature; head-body temperature differences are of considerable magnitude, and represent a lag effect. 2. 2. By contrast, when heated radiantly in the absence of water, there is considerable physiological control of head temperature. 3. 3. At thermal endpoints frequently used in tolerance studies, head-body temperature differences are large and should be taken into account in the future. 4. 4. The existence of internal temperature gradients in turtles frequently makes use of cloacal temperature as representative of “body temperature” of limited value. 5. 5. In turtles, maintaining rate of heating constant in different sized animals has drawbacks in some types of studies; it is suggested that in some investigations all sized animals be heated under identical conditions, rather than at equal heating rates.

Head-Body Temperature Differences in Lizards

Head-body temperature differences have been reported in a number of lizards and snakes (Heath 1964; DeWitt 1967; Hammel, Caldwell, and Abrams 1967; Campbell 1969; Webb and Heatwole 1971). A mechanism permitting the retention of venous blood in the head has been described by Bruner (1907) and its application to head-body temperature differences pointed out by Heath (1964, 1966). The possibility that head temperatures are more important than body temperatures in influencing various physiological and behavioral parameters has been suggested by Heath (1964), Hammel et al. (1967), Heatwole (1970), and Webb and Heatwole (1971). The present study reports the results of experiments designed to determine the magnitude of head-body temperature differences in a number of species under various laboratory and field conditions.

Panting thresholds of lizards—I. Some methodological and internal influences on the panting threshold of an agamid, Amphibolurus muricatus

Abstract 1. 1. Amphibolous muricatus undergoes thermal panting at body temperatures of approximately 40°C. 2. 2. Body size, site of temperature measurement, sex, moulting and rate and method of heating did not significantly influence the panting threshold. 3. 3. Rapid heating resulted in greater variability of panting threshold. 4. 4. Non-radiant heat caused greater variation in panting threshold than radiant heat. 5. 5. Repeated testing with short intervals between tests decreased panting threshold, whereas long intervals had no effect. 6. 6. Panting was weakly developed in skinks and snakes tested. 7. 7. The major source of variation in panting threshold is a day-to-day shift within individuals.

Thermoregulation in crocodilians--II. A telemetric study of body temperature in the Australian crocodiles, Crocodylus johnstoni and Crocodylus porosus.

Abstract 1. Body temperature of Crocodylus johnstoni and C. porosus were recorded using radio telemetry. 2. Mean preferred temperature ranges were similar for both species, but those of C. johnstoni (31·3-32·5°C) were slightly lower than those found of C. porosus (32·0–33·1°C). 3. Little variation occurred in the mean daily body temperature. 4. Thermoregulation was mainly behavioural; seeking of cooler environments (shade or water) being most effective in reducing body temperature.

Effect of Incubation Temperature on Development of Crocodylus johnstoni Embryos

The pattern of growth in wet mass of Crocodylus johnstoni embryos is sigmoid and can be modeled with the logistic equation. The inflection point (time of maximum absolute growth rate) occurs when the incubation period is 77%-81% complete. Growth constants (r) from the logistic equation increase significantly with incubation temperature (T₁) over the range 28°-33° C, but asymptotic mass decreases. High-temperature embryos grow relatively more quickly but hatch at a lower yolk-free mass than at lower temperatures. Absolute growth rates (g · d⁻¹) are most sensitive to T₁ early in development, during the period of differentiation and organogenesis. Rates of late-term somatic growth show no consistent trend with T₁. Rates of morphological change (differentiation) defined by development rate coefficients also increase at higher T₁, but the temperature effect differs from that on rates of growth in mass. Thus the relationship between rates of differentiation and growth in size may alter with T₁. Shifts in the relative timing of significant differentiation and growth events may alter the relative sizes and functional capacities of tissues and organs. Such variation among hatchlings is likely to be implicated in the long-term influence of the incubation environment on posthatch survival and growth in crocodilians.

Hawksbill sea turtles: can phylogenetics inform harvesting?

In their recent articles, Mortimer et al. (2007) and Bowen et al. (2007) imply that historical declines in hawksbill sea turtle (Eretmochelys imbricata) populations in the Caribbean together with new phylogenetic data provide solid evidence that hawksbills cannot be harvested on a sustainable level. We suggest that broad inferences on the impacts of harvesting based on phylogenetic data alone are insufficient as an argument against sustainable use of sea turtles. Rather, we recommend that the merits of harvesting schemes should be assessed on a case-by-case basis, which should enable beneficial and sustainable projects to proceed and also discourage unsustainable ones. As reported by Mortimer et al. (2007), recent data on mtDNA haplotype diversity show that rookeries and foraging areas in the Caribbean are connected, with juveniles moving across national boundaries from natal beaches to foraging grounds, and back again to natal beaches as adults (Bowen et al. 2007). Based on these associations, Bowen et al. (2007) suggest that harvest [of hawksbills] in the Caribbean foraging areas will deplete nesting populations across multiple jurisdictions, while Mortimer et al. (2007) state that any harvest on nesting beaches or feeding grounds could negatively impact hawksbill populations throughout the Caribbean region. We suggest that these claims are not necessarily true in all situations. A case in point is the current harvesting of hawksbills in Cuban waters (Carrillo et al. 1999) and the ongoing increase of the nearby nesting population of hawksbills in the Yucatán Peninsula (Garduño-Andrade et al. 1999). Published phylogenetic studies have reported that a significant source rookery for turtles harvested in Cuba is the Yucátan Peninsula (Díaz-Fernández et al. 1999; Bowen et al. 2007). A second example is the hawksbill rookery in Antigua. Phylogenetic data show that hawksbills from Antigua contribute significantly to foraging grounds in Cuba (Bass 1999; Díaz-Fernández et al. 1999; Bowen et al. 2007). And yet, numbers of nesting females in Antigua have been increasing over the last decade, despite the ongoing harvest of hawksbills in Cuba (Richardson et al. 2006a). Clearly, the situation regarding harvesting and its impacts on regional nesting populations is more complex than presented in Mortimer et al. (2007) and Bowen et al. (2007). A primary principle of wildlife management is that a target population can be kept at a level below its carrying capacity, through harvesting or culling, without causing a decline in the population, due to density-dependent rates of growth (Getz & Haight …

Effects of Incubation Temperature on the Size of Caiman latirostris (Crocodylia: Alligatoridae) at Hatching and after One Year

Abstract We investigated the effects of incubation temperature (29°C, 31°C, and 33°C) on total length (TL) and body mass (BM) of Caiman latirostris, a crocodilian with temperature-dependent sex determination (TSD), at hatching (N u200a=u200a 180) and in a sample of hatchlings (N u200a=u200a 40) after one year of raising. Size at hatching was strongly clutch-specific. Animals incubated at 31°C (100% females) were larger than at 29°C (100% female) and 33°C (100% males). Absolute growth to one year was higher for females (eggs incubated at 29°C and 31°C) than for males (eggs incubated at 33°C). The possibility that constant 33°C incubation temperature had compromised embryological development cannot be rejected. If so, it confirms that high incubation temperatures can have long-lasting effects on posthatching growth. If not, possible advantages of females growing more rapidly than males are discussed.

Critical thermal maxima of turtles: Validity of body temperature

Abstract 1. 1. At the critical thermal maximum (CTM) in turtles there are large head-body temperature gradients. 2. 2. CTM as measured by head temperature does not vary significantly with body size or heating rate, whereas if measured by posterior body temperature it does. 3. 3. CTMs measured by body temperature can lead to spurious conclusions. 4. 4. Temporal variations in CTM were detectable using head temperature but not when using body temperature.

Monitoring Saltwater Crocodiles (Crocodylus Porosus) in the Northern Territory of Australia

Saltwater crocodiles (Crocodylus porosus) were protected in the Northern Territory in 1971, and a General Survey Program Based on spotlight counts was initiated 3 yr later. In the mid-1980s, monitoring needs were reviewed and rationalized. The current monitoring program operates at two levels of resolution. At a local population level, annual spotlight counts are conducted in six river systems, to monitor closely the process of recovery in those systems. Sixteen years of survey data for the Blyth-Cadell River system are analyzed here. Changes in the age structure of the population during the period of recovery are discussed. At a total population level, current monitoring (since 1989) involves an annual helicopter count over 70 sample segments in 68 tidal rivers around the complete coastline. The results of this program to date are presented and discussed. The experience and results obtained in the Northern Territory emphasize the need to clearly establish levels of resolution within which monitoring aims, objectives, and programs are compatible.