Jonathan Webb | University of Technology Sydney (original) (raw)

Papers by Jonathan Webb

Conservation Genetics, Jun 1, 2010

Journal of Zoology, Mar 1, 2000

Global change biology, Jan 4, 2016

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures r... more Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current 'cold' nests (mean = 23.2 °C, range 10-33 °C) and future 'hot' nests (27.0 °C, 14-37 °C). 'Hot' incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 20...

Http Dx Doi Org 10 1643 Cp 06 182, Jan 14, 2009

ABSTRACT During pregnancy, the metabolic rate of females may Increase above basal levels to suppo... more ABSTRACT During pregnancy, the metabolic rate of females may Increase above basal levels to support metabolically active tissues and developing embryos. In mammals, this energetic cost of supporting the pregnancy (MCP) is an important component of reproductive effort, but less is known about the magnitude of this cost in ectothermic vertebrates. We estimated the metabolic cost of supporting pregnancy in a tropical viviparous snake, the Northern Death Adder, Acanthophis praelongus. We measured the metabolic rates of non-gravid and gravid females throughout gestation and following parturition. We also measured the oxygen consumption of a sample of neonates from each clutch within 24 h of birth. The metabolic rate of gravid females rose slowly during pregnancy, but was significantly elevated during the last three weeks of gestation. Considering the late term metabolism of gravid females as 100%, then the baseline metabolism of female Death Adders represented 36.6%, embryo metabolism accounted for 37.0%, and the cost of supporting the pregnancy was 26.4% of the total metabolic rate. Neonate metabolism during the first 24 h of birth was 2.9 times higher than the estimate for embryo metabolism. Thus, our results do not support the assumption that the metabolism of embryos (prior to birth) and neonates is similar in this species. Although gravid female Death Adders maintain high and constant body temperatures during late gestation, the energetic cost of supporting the pregnancy is only a minor component of the total reproductive effort for females of this species.

Ecological Management Restoration, Sep 1, 2012

Copeia, May 16, 1994

Page 1. 390 COPEIA, 1994, NO. 2 27708; AND (LHRP-D) COLE4AO DE PEIXES, INSTITUTO NACIONAL DE PESQ... more Page 1. 390 COPEIA, 1994, NO. 2 27708; AND (LHRP-D) COLE4AO DE PEIXES, INSTITUTO NACIONAL DE PESQUISAS DA AMAZ6NIA, ESTRADA DO ALEIXO, 1756, CAIXA POSTAL, 478., CEP 69011, MANAUS, AMAZONAS, BRAZIL. PRESENT ADDRESS: DE-...

Biological Journal of the Linnean Society, Jan 17, 2010

Australian Field Ornithology

Depredation of nests by native and introduced predators is contributing to the decline of beach-n... more Depredation of nests by native and introduced predators is contributing to the decline of beach-nesting shorebirds in many parts of Australia. Determining the relative importance of these predators is crucial for designing and implementing appropriate management strategies for shorebird conservation. We deployed and monitored 82 artificial Red-capped Plover Charadrius ruficapillus nests, on six beaches within a 140-km stretch of the New South Wales Lower North Coast, to identify the main predators of beach-nesting shorebird nests and their relative importance. After 18 days, 53 (63%) artificial nests were depredated. Australian Ravens Corvus coronoides and Forest Ravens C. tasmanicus were the chief nest-predators, and were responsible for depredating 40 (49%) nests collectively. Comparatively few nests were depredated by European Red Foxes Vulpes vulpes, which depredated 8 (10%) nests. The rate of depredation (nests depredated/2 days) by ravens was greater than the rate of depredati...

Animal Conservation, 2014

Physiological zoology

Studies of reptilian thermoregulation have tended to focus on diurnal heliothermic taxa that disp... more Studies of reptilian thermoregulation have tended to focus on diurnal heliothermic taxa that display overt thermoregulatory behavior, with nocturnal reptiles attracting less attention. We studied thermoregulation by the broad-headed snake (Hoplocephalus bungaroides), a small (mean snout-vent length = 57 cm) nocturnal elapid that spends long periods sequestered in diurnal retreat sites. The snakes selected body temperatures of 28.1 degrees-31.1 degrees C in laboratory thermal gradients. Prey-capture ability (strike speed and accuracy) increased at higher body temperatures over the range 20 degrees-30 degrees C. Using temperature-sensitive radio transmitters, we obtained 7,801 body-temperature measurements of 19 free-ranging snakes. Information on operative environmental temperatures was obtained at the same time. From these data, we quantified the degree to which the snakes exploit the environmental thermal heterogeneity available to them (i.e., the time they spent within their set-p...

Journal of Applied Ecology, 2015

Molecular Ecology Notes, 2005

A total of 15 microsatellite primers pairs were developed for the Australian small-eyed snake Rhi... more A total of 15 microsatellite primers pairs were developed for the Australian small-eyed snake Rhinoplocephalus nigrescens. Five primers were used to screen 93 individuals of R. nigrescens and were also tested against eight species of the closely related genus Suta. Allelic diversity in R. nigrescens was high in three loci (12–27) and there was high heterozygosity (0.58–0.82). Observed heterozygosity did not deviate from Hardy–Weinberg expectations for the five loci tested. These primers will be useful in studies of population genetics and mating systems of small-eyed snakes and related species.

General and Comparative Endocrinology, 2014

Most animals conduct daily activities exclusively either during the day or at night. Here, hormon... more Most animals conduct daily activities exclusively either during the day or at night. Here, hormones such as melatonin and corticosterone, greatly influence the synchronization or regulation of physiological and behavioral cycles needed for daily activity. How then do species that exhibit more flexible daily activity patterns, responses to ecological, environmental or life-history processes, regulate daily hormone profiles important to daily performance? This study examined the consequences of (1) nocturnal activity on diel profiles of melatonin and corticosterone and (2) the effects of experimentally increased acute melatonin levels on physiological and metabolic performance in the cane toad (Rhinella marinus). Unlike inactive captive toads that had a distinct nocturnal melatonin profile, nocturnally active toads sampled under field and captive conditions, exhibited decreased nocturnal melatonin profiles with no evidence for any phase shift. Nocturnal corticosterone levels were significantly higher in field active toads than captive toads. In toads with experimentally increased melatonin levels, plasma lactate and glucose responses following recovery post exercise were significantly different from control toads. However, exogenously increased melatonin did not affect resting metabolism in toads. These results suggest that toads could adjust daily hormone profiles to match nocturnal activity requirements, thereby avoiding performance costs induced by high nocturnal melatonin levels. The ability of toads to exhibit plasticity in daily hormone cycles, could have broad implications for how they and other animals utilize behavioral flexibility to optimize daily activities in response to natural and increasingly human mediated environmental variation.