Arboreal lizards

PROJECT DESCRIPTION: I developed a method to increase lizard captures by creating ‘artificial bark’ around the trunks of trees. These artificial bark shelters (made from cardboard or closed-cell foam) strapped to tree trunks with bungee cords allowed me to sample sheltering animals without pulling off real tree bark – a very destructive (albeit effective) way of finding animals under flaking bark.

• HIGHLIGHTS: Arboreal cover boards (ACBs) increased capture rates and represent unbiased size classes (ACBs allowed for capture of all age classes, whereas spotlighting is generally biased towards adults)
• Ecofriendly and effective monitoring technique for a variety of species
• PAPER LINK:

PROJECT DESCRIPTION: I measured the abundance of two arboreal lizards (diurnal tree skink, Cryptoblephorus australis and nocturnal house gecko, Gehyra dubia) among two habitat types and four grazing regimes (stocking rates). I quantified the prey availability for each species and measured their prey preference through fecal analysis.

• HIGHLIGHTS: Gehyra dubia were more abundant in heavily grazed areas, while C. australis showed no difference in abundance among grazing treatments.
• Both species showed selectivity for beetles and spiders, with high dietary niche overlap – although temporally partitioned (G. dubia are nocturnal and C. austalis are diurnal).
• PAPER LINK:

PROJECT DESCRIPTION: We measured the effects of cattle grazing at various stocking rates on arboreal and terrestrial reptile communities. In addition, we measured how grazing impacts the structural and complexity of vegetation in relation to reptile microhabitat use.

• HIGHLIGHTS: Arboreal reptile species were resistant to the impact of grazing, whereas terrestrial reptiles were negatively affected by heavy grazing. Terrestrial reptiles were positively associated with complex ground structures, which were greatly reduced in heavily grazed areas. Arboreal lizards responded positively to microhabitat features such as tree hollows.
• Arboreal and terrestrial reptiles have different responses to the impact of livestock grazing. This has implications for rangeland management, particularly if management objectives include goals relating to conserving certain species or functional groups. Arboreal reptiles showed resistance in a landscape that is grazed, but where trees have not been cleared. We highlight the importance of retaining trees in rangelands for both terrestrial and arboreal microhabitats.
• PAPER LINK:

PROJECT DESCRIPTION: Predator – prey dynamics are complex and often difficult to disentangle the mechanisms driving population changes. We tested two competing hypotheses regarding predation: (1) predation risk is dependent on predator density; and (2) predation risk is dependent on the availability of alternative prey sources. We use an empirical, multi-level, tropical food web (birds–lizards–invertebrates) and a mensurative experiment (seasonal fluctuations in abundance and artificial lizards to estimate predation risk) to test these hypotheses.

• HIGHLIGHTS: Birds were responsible for the majority of attacks on artificial lizards. Artificial lizards were attacked more frequently in the dry than the wet season despite a greater abundance of birds in the wet season. Lizard and invertebrate (alternative prey) abundances showed opposing trends; lizards were more abundant in the dry while invertebrates were more abundant in the wet season. Predatory birds attacked fewer lizards when invertebrate prey abundance was highest, and switched to lizard prey when invertebrate abundance reduced, and lizard abundance was greatest.
• Our study suggests predation risk is not predator density-dependent, but rather dependent on the abundance of invertebrate prey, supporting the alternative prey hypothesis.
• PAPER LINK

PROJECT DESCRIPTION: Vertebrates are the top predators in many systems, but large invertebrates such as spiders, mantids, and centipedes may also be important predators of small vertebrate groups. We used several approaches to determine the relative frequency of predation by invertebrate and vertebrate predators in terrestrial systems. We conducted 500 h of visual surveys and compiled observations of in situ predation events from 2014 to 2016 in north Queensland, Australia.

• HIGHLIGHTS: Predation events were rarely observed: in 500 h of visual searches, we observed 9 instances of predation (vertebrates consuming another vertebrate, n=4; invertebrates consuming a vertebrate, n=5). In addition to spotlight surveys, we deployed 800 lizard-shape models to quantify attack frequencies on small lizards. While vertebrate predators were responsible for the most attacks on lizard models (76.7% and 93.3%, wet and dry season respectively), invertebrate predators were responsible for 23.3% and 6.8% of attacks.
• While predation events (of any kind) were rarely observed, we suggest that predation by invertebrate predators on vertebrate prey should not be overlooked in terrestrial systems. Invertebrate predators may play an important predatory role in shaping populations of small vertebrates, similar to more “typical” predators such as snakes, birds, and mammals.
• PAPER LINK

PROJECT DESCRIPTION: High abundances of common, generalist species in disturbed habitats may be driven by reduced competition from specialists in similar habitats. We quantified habitat availability and use of three co-occurring arboreal geckos (Australian native house geckos [Gehyra dubia], northern velvet geckos [Oedura castelnaui] and eastern spiny-tailed geckos [Strophurus williamsi]) in four replicated grazing regimes in an experimental grazing trial in north Queensland, Australia.

• HIGHLIGHTS: We found evidence of interspecific competition among gecko species, in which native house geckos shifted their habitat selection in the presence of velvet geckos. In the absence of other geckos, native house geckos preferred rough, peeling bark and dead trees, yet in the presence of velvet geckos, native house geckos shifted away from dead trees, and used more structurally complex trees, probably due to high niche overlap with velvet geckos. Native house geckos were more resistant to the negative effects of livestock grazing than either velvet or spiny-tailed geckos. In the absence of other species, native house geckos used a wider range of microhabitats.
• The homogenizing effects on habitat structure caused by livestock grazing reduce diversity and suitability for microhabitat specialists. Reduced competition can therefore promote the abundance of microhabitat generalist species, such as Australian native house geckos, suggesting that livestock grazing leads to homogenization and simplification of habitat structure, which ultimately leads to changes in species composition through reduced competition.
• PAPER LINK

PROJECT DESCRIPTION: In tropical systems, thermal heterogeneity may remain high, even at night, allowing nocturnal ectotherms to thermoregulate through conduction on surfaces that retain heat after sunset. We investigated the thermoregulatory behavior of a tropical nocturnal gecko (Australian house gecko, Gehyra dubia) by measuring its preferred temperature in a thermal gradient and selected body temperatures using radio telemetry in relation to available operative environmental temperatures obtained using thermal models.

• HIGHLIGHTS: Preferred body temperatures of geckos ranged from 31.4 ± 0.59–34.5 ± 0.55 °C in a laboratory thermal gradient. In the field, during winter, geckos were more effective thermoregulators than in the summer. In low thermal quality habitats, geckos sought rare, warm microclimates at night to maintain body temperatures warmer than most available environmental temperatures and were highly effective thermoregulators.
• The ability to exploit rare microclimates is especially important for nocturnal species, as heterogeneity of environmental temperatures is reduced at night compared to the day.
• PAPER LINK