PhD Dissertation - 2018 - Impacts of cattle grazing on arboreal reptiles - James Cook University, Australia
My PhD research was conducted at the Wambiana Cattle Station, a dry tropical savanna woodland in Queensland, Australia, to investigate how arboreal reptiles are affected by livestock grazing. Species often respond to disturbance in different ways; some animals are more or less sensitive to changes in the environment than others.
My research focused on identifying mechanisms that allow arboreal reptiles to benefit from greater habitat disturbance, where many terrestrial species decline. I investigated various aspects of natural history and ecology, including movement patterns, habitat use (macro- and microhabitat scales), shelter site selection, competition, predation risk, and diet, to test which factors facilitated a positive response to livestock grazing in arboreal reptiles.
Chapter 1. Arboreal cover boards: using artificial bark to sample cryptic 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.
Chapter 2. Abundance, diet and prey selection of arboreal lizards in a grazed tropical woodland
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.
Chapter 3. Arboreality increases reptile community resistance to disturbance from livestock grazing
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.
Chapter 4. Predation risk is a function of alternative prey availability rather than predator abundance in a tropical savanna woodland ecosystem
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.
Chapter 5. Terrestrial invertebrates: An underestimated predator guild for small vertebrate groups
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.
Chapter 6. Reduced competition may allow generalist species to benefit from habitat homogenization
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.
Chapter 7. Heat seekers: A tropical nocturnal lizard uses behavioral thermoregulation to exploit rare microclimates at night
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.