A Two-Phase Model for Smoothly Joining Disparate Growth Phases in the Macropodid Thylogale billardierii

Generally, sigmoid curves are used to describe the growth of animals over their lifetime. However, because growth ratesoften differ over an animal’s lifetime a single curve may not accurately capture the growth. Broken-stick models constrainedto pass through a common point have been proposed to describe the different growth phases, but these are oftenunsatisfactory because essentially there are still two functions that describe the lifetime growth. To provide a single,converged model to age animals with disparate growth phases we developed a smoothly joining two-phase nonlinearfunction (SJ2P), tailored to provide a more accurate description of lifetime growth of the macropod, the Tasmanianpademelon Thylogale billardierii. The model consists of the Verhulst logistic function, which describes pouch-phase growth– joining smoothly to the Brody function, which describes post-pouch growth. Results from the model demonstrate thatmale pademelons grew faster and bigger than females. Our approach provides a practical means of ageing wildpademelons for life history studies but given the high variability of the data used to parametrise the second growth phaseof the model, the accuracy of ageing of post-weaned animals is low: accuracy might be improved with collection oflongitudinal growth data. This study provides a unique, first robust method that can be used to characterise growth overthe lifespan of pademelons. The development of this method is relevant to collecting age-specific vital rates fromcommonly used wildlife management practices to provide crucial insights into the demographic behaviour of animalpopulations

Forest fire management, climate change, and the risk of catastrophic carbon losses

Approaches to management of fireprone forests are undergoing rapid change, driven by recognition that technological attempts to subdue fire at large scales (fire suppression) are ecologically and economically unsustainable. However, our current framework for intervention excludes the full scope of the fire management problem within the broader context of fire−vegetation−climate interactions. Climate change may already be causing unprecedented fire activity, and even if current fires are within the historical range of variability, models predict that current fire management problems will be compounded by more frequent extreme fire-conducive weather conditions (eg Fried et al. 2004)

The influence of climatic change, fire and species invasion on a Tasmanian temperate rainforest system over the past 18,000 years

We aim to understand how did cool temperate rainforest respond to changes in climate and fire activity over the past 18 kcal yrs, interrogating the role that flammable plant species (such as Eucalyptus) have in the long-term dynamics of rainforest vegetation. We used high-resolution pollen and charcoal analysis, radiometric dating (lead and carbon), modern pollen-vegetation relationships, detrended correspondence analysis, rarefaction (palynological richness), rate of change and granger causality to understand the patterns and drivers of change in cool temperate rainforest from the sediments of Lake Vera, southwest Tasmania through time. We record clear changes in key rainforest taxa in response to climatic change throughout the record. The spread of rainforest through the lake catchment in the early and mid- Holocene effectively negated disturbance from fire despite a region-wide peak in fire activity. An anomalously dry period in the late-Holocene resulted in a local fire that facilitated the establishment of Eucalyptus within the local catchment. Granger causality tests reveal a significant lead of Eucalyptus over fire activity in the Holocene, indicating that fires were enhanced by this pyrogenic taxon following establishment

Climate, fire, and anthropogenic disturbance determine the current global distribution of tropical forest and savanna

Tropical forest and savanna biomes are pivotal in the functioning of the Earth system. Both are biodiverse and under increasing threat due to land clearing and anthropogenic climate change, and play important roles in the global carbon cycle, through maintenance of a large carbon pool in tropical forests, and exchange in savannas through extensive landscape fires. Reliable mapping of tropical forest and savanna is essential to understand how the current distribution of these vegetation types is controlled by climate land clearing and fire. Using Google Maps satellite imagery, we manually classified 24 239 random points as forest, savanna, or anthropogenic landscapes within the tropics and applied this novel dataset to defining the climatic zone where forest and savanna exist as alternative states. Because fire and climate are correlated, we developed separate geospatial models to rank the importance of climate, topography, and human influence on vegetation present. This modeling confirmed that those areas with more fires had lower probabilities of tropical forest, that forest was most likely in areas with high mean annual rainfall with little seasonal variation in precipitation, and that anthropogenic factors disrupt this environmental predictability. We also identified areas where tropical forest and savanna both co-occur, but these were relatively uncommon. These relationships suggest that future drier climates projected under anthropogenic climate change, combined with clearing and burning that have reduced tropical forest extent to a subset of its theoretical distribution, will lead to irreversible loss of tropical forests. Our modeling provides global mapping that can be used track further changes to distribution of tropical forests

Quantifying the drivers of larval density patterns in two tropical mosquito species to maximize control efficiency

Understanding the contribution of environmental variation and density feedback are essential for designing effective vector control. Monitoring datasets describing relative larval densities over 7 years of the two dominant mosquito species, Aedes vigilax (Skuse) and Culex annulirostris (Skuse), found in the greater Darwin area, Northern Territory, Australia, were analysed using generalised linear modelling and linear mixed-effects modelling to discover the environmental determinants of spatio-temporal patterns in relative abundance. The most important spatial drivers of Ae. vigilax and Cx. annulirostris larval densities were elevation above sea level and water presence. Ae. vigilax density was negatively correlated with elevation, whereas there was a positive relationship between Cx. annulirostris density and elevation. This result demonstrates how larval habitats used by the salt-water influenced breeder Ae. vigilax and the obligate fresh-water breeder Cx. annulirostris are separated in a tidally influenced swamp. The models examining temporal drivers of larval density also identified this discrimination between freshwater and saltwater habitats. Ae. vigilax larval densities exhibited positive relationships with maximum tide heights and high tide frequencies, whereas the Cx. annulirostris larval densities were positively related to elevation above sea level and rainfall. The most important temporal driver of the larval densities in both species was adult numbers from the previous month, providing a clear dynamical link between the two main life phases in mosquito development. This study demonstrates the importance of considering both spatial and temporal drivers, and intrinsic population dynamics, when planning vector control strategies, to reduce larval density, adult population density, and disease transmission effectively.Date:2009-0

Quantifying the drivers of larval density patterns in two tropical mosquito species to maximize control efficiency

Understanding the contribution of environmental variation and density feedback are essential for designing effective vector control. Monitoring datasets describing relative larval densities over 7 years of the two dominant mosquito species, Aedes vigilax (Skuse) and Culex annulirostris (Skuse), found in the greater Darwin area, Northern Territory, Australia, were analysed using generalised linear modelling and linear mixed-effects modelling to discover the environmental determinants of spatio-temporal patterns in relative abundance. The most important spatial drivers of Ae. vigilax and Cx. annulirostris larval densities were elevation above sea level and water presence. Ae. vigilax density was negatively correlated with elevation, whereas there was a positive relationship between Cx. annulirostris density and elevation. This result demonstrates how larval habitats used by the salt-water influenced breeder Ae. vigilax and the obligate fresh-water breeder Cx. annulirostris are separated in a tidally influenced swamp. The models examining temporal drivers of larval density also identified this discrimination between freshwater and saltwater habitats. Ae. vigilax larval densities exhibited positive relationships with maximum tide heights and high tide frequencies, whereas the Cx. annulirostris larval densities were positively related to elevation above sea level and rainfall. The most important temporal driver of the larval densities in both species was adult numbers from the previous month, providing a clear dynamical link between the two main life phases in mosquito development. This study demonstrates the importance of considering both spatial and temporal drivers, and intrinsic population dynamics, when planning vector control strategies, to reduce larval density, adult population density, and disease transmission effectively