Nicholas J. Beeton

Climate change not to blame for late Quaternary megafauna extinctions in Australia

Late Quaternary megafauna extinctions impoverished mammalian diversity worldwide. The causes of these extinctions in Australia are most controversial but essential to resolve, because this continent-wide event presaged similar losses that occurred thousands of years later on other continents. Here we apply a rigorous metadata analysis and new ensemble-hindcasting approach to 659 Australian megafauna fossil ages. When coupled with analysis of several high-resolution climate records, we show that megafaunal extinctions were broadly synchronous among genera and independent of climate aridity and variability in Australia over the last 120,000 years. Our results reject climate change as the primary driver of megafauna extinctions in the worlds most controversial context, and instead estimate that the megafauna disappeared Australia-wide ∼13,500 years after human arrival, with shorter periods of coexistence in some regions. This is the first comprehensive approach to incorporate uncertainty in fossil ages, extinction timing and climatology, to quantify mechanisms of prehistorical extinctions.

A tool for simulating and communicating uncertainty when modelling species distributions under future climates

Tools for exploring and communicating the impact of uncertainty on spatial prediction are urgently needed, particularly when projecting species distributions to future conditions. We provide a tool for simulating uncertainty, focusing on uncertainty due to data quality. We illustrate the use of the tool using a Tasmanian endemic species as a case study. Our simulations provide probabilistic, spatially explicit illustrations of the impact of uncertainty on model projections. We also illustrate differences in model projections using six different global climate models and two contrasting emissions scenarios. Our case study results illustrate how different sources of uncertainty have different impacts on model output and how the geographic distribution of uncertainty can vary. Synthesis and applications: We provide a conceptual framework for understanding sources of uncertainty based on a review of potential sources of uncertainty in species distribution modelling; a tool for simulating uncertainty in species distribution models; and protocols for dealing with uncertainty due to climate models and emissions scenarios. Our tool provides a step forward in understanding and communicating the impacts of uncertainty on species distribution models under future climates which will be particularly helpful for informing discussions between researchers, policy makers, and conservation practitioners.

Adaptive responses to cool climate promotes persistence of a non-native lizard

Successful establishment and range expansion of non-native species often require rapid accommodation of novel environments. Here, we use common-garden experiments to demonstrate parallel adaptive evolutionary response to a cool climate in populations of wall lizards (Podarcis muralis) introduced from southern Europe into England. Low soil temperatures in the introduced range delay hatching, which generates directional selection for a shorter incubation period. Non-native lizards from two separate lineages have responded to this selection by retaining their embryos for longer before oviposition—hence reducing the time needed to complete embryogenesis in the nest—and by an increased developmental rate at low temperatures. This divergence mirrors local adaptation across latitudes and altitudes within widely distributed species and suggests that evolutionary responses to climate can be very rapid. When extrapolated to soil temperatures encountered in nests within the introduced range, embryo retention and faster developmental rate result in one to several weeks earlier emergence compared with the ancestral state. We show that this difference translates into substantial survival benefits for offspring. This should promote short- and long-term persistence of non-native populations, and ultimately enable expansion into areas that would be unattainable with incubation duration representative of the native range.

What caused extinction of the pleistocene megafauna of sahul

During the Pleistocene, Australia and New Guinea supported a rich assemblage of large vertebrates. Why these animals disappeared has been debated for more than a century and remains controversial. Previous synthetic reviews of this problem have typically focused heavily on particular types of evidence, such as the dating of extinction and human arrival, and have frequently ignored uncertainties and biases that can lead to misinterpretation of this evidence. Here, we review diverse evidence bearing on this issue and conclude that, although many knowledge gaps remain, multiple independent lines of evidence point to direct human impact as the most likely cause of extinction.

Predicting the future range and abundance of fallow deer in Tasmania, Australia

Abstract Context. Since the introduction of fallow deer (Dama dama) to Tasmania in the early 1830s, the management of the species has been conflicted; the species is partially protected as a recreational hunting resource, yet simultaneously recognised as an invasive species because of its environmental impact and the biosecurity risk that it poses. The range and abundance of fallow deer in Tasmania has evidently increased over the past three decades. In the 1970s, it was estimated that ∼7000–8000 deer were distributed in three distinct subpopulations occupying a region of ∼400 000 ha (generally centred around the original introduction sites). By the early 2000s, the estimated population size had more than tripled to ∼20 000–30 000 deer occupying 2.1 million ha. No study has attempted to predict what further growth in this population is likely. Aims. The purpose of our study was to provide a preliminary estimate of the future population range and abundance of fallow deer in Tasmania under different management scenarios. Methods. We developed a spatially explicit, deterministic population model for fallow deer in Tasmania, based on estimates of demographic parameters linked to a species distribution model. Spatial variation in abundance was incorporated into the model by setting carrying capacity as a function of climate suitability. Key results. On the basis of a conservative estimate of population growth for the species, and without active management beyond the current policy of hunting and crop protection permits, abundance of fallow deer is estimated to increase substantially in the next 10 years. Uncontrolled, the population could exceed 1 million animals by the middle of the 21st century. This potential increase is a function both of local increase in abundance and extension of range. Conclusions. Our results identify areas at high risk of impact from fallow deer in the near future, including ecologically sensitive areas of Tasmania (e.g. the Tasmanian Wilderness World Heritage Area). Implications. The research approach and results are presented as a contribution to debate and decisions about the management of fallow deer in Tasmania. In particular, they provide a considered basis for anticipating future impacts of deer in Tasmania and prioritising management to mitigate impact in ecologically sensitive areas.

A comprehensive database of quality-rated fossil ages for Sahul's Quaternary vertebrates.

The study of palaeo-chronologies using fossil data provides evidence for past ecological and evolutionary processes, and is therefore useful for predicting patterns and impacts of future environmental change. However, the robustness of inferences made from fossil ages relies heavily on both the quantity and quality of available data. We compiled Quaternary non-human vertebrate fossil ages from Sahul published up to 2013. This, the FosSahul database, includes 9,302 fossil records from 363 deposits, for a total of 478 species within 215 genera, of which 27 are from extinct and extant megafaunal species (2,559 records). We also provide a rating of reliability of individual absolute age based on the dating protocols and association between the dated materials and the fossil remains. Our proposed rating system identified 2,422 records with high-quality ages (i.e., a reduction of 74%). There are many applications of the database, including disentangling the confounding influences of hypothetical extinction drivers, better spatial distribution estimates of species relative to palaeo-climates, and potentially identifying new areas for fossil discovery.

Untangling the model muddle: Empirical tumour growth in Tasmanian devil facial tumour disease

A pressing and unresolved topic in cancer research is how tumours grow in the absence of treatment. Despite advances in cancer biology, therapeutic and diagnostic technologies, there is limited knowledge regarding the fundamental growth and developmental patterns in solid tumours. In this ten year study, we estimated growth curves in Tasmanian devil facial tumours, a clonal transmissible cancer, in males and females with two different karyotypes (diploid, tetraploid) and facial locations (mucosal, dermal), using established differential equation models and model selection. Logistic growth was the most parsimonious model for diploid, tetraploid and mucosal tumours, with less model certainty for dermal tumours. Estimates of daily proportional tumour growth rate per day (95% Bayesian CIs) varied with ploidy and location [diploid 0.016 (0.014–0.020), tetraploid 0.026 (0.020–0.033), mucosal 0.013 (0.011–0.015), dermal 0.020 (0.016–0.024)]. Final tumour size (cm3) also varied, particularly the upper credible interval owing to host mortality as tumours approached maximum volume [diploid 364 (136–2,475), tetraploid 172 (100–305), dermal 226 (134–471)]. To our knowledge, these are the first empirical estimates of tumour growth in the absence of treatment in a wild population. Through this animal-cancer system our findings may enhance understanding of how tumour properties interact with growth dynamics in other types of cancer.

A model for the dynamics of Ross River Virus in the Australian environment

Abstract Ross River Disease is a mosquito-borne viral condition that affects pockets of the Australian human population, and can be debilitating in some instances. The evidence is that the virus reservoirs in marsupials, such as kangaroos, and this may account for the unpredictable outbreaks of the disease in humans. Accordingly, we present here a new model for the dynamics of Ross River Virus (RRV) in populations of mosquitoes and kangaroos. We calculate steady-state populations for the sub-groups in each species and demonstrate that naturally-occurring oscillations in the populations (limit cycles) do not occur. When seasonal forcing of vector populations and kangaroo birth rates is taken into account, however, the model may predict multi-annual outbreaks and chaos, perhaps explaining the unpredictability of some RRV disease epidemics, particularly across southern Australia. Detailed results in this case are presented.

Quantifying floristic and structural forest maturity: An attribute‐based method for wet eucalypt forests

1. Maintaining developmental heterogeneity of ecological communities within landscapes is crucial for sustainable native forest management. Consequently, methods to assess forest maturity (i.e. the degree to which the forest contains attributes and supports processes characteristic of late-successional forests) are valuable for making management decisions. However, no consistent, pragmatic method to quantify maturity that incorporates multiple ecosystem elements is available for many forest systems, including Australian wet eucalypt forests. 2. We draw upon forest community dynamics theory to develop a method to quantify maturity based on forest attributes, and use this method to create two metrics of wet eucalypt forest floristic and structural maturity. We then test the ability of remotely sensed and field-collected variables to predict these metrics.3. Both the floristic and structural maturity metrics performed well at capturing underlying trends of forest maturation. Remotely sensed LiDAR (Light Detection and Ranging) and photo-interpretation data provided estimates of moderate accuracy for both floristic and structural maturity (R2 = .57–.77). Field variables that are relatively efficient and accurate to measure provided greater model accuracy (R2 = .73–.85). Including more complex field variables increased model accuracy to high levels (R2 = .93). Therefore, while maturity predicted from remote-sensing data enables a useful and accessible large-scale maturity measure, field indices would provide a more accurate means of assessing maturity at the local stand level. 4. Synthesis and applications. The metrics developed in this study provide a powerful tool for undertaking consistent assessments of wet eucalypt forest maturity. This assessment tool could improve forest management by providing information to optimise practices such as prioritising stands for retention or harvesting, determining the effectiveness of restoration or management practices and monitoring changes in maturity over time. The method could be adapted to any forest system that undergoes well-defined directional development.