More than Mere Numbers: The Impact of Lethal Control on the Social Stability of a Top-Order Predator

Population control of socially complex species may have profound ecological implications that remain largely invisible if only their abundance is considered. Here we discuss the effects of control on a socially complex top-order predator, the dingo (Canis lupus dingo). Since European occupation of Australia, dingoes have been controlled over much of the continent. Our aim was to investigate the effects of control on their abundance and social stability. We hypothesized that dingo abundance and social stability are not linearly related, and proposed a theoretical model in which dingo populations may fluctuate between three main states: (A) below carrying capacity and socially fractured, (B) above carrying capacity and socially fractured, or (C) at carrying capacity and socially stable. We predicted that lethal control would drive dingoes into the unstable states A or B, and that relaxation of control would allow recovery towards C. We tested our predictions by surveying relative abundance (track density) and indicators of social stability (scent-marking and howling) at seven sites in the arid zone subject to differing degrees of control. We also monitored changes in dingo abundance and social stability following relaxation and intensification of control. Sites where dingoes had been controlled within the previous two years were characterized by low scent-marking activity, but abundance was similar at sites with and without control. Signs of social stability steadily increased the longer an area was allowed to recover from control, but change in abundance did not follow a consistent path. Comparison of abundance and stability among all sites and years demonstrated that control severely fractures social groups, but that the effect of control on abundance was neither consistent nor predictable. Management decisions involving large social predators must therefore consider social stability to ensure their conservation and ecological functioning

Accounting for complementarity to maximize monitoring power for species management

To choose among conservation actions that may benefit many species, managers need to monitor the consequences of those actions. Decisions about which species to monitor from a suite of different species being managed are hindered by natural variability in populations and uncertainty in several factors: the ability of the monitoring to detect a change, the likelihood of the management action being successful for a species, and how representative species are of one another. However, the literature provides little guidance about how to account for these uncertainties when deciding which species to monitor to determine whether the management actions are delivering outcomes. We devised an approach that applies decision science and selects the best complementary suite of species to monitor to meet specific conservation objectives. We created an index for indicator selection that accounts for the likelihood of successfully detecting a real trend due to a management action and whether that signal provides information about other species. We illustrated the benefit of our approach by analyzing a monitoring program for invasive predator management aimed at recovering 14 native Australian mammals of conservation concern. Our method selected the species that provided more monitoring power at lower cost relative to the current strategy and traditional approaches that consider only a subset of the important considerations. Our benefit function accounted for natural variability in species growth rates, uncertainty in the responses of species to the prescribed action, and how well species represent others. Monitoring programs that ignore uncertainty, likelihood of detecting change, and complementarity between species will be more costly and less efficient and may waste funding that could otherwise be used for management. Contabilizacion de la Complementariedad para Maximizar el Poder de Monitoreo para el Manejo de Especie

Effects of predation and rabbit haemorrhagic disease on rabbit population dynamics in New Zealand

This thesis investigated the effects of predation and a newly introduced biological control rabbit haemorrhagic disease (RHD) - on rabbit (Oryctolagus cuniculus) population dynamics in two bioclimatically diverse regions of New Zealand. In New Zealand, rabbits are classified as pests because they have a negative impact on agricultural and conservation values. The chronic rabbit problem areas are primarily in the ‘semi-arid’ unimproved grasslands of the South Island, and less so in lowland, moderate rainfall areas with improved pastures. This thesis investigated the hypothesised paradigm that rabbit populations in lowland areas, are generally driven by 'top-down' processes that keep them at low stable densities. The mechanism for this process is considered to be high mortality of young rabbits. In contrast, rabbit populations in mostly semi-arid areas are thought to be driven by ‘bottom-up’ processes (i.e., food availability). The effect of RHD on these processes was also investigated. One hypothesised effect of RHD epidemics is that the virus would depress rabbit populations so that they are more often within the range of densities at which top-down processes dominate. The corollary is that the efficacy of RHD may depend on predation of juvenile rabbits that develop age-specific immune responses to RHD. Predator-perturbation experiments were used to investigate this hypothesis and to determine the survival of juvenile rabbits. In both improved pasturelands (North Canterbury) and semiarid rangelands (Central Otago), rabbit abundance and pre- and post-emergent rabbit survival were monitored on four 30-ha sites, two of which were subject to predator removal. RHD spread through all sites during the study. The results provide support to the paradigm of top-down processes in lowland regions and bottom-up processes in semi-arid regions. In North Canterbury, rabbit abundance declined on all sites after an RHD epidemic, but the declines were more pronounced where predators were not removed. In contrast, in drier areas of Central Otago there was no apparent effect of predator reductions on rabbit abundance. There, rabbit densities declined at similar rates during the RHD epidemic regardless of the predator treatment. This suggests that predation; at least when combined with RHD, is a significantly stronger process in lowland regions than in the semi-arid regions of New Zealand. Survival of juvenile rabbits was a key factor determining population abundance between treatments. In North Canterbury, survival of young rabbits before they left the nest was lower on the two sites where predators were present (34%) than on the two sites where they were removed (51 %). In contrast, there was no measurable effect of predator reductions on pre-emergent survival in Central Otago (predator sites, 57%; predator-removal sites, 62%). Survival of post-emergent radio-collared juveniles were low for all sites (0-22%). It is likely that predation and RHD led to these low rates of post-emergent survival. The age at which juvenile rabbits become susceptible to RHD, the timing of RHD epidemics, and the abundance of predators are likely to be important in determining survival of juvenile rabbits. Demographic modelling of the rate of increase of rabbit populations in North Canterbury and Central Otago provided some support for the hypothesised top-down/bottom-up processes. In North Canterbury, rabbit populations on predator-removal sites had an annual rate of increase of 30%, whereas the rate of increase was effectively zero where predators were present. In contrast, there was little difference between predator and predator-removal sites in Central Otago (56-66%). Survival of juvenile rabbits and productivity were the key factors determining rate of increase. Rabbit haemorrhagic disease appears to be most effective in semi-arid regions of New Zealand, particularly in the Mackenzie Basin, and least effective in lowland North Canterbury. From 1974 to 2001, necropsy data were collected from c. 44000 rabbits to assess the impact of RHD on demography of rabbit populations in North Canterbury, the Mackenzie Basin, and Central Otago. There were proportionately more young rabbits in all three regions post-RHD, but there was no effect on time of birth or sex ratio. There was no consistent pattern between regions for carcass weights of rabbits older than 12 months, for productivity, and for pregnancy rates. However, in general reproductive rate and carcass weight of rabbits increased where RHD worked best. Three key mechanisms may explain the observed patterns. First, reproductive rate and carcass weight may be density-dependent. Second, RHD may result in differential mortality of rabbits, resulting in RHD causing mortality in lighter, older, weaker, or less fecund individuals. Third, RHD may result in differential levels of morbidity between populations, which may have sublethal impacts on their demography. Further research is required to determine the relative importance of the proposed mechanisms. The results of this study have significant implications for managers seeking to control ferrets to reduce the prevalence and spread of bovine Tb. Predator control in lowland regions such as North Canterbury may reduce the efficacy of RHD, and result in an increase in rabbit abundance, whereas predator control in semi-arid regions is unlikely to affect rabbit abundance. Further research is required to determine the relative importance of factors contributing to the observed top-down/bottom-up processes at these study sites, and how representative the results are for each region. Where ferret control is imperative in lowland regions, integrated control programmes that simultaneously control both ferrets and rabbits are recommended

Diet selection of European rabbits (Oryctolagus cuniculus) in the semi-arid grasslands of the Mackenzie Basin, New Zealand

There have been no previous quantitative studies of European rabbit (Oryctolagus cuniculus) diet in New Zealand, despite the prolonged and significant impact these introduced pests have had upon both pastoral and conservation values of this country's semi-arid grasslands. Knowledge of rabbit diet selection will allow us to better assess the current and potential impacts of rabbits. Diet selection was assessed on three replicate sites in the Mackenzie Basin, South Island of New Zealand, during the period December 1996 to March 1997. Selection ratios (Manly et al., 1993) were used to quantify diet selection, using Scott's (1965) height-frequency technique to estimate available vegetation and rabbit stomach contents analysis to estimate diet composition. Rabbits were generalists, feeding on a mean of 11 plant species per stomach sample and 33 plant species per site. The single largest dietary component was introduced Hieracium species; these comprised 32 to 39% of the diet composition at the three sites, which was proportional to their availability. Over all sites combined (n=90 rabbits), six plant species were positively selected, there was no selection for 17 species, and 24 species were negatively selected; this pattern was consistent across the sites. The negatively-selected species were sometimes common in the environment but never comprised an important part of the diet. In contrast, the positively selected species made up only 11% of the available vegetation but comprised a large part of the diet (44%). Sex and age of rabbits did not influence their diet selection. The nutritional composition of rabbit diet was very similar to the nutritional composition of the available vegetation. Of a range of nutrients measured in the vegetation, magnesium was the only one found to be significantly correlated with diet selection (negative correlation). The determinants of rabbit diet selection in this habitat therefore remain unclear. Selective grazing by rabbits will have implications for plant species diversity and richness, but further research will be required on plant community dynamics before these effects can be predicted

Artificial selection reveals sex differences in the genetic basis of sexual attractiveness

Mutual mate choice occurs when males and females base mating decisions on shared traits. Despite increased awareness, the extent to which mutual choice drives phenotypic change remains poorly understood. When preferences in both sexes target the same traits, it is unclear how evolution will proceed and whether responses to sexual selection from male choice will match or oppose responses to female choice. Answering this question is challenging, as it requires understanding, genetic relationships between the traits targeted by choice, mating success, and, ultimately, fitness for both sexes. Addressing this, we applied artificial selection to the cuticular hydrocarbons of the fly that are targeted by mutual choice and tracked evolutionary changes in males and females alongside changes in mating success. After 10 generations, significant trait evolution occurred in both sexes, but intriguingly there were major sex differences in the associated fitness consequences. Sexually selected trait evolution in males led to a genetically based increase in male mating success. By contrast, although trait evolution also occurred in females, there was no change in mating success. Our results suggest that phenotypic sexual selection on females from male choice is environmentally, rather than genetically, generated. Thus, compared with female choice, male choice is at best a weak driver of signal trait evolution in this species. Instead, the evolution of apparent female ornamentation seems more likely due to a correlated response to sexual selection on males and possibly other forms of natural selection

A genomic reference panel for Drosophila serrata

Here we describe a collection of re-sequenced inbred lines of , sampled from a natural population situated deep within the species endemic distribution in Brisbane, Australia. is a member of the speciose group whose members inhabit much of south east Asia and has been well studied for aspects of climatic adaptation, sexual selection, sexual dimorphism, and mate recognition. We sequenced 110 lines that were inbred via 17-20 generations of full-sib mating at an average coverage of 23.5x with paired-end Illumina reads. 15,228,692 biallelic SNPs passed quality control after being called using the Joint Genotyper for Inbred Lines (JGIL). Inbreeding was highly effective and the average levels of residual heterozygosity (0.86%) were well below theoretical expectations. As expected, linkage disequilibrium decayed rapidly, with r dropping below 0.1 within 100 base pairs. With the exception of four closely related pairs of lines which may have been due to technical errors, there was no statistical support for population substructure. Consistent with other endemic populations of other species, preliminary population genetic analyses revealed high nucleotide diversity and, on average, negative Tajima's D values. A preliminary GWAS was performed on a cuticular hydrocarbon trait, 2-Me-C revealing 4 SNPs passing Bonferroni significance residing in or near genes. One gene may be involved in the transport of CHCs from the site of production (oenocytes) to the cuticle. Our panel will facilitate broader population genomic and quantitative genetic studies of this species and serve as an important complement to existing panels that can be used to test for the conservation of genetic architectures across the genus

Data from: A genomic reference panel for Drosophila serrata

Here we describe a collection of re-sequenced inbred lines of Drosophila serrata, sampled from a natural population situated deep within the species endemic distribution in Brisbane, Australia. D. serrata is a member of the speciose montium group whose members inhabit much of south east Asia and has been well studied for aspects of climatic adaptation, sexual selection, sexual dimorphism, and mate recognition. We sequenced 110 lines that were inbred via 17-20 generations of full-sib mating at an average coverage of 23.5x with paired-end Illumina reads. 15,228,692 biallelic SNPs passed quality control after being called using the Joint Genotyper for Inbred Lines (JGIL). Inbreeding was highly effective and the average levels of residual heterozygosity (0.86%) were well below theoretical expectations. As expected, linkage disequilibrium decayed rapidly, with r2 dropping below 0.1 within 100 base pairs. With the exception of four closely related pairs of lines which may have been due to technical errors, there was no statistical support for population substructure. Consistent with other endemic populations of other Drosophila species, preliminary population genetic analyses revealed high nucleotide diversity and, on average, negative Tajima’s D values. A preliminary GWAS was performed on a cuticular hydrocarbon trait, 2-MeC28 revealing 4 SNPs passing Bonferroni significance residing in or near genes. One gene Cht9 may be involved in the transport of CHCs from the site of production (oenocytes) to the cuticle. Our panel will facilitate broader population genomic and quantitative genetic studies of this species and serve as an important complement to existing D. melanogaster panels that can be used to test for the conservation of genetic architectures across the Drosophila genus