Surviving drought: a framework for understanding animal responses to small rain events in the arid zone

Large rain events drive dramatic resource pulses and the complex pulse‐reserve dynamics of arid ecosystems change between high‐rain years and drought. However, arid‐zone animal responses to short‐term changes in climate are unknown, particularly smaller rain events that briefly interrupt longer‐term drought. Using arthropods as model animals, we determined the effects of a small rain event on arthropod abundance in western New South Wales, Australia during a longer‐term shift toward drought. Arthropod abundance decreased over 2 yr, but captures of 10 out of 15 ordinal taxa increased dramatically after the small rain event (\u3c40 \u3emm). The magnitude of increases ranged from 10.4 million% (collembolans) to 81% (spiders). After 3 months, most taxa returned to prerain abundance. However, small soil‐dwelling beetles, mites, spiders, and collembolans retained high abundances despite the onset of winter temperatures and lack of subsequent rain. As predicted by pulse‐reserve models, most arid‐zone arthropod populations declined during drought. However, small rain events may play a role in buffering some taxa from declines during longer‐term drought or other xenobiotic influences. We outline the framework for a new model of animal responses to environmental conditions in the arid zone, as some species clearly benefit from rain inputs that do not dramatically influence primary productivity

Seasonal stress physiology and body condition differ among co-occurring tropical finch species

Seasonal changes in avian hormonal stress responses and condition are well known for common species found at temperate and arctic latitudes, but declining and tropical species are poorly studied. This study compares stress and condition measures of co-occurring declining and non-declining tropical grass finch species in Australia. We monitored declining Gouldian finches (Erythrura gouldiae) and non-declining long-tailed and masked finches (Poepila acuticauda and P. personata) during two seasons that are potentially stressful: peak breeding (early dry season when food is plentiful) and moult (late dry to early wet season when food may be scarce). We measured body condition (muscle and fat), haematocrit, and stress response to capture using plasma corticosterone and binding globulin concentrations. All species had higher muscle and lower fat indices during breeding than moult. Haematocrit did not consistently differ between seasons. Long-tailed finches had higher stress responses during breeding than moult, similar to other passerines studied. Masked finches showed no seasonal changes in stress response. Gouldian finches had stress response patterns opposite to those of long-tailed finches, with higher stress responses during moult. However, seasonal trends in Gouldian and long-tailed finch stress responses sometimes differed between years or sites. The differences in stress response patterns between species suggest that the declining Gouldian finch is more sensitive to recent environmental changes which are thought to further reduce grass seed food resources during the late dry to early wet season. Retention of stress responsiveness during a protracted moult could increase the survival potential of Gouldian finches. This study highlights the utility of stress and condition indices to determine the sensitivity of co-occurring species to environmental conditions

Current insecticide treatments used in locust control have less of a short-term impact on Australian arid-zone reptile communities than does temporal variation

Context: Despite the regular use of pesticides to control locusts, there is a lack of information on the effects of locust-control treatments on reptiles worldwide. Exposure to pesticides poses a significant potential hazard to small reptiles, both from the direct effects of exposure, and indirectly because of their largely insectivorous diet and small home ranges. Aims: Our study aimed to monitor the effects of two insecticides applied operationally for locust control in Australia. A phenyl pyrazole pesticide, fipronil, and a fungal biopesticide, Metarhizium acridium (Green Guard®), were applied aerially in either a barrier or block treatment in the absence of dense locust populations, and effects on non-target arid-zone reptiles were measured. Methods: We monitored reptile-abundance and community-composition responses to treatments using a large field-based pitfall-trapping experiment, with replicated control and spraying treatments, which approximated the scale of aerial-based locust-control operations in Australia. Key results: Neither reptile abundance nor community composition was significantly affected by locust-control treatments. However, both abundance and community composition as detected by pitfall trapping changed over time, in both control and treatment plots, possibly as a result of a decrease in annual rainfall. Conclusions: The absence of any significant short-term pesticide treatment effects in our study suggests that the two locust-control application methods studied present a relatively insignificant hazard to reptiles at our site, based on a single application. Similar to other areas of Australia, climate and other factors are likely to be stronger drivers of reptile abundance and community structure. Implications: Monitoring over an area that approximates the scale of the current locust-control operations is an important step in understanding the possible effects of current pesticide exposure on reptile populations and will inform insecticide risk assessments in Australia. However, important information on the immediate response of individuals to insecticide application and long-term effects of exposure are missing. The preliminary research reported in the present paper should be complemented by future investigations on long-term and sublethal impacts of pesticide exposure on Australian native reptiles and the possible benefits provided to reptiles by the resource pulses represented in untreated high-density locust populations

Mosquito assemblages associated with urban water bodies; implications for pest and public health threats

Mosquitoes and mosquito-borne pathogens within urban regions may vary in response to short-term spatial and temporal changes in climate, as well as the distribution of water bodies, habitats and wildlife. Predicting where and when mosquito-borne pathogens are likely to occur is vital to safeguarding against outbreaks of human disease and developing strategic mosquito management programs. The aims of our study were to determine: 1) the spatial and temporal variability in mosquito communities over the late summer and early autumn in a metropolitan region; and, 2) the presence of arboviruses in the various mosquito species at the sites and the implications for mosquito-borne disease risk. Mosquito populations were sampled, and tested for the presence of arboviruses, using a replicated CO2 trap sampling design to determine the spatial and temporal variability in mosquito communities over the late summer and early autumn in the metropolitan region of Sydney, Australia. Eleven sites were classified as highly urban, suburban or estuarine, based on the water habitats present and distance from the central business district. Mosquito community composition within metropolitan urban regions was not significantly different from those in suburban areas with nearby bushland. However, areas associated with estuarine wetlands recorded significantly different mosquito fauna and a higher abundance of mosquitoes. Stratford virus was the only arbovirus detected in the study and was detected at a higher incidence at the three estuarine sites. This mosquito-borne pathogen is considered of only minor public health concern and while more hazardous viruses were not detected, the high abundance of known vector mosquito species highlights the potential risk and suggests the need for annual surveillance to assist local health authorities mange these risks. Our findings highlight the importance of considering estuarine areas separately when assessing the risk of mosquito-borne disease. This is critical for many cities globally, as important population centres are often located in coastal areas adjacent to estuarine wetlands

Surviving drought: a framework for understanding animal responses to small rain events in the arid zone

Large rain events drive dramatic resource pulses and the complex pulse‐reserve dynamics of arid ecosystems change between high‐rain years and drought. However, arid‐zone animal responses to short‐term changes in climate are unknown, particularly smaller rain events that briefly interrupt longer‐term drought. Using arthropods as model animals, we determined the effects of a small rain event on arthropod abundance in western New South Wales, Australia during a longer‐term shift toward drought. Arthropod abundance decreased over 2 yr, but captures of 10 out of 15 ordinal taxa increased dramatically after the small rain event (\u3c40 \u3emm). The magnitude of increases ranged from 10.4 million% (collembolans) to 81% (spiders). After 3 months, most taxa returned to prerain abundance. However, small soil‐dwelling beetles, mites, spiders, and collembolans retained high abundances despite the onset of winter temperatures and lack of subsequent rain. As predicted by pulse‐reserve models, most arid‐zone arthropod populations declined during drought. However, small rain events may play a role in buffering some taxa from declines during longer‐term drought or other xenobiotic influences. We outline the framework for a new model of animal responses to environmental conditions in the arid zone, as some species clearly benefit from rain inputs that do not dramatically influence primary productivity

Clean bill of health? Towards an understanding of health risks posed by urban ibis

Urban waterbirds are considered both serious pests and inspiring wildlife. Ibis and gulls are often vilified due to their dirty appearance and disruption of outdoor activities, while ducks are affectionately fed in parks. However, all waterbirds are potential reservoirs of zoonotic pathogens. In Sydney (Australia), we documented the relative prevalence of arbovirus exposure and Salmonella shedding in 72 Australian White Ibis (Threskiornis moluccus) at 2 urban sites in 2003 during a management cull and in 2015 as a response to increased public interest. We sampled during a period of peak human arbovirus and Salmonella infection risk in late summer and early autumn. In 2015, antibodies for the endemic West Nile virus Kunjin strain (WNVKUN) were detected in one bird. While not indicative of immediate public health risk, this highlights that an animal with a history of exposure was present or moved into a region not previously known to have endemic WNVKUN activity. However, the movement patterns of this individual and WNVKUN host competency of this species are unknown. An absence of other antibody responses suggests that ibis are not important viral reservoirs or flaviviruses are not widespread in Sydney. Assays failed to detect Salmonella in 2015, but 25% of individuals were positive in 2003. Further monitoring of the arguable health hazard represented by urban T. moluccus will facilitate informed decisions and solutions to urban bird and wetland management challenges

Effects of two locust control methods on wood-eating termites in arid Australia

Termites are ubiquitous detritivores and are a key influence on soil function and nutrient cycles, particularly in arid and semi-arid ecosystems. Locust control presents a unique hazard to termites and the effective functioning of ecosystems as a consequence of the overlap between pesticide applications and termite populations in grassland and desert landscapes. We monitored the effects of locust control methods using ultra-low-volume (ULV) barrier application of a chemical pesticide, fipronil, and a blanket application of a fungal biopesticide, Metarhiziumacridum, on wood-eating termites in arid western New South Wales, Australia. We tested the hypothesis that spray applications decrease termite activity at wood baits using a BACI designed field experiment over 2 years. Our replicated control and treatment sites represented the spatial scale of Australian locust control activities. There was no detectable impact of either locust control treatment on termite activity, bait mass loss or termite community composition measures. Non-significant differences in termite survey measures among sites suggested that climate and environmental conditions were stronger drivers of our termite measures than the single, localized and unreplicated application of pesticides more commonly used in locust control operations in arid Australia. A lack of evidence for an impact of our fipronil or Metarhizium application methods supports their use as low hazard locust control options with minimal large scale and longer-term effects on termites in Australian arid rangelands. Future research would be necessary to determine the probable short-term impacts of treatments on individual termite colonies and the possible impacts on non-wood eating termite species in the arid-zone

Short and long-term impacts of ultra-low-volume pesticide and biopesticide applications for locust control on non-target arid zone arthropods

While locust control is necessary to avoid the high cost of locust damage to agriculture, land managers are increasingly seeking to minimize the environmental impact of pesticide spray treatments used. The comparative impacts of different locust control treatments on non-target arid zone fauna are rarely studied in the field, leading to uncertainty as to which treatments represent the lowest hazard to the sprayed ecosystems. A phenyl pyrazole pesticide, fipronil, and a fungal biopesticide, Metarhizium acridum (Green Guard®) were applied aerially in either a barrier or blanket ULV treatment at replicated sites which mimicked the techniques employed for locust control operations in Australia. Effects of the two pesticide treatments were compared in the absence of dense locust populations. We measured the abundance and community composition of non-target arid-zone arthropods at control and treatment sites before and after pesticide applications using a large field-based pitfall trapping experiment. Arthropod community composition was not significantly affected over time by either locust control treatment. However, significant short-term times x treatment interactions were found for 6 of 11 most common taxa at family or higher taxonomic level (collembolans, acarians, coleopterans, psocopterans, gryllids, and dipterans). We also compared unsprayed and sprayed areas within fipronil and Metarhizium treatment sites, and found 2 of the 10 most common ant species (Formicidae: Rhytidoponera mayri and Iridomyrmex purpureus) showed significant time x treatment interactions for fipronil but none for Metarhizium, indicating that ants were more severely affected by fipronil within sites than between the three treatments. One year post-treatment, significant time x treatment interactions persisted for only two taxa (dipterans and blattodeans) at Metarhizium treatments, indicating full recovery of most taxa. The suppression of the ant R. mayri in fipronil sprayed areas within treatment sites persisted after one year, while I. purpureus had fully recovered. Relative arthropod abundance and community assemblage changed over time in control and treatment sites, probably reflecting changes in patterns of local rainfall over the study period. Most of the statistically significant treatment effects recorded for different taxa in our study were not long lasting, suggesting that the two locust control methods studied represent a relatively low and transient hazard to most arthropod taxa. The pronounced temporal variation in arthropod abundance across all sites indicated that climate and environmental factors are likely to be stronger drivers of arid zone arthropod abundance and community structure than single aerial applications of low-dose aerial pesticide treatments used to control locusts in arid and semi-arid regions of Australia

Applications of fipronil (Adonis 3UL) and Metarhizium acridum for use against locusts have minimal effect on litter decomposition and microbial functional diversity in Australian arid grassland

Litter and microbes are key drivers of nutrient cycles, particularly in arid ecosystems where decomposition rates are low. Locust control in arid regions represents a potentially important hazard to microbes, because local taxa are unlikely to have adapted to pesticide exposure and operations often occur during times of high microbial activity. We monitored the response of aboveground litter decomposition and soil bacteria functional diversity to aerial applications of fipronil (a chemical pesticide) barrier treatments and Metarhizium acridum (a fungal biopesticide) blanket treatments. Decomposition was monitored over 2 years (before and after treatments) using a replicated litter-bag experiment, whereas changes in bacteria functional diversity were measured over 1 month. Analysis of litter mass loss indicated there were no pesticide treatment effects relative to control. Less litter decomposed in small than large mesh bags, and less litter decomposed during the second year of the study. Litter had higher mean nitrogen (N) and carbon (C), and a lower C:N ratio, during the first year of the study. In contrast, within-treatment site analysis revealed a significant increase in litter mass remaining in bags at M. acridum-treated subsites. However, these values were only 4% different from control sites, suggesting that the effect detected may not be biologically significant. There appeared to be no pesticide treatment effect on bacterial community functional diversity and no significant temporal variation. The lack of large-scale pesticide treatment effects suggests that arid zone fungi and bacteria are resilient to such disturbances. Differences in decomposition was explained by differences in the activity of arthropods and in the shade provided by the two mesh sizes, and an annual decline could be attributed to lower litter C and N content and lower annual rainfall in Year 2. Results show the temporal variation possible in decomposition and microbe community measures in arid systems

Effectiveness of different herbivore exclusion strategies for restoration of an endangered rainforest community

Restoration practitioners commonly use plantings of young seedlings to restore endangered forest communities impacted by anthropogenic disturbance, such as weed invasion and deforestation. Forest recovery may be significantly hampered by browsing pressure from herbivores, and practitioners use a variety of plant guard techniques to reduce the negative impacts of browsing on plant establishment and facilitate ecosystem regeneration. However, there is limited knowledge of which herbivore exclusion methods are most effective in protecting growing seedlings from attack and whether such benefits vary amongst different resident plant species. We compared levels of herbivore damage for 54 native rainforest tree and shrub species amongst four guard treatments that are commonly deployed by restoration practitioners to protect revegetated seedlings from attack by non-native rusa deer (Cervus timorensis) and native vertebrate herbivores during their establishment: (1) small corrugated plastic guards; (2) tall wire guards that protect single seedlings from attack; (3) small fenced exclusion plots that protect multiple revegetated seedlings as well as passively regenerating plants simultaneously; (4) unguarded plants. We also evaluated the effects of exclusion plots on the richness and composition of passively regenerating native vegetation in addition to the growth of actively revegetated seedlings through reduced herbivore activity. Herbivore activity was briefly surveyed using camera traps, and swamp wallabies (Wallabia bicolor) were found to be more active at the site than non-native rusa deer. All guard treatments significantly reduced browsing damage compared with unguarded plants, but corrugated plastic guards were less effective than wire guards and fenced exclusion plots. The fenced exclusion plots had the additional benefit of facilitating the passive regeneration of native plant species that may be cost prohibitive to regeneration otherwise. We also found that species varied in susceptibility to browsing, with eight species suffering high browse damage and five species low damage when unguarded. These findings highlight the potential for exclusion fences to provide more efficient and effective protection of browser preferred plants in the context of rainforest restoration