No abstract

SUMMARY In contrast to previous studies of rapid cold-hardening (RCH), which have investigated the responses of insects maintained under `summer conditions'(20° to 25°C), this study focuses on the ability of low-temperature acclimated insects to undergo RCH. When the grain aphid Sitobion avenae Fabricus was low-temperature acclimated by rearing for three generations at 10°C, the discriminating temperatures (temperature that results in approximately 20% survival after direct transfer from the rearing temperature to a sub-zero temperature for a period of 3 h), of first instar nymphs and adult aphids were –11.5° and –12°C,respectively. Maximum rapid cold-hardening was induced by cooling aphids at 0°C for 2 h (nymphs) or 30 min (adults), resulting in survival at the respective discriminating temperatures increasing from 26% to 96% (nymphs) and 22% to 70% (adults). Cooling from 10° to 0°C at 1°, 0.1° and 0.05°C min-1 significantly increased survival of nymphs at the discriminating temperature, but not of adults. There were no `ecological costs' associated with rapid cold-hardening at 0°C, or with exposure of rapidly cold-hardened aphids to the discriminating temperatures; fecundity and longevity, in both nymphs and adults were either similar to control aphids or significantly increased. The study demonstrates that rapid cold-hardening ability is retained in aphids that have already undergone cold-acclimation, as would be the case in overwintering aphids. Both rapid cold-hardening and subsequent exposure at previously lethal temperatures can enhance fitness in surviving individuals.

The effect of long-term (seasonal) acclimation and rapid cold hardening is investigated on the cold torpor temperature ( CT min ) of adult grain aphids, Sitobion avenae, reared at 20 or 10 °C for more than 6 months before experimentation. Rapid cold hardening is induced by exposing aphids reared at 20 to 0 °C for 3 h and aphids reared at 10 to 0 °C for 30 min (acclimation regimes previously found to induce maximum rapid cold hardening). The effect of cooling aphids from the same rearing regimes from 10 to −10 °C at 1, 0.5 and 0.1 °C min −1 is also investigated. In the 20 °C acclimated population, rapid cold hardening and cooling at 0.1 °C min −1 both produce a significant decrease in CT min from 1.5 ± 0.3 to -0.9 ± 0.3 and -1.3 ± 0.3 °C, respectively. Rapid cold hardening also results in a significant reduction in CT min of the population reared at 10 °C from 0.8 ± 0.1 to -0.9 ± 0.2 °C. However, none of the cooling regimes tested reduces the CT min of the winter-acclimated (10 °C) population. The present study demonstrates that rapid cold-hardening induced during the cooling phase of natural diurnal temperature cycles could lower the movement threshold of S. avenae , allowing insects to move and continue feeding at lower temperatures than would otherwise be possible.

1. When first instar nymphs and adults of the grain aphid Sitobion avenae (Fabricius) (Hemiptera: Aphidiae) were maintained in long‐term cultures (>6 months) at 20 °C and 10 °C, the LT50 decreased from −8 and −8.8 °C to −16.0 and −13.5 °C, respectively. 2. When aphids from the 20 °C culture were transferred to 10 °C, there was a progressive increase in cold tolerance through three successive generations. Transfer of newly moulted pre‐reproductive adults reared at 10 °C for three generations back to 20 °C resulted in a rapid loss of cold hardiness in their nymphal offspring. 3. In all generations reared at 10 °C, first born nymphs were more cold hardy than those born later in the birth sequence. The LT50 of nymphs produced on the first day of reproduction in the first, second and third generations maintained at 10 °C were −14.8, −17.0 and −16.6 °C, respectively. Thereafter, nymphal cold hardiness decreased over the subsequent 14 days of reproduction in each generation at 10 °C with mean LT50 values of −10.3, −12.6 and −14.8 °C, respectively. By contrast, the cold tolerance of first born nymphs of aphids reared continuously at 20 °C did not differ in comparison with later born siblings. The LT50 of adult aphids was also unaffected by ageing. 4. The ecological relevance of these findings is discussed in relation to the overwintering survival of aphids such as S. avenae.

1. Shallow groundwater aquifers regularly support drought refuges for water-dependent ecosystems. However, many aquifers are impacted by over-extraction and pollution, potentially degrading their ability to support groundwater-fed drought refuges. 2. We investigated the response of groundwater-connected riverine forests to a drought considered equivalent in intensity to those predicted under severe climate change for 2030. The drought's impact was investigated in an area where shallow groundwater resources are heavily exploited and polluted by salinization. 3. We used remotely sensed vegetation productivity (enhanced vegetation index) data from a long-term data set (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011) at 475 riverine forest sites in the Campaspe catchment, southeastern Australia. Generalized additive mixed models and boosted regression trees were used to model the relationship between groundwater and other environmental covariates with forest change during drought. 4. Models explained up to 44% of the variation in forest change during drought. Forests underwent the greatest declines in areas of high salinity (>6000 lS cm À1 ) associated with shallow groundwater depths (0-5 m). Conversely, forests in areas of lowest salinity (<2000 lS cm À1 ) and groundwater depths of more than 7Á5 m showed the least decline during drought. 5. In landscapes where groundwater quality is not compromised, previous studies have shown that shallow groundwater provides important drought refuges and refugia. Here, we show that when groundwater salinization has occurred, forests connected to shallow groundwater are more vulnerable to drought. In effect, salinization reduces the capacity of groundwater-connected habitats to function as drought refuges. 6. Synthesis and applications. Currently, there is an emphasis on managing environmental flows to support freshwater ecosystems and associated forests under water stress. However, delivery of environmental water is restricted to areas within a linear stream network and there is often limited capacity to deliver environmental flows during drought. Alternatively, a focus on drought refuges and refugia and processes important for maintaining groundwater quality (e.g. catchment revegetation to reduce shallow groundwater salinization) may better allow drought effects to be managed across a catchment, without directly focusing on highly contested surface water resources.

Rivers provide many social and environmental services that benefit humanity. A critical role of water mangers is to prioritize water allocation options that trade off socio‐economic and hydro‐ecological benefits in rivers. Methods for multi‐criteria decision analysis (MCDA) provide a structured and systematic manner for researchers to aid in this process. In this paper, we describe a new MCDA method that prioritizes large multi‐dimensional sets of tradeoffs to support well‐informed water management in rivers. The method was developed based on an environmental flows planning study in the Goulburn‐Broken River catchment, Victoria, Australia. A combined simulation and heuristic optimization procedure was previously integrated into a hydrological catchment network model. That process resulted in a large set of viable daily water allocation schedules that traded off long‐term irrigation and hydro‐ecological benefits at the catchment outlet. We provided new guidance procedures to identify priority tradeoffs that can be used in stakeholder deliberations and catchment decision‐making. Our MCDA method included combined multi‐dimensional ordination and cluster analysis to spread the water allocation alternatives onto a two‐dimensional plane to discover alternatives with similar criteria tradeoffs. A geometric distance‐based method was performed on the full set of alternatives and on the identified clusters to rank the alternatives in accordance with minimizing the distance of the alternatives to an ideal but non‐feasible reference point in multi‐dimensional space. This method complements the use of elicitation procedures when water manager or other stakeholder interaction is not an option or when objectivity is desired. Copyright © 2016 John Wiley & Sons, Ltd.

No abstract

The regulation of flow in river systems and use of water for consumptive and economic purposes has led to detrimental effects on riverine, wetland and floodplain environments in river systems worldwide. In recent years, there has been a concerted effort to develop policies to return water to the environment to minimise these effects. However, there are far fewer instances of actual flows being delivered. One barrier to the delivery of environmental flows is the need to balance environmental and consumptive outcomes, optimising returns for both with a limited volume of water. Various methods are available to help define the flows required to protect specific ecological assets or to mimic aspects of natural flow regimes, but few consider consumptive uses as part of the same set of calculations. In this paper, we present a method of evaluating flow options using ecological response models incorporated into daily hydrology and irrigation river management models. A multi-objective optimisation approach produces the Pareto frontier of non-dominated solutions, which provides decision makers with a range of alternative optimal management options. An integrated water resource model of the Goulburn River, Victoria, Australia, is developed that represents the rivers, water storages, operational constraints, water management and consumptive demands on a daily timescale linked to climate. Models of ecological responses to flow are incorporated into the river model to simulate ecological response and generate environmental flow demands. Storage volumes are used to determine water allocations which in turn determine the area irrigated and relative value of the crop mix. We develop this eco-hydrology model and optimisation approach as a 'proof of concept' example, where the objective functions are to minimise terrestrial vegetation encroachment into the main river channel through the use of environmental flows, while maximising the net relative value of irrigation. The model is run over 35 years and the results indicate that a range of optimal solutions exist. In the best case for irrigation there is a net relative value (over the 35 years) of almost $17B while terrestrial vegetation encroachment could average approximately 13%. In contrast, it would be possible to reduce the terrestrial vegetation encroachment to just 2%, however, this would reduce net relative value of irrigation to around $12B. Interestingly the latter option would also result in some short-term periods of very high vegetation encroachment. This was because of much lower overall storage volumes resulting in 0% water allocations in some years. Our results highlight the importance of hydrological modelling of both consumptive use and ecological response to understand the feedback mechanism of some management decisions. Between the two extremes are a range of results that provide a clear understanding of what outcomes could be expected for both of the objective functions for all optimised solutions. The results presented in this paper are applied to a simple rep...