The impacts of environmental warming on Odonata: a review

Climate change brings with it unprecedented rates of increase in environmental temperature, which will have major consequences for the earth's flora and fauna. The Odonata represent a taxon that has many strong links to this abiotic factor due to its tropical evolutionary history and adaptations to temperate climates. Temperature is known to affect odonate physiology including life-history traits such as developmental rate, phenology and seasonal regulation as well as immune function and the production of pigment for thermoregulation. A range of behaviours are likely to be affected which will, in turn, influence other parts of the aquatic ecosystem, primarily through trophic interactions. Temperature may influence changes in geographical distributions, through a shifting of species' fundamental niches, changes in the distribution of suitable habitat and variation in the dispersal ability of species. Finally, such a rapid change in the environment results in a strong selective pressure towards adaptation to cope and the inevitable loss of some populations and, potentially, species. Where data are lacking for odonates, studies on other invertebrate groups will be considered. Finally, directions for research are suggested, particularly laboratory studies that investigate underlying causes of climate-driven macroecological patterns

Feeding in fear: Indirect effects of predatory fish on macrophyte communities mediated by altered crayfish foraging behaviour

The threat of predation influences decisions made by prey animals and alters the way that prey interact with other species in their environment. Animals often alter their foraging behaviour in response to a predatory threat by increasing or decreasing food consumption or by changing their feeding preferences to focus on foods that limit their exposure to the threat. Changes in grazing pressure and diet selectivity can have significant impacts on the abundance and diversity of the prey’s food resources. In this study, we examined the indirect effects of a predatory fish on macrophyte biomass, mediated by crayfish responses to predator odours.Largemouth bass (Micropterus salmoides, Centrarchidae) were housed in flow‐through stream mesocosms to produce odour cues that initiated a nonconsumptive effect on rusty crayfish (Faxonius rusticus, Cambaridae) held in an adjacent section of the stream. Crayfish were offered three species of macrophytes (Myriophyllum exalbescens, Haloragaceae; Elodea canadensis, Hydrocharitaceae; Chara spp., Characeae) and were allowed to graze for 48 hr. Consumption of each plant species was measured by weighing the plant samples before and after every trial. The plant samples were further analysed for total phenolic content using the Folin–Ciocalteu method. Foraging and shelter use behaviours were quantified by analysis of video recordings for time spent foraging in the mesocosm and time spent in the shelter zone of the mesocosm.Crayfish consumed greater quantities of macrophyte tissue when predator cues were present, and this result was unexpected and is contrary to most observations in the literature.When threatened, the crayfish also showed a preference for two of the macrophyte species, which did not exist in trials without bass odour. This could be due to differences in total phenolic content among the three plant species tested.The results provide evidence for a strong indirect effect of predatory fish on the macrophyte community mediated by changes in crayfish behaviour under threat. Crayfish act as keystone species in stream ecosystems; thus, changes in their foraging behaviour and dietary preferences caused by exposure to predator odour cues could have important effects on macrophyte communities in lotic systems.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146642/1/fwb13181_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146642/2/fwb13181.pd

Thermal acclimation increases the stability of a predator-prey interaction in warmer environments.

Global warming over the next century is likely to alter the energy demands of consumers and thus the strengths of their interactions with their resources. The subsequent cascading effects on population biomasses could have profound effects on food web stability. One key mechanism by which organisms can cope with a changing environment is phenotypic plasticity, such as acclimation to warmer conditions through reversible changes in their physiology. Here, we measured metabolic rates and functional responses in laboratory experiments for a widespread predator-prey pair of freshwater invertebrates, sampled from across a natural stream temperature gradient in Iceland (4-18℃). This enabled us to parameterize a Rosenzweig-MacArthur population dynamical model to study the effect of thermal acclimation on the persistence of the predator-prey pairs in response to warming. Acclimation to higher temperatures either had neutral effects or reduced the thermal sensitivity of both metabolic and feeding rates for the predator, increasing its energetic efficiency. This resulted in greater stability of population dynamics, as acclimation to higher temperatures increased the biomass of both predator and prey populations with warming. These findings indicate that phenotypic plasticity can act as a buffer against the impacts of environmental warming. As a consequence, predator-prey interactions between ectotherms may be less sensitive to future warming than previously expected, but this requires further investigation across a broader range of interacting species

Determining relative bulk viscosity of kilometre-scale crustal units using field observations and numerical modelling

Though the rheology of kilometre-scale polymineralic rock units is crucial for reliable large-scale, geotectonic models, this information is difficult to obtain. In geotectonic models, a layer is defined as an entity at the kilometre scale, even though it is heterogeneous at the millimetre to metre scale. Here, we use the shape characteristics of the boundaries between rock units to derive the relative bulk viscosity of those units at the kilometre scale. We examine the shape of a vertically oriented ultramafic, harzburgitic-lherzolitic unit, which developed a kilometre-scale pinch and swell structure at mid-crustal conditions (~ 600 °C, ~ 8.5 kbar), in the Anita Shear Zone, New Zealand. The ultramafic layer is embedded between a typical polymineralic paragneiss to the west, and a feldspar-quartz-hornblende orthogneiss, to the east. Notably, the boundaries on either side of the ultramafic layer give the ultramafics an asymmetric shape. Microstructural analysis shows that deformation was dominated by dislocation creep (n = 3). Based on the inferred rheological behaviour from the field, a series of numerical simulations are performed. Relative and absolute values are derived for bulk viscosity of the rock units by comparing boundary tortuosity difference measured on the field example and the numerical series. Our analysis shows that during deformation at mid-crustal conditions, paragneisses can be ~ 30 times less viscous than an ultramafic unit, whereas orthogneisses have intermediate viscosity, ~ 3 times greater than the paragneisses. If we assume a strain rate of 10⁻ ¹⁴ s⁻ ¹ the ultramafic, orthogneiss and paragneiss have syn-deformational viscosities of 3 × 10²², 2.3 × 10²¹ and 9.4 × 10²⁰ Pa s, respectively. Our study shows pinch and swell structures are useful as a gauge to assess relative bulk viscosity of rock units based on shape characteristics at the kilometre scale and in non-Newtonian flow regimes, even where heterogeneity occurs within the units at the outcrop scale