The Dilemma of Foraging Herbivores: Dealing with Food and Fear

For foraging herbivores, both food quality and predation risk vary across the landscape. Animals should avoid low-quality food patches in favour of high-quality ones, and seek safe patches while avoiding risky ones. Herbivores often face the foraging dilemma, however, of choosing between high-quality food in risky places or low-quality food in safe places. Here, we explore how and why the interaction between food quality and predation risk affects foraging decisions of mammalian herbivores, focusing on browsers confronting plant toxins in a landscape of fear. We draw together themes of plant–herbivore and predator–prey interactions, and the roles of animal ecophysiology, behaviour and personality. The response of herbivores to the dual costs of food and fear depends on the interplay of physiology and behaviour. We discuss detoxification physiology in dealing with plant toxins, and stress physiology associated with perceived predation risk. We argue that behaviour is the interface enabling herbivores to stay or quit food patches in response to their physiological tolerance to these risks. We hypothesise that generalist and specialist herbivores perceive the relative costs of plant defence and predation risk differently and intra-specifically, individuals with different personalities and physiologies should do so too, creating individualised landscapes of food and fear. We explore the ecological significance and emergent impacts of these individual-based foraging outcomes on populations and communities, and offer predictions that can be clearly tested. In doing so, we provide an integrated platform advancing herbivore foraging theory with food quality and predation risk at its core

Absolute Measurement of the Critical Properties of Second Sound at the Smectic-A-to-Nematic Phase Transition in 8OCB

Light scattered from the driven free surface of the smectic-A phase of octyloxy cyanobiphenyl (8OCB) provides a low-frequency measurement of second sound. This yields an absolute measurement of the smectic elastic constant, B. There is no dispersion in either the angular or frequency dependence of B for angles $35^{\circ}-83^{\circ}$ from the normal and for frequencies from 10-100 kHz. Near the smectic-A-to-nematic phase transition the smectic elastic constant can be described by $B=(6.03 \pm 0.05) \times 10^7 (T_{NA}-T)^{0.32 \pm 0.015} dyn/cm^2$.Engineering and Applied Science

Anomalous Temperature Dependence of the Elastic Constant B at the Smectic-to-Nematic Phase Transition in Binary Mixtures of Hexyloxycyanobiphenyl-Octyloxycyanobiphenyl (60CB-80CB)

In hexyloxycyanobiphenyl-octyloxycyanobiphenyl (60CB-80CB) binary mixtures displaying reentrant behavior, the smectic elastic constant, B, deviates from a simple power law of the form $B=B_1(T_{NA}-T)^{\varphi}$ and levels off as $T \rightarrow T_{NA}$. This behavior is consistent with the Nelson-Toner dislocation-unbinding model of the transition.Engineering and Applied Science

Synchrotron X-Ray Study of the Thickness Dependence of the Phase Diagram of Thin Liquid-Crystal Films

The phase diagram of freely suspended thin films of heptyloxybenzylidene-heptylaniline shows dramatic changes for thicknesses below 22 layers. The most surprising feature of the phase diagram is the inclusion of two phases lacking long-range crystalline order (smectic-F and hexatic-B phases) between two crystalline phases (crystalline smectic B and smectic G). Neither the smectic F nor the hexatic B occurs in bulk samples. Between sixteen and ten layers the width, in temperature, of the hexatic-B phase increases.Engineering and Applied Science

Synchrotron X-Ray Observation of Surface Smectic-I Hexatic Layers on Smectic-C Liquid-Crystal Films

Synchrotron x-ray diffraction methods employing a position-sensitive detector were used to study smectic-C (SmC) and smectic-I (SmI) phases in thin (2–6 molecular layers) liquid-crystal films of 4-(n-heptyloxy)benzylidene-4-(n-heptyl)aniline (7O.7). Above $\sim 78^{\circ}C$, the entire film is SmC and below $\sim 69^{\circ}C$, the entire film is SmI, a stacked tilted hexatic. Between $69^{\circ}C and 78^{\circ}C$, the surface layers of the films are hexatic SmI and the interior layers are SmC. There is a pretransitional broadening of the surface hexatic peaks as the surface layers melt into the SmC phase.Engineering and Applied Science

X-Ray and Optical Studies of the Thickness Dependence of the Phase Diagram of Liquid-Crystal Films

A comprehensive study of the thickness dependence of the phase diagram of freely suspended films of the liquid crystal 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) between $50 and 69^{\circ}C$ is reported. In thick films (thicker than about 300 layers and characteristic of bulk samples) there is a low-temperature crystalline-G phase followed by five crystalline-B phases with different stacking arrangements at higher temperatures. In thinner films there are two additional crystalline-B phases and two tilted hexatic phases, smectic-F and smectic-I, which do not appear in bulk samples. The in-plane and interlayer correlations in the tilted hexatic phases are anisotropic with a clear dependence on the molecular tilt direction; the in-plane correlations are more developed (longer range) perpendicular to the molecular tilt direction and the interlayer correlations are more developed parallel to the tilt direction.Engineering and Applied Science