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Ballistic seed dispersal (ballochory) involves the autonomous explosive release of seeds from adult plants. The unconventional mechanics of this strategy have understandably drawn considerable scientific attention. The explosive release of seeds is achieved by a variety of physical mechanisms but broadly involves the rapid coiling or shattering of seed pods to transfer kinetic energy to seeds, facilitated largely by either the evaporation or absorption of water in seed pod tissues. There has been a bias toward researching physiological and physical aspects of ballistic plants, with the evolutionary ecology being comparatively neglected. Although ballochory is represented in 23 plant families, it has never become common. This fact should invite curiosity regarding the selective pressures that encourage its evolution. Previous research has been unable to correlate ballochory with plant traits such as morphology, generation time or habitat preferences, and so we take an alternative approach in considering the evolutionary advantages that can provide insight on the shared set of circumstances that favour the evolution of this strategy. We review the known selective advantages that ballistic dispersal can confer to plants and promote a hypothesis that ballochory may be particularly selected for in instances of concentrated predation pressure on parental canopies. For plants in static and patchy landscapes, such a strategy could balance a trade‐off between escaping concentrated natural enemies while maximising the probability of transport to suitable habitat. We account for its rarity by considering the major opportunity cost that may only be justified when other seed dispersal mechanisms are limited. Moving forward, we suggest experimental manipulations to test this hypothesis and promote a research agenda in the field of ballistic seed dispersal that illuminates its intriguing evolution. This viewpoint article describes an initial hypothesis regarding the evolutionary ecology of explosive seed dispersal. Although the physical mechanisms of this unconventional process are well understood, the evolution of this plant trait has received comparatively little attention. We suggest that predation pressure on or beneath the parent plant could help explain the repeated evolution of this trait and hope to stimulate experimental manipulations to test this.

In many taxa the timing of metamorphosis is plastic in response to predation risk during the pre-metamorphic stage, and trends in both age and body size at metamorphosis have been the subject of much study. The responses to cues of predators are predominantly to be larger or equal-sized at the same age or older at metamorphosis. These observations are in direct contrast with existing theoretical treatments of this plasticity, which mostly predict earlier and smaller metamorphosis and never later and larger metamorphosis without invoking indirect effects on growth rate. Here we resolve the discrepancy between theory and observation using a dynamic state-dependent model that incorporates morphological and behavioral responses to predation risk. We allow prey to choose the optimal activity level and/or investment in defense over the growth period. We show that under certain conditions, metamorphosis at a larger size and later time is likely to be optimal. Our analysis allows us to make testable predictions about the changes in activity level of prey as they grow and how the effect of providing refuges will vary with predator type. Several of these predictions are supported by a meta-analysis of metamorphic responses to caged predators by larval amphibians and insects. Our predictions lead to insights about the feedback effects of antipredator responses on growth and subsequent implications for life history.

In experiments where subjects are allocated to different treatments, implementing allocation concealment simply means that procedures are used to prevent conscious or unconscious human bias influencing the allocation of particular subjects to particular treatments. It is a related, but distinct, procedure to blinding. Allocation concealment is a neglected, but potentially valuable, tool in improving the design of experiments, and it can always be applied inexpensively and easily to any experiment involving allocation of subjects between treatment groups. I feel allocation concealment should be adopted more widely.

Body size trends across environmental gradients are widely reported but poorly understood. Here, we investigate contrasting relationships between size (body mass) and depth in the scavenging and predatory demersal ichthyofauna (800-4800 m) of the North-east Atlantic. The mean size of scavenging fish, identified as those regularly attracted to baited cameras, increased significantly with depth, while in non-scavengers there was a significant decline in size. The increase in scavenger size is a consequence of both intra and inter-specific effects. The observation of opposing relationships, in different functional groups, across the same environmental gradient indicates ecological rather than physiological causes. Simple energetic models indicate that the dissimilarity can be explained by different patterns of food distribution. While food availability declines with depth for both groups, the food is likely to be in large, randomly distributed packages for scavengers and as smaller but more evenly distributed items for predators. Larger size in scavengers permits higher swimming speeds, greater endurance as a consequence of larger energy reserves and lower mass specific metabolic rate, factors that are critical to survival on sporadic food items.

Beauchamp and Ruxton explore the role of resource availability on vigilance patterns among animals. Beauchamp and Ruxton examine the role of scramble competition for resources and show that competition within a group may produce a steeper decline in vigilance with increasing group size than that predicted by purely antipredator models.

Prey capture by trapping is uncommon taxonomically, and generally requires highly evolved cognitive powers (humans) or specialist self-secreted materials (for example, spiders and caddisfly larvae). The most notable exception to this is the conical traps dug by antlion larvae. The relative uncommonness (taxonomically and ecologically) of such pitfall traps has been described as an unexplained mystery in recent publications. Here we suggest some potential routes that might lead to resolution to this mystery. We argue that although such pitfall traps have numerous benefits and are relatively cheap and easy to construct, they may suffer two significant disadvantages relative to, for example, spiders' webs. First, pitfall traps may require a quite specialist microhabitat. Second, antlion pitfall traps may only work to retain all but the smallest prey if the antlion is present at the bottom of the pit. Thus, antlion may be more functionally tied to their trap than spiders and (since traps are much more visually conspicuous than their owners) this may make them vulnerable to predators and parasitoids that cue on the traps. Both these hypothesised drawbacks are speculative in the absence of a strong body of data and so we discuss how both potential costs could be explored empirically.

Changes in the resources allocated to particular stages of reproduction are expected to influence allocation to, and performance in, subsequent reproductive stages. Experimental manipulation of individual investment patterns provides important evidence that such physiological trade-offs occur, and can highlight the key environmental variables that influence reproductive costs. By temporarily altering the thermal properties of starling nests, we reduced the energetic demand of first-clutch incubation, and examined the effect of this manipulation on performance during the same and the subsequent reproductive attempts. Compared with controls, starlings investing less in incubation were more successful in fledging young, and were more likely to hatch all their eggs if a subsequent reproductive attempt was made. Our results show that incubation demands can limit reproductive success, and that resources saved during incubation can be reallocated to later stages of the same reproductive attempt and to future reproductive attempts. This study also shows that small changes in thermal environment can affect breeding success by altering the energetic demands imposed on incubating parents, independently of the effect of temperature on other environmental variables such as food supply.

We elucidate the conditions under which an easy-to-catch edible prey species may evolve to resemble another edible species that is much more difficult to capture ('evasive Batesian mimicry'), and the conditions under which two or more edible but hard-to-catch species evolve a common resemblance ('evasive Müllerian mimicry'). Using two complementary mathematical models, we argue that both phenomena are logically possible but that several factors will limit the prevalence of these forms of mimicry in nature. Evasive Batesian mimicry is most likely to arise when it is costly in time or energy for the predator species to pursue evasive prey, when mimics are encountered less frequently than evasive models and where there are abundant alternative prey. Evasive Müllerian mimicry, by contrast, is most likely to arise when evasive prey species differ in abundance, predators are slow to learn to avoid evasive prey and evading capture is costly to the prey. Unequivocal evidence for evasive Batesian or Müllerian mimicry has not yet been demonstrated in the field, and we argue that more empirical work is needed to test whether putative examples are indeed a result of selection to signal difficulty of capture.

Chemical defences against predation often involve responses to specific predation events where the prey expels fluids, such as haemolymph or gut contents, which are aversive to the predator. The common link is that each predation attempt that is averted results in an energetic cost and a reduction in the chemical defences of the prey, which might leave the prey vulnerable if the next predation attempt occurs soon afterwards. Since prey appear to be able to control the magnitude of their responses, we should expect them to trade-off the need to repel the current threat against the need to preserve defences against future threats and conserve energy for other essential activities. Here we use dynamic state-dependent models to predict optimal strategies of defence deployment in the juvenile stage of an animal that has to survive to maturation. We explore the importance of resource level, predator density, and the costs of making defences on the magnitude of the responses and optimal age and size at maturation. We predict the patterns of investment and the magnitude of the deployment of defences to potentially multiple attacks over the juvenile period, and show that responses should be smaller when the costs of defences and/or predation risk are higher. The model enables us to predict that animals in which defences benefit the adult stage will employ different strategies than those that do not use the same defences as adults, and thereby experience a smaller reduction in body size as a result of repeated attacks. We also explore the effect of the importance of adult size, and find that the sex and mating system of the prey should also affect defensive strategies. Our work provides the first predictive theory of the adaptive use of responsive defences across taxa.

1. Starling (Sturnus vulgaris) clutches were manipulated so that sibling eggs were incubated within either natural-sized clutches, or clutches that had been experimentally enlarged but were still within the natural range of variation. Thus the consequences of incubated clutch size for hatching success were investigated. 2. Eggs incubated within enlarged clutches hatched less successfully than eggs incubated within natural-sized clutches, suggesting that clutch size affects the conditions experienced by embryos during incubation. 3. Eggs incubated in enlarged clutches may have hatched poorly because clutch enlargement altered nest microclimate, causing increased water loss during the incubation period. 4. There was no evidence that enlargement altered nest microclimate by energetically constraining parents from incubating effectively. Instead, intrinsic physical properties of enlarged clutches affected clutch temperature directly. 5. Parents that had incubated experimentally enlarged clutches subsequently fledged fewer chicks than control parents, suggesting that constraints imposed during incubation may influence the optimal number of eggs that parents should lay. 6. Future studies should investigate whether parents laying naturally large clutches can minimize the problems of incubating many eggs by adaptively tailoring the shape and composition of their eggs to their expected clutch size.