Evolutionarily stable defence and signalling of that defence

We examine the evolution and maintenance of defence and conspicuousness in prey species using a game theoretic model. In contrast to previous works, predators can raise as well as lower their attack probabilities as a consequence of encountering moderately defended prey. Our model predicts four distinct possibilities for evolutionarily stable strategies (ESSs) featuring maximum crypsis. Namely that such a solution can exist with (1) zero toxicity, (2) a non-zero but non-aversive level of toxicity, (3) a high, aversive level of toxicity or (4) that no such maximally cryptic solution exists. Maximally cryptic prey may still invest in toxins, because of the increased chance of surviving an attack (should they be discovered) that comes from having toxins. The toxin load of maximally cryptic prey may be sufficiently strong that the predators will find them aversive, and seek to avoid similar looking prey in future. However, this aversiveness does not always necessarily trigger aposematic signalling, and highly toxic prey can still be maximally cryptic, because the increased initial rate of attack from becoming more conspicuous is not necessarily always compensated for by increased avoidance of aversive prey by predators. In other circumstances, the optimal toxin load may be insufficient to generate aversion but still be non-zero (because it increases survival), and in yet other circumstances, it is optimal to make no investment in toxins at all. The model also predicts ESSs where the prey are highly defended and aversive and where this defence is advertised at a cost of increased conspicuousness to predators. In many circumstances there is an infinite array of these aposematic ESSs, where the precise appearance is unimportant as long as it is highly visible and shared by all members of the population. Yet another class of solutions is possible where there is strong between-individual variation in appearance between conspicuous, poorly defended prey

Global maps of soil temperature.

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km <sup>2</sup> resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km <sup>2</sup> pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Mimicry and the psychology of predation

SIGLEAvailable from British Library Document Supply Centre- DSC:D79051 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Ecological pharmacodynamics:prey toxin evolution depends on the physiological characteristics of predators

The use of toxic chemical defences to repel and deter predators is widespread across living organisms, yet there are surprisingly few formal models of toxin evolution. Published models tend to focus on a trade-off between individual benefits and costs of toxicity, and treat predators as simple agents of selection, reducing future attacks when they encounter toxic prey. In this paper we argue, however, that the physiological characteristics of predators may be crucial in determining the nature and outcomes of toxin evolution. To examine this idea we devised and explored a model in which prey defence evolves in the context of predator physiology. We represented this as dose-effect relationships in predators for nutrition and toxins along with variable rates of predator metabolism. Incorporating variables of predator physiology can change views of toxin evolution. A key point is that inclusion of predator physiological variables requires that the nutritional value of prey is explicitly represented in the model, and this directly affects predictions for toxin evolution. In our model costly toxins generally evolve to the point that they are 'minimally unprofitable': just toxic enough to make prey typically unprofitable given their nutritional value to predators. As the nutritional value of prey increases, so the minimally unprofitable toxin level of prey tends to increase in step; hence another general prediction from this model is that toxin levels within prey should often correlate with the nutritional value of the prey. Predator physiology and cognition also contribute to variation in the social nature of defence. We argue that incorporating representations of predator physiology is important in the comprehension of toxin evolution and make suggestions for directions of future work

Ecological pharmacodynamics:prey toxin evolution depends on the physiological characteristics of predators

The use of toxic chemical defences to repel and deter predators is widespread across living organisms, yet there are surprisingly few formal models of toxin evolution. Published models tend to focus on a trade-off between individual benefits and costs of toxicity, and treat predators as simple agents of selection, reducing future attacks when they encounter toxic prey. In this paper we argue, however, that the physiological characteristics of predators may be crucial in determining the nature and outcomes of toxin evolution. To examine this idea we devised and explored a model in which prey defence evolves in the context of predator physiology. We represented this as dose-effect relationships in predators for nutrition and toxins along with variable rates of predator metabolism. Incorporating variables of predator physiology can change views of toxin evolution. A key point is that inclusion of predator physiological variables requires that the nutritional value of prey is explicitly represented in the model, and this directly affects predictions for toxin evolution. In our model costly toxins generally evolve to the point that they are 'minimally unprofitable': just toxic enough to make prey typically unprofitable given their nutritional value to predators. As the nutritional value of prey increases, so the minimally unprofitable toxin level of prey tends to increase in step; hence another general prediction from this model is that toxin levels within prey should often correlate with the nutritional value of the prey. Predator physiology and cognition also contribute to variation in the social nature of defence. We argue that incorporating representations of predator physiology is important in the comprehension of toxin evolution and make suggestions for directions of future work

Effects of anti-predator defence through toxin sequestration on use of alternative food microhabitats by small herbivores

Many invertebrate herbivores sequester plant toxins from their food, and the availability of toxins and the costs and benefits of sequestering toxins may influence food patch choice. In many plants, young leaves contain higher concentrations of toxins than old leaves and so can be preferred by sequestering herbivores, even if herbivores are more readily detected by predators when on them. We modelled patch use and sequestration strategies for the growth period of herbivores, assuming that the effectiveness of a toxin against predators is positively related to its cost of sequestration and that high-reward patches have higher predation risk. We show that the empirically commonly-observed strategy of moving from a low-reward patch to a high-reward patch can be optimal in a range of circumstances, but especially those that are common in nature. Body size when herbivores are predicted to switch increases with increasing size of maturation under most conditions, whilst use of the high-reward patch increases. Our predictions about how the proportion of time spent in the high-reward patch changes with the distribution and potency of toxins indicate a reason for plant toxins to be relatively mild. We provide further testable predictions about the role of the plant's defence strategy and herbivore behaviour in tritrophic interactions

The dual benefits of aposematism: predator avoidance and enhanced resource collection

Theories of aposematism often focus on the idea that warning displays evolve because they work as effective signals to predators. Here, we argue that aposematism may instead evolve because, by enhancing protection, it enables animals to become more exposed and thereby gain resource-gathering benefits, for example, through a wider foraging niche. Frequency-dependent barriers (caused by enhanced conspicuousness relative to other prey and low levels of predator education) are generally assumed to make the evolution of aposematism particularly challenging. Using a deterministic, evolutionary model we show that aposematic display could evolve relatively easily if it enabled prey to move more freely around their environments, or become exposed in some other manner that provides fitness benefits unrelated to predation risk. Furthermore, the model shows that the traits of aposematic conspicuousness and behavior which lead to raised exposure positively affect each other, so that the optimal level of both tends to increase when the traits exist together, compared to when they exist in isolation. We discuss the ecological and evolutionary consequences of aposematism. One conclusion is that aposematism could be a key evolutionary innovation, because by widening habitat use it may promote adaptive radiation as a byproduct of enhanced ecological opportunity