Table 1.

Definitions of key terms.

term	definition	examples
living system	A self-sustaining biological system, characterized by flows of energy, materials and information processing. Synonyms: biological system, ecological system.	Cells, organisms, populations, symbioses, some communities.
cue	Environmental variable (either abiotic or biotic) that triggers an event or process and is predictive of a future environmental condition [26].	Variable features of the environment such as photoperiod, temperature, rainfall. For example, temperature is an environmental cue for sexual reproduction in many algal species, dispersal in fish or diapause in invertebrates. By sensing cues early in the season, organisms can anticipate the best time to initiate seasonal reproduction, migration, dormancy, etc., or to produce a particular seasonal morph, thereby matching their phenotypes to the expected conditions [27].
signal	Signals have four components [28]: (1) acts or structures produced by signalers, which (2) evolved for the purpose of conveying information to recipients, such that (3) the information elicits a response in recipients, and (4) the response results in fitness consequences that, on average, are positive for both the signaller and the recipient. By contrast to cues, which may contain information as a by-product of organisms' behaviour, signals have evolved for the specific purpose of conveying information and influencing others’ behaviour.	Pheromone trails laid by ants, peacocks' ornamented tail, electric pulses used by electric fish to communicate in water, bird songs.
prediction	A probabilistic conditional expectation about the future, informed by past and present events and an internal model. Allows organisms to prepare for impending changes in the environment [16]. ‘Prediction is not prescience but simply “output from an anticipatory model”’ [25].	Cells can internalize correlations between multiple environmental variables (e.g. temperature and oxygen), which allows them to express an appropriate energy-extracting metabolic pathway at the right time. Predictive behaviour is in contrast to stochastic switching, or diversified bet hedging, which allows for diverse phenotypes but does not require prediction of any particular future environmental state.
internal model	A simplified description of a system [25]. In organisms, this may be the physical instantiation of a probabilistic model [16]. We learn something new about a system by studying its internal model.	A model can be encoded in the pathways of a gene or metabolic regulatory network.
feedback homeostatic control	A process or mechanism whereby a system quantity can be returned to a constant level (the set-point), within a fluctuating environment. A deviation from the controlled set-point is countered by a controller that modifies the dynamics of the controlled system so as to diminish the error [29]. Homeostasis typically involves a negative feedback loop that counteracts the error. This type of control only responds to the state of the controlled system rather than that of the environment.	Thermoregulation in endotherms, food switching to achieve stoichiometric homeostasis (i.e. regulate elemental composition) [30,31].
feedforward homeostatic control	In a feedforward system, the control variable adjustment is not based on the self-state. Rather, the controller senses an environmental quantity, e(t), whose value is correlated to a likely future value of the state of the controlled system, z(t + τ). This introduces the role of prediction. The controller can modify the dynamics of z(t) according to the present value of e(t) and the state of z(t), so as to maintain constant the state of z(t). In feedforward control, disturbances are detected and accounted for before they have time to affect the system.	Negative phototropism, autumnal plant cessation of growth, immune priming, heat hardening, etc.
anticipatory system	To anticipate means to expect or predict. Rosen [24] defined an anticipatory system as a natural system that contains an internal predictive model of itself and of its environment, which allows it to change state in accord with the model's predictions pertaining to a later instant. In contrast to a reactive system, which can only react in the present to changes that have already occurred in the causal chain, an anticipatory system's present behaviour involves aspects of past, present and future.	An individual organism (an Escherichia coli cell, a tree, a copepod), any natural system that contains an internal model. See table 2.
phenotypic plasticity	Phenotypic plasticity refers to the ability of a single genotype to produce different phenotypes under different environmental conditions [27]. To do so organisms may use cues.	Plastic responses such as changes in development, behaviour and allocation of resources to competing demands can allow individuals to match their phenotypes (or those of their offspring, in the case of plastic maternal effects) to spatial or temporal variations in their abiotic and biotic environments. For phenotypic plasticity to be effective, organisms must be able to accurately forecast environmental challenges affecting their fitness.
colour of environmental noise (spectral colour)	Refers to the power spectrum of a stochastic environmental signal estimated by a Fourier analysis of the signal. By analogy to light, the colour refers to the profile of power across the signal's frequency spectrum [32].	Pink or red noise corresponds to variation that has more power at low frequencies; white noise is temporally uncorrelated and variance is spread equally across all frequencies [32,33].