Calculating Starvation Risk

Behavioural Biology and Obesity

Insecurity, Inequality, and Obesity in Affluent Societies ◽

10.5871/bacad/9780197264980.003.0004 ◽

2012 ◽

Author(s):

Trenton G. Smith

Keyword(s):

Body Weight ◽

Energy Homeostasis ◽

Population Level ◽

Broad Array ◽

Excessive Body Weight ◽

Calorie Diet ◽

Behavioural Biology ◽

The Impact ◽

Starvation Risk ◽

High Calorie Diet

While conventional wisdom holds that excessive body weight is the product of some combination of a high-calorie diet and a sedentary lifestyle, public health measures aimed at these factors have been met with only limited success. This chapter considers the possibility that obesity might be better understood in terms of the biologist's notion that humans and other animals evolved the ability to store body fat as an optimal response to the presence of starvation risk. Evidence from a broad array of disciplines is consistent with this view, including the neuroendocrinology of energy homeostasis, parallels between human and animal fattening behaviour, the effect of stress on dietary intake, population-level studies of the impact of economic insecurity on body weight and international variation in obesity rates.

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Managing uncertainty: information and insurance under the risk of starvation

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2002.1061 ◽

2002 ◽

Vol 357 (1427) ◽

pp. 1519-1526 ◽

Cited By ~ 70

Author(s):

Sasha R. X. Dall ◽

Rufus A. Johnstone

Keyword(s):

Value Of Information ◽

Food Sources ◽

Initial Increase ◽

Energy Reserves ◽

Relative Value ◽

Uncertainty Information ◽

Starvation Risk ◽

Overall Risk

In an uncertain world, animals face both unexpected opportunities and danger. Such outcomes can select for two potential strategies: collecting information to reduce uncertainty, or insuring against it. We investigate the relative value of information and insurance (energy reserves) under starvation risk by offering model foragers a choice between constant and varying food sources over finite foraging bouts. We show that sampling the variable option (choosing it when it is not expected to be good) should decline both with lower reserves and late in foraging bouts; in order to be able to reap the reduction in uncertainty associated with exploiting a variable resource effectively, foragers must be able to afford and compensate for an initial increase in the risk of an energetic shortfall associated with choosing the option when it is bad. Consequently, expected exploitation of the varying option increases as it becomes less variable, and when the overall risk of energetic shortfall is reduced. In addition, little activity on the variable alternative is expected until reserves are built up early in a foraging bout. This indicates that gathering information is a luxury while insurance is a necessity, at least when foraging on stochastic and variable food under the risk of starvation.

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Personality predicts individual responsiveness to the risks of starvation and predation

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2011.2227 ◽

2011 ◽

Vol 279 (1735) ◽

pp. 1919-1926 ◽

Cited By ~ 70

Author(s):

J. L. Quinn ◽

E. F. Cole ◽

J. Bates ◽

R. W. Payne ◽

W. Cresswell

Keyword(s):

Life Histories ◽

Parus Major ◽

Poor Quality ◽

Trade Off ◽

Quality Food ◽

Individual Personality ◽

Temporal And Spatial ◽

Time Spent Feeding ◽

Individual Responsiveness ◽

Starvation Risk

Theory suggests that individual personality is tightly linked to individual life histories and to environmental variation. The reactive–proactive axis, for example, is thought to reflect whether individuals prioritize productivity or survival, mutually exclusive options that can be caused by conflicts between foraging and anti-predation behaviour. Evidence for this trade-off hypothesis, however, is limited. Here, we tested experimentally whether exploration behaviour (EB), an assay of proactivity, could explain how great tits ( Parus major ) respond to changes in starvation and predation risk. Individuals were presented with two feeders, holding good or poor quality food, which interchanged between safe and dangerous positions 10 m apart, across two 24 h treatments. Starvation risk was assumed to be highest in the morning and lowest in the afternoon. The proportion of time spent feeding on good quality food (PTG) rather than poor quality food was repeatable within treatments, but individuals varied in how PTG changed with respect to predation- and starvation-risk across treatments. This individual plasticity variation in foraging behaviour was linked to EB, as predicted by the reactive–proactive axis, but only among individuals in dominant social classes. Our results support the trade-off hypothesis at the level of individuals in a wild population, and suggest that fine-scale temporal and spatial variation may play important roles in the evolution of personality.

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Mass-dependent predation risk and lethal dolphin–porpoise interactions

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2007.0786 ◽

2007 ◽

Vol 274 (1625) ◽

pp. 2587-2593 ◽

Cited By ~ 33

Author(s):

R MacLeod ◽

C.D MacLeod ◽

J.A Learmonth ◽

P.D Jepson ◽

R.J Reid ◽

...

Keyword(s):

Predation Risk ◽

Bottlenose Dolphins ◽

Flight Performance ◽

Energy Reserves ◽

Trade Off ◽

Fat Reserves ◽

Ecological Principle ◽

Mass Dependent ◽

Starvation Risk ◽

Individual Mass

In small birds, mass-dependent predation risk (MDPR) is known to make the trade-off between avoiding starvation and avoiding predation dependent on individual mass. This occurs because carrying increased fat reserves not only reduces starvation risk but also results in a higher predation risk due to reduced escape flight performance and/or the increased foraging exposure needed to maintain a higher body mass. In principle, the theory of MDPR could also apply to any animal capable of storing energy reserves to reduce starvation and whose escape performance decreases with increasing mass. We used a unique situation along certain parts of coastal Britain, where harbour porpoises ( Phocoena phocoena ) are pursued and killed but crucially not eaten by bottlenose dolphins ( Tursiops truncatus ), to investigate whether a MDPR effect can occur in non-avian species. We show that where high levels of dolphin ‘predation’ occur, porpoises carry significantly less energy reserves than would otherwise be expected and this equates to reducing by approximately 37% the length of time that a porpoise could survive without feeding. These results provide the first evidence that a mass-dependent starvation–predation risk trade-off may be a general ecological principle that can apply to widely different animal types rather than, as is currently thought, only to birds.

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