Predation risk allocation hypothesis

Last updated

The predation risk allocation hypothesis attempts to explain how and why animals' behaviour and foraging strategies differ in various predatory situations, depending on their risk of endangerment. [1] The hypothesis suggests that an animal's alertness and attention, along with its willingness to hunt for food, will change depending on the risk factors within that animal's environment and the presence of predators that could attack. The model assumes there are different levels of risk factors within various environments and prey animals will behave more cautiously when they are found in high-risk environments. [2] The overall effectiveness of the model for predicting animal behaviour varies, therefore, its results are dependent on the prey species used in the model and how their behaviour changes. There are several reasons the predation risk allocation hypothesis was developed to observe how animal behaviour varies depending on its risk factors. Mixed results have been found for the model's effectiveness in predicting predator defensive behaviour for various species.

Contents

Hypothesis background

The hypothesis attempts to explain how animals demonstrate anti-predator behaviours in different environments depending on risk factors, i.e. predatory threats. [1] Threat levels can vary among different habitats, depending on the type of terrain and other animals inhibiting that zone.

There are two main predictions used in the predation risk allocation hypothesis. The first assumes that animals will increase foraging in safer environments, at times when predators are not present. The predicted advantage of foraging while predators are absent allows animals to eat and gain energy to then fight against predators upon their arrival. [2]

The second prediction anticipates that animals will demonstrate less anti-predator behaviours when they have been in a high-risk environment for a long period of time. [3] [1] When significant time has passed in the same environmental location, the animal needs to eat to survive, therefore they are more likely to forage and spend less energy defending against predators when they have been in the same environment for a long period of time. These animals have to be less selective over their foraging times since they are not left with many options. [3] [1]

The model cannot be used for animals that exhibit control over their predation risk. These animals would not demonstrate the anticipated behavioural responses in accordance with the hypothesis predictions. [1] For instance, if animals could control their predation risk, they would not exhibit avoidance behaviours in response to predation in safer situations and therefore not supporting the hypothesis. [1] Another observation found animals with more time to learn about risk factors in their habitats were then better able to demonstrate behaviours found to be consistent with this hypothesis. [4] Likewise, those animals without sufficient time to learn or understand the risk factors in their area will not display behaviours that support the hypothesis. [4]

Case studies

Various studies have observed the effectiveness of the predation risk allocation hypothesis for both vertebrate and invertebrate animals. The results both support and refute the hypothesis.

Snails

Freshwater physid snails (Physella gyrina) act in accordance with the hypothesis in response to crayfish predators in their environments. The snails' frequency of activity, response to predators and interaction behaviours with their environments have been observed in different contexts. The physid snails' behaviour occurs in response to the level of predatory threat in their habitat area, they increase foraging and demonstrate higher activity measures in lower predation risk levels whereas they will decrease these behaviours in high risk predation areas. [5]

Fish

Male Convict Cichlid Male Convict Cichlid.jpg
Male Convict Cichlid

The convict cichlids (Archocentrus nigrofasciatus) have been observed in two different contexts, high and low-risk predatory settings. These fish behave with less anti-predator and foraging behaviours when located in dangerous predatory areas, high-risk compared to the low-risk zones. These behaviour adjustments in various contexts support the risk allocation hypothesis since the animals follow its assumptions. [2]

Tadpoles

Tadpoles of the pool frog (Rana lessonae) do not follow the predictions risk allocation hypothesis with their foraging behaviours. Tadpoles were observed and these animals did not increase their foraging behaviours in zones with less threat. Instead, they continued a constant feeding pattern, not dependent on their living condition. [3]

Voles

Bank voles Bank voles.jpg
Bank voles

Behaviour of bank voles (Clethrionomys glareolus) in response to least weasel prey does not support the risk allocation hypothesis, which can demonstrate that bank voles cannot assess risk in their territories. There were no changes in the foraging behaviours in different risk contexts or the amount of time these animals spent in these zones. The voles demonstrated more anti-predator behaviour in the high-risk situation however they did not increase their foraging behaviour in the high-risk zones. Since the bank vole behaviour was not demonstrated as predicted in both zones, they cannot be used to support the hypothesis. [6]

Hypothesis application

The predation risk allocation hypothesis can help researchers learn how animals make behavioural responses to predators, since it is the first research that observes temporal variation in different risk situations. [7] Animals' responses to predators can be better understood by observing behaviour adjustments to modified risk levels. The hypothesis however, does not explain behaviour in all types of variable risk situations, since this concept assumes that risk levels in every environment will change over time. [7] The risk allocation hypothesis best supports observations of animal behaviour for those animals that developed and evolved in the same environments where they received information about that zone's local predators. [8] These animals would therefore be most informed on what to expect and how to react in their environments. [8] Animals that are exposed to risky situations i.e. predation, more frequently, may demonstrate similar behaviours in both high-risk and safe situations due to habituation. [9] These animals become used to the constant threat and therefore would not act the same compared to animals who are not used to high-risk situations since they have become more immune to these instances. [9]

Related Research Articles

<span class="mw-page-title-main">Predation</span> Biological interaction

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism. It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators.

<span class="mw-page-title-main">Crepuscular animal</span> Animal behavior primarily characterized by activity during the twilight

In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal, vespertine/vespertinal, or both. This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylight and of darkness, respectively. Some crepuscular animals may also be active by moonlight or during an overcast day. Matutinal animals are active only before sunrise, and vespertine only after sunset.

<span class="mw-page-title-main">Foraging</span> Searching for wild food resources

Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavior of animals in response to the environment where the animal lives.

<span class="mw-page-title-main">Anti-predator adaptation</span> Defensive feature of prey for selective advantage

Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.

<i>Schreckstoff</i> Alarm substance in ostariophysan fish

In 1938, the Austrian ethologist Karl von Frisch made his first report on the existence of the chemical alarm signal known as Schreckstoff in minnows. An alarm signal is a response produced by an individual, the "sender", reacting to a hazard that warns other animals, the receivers, of danger. This chemical alarm signal is released only when the sender incurs mechanical damage, such as when it has been caught by a predator, and is detected by the olfactory system. When this signal reaches the receivers, they perceive a greater predation risk and exhibit an antipredator response. Since populations of fish exhibiting this trait survive more successfully, the trait is maintained via natural selection. While the evolution of this signal was once a topic of great debate, recent evidence suggests schreckstoff evolved as a defense against environmental stressors such as pathogens, parasites, and UVB radiation and that it was later co-opted by predators and prey as a chemical signal.

Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different from their species in a way that makes it more likely for them to be ignored by their predators. It operates on polymorphic species, species which have different forms. In apostatic selection, the common forms of a species are preyed on more than the rarer forms, giving the rare forms a selective advantage in the population. It has also been discussed that apostatic selection acts to stabilize prey polymorphisms.

<span class="mw-page-title-main">Alarm signal</span> Signal made by social animals to warn others of danger

In animal communication, an alarm signal is an antipredator adaptation in the form of signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning conspecifics of approaching predators. For example, the alarm call of the blackbird is a familiar sound in many gardens. Other animals, like fish and insects, may use non-auditory signals, such as chemical messages. Visual signs such as the white tail flashes of many deer have been suggested as alarm signals; they are less likely to be received by conspecifics, so have tended to be treated as a signal to the predator instead.

<span class="mw-page-title-main">Cathemerality</span> Irregular organismal activity pattern

Cathemerality, sometimes called "metaturnality", is an organismal activity pattern of irregular intervals during the day or night in which food is acquired, socializing with other organisms occurs, and any other activities necessary for livelihood are undertaken. This activity differs from the generally monophasic pattern of nocturnal and diurnal species as it is polyphasic and is approximately evenly distributed throughout the 24-hour cycle.

<span class="mw-page-title-main">Phenotypic plasticity</span> Trait change of an organism in response to environmental variation

Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompasses all types of environmentally induced changes that may or may not be permanent throughout an individual's lifespan.

<span class="mw-page-title-main">Mobbing (animal behavior)</span> Antipredator adaptation in which individuals of prey species cooperatively attack a predator

Mobbing in animals is an antipredator adaptation in which individuals of prey species cooperatively attack or harass a predator, usually to protect their offspring. A simple definition of mobbing is an assemblage of individuals around a potentially dangerous predator. This is most frequently seen in birds, though it is also known to occur in many other animals such as the meerkat and some bovines. While mobbing has evolved independently in many species, it only tends to be present in those whose young are frequently preyed upon. This behavior may complement cryptic adaptations in the offspring themselves, such as camouflage and hiding. Mobbing calls may be used to summon nearby individuals to cooperate in the attack.

Prey detection is the process by which predators are able to detect and locate their prey via sensory signals. This article treats predation in its broadest sense, i.e. where one organism eats another.

Prey switching is frequency-dependent predation, where the predator preferentially consumes the most common type of prey. The phenomenon has also been described as apostatic selection, however the two terms are generally used to describe different parts of the same phenomenon. Apostatic selection has been used by authors looking at the differences between different genetic morphs. In comparison, prey switching has been used when describing the choice between different species.

The selfish herd theory states that individuals within a population attempt to reduce their predation risk by putting other conspecifics between themselves and predators. A key element in the theory is the domain of danger, the area of ground in which every point is nearer to a particular individual than to any other individual. Such antipredator behavior inevitably results in aggregations. The theory was proposed by W. D. Hamilton in 1971 to explain the gregarious behavior of a variety of animals. It contrasted the popular hypothesis that evolution of such social behavior was based on mutual benefits to the population.

Antipredatory behaviors are actions an animal performs to reduce or rid themselves of the risk of being prey. Many studies have been done on elk to see what their antipredator behaviors consist of.

Animals have many different tactics for defending themselves, depending on the severity of the threat they are encountering. Stages of threat vary along a spectrum referred to as the "predatory imminence continuum", spanning from low-risk (pre-encounter) to high-risk (interaction) threats. The main assumption of the predatory imminence continuum is that as threat levels increase, defensive response strategies change. During the pre-encounter period, an animal may engage in activities like exploration or foraging. But if the animal senses that a predator is nearby, the animal may begin to express species specific defense reactions such as freezing in an attempt to avoid detection by the predator. However, in situations where a threat is imminent, once the animal is detected by its predator, freezing may no longer be the optimal behaviour for survival. At this point, the animal enters the circa-strike phase, where its behaviour will transition from passive freezing to active flight, or even attack if escape is not possible.

Vigilance, in the field of behavioural ecology, refers to an animal's monitoring of its surroundings in order to heighten awareness of predator presence. Vigilance is an important behaviour during foraging as animals must often venture away from the safety of shelter to find food. However, being vigilant comes at the expense of time spent feeding, so there is a trade-off between the two. The length of time animals devote to vigilance is dependent on many factors including predation risk and hunger.

<span class="mw-page-title-main">Pursuit predation</span> Hunting strategy by some predators

Pursuit predation is a form of predation in which predators actively give chase to their prey, either solitarily or as a group. It is an alternate predation strategy to ambush predation — pursuit predators rely on superior speed, endurance and/or teamwork to seize the prey, while ambush predators use concealment, luring, exploiting of surroundings and the element of surprise to capture the prey. While the two patterns of predation are not mutually exclusive, morphological differences in an organism's body plan can create an evolutionary bias favoring either type of predation.

Native to both South and Central America, Cane toads were introduced to Australia in the 1930s and have since become an invasive species and a threat to the continent's native predators and scavengers.

Pollutant-induced abnormal behaviour refers to the abnormal behaviour induced by pollutants. Chemicals released into the natural environment by humans impact the behaviour of a wide variety of animals. The main culprits are endocrine-disrupting chemicals (EDCs), which mimic, block, or interfere with animal hormones. A new research field, integrative behavioural ecotoxicology, is emerging. However, chemical pollutants are not the only anthropogenic offenders. Noise and light pollution also induce abnormal behaviour.

<span class="mw-page-title-main">Hunting success</span> Likelihood of a hunt ending in success

In ecology, hunting success is the proportion of hunts initiated by a predatory organism that end in success. Hunting success is determined by a number of factors such as the features of the predator, timing, different age classes, conditions for hunting, experience, and physical capabilities. Predators selectivity target certain categories of prey, in particular prey of a certain size. Prey animals that are in poor health are targeted and this contributes to the predator's hunting success. Different predation strategies can also contribute to hunting success, for example, hunting in groups gives predators an advantage over a solitary predator, and pack hunters like lions can kill animals that are too powerful for a solitary predator to overcome.

References

  1. 1 2 3 4 5 6 Lima and Bednekoff. (1999) Temporal Variation in Danger Drives Antipredator Behavior: The Predation Risk Allocation HypothesisThe American Naturalist, 177, 143-146
  2. 1 2 3 Ferrari, M. C. O., Sih, A., & Chivers, D. P. (2009) The paradox of risk allocation: A review and prospectus. Animal Behaviour, 78, 579-585
  3. 1 2 3 Buskirk, J. V., Muller, C., Portmann, A., & Surbeck, M. (2002) A test of the risk allocation hypothesis: Tadpole responses to temporal change in predation risk. Ecology, 13, 526-530.
  4. 1 2 Ferrari, M. C. O., Rive, A. C., MacNaughton, C. J., Brown, G. E., & Chivers, D. P. (2008) Fixed vs. random temporal predictability of predation risk: An extension of the risk allocation hypothesis. Ethology, 114, 238-244.
  5. Sih, A., & McCarthy, T. M. (2002) Prey responses to pulses of risk and safety: Testing the risk allocation hypothesis. Animal Behaviour, 63, 437-443
  6. Sundell, J., Dudek, D., Klemme, I., Koivisto, E., Pusenius, J., & Ylönen, H. (2004) Variation in predation risk and vole feeding behaviour: A field test of the risk allocation hypothesis Oecologia, 139, 157-162
  7. 1 2 Lima, S. L.; Bednekoff, P. A. (1999). "Temporal variation in danger drives antipredator behaviour: The predation risk allocation hypothesis". The American Naturalist. 153: 649–659. doi:10.2307/2463621. JSTOR   2463621.
  8. 1 2 Luttbeg, B. (2017). "Re-examining the causes and meaning of the risk allocation hypothesis". The American Naturalist. 189 (6): 644–656. doi:10.1086/691470. PMID   28514637. S2CID   3907603.
  9. 1 2 Mirza, R. S., Mathis, A., Chivers, D. P. (2005). Does Temporal Variation in Predation Risk Influence the Intensity of Antipredator Responses? A Test of the Risk Allocation Hypothesis. Ethology, 112, 44-51.