Behavioral ecology
Encyclopedia
Behavioral ecology, or ethoecology, is the study of the ecological
and evolution
ary basis for animal behavior, and the roles of behavior in enabling an animal to adapt to its environment (both intrinsic and extrinsic). Behavioral ecology emerged from ethology
after Niko Tinbergen (a seminal figure in the study of animal behavior) outlined the four causes of behavior
.
If an organism has a trait which provides them with a selective advantage (i.e. has an adaptive significance) in a new environment natural selection will likely favor it. Adaptive significance therefore refers to the beneficial qualities, in terms of increased survival and reproduction, a trait conveys.
For example, the behavior of flight
has evolved numerous times in reptiles (Pterosaur
), birds, many insects and mammals (bat
s) due to its adaptive significance—for many species, flight has the potential to increase an animal's ability to escape from predators and move swiftly between habitat areas, among other things, thereby increasing the organism's chances of survival and reproduction. In all instances, the organism adapting to flight
had to have "pre-adaptions" to these behavioral and anatomical changes. Feathers in birds initially evolving for thermoregulation
then turned to flight due to the benefits conveyed (see Origin of avian flight
); insect wings evolving from enlarged gill plates used to efficiently "sail" across the water, becoming larger until capable of flight are two good examples of this. At every stage slight improvements mean higher energy acquisition, lower energy expenditure or increased mating opportunities causing the genes that convey these traits to increase within the population. If these organisms did not have the required variation for natural selection to act upon either due to phylogenetic or genetic constraints, these behaviors would not be able to evolve.
However, it is not sufficient to apply these explanations where they seem convenient. Viewing traits and creating unsubstantiated theories or "Just-so story
" as to their adaptive nature have been deeply criticized. Stephen Jay Gould
and Richard Lewontin
(1979) described this as the "adaptationist programme". To be rigorous, hypotheses regarding adaptations must be theoretically or experimentally tested as with any scientific theory.
The hypothesis of the evolution of insect flight for example has been tested through wing manipulation experiments. Empirical observations which adhere to the conditions prosed also provide evidence. For instance, one can suppose that when birds are not at risk of being eaten they might lose the ability to fly as the construction of functional wings are costly to produce and take away energy which could be used to increase offspring production or survival, a trend many island flightless birds such as the Kakapo
, the Penguin
and the now extinct Dodo
demonstrate in the absence of natural predators.
and mechanistic. Ontogenetic factors are the entire sum of experience throughout the lifetime of an individual from embryo to death. Hence, factors included are learning the genetic factors giving rise to behavior in individuals. Mechanistic factors, as the name implies, are the processes of the body that give rise to behavior such as the effects of hormones on behavior and neuronal basis of behavior.
is a concept that stipulates strategies that offer the highest return to an animal given all the different factors and constraints facing the animal. One of the simplest ways to arrive at an optimal solution is to do a cost/benefit analysis. By considering the advantages of a behavior and the costs of a behavior, it can be seen that if the costs outweigh the benefits then a behavior will not evolve and vice versa. This is also where the concept of the trade-off becomes important. This is because it rarely pays an animal to invest maximally in any one behavior. For example, the amount of time an ectothermic animal such as a lizard spends foraging is constrained by its body temperature. The digestive efficiency of the lizard also increases with increases in body temperature. Lizards increase their body temperature by basking in the sun. However, the time spent basking decreases the amount of time available for foraging. Basking also increases the risk of being discovered by a predator. Therefore, the optimal basking time is the outcome of the time necessary to sufficiently warm itself to carry out its activities such as foraging
. This example shows how foraging is constrained by the need to bask (intrinsic constraint) and predation
pressure (extrinsic constraint).
A often quoted behavioral ecology hypothesis is known as Lack's brood reduction hypothesis (named after David Lack
). Lack's hypothesis posits an evolutionary and ecological explanation as to why birds lay a series of eggs with an asynchronous delay leading to nestlings of mixed age and weights. According to Lack, this brood behavior is an ecological insurance that allows the larger birds to survive in poor years and all birds to survive when food is plentiful.
just as with any other trait. Therefore animals that employ optimal behavioral strategies specific to their environment will generally leave greater numbers of offspring than their suboptimal conspecifics. Animals that leave a greater number of offspring than others of their own species are said to have greater fitness. However, environments change over time. What might be good behavior today might not be the best behavior in 10,000 years time or even 10 years time. The behavior of animals has and will continue to change in response to the environment. Behavioral ecology is one of the best ways to study these changes. As geneticist Theodosius Dobzhansky
famously wrote, "nothing in biology makes sense except in the light of evolution."
(or ESS). This term, derived from economic game theory
, became prominent after John Maynard Smith
(1982) recognized the possible application of the concept of a Nash equilibrium
to model the evolution of behavioral strategies.
In short, evolutionary game theory
asserts that only strategies
that, when common in the population, cannot be "invaded" by any alternative (mutant) strategy will be an ESSs, and thus maintained in the population. In other words, at equilibrium every player should play the best strategic response to each other. When the game is two player and symmetric each player should play the strategy which is the best response to itself.
Therefore, the ESS is considered to be the evolutionary end point subsequent to the interactions. As the fitness conveyed by a strategy is influenced by what other individuals are doing (the relative frequency of each strategy in the population), behavior can be governed not only by optimality but the frequencies of strategies adopted by others and are therefore frequency dependent (frequency dependence
).
Behavioral evolution is therefore influenced by both the physical environment and interactions between other individuals.
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary basis for animal behavior, and the roles of behavior in enabling an animal to adapt to its environment (both intrinsic and extrinsic). Behavioral ecology emerged from ethology
Ethology
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....
after Niko Tinbergen (a seminal figure in the study of animal behavior) outlined the four causes of behavior
Tinbergen's four questions
Tinbergen's four questions, named after Nikolaas Tinbergen, are complementary categories of explanations for behavior. It suggests that an integrative understanding of behavior must include both a proximate and ultimate analysis of behavior, as well as an understanding of both...
.
If an organism has a trait which provides them with a selective advantage (i.e. has an adaptive significance) in a new environment natural selection will likely favor it. Adaptive significance therefore refers to the beneficial qualities, in terms of increased survival and reproduction, a trait conveys.
For example, the behavior of flight
Flight
Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....
has evolved numerous times in reptiles (Pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
), birds, many insects and mammals (bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s) due to its adaptive significance—for many species, flight has the potential to increase an animal's ability to escape from predators and move swiftly between habitat areas, among other things, thereby increasing the organism's chances of survival and reproduction. In all instances, the organism adapting to flight
Flight
Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....
had to have "pre-adaptions" to these behavioral and anatomical changes. Feathers in birds initially evolving for thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
then turned to flight due to the benefits conveyed (see Origin of avian flight
Origin of avian flight
Around 350 BCE, Aristotle and other philosophers of the time were attempting to explain the aerodynamics of avian flight. Even after the discovery of the ancestral bird Archaeopteryx, over 150 years ago, debates still persist regarding the evolution of flight...
); insect wings evolving from enlarged gill plates used to efficiently "sail" across the water, becoming larger until capable of flight are two good examples of this. At every stage slight improvements mean higher energy acquisition, lower energy expenditure or increased mating opportunities causing the genes that convey these traits to increase within the population. If these organisms did not have the required variation for natural selection to act upon either due to phylogenetic or genetic constraints, these behaviors would not be able to evolve.
However, it is not sufficient to apply these explanations where they seem convenient. Viewing traits and creating unsubstantiated theories or "Just-so story
Just-so story
A just-so story, also called the ad hoc fallacy, is a term used in academic anthropology, biological sciences, social sciences, and philosophy. It describes an unverifiable and unfalsifiable narrative explanation for a cultural practice, a biological trait, or behavior of humans or other animals...
" as to their adaptive nature have been deeply criticized. Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
and Richard Lewontin
Richard Lewontin
Richard Charles "Dick" Lewontin is an American evolutionary biologist, geneticist and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the notion of using techniques from molecular biology such as gel electrophoresis to...
(1979) described this as the "adaptationist programme". To be rigorous, hypotheses regarding adaptations must be theoretically or experimentally tested as with any scientific theory.
The hypothesis of the evolution of insect flight for example has been tested through wing manipulation experiments. Empirical observations which adhere to the conditions prosed also provide evidence. For instance, one can suppose that when birds are not at risk of being eaten they might lose the ability to fly as the construction of functional wings are costly to produce and take away energy which could be used to increase offspring production or survival, a trend many island flightless birds such as the Kakapo
Kakapo
The Kakapo , Strigops habroptila , also called owl parrot, is a species of large, flightless nocturnal parrot endemic to New Zealand...
, the Penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
and the now extinct Dodo
Dodo
The dodo was a flightless bird endemic to the Indian Ocean island of Mauritius. Related to pigeons and doves, it stood about a meter tall, weighing about , living on fruit, and nesting on the ground....
demonstrate in the absence of natural predators.
Proximate causation
Proximate causation is also divided into two factors which are ontogeneticOntogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
and mechanistic. Ontogenetic factors are the entire sum of experience throughout the lifetime of an individual from embryo to death. Hence, factors included are learning the genetic factors giving rise to behavior in individuals. Mechanistic factors, as the name implies, are the processes of the body that give rise to behavior such as the effects of hormones on behavior and neuronal basis of behavior.
Optimization theory
Behavioral ecology, along with other areas of evolutionary biology, has incorporated a number of techniques which have been borrowed from optimization theory. OptimizationOptimization (mathematics)
In mathematics, computational science, or management science, mathematical optimization refers to the selection of a best element from some set of available alternatives....
is a concept that stipulates strategies that offer the highest return to an animal given all the different factors and constraints facing the animal. One of the simplest ways to arrive at an optimal solution is to do a cost/benefit analysis. By considering the advantages of a behavior and the costs of a behavior, it can be seen that if the costs outweigh the benefits then a behavior will not evolve and vice versa. This is also where the concept of the trade-off becomes important. This is because it rarely pays an animal to invest maximally in any one behavior. For example, the amount of time an ectothermic animal such as a lizard spends foraging is constrained by its body temperature. The digestive efficiency of the lizard also increases with increases in body temperature. Lizards increase their body temperature by basking in the sun. However, the time spent basking decreases the amount of time available for foraging. Basking also increases the risk of being discovered by a predator. Therefore, the optimal basking time is the outcome of the time necessary to sufficiently warm itself to carry out its activities such as foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
. This example shows how foraging is constrained by the need to bask (intrinsic constraint) and predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
pressure (extrinsic constraint).
A often quoted behavioral ecology hypothesis is known as Lack's brood reduction hypothesis (named after David Lack
David Lack
David Lambert Lack FRS, was a British evolutionary biologist who made contributions to ornithology, ecology and ethology. His book on the finches of the Galapagos Islands was a landmark work.- Early life :...
). Lack's hypothesis posits an evolutionary and ecological explanation as to why birds lay a series of eggs with an asynchronous delay leading to nestlings of mixed age and weights. According to Lack, this brood behavior is an ecological insurance that allows the larger birds to survive in poor years and all birds to survive when food is plentiful.
Differential reproductive success
Ultimately, behavior is subject to natural selectionNatural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
just as with any other trait. Therefore animals that employ optimal behavioral strategies specific to their environment will generally leave greater numbers of offspring than their suboptimal conspecifics. Animals that leave a greater number of offspring than others of their own species are said to have greater fitness. However, environments change over time. What might be good behavior today might not be the best behavior in 10,000 years time or even 10 years time. The behavior of animals has and will continue to change in response to the environment. Behavioral ecology is one of the best ways to study these changes. As geneticist Theodosius Dobzhansky
Theodosius Dobzhansky
Theodosius Grygorovych Dobzhansky ForMemRS was a prominent geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis...
famously wrote, "nothing in biology makes sense except in the light of evolution."
Evolutionarily stable strategies
The value of a social behavior depends in part on the social behavior of an animal's neighbors. For example, the more likely a rival male is to back down from a threat, the more value a male gets out of making the threat. The more likely, however, that a rival will attack if threatened, the less useful it is to threaten other males. When a population exhibits a number of interacting social behaviors such as this, it can evolve a stable pattern of behaviors known as an evolutionarily stable strategyEvolutionarily stable strategy
In game theory and behavioural ecology, an evolutionarily stable strategy , which is sometimes also called an evolutionary stable strategy, is a strategy which, if adopted by a population of players, cannot be invaded by any alternative strategy that is initially rare. An ESS is an equilibrium...
(or ESS). This term, derived from economic game theory
Game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
, became prominent after John Maynard Smith
John Maynard Smith
John Maynard Smith,His surname was Maynard Smith, not Smith, nor was it hyphenated. F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he took a second degree in genetics under the well-known biologist J.B.S....
(1982) recognized the possible application of the concept of a Nash equilibrium
Nash equilibrium
In game theory, Nash equilibrium is a solution concept of a game involving two or more players, in which each player is assumed to know the equilibrium strategies of the other players, and no player has anything to gain by changing only his own strategy unilaterally...
to model the evolution of behavioral strategies.
In short, evolutionary game theory
Evolutionary game theory
Evolutionary game theory is the application of Game Theory to evolving populations of lifeforms in biology. EGT is useful in this context by defining a framework of contests, strategies and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Maynard Smith...
asserts that only strategies
Strategy (game theory)
In game theory, a player's strategy in a game is a complete plan of action for whatever situation might arise; this fully determines the player's behaviour...
that, when common in the population, cannot be "invaded" by any alternative (mutant) strategy will be an ESSs, and thus maintained in the population. In other words, at equilibrium every player should play the best strategic response to each other. When the game is two player and symmetric each player should play the strategy which is the best response to itself.
Therefore, the ESS is considered to be the evolutionary end point subsequent to the interactions. As the fitness conveyed by a strategy is influenced by what other individuals are doing (the relative frequency of each strategy in the population), behavior can be governed not only by optimality but the frequencies of strategies adopted by others and are therefore frequency dependent (frequency dependence
Frequency dependent selection
Frequency-dependent selection is the term given to an evolutionary process where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population. In positive frequency-dependent selection the fitness of a phenotype increases as it becomes more common...
).
Behavioral evolution is therefore influenced by both the physical environment and interactions between other individuals.
Further reading
- J.R. KrebsJohn KrebsJohn Richard Krebs, Baron Krebs FRS is a world leader in zoology and more specifically bird behaviour. He is currently the Principal of Jesus College, Oxford University...
and Nicholas Davies, An Introduction to Behavioural Ecology, ISBN 0-632-03546-3 - J.R. KrebsJohn KrebsJohn Richard Krebs, Baron Krebs FRS is a world leader in zoology and more specifically bird behaviour. He is currently the Principal of Jesus College, Oxford University...
and Nicholas Davies, Behavioural Ecology: an evolutionary approach, ISBN 0-86542-731-3