Behavioral ecology
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Behavioral ecology is the study of the ecological and evolutionary 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 (bats) due to is adaptive significance of increased ability to escape from predators and move swiftly between habitat areas, amongst others, which increase the organisms chance of survival and ultimately their reproductive success. 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 Stories" 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.[1] 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 and the now extinct Dodo demonstrate in the absence of natural predators prior to human colonization.
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[edit] Proximate causation
Proximate causation is also divided into two factors which are ontogenetic 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.
[edit] Optimization theory
Behavioral ecology, along with other areas of evolutionary biology, has incorporated a number of techniques which have been borrowed from optimization theory. Optimization 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).
[edit] Differential reproductive success
Ultimately, behavior is subject to natural selection 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."
[edit] Evolutionarily stable strategies
Another driving force in the evolution of animal behavior is the concept of an evolutionarily stable strategy (or ESS), a term derived from economic game theory which became prominent after John Maynard Smith(1982) [2] 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.
[edit] See also
[edit] References
[edit] Further reading
- J.R. Krebs and Nicholas Davies, An Introduction to Behavioural Ecology, ISBN 0-632-03546-3
- J.R. Krebs and Nicholas Davies, Behavioural Ecology: an evolutionary approach, ISBN 0-86542-731-3
