Adaptive behavior (ecology)

In behavioral ecology, an adaptive behavior is a behavior which contributes directly or indirectly to an individual's survival or reproductive success and is thus subject to the forces of natural selection.^[1] Examples include favoring kin in altruistic behaviors, female selection of the most fit male, and defending a territory or harem from rivals.

Conversely, a non-adaptive behavior is a behavior or trait that is counterproductive to an individual's survival or reproductive success. These might include altruistic behaviors which do not favor kin, adoption of unrelated young, and being a subordinate in a dominance hierarchy.

Adaptations are commonly defined as evolved solutions to recurrent environmental problems of survival and reproduction.^[2] Individual differences commonly arise through both heritable and nonheritable adaptive behavior. Both have been proven to be influential in the evolution of species adaptive behaviors, although heritable adaptation remains a controversial subject.^[2]

Nonheritable

Populations change through the process of evolution. Each individual in a population has a unique role in their particular environment. This role is commonly known as an ecological niche, and is simply how an organism lives in an environment in relation to others.^[3] Over successive generations, the organism must adapt to their surrounding conditions in order to develop their niche. An organism's niche will evolve as changes in the external environment occur. The most successful species in nature are those that are able to use adaptive behaviors to build on prior knowledge, thereby increasing their overall knowledge bank. In turn, this will increase their overall survival and reproductive success.

Learning

Many species have the ability to adapt through learning.^[3] Organisms will often learn through psychological processes, such as operant and classical conditioning, discrimination memory, and other cognitive processes.^[3] This learning process allows organisms to modify their behavior to survive in unpredictable environments.^[3] Organisms begin as naive individuals and learning allows them to obtain the knowledge they need to adapt and survive. It is important to remember that learnt adaptive behavior must have a psychological, as well as a biological, component. Without the integration of these two disciplines, behavioral adaptation cannot occur.

Kin selection

Kin selection (commonly referred to as altruism, even though it is just a sub-type) is an example of an adaptive behavior that directly influences the genetic composition of a population. It involves evolutionary strategies that favour the persistence of an organism's relatives, often at the cost of their own survival and reproduction.^[4] This will result in population gene frequency variation over successive generations, based on the interactions between related individuals. The probability of altruism increases when the cost is low for the donor, or when there is a high level of gain for the beneficiary. In addition, individuals often display altruistic behaviors when the relative is genetically similar to them.^[4] This means offspring or siblings are more likely to benefit from altruism than someone more distantly related, such as a cousin, aunt, or uncle.^[5] Kin selection has played a large role in the evolution of social and adaptive behaviors in chimpanzees. Closely related chimpanzees will form a kin group that cooperates to protect a territory, thereby increasing their access to females and resources.^[6] By working together with close relatives, they can ensure that their genes will persist in the next generation, even if circumstances make them unable to reproduce themselves.^[6] This behavioral adaptation coincides with chimpanzee's ability to distinguish kin from non-kin (referred to as visual kin selection).^[7] This allows chimpanzees to formulate large, complex societies, where they use altruistic methods to ensure their genes persist in future generations. A wide variety of species have displayed kin selection as an adaptive behavior. Examples include lions,^[8] honeybees,^[9] and insects.^[10]

Territorial defense

As mentioned above, chimpanzees work together with closely related kin to protect their territory. A territory can be simply defined as any defended area.^[11] Defending territory from rivals (known as territoriality) is a learnt adaptive behaviour performed by several ecological species. The advantage of being territorial varies depending on the species of interest. However, the underlying principle is always to increase their overall fitness.^[12] Many species will display territoriality in order to acquire food, compete for mates, or have the safest lair. Bird song is an example of learnt territorial defense. Studies show that birds with high-quality song will use it as a stimulus to deter predators from their territorial range.^[13] Higher quality songs have been proven to act as the best defense mechanisms in a variety of bird species, such as the red-winged blackbird (Agelaius phoeniceus).^[14] Therefore, correct learning of the birdsong early in life is necessary for territory defense in birds. European beavers (Castor fiber) are another species that use territory defense. Beavers are very defensive of their territory because they spend a great deal of time and energy becoming familiar with the location and building a habitat. They are unique because they have developed the technique of scent-marking as a way to intimidate intruders.^[15] This scent acts as a "psychological fence", thereby decreasing the possibility of injury or death by predation.

Controversy

There is debate regarding whether there is a biological component associated with the learning process in ecological adaptive behavior. Many researchers suggest that there is integration between biological and psychological disciplines; however others believe that the nonheritable component is strictly psychological, and argue that nonheritable traits cannot evolve over successive generations.^[16]

Heritable

Male northern elephant seals will fight to defend their harems from rival males, note the pink scaring on the neck of the dominant male.

Organisms can also express heritable adaptive behaviors. These behaviors are encoded in their genes and inherited from their parents. This gives species the ability to respond to situations with innate response mechanisms. Using this mechanism, they can respond appropriately to their internal and external environment without having to learn.^[3]

Natural selection

Heritable adaptive behavior evolves through natural selection in which some genes cause individuals to respond appropriately to environmental or physiological cues, thereby increasing reproductive success and causing these genes to persist in future generations; non-adaptive behaviors cause a decrease in reproductive success so the genes are lost from future generations.^[3] These adaptive and non-adaptive characteristics arise through random mutation, recombination, or genetic drift.^[2] Essentially, natural selection is a mechanism that contributes to directional gene selection in individuals that reproduce. Traits that cause greater reproductive success of an organism are favored, whereas those that reduce reproductive success are selected against.^[17][18]

In contrast to learning, natural selection is solely a biological concept. It is the biological and genetic component that allows an adaptive behavior to be inherited with no connection to the environment. This form of adaptive behavior is most commonly considered in ecological studies, and therefore natural selection is often used to explain ecological adaptive behavior in organisms.

Sexual selection

While kin selection is nonheritable and a direct result of the environment, sexual selection is a heritable adaptive behavior, and can therefore be characterized as a form of natural selection. Sexual selection refers specifically to competition for mates.^[19] Many traits or features that are characteristic of a certain species can be explained by sexual selection as an adaptive behavior; this is because competition for mates results in specific traits being inherited.^[19] Only the species that are able to successfully compete and obtain a mate will reproduce and pass their genes on to the next generation. Therefore, species-specific genetic traits must be inherited, allowing individuals to be successful in their designated environments. There are many environmental examples of sexual selection as an adaptive behavior; one popular example is sexual dimorphism. Sexual dimorphism is a morphological, phenotypic difference between males and females same species.^[20] A common example of sexual dimorphism is difference in body size.^[20] Sexual dimorphism can specifically be seen in the fish species, Lamprologus callipterus.^[21] These male fish are substantially larger (sometimes up to 60 times) than their female counterparts.^[21] The male's increased size is advantageous because the larger individual's are able to compete for female mates, and subsequently defend their offspring, which grow inside empty snail shells until birth.^[21] Basically, the larger the male fish, the bigger the adaptive benefit. The advantage of being larger and more powerful is demonstrated in the male's ability to compete and protect. In contrast to the males, the female fish must remain small in order to lay eggs inside the snail shells.^[21] It is evident that size plays a significant role in the reproductive success of this particular fish species.^[22] Large size is a common adaptive behavioral trait that is inherited through sexual selection and reproduction, as demonstrated in Lamprologus callipterus and other sexually dimorphic species.

Importance

It has been proven that adaptive behavior is crucial in the process of natural selection, and thus is important in the evolutionary process. Species that possess positive adaptive behaviors will inherently acquire evolutionary advantages. For example, adaptive behavior is a mechanism of population stabilization.^[23] In natural communities, organisms are able to interact with each other creating complex food webs and predator-prey dynamics. Adaptive behavior helps modulate the dynamics of feeding relationships by having a direct effect on their feeding traits and strategies.^[23] These adaptive behaviors allow for resilience and resistance in the face of disturbances and a changing environment.^[23] In ecology, the coexistence of organisms in natural ecosystems and the stability of populations are central topics. Currently, we live in a world experiencing great changes at a fast rate, mostly due to anthropogenic impacts on organisms and the environment.^[23] By studying adaptive behavior one can understand ecosystem complexity – how it emerges, how it evolves, and how it can be maintained.

Measurement

An organism's behavioral strategies and ability to adapt will determine how they respond under different environmental conditions. Fitness is a common measure of adaptive success, and can be defined as the number of descendants left over after a group exhibits a particular behavioral strategy.^[24] Successful strategies will result in increased survival and reproduction, which in turn can be characterized as a profitable behavioral adaption.

References