Organismal Biology





Key Concepts




Chapter  16 - Animals -






Behavior Patterns



The study of animal behavior in their natural habitats is called ethology, although it isn't wrong to call these researchers animal behaviorists.  When animal behavior is studied, there are a few basic behavior patterns that are looked for.

Behavior that seems "hard-wired" in, called variously instinctive, sterotyped, or fixed action patterns, generally presents as widely predictable reactions to particular stimuli.  There is, of course, a strong genetic element to behavior that's basically pre-programmed, but it has been found in some cases that complex behaviors may have relatively simple genetic components.  Stimuli that trigger such responses are called releasers, which can sometimes be reduced down to some critical detail of the releaser, the sign stimulus.  For flowers that entice beetle pollinators with sex, the flower does not have to duplicate a female, just a smell and a simplified abdomen;  males land on the flower to "mate," unaware that this is not a female.  Instinctive behavior is not totally unchangeable, as seen in many domestic animals, but changes are best accomplished by understanding the triggers and the various ways that the responses can play out and be therefore altered.

Behavior that grows and changes based upon experience is learned behavior;  it may be platformed on a stereotyped behavior which changes.  A frog follows instinctive responses to orient to and snatch up small prey animals, but when a particular type of prey turns out to be a bad choice, such as a bee or a millipede, the frog learns to avoid those animals, often now programmed in as a response to warning colors.  This requires some ability to connect cause and effect.  In this example, the frogs show sensitization:  they are sensitized to a stimulus, high-contrast markings or black markings,  that did not previously produce a particular response.  Frogs may also show habituation, a reduction of response to things that they are "used to":  early in their lives, they might dive for cover when any larger animal moves nearby, but later, they might ignore nonpredators like ducks.

One type of combined behavior pattern is imprinting, usually a particular type of learning that is strongly instinctive.  To sing a proper song, male canaries must be exposed to adult male song during a critical window of time while they are young.  If they are not exposed to proper song, or are exposed before or after that time window, they will sing as adults, but won't produce a song that females will respond to.  For a short time after hatching, baby geese will imprint on any large animal near them (that is, the sign stimuli are size and movement);  once imprinted, they will follow that animal wherever it goes.  In the wild, that large animal would always be a parent goose, but in domestic situations they often imprint on humans.






Social Behavior



Behavior is considered social only within groups of the same species, with a certain level of interaction beyond just being around each other.  Therefore, some herds are considered social, such as horses or wolfpacks, and some are not, such as impalas or flocks of many types of birds.  Some of the advantages of social behavior are just advantages of "hanging out in groups."

There are simple defensive advantages that derive from just being in a group:  each individual may just be looking out for itself, but the others can be alert not just for predators, but for other individuals' response to detected predators.  So when a bird on the edge of a flock detects danger and takes off, it is not purposely alerting the others, but they will probably take to the air as well.  This makes it much harder for predators to sneak up on a group than an individual.  A case could be made for safety in numbers:  when an individual is taken, the odds of any individual being the unlucky one are associated with the number of individuals around it.

There are reproductive advantages to associating with a group:  there are available mates.  In groups with no established heirarchy of mate access (covered below), it is not unusual for there to be a high level of synchronicity of fertility in a group, where all of the females are "in heat" at the same time.  Males may compete for access, but that competition is spread out, as opposed to a large group with just one female in heat at any given time.  In humans, when many adult females live in close proximity, their fertility cycles tend to synchronize - the dormitory effect - which may be a holdover from our distant ancestors (recent studies have thrown some doubt on this phenomenon).

Social groups are often biological colonies , with members within the group doing different jobs to support the group or groups within the groups.  Some biologists treat these groups as superorganisms.  Evolution may select useful features, but there may be many useful features in a colony, and is the colony itself an evolving unit?  Going back to Darwin's time, some people used that idea to justify the subjugation of indigenous populations by "superior" Western cultures, and the concept of group selection was abandoned.  It still is considered controversial and treated as a non-factor by many evolutionary biologists.

Cooperation becomes a major element of social interaction within colonial species.  This may include the search for food, the protection of the group, or the construction of housing, as done for example by bees, ants, or humans.

There are disadvantages to grouping bahavior, reflected in advantages of solitary behavior.  For instance, camouflage works well for individuals, but not really for groups.  When food is difficult to find and can't be shared, it's better to get it by yourself, as snakes do.  When food is very limited, it's easier to feed individuals than groups.  When there is an abundance of food, groups still tend to exhaust it locally, giving an advantage to populations spread through the ecosystem.  In general, the carrying capacity of an ecosystem - how many individuals of a particular species it can sustain indefinitely - is higher for solitary species than grouping species.

Although solitary species may have a more difficult time matching up mating pairs, the reproductive exclusivity can be advantageous, with a lack of conflict and surer parenting.  The sure-parenting aspect can be especially important when parents cooperate in the care of the young - there's only a premium for the father putting in the effort if he's helping his own offspring.









Aggression can be action or the threat of action as a way to resolve some sort of conflict.  It is not action by a predator on prey, but it certainly can be action of the prey against a predator.  Aggression rises to agonistic behavior if physical fighting is involved.  Agonistic behavior often involves weapons of various kinds;  these could be the weapons that predators use on prey, weapons prey use in defense, or weapons used in competition for various resources.  In general, weapons used intraspecies, between members of the same species for mating access, territory, etc., are nonlethal.  Interspecies weapons tend to be potentially lethal.

Avoiding fighting
is a common behavior, and often involved ritualized behaviors and responses.  Males in competition for females are very likely to "perform" to establish dominance, to demonstrate their likelihood of winning the fight, as a way to keep from actually fighting.  Sometimes the ritualized behavior is aimed at the female, such as a display of a peacock's tail;  the female makes the choice without the males having to fight each other.  In many of these cases, the male is demonstrating not his potential fighting prowess, but his ability to gain resources:  in the case of the peacock, a large tail shows the abundance of resources he "wasted" to build it and the ability to avoid predators even with that tail weighing him down.

Many social groups are built around a single male, with several females and young.  For reproductive access, an outside male must drive the resident male from the group.  This usually involves aggressive behavior between the males;  the females just "go along" with whatever male has taken over, even when the new male kills or drives out the previous male's offspring.

In groups that require multiple male members, a pecking order pattern is established, a type of social heirarchy where conflict is limited to those few members with near-equal status on the social ladder.  This system is found in baboons and humans - and chickens, where the term originated.









Territory is a geographical zone that an individual, pair or group will defend against others who would use the same resources or threaten the inhabitants.  A territory can be very small, such as the area a male frog may present to an egg-laying female, or large enough to only sort-of exist, such as grizzly bear home ranges that actually overlap, but the bears encounter each other so rarely, and mark boundaries so sporadically, that they don't readily know that they overlap.  Territory has an obvious cost-benefit aspect.  The cost of defending the territory must provide a benefit that makes it worth it.









Passing messages from one individual to another is the basic definition of communication.  The recipient must be able to receive the message - a rattling rattlesnake is not sending a signal to other snakes, who could not hear it, but to potential threat that can hear, so communication must stimulate appropriate senses.  The messages are often simple, and both the message and the response may be stereotyped.

Messages often take the form of displays, which can be actions or appearances.  Warning displays, usually high-contract markings of black and lighter colors, are a message that the possessors have some particularly nasty threat response, such as poison or bad taste - owners of warning colors want to stand out in the environment.  A rattlesnake is an odd example of an animal that is camouflaged to hide from prey but uses its warning display - the rattle - to stand out to possible threats.  Reproductive displays might be warnings to potential competitors, or might be signs of particular fitness, such as the peacock tail mentioned above.  These might involve nuptial gifts, offered by the male to the female.  Sometimes, when the female could potentially kill the male, a nuptial gift is a distraction, giving the male time to dash in, copulate, and maybe escape.

Some defensive displays are offered as warnings, such as a dog baring its teeth.  Some are deceptions, such as when animals puff up to seem bigger than they actually are.  Some are intended to startle or distract, such as a cuttlefish "flashing" and the scooting off, or an octopus leaving a cloud of ink.






Click on term to go to it in the text.
Terms are in the order they appear.



Fixed Action Patterns
Sign Stimulus
Learned Behavior
Warning Colors

Social Behavior
Colony Behavior
Group Selection
Solitary Behavior
Carrying Capacity
Agonistic Behavior
Ritualized Behavior
Dominance in Behavior
Pecking Order
Communication, Animal
Warning Colors
Reproductive Displays
Defensive Displays





Organismal Biology

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