Organisms Respond to Environmental Cues (College Board AP® Biology)

Responses to External Cues

• In order to increase reproductive fitness, individuals can act on information and communicate it to others

  • Both intraspecifically and interspecifically

• Communication occurs through various mechanisms

  • Organisms have a variety of signaling behaviors that cause changes in the behavior of other organisms and can result in different degrees of reproductive success

  • Animals use visual, audible, tactile, electrical and chemical signals to indicate a variety of signals

    • Dominance

    • How/where to find food

    • To establish territory

    • To warn of predators

  • All of these mechanisms are designed to ensure reproductive success

  • These signals act as stimuli to other organisms, whose responses govern the signaling animal's reproductive success

• Responses to information and communication of information are vital to natural selection and evolution

  • Natural selection favors innate and learned behaviors that increase survival and reproductive fitness

  • Cooperative behavior tends to increase the fitness of the individual and the survival of the population

    • Rather like members of a sports team working cooperatively towards a winning performance

  • Individuals can act on information and communicate it to others

• There are many examples of this kind of behavior in Nature, some of which are set out below

  • These are set out for illustration purposes, the details of these systems are beyond the scope of the AP Exam

Examples of Responses to Environmental Cues

• Photoperiodism and phototropism in plants

  • Plants respond to the direction of the light that reaches them and grow accordingly

  • Photoperiodism is the plant's response to day length that affects fruiting and leaf shedding according to the seasons

• Taxis and kinesis in animals

  • Taxis is the movement towards or away from a stimulus eg. food

  • Kinesis is a random movement that leads to an animal finding food, more so than it would have found by staying stationary

• Nocturnal and diurnal activity

  • Nocturnal (nighttime wakefulness) animals might prefer the night because it is cooler for hunting, or there is greater availability of prey / fewer predators

  • Diurnal (daytime wakefulness) animals make use of light and hotter temperatures for hunting, foraging and for warming their cells (ectotherms)

• Fight-or-flight response

  • This is the hormonal response to an existential threat (eg. a predator emerging), brought about by adrenaline (epinephrine)

• Predator warnings

  • Some animals warn their relatives if a predator is at large

  • Meerkats post sentries at the entrances to their burrows to bark loudly to warn other meerkats (who are feeding outside the burrow) of the presence of a predator

• Plant responses to herbivory

  • Some plants contain spikes, trichomes, thorns and foul tasting chemicals to deter herbivores

  • When a plant is being eaten by a herbivore, it can secrete poisonous chemicals in self defense

• Territorial marking in mammals

  • Scent marking eg. by male cats deters intraspecific competition from other males who may wish to exploit that territory for a mate or for food

• Coloration in flowers

  • This attracts insects for pollination

• Bird songs

  • This allows birds to attract a mate

• Pack behavior in animals

  • This allows a group of animals to achieve a task collectively that one individual could not eg. a pack of wild dogs hunting a much larger prey animal such as a wildebeest

  • The dogs chase, harry, would and kill the prey individually in turn, working as a team, then share the feed at the end

• Parent and offspring interactions

  • This allows behaviors to be learned, such as the young grizzly bear learning fishing skills from its mother

• Courtship and mating behaviors

  • This enables individuals to identify a potential mate of the same species

  • And to identify advantageous alleles in the mate that can be passed on

• Herd, flock, and schooling behavior in animals

  • This allows 'safety in numbers' eg. sardines school into a large group, which reduces the probability of any one individual being predated on eg. by bluefin tuna

• Colony and swarming behavior in insects

  • This increases the chance of finding an alternative habitat eg. bees swarming from a nest that has reached its capacity to carry bees

• Kin selection

  • An individual animal sacrifices itself to the benefit of the genetic fitness of its relatives

  • An example might be an old, injured moose giving itself up in a hunt by wolves, to allow its younger, stronger relatives to get away