Responses to the Environment (College Board AP® Biology): Study Guide

Internal & external environmental cues

Behavioral and physiological mechanisms

• Organisms respond to environmental changes to maintain homeostasis and improve survival

• Responses include:

  • behavioral mechanisms, which are characterized by the actions of an organism

  • physiological mechanisms, which are the biological processes occurring within the organism to help maintain homeostasis

• Responses are triggered by

  • internal stimuli such as hormone fluctuations

  • external stimuli such as temperature, light, or predators

Responses to environmental cues

• Organisms, both animals and plants, can respond to external stimuli in a variety of ways

• Plants:

  • Phototropism: This leads to growth toward light to optimize photosynthesis

  • Photoperiodism: Where seasonal flowering and leaf shedding is triggered by day length

• Animals:

  • Taxis: Directed movement toward/away from stimuli (e.g., food or light) to enhance growth and survival

  • Kinesis: Random movement to locate favorable conditions (e.g., dark or damp)

  • Nocturnal and diurnal activity:

    • Nocturnal animals (e.g., owls) exploit nighttime safety or prey availability

    • Diurnal animals (e.g., eagles) rely on daylight for hunting or warmth

Cues and natural selection

• Organisms also communicate with other organisms in response to internal changes and external cues

• Effective responses to environmental cues and the exchange of information between organisms influence behavior

  • This can impact survival and reproduction with an effect on the evolutionary fitness of the species

• The fight-or-flight response in animals:

  • Adrenaline release provides an internal cue that drives a behavioral reaction to immediate threats

• Plant responses to herbivory:

  • Mechanical damage from the herbivore triggers the release of toxic chemicals used to deter the herbivore from further feeding

The effect of internal & external cues on fitness

Communication and behavioral adaptations

• Organisms act on information and share it with others

  • between members of the same species - intraspecifically

  • between different species - interspecifically

• Communication mechanisms include visual, audible, tactile, electrical, and chemical signals, which are used for:

  • establishing dominance

  • locating food

  • defending territory

  • warning of predators

• Behavioral signaling influences reproductive success by conveying important information to potential mates, rivals, and social partners,

  • Behaviour signalling indicates reproductive fitness, social status, or genetic quality

  • This therefore triggers adaptive responses in others

Natural selection and cooperative behavior

• Some behavioral responses of organisms aim to increase reproductive fitness, ensuring organisms survive to reproduce, find mates, and pass on their genes

• E.g.,

  • Innate and learned behaviors that improve survival and reproduction are favoured by natural selection mechanisms

  • Cooperative behavior benefits individuals and populations, increasing overall fitness (e.g. wolves hunting in packs, shared parental care or bees swarming)

• These behaviors therefore influence the overall success of the population

Examples of behavioral responses

• Territorial marking: scent marking by mammals deters competitors

• Bird songs: to attract mates and establish territory

• Parent-offspring interactions: this can facilitate learning of survival skills (e.g., grizzly cubs learning to fish)

• Courtship and mating behaviors: used to help identify suitable mates with the most advantageous traits

• Herding, flocking and schooling: safety in numbers reduces predation risk (e.g., sardines schooling)

• Colony and swarming: ensures species survival (e.g., bee colonies finding new habitats)

• Kin selection: sacrificial behavior benefits relatives’ genetic fitness (e.g., an older moose diverting predators)