Responses to the environment: behavior, communication and fitness

What the exam asks

• Explain how behavioral and physiological responses relate to internal or external environmental changes.
• Describe how organisms exchange information via visual, audible, tactile, electrical, and chemical signals.
• Explain how signaling, innate, learned, and cooperative behaviors lead to differential survival and reproductive success (fitness).
• Identify independent variables, dependent variables, and appropriate controls in behavioral or physiological investigations.

Core ideas

1. Responding to environmental cues

An organism’s environment is constantly shifting. Both internal changes (such as a drop in blood glucose or dehydration) and external changes (such as day length, temperature, or predator presence) act as stimuli.

• Behavioral responses are actions an organism takes to adjust to a stimulus. Examples include taxis (directed movement toward or away from a stimulus, such as positive phototaxis in Euglena swimming toward light or negative phototaxis in planarians moving away from light), kinesis (random, undirected movement rate that changes with stimulus intensity, such as pillbugs moving faster in dry air until they happen upon a moist area), hibernation, migration, and basking.
• Physiological responses are internal functional adjustments, such as shivering, sweating, opening or closing leaf stomata, or altering metabolic rates.

In plants, phototropism (bending toward light) and photoperiodism (flowering in response to changes in night length) coordinate growth and reproduction with seasonal availability of light and pollinators.

2. Modes and functions of communication

Organisms produce signals that alter the behavior of receivers. Natural selection favors signaling behaviors that increase the sender’s and receiver’s reproductive success.