Sunbathing combines behavioral and physiological adaptation.
The environment changes organisms and organisms change the environment; thus, changed environments change organisms. This is the dialectic of evolution. Adaptations are episodes in this drama, wherein organisms undergo individual changes in response to changes in the environment. These changes in organisms might better ensure the survival of individuals, or they might evolve a new reproductive strategy that benefits species' survival in spite of dangers to individuals.
Adaptation -- Product or Process
Adaptations are often seen as products or features of an organism that are already manifest, like an opposable thumb or a protective coloration. But adaptation is also a process -- a process embedded within many variable processes, unlike the singular, controlled processes that are produced in a laboratory. For this reason, any taxonomy of adaptation is bound to be incomplete because the interactions that contribute to adaptation are innumerable. The three categories of adaptation, then, should be understood as abbreviations that do not fully capture the complexity of adaptation. With that caveat, three useful categories for adaptation are structural, behavioral and physiological.
Structural
Structural adaptation to environment involves changes in the morphology of the organism. Everyone has seen the pictures of the fish with feet that has come to represent the process of evolution. This is a crude representation of what structural adaptation means. Dogs have adapted to heat by ventilating through panting, while humans cool off by sweating. Predators have eyes facing the front to focus on prey, while prey animals have side-facing eyes to see threats circumferentially. These are structural adaptations.
Behavioral
Many animals have evolved the neurological capacity to learn, even if by conditioned reflex. While two chickens might be genetically (structurally) identical, one might grow up around a well-trained dog and never learn to fear it, and later be vulnerable to a different dog. A chicken that has been attacked by a dog and survived will adapt her behavior by avoiding dogs. Humans are structurally adapted to learn so well that the majority of our behaviors are heavily conditioned by behavioral adaptations, as differences in culture demonstrate. Behavioral adaptation is made possible by pre-existing structures -- like a brain -- but it is not structural adaptation.
Physiological
Physiological adaptation is any adaptation that is made in an individual organism that responds directly to an environmental change. Lack of food causes a mammal's basal metabolic rate to fall to conserve tissues and prevent wasting. A man's skin darkens when he works in the sun to protect him from burning. These are not behavioral changes, nor are they structural changes wrought by genetic mutations. They are simply physiological adaptations to environmental change.
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