Move in/on Solids
To obtain needed resources or escape predators, some living systems must move on solid substances, some must move within them, and others must do both. Solids vary in their form; they can be soft or porous like leaves, sand, skin, and snow, or hard like rock, ice, or tree bark. Movement can involve a whole living system, such as an ostrich running across the ground or an earthworm burrowing through the soil. It can also involve just part of a living system, such as a mosquito poking its mouthparts into skin. Solids vary in smoothness, stickiness, moisture content, density, etc, each of which presents different challenges. As a result, living systems have adaptations to meet one, and sometimes multiple, challenges. For example, some insects must be able to hold onto both rough and slippery leaf surfaces due to the diversity in their environment.
Attach Temporarily
Living systems must sometimes, temporarily, stay in one place, climb or otherwise move around, or hold things together. This entails attaching temporarily with the ability to release, which minimizes energy and material use. Some living systems repeatedly attach, detach, and reattach for an extended time, such as over their lifetimes. Despite being temporary, these attachments must withstand physical and other forces until they have achieved their purpose. Therefore, living systems have adapted attachment mechanisms optimized for the amount of time or number of times they must be used. An example is the gecko, which climbs walls by attaching its toes for less than a second. Other examples include insects that attach their eggs to a leaf until they hatch, and insects whose wings temporarily attach during flight but separate after landing.
Modify Material Characteristics
The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.
