What is substratum?
In Biology, the substratum (or substrate) is the surface on/in which an organism lives.
How does substratum vary?
Substratum varies in many characteristics:
- Type: organic (e.g. tree trunk) or inorganic (e.g. rock)
- Natural (e.g. forest floor) or artificial (e.g. cement fence)
- Size: clay (<0.00006 mm) to fine sand (<2 mm) to boulder (>4096 mm) to bedrock rock
- Rugosity (surface roughness): smooth to very rough
- Colour: e.g. white, black, brown
- Aspect: e.g. north, south, east, west
- Inclination: 0º to 90º
Why is substratum biologically important?
Substratum can provide refuge sites (e.g. under logs) from predators and environmental stresses.
Surfaces on logs, trunks and rocks also provide sites where plants can grow above the forest floor (e.g. moss, lichen, some ferns). Various invertebrates (e.g. pillbugs, beetles) also live in these habitat patches.
The texture or rugosity of substratum can affect the rate of movement of animals. Some animals move slower on fine soil or on a more complex substratum than on a smooth substratum such as rock or tree bark. This in turn, can affect their predation risk and competitive abilities.
Surfaces on logs, trunks and rocks also provide sites where plants can grow above the forest floor (e.g. moss, lichen, some ferns). Various invertebrates (e.g. pillbugs, beetles) also live in these habitat patches.
The texture or rugosity of substratum can affect the rate of movement of animals. Some animals move slower on fine soil or on a more complex substratum than on a smooth substratum such as rock or tree bark. This in turn, can affect their predation risk and competitive abilities.
How do animals sense substratum?
Aspects of substratum can be sensed using various sensory organs:
- Many insects, crustaceans, and gastropods have eyes that can form images, allowing them to see the substratum.
- Sensory hairs (sensilla or mechanoreceptors) on the surface of the antennae and legs allow some animals to determine the location, shape and texture of the substratum through touch.
- Other sensory hairs (aesthetascs) are involved in chemoreception, which can also be used in assessing the chemical nature of substratum.
- Some crustaceans rely more upon internal receptors (called proprioceptors), which detect the position and movement of limbs, to assess their environment. Gastropods (e.g. snails) also use internal receptors located on their tentacles and/or foot to assess nearby objects.
- Statocysts provide information on orientation (e.g. is the animal moving up or down a hill).
How do animals respond to variation in substratum?
- Invertebrates may choose and/or move to substrata that provide a benefit (e.g. predator avoidance).
- The rate of movement may also change. Animals may move more rapidly over substrata with greater risk of predation or stressful abiotic conditions. Or, they may move more slowly across substrata that make locomotion difficult.
- The rate or frequency of movement of body parts involved in sensing substratum (e.g. flicking of antennae) may also change.
To learn more:
Freeman S, Harrington M, Sharp J. 2014. Biological science. 2nd Canadian ed. Toronto: Pearson.
Smith TM, Smith RL, Waters I. 2014. Elements of ecology. Canadian ed. Toronto: Pearson.
Note: Any edition of the above books or other biology and/or ecology textbooks could be useful.
Freeman S, Harrington M, Sharp J. 2014. Biological science. 2nd Canadian ed. Toronto: Pearson.
Smith TM, Smith RL, Waters I. 2014. Elements of ecology. Canadian ed. Toronto: Pearson.
Note: Any edition of the above books or other biology and/or ecology textbooks could be useful.