The signs used depend on the species being surveyed and include the presence of runways and tracks on * 1 point
(a). soft substrates
(b) hard substrate
(c) dry mud
(d) rocks

(a). soft substrates

Explanation:

Mobile organisms can be measured by both direct and indirect methods. Direct methods may involve observing the actual behavior (e.g., scoring via timing). Moreover, indirect methods are those where the technique used depends on the species being examined, collecting information such as through recording of tracks in the soft substrate (e.g., mud, sand, snow), presence of fur/feathers, droppings (mammals), etc. For example, indirect observation of insects may involve the determination of exoskeletons, sounds, etc.

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