Romantic relationships and sexual activeness are also sensitive areas where competition among men is unseen but felt.
1.1 (Especially of a feeling or atmosphere) so intense as to be almost touched or felt:
late 14c., "that can be touched,"
from Late Latin palpabilis "that may be touched or felt,"
from Latin palpare "touch gently, stroke" (see feel (v.)).
Figurative sense of "easily perceived, evident" also is from late 14c. Related: Palpably.
Old English felan "to touch or have a sensory experience of; perceive, sense (something)," in late Old English "have a mental perception," from Proto-Germanic *foljan (cognates: Old Saxon gifolian, Old Frisian fela, Dutch voelen, Old High German vuolen, German fühlen "to feel," Old Norse falma "to grope"), from PIE root *pal- "to touch, feel, shake, strike softly" (cognates: Greek psallein "to pluck (the harp)," Latin palpare "to touch softly, stroke," palpitare "to move quickly"), perhaps ultimately imitative.
The meaning in Old English was "to perceive through senses which are not referred to any special organ." Sense of "be conscious of a tactile sensation, sense pain, pleasure, illness, etc.; have an emotional experience or reaction," developed by c.1200, also "have an opinion or conviction;" that of "to react with sympathy or compassion" is from mid-14c. Meaning "to try by touch" is from early 14c. From late 14c. as "know (something) beforehand, to have foreknowledge of." To feel like "want to" attested from 1829.
From General George E. Pickett in Life and Legend, by Lesley J. Gordon:
An unchaperoned white southern woman journeying with her baby, she experienced a palpable sense of fear: “Perhaps no timid little waif thrown out upon the deep sea of life ever felt more utterly desolate.
From If They Move... Kill 'Em!: The Life and Times of Sam Peckinpah, by David Weddle:
As soon as she walked into the room he felt it: a palpable sensuality and, just beneath it, the claws of a wildcat.
Only single-word answer that comes to my mind is present.
Romantic relationships and sexual activeness are also sensitive areas where competition among men is present.
If you'll settle for a multiple word answer then idiom In the air might be good.
able to be felt or noticed
"Below the surface" might work for an alternative phrase and perhaps subliminal for a single word
It's not so much that the competition is "unseen but felt", it is definitely acted out in many subtle and not-so-subtle ways, as sociologists have chronicled.
It's the sense of competition that is felt, but never talked about. There is an unstated emotional undercurrent, a tacit competitiveness; a primal urge to outdo one another in attracting and keeping a mate, that results in instinctive, animalistic behaviors triggered by subtle cues.
As others have mentioned, this is partly subliminal, below the level of rational thought, as if based on sense of smell (which it partly is; the comment about smelling the testosterone is not far off at all).