  Sensory mechanisms in biology, from cells to humans, have the property of
adaptivity, whereby the response produced by the sensor is adapted to the
overall amplitude of the signal; reducing the sensitivity in the presence of
strong stimulus, while increasing it when it is weak. This property is
inherently energy consuming and a manifestation of the non-equilibrium nature
of living organisms. We explore here how adaptivity affects the effective
forces that organisms feel due to others in the context of a uniform swarm,
both in two and three dimensions. The interactions between the individuals are
taken to be attractive and long-range, of power-law form. We find that the
effects of adaptivity inside the swarm are dramatic, where the effective forces
decrease (or remain constant) with increasing swarm density. Linear stability
analysis demonstrates how this property prevents collapse (Jeans instability),
when the forces are adaptive. Adaptivity therefore endows swarms with a natural
mechanism for self-stabilization.
