Three kinds of memory help herbivores track changes in the environment
. The first is the collective memory of the species with genetic instr
uctions that have been shaped by the environment through millennia. Th
is includes skin and gut defense systems. Auditory and visual stimuli
and sensations of pain impinge upon the skin defense system that evolv
ed in response to predation. The taste of food and the sensations of n
ausea and satiety are an integral part of the gut defense system that
evolved in response to toxins and nutrients in plants. The second kind
of memory in social mammals is represented by the mother, a source of
transgenerational knowledge, who increases efficiency and reduces ris
k of learning about foods and environments. The third kind of memory i
s acquired by individual experience. Post-ingestive feedback from nutr
ients and toxins enables individuals to experience the consequences of
food ingestion and to adjust food preference and selection commensura
te with a food's utility. The three memories interact, each linking th
e past to the present, and collectively shape the present and future o
f every individual. Thus, the dynamics of foraging involves appreciati
ng the uniqueness of individuals and subgroups of animals, each with t
heir own genetic and behavioral history, and recognizing that foraging
behaviors may not be stable, optimal, or even predictable in the conv
entional sense.