181. If their population is tracked through time, it will be seen to be particularly unstable—soaring and plummeting in irregular cycles.

 

182. A massive oak claims its ground for 200 years or more, outcompeting all other would-be canopy trees by casting a dense shade and drawing up any free water in the soil.

 

183. Although oaks produce thousands of acorns, the investment in a crop of acorns is small compared with the energy spent on building leaves, trunk, and roots.

 

184. A population of oaks is likely to be relatively stable through time, and its survival is likely to depend more on its ability to withstand the pressures of competition or predation than on its ability to take advantage of chance events

 

185. It should be noted, however, that the pure opportunist or pure competitor is rare in nature, as most species fall between the extremes of a continuum, exhibiting a blend of some opportunistic and some competitive characteristics.

 

186. Some follow each other in solemn parades, but others swirl about, sideways and upside down.

 

187. The animals are bulls, wild horses, reindeer, bison, and mammoths outlined with charcoal and painted mostly in reds, yellow, and browns.

 

188. It is possible that tubes made from animal bones were used for spraying because hollow bones, some stained with pigment, have been found nearby.

 

189. Because some paintings were made directly over others, obliterating them, it is probable that a painting’s value ended with the migration it pictured.

 

190. Unfortunately, this explanation fails to explain the hidden locations, unless the migrations were celebrated with secret ceremonies.