Sci-fi ecosystems- some more novels

This is my fourth blog entry. It will focus on two novels- Tunnel in the Sky, by Robert Heinlein, and Helliconia Spring, by Brian Aldiss. The first novel describes the trials of a group of students accidentally left on an alien planet during a survival test. The second is the first novel in the Helliconia trilogy and chronicles the dawn of a new age on Helliconia, which has an extremely long and unusual orbit around a binary star system. This causes it to go through periodic “winters” and “summers” every few thousand years, during which all life and civilization is overthrown and then rebuilt.
Tunnel in the Sky takes place on a very Earth-like planet. All the life-forms appear similar to Earthly ones and occupy almost identical niches. This could merely mean the author did not want to think up a whole new ecosystem, or it could mean that he wants to put forth the idea that on any Earth-like planet, evolution will take a similar course and the same structures, behaviors, and relationships will prevail. The specific ecosystems described are all various tropical forests and grasslands, with their attendant animals. One animal is notable- a small carnivore called a “dopy joe” changes once a year from an ambush hunter of small mammals (it seems like the large animals are mammalian) to an aggressive creature that forms mobs and drives other animals before it in a mad bloodlust. Unfortunately, there is no good explanation given for why they do this. The other animals counteract this by running away, which works well.
Helliconia Spring centers around the idea that all the ecosystems of a planet are dependent on its astronomical conditions, and that these define life on the planet. Additionally, rather than have an impoverished environment at each new spring or fall, organisms will find some way to outlast poor conditions, and this evasion of death also characterizes the environment. The set of species living in the “winter” (in ice age conditions) primarily consists of mosses, lichens, deer-like animals of various kinds, small animals, dog-like predators, fish, white birds, humans, and phagors. These last are intelligent white-furred bipedal carnivores with man-like hands, and goat-like legs, muzzles, and horns. Their civilization dominates the planet during the “winter”, but is overthrown and replaced by a human culture in the spring and summer. Most of the large animals of the “winter” are necrogenes- they reproduce by mating, then dying at specific times and places and allowing the maggot-like young produced by mating to eat their carcass as they grow up. Large migrations to favorable death-places take up much of the life-cycle of the necrogenes. Presumably, having such a large source of food for the young is a boon in the hard winter conditions.
In spring, the larval forms of various animals emerge from the ground, and the hard, lifeless boles of certain trees explode, hurling their seeds out into the world. The other plants emerge from tough seeds that have laid in the ground for thousands of years, and become fodder for animals like the antelope-like hoxney. The new set of large animals seems mammalian, and they live among temperate forests and grasslands. There are several creatures that live throughout the year and do not have to resort to crystalline cocoons to survive winter. One is a dragon whose wingless larva lives in tunnels deep in the earth, and the other is a stungebag, a huge worm-like animal with a hard wood-like covering and a large mouth buried under a concealed pit in the ground. Animals fall in and are eaten.