| Abstract: |
This a response from an earlier argument in the pages of Amer. Anthropologist to the effect that rain forests could never have supported human populations based solely on hunting and gathering. Therefore people needed to supplement their diets with crop plants. pg 153 Authors say the reasons for high primary production in rainforests is high temperatures and unlimited water. Limits to production are probably set by the carbon dioxide concentration of the air. the effective nutrient retrieval system of trees that allows full advantage to be taken of constant moisture and warmth. Wind dispersal doesn't work so well in rainforests, water dispersion also minimal. What is left are animals to do the job. So plant-animal communication is especially important. Must get communication mode with animals going. Hence shamanic plants. That's why rain forests are primarily systems of frugivores. Hence the primary producers in the rainforest are adapted by 'natural selection' - (again note the effect is mistaken as the cause). to provide food for foraging animals as lures for seed transport. pg 154 Plants have, generally, two types of poisons (sic) in their plants tissues: tannins, which work by precipitating proteins, and alkaloids. Tannins are energetically costly to the plant, but kill nearly everything (quantitative defense). Alkaloids are more specific, and some insects ran render them harmless (qualitative defense). Alkaloids are focused on sensitive parts, like seeds, and less tannins are used. Consequently more parts of the plant are edible by mammals. Compared to temperate forests loaded with tannins, to toxic, selective defenses provided to scattered, succession rainforest trees by their alkaloids. Gibbons relied on the produce of 260 species of plants during the course of a year. Rain forest are highly favored places for any organism capable of discrimination or learned foraging on fruits and seeds High foliage and relatively low wood production are precisely what is to be expected of a rapidly growing, perpetually disturbed system like the Amazonian rainforest. Bailey et al. (1989) make the classic error of confusing standing crop with productivity when they quote data to suggest that only 2% of the standing crop of biomass in the rainforest is in leaves and other potential edible portions of plants. This stading ratio doe snto imply that productivity of edible tissue is low, but merely that the ratio of actively living tissue to accumulated structure is low. pg 155 Rain forest leaves unprotected by tannins are rapidly scavenged,. as are wood. Grubs of wood feeding insects are abundant, as are animals that feed on grubs. To the production ecologists, a tropical rainforest can be likened to a highly productive prairie raised off the ground on stilts 20 m high. There is then high secondary productivity in the canopy for any hunter with the means to crop it. Also forest gaps are productive spots. A resource that Bailey et al (1989) do not mention is that of fish. pg 156 The 'refugia' hypothesis that a former era of aridity in the amazon produced disjunctions of biota. Proposed that there were 'islands' of wet climate that produced these modern disjunctions in species distribution. Colinvaux disputes this according to paleoecological evidence. High yields have prevailed in the Amazon throughout all stages of a glacial cycle. Tropical rainforests are disturbance systems sensitive to short-term climactic changes. Amazon is the archetypal rainforest: where diversity is high, succession does not proceed to climax, trees do not usually grow in single species stands, and food yields to foragers are high. Conclusion: diverse rainforests are likely to have been prime habitants for hunting and gathering before agriculture became widespread.
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