Chapter 6 Energy and Nutrient Relations  Trophic types of organisms Autotrophs: photosynthetic chemosynthetic Heterotrophs: organisms live on organic matter. Trophic types are diverse in the biological kingdom (Fig.6.2)Fig.6.2

Sunlight spectrum

 Ultraviolet can be divided as: UV-A: 320nm—380nm, no harmful effect on the organisms; UV-B: 280nm--320nm, harmful to the organisms, but most of it is absorbed in the upper atmosphere; UV-C: <280nm, harmful to organisms, is absorbed in the upper atmosphere.

 Chemical Composition of organisms: --All the organism have similar chemical composition: 93~97% of [C], [O], [H], [N], and [P]. --Different organisms have different C:N, (Fig.6.7) --Other elements in organisms: Essential elemental : K, Ca, Mg, S, Cl, Fe, Mn, B, Zn, Cu, Mo, Na, I.

 Herbivores: Organisms that eat plants. Plant’s defense to herbivores --Physical defense: thorns (Fig.6.8); toughFig.6.8 tissue difficult to chew. --Chemical defense: High C:N; Toxins; Digestion-reducing substances. (Tropical plants and algae appear to posses stronger chemical defense) Fig Limited roles of chemical defenses: Particular toxin is defensible for particular herbivore species.

Herbivore’s evolution: Some can excrete toxin; Some can use plant toxin as a source of nutrition.

 Detritivores: Organisms that feed on nonliving organic matter, usually the remains of plants.  Carnivores: Organisms that mainly eat animals. Defenses of preys: --Camouflage ( 伪装 ); --Anatomical defenses: such as spines, shells, repellents( 防护剂 ), poisons, and behavioral defenses; --Mimicry Fig.6.13Fig.6.13

Low catch success: Wolves’ capture on moose about 8%; Bald-faced hornets ( 大黄蜂 ) ‘capture on insect prey, <1%.

 Coevolution between carnivores and herbivores: Predators eliminate poorly defended individuals in the population and average prey defenses improve. As average prey defenses improve, the poorer hunters go hungry and leave fewer offspring, so that the average hunting abilities improve.