**4. Conclusions**

with UV exposure and photoactive properties, and more toxic plants support a lower diver-

Sometimes, plant species can response locally to different herbivores, as *Datura stramonium*: the plant can be eaten by generalist and specialist herbivores at great geographic range and produces the alkaloid atropine and its derivate, less toxic, scopolamine. The secondary plant compound is more effective against herbivores specialist, but the precursor is still effective against generalist. Then, when there is a community of generalists, *D. stramonium* produces

Another example is *Zamia stevensonii*, which produces azoxy glycosides (AZGs), highly toxics with mutagenic and carcinogenic properties. AZGs are an excellent defense against generalist

Another important group of chemical compounds, relevant in defensive plant traits, is phenols, including tannins, which at media concentration reduces herbivory, through reduction

Terpenes also are present at plants in tropical forest; in that, these compounds protect against abiotic factors such as light, heat, and drought and against herbivores. In Borneo rain forest, foliar terpene presence in 73 of 75 plant species has been analyzed (97%), 15 monoterpenes and 65 sesquiterpenes. This suggests that terpenes can be a favorable selective trait in rainforest [46]. Currently 25,000 structures of terpenes approximately have been reported; some of them are volatile and can be synthesized de novo or are stored in leaves, stems, and trunks and are released in response to attack [85]. One plant can release a highly complex blend, which can include up to 200 volatile terpenes, and its effect is due to direct toxicity, repulsion to herbi-

Among defensive traits in tropical forest, some are strongly correlated with herbivore damage: leaf size, shearing resistance, cellulose, and ash content. Then, large leaves are more susceptible to herbivory. Other three factors—shear toughness, cellulose content, and ash, which is a mixture of calcium oxalates and phytoliths—reduce herbivore damage acting as structural defenses. These strategies are very efficient and have a relatively low energetic cost [45]. Interestingly, lianas have increased cover and abundance. That plant forms are genetically predisposed to reduce structure and defense traits for investment more in chemical implicates in growth and light capture, wherewith lianas response to stress conditions, like warmer and

At tropical forest are common indirect defenses to reduce herbivore attack. In that way, plants provide house, nourish or attract organisms like ants or parasitoids [88], by production of refuges or nesting sites, extrafloral nectar, food bodies or/ and volatile compounds (VOCs) [89]. For example, extrafloral nectar production increases in herbivory and diminishes in the herbivore absence, because that is the secret to attract predators like ants, who defend their food sources and parasitoids. Extrafloral nectar consists in sugars, proteins, lipids, mineral nutriments, and antioxidants and can attract organisms like mites, ladybird beetles, wasp, lace-

sity of specialist herbivores [81].

100 Pure and Applied Biogeography

herbivores, but are not sufficient to specialist [83].

vores, or attraction of herbivore enemies [85, 86].

drier conditions [87].

wing larvae, and spiders [90, 91].

of digestibility of plant tissues, and increases immune responses [84].

atropine [82].

Every ambient has their own biotic and abiotic selective pressures, and plants are able to respond differentially. In general, there are a great variety of defensive traits in plants, and they are different at distinct environments. In aquatic environment, the principal defensive traits must be water soluble and diffusible, but their action time and range are short, because aquatic plants need to produce this constantly. For aquatic plants, biomass production is more relevant than defensive traits outlay, then they prefer investment in growth and photosynthesis.

In terrestrial environments, plants need to accumulate defensive compounds for an eventual attack, but the quantity depends on biomass replacement rate. If ambient conditions allow rapid biomass formation, plant accumulates less defensive compounds; in contrast, slow accumulation in biomass induces the great defensive compound accumulation. Because at temperate forest, plants accumulate greater quantity of defensive compounds, particularly resins and phenolics.

Herbivore diversity and pathogens also contribute in plant chemical production. In places, with high herbivore diversity, plants produce a plethora of compounds for defense so much for generalist such as specialist; then at tropical forest, there are a greater variety of chemical defensive compounds, especially complex chemical mixtures.
