Herbivore tolerance

Proximate Mechanisms of Herbivore Tolerance 10.2.1 Defining Tolerance ... 

By necessity, herbivores have evolved GIT and systemic compensatory mechanisms that allow them to subsist on plant-based diets that have limited nutrient quality and include phytochemicals. Still, herbivores remain susceptible to some of the anti-nutrient and toxic phytochemicals. For example, several herbivores are sensitive to the phytotoxins associated with autumn crocus, which include colchicine (Yamada et al, 2000). As a consequence, herbivores tend to select species and portions of plants based on a combination of nutrient quality and concentrations of phytochemicals (Yeager et al, 1997), and this has an impact on habitat selection and plant ecology (Duncan and Gordon, 1999). Carnivorous species have not been under selective pressure to develop similar compensatory mechanisms, generally have only limited abilities to subsist on plant-based diets, and in many cases are less tolerant of phytochemicals. 

Temporal and spatial shifts in the abundance of chemically undefended algae and cyanobacteria may leave grazers with few dietary options except to consume low-quality, chemically defended food items. While some herbivores may be able to either tolerate or inactivate these toxins (Samelle and Wilson 2005), species that lack tolerance may be faced with the dilemma of either remaining on a low-quality patch or migrating to a different patch, thus increasing their risk of predation by visual predators (Krivan and Vrkoc 2000). In systems that experience seasonal... 

Leimu R, Koricheva J (2006) A meta-analysis of tradeoffs between plant tolerance and resistance to herbivores combining the evidence from ecological and agricultural studies. Oikos 112 1-9 Lesser MP (2006) Oxidative stress in marine environments biochemistry and physiological ecology. Annu Rev Physiol 68 253-278... 

Steinberg PD, Van Altena I (1992) Tolerance of marine invertebrate herbivores to brown algal phlorotannins in temperate Australasia. Ecol Monogr 62 189-222 Stem JL, Hagerman AE, Steinberg PD, Winter FC, Estes JA (1996) A new assay for quantifying brown algal phlorotannins and comparisons to previous methods. J Chem Ecol 22 1273-1293... 

If feeding behaviors, assimilation efficiency, or fitness are reasonable proxies for tolerance of secondary metabolites, then it is clear that herbivore individuals, populations, and species profoundly vary in their tolerance (Paul et al. 2001 Stachowicz 2001 Targett and Arnold 2001). Such differential tolerance was recognized early within the emerging field of marine plant-herbivore interactions (Hay 1992 Hay and Steinberg 1992 Paul 1992), much to the dismay of these scholars. The same metabolite may show considerable difference in its effects even on closely related species of herbivores (Paul 1992). 

Are Tropical Herbivores More Tolerant of Lipophilic Metabolites Than Are Temperate Herbivores ... 

In each case, small herbivores tend to be more tolerant of chemically rich seaweeds relative to larger consumers. This is not always the case, and in fact the... 

Decomposition rates of some organic substrates are reduced. Substantial changes in the species composition of primary producers occur. The richness of phytoplankton species is reduced, while biomass and productivity of phytoplankton are not reduced by acidification. The biomass of herbivorous and predaceous zooplankton is probably reduced because of reductions in numbers of organisms and/or reduction in their average size. Many benthic invertebrates such as species of snails, clams, crayfish, amphipods, and various aquatic insects are intolerant of low pH and are seldom found in acidic lakes. However, certain large aquatic insects such as water boatmen and gyrinids are very acid tolerant and may become the top predators in some acidified lakes. Acidification of aquatic systems has major effects on fish population. 

The great diversity of terpenes helps to cormteract tolerance by herbivores. In all, terpenes are not very toxic to vertebrates. Many mammals ingest a significant amount of terpenoids with their diet. Monoterpenes from pine oil added to the diet reduces food intake in red deer, Cervuselaphus, calves (Elliot and Loudon, 1987). The brush-tailed possmn, Trichosurus vulpecula, detoxifies (-l-)-a-pinene to alcohol and carboxylic acid derivatives. 

Nolte, D. L., Mason, J. R., and Lewis, S. L. (1994a). Tolerance of bitter compounds by an herbivore, Caviaporcellus. Journal of ChemicalEcology 20,303-308. 

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