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Herbivory. Monarch caterpillar and Milkweed leaf. Plant Resource Defense. Qualitative defense - highly toxic substances, small doses of which can kill predators
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Herbivory Monarch caterpillar and Milkweed leaf
Plant Resource Defense • Qualitative defense - highly toxic substances, small doses of which can kill predators • high nutrient environment/fast growth (high turnover in plants) - use toxins (plant secondary compounds) that often require N, expensive to make (must be replaced often), but can be made rapidly - cyanide compounds, cardiac glycosides, alkaloids - small molecules
Plant Resource Defense • Quantitative defense - substances that gradually build up inside an herbivore as it eats and prevent digestion of food • low nutrient environment/slow growth (low turnover in plants) - primarily use carbon structures - wood, cellulose, lignin, tannins - large molecules - makes plant hard or unpleasant to eat (woodiness, silica), but plants are slow to make these defenses
Induced Defenses • Another aspect of plant defenses is that plants do not always have tissues loaded with defensive chemicals - in many plants, defensive chemicals are only produced when they are needed, usually after the plant has experienced some herbivory - this is an induced defense
Plant defenses are developed at a cost to fitness when: 1. Organisms evolve more defenses if they are exposed to much damage and fewer defenses if cost of defense is high 2. More defenses are allocated within an organism to valuable tissues that are at risk 3. Defense mechanisms are reduced when enemies are absent and increased when plants are attacked - mostly true for chemicals not structures 4. Defense mechanisms are costly and cannot be maintained if plants are severely stressed by environmental factors
Serengeti Grazing System • 1 million wildebeest • 600,000 Thomson’s gazelles • 200,000 zebra • 65,000 Cape buffalo • Unknown numbers of 20 other species of large grazing mammals • 36 species of rodents • 38 species of grasshoppers • Area of about 23,000 square kilometers
Grazing facilitation • Grazing facilitation occurs when the feeding activity of one herbivore species improves the food supply for a second species
Summary of Ecological Effects of Herbivores • Herbivores can affect plant fitness: • Reduce plant growth rate • Reduce plant reproduction: • Directly by preying on seeds • Indirectly by reducing plant growth
Summary of Ecological Effects of Herbivores • Herbivores may control plant distribution and abundance
Summary of Ecological Effects of Herbivores • Through alterations of plant distribution and abundance, herbivores can alter plant community structure and composition
Summary of Ecological Effects of Herbivores • The effects of herbivores on plants depends on the degree of feeding specialization of the herbivore
Feeding Specializations- high crowned teeth Bos – cow; Bison – bison; m3 – third molar
Symbiosis • Symbioses - species living in close association • Parasitism +,- parasite benefits, host harmed • Commensalism +,0 or 0,0 can have positive effect for one species or for neither • Mutualism +,+ both species benefit
Epiphytes Bird’s Nest Fern
Nalini Nadkarni studying epiphytes
Epiphytes Figure 1: Hypothetical tree illustrating how vascular epiphytes in humid forests tend to partition substrates illustrating sensitivity to micro climate, particularly humidity, and associated development of the organic rooting media required by some populations.
Parasitism and Disease Lyme Disease Cycle in the UK
Parasitism • Parasitism - intimate association between two species in which the parasite obtains its nutrients from a host - parasite usually causes some degree of harm to its host - either reduced growth or reproduction • Pathogen – disease causing agent • Disease – abnormal condition of host due to infection by a pathogen that impairs physiological functioning
