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

Evolutionary “Arms” Races Monarch and milkweed

Evolutionary “Arms” Races

Evolutionary “Arms” Races California garter snake Pacific newt

Other Plant Defenses Include: mechanical defenses - plant thorns and spines deter many vertebrate herbivores, but may not help much against invertebrate herbivores failure to attract predators - plants somehow avoid making chemicals which attract predators reproductive inhibition - some plants such as firs (Abies) have insect hormone derivatives which if digested, prevent successful metamorphosis of insect juveniles masting - the synchronous production of very large numbers of progeny (seeds) by trees of one species in certain years

Traumatic Resin Ducts – Norway Spruce Produces terpene containing resins to inhibit feeding

Eurasian Jay with Acorn

Masting

Masting

Fagus sylvaticus – European Beech

Dipterocarp distribution

Dipterocarp trees

Dipterocarp seeds

Beech seeds and boring moth

Lyme’s disease life cycle

Masting and Human Health - Lyme’s Disease

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

Impact of Herbivores Is Not Uniformly Experienced

Aphids attacking Alfalfa Spotted Alfalfa Aphid

Induced defenses in Birch Trees

Induced defenses in Birch Trees

Induced defenses in Birch Trees

Rubus prickles

Acacia depanolobium

Giraffe and Acacia

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

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

Pine beetle infestation – British Columbia

Pine Beetle and Pitch Tube

Serengeti Grazing System

Serengeti Grazing System

Serengeti Grazing System 1 million wildebeest 600,000 Thompson’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

Serengeti Grazing System

Grazing facilitation Grazing facilitation occurs when the feeding activity of one herbivore species improves the food supply for a second species

Opuntia stricta – prickly pear

Prickly pear infestation in Australia

Area infested with prickly pear before biocontrol

Same area after biocontrol

Biocontrol Agent – Cactoblastis cactorum

Symbiosis

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

Gopher Tortoise – Commensal Host

Gopher Tortoise Distribution

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