Challenges Herbivores Face in Foraging

Transcription

1 Challenges Herbivores Face in Foraging Primary Compounds Energy, protein, and mineral concentrations vary in different plant species and parts 1

2 Foraging Challenges Primary Compounds Can herbivores sense nutrients and if so by what mechanisms? Secondary Compounds Secondary compounds vary in kind and amount in different plant species and parts 2

3 All plants contain secondary compounds glucosinolates cyanogenic glycosides glycoalkaloids tomatine alkaloids Secondary Compounds in Grasses ALKALOIDS: wiregrass, reed, oat, bamboo, brome grasses, Rhodes grass, orchard grass, fescue, barnyard grass, millet, barley, spear grass, ryegrass, rice, switch grass, bluegrass, sorghum grasses, corn. CYANOGENIC GLYCOSIDES: wheat grasses, bentgrass, big bluestem, broomsedge, oat, bamboo, grama grass, fescue, mannagrass, barley, ryegrass, rice, switchgrass, bluegrass, sugarcane, sorghum grasses, wheat, corn PHENOLICS: nearly all grasses, including canarygrass, bromegrass, wildrye, sorgum, corn, oats, timothy TERPENES: Monoterpenes - 4 genera, Sesquiterpenes - 2 genera, Triterpenes 36 genera SAPONINS: 25 genera and numerous species of grasses SILICA: wide variety of grass and sedge species NITRATES: oats, rye, wheat, corn, Sudan grass, Johnson grass, flax CONDENSED TANNINS: switchgrass, wiregrass, big bluestem, broomsedge PROTEINASE INHIBITORS: grama, barley, wheat, big bluestem, broomsedge 3

4 Plants that Contain Poisonous Plants Secondary Compounds Tannins 4

5 Terpenoids Alkaloids 5

6 6

7 Secondary Compounds Can herbivores detect secondary compounds and if so by what mechanisms? 7

8 Foraging Challenges Variability Spatial and Temporal Primary and secondary compounds vary spatially and temporally 8

9 How does the environment where a plant is growing affect concentrations of secondary compounds? 9

10 Plant Growth Foraging Challenges Carbon-Nutrient Balance Grow/Differentiate Nutrient Stress Resource Availability Production of Compound decrease same increase decrease = same = increase = Carbon-Nutrient Balance Carbon-based metabolites (e.g., phenolics, tannins, terpenes) Nitrogen-based metabolites (e.g., alkaloids, cyanogenic glycosides) 10

11 Nutrients and water typically Terpenes Tannins decrease carbon-based compounds and increase palatability Carbon-Nutrient Balance Grow High Defend Low Resource Availability (nutrients, light, water) Carbon-Nutrient Balance Carbon-based metabolites (e.g., phenolics, tannins, terpenes) Nitrogen-based metabolites (e.g., alkaloids, cyanogenic glycosides) 11

12 Cyanogenic glycosides in white clover and serviceberry, and alkaloids in lupine, larkspur, and hemlock are higher in plants growing on dry sites than on wet sites and in dry year than in wet years. Cyanogenic glycosides in sorghum, sudangrass and cassava, and alkaloids in lupine, tobacco and fescue are higher in plants fertilized with nitrogen than in nitrogen-limited plants. Tall Fescue Larkspur 12

13 Relative Toxicity Foraging Challenges Endophyte-Infected Tall Fescue Fertilize (spring vs fall) Graze (vegetative vs reproductive) High Toxic Window for Larkspur Low Toxic Window Timing of grazing in relation to secondary compounds 13

14 Variability Spatial and Temporal How well do herbivores position themselves in the environment to maximize encounters with nutritious mixtures of forages? Morphological Defenses Morphological defenses vary among different plant species 14

15 15

16 Intake = bite size x bite rate x grazing time Morphological Defenses How effective are herbivores at coping with morphological defenses? 16

17 Unfamiliar Environments Unfamiliar environments present herbivores with unknown risks and opportunities Biophysical and Social Acts of Nature Fires, Floods, Emigration Biophysical Environments 17

18 Social Environments Unfamiliar Environments How well do herbivores adjust to unfamiliar environments? 18

19 19