2 BIO 4134: Plant-Animal Interactions

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1 1 Characteristic Invertebrates Vertebrates Body Size Small Large Metabolic Rate Low High Population Density Large Small Food Specificity High Low Bite Size Small Large Mobility Low-High Low-High Starvation Tolerance Low High 2 3 1

2 Short Greens Long Grasses Standing Crop April 20 ± ± 32 July 58 ± ± 35 October 52 ± ± 38 Production April-October 207 ± ± 102 4! Varies within and between years! Leads to migrations! Quality of food varies too 5 OH! Plant allelochemicals have one of 3 kinds of composition Phenolics Alkaloids Terpenoids 6 2

3 ! Silica evolved as physical defense Originally structural Modified into saws! Induced toxicity by fungal endophytes 7 Classes Abundance Nectarivores Gumivores Frugivore/omnivores Frugivore/granivores Frugivore/herbivore Herbivore/browser 3% 10% 40% Herbivore/grazer 23% 8! Metabolic needs increase * (body mass) 0.75! Digestive capacity increase * (body mass)

4 ! Adaptations towards particular forms of mobility lead to reductions in others 10! First treatment of food is in mouth: saliva and mastication! In order to extract nutrients, must break all cell walls Release proteins, dissolved carbohydrates 11! Slow down food! Maximize fermentation by symbionts! Fore-gut (Pre-gastric)! Hind-gut (Postgastric) 12 4

5 13! Hierarchy of scales for decision-making! Herbivores select among genotypes and ecotypes! General preference for male plants or plant parts! Plant susceptibility may depend on identity of neighbour Associational resistance 14 Lepus timidus foraging on Betula pubescens 15 5

6 ! 3 Main Assumptions: 1) Decision (which of forager s problems to analyze?) 2) Currency (how to evaluate the choices?) 3) Constraint assumptions (what limits the choices?) Intrinsic, extrinsic or life-history related 16 Action Magnitude Feeding 10,000 bites Trampling 25 m 2 Defecation Urination 14 pellets (2kg dry matter) 10L Alces alces: ecological engineers 17! Continuum from death to no response! Trade off exists between protection and recuperation! In general, herbivory decreases plant fitness Browsing in Vaccinium myrtilloides caused a decrease in flower and fruit production Browsing in Pinus sylvestris led to a decrease in cone production 18 6

7 ! Grazing shown to increase NPP Does it increase fitness?! Timing of herbivory can affect plant response 19! Increase in ratio my help to explain vigorous regrowth Roots intact, fewer actively growing points! Priority often recuperate leaf area via reduction of belowground productivity Return to original root:shoot 20! Better studied in insects! Boreal forest: 4 spp. produce unpalatable reshoots following hare browsing 21 7

8 ! Some spp. show increased spinescence following browsing Acacia, Ilex! Others show increased vegetative growth Rubus vestitus 22! Browsing increases palatability or biomass! Grazed patches in Serengeti or NAm Tallgrass prairies! Termed management of resource but only if territoriality observed 23! Affect plants through extinction/colonization rates! Common/dominant sp. may become disproportionate! Trade-off between palatability and competitiveness! Intermediate disturbance hyp 24 8

9 ! Depends whether animal prefers early or late successional species! Generalized grazing leads to maintenance of grasslands Reinforced by fire 25! Chemistry! Leaf litter! Canopy cover! Microclimate 26! 4 major mechanisms in boreal forest (Pastor et al., 1997) 1) short-term compensatory growth 2) deposits of feces and urine 3) long-term change in spp. composition due to succession 4) changes in physical environment due to previous 3 examples 27 9

10 ! Functional response Change foraging behaviour as a function of food quality and quantity 28! Numerical Response Birth and death rates are affected! Biological Conundrum: population cycles