BIOS 5970: Plant-Herbivore Interactions Dr. Stephen Malcolm, Department of Biological Sciences

Transcription

1 BIOS 5970: Plant-Herbivore Interactions Dr. Stephen Malcolm, Department of Biological Sciences Week 8. Pollination and fruit dispersal: Lecture summary: Mutualisms between plants and animals: Pollination Seed and fruit dispersal Frugivory Click here! for video Resplendent quetzal dispersing wild avocado fruit in Costa Rican cloud forest (Living Earth Foundation The Rainforest) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 1

2 2. Mutualisms: Mutualisms exist when two or more species enhance each other's fitnesses. Symbiotic mutualisms involve species that live in close physical contact. But here we consider nonsymbiotic mutualisms such as: Pollination, seed dispersal and protection see Table 6-1. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 2

3 3. Pollination: Angiosperm flower evolved as an elaborate device for: (1) Capturing pollen from other plants of the same species. (2) Distributing its own pollen to other flowers of the same species (Fig. 6-1). BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 3

4 4. Flowers: Petals and sepals are modified leaves with two key functions: (1) Attract animals with bright pigments, odors and sometimes with nectar-producing tissues: Apomorphic or derived characters. (2) Protect the developing flower bud/ovary from foraging insects: Plesiomorphic or primitive characters. Various pollinators attracted with a range of signals (Table 6-2). BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 4

5 5. Pollinator rewards: Sugar concentrations in nectar can vary from 15 to 88% by weight. Ratios of different sugars also vary according to the predominant pollinator group (Table 6-3): Hummingbirds (neotropics) prefer a high ratio of the disaccharide sucrose to the monosaccharides glucose and fructose. Sunbirds (old world) and some insects prefer lower ratio of disaccharide:monosaccharide. Amino acids highest in nectar of flowers that are pollinated by species that do not eat pollen BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 5

6 6. Seed and Fruit dispersal: Dispersal mutualisms older than pollination mutualisms: Cycad seeds dispersed by reptiles 200 million years ago. Today, up to 90% of trees and virtually all the shrubs in tropical rainforests produce fruits adapted to attract birds or mammals!! BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 6

7 7. Functions of angiosperm fruit: (1) Nourishment for the diploid zygote from triploid endosperm: Carbohydrates, fats & protein (see Table 6-5). (2) Protection: From protective maternal diploid seed coat. (3) Dispersal of plant embryos: Dispersal structures: Wings, nutritious aril (vertebrates) or elaiosome (ants). Dispersal syndromes (Table 6-4) analogous to pollination syndromes: Predators may disperse seeds as they eat their seed-eating prey: e.g. owls and finches in the Galapagos Islands BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 7

8 8. Frugivory: Fruit-eating birds and mammals that depend on fleshy fruits for food are frugivores: Often have color vision. Visual and olfactory displays by plants are highly conspicuous signals. Herbivorous guts mostly destroy seeds inside fruit But frugivores eat large amounts of fruit (low protein) and often have short digestive tracts to speed seed passage and ensure gentle treatment while the consumer digests the pulp. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 8

9 9. Plant manipulation of frugivore dispersers: Plants can produce laxatives that speed seed passage rates and increase plant reproductive success: E.g. Murray, K.G., S. Russell, C.M. Picone, K. Winnett-Murray, W. Sherwood, and M.L. Kuhlmann Fruit laxatives and seed passage rates in frugivores: consequences for plant reproductive success. Ecology 75(4): BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 9

10 Fruit pulp speeds passage of pioneer shrub fruits through black-faced solitaires: Cumulative passage times of natural fruits ( ), artificial fruits with pulp extract ( ) and artificial fruits without pulp ( ). Fig. 1 from Murray, et al Ecology 75(4): BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 10

11 Germination success of seeds decreases with increased time in bird guts: Fig. 2 from Murray, et al Ecology 75(4): Dashed line is germination success of seeds removed from fruits by hand BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 11

12 Dispersal distance increases with time spent in bird guts: Fig. 3 from Murray, et al Ecology 75(4): BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 12

13 Table 6-1: BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 13

14 Table 6-3: BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 14

15 Table 6-4: BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 15

16 Table 6-5: BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 16

17 Bright red pigments attract hummingbirds: Green hermit hummingbird, South America (Living Earth Foundation The Rainforest) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 17

18 Orchid odors attract euglossine bees: Euglossine bee in Costa Rica leaving an orchid with pollinia attached to its back. The orchid manipulates the male bee with pheromones which the bee then uses to attract females (Living Earth Foundation The Rainforest) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 18

19 Nectar and color attract butterflies: Dircenna dero butterfly in Peru (Living Earth Foundation The Rainforest) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 19

20 Tropical fruit diversity: Diversity of fruits with toxic seeds available to foraging macaws in Peru (National Geographic 1994, 185(1): 130) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 20

21 Macaws and hornbills eat fruit pulp and disperse seeds: Blue-and-yellow macaw in Peru (National Geographic 1994, 185(1): 131) Rhinoceros hornbill eating strangler fig fruit in Borneo (National Geographic 1997, 191(4): 41) BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 8: Pollination and fruit dispersal Slide - 21