Plant Ecology - Chapter 7

1. Plant Ecology - Chapter 7 Growth & Reproduction

2. Plant Growth - Modular

3. Plant Growth - Modular • Apical meristems • Intercalary meristems • Axillary meristems • Vascular cambium

4. Plant Architecture • Raunkaier classification system of perennial growth forms • >25 cm • <25 cm • At ground level • Below ground level

5. Plant Architecture • Plasticity can change plant shape in response to environmental conditions • Sun vs. shade • Self-pruning

6. Clonal Plants • Spatial distribution of ramets affected by: • Competition among genets • Spatial variation in resource distribution

7. Clonal Plants • Two growth forms • Phalanx - tightly grouped advancing front • Guerilla - isolated ramets penetrating competitors’ turf • All in the perspective

8. Clonal Plants - Why variation? • Mechanics of clonal spread • “Foraging” for resources • Following the resource distribution • Integration within clone to minimize environmental variation

9. Vegetative Reproduction • Apomixis - general term for asexual reproduction • Can take on many different forms

10. Vegetative Reproduction • Stolons - runners - branches that spread at surface of the soil, generate new ramets

11. Vegetative Reproduction • Rhizomes - underground horizontal stems growing near soil surface • Many grasses (like bamboo)

12. Vegetative Reproduction • Bulbs - underground rosette stems that store nutrients • Tulips, onions, daffodils

13. Vegetative Reproduction • Suckers - bud formation on some of near-surface roots • Quaking aspen clones can cover many hectares

14. Vegetative Reproduction • Clonal fragmentation - pieces break off, are capable of rooting to form new plants • Mother of thousands

15. Vegetative Reproduction • Bulbils - bulblike organs produced in leaf axils

16. Seeds Produced Asexually • Agamospermy - partial meiosis without reduction division - new embryos are clones

17. Seeds Produced Asexually • Grasses, raspberries, nettles

18. Sexual Life Cycles • Alternation of generations • Gametophyte • Sporophyte • Lower plants - gametophyte dominant • Higher plants - sporophyte dominant

19. Pollination Ecology • Pollination of typical, showy flowers done by birds or insects • But many flowers not showy, and likely are pollinated by wind

20. Pollination Ecology • Pollen transfer in most grasses and temperate-zone trees is by wind • Human allergies to pollen (hay fever) due to huge amounts of pollen in air

21. Pollination Ecology • Wind-pollinated flowers are not showy • Waste of energy to produce big, colorful petals, scents, nectar • Grasses often lack petals, sepals (interfere with pollen transfer by wind)

22. Pollination Ecology • Wind-pollinated plants produce massive quantities of pollen • Little influence over where pollen goes

23. Pollination Ecology • Wind-pollinated plants have higher pollen:ovule ratios than their animal-pollinated relatives

24. Pollination Ecology • Wind pollination most common in plants of open habitats • Usually flower before leaves emerge in spring • Also windiest time of year • Pollen can travel 100s of miles

25. Pollination Ecology • Wind pollination might be evolutionarily primitive • But wind pollination is common in both “old” and “new” taxa • Both can be present in same group

26. Visual Displays • Flower shape and color are advertisements of the rewards an animal can expect to receive from the flower • But both sides cheat

27. Visual Displays • Insects usually see colors at shorter wavelengths than humans (e.g., ultraviolet) • Birds more sensitive to colors in middle and red parts of spectrum • Birds may not see or be attracted to flowers bees can see

28. Visual Displays • Many bee-pollinated flowers are yellow • Bird-pollinated flowers often orange or red • Moths: white to pale yellow • Bats: white to brown

29. Visual Displays • Some flowers reflect light in several different wavelengths - can be seen by different pollinators • Contrasting colors may help guide pollinator - nectar guide

30. Visual Displays • Some plants have modified other plant parts to attract pollinators • Poinsettias - red bracts, leaves more attractive than small, yellow flowers

31. Visual Displays • Some plants arrange flowers into various aggregations - inflorescences • Increase the size of the attractive display without altering the flowers themselves

32. Floral Odors • Scents act as attractants over longer distances than visual attractants • First locate generally by scent, then locate specifically by sight

33. Floral Odors • Odors can vary independently of colors • Odors of different species can be highly variable, to attract different pollinators

34. Floral Odors • Bees attracted to sweet odors (like we are) • Bats like musty odors • Flies like rotting flesh and dung odors

35. Restricting Visitors • Adaptations to attract right visitor, repel unwanted visitors • Change flower shape from unspecialized bowl to something else • Only long tongues/mouthparts can access rewards

36. The Reward • Usually nectar (sugars) or pollen (protein) • Can also be oils, scent • Timing of reward also changeable (day vs. night) • Nectar robbers

37. Pollination Syndromes • Certain combinations of flower color, shape, odor, reward type, timing of rewards often associated with certain types of pollinators • Tightly coevolved mutualisms

38. Pollination Syndromes • Bee-pollinated flowers - yellowish, sweet-smelling, broad to allow bee contact with anthers, stigma, produce nectar during daytime

39. Pollination Syndromes • Bird-pollinated flowers - red or orange, little scent, produce lots of nectar during the day, shape with long tubes or spurs

40. Pollination Syndromes • Strength, generality of pollination syndromes may be overstated • Syndromes are tendencies rather than laws • Animals “outside” syndrome can accomplish significant pollination

41. Pollination Syndromes • Syndromes emphasize specialist pollinators, but neglect the generalist pollinators, which may be more important

42. Complex Interactions! • St. Johnswort on shores of Florida ponds • Plants growing by fish-free ponds more pollen-limited than those around fish ponds

43. Aquatic Pollinators? • Most aquatic plants bear flowers above water surface • Plants pollinated by insects or wind

44. Aquatic Pollinators? • Large numbers of aquatic plants have underwater flowers • One strategy: make pollen dispersal units bigger, disperse/receive at surface (Vallisneria) • Others: sticky pollen in rafts, elongated pollen

45. Plant Mating Systems • Factors that govern who can mate with whom • Many complications because of widely varying gender expression

46. Plant Mating Systems • Obligatory self-fertilization - inbreeding - individuals can only pollinate themselves • Outcrossing - mechanisms preventing self-fertilization • Something in between

47. Gender Issues • Some individual plants are cosexual - function as both males and females simultaneously • Hermaphroditism - most common type of gender expression in plants • Individuals have perfect flowers containing both functional stamens and functional stigmas

48. Monoecy • Individual plants have some flowers with functional stamens only (staminate flowers) and some with functional stigmas only (pistillate flowers)

49. Monoecy • All individuals have both types of flowers

50. Monoecy