Chapter7

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Plant Ecology - Chapter 7: 

Plant Ecology - Chapter 7 Growth & Reproduction

Plant Growth - Modular: 

Plant Growth - Modular

Plant Growth - Modular: 

Plant Growth - Modular Apical meristems Intercalary meristems Axillary meristems Vascular cambium

Plant Architecture: 

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

Plant Architecture: 

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

Clonal Plants: 

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

Clonal Plants: 

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

Clonal Plants - Why variation?: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

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

Vegetative Reproduction: 

Vegetative Reproduction Bulbils - bulblike organs produced in leaf axils

Seeds Produced Asexually: 

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

Seeds Produced Asexually: 

Seeds Produced Asexually Grasses, raspberries, nettles

Sexual Life Cycles: 

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

Pollination Ecology: 

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

Pollination Ecology: 

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

Pollination Ecology: 

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)

Pollination Ecology: 

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

Pollination Ecology: 

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

Pollination Ecology: 

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

Pollination Ecology: 

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

Visual Displays: 

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

Visual Displays: 

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

Visual Displays: 

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

Visual Displays: 

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

Visual Displays: 

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

Visual Displays: 

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

Floral Odors: 

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

Floral Odors: 

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

Floral Odors: 

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

Restricting Visitors: 

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

The Reward: 

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

Pollination Syndromes: 

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

Pollination Syndromes: 

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

Pollination Syndromes: 

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

Pollination Syndromes: 

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

Pollination Syndromes: 

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

Complex Interactions!: 

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

Aquatic Pollinators?: 

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

Aquatic Pollinators?: 

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

Plant Mating Systems: 

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

Plant Mating Systems: 

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

Gender Issues: 

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

Monoecy: 

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

Monoecy: 

Monoecy All individuals have both types of flowers

Monoecy: 

Monoecy

Dioecy: 

Dioecy At least some plants in a population have only pistillate or only staminate flowers Function as female only or male only

Mixed gender expression: 

Mixed gender expression 3 systems of gender expression can exist in combination with one another E.g., gynomonoecy, androdioecy

Mixed gender expression: 

Mixed gender expression Sequential hermaphroditism - often begin life as male, then gradually switch to female

Self-fertilization: 

Self-fertilization Cosexual plants may or may not be capable of self-fertilization 25% of wind-pollinated cosexual plants are mainly inbreeding - remainder strongly outcrossing

Self-fertilization: 

Self-fertilization Animal-pollinated cosexual plants evenly divided among strongly inbreeding, strongly outcrossing, and mixtures of inbreeding and outcrossing

Confusion: 

Confusion Different forms of gender expression can occur at same time within a population Difficult to determine how they actually function

Competition for Pollinators & Pollen: 

Competition for Pollinators & Pollen Plants produce excess ovules that never produce viable seeds Competition for pollinators, pollen? Too few pollinators, or very inefficient at transferring pollen

Sexual Selection: 

Sexual Selection Differential success at mating among plants Male-to-male competition Female choice

Sexual Selection: 

Sexual Selection Male-to-male competition results in extremes of floral displays Large inflorescences where most flowers function only to attract pollinators Functionally male - reproduce only by having pollen taken elsewhere

Sexual Selection: 

Sexual Selection Female choice occurs at site of pollination Competition among pollen grains Female flower “chooses” pollen via biochemical interactions Affect pollen germination, rate of pollen tube growth May selectively abort certain seeds

Pollen Dispersal: 

Pollen Dispersal Inbreeding common in plants Most matings occur among neighbors, which tend to be relatives

Pollen Dispersal: 

Pollen Dispersal Animal-pollinated plants Plants are clumped, pollinators don’t move much

Pollen Dispersal: 

Pollen Dispersal Wind-pollinated plants Most pollen grains fall nearest their source Plants releasing single pollen grains most likely to mate with most distant individuals Clumped pollen - mating with nearest neighbors

Assortative Mating: 

Assortative Mating Plants with similar phenotypes mate with one another more often than they would by chance Time of flowering, flower color, influence the pollinator

Negative Assortative Mating: 

Negative Assortative Mating Plants with dissimilar phenotypes mate with one another more often than they would by chance Heterostyly - styles/stigmas of different lengths - cause obligate outcrossing

Fruits and Seeds: 

Fruits and Seeds Fruit - mature ovary with seeds - great variety Two functions - protect developing seeds, affect dispersal of seeds

Fruits and Seeds: 

Fruits and Seeds Compromise between protecting seeds from being eaten, and attracting animal consumers to aid in seed dispersal

Fruits and Seeds: 

Fruits and Seeds Wind dispersal - float, flutter based on mass, surface area, shape

Fruits and Seeds: 

Fruits and Seeds Animal dispersal - attract/reward disperser, but protect seeds Thick, hard seed coats Spit out, regurgitated, pass with feces

Seed Banks: 

Seed Banks Dispersal in time Seedbank - collection of seeds in the soil Short-lived plants tend to have long-lived seeds, and vice versa