Plant Ecology - Chapter 7 - Winona

Plant Ecology - Chapter 7 - Winona

Plant Ecology - Chapter 7 Growth & Reproduction Plant Growth - Modular Plant Growth - Modular Apical meristems Intercalary meristems Axillary

meristems Vascular cambium Plant Architecture Raunkaier classification system of perennial growth forms

>25 cm <25 cm At ground level Below ground level Plant Architecture Plasticity can change plant shape in response to environmental

conditions Sun vs. shade Self-pruning Clonal Plants Spatial distribution of ramets affected by: Competition

among genets Spatial variation in resource distribution Clonal Plants Two growth forms Phalanx - tightly grouped advancing front

Guerilla - isolated ramets penetrating competitors turf All in the perspective Clonal Plants - Why variation? Mechanics of clonal

spread Foraging for resources Following the resource distribution Integration within clone to minimize environmental variation

Vegetative Reproduction Apomixis general term for asexual reproduction Can take on many different forms Vegetative Reproduction Stolons runners branches that

spread at surface of the soil, generate new ramets Vegetative Reproduction Rhizomes underground horizontal stems growing near soil

surface Many grasses (like bamboo) Vegetative Reproduction Bulbs underground rosette stems that store nutrients Tulips, onions,

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

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

Vegetative Reproduction Bulbils bulblike organs produced in leaf axils Seeds Produced Asexually Agamospermy partial meiosis without reduction division - new

embryos are clones Seeds Produced Asexually Grasses, raspberries, nettles Sexual Life Cycles Alternation of

generations Gametophyte Sporophyte Lower plants gametophyte dominant Higher plants sporophyte dominant 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 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

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

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

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 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 Flower shape and color are advertisements of

the rewards an animal can expect to receive from the flower But both sides cheat 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 Many beepollinated flowers are yellow Bird-pollinated flowers often orange or red Moths: white to pale yellow Bats: white to

brown 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 Some plants have modified other plant parts to attract pollinators Poinsettias - red

bracts, leaves more attractive than small, yellow flowers Visual Displays Some plants arrange flowers into various aggregations inflorescences

Increase the size of the attractive display without altering the flowers themselves Floral Odors Scents act as attractants over longer distances

than visual attractants First locate generally by scent, then locate specifically by sight Floral Odors Odors can vary independently of

colors Odors of different species can be highly variable, to attract different pollinators Floral Odors Bees attracted to sweet odors (like

we are) Bats like musty odors Flies like rotting flesh and dung odors 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 Usually nectar (sugars) or pollen (protein) Can also be oils, scent Timing of reward also changeable (day vs. night) Nectar robbers

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 Bee-pollinated flowers - yellowish, sweet-smelling, broad to allow bee contact with anthers, stigma,

produce nectar during daytime 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 Strength, generality of pollination syndromes may be overstated Syndromes are tendencies rather than laws

Animals outside syndrome can accomplish significant pollination Pollination Syndromes Syndromes emphasize specialist pollinators, but neglect the

generalist pollinators, which may be more important 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? Most aquatic plants bear flowers above water surface

Plants pollinated by insects or wind 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 Factors that govern who can mate with whom

Many complications because of widely varying gender expression Plant Mating Systems Obligatory selffertilization inbreeding individuals can only pollinate themselves Outcrossing mechanisms

preventing selffertilization Something in between 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 Individual plants have some flowers

with functional stamens only (staminate flowers) and some with functional stigmas only (pistillate flowers) Monoecy All individuals

have both types of flowers Monoecy 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 3 systems of gender expression can

exist in combination with one another E.g., gynomonoecy, androdioecy Mixed gender expression Sequential hermaphroditism

- often begin life as male, then gradually switch to female Self-fertilization Cosexual plants may or may not be capable of selffertilization 25% of windpollinated cosexual

plants are mainly inbreeding remainder strongly outcrossing Self-fertilization Animal-pollinated cosexual plants evenly divided among strongly inbreeding,

strongly outcrossing, and mixtures of inbreeding and outcrossing 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 Plants produce

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

Sexual Selection Differential success at mating among plants Male-to-male competition Female choice 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 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 Inbreeding common in plants Most matings occur among

neighbors, which tend to be relatives Pollen Dispersal Animal-pollinated plants Plants are clumped, pollinators dont

move much 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 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 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 Fruit - mature ovary with seeds great variety Two functions protect developing seeds, affect dispersal of seeds Fruits and Seeds Compromise between protecting

seeds from being eaten, and attracting animal consumers to aid in seed dispersal Fruits and Seeds Wind dispersal float, flutter based on mass, surface area, shape

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

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

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