8/10/2019 aizen2003

1/7

Down-Facing Flowers, Hummingbirds and Rain

Author(s): Marcelo A. AizenSource: Taxon, Vol. 52, No. 4 (Nov., 2003), pp. 675-680Published by: International Association for Plant Taxonomy (IAPT)Stable URL: http://www.jstor.org/stable/3647342.

Accessed: 17/06/2014 01:46

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at.http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of

content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.

.

International Association for Plant Taxonomy (IAPT)is collaborating with JSTOR to digitize, preserve and

extend access to Taxon.

http://www.jstor.org/action/showPublisher?publisherCode=iapthttp://www.jstor.org/stable/3647342?origin=JSTOR-pdfhttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/stable/3647342?origin=JSTOR-pdfhttp://www.jstor.org/action/showPublisher?publisherCode=iapt

8/10/2019 aizen2003

2/7

8/10/2019 aizen2003

3/7

Aizen

*

Down-facing

lowers,

ummingbirds

nd

rain

being

ainwashed

rom

nthersnd

stigmas

i.e.,

the

pollen-protection

ypothesis ;adey

Aizen,

001).

Direct

ollen

osses romnthers

ould ecrease

he

rac-

tion f

pollen

hats

exported

nd he

mountvailable

for ertilization

see

also

Bynum

Smith,

001).

Pollen

wetting

ould lso affectts

viability

nd

germinability

(Huang

al.,2002).

Here,

reviewnd

provide

ew

vidence

elatedo

the

ollowingredictions

erivedrom

prengel's

lood-

ing

nd he

ollen-protection

ypotheses:

1.

Taxawith

own-facing

lowers

hould erelative-

ly

more

ommon

n

high-precipitation

nvironments

nd

associated ith ertebrate

ollinators

hat

emain

ctive

during

ain,

uch

s

hummingbirds.

2. Within

species,

lowers

hat acedown hould

have

heir ectaress diluted

uring

ain han lowers

that ace

p.

3. Within

species,

irect

ollen

osses romnthers

and

tigmas

hould

e

greater

n

up-

han

own-facing

flowers.

I

MATERIALSND METHODS

I

conducted

screening

f he

ropical

Amazonian)

rainforestlora fLos

Amigos

onservation

rea,

Madre

de

Dios,

PerN 1234'

S,

70006'

W) (R.

Foster,

.

Betz,

R.

Burnham,

npubl.)

nd he

emperate

Valdivian)

ain-

forest

lora fPuerto

lest,

Rio

Negro,

rgentina

41

08'

S,

7148'

W;

Brion

al.,

1988).

Based

n

photographs

showinglose-up

lowerr nflorescence

mages

92

and

42

species

or os

Amigos

ndPuerto

lest,

espective-

ly), estimatedhe roportionf pecies ith own-fac-

ing

lowers

i.e., pecies

ith lowers

howing,

n

ver-

age,

ngles

0 relativeo

the

horizontal)mong

um-

mingbird-

nd

nsect-pollinated

oody lants

see

also

Tadey

Aizen,

002).

n

the

ase

of

Los

Amigos,

olli-

nator

ype

was assumed ased

on flower

hape

nd

colour

e.g.,

roctor

al.,

1996)

whereas

n he lora f

Puerto

lest,

classification

as based on

published

accounts

n the

dentity

f

flower

isitors

Smith-

Ramirez,

993;

Smith-Ramirez

Armesto, 994;

Vazquez

&

Simberloff,

002).

Differences

etween

at-

egories

ere ssessed

y

Fisher's

xact est.

I

also

estimated

he

roportion

f

nsect-ndhum-

mingbird-pollinatedoody enera ith lowersxhibit-

ingnegative

ngles

t

five

ocalities

Bariloche,

lao-

Llao,

Puerto

lest,

Antillanca,

nd

Chiloe)

distributed

along

strong

-W rainfall

radient

cross

heAndes

between

0 and

2S,

based

ntheist f

plant enera

compiled

y

Aizen Ezcurra

1998).

Distance

etween

the asternmostite

Bariloche)

o thePacific

Ocean

(Chiloe)

s about

30

km.

Rainfall

anges

rom

00

mm

at

Bariloche

o 000

mm

tAntillanca.

espite

ainfall

t

theChiloe ite

-2800

mm) eing

omewhatower han

at

Antillanca,

ir

humidity

s

very igh ear-round

ue o

proximity

o the

acific cean. lower rientationas

assigned

o oneof two

ategorieseitherp-

or down-

facing

based nflower

hotographs

nd/or

irect

ield

observations.ost

genera

ere

epresentedy ust

ne

species t a singleocality,nd n thefew nstances

wheremore han ne

species ergenus

ccurred

hey

had he ame

ype

fflowerrientation.

hanges

n

he

proportion

f

genera

ith

own-facing

lowers

long

his

E-W

gradient

as ssessed

sing egression

nalysis

or

categorical

ata

see

Aizen

Ezcurra,998,

ormethod-

ological

etails).

In

May

002

group

f

tudentsnd conducted

n

experiment

t

Los

Amigos

onservation

rea, eru,

n

which

e simulated

mm frainfalln

fresh

ut low-

ers of

hummingbird-pollinated

esleria

sprucei

(Gesneriaceae),

large

herb hat

ypicallyroduces

down-facing

lowers

Fig.

a).

We

applied

hree reat-

ments:lowerseld t heirverageaturalown-facing

orientation

~

-70 relative

o

the

horizontal)

hile

exposed

o

rain,

lowers

eld

p-facing

-

+70)

while

exposed

o

rain,

nd

flowers

ot

xposed

o rain.

ain

was simulated

sing plastic

lass

with

minute

erfora-

tions.

Nectar olume

in

pl)

and

concentration

in

%

sucrose

quivalents)

eremeasured

n

flowers

ampled

after

5, 60, 120,

360

min

using

alibrated

apillary

tubes

nd hand

efractometer,

espectively-10

flow-

ers

per

reatmenttime

ombination).

ectar ariables

were

nalyzed

sing two-way

NOVAwith reatment

andtime s fixed actors.olume as transformeds

log x+1)

tomeet

riteria

f

normality

ndhomoscedas-

ticitySokal& Rohlf,981).

* DOWN-FACING

FLOWERS,

HUM-

MINGBIRDS

AND RAIN

Hummingbirds

re

the

most

mportant

ertebrate

pollinators

n

he

ewWorld.

pecies ollinated

y

hese

vertebrates

epresent

sizable

ercent

f

many ropical

and even

emperate

loras

n

theAmericas

Grant

Grant,

968;

Gentry,

982;

Aizen &

al.,

2002).

Hummingbirds

re

ble o

forage

nder

eavy

ain,

nd

even

during

nowfalls

Burton,

001).

Furthermore,

hummingbirdlowersre enerallyong-livednd onot

close

during

ain

pers.

bserv.).

herefore,

down-fac-

ingmorphology

hould

ecommon

mong ummingbird

flowers.

In

both ainforest

loras,

he

ropical

f

Los

Amigos

and he

emperate

f Puerto

lest,

85% of

thehum-

mingbird-pollinated

pecies roduce

own-facing

low-

ers

i.e., xhibiting

ean

ngles

0with

espect

o he

horizontal).

s a

contrast,

35%

of

he

nsect-pollinated

676

TAXON

52

November 003:

XX-XY

This content downloaded from 62.122.76.48 on Tue, 17 Jun 2014 01:46:54 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsphttp://www.jstor.org/page/info/about/policies/terms.jsp

8/10/2019 aizen2003

4/7

Aizen

*

Down-facing

flowers,

hummingbirds

and rain

Fig.

1.

Species

tested

experimentally

or ffects f rainon nectar nd

pollen.

A,

a flower f

Besleria

sprucei

over

deve-

lopment,

flowers bend

from a

slightly down-facing position,

as

shown,

to

an

-

-70; B,

a

pendant

inflorescence of

Tristerix

corymbosus showing

their

down-facing

flowers.

LOS AMIGOS

100

P