BBC Wildlife - UK (2020-08)

TheExplainer

Beech: Derek Croucher/Alamy(x2); penguin: Tui De Roy/NPL; anole: James Christensen/NPL; anemone: NOAA Photo Library/Wikipedia/Creative Commons

Whydotreeleavesturn

darkerinsummer?

S

pringintemperate

climatesis a carnivalof

colour.Asdayslengthen

andtemperaturesrise,the

electric-greenoffreshfoliage

transformsthedulllandscapes

ofwinter.Yetseveralmonths

later,thosebrightleaveshave

turneddarkgreen,givingwoods

a dullerappearance.

Springfoliageis a magnetfora

multitudeofcaterpillarsandother

insectlarvae,whichcan’twaittoget

theirjawsonthesoftandsupple,

cellulose-rich leaves. So, to repel this

armyofleaf-

munchers,plants

defendthemselves

byproducing

darktannins.

Thesebitter-tasting

chemicalsarea

naturalpestcontrol.

Theybecomeactivated

whentheleafis eaten,andarecapable

ofdamagingthemouthandstomach

proteinsofattackinginsects.Assummer

wearson,theleavesgeteverdarkerand

moredistastefulastanninsbuildupto

fend off the onslaught.Ed Drewitt

BOTANY

Lizardssuchasthegrass

anole sport dewlaps.

A strangewordforanequally

strangeaccoutrement,‘dewlap’

referstoa wobblyflapofskin

underthechin.It’snormally

associatedwithlargeherbivores,

suchasthemoose,eland(an

Africanantelope)andkouprey

(ararespeciesofAsianwild

cattle).Somelizards,including

iguanasandagamas,alsohave

foldabledewlaps.Asa rule,these

peculiarthroatflagsareused

byadultmalesfordisplay– to

intimidaterivalsandimpress

females– butthere’salsoa

theorytheymayhaveevolved

to regulatetemperature.

Ben Hoare

Dewlap

Thedarktannins

producedinleaves

leavea bittertaste

inthemouthsof

hungry caterpillars.

Whyarethere

nopenguins in

theArctic?

B

esidesa lonespeciesuniqueto

theGalápagosIslandsonthe

equator,penguinsliveonlyinthe

SouthernHemisphere– everywhere

fromAntarcticatovariousremote

islandsandthesoutherncoastsof

Africa,Australia,NewZealandand

SouthAmerica.Butwhy?Contrary

topopularbelief,they’renot

specificallydependentona cold

climate,butonnutrient-richwaters

thatsustaina productiveenough

food-chaintokeeptheminfish.In

thetropicalGalápagosandPeru,

thisis deliveredbyupwellingsof

deepoceanicwater.

It’slikelypenguinshaven’tspread

furthernorthbecauseflightlessness

limitstheirabilitytomigrateand,

movingnorthfromhere,thereare

vastzonesoflessproductivetropical

watersbeforethenextbigupwellings.

Beingground-nestingandunabletofly,

penguinsarealsorestrictedtoplaces

withoutlandpredators,sowouldbe

vulnerableintheArcticwithitsfoxes,

wolves and polar bears.Ellen Husain

ORNITHOLOGY

Galápagos

penguinsare

theonlyones

tohaveedged

northofthe

equator.

August 2020

Q&A