Spread of hu­mans across planet led to other mam­mals get­ting smaller

The Woolwich Observer - - LIVING HERE - WEIRD NOTES

Q. Why don’t de­cid­u­ous trees — maples, oaks, birches, etc. — keep their leaves year round? A. They’re sav­ing their lives by shed­ding their leaves as the sea­son changes, says Dan Lewis on his “Now I Know” web­site. Dur­ing the warmer months, the green leaves ab­sorb sun­light and turn it into food for the trees. But as the air gets colder, water in the leaves starts to freeze and so the trees, un­able to rely on pho­to­syn­the­sis, go into a sort of hi­ber­na­tion. Ac­cord­ing to the Na­tional Wildlife Foun­da­tion, if they’re not eat­ing, “th­ese trees need to con­serve en­ergy and re­duce them­selves to their tough­est parts.”

So off come the leaves, since any water in their veins will freeze and kill them. More­over, when a tree comes out of hi­ber­na­tion, too many dead leaves will doom it. But be­fore that hap­pens, a hor­monal change takes place: “ab­scis­sion” cells (the same root as “scis­sors”) ap­pear where the leaf stem meets the branch and even­tu­ally a thin bumpy line of cells push the leaf away from the stem (NPR). Be­cause the con­nec­tion is weak­ened, an au­tumn breeze will blow the leaves off the tree, leav­ing their col­or­ful re­mains on the ground be­low. And the trees are saved to await new leaves when the sea­son changes again. Q. “Honey, I Shrank the Mam­mals,” the ar­ti­cle ti­tle reads. What’s the story here? A. “Where hu­mans mi­grate, mam­mals be­come smaller,” says Mark Fis­chetti in “Sci­en­tific Amer­i­can.” For 65 mil­lion years, mam­mals got big­ger, and ex­tinc­tion rates among all sized mam­mals were sim­i­lar. But in the past 100,000 years, larger species started dy­ing off faster, as ho­minin species shifted across the con­ti­nents — Eura­sia, Aus­tralia, then North and South Amer­ica 15,000 years ago.

Ac­cord­ing to pa­le­oe­col­o­gist and lead re­searcher Felisa Smith, “hefty an­i­mals suf­fered from be­ing hunted, as well as from habi­tat change and fires caused by hu­man ac­tiv­i­ties . ... Two cen­turies from now, cows may top the size chart.”

“We have changed the en­tire Earth,” Smith says. “Now we have to be na­ture’s stew­ards.” Q. Whether it’s melodic bird­song, a cho­rus of in­sects, the howl of a coy­ote, or the barks and purrs of our do­mes­tic com­pan­ions, the an­i­mal king­dom is a de­light­fully noisy place — on land, that is. But why not underwater? A. In fact, underwater an­i­mals are just as noisy! But we are not “well adapted to hear­ing when our ears are full of water,” says He­len Scales in “Discover” mag­a­zine. Also, “most sound waves don’t pierce the wa­ter­line, but in­stead bounce back into the depths.” Even if we do man­age to hear underwater noises, since sound trav­els much faster in water than in air, we are not adept at pin­point­ing the source.

The in­ten­sity and di­ver­sity of underwater noise be­came clear with the de­vel­op­ment of sonar and hy­drophones in World War II, and while some is at­trib­ut­able to waves, wind and tides, it was soon de­ter­mined that an­i­mals were chiefly to blame. “Fish were so noisy they trig­gered underwater bombs which were sup­posed to det­o­nate only at the sounds and vi­bra­tions of a nearby sub­ma­rine.”

Fol­low­ing the war, one sci­en­tist at the fore­front of underwater noise re­search was a woman aptly named Bob­bie Fish, who for 20 years recorded and iden­ti­fied underwater sounds, even­tu­ally coau­thor­ing the sem­i­nal “Sounds of Western North At­lantic Fishes.” Booms, rat­tles, pig-like grunts, rusty-hinge squeaks-the di­ver­sity is stag­ger­ing, and the fish species in­volved num­ber in the hun­dreds.

Yet lit­tle is known about the pur­pose of fish talk, or even how and how well fish can hear th­ese sounds. Af­ter all, “they don’t have ears, at least not ones that stick out of their heads!”

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