Spe c ie s Ric hne ss MODUL E 13: SPE CI E S RI CHNE SS UNI - PDF document

Spe c ie s Ric hne ss MODUL E 13: SPE CI E S RI CHNE SS UNI T 3: E COL OGI CAL BI OGE OGRAPHY Ob je c tive s  At the e nd o f this se rie s o f le c ture s yo u sho uld b e a b le to :  De fine te rms.  De sc rib e the ro le o f isla nds in b io g e o g ra phy a nd c o mmunity e c o lo g y  Diffe re ntia te b e twe e n the Sta tic T he o ry o f I sla nds a nd the E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy.  De sc rib e the Spe c ie s-Are a a nd Spe c ie s-I so la tio n re la tio nships  Disc uss Pre sto n’ s e xpla na tio n o f the Spe c ie s-Are a re la tio nship.  Disc uss a nd g ive e xa mple s o f spe c ie s turno ve r.  E xpla in a nd de mo nstra te the E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  Disc uss the a dva nta g e s a nd limita tio ns o f the E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy. 1

I sla nds a re I nflue ntia l  We ll de fine d  Re la tive ly simple b io ta s  Nume ro us  Na tura l e xpe rime nts  Are a  I so la tio n  Pre da tio n a nd c o mpe titio n Sta tic T he o ry o f I sla nds  Co mmunity struc ture o n isla nds wa s fixe d  E vo lutio na ry e ve nts (o ve re mpha size d)  Uniq ue immig ra tio n e ve nts (no g e ne ra l pa tte rn)  Uniq ue e xtinc tio n e ve nts (no g e ne ra l pa tte rn)  Numb e r o f nic he s o n the isla nd we re fixe d  “E ithe r a spe c ie s ha d a lre a dy c o lo nize d a n isla nd o r it ne ve r wo uld.”  No g e ne ra l e xpla na tio ns o r mo de ls 2

Dyna mic E q uilib riums  Oppo sing fo rc e s ma inta in c o nsta nc y in so me c ha ra c te ristic o f a syste m de spite c o ntinua l c ha ng e s in o the r intrinsic pro pe rtie s o f the syste m.  Wa rm-b o die d a nima l e xa mple .  Pa ra dig m shift  So ug ht g e ne ra l pa tte rns  So ug ht g e ne ra l e c o lo g ic a l e xpla na tio ns to tho se pa tte rns  L e ss e mpha sis o n e xpla ining the idio sync ra tic o r e xc e ptio na l o b se rva tio ns. I sla nd Pa tte rns  T he numb e r o f spe c ie s te nds to inc re a se with isla nd a re a  T he numb e r o f spe c ie s te nds to de c re a se with inc re a se d iso la tio n o f the isla nd. 3

Spe c ie s-Are a Re la tio nship  Sc ho e ne r -- “o ne o f c o mmunity e c o lo g y’ s fe w la ws”  Mo st g e ne ra l, b e st-do c ume nte d pa tte rns in na ture . Spe c ie s-Are a Re la tio nship  Arrhe nius e q ua tio n / Po we r mo de l  Mo difie d fro m the Allo me tric e q ua tio n (sc a ling mo rpho lo g y a nd me ta b o lic pro c e sse s)  Also c a lle d the po we r mo de l 4

Spe c ie s-Are a Re la tio nship  Arrhe nius e q ua tio n / Po we r mo de l  S = Spe c ie s ric hne ss  c = A fitte d c o nsta nt (ta xo no mic g ro up a nd re g io n – spe c ie s so urc e )  A = Are a  z = A fitte d c o nsta nt (re g io n – the type o f the a re a sa mple d) Spe c ie s-Are a Re la tio nship  Arrhe nius e q ua tio n / Po we r mo de l  L o g tra nsfo rm o f the po we r mo de l  We c a n no w e stima te c a nd z fro m simple line a r re g re ssio n o n the lo g tra nsfo rme d spe c ie s ric hne ss a nd lo g tra nsfo rme d a re a . 5

Spe c ie s-Are a Re la tio nship  c is fre q ue ntly inte rpre te d a s the inte rc e pt (this fo llo ws fro m the lo g tra nsfo rme d line a r e q ua tio n)  T he a c tua l inte rc e pt o f the po we r mo de l is 0  z is fre q ue ntly inte rpre te d a s the slo pe (this fo llo ws fro m the lo g tra nsfo rme d line a r e q ua tio n)  z de sc rib e s the re la tio nship b e twe e n L o g S a nd L o g A – no t the re la tio nship b e twe e n S a nd A  T he re la tio nship b e twe e n S a nd A (ho w q uic kly S inc re a se s a s A inc re a se s) is influe nc e d b y b o th c a nd z. 6

Spe c ie s-Are a Re la tio nship  Mo st a rg ume nts re la te d to spe c ie s-a re a re la tio nships fo c us o n c o mpa riso ns o f the “slo pe ” z a s if z wa s the e ntire sto ry.  z va rie s o nly slig htly  T ypic a lly b e twe e n 0.15 a nd 0.35  Co ntine nts te nd to 0.15  I sla nds te nd to 0.35  T he o re tic a l va lue 0.25 (de rive d b y Pre sto n – mo re o n this in a mo me nt)  c va rie s c o nside ra b ly  By o nly c o mpa ring z-va lue s we a re missing the po int. Spe c ie s-Are a Re la tio nship  Pre sto n’ s e xpla na tio n fo r the Spe c ie s-Are a Re la tio nship  A c o mmunity’ s spe c ie s a b unda nc e c urve te nds to a ppro xima te a trunc a te d o r c a no nic a l lo g no rma l distrib utio n.  T runc a tio n o r ve il line 7

Spe c ie s-Are a Re la tio nship  Pre sto n’ s e xpla na tio n fo r the Spe c ie s-Are a Re la tio nship  As the a re a inc re a se s the numb e r o f individua ls sa mple d will inc re a se – inc re a sing the pro b a b ility tha t a n individua l o f a ra re spe c ie s is inc lude d – inc re a sing the spe c ie s ric hne ss.  L a rg e r a re a s will inc o rpo ra te ne w kinds o f ha b ita ts with its a sso c ia te d spe c ie s. 8

Spe c ie s-I so la tio n Re la tio nship  I sla nds fa r o ut in a n o c e a n suppo rt fe we r spe c ie s tha n isla nds tha t a re ne a re r to c o ntine nts.  Assuming tha t pa tte rn is the re sult fro m a de c line in dispe rsa l ra te s with iso la tio n the re la tio nship b e twe e n spe c ie s ric hne ss a nd iso la tio n sho uld b e :  Ne g a tive e xpo ne ntia l func tio n  Ne g a tive sig mo ida l func tio n 9

Spe c ie s-I so la tio n Re la tio nship  L e ss g e ne ra l tha n the spe c ie s-a re a re la tio nship  I nc lude b ro a d ra ng e s o f diffe re nc e s in a re a , b ut o nly limite d ra ng e s o f diffe re nc e s in iso la tio n.  Re le va nt me a sure s o f iso la tio n a re c ha lle ng ing . Spe c ie s T urno ve r  K ra ka ta u  Pa tte rn  Spe c ie s ric hne ss inc re a se s ra pidly initia lly  Spe c ie s ric hne ss the n sta b ilize s –re ma ining re la tive ly c o nsta nt  Cha ng e s in the c o mpo sitio n o f the b io ta c o ntinue s.  Spe c ie s ric hne ss re ma ins re la tive ly c o nsta nt, b ut the ide ntity o f the spe c ie s c o ntinue s to c ha ng e . 10

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  Ama zo n Re vie w E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy 11

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  I nc o rpo ra te s the diffe re nt isla nd pa tte rns tha t we ha ve disc usse d.  Spe c ie s-Are a re la tio nship  Spe c ie s-I so la tio n re la tio nship  Spe c ie s turno ve r E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  Spe c ie s ric hne ss o n isla nds c a n b e e xpla ine d b y two fa c to rs.  I sla nd a re a  I sla nd iso la tio n 12

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  Are a re g ula te s spe c ie s ric hne ss o n isla nds b y c o ntro lling po pula tio n size  A stro ng inve rse c o rre la te o f e xtinc tio n.  T he sma lle r the isla nd the sma lle r the po pula tio n tha t c a n b e suppo rte d o n the isla nd.  T he sma lle r the po pula tio n size the mo re like ly it will b e c o me e xtinc t.  T he sma lle r the isla nd the g re a te r the pro b a b ility o f a ny spe c ie s g o ing e xtinc t. E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  On a diffe re nt b ut re la te d to pic .  T he g re a te r the numb e r o f spe c ie s in a ny c o mmunity the g re a te r the pro b a b ility tha t a ny o ne spe c ie s will g o e xtinc t. 13

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  No w we c a n c o mb ine the two c o nc e pts re la te d to e xtinc tio n into a sing le g ra ph. 14

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  All spe c ie s ha ve so me limit to the ir dispe rsa l a b ility.  So me spe c ie s will b e a b le to dispe rse lo ng dista nc e s.  So me spe c ie s will a b le to dispe rse o nly sho rt dista nc e s.  T he isla nds ve ry c lo se to a c o ntine nt will ha ve a ll o f the spe c ie s (spe c ie s c a pa b le o f o nly limite d dispe rsa l a nd tho se c a pa b le o f lo ng dista nc e dispe rsa l)  I sla nds isla nd ve ry fa r a c o ntine nt will ha ve ve ry fe w spe c ie s (o nly tho se spe c ie s c a pa b le o f lo ng dista nc e dispe rsa l).  T he numb e r o f spe c ie s o n a n isla nd will b e inve rse ly re la te d to its dista nc e fro m a c o ntine nt. 15

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  On a diffe re nt b ut re la te d to pic .  T he mo re spe c ie s o n a n isla nd the le ss like ly tha t a ny immig ra nt a rriving a t the isla nd will re pre se nt a ne w spe c ie s.  T he re fo re the immig ra tio n ra te de c line s with inc re a se d spe c ie s ric hne ss o n a n isla nd. 16

E q uilib rium T he o ry o f I sla nd Bio g e o g ra phy  No w we c a n c o mb ine the two c o nc e pts re la te d to e xtinc tio n into a sing le g ra ph. 17