7/29/2019 Measuring Ecological
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Ma rine Bio logy 106 , 305-3 08 (1990) Mar i ne===.,Biology
Springer-Ve rlag 1990
M e as u r in g e c o log i c a l st r es s: var ia t ion s on a
th em e b y R . M . W ar wic kJ . W . M c M a n u s l a n d D . P a
u l y 21 Univers i ty o f Rhode I s land and Mar ine Sc ience Ins t
i tu te , Univers i ty o f the Ph i l ipp ines , Di l iman , Quezon
Ci ty 1101 , The Ph i l ipp ines2 I n t e r n a t i o n a l C e n t
e r f o r L i v in g A q u a t i c R e s o u r ce s M a n a g e m e
n t , M C P .O . B o x 1 5 0 1 , M a k a t i , M e t r o M a n i l
a , T h e P h i l i pp i n e sD a t e o f f in a l m a n u s c r i
p t a c c e p t a n c e : A p r i l 2 4, 1 9 9 0 . C o m m u n i c
a t e d b y M . A n r a k u , T o k y o
A b s t r a c t . Tw o n e w i n d i c e s a r e p r e s e n t e
d w h i c h r e f l e c tq u a n t i t a t i v e l y t h e c h a n
g e s t o b e e x p e c t e d i n a n e c o l o g i c a lc o m m u
n i t y u n d e r s t r e s s , a s p r e v i o u s l y d e s c r i
b e d b yR . M . W a r w i c k . T h e i n di c es s u m m a r i z
e i n f o r m a t i o nw h i c h h e p r e s e n t e d g r a p h i
c a l l y , a n d p e rm i t a n a l y s e s o ft rends and in
feren t ia l t es t s . We sugges t tha t these ind icess h o u l d
b e t e s t e d w i t h a w i d e v a r i e t y o f e c o l o g ic
a l t im e -ser ies da t a in o r der to eva lu a te the feas ib i
l i ty o f in fer ringeco log ica l s t res s f rom s ta t i c da
ta .
I n t r o d u c t i o n
Eco log ica l s t res s is an e lus ive and i l l -def ined conc
ep t , an dc o n s e q u e n t l y o n e w h i c h i s d i f f i c
u l t t o m e a s u re . A f e wd e c a d e s a g o , a p a r a d i
g m e x i s te d in w h i c h i t w a s a s s u m e dt h a t e c o
l o g i c a l c o m m u n i t i e s t e n d t o w a rd a s t a b l
e s ta t e o fh i g h d i v e r s i t y , a n d t h a t v a r i o u
s h u m a n - i n d u c e d d i s t u r -b a n c e s w o u l d d r
i v e t h e m i n t o a l e s s - st a b l e s t a t e o f l o w e
rd i v e r si t y . I t w a s t h e r e fo re a s s u m e d t h a t
a n i n d e x o f d iv e r -s i t y c o u l d b e u s e d t o i n d
i c a t e t h e d e g re e t o w h i c h ac o m m u n i t y w a s s
t r e s s e d , f o r e x a m p l e , b y p o l l u t i o n (w eu s
e " p o l l u t io n " a n d " s t r e s s " i n t e r c ha n g e a
b l y t h r o u g h o u tt h i s p a p e r ) . R a t h e r t h a n
a t t e m p t i n g t o t h o ro u g h l y e s t a b -l i sh the va
l id i ty o f re la t ing d ive rs i ty va lues to eco log ica ls t
re s s b y s t u d y i n g t h e b e h a v i o r o f s u c h a n i
n d e x u s i n gt i m e s er ie s o f d a t a f ro m c o m m u n i
t i e s s u b j e c t e d t o k n o w nc h a n g e s i n s t r es s
, m a n y e c o l o g i st s a s s u m e d t h a t t h e c o n -c e
p t s w e re v a l i d a n d u s e d t h e i n d i c e s w i t h o
u t a d e q u a t ep r io r t es t ing (G reen 1979) . Recen t ly ,
it has been show ntha t the re la t ionsh ip s be twe en d ivers i
ty , s t ab i l i ty , ands t r e s s a r e f a r m o re c o m p l
e x t h a n p r e v i o u s l y i m a g i n e d(M a y 1 9 7 3, C o
n n e l 1 1 9 7 8 , H u s t o n 1 97 9) . F e w p e o p l e n o wa
s s u m e t h a t e c o l o g i c a l s t re s s c a n b e i n f e
r r e d f ro m d i v e rs i -ty a lone .W a rw i c k (1 9 8 6 ) s u
m m a r i z e d p r e v a i l i n g v i e w s i n t o an e w c o n
c e p t u a l m o d e l f o r p r e d i c t i n g c h a n g e s in
a m a c ro -b e n t h i c c o m m u n i t y b e i n g g r a d u a l
l y m o re p o l l u t e d . Th em o d e l i n c l u d e s t h e fo
l l o w i n g a s s u m p t i o n s : ( 1 ) P r i o r t ob e i n g
s tr e s s ed , t h e c o m m u n i t y t e n d s t o w a rd s a n
e q u i l i b r i-
u m c o m p o s i t i o n . ( 2 ) A s i t a p p ro a c h e s e q
u i l i b r i u m , t h eb i o m a s s b e c o m e s d o m i n a t
e d b y a f e w s p e c ie s w i t h i n d i-v i d u a l s t h a t
a r e l a rg e b u t f e w i n n u m b e r . ( 3) Th e s p e c i e
sd o m i n a t i n g t h e b i o m a s s a p p r o a c h a s ta t e
o f e q u i l i b r iu mw i t h a v a i l a b l e r e s o u rc e s
. ( 4 ) N u m e r i c a l d o m i n a n c e i sma in ta ine d by
spec ies wh ich a re smal l . Th is resu l t s in am o r e e v e n
d is t r i b u t i o n o f n u m b e r s o f i n d i v id u a l s a
m o n gspec ies than b iom ass am ong spec ies. (5 ) The sm al le r
spe-c ies a re o u t o f equ i l ib r ium wi th av a i lab le resou
rces ( i t i simpl ied tha t th i s he lps to exp la in Assumpt ion
4 ) . (6 ) Thea b u n d a n c e s o f t h e s m a l le r s p e c i
es a r e s u b j e c t t o m o res tochas t i ca l ly con t ro l l
ed var ia t ion than the l a rger spec ies(p e rh a p s b e c a u s
e o f A s s u m p t i o n 5 , b u t t h i s is n o t u s u a l l ys
t a t e d ) . ( 7 ) U n d e r m o d e ra t e p o l l u t i o n , t
h e l a rg e d o m i -nan ts a re e l imina ted , resu l t ing in l
es s d i f fe rence be tweene v e n n e s s i n t e rm s o f b i o
m a s s a n d n u m b e r s . ( 8) U n d e rs e v e re p o l l u t
i o n , c o m m u n i t i e s b e c o m e n u m e r i c a l l y d o
m i -na te d by a few very smal l spec ies . (9 ) U nd er severe po
l lu -t ion , the few remain ing la rge spec ies wi ll con t r ib u
te p ro -p o r t i o n a l l y m o re t o t h e t o t a l c o m m u
n i t y b i o m a s s r el a t iv et o t h e i r a b u n d a n c e
t h a n w i l l t h e n u m e r i c a l l y d o m i n a n ts m a l
l s pe c ie s . Th e n e t e f f e c t o f A s s u m p t i o n s 8
a n d 9 ist h a t t h e b i o m a s s w i l l b e m o re e v e n l
y d i s t ri b u t e d a m o n gs p e c ie s th a n n u m b e r s o
f i n d i v id u a l s a r e .Ea c h o f th e s e a s s u m p t i o
n s i s d e b a t a b l e . F o r e x a m p l e ,t h e a s s u m p
t i o n t h a t c o m m u n i t i e s g e n e ra l l y t e n d t o
w a rda n e q u i l i b r i u m s t a t e h a s b e e n q u e s t i
o n e d b y C o n n e l l a n dS o u s a (1 98 3) . F e w s t u d i
e s o f c o m m u n i t y b e h a v i o r h a v eb e e n c o n d u
c t e d a c ro s s t i m e - f r a m e s w h i c h a r e a p p ro p
r i -a te ly long re la t ive to the li fe spans o f the o rgan ism
s in thec o m m u n i t y . Th e s a m e c o u l d b e s a i d fo r
e v a l u a t i n g m a n yo f th e o t h e r a s s u m p t i o n s
l i st e d h e r e . H o w e v e r , t h e f a c tt h a t t h e y a
r e p r e s e n t e d i n a m e a n i n g fu l c o n t e x t c a n
s e rv et o fo c u s r e s e a r c h o n t h e i r v a l i d i t y
, a n d t h e a s s u m p t i o n shave the adm irab le qua l i ty
o f be ing t es tab le in a fa l s if i -a b l e m a n n e r .U l t
i m a t e l y , t h e u t i l i ty o f t h e m o d e l i m p l i e
d b y A s -s u m p t i o n s I t o 9 , m u s t b e d e t e rm i n e
d f ro m i t s a b il i t y t op re d i c t c h a n g e s in d a t
a s e ts o f k n o w n p ro p e r t y . Th eg ra p h i c a l a p p
ro a c h o f W a rw i c k (1 9 86 ) i n v o l v e s p r e s e n t
-i n g c o m m u n i t y s t r u c t u r e d a t a i n th e fo rm o
f k -d o m i -
